Excitation of phasically firing hypothalamic supraoptic neurones by carotid occlusion in rats.

Abstract

The activity of supraoptic neurons was recorded extracellularly during bilateral occlusion of the common carotid arteries in anesthetized rats. In lactating rats occlusion liberated sufficient amounts of neurohypophysial hormones to cause a rise in intramammary pressure 15-25 s after the onset of occlusion. Of the phasic neurons (defined as those showing bursts of activity alternating with periods of silence), 91% were activated by carotid occlusion less than 10 s after the onset of occlusion. Most randomly firing neurons were inhibited or were unaffected. The activation of phasic neurons is unlikely to be just a non-specific effect, because in the same animals, phasic neurons were excited while random neurons were not. Moreover, in phasic neurons, statistical analysis shows that the intervals during which an occlusion was performed were significantly shorter than the intervals between spontaneously occurring bursts, and that this activation was followed by a period of reduced firing probability. The results are discussed with reference to the correlation of supraoptic neuronal activity with hormone release. The possibility is considered of relating the tendency of some supraoptic neurons to fire in bursts with the secretion of vasopressin.