DISTRIBUTION AND EXPRESSION OF GLUCOCORTICOID RECEPTOR MESSENGER-RNA IN THE FOREBRAIN OF THE RAINBOW-TROUT

The expression and distribution of glucocorticoid receptor mRNA was st udied in the forebrain of mature female and immature undifferentiated rainbow trout (Oncorhynchus mykiss) by means of Northern blotting and in situ hybridization. A single mRNA species of 7.5 kb was detected in mRNA polyA(+) prepared from the anterior brain. In situ hybridization was carried out using a S-35-labelled riboprobe corresponding to the A/B-domain (between nucleotides 1224 and 1763) of the recently cloned rainbow trout glucocorticoid receptor cDNA. Comparison of adjacent sec tions hybridized with the sense and antisense probes allowed detection of a specific signal with a similar distribution pattern in all anima ls studied. In the telencephalon, a specific hybridization was detecte d in scattered cells of the dorsal telencephalic hemisphere, but the s tronger signal was consistently observed in the dorsal nucleus, and to a lesser degree in the ventral nucleus of the ventral telencephalon. Heavy hybridization staining was consistently observed in all subdivis ions of the preoptic nucleus and the nucleus lateralis tuberis, which are the main hypophysiotrophic regions in fish. A weaker signal was de tected in the nucleus anterior is periventricularis, nucleus suprachia smaticus and thalamic region. The presence of a strong signal in virtu ally all magnocellular neurons of the nucleus preopticus, known for pr oducing vasotocin, isotocin and corticotropin-releasing factor favors a direct function of cortisol in regulating its own secretion.