COEXPRESSION OF STEROID-HORMONE RECEPTORS IN OPIOID PEPTIDE-CONTAINING NEURONS CORRELATES WITH PATTERNS OF GENE-EXPRESSION DURING THE ESTROUS-CYCLE

The anteroventral periventricular nucleus (AVPV) of the preoptic regio n represents an essential component of neural pathways regulating gona dotropin secretion, and contains sexually dimorphic populations of neu rons that express dynorphin or enkephalin. In the present study we use d in situ hybridization to measure prodynorphin (PDYN) and proenkephal in (PENK) mRNA in the AVPV of intact animals killed on each day of the cycle. Levels of PDYN mRNA were lowest in animals killed on the after noon of proestrus and then increased by over 60% by the morning of the following day. Expression of PENK mRNA was generally stable during th e cycle, but a small yet significant reduction was detected on proestr us relative to levels of PENK mRNA in animals killed on the day of die strus. In addition, we used double in situ hybridization: to demonstra te that the majority of PDYN mRNA-containing neurons express both estr ogen (50%) and progesterone receptor (85%) mRNAs. Only one quarter of the PENK-containing neurons also co-express estrogen receptor mRNA, an d fewer than 10% of the PENK mRNA neurons express PR mRNA. Thus, the d ifferential expression of PDYN and PENK during the cycle generally cor relates with distinct differences in the degree of colocalization of E R and PR mRNA in PDYN and PENK mRNA-containing neurons in the AVPV.