Activity patterns of temperature-reactive dorsal horn neurons and their reactions to peripheral receptor stimulation by Ca.

Unit responses of dorsal horns 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 warm-reactive). 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 step sigmoid temperature-activity-relation curves with a temperature-dependent range of 1-5 degrees 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 warm-reactive DHNs as well.