INDUCTION OF INTERLEUKIN-1-BETA MESSENGER-RNA IN THE HYPOTHALAMUS FOLLOWING SUBCUTANEOUS INJECTIONS OF FORMALIN INTO THE RAT HIND PAWS

The induction of interleukin-1 beta (IL-1 beta) mRNA in the rat brain following subcutaneous injection of formalin into the hind paws was in vestigated by in situ hybridization. IL-1 beta mRNA was markedly induc ed in the hypothalamus after the injection of formalin into both hind paws. On the other hand, IL-1 beta mRNA was scarcely observed in the h ypothalamus of saline-injected control rats. The type of cells express ing IL-1 beta mRNA was likely glia because their nuclei were densely s tained by Cresyl violet and were relatively small. The present results suggest that IL-1 beta mRNA is induced in the glial cells of the hypo thalamus by persistent pain which is caused by formalin injection.