Abstract
Unit responses of dorsal horn neurons (DHNs) of rats to thermal stimulation of the scrotal skin were recorded extracellularly. Fifty-five out of 74 DHNs increased their activity during scrotal skin warming, while the activity of 14 neurons was accelerated by cooling. Tonic activities of 3 neurons were inhibited by warming (inverse warmreactive). Two neurons demonstrated a complex response and were activated during cooling and warming. Most of the warm-reactive and all of cold-reactive DHNs had steep sigmoid temperature-activity-relation curves with a temperature-dependent range of 1-5°C.
Injections of 5-10 mg/kg CaCl2 into the lower abdominal aorta produced excitation in 30 out of 33 warm-reactive DHNs and inhibition in 3 neurons. Only 3 out of 8 cold-reactive DHNs demonstrated inhibition, while the remaining 5 were activated. All three inverse warm-reactive neurons were inhibited. DHNs which exclusively reacted to mechanical stimuli or did not respond to any peripheral stimulation were not affected by peripheral Ca administration. The results suggest that a number of cold-reactive DHNs receive inputs from warm-and cold-sensitive afferents and that there may exist such double innervation in some warmreactive DHNs as well.
