Effects of selective cutaneous denervation on hypothalamic thermosensitivity in rats

The effect of altering input from cutaneous thermoreceptors of the face and trunk on the relationship between hypothalamic temperature (Thy) and heat production (HP) was studied in three rats. The signal from cutaneous receptors was altered in two ways: by altering skin temperature (Tsk) and by sectioning nerves supplying cutaneous receptors. It was found that when Tsk was lowered in normal rats Thy threshold for thermoregulatory HP was elevated, but the slope of the relationship between Thy and HP was not significantly altered. After the spinal nerves serving the trunk skin were sectioned, the slope was reduced and the threshold was elevated markedly at both test ambient temperatures (Ta), but Ta had essentially the same effect on the Thy vs. HP relationship after cutaneous denervation as before. Clearly, eliminating input from trunk cutaneous thermoreceptors has a different effect than does lowering or raising Tsk, but thermoregulation is being achieved by the same basic mechanism before and after cutaneous denervation. After the cranial nerves supplying the skin of the face were also sectioned, there was a further elevation in the Thy threshold for HP at Ta = 25 degrees C but no change at Ta = 15 degrees C. It is concluded that cutaneous denervation does not substantially interfere with the rat's ability to regulate its body temperature, and that the reduced Thy sensitivity and increased Thy threshold exhibited after cutaneous denervation is the result of input from intact warm- and cold-thermoreceptors located in the core and in tissues intermediate to core and skin.