DISSOCIATION BETWEEN PERIPHERAL AND CENTRAL COMPONENTS OF TOLERANCE TO BEHAVIORAL-EFFECTS OF INTERLEUKIN-1

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-mu-g Il-1 per day rapidly became tolerant to the behavioural and toxic effects of this cytokine. Acute challenge with Il-1 reversed this tolerance when the cytokine was injected intraperitoneally (3-mu-g/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.