Electrical stimulation of the hypothalamus: new observations on the parameters necessary for ovulation in rats anaesthetised with pentobarbitone during the pro-oestrous "critical period".

The experiments were designed to specifiy optimal parameters of hypothalamic electrical stimulation to induce ovulation in rats anaesthetised with pentobarbitone during the "critical period" on the afternoon of pro-oestrous. We have established that duration of stimulation in the arcuate region of the hypothalamus is of greater importance than total number of pulses delivered. The minimum period of stimulation to ensure that all rats ovulated was 45 min. However, stimulation in the arcuate region did not have to be continuous throughout this period. Indeed, three 5-min bursts at 100 Hz distributed equally through 45 min always caused ovulation whereas a continuous 15-min stimulation at the same frequency was without effect. With 30 min of continuous stimulation in the arcuate region, at frequencies ranging from 10 to 100 Hz, approximately half of the rats ovulated.