Neurones in the dorsal horn of the rat responding to scrotal skin temperature changes.

1. Micro-electrode recordings have been made from single neurones in the dorsal horn of male rats anaesthetized with urethane. Scrotal temperature was altered within the range 13-43 degrees C by means of a thermode. The mean firing rate of neurones was correlated with step and ramp changes of temperature.2. In the region where the scrotal nerve enters the cord, 47% of the neurones were responsive to scrotal temperature: half were excited by warming and half by cooling. Most of these thermally responding units were not affected when the scrotal skin was touched and only one-fifth responded to both modalities.3. Both the ;warm' and ;cold' groups of neurones showed responses to step changes of temperature which were classified as dynamic plus static, dynamic only or static only. Comparison of these responses with those published for the scrotal thermoreceptors showed that the incoming thermal information was being processed in the dorsal horn.4. Histological examination of the cord showed that recording sites were in laminae I to V of the dorsal horn.