Effects of leukocytic pyrogen and sodium salicylate on hypothalamic thermosensitive neurons in vitro

The effects of leukocytic pyrogen and sodium salicylate (Sal) were studied on the single-unit activities of neurons in the preoptic and anterior hypothalamus (PO/AH) recorded in tissue slices in vitro. The pyrogen applied to the immediate vicinity of the recorded neurons decreased the firing rate of the majority of warm-sensitive neurons, but had no effect on the activities of thermally insensitive neurons. The pyrogen-induced inhibition of warm-sensitive neurons was reversibly blocked by local application of Sal. The results support the view that the pyretic and antipyretic effects of intrahypothalamic pyrogen and Sal are caused by their offsetting actions on the PO/AH thermosensitive neurons.