Localization and possible function of peptidergic neurons and their interactions with central catecholamine neurons, and the central actions of gut hormones.

The localization of various neuropeptides is described in the gut and in the hypothalamus in the rat. Evidence is given for the presence of material resembling corticotropin-like intermediate peptide in arcuate and periarcuate neurons, projecting to various hypothalamic nuclei, limbic areas and the thalamus. beta-Endorphin and glucagon decrease dopamine turnover in the median eminence, while secretin increases dopamine turnover and vasoactive intestinal polypeptide (VIP) has no effect. beta-Endorphin, VIP, secretin, and glucagon all produce discrete changes in norepinephrine turnover in various hypothalamic nuclei. Mainly increases of norepinephrine turnover were observed. These catecholamine turnover changes appear to cause changes in the secretion of prolactin and growth hormone. The results therefore indicate that gut hormones and opioid peptides may act directly on the hypothalamus on specific types of receptors to participate in the control of hypothalamic functions such as control of hormone secretion from the anterior pituitary and of food intake. It seems possible that gastrointestinal peptides released from the gastrointestinal tract into the circulation under certain circumstances could reach the hypothalamus and modulate its activity via the above-mentioned mechanisms. It may therefore be speculated that disturbances in gastrointestinal functions could lead to pathological changes in food intake via modulation of hypothalamic activity.