Vestibular projections to hypothalamic supraoptic and paraventricular nuclei.

The effects of electrical stimulation of the eighth nerve and caloric stimulation of the labyrinth were tested on the spontaneous or evoked electrical activity of single neurons located in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. It was found that these neurons responded to both kinds of stimulation. In particular, the neurons of the SON showed a predominant response pattern characterized by a sequence of excitation-inhibition, whereas the neurons of the PVN showed different patterns of response with various combinations of inhibition and excitation sequences. The latencies of these neuronal responses to the electrically induced eight nerve volleys were compatible only with a polysynaptic connection. The possible pathways involved in this vestibulo-hypothalamic relation as well as their functional role are discussed.