Wayne Hodgson; Week 9 MED1011; Pharmacology
There are over 50 transmitters, can be excitatory or inhibitory, some examples are biogenic amines (monoamines, acetylcholine), amino acids (GABA, glutamate), peptides (ENK), others (NO, adenosine). Neurotransmitters are synthesised and released from nerves. There should be an active mechanism for termination of the activity of the neurotransmitter. Parasympathetic nerve ganglia are closer to organs than sympathetic nerves. Somatic do not have ganglia, are involved in breathing and movement. NA releasers are adrenergic, ACh are cholinergic.
Adrenergic transmitters are NA, A, dopamine and all are formed from tyrosine. Adrenergic nerves can have two receptor subtypes, alpha or beta. Heart and lungs are mainly beta, blood vessels are both, these classifications are linked to second messengers. They are involved in fright/flight reactions. Inactivated mainly by reuptake into nerve, blocked by cocaine, enzymatic breakdown is from monoamine oxidases and COMT. Adrenergic release can be caused by amphetamines and indirectly acting sympathomimetic
Cholinergic nerves are nicotinic or muscarinic. ACh is produced by choline. Particularly innervates skeletal muscle (N), heart (M), GIT (M). Inactivation is mainly due to breakdown in synapse, must be removed/inactivated almost immediately (occurs in <1ms, much quicker than adrenergic or M cholinergic).
5-HT mediates neurotransmission at CNS and PNS, found at high concentrations in blood platelets for aggregation and intestinal wall for motility as well as the brain. Has a role in migraine, emesis, appetite, sleep/wake cycle and depression.
NO is an important mediator, is unconventional, an unstable gas and is synthesised on demand. Acts on endothelial cell to relax blood vessels. It is produced by O2 + arginine -> citrulline + NO. It is expressed in response to pathological stimuli and is present under physiological conditions.
Presynaptic modulation by either ACh or NA may enhance or inhibit transmitter release, or cotransmitters may have an effect on each other (many transmitters from one axon).