Modulation of Striatal Dopamine System by Thyrotropin-Releasing Hormone and Cyclo(His-Pro)

Abstract

Dopamine (DA) was believed to be precursor in the synthesis of norepinephrine. DA is the normal constituent of the mammalian brain and accounts for as much as 50% of the total brain catecholamine. DA might serve as a neurotransmitter in brain. Studies of the neuroanatomy of the rat brain have shown that up to six or more defined DA pathways may exist within the central nervous system. Among these the highest amount of DA is present in the caudate nucleus and putamen regions. Striatum is also richly endowed with a number of peptides including cholecystokinin, somatostatin, enkephalin, vasoactive intestinal peptide, alpha-MSH, neuropeptide-Y, TRH, and cyclo. Many of these peptides are intrinsic to striatum whereas others are of either extrinsic or unkown origin. The chapter reviews the work performed on the modulation of striatal DA system by TRH and cyclo.