Ovulation in Rats from Preoptic Stimulation Through Platinum Electrodes. Importance of Duration and Spread of Stimulus

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Abstract
Adult female rats in proestrus, their spontaneous ovulation blocked by pentobarbital, were stimulated through platinum electrodes placed bilaterally 2 mm apart across the medial preoptic areas of the brain. Biphasic pairs of 1 msec rectangular pulses, 1 mamp peak-to-peak, 30/sec, were passed in 30-sec trains at 30-sec intervals. Full ovulation (9-12 ova) occurred overnight in all of 8 rats thus stimulated for 60 min. Shorter stimulation (15-30 min) led to fewer rats ovulating and smaller numbers of ova. Ovulation failed (5 rats) when stimulation lasted only 10 min. One tubal ovum among 5 rats was obtained after electrodes were simply inserted for 60 min. Stimulation for 60 min across the lateral preoptic area gave mostly negative results. Besides demonstrating the feasibility of stimulating “electrically” rather than by the electrolytic deposition of iron previously employed, the results emphasize the importance of time and of the degree of involvement of a postulated diffuse neuronal system traversing the medial preoptic brain in governing the amount of “LH” released by the adenohypophysis. Certain implications are mentioned concerning attempts in other species to induce ovulation by brain stimulation. (Endocrinology 76: 1195, 1965)