Rhythmic aftereffects in the osmotic stimulation-induced spike activity of thermosensitive neurons of the preoptic region

Acute experiments on cats showed that mild shifts in osmotic homeostasis (within physiological limits) result in modifications of the spike activity in a significant share of thermosensitive neurons of the Preoptic region (RPO); in particular, rhythmic aftereffects (RAE) are induced in these units. The neurons were identified as thermosensitive cells according to their responses to local heating/cooling (±7°C) of the pad surface of the contralateral forelimb. Osmotic stimulation was performed by infusions of 0.1–0.3 ml of 3.0 or 0.2% NaCl solutions in thea. carotis communis dextra. The RAE phenomenon more frequently developed in thermosensitive neurons after infusions of the hyportonic solution (13/34) than after hypotonic infusions (6/34), while in non-thermosensitive neurons the situation was reverse: hypotonic infusions induced RAE more frequently. Certain specificities were also observed in localization of the thermosensitive RPO neurons, in which osmotic stimulation-induced RAE was observed. The mechanisms of such induction and possible functional role of spike grouping in the activity of thermosensitive neurons are discussed.