Feeding following intrahypothalamic injections of calcium and magnesium ions in sheep

To study ionic effects on hypothalamic control of feeding, seven sheep were each prepared with six bilateral medial-hypothalamic guides. Hypothalamic loci were identified where feeding resulted following 1 mu 1 injections of calcium chloride and/or magnesium chloride. Doses of 1 and 2 mumol were most effective to induce feeding, and potassium chloride was not effective. Injections of phentolamine, LB-46, carbachol, atropine, or prostaglandin E1 did not inhibit the feeding responses following magnesium chloride injections into magnesium ion responsive loci. Feeding following calcium chloride injections into calcium ion responsive loci was blocked by atropine and reduced by phentolamine. Carbachol and prostaglandin E1 elicited feeding when injected into magnesium but not calcium ion responsive loci. Injections of carbachol followed by magnesium chloride resulted in greater feeding than when either chemical was injected alone. Calcium and/or magnesium ion bound feeding loci were in the anterior, ventromedial, dorsomedial, posterior and lateral hypothalamus, and the mammillary bodies. These ions elicited feeding in sheep perhaps by decreasing excitability of feeding-inhibitory neural pathways in the hypothalamus.