Effect of interhemispheric sections of the hypothalamus on milk-ejection bursts of supraoptic oxytocin neurones during bilateral and unilateral suckling in the rat

Abstract

The burst activity of oxytocin neurones was recorded from the supraoptic nucleus of lactating rats with or without interhemispheric sectioning of the hypothalamus during bilateral or unilateral suckling. The results showed that extensive interhemispheric sectioning did not abolish the burst of oxytocin neurones during bilateral and contralateral suckling (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 rostral or caudal hypothalamus was attempted, but either sectioning partially blocked the occurrence of the bursts during ipsilateral suckling. These results suggest that there are two separate gates located on different sides of the hypothalamus and that the neural connections between the gates seem distributed diffusely.