An electrophysiological analysis of caudally-projecting neurones from the hypothalamic paraventricular nucleus in the...

Using anaesthetized rats, experiments were performed to test whether neurones located in the hypothalamic paraventricular nuclei and sending axons caudally, could be identified electrophysiologically. Neurones projecting caudally were localized by antidromic invasion following electrical stimulation within the region of the dorsal motor nucleus of the vagus, the nucleus of the tractus solitarius and the hypoglossal nucleus. Stimulation of more ventral regions in the medulla oblongata was not effective. Caudally-projecting neurones were dispersed throughout the paraventricular nuclei and were often found close to magnocellular neurones antidromically invaded by stimulation of the pituitary stalk. About one-third of the caudally-projecting neurones were synaptically activated by pituitary stalk stimulation, but only at currents sufficient to antidromically invade the magnocellular neurones. This suggests a synaptic interaction between magnocellular and some caudally-projecting paraventricular neurones. The possible physiological significance of these findings is discussed.