Effects of intraventricular injections of Ca2+ and(or) Mg2+ on eating behavior, water intake and cardiac rhythm in sheep.

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 mumoles 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 mumoles of each), they did not antagonize each other, but instead elicited an eating response that was additive and equal to that elicited by 20 mumoles of Ca2+. Water intake varied markedly and was not related to the experimental treatments. Cardiac rate was decreased by the injections of 20 mumoles 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.