Hypothermia-induced changes of afferent sensory transmission to the VPM thalamus of rats and hamsters

Effects of hypothermia on the afferent somatosensory transmission to the ventroposteromedial (VPM) thalamus were determined in anesthetized rats and hamsters. Hamsters showed a gradual suppression of afferent sensory transmission during cooling (to 18 degrees C) and disinhibition during subsequent warming of body temperature (Tb). However, rats exhibited steep inhibition from Tb 26 degrees C to complete absence of sensory transmission at Tb 20 degrees C and abrupt disinhibition during subsequent warming. Species difference at thalamic level was quite similar to our previous results in the primary somatosensory (SI) cortex, suggesting that changes of sensory transmission observed in the SI cortex may have already occurred at thalamic level. Differences between the cortex and the thalamus were observed only during deep hypothermia in rat and during the final period of warming in hamster. Conduction latencies of thalamocortical system of both species were not influenced during Tb lowering until 24 degrees C (equivalent to brain temperature 25-26 degrees C). These results suggest inherently different adaptability to hypothermia in processing somatosensory information between hibernator and non-hibernator, but similar sustainability of sensory functions of the thalamocortical system during hypothermia in both species.