REGULATION OF SECRETION OF POMC PEPTIDES IN BRAIN

各种行为、生化和神经调节作用

Various, behavioral, biochemical and neuromodulatory effects have been produced in brain by ACTH, alpha-MSH, beta- endorphin, and related peptides derived from processing of their precursor, pro-opiomelanocortin (POMC), which is synthesized by neurons. Despite a variety of in vivo studies investigating different variables on brain levels of POMC-related peptides, a clear conception of the physiological regulation of POMC peptides in brain remains to be established. To understand the regulation of brain POMC peptides by delineating potential physiological regulators, a variety of substances will be studied for effects on altering secretion of POMC peptides from brain cells. We will test hypotheses that brain secretion of POMC peptides is: 1) regulated by neurotransmitters modifying neuronal functions, by substances modifying brain POMC peptides in vivo, and by substances (CRF, glucocorticoids, beta- endorphin) which regulate secretion of pituitary POMC peptides; 2) regulated differently in hypothalamic and extrahypothalamic brain; 3) non-coordinated; 4) dependent on neuroanatomical relationships; 5) independent of cellular content of POMC peptides. We will use in vitro models to study secretion which is difficult to study in vivo. Regulatory effects of classical neurotransmitters on secretion will be evaluated in a static system of dissociated fetal rat hypothalamic cells by measuring (RIA) POMC peptides (ACTH, alpha-MSH, beta-endorphin) and comparing results to those in perifusion systems of cells and explants. Pharmacological antagonism of neurotransmitter- altered secretion will be assessed. Neurotransmitter effects on POMC peptide secretion will be further evaluated in cells from extrahypothalamic forebrain and medulla oblongata. Effects of other regulatory candidates will subsequently be studied and compared in hypothalamic and extrahypothalamic cells. Effects of chronic exposure of selected substances on secretion and content of POMC peptides will also be assessed. Molecular forms of POMC peptides will be characterized and molar relationships analyzed to indicate if regulation of secretion is coordinated or non-coordinated. Completing this project will help understand the physiological regulation of secretion of POMC peptides, could help understand brain regulation of synthesis and processing of POMC peptides, and could lead to studies elucidating their CNS function and models indicating whether alterations in regulation of POMC peptide metabolism produce or exacerbate CNS disorders (schizophrenia, SIDS, seizures, infantile spasms).