For each of the substances associated with synaptic transmission A–E, select the best option for its possible function from the following list

A. Option 3 Involved in the breakdown of catecholamines. Catecholamines are inactivated by oxidation by the enzyme MAO that is found in some neurones.

B. Option 5 Involved in the breakdown of acetylcholine. Cholinesterase is found in high concentration near motor nerve endings in muscle and rapidly hydrolyses acetylcholine following its release from the nerve endings.

C. Option 2 Involved in the genesis of inhibitory post-synaptic potentials (IPSPs). GABA is released from pre-synaptic nerve endings and causes hyperpolarization of the post-synaptic membrane so causing an IPSP.

D. Option 4 A neurotransmitter in the brain involved in basal ganglia activity. Degeneration of dopaminergic neurones in the substantia nigra is associated with Parkinson’s disease.

E. Option 1 A neurotransmitter in the brain involved in determining mood. Serotonin containing nerves have been found in the brain stem. Selective serotonin uptake inhibitor drugs are used in the treatment of depression.