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Effect of Intraventricular Injections of Ca²⁺ and(or) Mg²⁺ on Eating behavior, Water Intake and Cardiac Rhythm in Sheep¹

Faculté des Sciences de l'agriculture et de l'alimentation et Centre de recherches en nutrition, Université Laval, Québec, Canada G1K 7P4

Abstract

Feeding behavior, water intake and cardiac rhythm were measured following injections of Ca²⁺ and(or) Mg²⁺ into the lateral ventricles of sheep. Injections of 20 µmoles of either Ca²⁺ or Mg²⁺ elicited an eating response approximately three to four times greater than normal. The effect of Ca²⁺, however, appeared to be more powerful than that of equimolar doses of Mg²⁺. When both ions were injected in an equimolar mixture (10 µmoles of each), they did not antagonize each other, but instead elicited an eating response that was additive and equal to that elicited by 20 µmoles of Ca²⁺. Water intake varied markedly and was not related to the experimental treatments. Cardiac rate was decreased by the injections of 20 µmoles of Ca²⁺, with the T-P interval of the electrocardiogram affected most. The other experimental treatments did not affect cardiac rate, although the intervals between the waves QRS, T and P of the electrocardiogram were slightly modified. It is concluded that lateral ventricular injections of Ca²⁺ and Mg²⁺ can affect the excitability of neurons controlling feeding behavior without necessarily affecting other autonomic centers in sheep, unless the ions reach the vicinity of the fourth ventricle at relatively high concentrations.

¹ The authors acknowledge the technical assistance of P. Castonguay, L. Marois and L. Bédard. This research was supported by grant from the national Research Council of Canada (Grant #A0090).