Neuropharm Notes

Chapter 5 Notes * Dopamine and the related substances norepinephrine (NE) and epinephrine (EPI) comprise a small but important group of neurotransmitters and hormones called catecholamines. * Catecholamine contains two chemical similarities: a core structure of catechol and a nitrogen-containing group called an amine. The catecholamines, in turn, belong to a wider group of transmitter called either monoamines (transmitters that possess one amine group) or biogenic amines * EPI – adrenergic. NE- noradrenergic * Varying amount of these substances are found within the CNS, PNS, and the inner part of the adrenal glands (adrenal medulla). * The adrenal medulla secretes EPI and NE into the bloodstream, where they act as hormones. * The synthesis of catecholamine neurotransmitters occurs in several steps. * The biochemical pathways begins with the amino acid tyrosine. Tyrosine comes from dietary protein that is transported from blood to brain. * Neurons that use DA as their transmitter contain only the first two enzymes: tyrosine hydroxylase (TH) and aromatic acid decarboxylase (AADC), and thus the biochemical pathway stops at DA. * In contrast, neurons that need to synthesize NE also possess the third enzyme, which is called dopamine Beta-hydroxylase (DBH) * The conversions of tyrosine to DOPA by TH occurs at a slower rate than the subsequent reactions in the biochemical pathway. TH is the rate-limiting enzyme in the pathway, because it determines the overall rate of DA or NE formation. * The activity of TH is regulated by a variety of factors, including how much DA or NE is present within the nerve terminal.

* Catecholamine formation can be increased by the administration of a biochemical precursor such as L-DOPA. * Vesicular packaging is important not only because it provides a means for releasing a predetermined amount of neurotransmitter (usually several thousand molecules per vesicles)