EXPRESSION OF HISTONE H1-DEGREES IN TRANSCRIPTIONALLY ACTIVATED SUPRAOPTIC NEURONS

This study has analysed by immunocytochemistry the expression pattern of histone H1 degrees after the osmotically induced activation of tran scription in supraoptic nucleus neurons of the rat. In control rats, h istone H1 degrees was constitutively expressed in neuronal and glial c ell nuclei of supraoptic nucleus. After chronic neuronal stimulation b y intermittent salt-loading, the majority of neuronal cell nuclei exhi bited a marked reduction of immunostaining, which was confirmed by den sitometric analysis of immunoreactivity. This effect was reversible, s ince optical density values returned to control levels when the stimul ation of supraoptic neurons was suppressed by rehydration. Ultrastruct ural immunocytochemistry of histone H1 degrees showed that immunogold particles specifically decorated chromatin fibers, with the highest ac cumulation of particles being on the condensed inactive chromatin. The se results indicate that transcriptional activation in supraoptic neur ons is accompanied by a depletion of the chromatin-associated histone H1 degrees, and also suggest that this transcription-dependent express ion of histone H1 degrees may be involved in regulating chromatin cond ensation and gene expression in mature neurons that constitutively exp ress this protein.