Homeostatic alterations after intrapallidal microinjection of interleukin-1β in the rat

To elucidate the homeostatic consequences of direct pallidal administration of interleukin-1β (IL-1β), short- (2 h) and long-term (12 h) food intakes, water intake and body temperature were measured after bilateral microinjection of IL-1β (with or without paracetamol/PAR/pretreatment) into the ventro-medial part of the globus pallidus (GP). The effects were compared with those found in vehicle- or vehicle+PAR-treated control animals and intraperitoneally (i.p.) injected IL-1β, IL-1β+PAR or control rats. Direct GP microinjection of IL-1β, similar to the peripheral (i.p.) administrations, reduced remarkably short-term food intake in food deprived animals. However, there were no significant differences among the groups in long-term food intakes and in water intakes as well. IL-1β microinjection into the GP caused a significant increase in body temperature. This IL-1β induced hyperthermia was attenuated by PAR pretreatment, whereas food intake was not affected. Results of the electrophysiological experiments revealed substantial changes in GP extracellular single neuron activity in response to the microelectrophoretic administration of IL-1β. The present findings, along with previous data, are discussed in terms of the glucose-monitoring neural circuitry through which cytokines exert their direct modulatory effect on central homeostatic regulation.