Calmodulin-induced feeding in the satiated cat: evidence for involvement of calcium and norepinephrine in the brain.

The central effect of the Ca++ binding protein, calmodulin (CaM) on spontaneous feeding as well as on core temperature was examined in the satiated cat in which chronically indwelling cannulae were permanently implanted for intracerebroventricular (ICV) infusion. When CaM was injected ICV in doses of 2.5-10.0 micrograms, the intake of food was significantly enhanced in the satiated cat without any notable change in the animal's core temperature. Ca++ ions infused similarly in a solution of 6.25-25.0 mM also augmented the spontaneous ingestion of food, which was accompanied by a concentration-related decline in core temperature. When infused separately, neither CaM in a low dose (1.25 micrograms) nor Ca++ ions (3.0 mM) given ICV altered the intake of food of the satiated cat. However, the simultaneous infusion of CaM and Ca in these concentrations enhanced significantly the amount of food consumed by as much as 60 g. When the same concentration of Ca++ ions was infused ICV simultaneously with 5.0 micrograms troponin C, a Ca++ binding protein of an identical molecular weight, the intake of food was unaltered. Further, the spontaneous feeding induced by CaM could be attenuated either by the central chelation of Ca++ ions by 1.0-1.5 mM EGTA or by 30 micrograms calcineurin, a specific CaM inhibitor, when either was given ICV. Pre-treatment of the cat with ICV phentolamine (50 micrograms) also reduced the CaM-induced feeding response significantly, whereas the similar pre-treatment with ICV propranolol (50 micrograms) or naloxone (100 micrograms) failed to affect CaM-induced feeding behavior.(ABSTRACT TRUNCATED AT 250 WORDS)