FOS AND JUN EXPRESSION IN RAT SUPRAOPTIC NUCLEUS NEURONS AFTER ACUTE VS REPEATED OSMOTIC STIMULATION

Using a double-label immunofluorescence method, we analyzed the time c ourse of the appearance of Fos and Jun in the nuclei of supraoptic nuc leus (SON) neurons following intraperitoneal injection of hypertonic s aline. Fos and Jun immunostaining appeared within 30 min, peaked at 90 -120 min, and disappeared 4-5 h later. At all time points (30, 60, 120 , 180, 240 min postinjection), colocalized Fos and Jun immunostaining was observed (>90% colocalized staining in labeled neurons). At 4 h po st-saline injection, some rats received a second injection of normal o r hypertonic saline. A second injection of normal saline resulted in n o Fos/Jun immunostaining 90 min later, while hypertonic saline induced combined Fos/Jun staining in only 17% of SON neurons. Of the remainin g SON cells, 23% had staining to Fos alone and 4% of the cells stained for Jun only. in spite of the delivery of an effective second osmotic stimulus, determined by assessment of plasma osmolality and sodium co ntent, SON neurons exhibited less colocalized Fos/Jun immunostaining, dramatically less Jun expression, and substantial, but attenuated, imm unostaining for Fos. These results are discussed in the context of kno wn negative feedback mechanisms that control the re-expression of thes e transcription factors.