Neurotransmitter

1. Neurotransmitters
Dr. Surakshya Gautam
Department of Biochemistry

2. Objectives
Neurotransmitters : Definition, properties
Synaptic transmission
Neuromuscular transmission
Neurotransmitter receptors
Types : Acetyl choline, Dopamine, NE, E, GABA,
Serotonin, NO

3. Structure of neuron
Chemical
activity

4. Synaptic
transmission
Synaptic
cleft
Synaptic
vesicles
Neurotransmitter
Around 10,000 molecules of NT are
contained in vesicle

5. NEUROTRANSMITTERS
• Neurotransmitters are endogenous chemicals that
transmit signals across a synapse from one neuron (brain
cell) to another 'target' neuron.
• Neurotransmitters are packaged into synaptic vesicles
clustered beneath the membrane in the axon terminal, on
the presynaptic side of a synapse.

6. Criteria for Neurotransmitter
1. Must be present or synthesized within neuron
2. Must be stored within the nerve ending prior to
release, e.g. in synaptic vesicles
3. Must be released from the presynaptic ending in
response to an action potential
4. Must recognize and bind the receptors present on
the postsynaptic neuron or effector cell
5. Some mechanisms must exist for the inactivation of
the biological activity after chemical’s work is done

7. Classification of Neurotransmitters
Neurotransmitters can be broadly split into two groups:
• Based on chemical composition
– the ‘classical’, small molecule neurotransmitters, and
– the relatively larger neuropeptide neurotransmitters
• Based on the effect on postsynaptic end
– Excitatory
– Inhibitory

8. Resting membrane
potential inside the
neuron is -70mv

9. Excitatory
(1) Opening of Na+ channels
(2) Depressed conductance Cl- or K+ channels or both
Inhibitory
(1) Opening of Cl- ion channels through receptor.
(2) ↑ in conductance of K+ ions through the receptor.

10. Classical Small Molecule NTs
Type Neurotransmitter Postsynaptic effect
Choline ester Acetylcholine Excitatory
Amino acids γ-aminobutyric acid (GABA) Inhibitory
Glycine Inhibitory
Glutamate Excitatory
Aspartate Excitatory
Biogenic amines Dopamine (DA) Excitatory
Epinephrine (Epi) Excitatory
Norepinephrine (NE) Excitatory
Serotonin (5-HT) Excitatory
Histamine Excitatory
Gases Nitric oxide (NO) Excitatory and Inhibitory
Carbon Monoxide (CO) Excitatory and Inhibitory

11. Larger Neuropeptide NTs
Large transmitter molecules composed of 3 to 36 amino acids
1. Opioid: enkephalins; β-endorphin
2. Neurohypophyseal: vasopressin; oxytocin; neurophysins
3. Tachykinins: substance P; neurokinin A; neurokinin B
4. Gastrins: gastrin; cholecystokinins
5. Somatostatins: somatostatin 14; somatostatin 28
6. Glucagon-related: vasoactive intestinal polypeptide
7. Pancreatic-polypeptide
8. Miscellaneous: bombesin; neurotensin; bradykinin;
angiotensin; calcitonin gene-related peptide

12. Specific to ion

14. Neurotransmitter receptors
They are protein embedded in the plasma
membrane of postsynaptic cells
Domains of receptor molecules extend into the
synaptic cleft bind neurotransmitters
This will directly or indirectly cause ion channels in
the post synaptic membrane to open or close
Resulting ion fluxes will change the membrane
potential of post synaptic cell and thus mediating
the transfer of information across the synapse.

15. Neurotransmitter Receptors
Two main families:
A. Ionotropic receptors
ligand gated ion channels
B. Metabotropic receptors
coupled to G-protein
uses cAMP or IP3 as 2nd messenger

16. Ionotropic receptors
Fast acting ligand-gated
ion channels
It combine transmitter
binding and channel
function into single
entity
Multimers made up of at
least 4 or 5 individual protein
subunits, each of which
contributes to the pore of
the ion channel

17. Metabotropic Receptor
• Slow acting G-proteins coupled receptors

18. • These receptors do not have ion channels as part of
their structure; instead, they affect channels by the
activation of intermediate molecules called G-proteins
• Aks G-protein-coupled receptors
• Are monomeric proteins with an extracellular domain
that contains a neurotransmitter binding site and an
intracellular domain that binds to G-proteins.

19. Thus, G-proteins can be thought of as transducers that
couple neurotransmitter binding to the regulation of
postsynaptic ion channels

20. Most neurotransmitters can activate
multiple receptor subtypes and receptor
classes

21. Receptors for Various
Neurotransmitters

22. Steps in chemical transmission

23. Removal of neurotransmitters
• Diffusion away from the postsynaptic receptors, OR
• Reuptake into nerve terminals or surrounding glial
cells, OR
• Degradation by specific enzymes, OR
• Combination of these mechanisms.