ELECTRICAL-STIMULATION OF TOOTH-PULP INCREASES THE EXPRESSION OF C-FOS IN THE CAT SUPRAOPTIC NUCLEUS BUT NOT IN THE PARAVENTRICULAR NUCLEUS

Immunoreactivity to Fos protein was detected in the supraoptic (SON) and para-ventricular (PVN) nuclei of the cat using immunohistochemical methods. In the intact animal group, only a few Fos-positive neurons were observed in the PVN, but the SON did not contain any positive neurons. Intraperitoneal injection of pentobarbital sodium (Nembutal: 35 mg/kg) induced c-fos expression in the SON, but not in the PVN. Electrical stimulation of tooth pulp with an intensity that was 3 times the threshold of the jaw-opening reflex (200-600 muA) increased the number of Fos-positive neurons in the SON by up to 388% as compared with those of the Nembutal group, whereas the stimulation did not alter the number in the PVN. The increase was observed throughout the extent of the SON. In addition, morphine treatment (2 mg/kg, i. p.), 5 minutes before tooth pulp stimulation, considerably inhibited the increase in the SON. There were no significant differences among the 3 groups (intact, Nembutal, morphine) in the number of positive neurons in the PVN. These findings suggest that these hypothalamic nuclei have different functional roles and that the SON is involved in nociception and/or the consequent emotional and visceral reactions.