Vagotomy attenuates the behavioural but not the pyrogenic effects of interleukin-1 in rats

Vagal afferent signals, have been implicated in cytokine mediated interacti ons between the periphery and the central nervous system. Studies in experi mental animals have shown that cytokine induced activation of brain mediate d responses to infection such as fever, sickness behaviour and pituitary-ad renal activation, are inhibited by subdiaphragmatic vagotomy. We have previ ously proposed that the peripheral signal to the brain in fever is of a hum oral nature while others have suggested that either neural afferents or a m ixture of both humoral and neural signals may be involved. The objective of the present study was to examine further the role of vagal transmission, i n mediating the febrile response to a systemic injection of IL-1 beta in ra ts and to compare this with changes in social exploration behaviour. Intrap eritoneal injection of IL-1 beta (1.0-30.0 mug/kg) inhibited social explora tion in rats and this was attenuated in vagotomized animals. Injection of i ncreasing concentrations of IL-1 beta (0.1-1.0 mug/rat) induced significant (P<0.001) increases in core body temperature. However, in contrast to effe cts on social exploration, the increase in temperature was not inhibited by vagotomy at any of the doses used. These observations demonstrate a dissoc iation between the two brain mediated events, one of which is dependent on the integrity of the vagus nerve (social exploration) while the other (feve r) is apparently generated by different mechanisms which may include circul ating pyrogens. (C) 2000 Elsevier Science B.V. All rights reserved.