Central Nervous System Neurotransmitters, Receptors, and Drug Targets
Many substances within the CNS modulate neurotransmitter actions. ACh and norepinephrine (NE), predominant in the PNS, also function in the CNS. Dopamine and 5HT (serotonin)—more prominent in the CNS—and peptides such as endorphins are important in CNS function. Transduction mechanisms for neurotransmitter action are similar to those in the PNS: ionotropic types include voltagegated ion channels (respond to membrane potential changes) and ligandgated ion channels (alter membrane ion permeability in response to ligands such as neurotransmitters or drugs). Metabotropic types include GPCRs and involve secondmessenger pathways (affect ion channels or biochemical reactions). Drugs affect various sites along neuronal pathways, including neurotransmitter synthesis, storage, and release; receptor activation and inhibition; modulation of intrasynaptic neurotransmitter metabolism or reuptake; and direct secondmessenger pathway effects.