[Responses of midbrain central gray neurons activated by hypothalamic paraventricular nucleus (PVH) stimulation to somatic afferent input in rats].

Extracellular single unit recordings were made from 318 neurons within the midbrain central gray in urethane-anesthetized rats. Following electrical stimulation of the hypothalamic paraventricular nucleus (PVH), 10% of the units in central gray (CG) were antidromically activated, while 7.5% were orthodromically excited, and 0.7% were orthodromically inhibited. Among these antidromically activated neurons, 28 units were further examined for their responsiveness to peripheral somatic sensory stimulation. Strong electrical stimulation of contralateral sciatic and tibial nerve, and tail pinching produced excitation in 12 and inhibition in 2 units. No significant responses to non-noxious stimulation were observed in these units. Of the 26 orthodromically activated units, 14 were excited and 4 inhibited by the sciatic nerve stimulation or tail pinching. These results support the hypothesis that CG is one of the relay stations in the afferent pathway of somatic sensory especially, noxious, information transmitting to the PVH, and that the PVH may play a role in central pain control or modulation via their descending influence on CG unit.