Effects of interleukin-1 beta injections into the subfornical organ and median preoptic nucleus on sodium appetite, blood pressure and body temperature of sodium-depleted rats

Abstract

Interleukin-1β (IL-1β) appears to be the mediator of the reciprocal communication between the brain and the immune system. IL-1β has been shown to modulate homeostatic functions including fever, feeding, drinking and cardiovascular control. The aim of the present study was to investigate the effects of IL-1β injections directly into the subfornical organ (SFO) and the median preoptic nucleus (MnPO) on salt appetite, hedonic response, locomotion, body temperature and blood pressure in sodium-depleted rats. IL-1β injections into the SFO and MnPO at the doses of 0.2, 0.4, 0.8 and 1.6ng/0.2μl promoted a dose-dependent inhibition of salt intake in sodium-depleted rats. Results of the “dessert” test and the “open field” test suggested that the inhibition of salt appetite is not due to any changes in the hedonic aspect of ingestive behavior or to changes in locomotor activity. As expected, IL-1β injections into the SFO and MnPO promoted an increase in body temperature. However, the fever induced by IL-1β injected into the SFO was slower than the increase in body temperature obtained following IL-1β injection into the MnPO. Furthermore, IL-1β at a dose of 1.6ng/0.2μl directly injected into the MnPO led to a significant increase in blood pressure, while injection of the same concentration of IL-1β into the SFO caused no significant change in blood pressure or heart rate. The action of pro-inflammatory cytokines may interfere with the normal control of body temperature, blood pressure and fluid homeostasis, producing the adjustment required to cope with infection and inflammation. Further studies are required to clarify the mechanisms involved in fever, blood pressure increase and inhibition of sodium appetite induced by injections of IL-1β into the SFO and MnPO in sodium-depleted rats.