c-fos mRNA is present in axons of the hypothalamo-neurohypophysial system of the rat.

In situ hybridization revealed that c-fos encoding transcripts occur in the median eminence of rats. Osmotic stress resulted within 15 min. in additional labeling of the magnocellular nuclei, while osmotically stimulated rats that had been pretreated with colchicine failed to show c-fos hybridization in the magnocellular perikarya. Rats, pretreated with a polymerase II inhibitor, showed 15 min. after osmotic stimulation c-fos hybridization in the hypothalamic nuclei, whereas the median eminence was depleted of hybridization signal. c-fos is probably among the transcripts, stored in axons of the hypothalamo-neurohypophysial system, to be transported retrogradly upon osmotic stimulation.