Satiety, hunger and regional brain content of cholecystokinin/gastrin and met-enkephalin immunoreactivity in sheep

Cholecystokinin (CCK) and met-enkephalin (MEK) related peptides have been shown to alter feeding behavior subsequent to their injection into the peripheral circulation or directly into the brains of several species. To evaluate the potential role of endogenous brain pools of these peptides in feeding, groups of sheep were sacrificed either immediately following a meal (satiated) or after various intervals of food deprivation (hungry). Content of CCK-gastrin immunoreactivity in the anterior hypothalami of satiated sheep was elevated compared to 2, 4, or 24 hours of food deprivation. Content of MEK increased progressively with longer intervals of fasting (4 and 24 hours) in the amygdala and basomedial hypothalamus, whereas olfactory bulb content decreased with a similar time course. The results support a potential role for anterior hypothalamic CCK/gastrin in behaviors of satiety, whereas MEK neurons of limbic/rhinencephalic regions appear to form part of a separate circuit gradually activated by increasing hunger. Results are discussed in terms of potential target regions of the peptides, as well as the regional levels and feeding response of sheep as compared to available data from other species.