The document discusses neurotransmitters in the central nervous system. It defines the central nervous system and peripheral nervous system. Neurotransmitters are chemical messengers that transmit signals between neurons. The major neurotransmitters in the central nervous system are amino acids like glutamate and GABA, and amines like dopamine, serotonin, and acetylcholine. Neurotransmitters are synthesized and stored in neurons, then released into the synaptic cleft to activate receptors on the receiving neuron. This activation can be excitatory or inhibitory. The document discusses the synthesis, receptors, and functions of several important neurotransmitters like GABA, glutamate, dopamine, and acetylcholine.

2. CONTENTS
 Introduction
 Neurochemical transmission
 Neurotransmitters in Central Nervous System(CNS)
 Drugs act on Central Nervous System(CNS)

3.  Introduction :-
 The nervous system in higher animals can be divided in to
Central nervous system (CNS)
Peripheral nervous system (PNS)
Autonomic nerve fibres Somatic nerve fibres
 Not only concerned with regulation of specialized functions like circulation,
digestion & respiration responsible for the psychic processes such as felling
, attitude , thoughts & memory .
 CNS & PNS are analogous to elaborate system of telegraphy where in
numerous wires & connections in the form of neurons & synapses being
information from internal & external sources .
 The information is received , decoded are made by various centres in CNS
and instructions sent to peripheral tissues to produce responses
Psychic : Change in emotions , thought & attitude
 Somatic : Changes in various types of body movements
Autonomic : Changes in visceral , circulation &
respiration functions

5. Neurochemical transmission in nervous system :
 Mammalian nervous system is almost exclusively through chemical
messenger
 Neurosecretion is a fundamental property of all neurons
 Neurosecretion is a chemical released at nerve terminals those related to
blood circulation Neurohormones.
 E.g. : Hypothalamic hormones released from hypothalamopitutury
circulation
Neurotransmission
 3process Neuromediation
Neuromodulation

6. Neurotransmission :-
 Impulse is transmitted across a synapse between two neurons .
 Neurotransmitters (NT) are released in to synaptic cleft either by stimulation
or inhibit the post synaptic neuron
Certain criteria in order to accept NT:
 Must be present in the neurons & presynaptic nerve endings should have a
discrete rather than uniform pattern of distribution
 Must be released from presynaptic nerve terminal
 Enzymatic mechanisms capable of synthesizing and degraded the substance
should be present with in the neuron
 Local concentration of the substance related to function of neuronal
structure & fluctuations in its concentration
 Blocking agents should produce demonstrable effects by preventing the
access of transmitter

7.  Neuromediation :-
 Implies the elicitation of the post synaptic response to release
neurotransmitter through secondary response
 Such as cAMP , cGMP & inositol phosphate
 Neuromodulation :-
 Less clearly defined process than neuro-transmission
 Occur at pre & post synaptic levels to regulate the release of NTs
 Arise from neurons as well as from non-neuronal cells they are not stored or
released like neurotransmittors
 Act with a longer duration of action & longer latency of action
 E.G: Adenosine , prostaglandins , nitric oxide

8. CNS neurotransmitters
 CNS has both excitatory & inhibitory chemicals transmitters
 They are Amines : Ach , nor adrenaline , dopamine , serotonin , histamine
Amino acids :- L-glutamic acid & aspartic acid , GABA , glycine
Peptides : substance p , cholecystokinin
• GABA &glycine are inhibitory NT where as dopamine is selectively either
stimulatory or inhibitory at different sites
• Many drugs which modify the functions of CNS and affect the
concentration of one or more of them in Central as well as Peripheral
nervous system
• Many of the endogenous peptides are discovered in the brain e.g.
angiotensin , endorphins , vasopressin , endocrine peptides & gut peptides
• They regulate neuronal functions by themselves

10. Gamma amino butyric acid (GABA)
 Major inhibitory amino acid in NT in brain
 Most of the GABA receptors are composed of α,β,γ subunits
 Receptors composed of α & β subunits produce functional GABAA receptor
bind to barbiturates does not to benzodiazepines
 γ assemble with benzodiazepines
 Absence of GABA benzodiazepines have no effect on GABAA
 GABAB is a metabotropic receptor , activates drug baclofen relaxes muscle
relaxant

11. synthesis
 Glutamine Glutamate
GABA
vesicles
Exocytosis
Presynaptic nerve terminal via
GABA transporters & repacked in
vesicle
Glutamine
Decarboxylation
l-glutamic acid
decarboxylase
stored
Released in synaptic cleft
After release

12. Glutamate & Aspartate
 Is a essential amino acid (EAA)
 These are A.A are present in various parts of brain
 Plays an important role excitatory in NT throughout CNS
 Released from presynaptic nerve terminals & binds to several glutamate
receptors
 Their activation increases the conductance of Na⁺ & Ca⁺⁺ in to cells leading
to depolarization (inotropic glutamate receptors) or stimulates
(metabotropic glutamate receptors)
 2 Inotropic glutamate receptors are NMDA (n-methyl D-aspartic acid) &
non-NMDA (a-amino-3-hydroxy-5-methyl-4-isooxasole propionic acid)
 Non-NMDA associated with excitatory postsynaptic potentials at
glutamatergic synapsis
 NMDA is associated with LTP prolonged increase in size of post synaptic
response to a presynaptic stimulus
 EAA involved in brain process such as learning ,memory, thinking
 Very high concentrations of glutamine can cause neuronal cell death

14. Dopamine and its receptors
 Dopamine is primarily an inhibitory neurotransmitter. Its deficiency causes
extrapyramidal disturbances. There are five receptors identified – D1-D5.
Activation of D1 and D5 stimulate adenylyl cyclase and increase the release
of cAMP;
 D2-4 inhibits adenylyl cyclase and decrease the release of cAMP. The
locations of these receptors are –
 D1 – Nigrostriatal pathway (putamen, nucleus accumbens and olfactory
tubercle). Its inhibition causes extrapyramidal disorders.
 D2 – Striatum, substantia nigra and pituitary. It is involved in the control of
the behavior, voluntary movements, prolactin release and other endocrine
consequences.
 D3 – Midbrain, nucleus accumbens and hypothalamus.
 D4 – Mesocortical pathway (frontal cortex, medulla and midbrain). Some
of the atypical neuroleptics possess D3 and D4 antagonistic activity, but
their exact role in schizophrenia is not yet fully established.
 D5 – Hypothalamus and hippocampus. Its exact role is not known.

15. Dopamine synthesis

16. Acetyl choline
 First neurotransmitter discovered & described as vagus stuff by Otto Loewi
 Known to be neurotransmitter at autonomic ganglia
 It is mainly found in interferon's
Synthesis
 Glucose enters the nerve terminals by passive transport
 Glycolysis occur in neuronal cytoplasm & pyruvic acid molecules are
generated
 Pyruvate mitochondria and an acetyl group is derived from pyruvic
acid + coenzyme-A present in mitochondria to form acetyl coenzyme-A
 Ach is actively transported to neuronal terminal from synaptic cleft (via
sodium & choline transporters)
 Ach is synthesized in cytoplasm of nerve terminal from choline & acetyl
coenzyme-A in presence of an enzyme choline acetyltransferase
 Ach is transported to vesicles and stored
 Released in to synaptic cleft by exocytosis

17. Acetyl choline synthesis

18. Regulations in neurotransmission release
 Located on specialized release sites on presynaptic memberaine
 Neurons communicate with each other through NTs highly localized Ca⁺⁺
influence act as stimulus to rapid release of NT
 Activation of presynaptic receptors closes a feedback loop which leads to
enhancement or inhibition of NTs release
 These receptors are called as auto receptors
 Presynaptic receptors are several types include both G protein linked
(metabotropic) & multi unit ion channel (ionotropic) types
 Activation of G-protein linked receptors leads to reduction in evoked NT
release closes negative feed back loop
 Activation of ionotropic releases NT as a result ability to raise the calcium
ions in the terminals directly
 Presynaptic terminals may also have receptors responding to NTs released
from neurons


19.  Activation of hetero receptors influence the release of NTs
 Presynaptic receptors are important from neurophysiological point of view
& as potential targets for therapeutic agents
 Neurotropic factors :-
 These neuropeptides produced by neurons, astrocytes , microglia &
inflammatory cells assist in repair in tissue damage

20. References
Medical Pharmacology
Seventh Edition
KD TRIPATHI MD
Ex-Director-Professor and Head of Pharmacology
Maulana Azad Medical College and associated
LN and GB Pant Hospitals

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