Varying changes in heart rate produced by nociceptive stimulation of the skin in rats at different temperatures.

The effect of nociceptive stimulation of various skin areas of the neck, chest and abdomen on the heart rate was examined in anesthetized rats with the cord intact and in acute spinal rats, at different body temperatures. In the anesthetized rats with the cord intact, the stimulation on the neck, chest and abdominal skin areas caused reflex changes in heart rate. At a rectal temperature of 38.0-38.9 degrees C the response was usually an increase in heart rate, whereas the response at 36.0-36.9 degrees C was a decrease. The heart rate reflex response at 37.0-37.9 degrees C was a monophasic increase or decrease, or a biphasic initial decrease followed by an increase. The reflex increase or decrease in heart rate produced by cutaneous stimulation was mediated by a reflex increase or decrease in the efferent discharges of the cardiac sympathetic nerve. In acute spinal rats, only stimulation on the chest skin area, at a rectal temperature of 36.0-38.9 degrees C, would always produce a reflex increase in heart rate. This reflex increase in heart rate was also produced by an increase in efferent discharges of the cardiac sympathetic nerve.