Release of hypothalamic cholecystokinin in cats: effects of nutrient and volume loading

Systemic cholecystokinin (CCK) suppresses food intake in various species and has therefore been proposed to act as a satiety factor. Because CCK is also present in the hypothalamus and furthermore meets neurotransmitter criteria, the hypothesis was tested whether CCK participates in the transmission of satiety messages at the lateral hypothalamic (LH) level. The results of this study demonstrate that in halothane-anesthetized cats, neurons located in the LH will indeed release CCK-like material after a carbohydrate-protein meal in a time-dependent fashion. This release, as water loads demonstrate, is most likely due to volumetric distension rather than to the nutrient content. The releasable CCK does not originate from peripheral sources, since intravenously infused CCK octapeptide (CCK-8) does not appear in the perfusate. The release occurs only in discrete neurons and is not universal to CCK-releasing systems within the LH, and also, CCK-releasing systems are not present at all locations. The molecular form of CCK in feline hypothalamus is the COOH-terminal octapeptide (CCK-8) as shown by high-performance liquid chromatography. No gastrin-17 is present. CCK-8 is also the predominant form found in meal-induced as well as in KCl-induced CCK released from hypothalamic neurons. These results suggest a correlated role for hypothalamic CCK in the termination of food intake.