Dissociation between peripheral and central components of tolerance to behavior effects of interleukin-1 in rats

Interleukin-1 (Il-1) is an endogenous pyrogen which is released by accessory immune cells and which has potent neural effects. Rats implanted subcutaneously with an osmotic mini-pump delivering 2 micrograms Il-1 per day rapidly became tolerant to the behavioral and toxic effects of this cytokine. Acute challenge with Il-1 reversed this tolerance when the cytokine was injected intraperitoneally (3 micrograms/rat) but not when it was injected into the lateral cerebral ventricle (3 ng/rat). These results suggest a differential regulation of the peripheral and central receptors mediating the effects of Il-1.