DOUBLE IMMUNOFLUORESCENCE STAINING OF FOS AND JUN IN THE HYPOTHALAMUSOF THE RAT

The nuclear factor Fos participates in the transcriptional regulation of genes that contain a functional AP-1 binding site. Hyperosmotic str ess induces Fos-like immunoreactivity in neurons of the hypothalamus. Fos appears to depend on the co-expression of the nuclear factor Jun, with which it dimerizes, to complete its regulatory role. The immunocy tochemical co-localization of both peptides, however, has not been rep orted. The present study was designed to analyze the distribution of F os and Jun by double immunofluorescence staining in Long-Evans rats th at were osmotically challenged by a single intraperitoneal injection o f 1.5 M NaCl. Non-injected and isotonic saline-injected animals were u sed as controls. Hypertonic saline injection induced Jun immunoreactiv ity in cell nuclei in the supraoptic nucleus, paraventricular nucleus, and median preoptic nucleus. The immunofluorescence for Jun was stron g in the supraoptic and paraventricular nuclei, but weak in the median preoptic nucleus. The immunofluorescence for Fos in all 3 nuclei foll owed a similar pattern to that for Jun. Double immunofluorescence stai ning revealed colocalization of Jun with Fos in 87.4% of the cells of the supraoptic nucleus. Neither Jun nor Fos immunofluorescence was det ected in control animals. The data support a role for Jun in transcrip tional regulation of genes in hypothalamic neurons during acute hypero smotic stress. Moreover, the findings are compatible with the suggesti on that Fos and Jun act cooperatively in the regulation of gene transc ription in neuroendocrine systems involved in the control of water bal ance during acute hyperosmotic stimulation.