Interleukin-1 activation of FOS proto-oncogene protein in the rat hypothalamus.

The activation of FOS proto-oncogene protein has been used as an anatomical marker of activated brain areas. Immunocytochemical detection of FOS can provide information about the sites of action of extracellular stimuli, in spite of the relative absence of specific receptors, at the level of single cell resolution. Following the intracerebroventricular (i.c.v.) injection of recombinant human interleukin-1 (alpha) the c-fos mRNA levels isolated from rat hypothalamus were activated rapidly. In association with c-fos mRNA activation, the i.c.v. injection of interleukin-1 (alpha and beta) markedly induced the FOS immunoreactivity in the hypothalamus including periventricular (PE), paraventricular (PVN), supraoptic (SON), arcuate (ARC), and supramammillary (SuM) nuclei. Within the magnocellular neurons of the SON and PVN, activation of FOS by IL-1 appeared to be greater in areas known to have a high proportion of oxytocin-containing cells than in those of vasopressin-containing cells. Parvocellular neurons were also activated in the PVN. These data suggest sites of action of interleukin-1 in the rat hypothalamic areas reported to have relative absence of interleukin-1 receptor expression.