Biogenic amine transmitters: Acetylcholine, norepinephrine, and dopamine

This chapter explores the use of drugs for veterinary mental health care and behavior modification and focuses on biogenic amine transmitters. Acetylcholine was the first compound to be identified as a neurotransmitter in the peripheral nervous system. Acetylcholine released from neurons into the synaptic cleft is hydrolyzed by the membrane bound enzyme, acetylcholinesterase, which represents the mechanism for termination of the signal in cholinergic neurotransmission. The neurotransmitter norepinephrine is distributed throughout the brain. Norepinephrine interacts with both alpha and beta adrenergic receptors expressed in the brain. The renewed attention on noradrenergic pathways is consistent with the original formulation of the biogenic amine theory of affective disorders which posited that depressive symptoms arose from a deficiency of biogenic amines such as norepinephrine. Dopamine is a catecholamine neurotransmitter originally believed to function only as a precursor for norepinephrine and epinephrine biosynthesis.