EFFECT OF INTERHEMISPHERIC SECTIONS OF THE HYPOTHALAMUS ON MILK-EJECTION BURSTS OF SUPRAOPTIC OXYTOCIN NEURONS DURING BILATERAL AND UNILATERAL SUCKLING IN THE RAT

The burst activity of oxytocin neurones was recorded from the supraopt ic nucleus of lactating rats with or without interhemispheric sectioni ng of the hypothalamus during bilateral or unilateral suckling. The re sults showed that extensive interhemispheric sectioning did not abolis h the burst of oxytocin neurones during bilateral and contralateral su ckling (100% of 25 neurones and 95% of 20 neurones, respectively), but significantly reduced the number of oxytocin neurones that showed the burst during ipsilateral suckling (5.3% of 19 neurones). To orientate the crossing site of the signals for bilateral synchronization of the bursts of oxytocin neurones, interhemispheric sectioning of the rostr al or caudal hypothalamus was attempted, but either sectioning partial ly blocked the occurrence of the bursts during ipsilateral suckling. T hese results suggest that there are two separate gates located on diff erent sides of the hypothalamus and that the neural connections betwee n the gates seem distributed diffusely. (C) 1997 Elsevier Science Irel and Ltd.