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GABA RECEPTOR
DR. NITIN SHINDE
FYR DEPARTMENT OF PHARMACOLOGY
Lokmanya Tilak Municipal Medical
College & GH SION MUMBAI-22...
CONTENTS
Section-A :
(Basic Understanding Of GABA Receptors And Their Types)
1. Neurotransmitter :- GABA
2. GABA: SYNTHESI...
Neurotransmitter :- GABA
4-aminobutanoic acid
• Chief inhibitory neurotransmitter in mammalian central
nervous system.
• A...
GABA: SYNTHESIS, UPTAKE, AND
METABOLISM
Synthesized in brain – GABA shunt
GABA: SYNTHESIS, UPTAKE, AND
METABOLISM
A,B,C……Types of GABA Receptor
• Three main types: A, B, and C.
• The GABAA receptor, is a ligand-gated Cl– ion channel,
an...
Subunits at GABA – A
SUBUNITS OF GABA
GABAA receptor structure
• It is a multimeric transmembrane
receptor that consists of 5 subunits
arranged around a central...
• Each subunit is composed of a polypeptide sequence of
approximately 450–630 amino acids (40–60 kDa) with large N-
termin...
GABAA receptor MOA
• Binding of GABA triggers opening of the Cl− ion pore.
• This drives the membrane potential towards th...
Video clip
Extrasynaptic GABAA Receptors
• Synaptic GABAA receptors Underlie
“phasic” inhibition
• By contrast, extra-synaptic recept...
Extrasynaptic GABAA Receptors
• The occurrence of tonic GABAA inhibition coincides with the
expression of relatively rare ...
Extrasynaptic GABAA Receptors
& drugs
Studies have begun to identify extrasynaptic GABAARs as
novel targets for a diverse ...
SUBUNIT AND PHARMACOLOGICAL
ACTION
GABAB - discovery
• Baclofen was first synthesized in 1962 by a
chemist Heinrich Keberle and was shown to exert
potent mus...
Molecular Structure
of GABA
(B)Receptors
Heterodimer composed of two similar subunits each with a seven trans-membrane
α-helix (7 TM) topology.
GABA (B) R1 and GAB...
GABA-B
RECEPTOR
MOA
GABA-B RECEPTOR MOA
GABA-ρ subclass ( GABAC)
• A subclass of ionotropic GABA receptors, insensitive to
typical allosteric modulators
• GABAС r...
• Three homologous
ρ-subunits, ρ1 to ρ3,
have now been
identified.
• There is only limited evidence that the ρ-subunits co...
GABA –C MOA
• Its is ionotropic receptor with action
similar to GABA-A Receptor.
• These receptors, are Cl- pores that are...
PHARMACOLOGICAL
APPLICATION OF GABA-A
• BZD RECEPTOR MODULATORS
• ALCOHOL & GABA
• ROLE IN ANTIEPILEPTICS.
• Neuroactive s...
BASICS...
• Agonists: Bind to the main receptor site - also referred to as the
"active" or "orthosteric" site- and activat...
GABA – AAgonist
Ibotenic acid and Muscimol
• Contained in Amanita muscaria/pantherina/gemmata
(hallucinogenic mushroom) with muscarine, mu...
GABOXADOL
• Extrasynaptic GABAA agonist
• Increases deep sleep (stage 4).
• BZDs/Z drugs work on the α1 subtype of recepto...
GABAA Antagonist
Various GABAA antagonists
Drug Detail
Bicuculline •Competitive antagonist of GABAA receptors
•Utilized in laboratories in ...
Various GABAA antagonists
Drug Detail
Thujone •Found in a number of plants, such as arborvitae
(Thuja)
•Used in herbal med...
Positive allosteric
modulators
GABAA receptor allosteric MODULATORS
Benzodiazepines (BDZ)
• Benzodiazepines act at GABAA
receptors by binding directly to a
specific site, distinct from that ...
Benzodiazepines bind across
the interface between the α
and γ subunits but only to
receptors that contain γ2 and
α1, α2, α...
MOA….
Benzodiazepines (BDZs) bind to the gamma sub-unit of the
GABA-A receptor. Their binding causes an allosteric (struct...
Binding Affinity at various subunits
CLINICAL USES OF BDZ
MODULATORS
NON BENZODIAZEPINE GABA
MODULATORS
• commonly referred to as "Z compounds".
• They include:-
• zolpidem (AMBIEN),
• zalepl...
ZALEPLON
• Pyrazolopyrimidine class of
compound.
• Zaleplon preferentially binds to the
benzodiazepine-binding site on
GAB...
ZOLPIDEM
Imidazopyridine
• Although the actions of zolpidem are
due to agonist effects on GABAA
receptors and generally re...
ESZOPICLONE
• Active S(+) enantiomer of
zopiclone. Eszopiclone has no
structural similarity to
benzodiazepines, zolpidem, ...
Inverse agonist at BZD Receptor
• Inverse agonists at the BZD site act as negative allosteric
modulators of GABA-receptor ...
Sarmazenil •Partial inverse agonist at
the benzodiazepine site.
•It is used in veterinary medicine to reverse
the effects ...
BZD-site Antagonist
FLUMAZENIL: A BENZODIAZEPINE
RECEPTOR ANTAGONIST
• Flumazenil (ROMAZICON, generic), the only member of this
class, is an i...
FLUMAZENIL
• Can be used to reverse the effect of benzodiazepine
overdosage , or to reverse the effect of benzodiazepines ...
Barbiturates:
Barbiturates also facilitate the actions of GABA -A at multiple sites in
the central nervous system, but—in ...
Antiepileptic actions at
GABAA Receptors
• Modulate GABAA receptor
activation
• Phenobarbital
• Clonazepam, Diazepam
• Top...
GABAergic terminal
Inhibition of uptake increases GABA
action
VALPROIC ACID
• An analogue of valeric acid
• Believed to affect the function of the neurotransmitter GABA in
the human br...
VALPROIC ACID
Indications
• Manic episodes associated with bipolar disorder.
• As an anticonvulsant in
Absence seizures Ju...
VIGABATRIN
• VIGABATRIN is a “suicide
inhibitor” of GABA transaminase.
• It blocks the conversion of GABA to
succinic semi...
TIAGABIN
• Tiagabine (GABITRIL) is a
derivative of nipecotic acid
• Approved by the FDA as
adjunct therapy for partial
sei...
GABAPENTIN & PREGABALIN
• Gabapentin (NEURONTIN, others) and
pregabalin (LYRICA) are anti-seizure drugs
that consist of a ...
• P.K - Gabapentin and
pregabalin are absorbed
after oral administration . It
is neither metabolised nor
bound to plasma p...
Role OF GABA RECEPTORS IN
ANAESTHESIA
Anaesthetics primarily act by either enhancing inhibitory
signals or by blocking exc...
GENERAL ANAESTHETICS
• Currently, there are 5 major
inhalational and 5 intravenous
anesthetics used to induce or
maintain ...
General anaesthetics
• The extrasynapic α5ß3γ2 receptor in hippocampus is probably
assosciated with amnestic action of ana...
Single amino acids determine i.v.
anaesthetic activity ?
• If GABA-A receptors are important targets for general
anaesthet...
A binding site for volatile anaesthetics?
• The effects of volatile agents on GABA-A receptor activity are also
influenced...
Neuroactive steroids
Synthesized in the central and peripheral nervous system, especially in
myelinating glial cells, from...
NEUROACTIVE STEROIDS
• Allopregnanolone and tetrahydrodeoxycorticosterone have
been surmised to enhance GABA-mediated Cl¯ ...
This animation shows one model for how neurosteroids may increase Cl–
flux through a GABA-A receptor. Binding of the neuro...
ALPHAXOLONE
Neurosteroid general anaesthetic.
A study 1987 found the primary
mechanism for the anaesthetic
action of alfax...
OTHER NEUROACTIVE STEROIDS
Drug Details
Hydroxydione
•Proved to be a useful anaesthetic drug with a
good safety profile.
•...
ALCOHOL & GABA
RECPTOR
Alcohol
• Ingestion of ethanol results in a
dose-dependent reduction of
central nervous system (CNS)
activity.
• For sever...
NEUROSTEROID INVOLVEMENT IN THE
GABAMIMETIC PROFILE OF ETHANOL
Following ethanol consumption there is activation of the hy...
GABA
-
GLUTAMATE
+
Alcohol
GABA
-
GLUTAMATE
+
Chronic Alcohol
ROLE OF GABA IN ALCOHOL
WITHDRAWAL
Thaugh benzodiazepines have been the primary treatment
modality for alcohol withdrawal....
GHB (Gamma hydroxy butyric acid)
Gamma-hydroxybutyric acid (GHB)
gammaaminobutyric
acid (GABA) that has been used in
resea...
GHB (Gamma hydroxy butyric acid)
• GHB usually exists either as a free acid, or as a sodium salt. The sodium
salt is calle...
EPIDEMIOLOGY OF GHB ABUSE
Effects…
NEGATIVE POINTS POSITIVE POINTS
Rave drug Can be used in narcolepsy
Date rape drug Tried for alcohol withdrawal
Body build...
GABAB Agonist
BACLOFEN
Derivative of GABA (β-
parachlorophenyl GABA)
It is primarily used to
treat spasticity. In disorders like
multipl...
Baclofen
• Primary site is possibly the spinal cord
where it depresses both polysynaptic
and monosynaptic reflexes
• Also ...
Phenibut
• β-Phenyl-γ-aminobutyric acid is a derivative of GABA.
• Binds the GABAB metabotropic receptor.
• The addition o...
Phenibut
• Structurally similar to baclofen & phenylethylamine.
– Pharmacological effects of phenibut are similar to baclo...
Phenibut
• Used to treat a wide range of ailments including post-traumatic
stress disorder, anxiety, and insomnia.
• It ha...
GABAB Antagonist
Saclofen & Phaclofen
• These are competitive antagonist at GABAB receptor.
• This drug is an analogue of the GABAB agonist...
GABA analogues
Progabide
• Analog and prodrug of GABA used in the treatment of
epilepsy.
• Agonist at both the GABAA and GABAB receptors....
Progabide
• Also being investigated for
– Parkinson's disease
– Schizophrenia
– Depression
– Anxiety disorder
– Spasticity...
Picamilon
• Dietary supplement formed by combining
niacin with GABA.It was developed in
the Soviet Union in 1969 by the Al...
Picamilon
In Russia, Picamilon is used for treatment of
these illness.
1. Ischemic stroke
2. Asthenia
3. Depression
4. Sen...
GABA –C AGONIST
• CACA – C Amino caproic acid . Weak agonist.
• TACA – Trans isomer of CACA.strongest agonist at GABA –
C ...
TPMPA, Selective GABA-C
Antagonist
• Tetrahydropyridine ring of isoguvacine was
unfavourable for interactions with GABAB
r...
GABA C
• Recombinant receptor technology. The cloning of ρ1 and ρ2
cDNAs from a human retinal library enabled expression o...
CRITERIA GABA-A GABA-B GABA-C
Distribution Mammalian CNS Cerebellum &
interpeduncular
nuclei
retina, spinal cord,
superior...
Section III Herbal Preperations and
GABA Receptors
• Many herbal medicines are used to influence brain function in
order t...
Bicuculline
First isolated from the plant Dicentra
cucullaria and subsequently from a
variety of Corydalis,Dicentra, and
A...
Picrotoxin
Picrotoxin is an equimolar mixture of
picrotoxinin and picrotin isolated from
Anamirta cocculus and related poi...
Muscimol
• Muscimol is one of the most widely
used agonists in the investigation of
ionotropic GABA receptors.
• It is a m...
Apigenin – GABA Receptor Modulator
• Common flavonoid found in a range of
plants, including chamomile
tea(Matricariarecuti...
Epigallocatechin gallate (EGCG)
• Epigallocatechin gallate (EGCG) is the
major polyphenol in green tea (Camellia
sinensis)...
Hispidulin and Related Flavonoids
• Hispidulin (the 6-methoxy derivative of
• apigenin) was isolated together with apigeni...
Section IV
CURRENT KNOWEDGE
SCENARIO & FUTURE
TRENDS
GAD 65 OR GAD 67 ?
Knockout of GAD65 has major impact on synaptic
GABA synthesized from astrocyte-derived
Glutamine.1
• Tw...
GENE ORGANISATION OF
SUBUNITS
The majority of genes
coding for the
GABA-A receptor
subunits are organized
into four cluste...
• Pharmacological
analysis of GABA
receptor was simplified
after introduction of
animal models in which
particular GABA- A...
GABA OLD RECEPTOR
NEW TARGETS
GABA – AS IMMUNOMODULATOR
• In lymphocytes,exposure to GABA reduced but did not
abolish the transient increase in the intr...
GABA – AS IMMUNOMODULATOR
• GABA appears to have a role in autoimmune diseases
• like MS, type 1 diabetes and rheumatoid a...
Role of GABA – IN TYPE- I DM
• Currently a trial with hypothesis that GABA, a naturally
occurring substance, has the poten...
GABA & SCHIZOPHRENIA
• In subjects with schizophrenia, impairments in working
memory are associated with dysfunction of th...
GABA-B Receptor Complex Target
for Tumor Therapy
A positive correlation between
GABA
B2 (minor b1)expression and that
of t...
INTERVENTION CONDITION STATUS
1. GAD-Alum Juvenile onset type-1
DM.
PHASE – 1 A
2. Merck L-830982
GABA-A Alpha2/3
Receptor...
Conclusion….
• Despite the overwhelming representation of the
GPCRs in the human genome, it is the ionotropic
receptors wh...
THANK YOU….
Gaba Receptor
Gaba Receptor
Gaba Receptor
Gaba Receptor
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  • GABAB receptors (see Bettler et al., 2004) are located pre- and postsynaptically, and they are typical G-protein-coupled receptors, but unusual in that the functional receptor is a dimer consisting of two different subunits (see Ch. 3). Apart from minor splice variants, only a single isoform is known-also unusual among G-protein-coupled receptors. GABAB receptors exert their effects by inhibiting voltage-gated calcium channels (thus reducing transmitter release) and by opening potassium channels (thus reducing postsynaptic excitability), these actions resulting from inhibition of adenylyl cyclase.
  • Transcript of "Gaba Receptor "

    1. 1. GABA RECEPTOR DR. NITIN SHINDE FYR DEPARTMENT OF PHARMACOLOGY Lokmanya Tilak Municipal Medical College & GH SION MUMBAI-22 DATE:11-01-2014.
    2. 2. CONTENTS Section-A : (Basic Understanding Of GABA Receptors And Their Types) 1. Neurotransmitter :- GABA 2. GABA: SYNTHESIS, UPTAKE, AND METABOLISM 3. A,B,C ,… types of GABA receptors. 4. GABA : A receptor a) GABA –A- structure b) GABA –A- subunits c) GABA –A- MOA 5. Extra Synaptic GABA A receptors 6. GABA B receptors a) Introduction b) Molecular structure of GABA B receptor c) M.O.A of GABA B receptor
    3. 3. Neurotransmitter :- GABA 4-aminobutanoic acid • Chief inhibitory neurotransmitter in mammalian central nervous system. • Approximately 40 % neurons in mamalian CNS are purely gabaminergic. Synthesis of GABA
    4. 4. GABA: SYNTHESIS, UPTAKE, AND METABOLISM Synthesized in brain – GABA shunt
    5. 5. GABA: SYNTHESIS, UPTAKE, AND METABOLISM
    6. 6. A,B,C……Types of GABA Receptor • Three main types: A, B, and C. • The GABAA receptor, is a ligand-gated Cl– ion channel, an "ionotropic receptor.“ • The GABAB receptor is a GPCR.metabotropic. • The GABAC receptor is a transmitter-gated Cl– channel.Newly discovered.
    7. 7. Subunits at GABA – A
    8. 8. SUBUNITS OF GABA
    9. 9. GABAA receptor structure • It is a multimeric transmembrane receptor that consists of 5 subunits arranged around a central Cl− ion pore. • Members of family of Cys-loop ligand-gated ion channels (loop formed by a disulfide bond betn 2 cysteine residues) • The receptor is usually located postsynaptically. However, some isoforms may be found extrasynaptically
    10. 10. • Each subunit is composed of a polypeptide sequence of approximately 450–630 amino acids (40–60 kDa) with large N- terminal and smaller C-terminal extracellular domains. • individual subunits contain four distinct transmembrane(TM) domains, with the second transmembrane domain (TM2) lining the channel lumen. • A large intracellular loop connects the TM3 and TM4 regions providing sites for phosphorylation by a range of serine, threonine, aspargine & tyrosine kinases
    11. 11. GABAA receptor MOA • Binding of GABA triggers opening of the Cl− ion pore. • This drives the membrane potential towards the reversal potential of the Cl¯ ion which is about –65 mV in neurons, inhibiting the firing of new action potentials. • This makes it more difficult for excitatory neurotransmitters to depolarize the neuron. • The net effect is typically inhibitory, reducing the activity of the neuron.
    12. 12. Video clip
    13. 13. Extrasynaptic GABAA Receptors • Synaptic GABAA receptors Underlie “phasic” inhibition • By contrast, extra-synaptic receptors are usually exposed to low but persistent GABA concentrations leading to “tonic” inhibition. • Compared to their synaptic counterparts, these show i. Increased sensitivity to GABA ii. Reduced propensity to desensitize iii. More rapid deactivation phase after removal of GABA
    14. 14. Extrasynaptic GABAA Receptors • The occurrence of tonic GABAA inhibition coincides with the expression of relatively rare receptor subunits, articularly the α4, α6, and δ subunits, and as a general rule-of-thumb, δ subunit-containing receptors are extrasynaptic. • The subunit can also govern receptor pharmacology: – extrasynaptic GABAARs are insensitive to benzodiazepine agonists – but highly sensitive to the GABAAR “super agonist” tetrahydroisoxazolopyridineol (THIP/gaboxadol)
    15. 15. Extrasynaptic GABAA Receptors & drugs Studies have begun to identify extrasynaptic GABAARs as novel targets for a diverse array of endogenous and clinically relevant agents, including : • Certain Neuroactive steroids • Amino acid Taurine • Ethanol • Several Anesthetic • Hypnotic agents • Analgesics • Some Anticonvulsant drugs.
    16. 16. SUBUNIT AND PHARMACOLOGICAL ACTION
    17. 17. GABAB - discovery • Baclofen was first synthesized in 1962 by a chemist Heinrich Keberle and was shown to exert potent muscle-relaxant and analgesic properties • . A report from Bowery et al. holds an invaluable pharmacological tool in elucidating the role of GABAB receptors in several disorders including epilepsy, cognition defect. • Bowery and Hudson described a bicuculline insensitive action of GABA in beclofen which lead to the discovery of GABA B later.
    18. 18. Molecular Structure of GABA (B)Receptors
    19. 19. Heterodimer composed of two similar subunits each with a seven trans-membrane α-helix (7 TM) topology. GABA (B) R1 and GABA (B) R2. Each subunit comprises a large N terminal extracellular domain followed by 7-transmembrane helicesand an intracellular C-terminus. GABA (B) R1 binds to ligand and initiates a conformational change in the receptor complex, GABA (B) R2 interacts with and transmits this signal to the intracellular G-protein trimer. Two GABA (B) R1 isoforms, GABA (B)R1a and GABA (B) R1b, are expressed in the brain. Two “Sushi motifs” are present GABA (B) R1a and absent in GABA (B) R1b.
    20. 20. GABA-B RECEPTOR MOA
    21. 21. GABA-B RECEPTOR MOA
    22. 22. GABA-ρ subclass ( GABAC) • A subclass of ionotropic GABA receptors, insensitive to typical allosteric modulators • GABAС receptors are exclusively composed of ρ (rho) subunits that are related to GABAA receptor subunits • Designated as the ρ subfamily of the GABAA receptors (GABAA-ρ). • These receptors are found in the retina, spinal cord, superior colliculus, and pituitary.
    23. 23. • Three homologous ρ-subunits, ρ1 to ρ3, have now been identified. • There is only limited evidence that the ρ-subunits co- assemble with any of the other GABAA receptor subunits. • The genes encoding the ρ1- and ρ2-subunits are found on chromosome 6 of man, and are thus distinct from the clusters of receptor subunit genes which are found on • Chromosomes 4, 5, 15 and X with the exception of δ, which is found on chromosome 1.
    24. 24. GABA –C MOA • Its is ionotropic receptor with action similar to GABA-A Receptor. • These receptors, are Cl- pores that are insensitive to both bicuculline and baclofen. • They are designated GABAC in 1984 but An IUPHAR nomencleature:the term GABAC be avoided and classifies it as bicuculline and baclofen-insensitive GABA receptors as a minor group
    25. 25. PHARMACOLOGICAL APPLICATION OF GABA-A • BZD RECEPTOR MODULATORS • ALCOHOL & GABA • ROLE IN ANTIEPILEPTICS. • Neuroactive steroid
    26. 26. BASICS... • Agonists: Bind to the main receptor site - also referred to as the "active" or "orthosteric" site- and activate it • Antagonists: Bind to the main receptor site but do not activate it. • Positive Allosteric Modulators: Bind to allosteric sites on the receptor complex and affect it in a positive manner, causing increased efficiency of the main site and thus increase in Cl- conductance. • Negative Allosteric Modulators: Bind to an allosteric site on the receptor complex and affect it in a negative manner, causing decreased efficiency of the main site. • Uncompetitive Channel Blockers: Bind to or near the central pore of the receptor complex and directly block Cl- conductance.
    27. 27. GABA – AAgonist
    28. 28. Ibotenic acid and Muscimol • Contained in Amanita muscaria/pantherina/gemmata (hallucinogenic mushroom) with muscarine, muscazone. • GABAA agonist + potent partial GABAC agonist • Muscimol is as much as 10 times more potent • Effects are frequently compared to a lucid dream state. • Psychoactive dose of muscimol is around 10–15 mg
    29. 29. GABOXADOL • Extrasynaptic GABAA agonist • Increases deep sleep (stage 4). • BZDs/Z drugs work on the α1 subtype of receptors for the neurotransmitter GABA -- that's akin to an 'on/off switch' for the central nervous system. • On the other hand, gaboxadol works on another subtype, called α4 -- it's more of a 'dimmer switch' that might help regulate sleep in a less disruptive way
    30. 30. GABAA Antagonist
    31. 31. Various GABAA antagonists Drug Detail Bicuculline •Competitive antagonist of GABAA receptors •Utilized in laboratories in the in vitro study of epilepsy •Routinely used to isolate glutamatergic (excitatory amino acid) receptor function. Gabazine •Antagonist at GABAA receptors •Used in scientific research and has no role in medicine •Phasic (synaptic) inhibition is gabazine- sensitive, tonic (extrasynaptic) inhibition is relatively gabazine- insensitive Cicutoxin & Oenantho- toxin •Found in various plants, most notably water hemlock (Cicuta & Oenanthe species) •Potent noncompetitive GABA receptor antagonist •Nausea, emesis and abdominal pain within 60 mins of ingestion. Can lead to tremors, seizures & death
    32. 32. Various GABAA antagonists Drug Detail Thujone •Found in a number of plants, such as arborvitae (Thuja) •Used in herbal medicine, mainly for their immune- system stimulating effects •Reported to be toxic to both brain and liver cells •Side-effects include anxiety and sleeplessness, seizures at high dose Picrotoxin (cocculin) •Poisonous crystalline plant compound •Found in the fruit (fishberry) of climbing plant Anamirta cocculus. •Noncompetitive antagonist for GABAA receptor - Channel blocker •Can be used to counter barbiturate poisoning
    33. 33. Positive allosteric modulators
    34. 34. GABAA receptor allosteric MODULATORS
    35. 35. Benzodiazepines (BDZ) • Benzodiazepines act at GABAA receptors by binding directly to a specific site, distinct from that of GABA. • They do not activate GABAA receptors directly but rather require GABA to express their effects; i.e., they only modulate the effects of GABA. • Studies of cloned GABAA receptors have shown that the coassembly of a γ subunit with α and β subunits confers benzodiazepine sensitivity to GABAA receptors
    36. 36. Benzodiazepines bind across the interface between the α and γ subunits but only to receptors that contain γ2 and α1, α2, α3 or α5 subunits.1 BDZ BINDING SITE…
    37. 37. MOA…. Benzodiazepines (BDZs) bind to the gamma sub-unit of the GABA-A receptor. Their binding causes an allosteric (structural) modification of the receptor that results in an increase in GABA A receptor activity. BDZs do not substitute for GABA, which bind at the alpha sub-unit, but increase the frequency of channel opening events which leads to an increase in chloride ion conductance and inhibition of the action potential
    38. 38. Binding Affinity at various subunits
    39. 39. CLINICAL USES OF BDZ MODULATORS
    40. 40. NON BENZODIAZEPINE GABA MODULATORS • commonly referred to as "Z compounds". • They include:- • zolpidem (AMBIEN), • zaleplon(SONATA), • zopiclone (Not marketed in the U.S.), and • eszopiclone (LUNESTA), which is the S(+) enantiomer of zopiclone
    41. 41. ZALEPLON • Pyrazolopyrimidine class of compound. • Zaleplon preferentially binds to the benzodiazepine-binding site on GABAA receptors containing the α1receptor subunit. • P.K - Absorbed rapidly and reaches peak plasma concentrations in ~1 hour. Its bioavailability is ~30% because of presystemic metabolism volume of distribution of ~1.4 L/kg and plasma-protein binding of ~60%. • Metabolised by aldehyde oxidase. • Zaleplon (usually administered in 5-, 10-, or 20-mg doses) has been studied in clinical trials of patients with chronic or transient insomnia.
    42. 42. ZOLPIDEM Imidazopyridine • Although the actions of zolpidem are due to agonist effects on GABAA receptors and generally resemble those of benzodiazepines, it produces weak anticonvulsant effects in experimental animals. • During U.S. clinical trials, withdrawal effects within 48 hours of drug discontinuation occurred at an incidence of 1% or less. Post- marketing reports of abuse, dependence, and withdrawal have been recorded. • zolpidem is approved only for the short-term treatment of insomnia. • Therapeutic doses (5 to 10 mg) zolpidem infrequently produces residual daytime sedation or amnesia adverse effects(e.g.GI complaints or dizziness) is also low.
    43. 43. ESZOPICLONE • Active S(+) enantiomer of zopiclone. Eszopiclone has no structural similarity to benzodiazepines, zolpidem, or zaleplon. • Eszopiclone is used for the long- term treatment of insomnia and for sleep maintenance. It is prescribed to patients who have difficulty falling asleep as well as those who experience difficulty staying asleep, and is available in (1-, 2-,or 3- mg)tablets. • Eszopiclone received FDA approval based on six randomized placebo- controlled clinical trials that showed it has efficacy in treating transient and chronic insomnia
    44. 44. Inverse agonist at BZD Receptor • Inverse agonists at the BZD site act as negative allosteric modulators of GABA-receptor function. • Their interaction with BZD sites on the GABAA receptor can produce anxiety and seizures.
    45. 45. Sarmazenil •Partial inverse agonist at the benzodiazepine site. •It is used in veterinary medicine to reverse the effects of benzodiazepine sedative drugs in order to rapidly re-awaken anaethetised animals. β Carbolines •In addition to their direct actions, these molecules can block the effects of benzodiazepines. •Uses as convelsants. Negative allosteric modulators at benzodiazepine
    46. 46. BZD-site Antagonist
    47. 47. FLUMAZENIL: A BENZODIAZEPINE RECEPTOR ANTAGONIST • Flumazenil (ROMAZICON, generic), the only member of this class, is an imidazobenzodiazepine that behaves as a specific benzodiazepine antagonist. • Flumazenil binds with high affinity to specific sites on the GABA-A receptor, where it competitively antagonizes the binding and allosteric effects of benzodiazepines and other ligands. • Flumazenil antagonizes both the electrophysiological and behavioral effects of agonist and inverse-agonist benzodiazepines and B-carbolines. • Recommended dose 1mg IV . t1/2 of ~1 hour.dose repeated till 5 mg
    48. 48. FLUMAZENIL • Can be used to reverse the effect of benzodiazepine overdosage , or to reverse the effect of benzodiazepines such as midazolam used for minor surgical procedures. • It has been found to be effective in overdoses of non- benzodiazepine sleep enhancers - zolpidem and zaleplon. • Use in hepatic encephalopathy & alcohol intoxication have yielded mixed results. • Used as a PET radioligand labeled with carbon-11 to visualize the distribution of GABAA receptors in brain. • Flumazenil is not effective in single dose overdoses with either barbiturates or Tricyclic antidepressants rather it may cause seizures in patients poisoned with TCA’S.
    49. 49. Barbiturates: Barbiturates also facilitate the actions of GABA -A at multiple sites in the central nervous system, but—in contrast to benzodiazepines—they appear to increase the duration of the GABA-gated chloride channel openings. At Higher concentrations, barbiturates directly increase chloride ion conductance.
    50. 50. Antiepileptic actions at GABAA Receptors • Modulate GABAA receptor activation • Phenobarbital • Clonazepam, Diazepam • Topiramate • Increase GABA biosynthesis • Valproate • Decrease GABA degradation • Tiagabine • Vigabatrin
    51. 51. GABAergic terminal
    52. 52. Inhibition of uptake increases GABA action
    53. 53. VALPROIC ACID • An analogue of valeric acid • Believed to affect the function of the neurotransmitter GABA in the human brain by inhibition of GABA transaminase. • Other mechanisms of action  Blocks the voltage-gated Na+ channels  Blocks T-type Ca++ channels.  Inhibits the enzyme histone deacetylase 1 (anti convulsant action)
    54. 54. VALPROIC ACID Indications • Manic episodes associated with bipolar disorder. • As an anticonvulsant in Absence seizures Juvenile myoclonic epilepsy Tonic -clonic seizures Posttraumatic epilepsy Complex partial seizures Lennox-Gastaut syndrome • Valproic acid is cytotoxic to many different cancer types through its action as a histone deacetylase inhibitor. • Being tried in multiple, myeloma, glioma, melanoma, breast cancer, cervical cancer and ovarian cancer.
    55. 55. VIGABATRIN • VIGABATRIN is a “suicide inhibitor” of GABA transaminase. • It blocks the conversion of GABA to succinic semialdehyde,resulting in high intracellular GABA concentrations and increased synaptic GABA release. • Primary indication for vigabatrin treatment of simple and complex partial seizures but it can also be used for generalised seizures. Other Uses – Drug refractory epilepsy and infantile spasm. Dose:- 2 gm/ day . Side Effects:-1.Behavioural changes. sedation ,Amnesia ,Weight gain In 1% of cases visual field defects due to peipheral retinal atrophy.
    56. 56. TIAGABIN • Tiagabine (GABITRIL) is a derivative of nipecotic acid • Approved by the FDA as adjunct therapy for partial seizures in adults. • Tiagabine inhibits the GABA transporter, GAT-1, and thereby reduces GABA uptake into neurons and glia. • Paradoxically, tiagabine has been associated with the occurrence of seizures in patients without epilepsy • Its contraindicated in absence seizure. Other side effects – Sedation, fatigue, tremors and confusion. Dose:- 20-60 mg per day in 3 to 4 equally divided doses.
    57. 57. GABAPENTIN & PREGABALIN • Gabapentin (NEURONTIN, others) and pregabalin (LYRICA) are anti-seizure drugs that consist of a GABA molecule covalently bound to a lipophilic cyclohexane ring or isobutane respectively. • Pregabalin increases neuronal GABA levels by producing a dose-dependent increase in glutamic acid decarboxylase activity. • Gabapentin & pregabalin bind to the α2δ (alpha2delta) subunit of the voltage- dependent calcium channel in the central nervous system and decrease the synaptic release of glutamate.. Recent evidence suggest that they also function as GABAB receptor agonist.
    58. 58. • P.K - Gabapentin and pregabalin are absorbed after oral administration . It is neither metabolised nor bound to plasma proteins and are excreted unchanged, mainly in the urine. • Their half-lives, approximate 6 hours. • These compounds have no known interactions with other anti-seizure drugs. Therapeutic Uses: Drug resistant partial seizures & G.T.C . also is being used for the treatment of migraine, chronic pain, and bipolar disorder. FDA Approves Lyrica (Pregabalin) for Treatment of Neuropathic Pain in 2005. Side effects :- Somnolence, dizziness, ataxia, and fatigue. Dose – 200-300 mg TDS.
    59. 59. Role OF GABA RECEPTORS IN ANAESTHESIA Anaesthetics primarily act by either enhancing inhibitory signals or by blocking excitatory signals
    60. 60. GENERAL ANAESTHETICS • Currently, there are 5 major inhalational and 5 intravenous anesthetics used to induce or maintain general anesthesia. • Inhalational:Nitrous Oxide, Isoflurane, Sevoflurane, Desflurane and Xenon. • Intravenous: Propofol, Etomidate, Ketamine, Methohexital and Thiopental. Of these 10 general anesthetics, except ketamine, nitrous oxide and xenon other7 general anesthetics and sedatives like midazolam, diazepam and lorazepam share a common target and mechanism of action,i.e. they all enhance the function of GABA-A receptors.
    61. 61. General anaesthetics • The extrasynapic α5ß3γ2 receptor in hippocampus is probably assosciated with amnestic action of anaesthetic. • Those receptors having δ subunit s at ventrobasal thalamic nucleus may be linked to intruding reversible loss of consciousness during anaesthesia. • Since general anaesthetics are hydrophobic and need to access the CNS they target hydrophobic pockets within the transmembrane domains of the receptor.
    62. 62. Single amino acids determine i.v. anaesthetic activity ? • If GABA-A receptors are important targets for general anaesthetics,are all receptors equally sensitive to their effects? or are certain subunit combinations more sensitive than others? • Etomidate which demonstrates selective effects for receptors containing certain subtypes of the ßsubunit. For example, receptors containing ß2or ß3, but not ß1subunits are particularly sensitive to the modulatory effects of this anaesthetic.4 Studies using a molecular techniques demonstrated that the selectivity of etomidate maps to a single amino acid located within the second transmembrane domain (TM2) of the b subunit (asparagine for ß2 and ß3, and serine for ß1 subunits). Exchanging the asparagine for serine at ß2 increased the sensitivity of etomidate.
    63. 63. A binding site for volatile anaesthetics? • The effects of volatile agents on GABA-A receptor activity are also influenced by a single amino acid. (serine) is located within the TM2 region in the α subunit. • Subsequent studies demonstrated that the volume of this amino acid correlated with the activity of volatile anaesthetics on GABA-A receptors. Specifically, substitution with small volume amino acids enhanced the potentiating activity of isoflurane,halothane, and chloroform, whereas the presence of bulkier amino acids reduced anaesthetic activity. • Use of volatile agents of differing size (isoflurane, 144 A ° ; halothane, 110 A ° , and chloroform, 90 A ° ) led to the proposalthat the four amino acid residues from the extracellular end of TM1, TM2, TM3, and TM4 domains of the a subunit contribute towards an anaesthetic binding pocket for volatile agents
    64. 64. Neuroactive steroids Synthesized in the central and peripheral nervous system, especially in myelinating glial cells, from cholesterol or steroidal precursors. • These include pregnenolone (PREG) and dehydroepiandrosterone (DHEA), their sulfates, and reduced metabolites. • Neurosteroids have a wide range of potential clinical applications from sedation to treatment of epilepsy and traumatic brain injury.
    65. 65. NEUROACTIVE STEROIDS • Allopregnanolone and tetrahydrodeoxycorticosterone have been surmised to enhance GABA-mediated Cl¯ currents, whereas pregnenolone sulfate & dehydroepiandrosterone (DHEA) sulfate display functional antagonistic properties at GABAA receptors. • Ganaxolone, an analog of the endogenous neurosteroid allopregnanolone, is under investigation for the treatment of epilepsy and was effective in the treatment of partial seizures in adults and was tolerated.
    66. 66. This animation shows one model for how neurosteroids may increase Cl– flux through a GABA-A receptor. Binding of the neurosteroid (ALLO) allows a protein kinase C (PKC) phosphorylation site to become accessible. Phosphorylation of the channel increases flux through the channel, allowing more Cl– ions to flow through the channel in the presence of GABA than when the channel is activated by GABA without prior phosphorylation. The top of this animated gif shows how the channel, the ligands, and G protein-activated PKC may be interacting at the plasma membrane. The bottom of the animation shows how these interactions affect the current trace recorded using electrophysiological techniques. In the current trace, the size of the signal is smaller in the absence of neurosteroid compared to the size of the signal after exposure to neurosteroid and subsequent phosphorylation of the channel.
    67. 67. ALPHAXOLONE Neurosteroid general anaesthetic. A study 1987 found the primary mechanism for the anaesthetic action of alfaxalone to be modulation of neuronal cell membrane chloride ion transport, induced by binding of alfaxalone to GABAA cell surface receptors. It is licensed for use in both dogs and cats. Unlike some of its predecessors alfaxalone is not associated with histamine release and anaphylaxis. • A 1994 study found that alfaxalone binds to a different region of this receptor than the benzodiazepines. • Alfaxalone is metabolised rapidly in the liver. Alfaxalone has a very short plasma elimination half-life in dogs and cats
    68. 68. OTHER NEUROACTIVE STEROIDS Drug Details Hydroxydione •Proved to be a useful anaesthetic drug with a good safety profile. •But was painful and irritating when injected probably due to poor solubility Althesin (alphaxolone + alphadolone) •Withdrawn from human use due to rare but serious toxic reactions, but is still used in veterinary medicine Minaxolone •Around three times more potent than althesin without the toxicity problems. •Withdrawn because animal studies suggested potential carcinogenicity
    69. 69. ALCOHOL & GABA RECPTOR
    70. 70. Alcohol • Ingestion of ethanol results in a dose-dependent reduction of central nervous system (CNS) activity. • For several decades, it was presumed that this CNS depression was due to a major effect of ethanol is through BZD receptors on GABA. • But, a lack of ethanol’s effect on GABA responsiveness from isolated neurons with this receptor subtype discontinued this contention. • Direct action of ethanol on α4β3δ or α6β3δ selectivity for separate GABA mimetic action is proved today.
    71. 71. NEUROSTEROID INVOLVEMENT IN THE GABAMIMETIC PROFILE OF ETHANOL Following ethanol consumption there is activation of the hypothalamicpituitary- adrenal (HPA) axis (denoted by the darkened arrows), ethanol increases neurosteroid precursors from the adrenal, which in turn results in increased neurosteroids in brain . Since neuroactive steroids enhance GABA responsiveness (Lambert et al, 2001, 2003; Paul and Purdy, 1992), it is proposed that the ethanol-induced enhancement of neurosteroid presence in brain synergizes theeffect of GABA released by ethanol (Criswell and Breese, 2005).
    72. 72. GABA - GLUTAMATE + Alcohol
    73. 73. GABA - GLUTAMATE + Chronic Alcohol
    74. 74. ROLE OF GABA IN ALCOHOL WITHDRAWAL Thaugh benzodiazepines have been the primary treatment modality for alcohol withdrawal. A growing number of preclinical and clinical studies suggest that the anticonvulsants like gabapentin m Two RCT – First (n=60) and second (n=21) proved that gabapentin was significantly more effective than placebo for prevention of alcohol withdrawal symptoms But except insomnia. Other drugs which are currently investigated for alcohol withdrawal effect are –Baclofen and GHB.
    75. 75. GHB (Gamma hydroxy butyric acid) Gamma-hydroxybutyric acid (GHB) gammaaminobutyric acid (GABA) that has been used in research and clinical medicine for many years. is a naturally occurring analog of
    76. 76. GHB (Gamma hydroxy butyric acid) • GHB usually exists either as a free acid, or as a sodium salt. The sodium salt is called Sodium Oxybate • and is soluble in water and methanol. • GHB as is used to treat cataplexy and excessive daytime sleepiness in patients with narcolepsy. • MOA: • GHB has at least two distinct binding sites in the CNS. – Agonist at the newly-characterized GHB receptor, which is excitatory • Weak agonist at the GABAB receptor, which is inhibitory. Previously used as an anesthetic in 1960s but • was withdrawn due to its side effects like seizures and • coma. Due to its euphoric effects, it is nowadays used as • ‘POTENNTIAL ABUSIVE DRUG’
    77. 77. EPIDEMIOLOGY OF GHB ABUSE
    78. 78. Effects…
    79. 79. NEGATIVE POINTS POSITIVE POINTS Rave drug Can be used in narcolepsy Date rape drug Tried for alcohol withdrawal Body builders addiction. Excellent dilator of cervix Euphoria & crime Can be used as an aphrodesiac GHB Rage or reprive?
    80. 80. GABAB Agonist
    81. 81. BACLOFEN Derivative of GABA (β- parachlorophenyl GABA) It is primarily used to treat spasticity. In disorders like multiple sclerosis,ALS,Spinal injuries. However its relatively ineffective in stroke , parkinsonism Cerebral palsy and rheumatic muscle spasm. Tolerance does not develop - baclofen retains its therapeutic anti- spasmodic effects even after years of use.
    82. 82. Baclofen • Primary site is possibly the spinal cord where it depresses both polysynaptic and monosynaptic reflexes • Also used in tardive dyskinesia and alcohol withdrawal • ADR - Sedation (less than BZDs), confusion, weakness. • Baclofen can be delivered directly into the space around the spinal cord by use of a surgically implanted pump and an intrathecal catheter. Excreted unchanged in urine with t1/2- 3 to 4 hrs Dose -10 to 25 mg TDS.
    83. 83. Phenibut • β-Phenyl-γ-aminobutyric acid is a derivative of GABA. • Binds the GABAB metabotropic receptor. • The addition of a phenyl group in the β position allows phenibut to cross the blood brain barrier. • Only the R enantiomer is biologically active • Sold as a dietary supplement in the United States, while in Russia it is sold as a neuropsychotropic drug.
    84. 84. Phenibut • Structurally similar to baclofen & phenylethylamine. – Pharmacological effects of phenibut are similar to baclofen, but less potent. – Additionally, can function as a phenylethylamine receptor antagonist. – Furthermore, phenibut has been shown to enhance levels of dopamine. • Has anxiolytic effects in both animal models and in humans.
    85. 85. Phenibut • Used to treat a wide range of ailments including post-traumatic stress disorder, anxiety, and insomnia. • It has been reported by some to possess neurotropic actions for its ability to improve neurological functions, • ADR - Sedation
    86. 86. GABAB Antagonist
    87. 87. Saclofen & Phaclofen • These are competitive antagonist at GABAB receptor. • This drug is an analogue of the GABAB agonist Baclofen. • The action of saclofen on the CNS is understandably modest, because G-proteins rely on an enzyme cascade. • However, in animal experiments, saclofen is paradoxically observed to have an antiepileptic effect.
    88. 88. GABA analogues
    89. 89. Progabide • Analog and prodrug of GABA used in the treatment of epilepsy. • Agonist at both the GABAA and GABAB receptors. • Approved for either monotherapy or adjunctive use in the treatment of epilepsy—specifically, generalized tonic-clonic, myoclonic, partial, and Lennox-Gastaut syndrome seizures— in both children and adults
    90. 90. Progabide • Also being investigated for – Parkinson's disease – Schizophrenia – Depression – Anxiety disorder – Spasticity with various levels of success. • Tolgabide - analogue of progabide and acts similarly to it as a prodrug of GABA, and therefore as an indirect agonist of the GABA receptors.
    91. 91. Picamilon • Dietary supplement formed by combining niacin with GABA.It was developed in the Soviet Union in 1969 by the All-Union Vitamins Scientific Research Institute • Crosses BBB and is hydrolyzed into GABA and niacin. The released GABA would activate GABA receptors potentially producing an anxiolytic response • The second released component, niacin acts as a strong vasodilator, which might be useful for the treatment of migraine headaches
    92. 92. Picamilon In Russia, Picamilon is used for treatment of these illness. 1. Ischemic stroke 2. Asthenia 3. Depression 4. Senile psychosis 5. Alcohol intoxication 6. Migraine 7. Craniocerebral trauma 8. Neuroinfections 9. Primary open-angle glaucoma
    93. 93. GABA –C AGONIST • CACA – C Amino caproic acid . Weak agonist. • TACA – Trans isomer of CACA.strongest agonist at GABA – C receptor. • R- CAMP:- Recemic mixture of C-AMP acts as agonist .
    94. 94. TPMPA, Selective GABA-C Antagonist • Tetrahydropyridine ring of isoguvacine was unfavourable for interactions with GABAB receptors, while the • methylphosphinic moiety of 3-APMPA was unfavourable for interactions with GABA-A receptors led to the synthesisof TPMPA which incorporates both the tetrahydropyridine and methylphosphinic acid moieties in the one compound. • TPMPA has been used to provide evidence of functional GABAC receptors in the rat superior colliculus • mediating disinhibition , in cells in the gut involved in neuroendocrine secretion and in rat spinal cord . • TPMPA has been shown to enhance memory in chicks .
    95. 95. GABA C • Recombinant receptor technology. The cloning of ρ1 and ρ2 cDNAs from a human retinal library enabled expression of receptors in Xenopus oocytes that showed the characteristics expected of GABAC receptors . • GABAC receptors are expected to mediate the lateral inhibition of light responses and have been shown to inhibit transmitter release at bipolar cell terminals.
    96. 96. CRITERIA GABA-A GABA-B GABA-C Distribution Mammalian CNS Cerebellum & interpeduncular nuclei retina, spinal cord, superior colliculus, pituitary, and gastrointestinal tract. CATEGORY LGCC GPCR LGCC AGONIST GABA, Muscimol,THIP Baclofen SKF 97541 CACA ,GABA Isoguvacine(p) MODULATOR Benzodiazepines Anaesthetics Barbiturate Alcohol Neuroactive steroids ……. Zinc ANTAGONIST Bicucillin. Picrotoxin Gabazine Phaclofen Saclofen TPMPA THIP Picrotoxin Low conc.Zinc ion
    97. 97. Section III Herbal Preperations and GABA Receptors • Many herbal medicines are used to influence brain function in order to treat anxiety, cognitive disorders, and insomnia involving GABA receptor. • Usually Herbal products act as second order modulators i.e.they enhance the effect of first order modulators. • GABA itself is an important plant constituent, and thus it should not be surprising that plants contain a range of other chemicals that can influence GABA function
    98. 98. Bicuculline First isolated from the plant Dicentra cucullaria and subsequently from a variety of Corydalis,Dicentra, and Adlumia species. Competitive antagonist of GABAA receptor activation. •Utilized in laboratories in the in vitro study of epilepsy •Routinely used to isolate glutamatergic (excitatory amino acid) receptor function.
    99. 99. Picrotoxin Picrotoxin is an equimolar mixture of picrotoxinin and picrotin isolated from Anamirta cocculus and related poisonous plants of the moonseed family. Picrotoxinin is relatively nonspecific in that it is a potent antagonist at GABA-A and GABA-C, moderate at glycine, and weak at 5HT3 receptors. Can be used to counter barbiturate poisoning It is clear that bicuculline and picrotoxinin act at different sites to antagonize GABA.
    100. 100. Muscimol • Muscimol is one of the most widely used agonists in the investigation of ionotropic GABA receptors. • It is a more potent agonist at GABA- C receptors than at GABA-A receptors. • The agonist action of muscimol at GABA-C receptors is not blocked by bicuculline but is sensitive to picrotoxin • (Gaboxadol) is a conformationally restricted analogue of muscimol with analgesic and sleep-promoting properties It was investigated for the treatment of insomnia, but was recently withdrawn from phase III clinical trials due to efficacy and side-effect problems.
    101. 101. Apigenin – GABA Receptor Modulator • Common flavonoid found in a range of plants, including chamomile tea(Matricariarecutita). • The chamomile tea used in treatment for insomnia and anxiety led to investigations of its active constituents, including apigenin.Apigenin was found to have anxiolytic properties,and it competitively inhibited the binding of flunitrazepam to brain membranes • Enhancement of the diazepam-induced positive allosteric modulation of GABA responses by lower concentrations of apigenin , described as a second-order modulation
    102. 102. Epigallocatechin gallate (EGCG) • Epigallocatechin gallate (EGCG) is the major polyphenol in green tea (Camellia sinensis). • Studies on α1ß2γ2GABA-A receptors showed that EGCG at low concentrations has a potent second- order modulatory action on the first- order modulation by diazepam ( more than apegenin) • In well-controlled epidemiological studies it alters brain-aging processes and to serve as possible neuroprotective agents in progressive neurodegenerative disorders. e.g. Parkinson’s and Alzheimer’s diseases
    103. 103. Hispidulin and Related Flavonoids • Hispidulin (the 6-methoxy derivative of • apigenin) was isolated together with apigenin from • Salvia officinalis (sage) recently using a benzodiazepine binding assay- guided fractionation. • Hispidulin was some 30 times more potent than apigenin in displacing flumazenil binding. • Used in herbal medicine to assist memory. • An extract of Salvia lavandulaefolia (Spanish sage) has been shown to enhance memory in healthy young volunteers.
    104. 104. Section IV CURRENT KNOWEDGE SCENARIO & FUTURE TRENDS
    105. 105. GAD 65 OR GAD 67 ? Knockout of GAD65 has major impact on synaptic GABA synthesized from astrocyte-derived Glutamine.1 • Two isoforms : GAD- 65 & GAD- 67 • GAD65 is crucial for maintenance of biosynthesis of synaptic GABA particularly by direct synthesis from astrocytic glutamine via glutamate. • The GAD67 was found to be important for synthesis of GABA from glutamine both via direct synthesis and via a pathway involving mitochondrial metabolism.
    106. 106. GENE ORGANISATION OF SUBUNITS The majority of genes coding for the GABA-A receptor subunits are organized into four clusters on chromosomes 4, 5, 15, and X in the human genome
    107. 107. • Pharmacological analysis of GABA receptor was simplified after introduction of animal models in which particular GABA- A receptor subunits are either inactivated (knock out) or selectively point mutated ( knock in). KNOCK OUT SUBUNIT RESPONSE α6 Motor impairing action of mice on rota rod to daiazapine. ß3 Die in neonatal period. Epileptic seizure. γ2 Sleep time was prolonged. No action of benzodiazapines. δ Increased sleep time and convulsions.No action of alcohol. GENE KNOCKOUT & KNOCK IN TECHNIQUE
    108. 108. GABA OLD RECEPTOR NEW TARGETS
    109. 109. GABA – AS IMMUNOMODULATOR • In lymphocytes,exposure to GABA reduced but did not abolish the transient increase in the intracellular calcium concentration that was associated with activation of the cells (Alam et al.2006). • GABA activated GABA-A ionchannel currents in T cells and macrophages (Bjurstom et al. 2008; Bhat et al. 2010; • GABA application resulted in decreased cytokine secretion and T cells proliferation (Mendu et al. 2011)
    110. 110. GABA – AS IMMUNOMODULATOR • GABA appears to have a role in autoimmune diseases • like MS, type 1 diabetes and rheumatoid arthritis and maymodulate the immune response to infections (Bhat et al. 2010; Mendu et al. 2011; Soltani et al. 2011; Tian et al. 2011; Wheeler et al. 2011). • Has even a role in Alzheimer disease, stroke and traumatic brain injury (Popovich and Longbrake 2008; Schwartz and Shechter 2010)
    111. 111. Role of GABA – IN TYPE- I DM • Currently a trial with hypothesis that GABA, a naturally occurring substance, has the potential to reduce the inflammation and protect the pancreatic beta cells from autoimmune destruction. • GAD-alum may contribute to the preservation of residual insulin secretion in patients with recent onset, Type I Diabetes. • condition :Type I Diabetes • Drug: Glutamic Acid Decarboxylase in alum formulation • Status :-Phase 1
    112. 112. GABA & SCHIZOPHRENIA • In subjects with schizophrenia, impairments in working memory are associated with dysfunction of the dorsolateral prefrontal cortex (DLPFC). • This dysfunction appears to be due, at least in part, to abnormalities in Gamma-aminobutyric acid (GABA)-mediated inhibitory circuitry. • Various experimental findings suggest that schizophrenia is associated with alterations in inhibitory inputs from SST/NPY- containing and CCK containing subpopulations of GABA neurons and its signaling via certain GABA-A receptors that mediate synaptic (phasic) or extrasynaptic (tonic) inhibition .
    113. 113. GABA-B Receptor Complex Target for Tumor Therapy A positive correlation between GABA B2 (minor b1)expression and that of thyroid tumors is seen. GABAB1 immunostaining of human ductal breast cancer tissues (from patents shows Intensive b unit staining in the cytosol and less frequently in the nucli.
    114. 114. INTERVENTION CONDITION STATUS 1. GAD-Alum Juvenile onset type-1 DM. PHASE – 1 A 2. Merck L-830982 GABA-A Alpha2/3 Receptor Agonist Schizophrenia PHASE – 2. 3. Pregabalin Pain after posteriar spinal fusion. PHASE - 4 4. Vigabatrin Coacaine abuse PHASE -2 A. 5. Gabapentin Smoking PHASE – 1. 6. Lomazenil ALCOHOL ABUSE PHASE -1. Trial scenario related to GABA…
    115. 115. Conclusion…. • Despite the overwhelming representation of the GPCRs in the human genome, it is the ionotropic receptors which achieved most visibility till today. The paucity of molecular heterogeneity exhibited by the GABA-B receptors has proved problematic for specific drug targeting. • Pharmacologists had to wait till gene knockout tecnique and readymade animal models became available till early 2000. • The next decade will undoubtedly prove Exciting with these recent genetic tools in hand...........
    116. 116. THANK YOU….
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