Reflex activation of rat fusimotor neurons by body surface cooling, and its dependence on the medullary raphé

Abstract

The nature of muscle efferent fibre activation during whole body cooling was investigated in urethane-anaesthetizedrats. Multiunit efferent activity to the gastrocnemius muscle was detected when the trunk skin was cooled by a water-perfused jacket to below 36.0 ± 0.7°C That efferent activity was not blocked by hexamethonium (50 mg kg-1, I.V.) and was not associated with movement or electromyographic activity. Cold-induced efferent activity enhanced the discharge of afferent filaments from the isotonically stretched gastrocnemius muscle, demonstrating that it was fusimotor. Fusimotor neurons were activated by falls in trunk skin temperature, but that activity ceased when the skin was rewarmed..