Does α-MSH of Pars Intermedia of Pituitary and Hypothalamus modulate Fos expression in brain of rats induced by IL-1β?

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Hyperalgesia was induced by intracerebroventricular(ICV) administration of a recombinant human Interleukin-1β(IL-1β) of 1pg - 1ng/kg in rats and the effect of IL-1β was inhibited by amelanocyto stimulating hormone (α-MSH). It has been described that an ICV injection over 100ng IL-1β induced Fos expression in the paraventricular nucleus (PVN) of the hypothalamus in rats, but not in lower doses inducing hyperalgesia. Therefore It is important to know where the sensory response to IL-1β is mediated in the central nerves system (CNS). In order to establish the activated part in the CNS by IL-1β, we examined Fos protein expression in the hypothalamus and modulation by α-MSH for the response to IL-1β in rats. Following the ICV injection of 10 pg IL-1β, a hyperalgesia was induced and Fos was expressed in the PVN and the arcuate nucleus (ARC) which contained α-MSH neurons. But IL-1β did not induce Fos expression in pars intermedia (PI) of pituitary gland which is α-MSH secrete organ in the periphery. A ICV pre-injection of 30 ng α-MSH inhibited hyperalgesia and Fos expression in the PVN and the ARC. This observation demonstrated that PVN neurons were activated by IL-1β and α-MSH inhibited these effects of IL-1β in the PVN. Therefore it is possible that α-MSH neurons in the ARC, which contains endogenous α-MSH were activated to inhibit the effects of IL-1β but α-MSH cells in the PI were not committed with this reaction.