Question

Csondier the steps at synaptic trasmission (communication from one neuron to another across the synapse. describe two different ways that drugs can act at various points in the process of synaptic transmission. For each drug, describe 10) at what point in the process of synaptic transmission it acts, and what its effect is, 2 what effect this has on the amount of neurotransmitter available in the synapse, and 3) what effect this has on the post-synaptic cell.

Answer 1

Drugs acting on Synaptic Neurotransmission

Two different ways that drugs can act at various points in the process of synaptic transmission are:

A) By inhibiting Anticholinesterase enzyme

Acetylcholine is one of the important neurotransmitters. It is a chemical message released by nerve cells (presynaptic neuron) to send signals to other cells (postsynaptic neurons). Anticholinesterases (AChE) promotes acetylcholine hydrolysis by forming an acetyl-AChE intermediate with the release of choline. Choline is transported back into presynaptic neuron and used again for formation of Acetylcholine. Thus AChE terminates neurotransmission at cholinergic synapses.

Anticholinesterases inhibit this cholinesterase enzyme thus prolong neurotranmission by preventing hydrolysis of ACh. 1. In the process of synaptic transmission, it acts on the ACh between synapse and Ach on its receptors on post synaptic neuron (or cell). The effect is longer neurotransmission.

2. It increase the amount of neurotransmitteravailable in the synapse.

3. In the post synaptic cell, there is continous firing and neurotransmission of signals.

Examples of Anticholinesterase - Carbamates such as Physostigmine, Neostigmine, Pyridostigmine, Rivastigmine etc

B) By blocking postsynaptic receptors

Many receptors for neurotransmitters are present on post synaptic nerve cells. Binding of neurotransmitters on postsynaptic receptors either cause excitation or inhibition.

Many drugs can antagonise these receptors by inhibiting neurotransmission in post synaptic cells. Thus the synaptic transmission can be stopped or reduced.

Examples: Atropine blocks the effect of Acetylcholine (ACh)

Check this picture for more exaples, targets and types of drugs acting on synaptic transmission.

2 Drug serves as precursor AGO (e.g., L-DOPA-dopamine) Precursor Drug inactivates synthetic enzyme inhibits synthesis of N.T ANT (e.g., PCPA-serotonin) Enzyme Drug prevents storage of N.T in vesicles ANT (e.g., reserpine-monoamines) Transmitter substance Drug stimulates autoreceptors; inhibits synthesis/release of N.T ANT (e.g., apomorphine-dopamine) Drug stimulates release of N.T AGO (e.g., black widow spider venom—ACh) Drug blocks autoreceptors; increases synthesis/release of N.T AGO (e.g., clonidine-norepinephrine) Drug inhibits release of N.T ANT (e.g., botulinum toxin—ACh) Inhibition Drug stimulates postsynaptic receptors AGO (e.g., nicotine, muscarine-ACh) Drug blocks reuptake AGO (e.g., cocainedopamine) Choline acetate Асh ба ACHE Drug blocks postsynaptic receptors ANT (e.g., curare, atropine-ACh) Drug inactivates acetylcholinesterase AGO (e.g., physostigmine-ACh) Molecules of drugs