Effects of lesions in central thermosensitive areas on thermoregulatory responses in rat

Behavioral and autonomic responses elicited by ambient heat were tested before and after lesioning five thermosensitive areas previously localized in the rat brain. Lesions in the PO/AH area, where local warming elicits prone body extension, markedly reduced or abolished extension but had no effect on locomotion, grooming, or tail vasodilation. Lesions in the posterior hypothalamus, where local warming induces grooming, and lesions in the septum, medial midbrain, and dorsomedial medulla, where local warming evokes locomotion, had no significant effects on thermoregulatory responses except for reduced body extension following midbrain lesions, which may have interrupted the efferent path from PO/AH thermosensors. It was concluded that extension is predominantly dependent on PO/AH thermosensors and/or integrative interneurons, while locomotion, grooming, and vasodilation are controlled by input from peripheral and central sensors. The present and earlier data from the rat are less consistent with a relatively localized general integrating mechanism producing a unitary output signal to thermoregulatory effectors than with a spatially distributed network of specific paths from sensors to separate response mechanisms, where summation of inputs may occur.