Adrenergic Neurons: Neurotransmission

Adrenergic neurons in postganglionic sympathetic fibers release NA as the principal neurotransmitter.

NA is a catecholamine derived biosynthetically from its metabolic precursor tyrosine—an amino acid transported into the neuron via a sodium-dependant carrier.

In the cytoplasm, tyrosine is enzymatically hydroxylated to DOPA, which is further decarboxylated to DA.

Through amine transporters, DA moves from the cytoplasm to the synaptic vesicles and undergoes β-hydroxylation to yield NA.

The arrival of neuronal action potential triggers Ca²⁺  influx into the neuronal cytoplasm leading to vesicular exocytosis, releasing NA in the synaptic space.

The released NA binds to receptors on nerve endings or effector organs. This triggers a cellular cascade and the formation of second messengers, transducing the signal into an effect.

The unused NA either diffuses into the systemic circulation, is inactivated by COMT in the synapse or undergoes neuronal reuptake. Post-reuptake, NA is either taken up by synaptic vesicles or oxidized by MAO.