Vasopressin: An Integrator of Proopiomelanocortin Activity in Brain and Pituitary
β-Endorphin (βE) and related peptides are synthesized as components of the multifactorial precursor molecule proopiomelanocortin (POMC), which also functions as the prohormone for corticotropin (ACTH), and melanotropin (α -MSH). Like ACTH and α-MSH, βE is liberated from this precursor molecule by proteolytic cleavage (Mains et al. 1977; Herbert et al. 1980). In the rat, POMC is synthesized in a variety of tissues including the corticotroph cells of the anterior lobe and the melanotroph cells of the intermediate lobe of the pituitary gland (Mains et al. 1977; Mains and Eipper 1979; Herbert et al. 1980). In the brain, POMC-containing neuronal cell bodies have been identified in different loci. The major cell group is located in the arcuate nucleus of the mediobasal hypothalamus (Watson et al. 1977; Bloom et al. 1978). Additional groups of neurons are found in the caudal part of the nucleus of the tractus solitarius (NTS) and in the nucleus commisuralis (Khachaturian et al. 1985; Palkovits et al. 1987). Numerous studies using immunocytochemical and biochemical techniques have dealt with the anatomy of these POMC-containing neuronal systems, and a wide array of brain structures appears to be innervated by POMC neurons (Watson et al. 1977; Finley et al. 1981). In particular, the POMC neurons in the arcuate nucleus form extensive projections to limbic and midbrain regions, whereas those found in the NTS area are thought to innervate primarily regions in the brainstem (Khachaturian et al. 1985; Palkovits et al. 1987). POMC-derived neuropeptides (including βE) can be secreted at the synaptic endings of these neurons, to act as neurotransmitters or neuromodulators and alter neuronal activity in a variety of brain circuits. As such, these peptides are involved in the regulation in the brain of cognitive, autonomous, and endocrine functions (O’Donohue and Dorsa 1982). In view of the differenting and often antagonistic activities in this respect of peptides related to ACTH/α-MSH and βE, POMC may be viewed as a multifactorial controller of homeostatic functions (de Wied 1987).
KeywordsDopamine Adenosine Arginine Neurol sTyr
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