Identification and localization of glucagon-related peptides in rat brain

Immunochemical and immunocytochemical techniques have been used to identify and characterize glucagon-related peptides of the rat central nervous system. These peptides show immunoreactivity with antiglucagon sera directed towards the central portion of the hormone, but not with antisera specific for the free COOH terminus of glucagon. Highest concentrations were found in hypothalamus (6.1 +/- 1.6 ng/g wet weight) although lower amounts (approximately 2 ng/g) were found in cortex, thalamus, cerebellum, and brain stem. Gel filtration of brain extracts revealed at least two immunoreactive forms, which have molecular weights of about 12,000 and 8000. Both peptides had radioimmunoassay dilution curves parallel to the curve for glucagon and both had identical counterparts in extracts of rat intestine. Digestion of the brain and intestinal peptides with trypsin plus carboxypeptidase B released the immunoreactive COOH-terminal tryptic fragment of pancreatic glucagon from these larger forms. Immunocytochemical studies using antiglucagon serum and peroxidase-antiperoxidase staining identified glucagon-like material in neuronal cell bodie and processes in the magnocellular portion of the paraventricular nucleus, as well as in scattered cells in the supraoptic nucleus and in fibers in the median eminence. These results suggest that glucagon-containing peptides that have undergone the intestinal type of posttranslational modification are present in neuronal cells of the rat hypothalamus.