Abstract
The cutaneous blood flow (mbl), rate of oxygen consumption (Vo2), rectal (Tre) and cutaneous (Tsk) temperatures, and shivering activity were measured in unanthetized male rats during a 2-h exposure to 26, 33, or 5 degrees C 2 wk after selective bilateral hypothalamic microknife cuts. Animals with preoptic-anterior hypothalamic (PO/AH) junction cuts 1.5 or 3.0 mm lateral to the midline, as well as parasagittal cuts which separated connections between the PO/AH and medial forebrain bundle exhibited a higher mbl at 26 degrees C than did sham-operated rats. At 5 degrees C the extended (3.0 mm) PO/AH cuts as well as the parasagittal cuts prevented cutaneous vasoconstriction but had no effect on shivering activity; hence Tre was not maintained. None of the cuts demonstrably impaired thermoregulation in the 33 degrees C environment. These results suggest that different sites in the hypothalamus may separately control cold-induced skin vasoconstriction and shivering activity, as well as heat-induced skin vasodilation. It would seem therefore that the integrity of the PO/AH is indispensable in rats for cold-induced cutaneous vasoconstriction but not for cold thermogenesis, and also not for heat-induced cutaneous vasodilation.
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