DUAL-LABEL IN-SITU HYBRIDIZATION STUDIES PROVIDE EVIDENCE THAT LUTEINIZING-HORMONE-RELEASING HORMONE NEURONS DO NOT SYNTHESIZE MESSENGER-RIBONUCLEIC-ACID FOR MU-OPIATE, KAPPA-OPIATE, OR DELTA-OPIATE RECEPTORS

Abundant evidence suggests that opiatergic neurons play an important i ntermediary role in the regulation of LHRH release by ovarian steroids ; however, it is unclear whether opiates communicate directly or indir ectly with LHRH neurons. To investigate this issue, we used dual label in situ hybridization histochemistry to determine whether LHRH neuron s synthesize messenger RNA (mRNA) for mu, kappa, and/or delta opiate r eceptors. For these studies, we examined both intact (n = 3) and ovari ectomized, steroid-treated rats. Ten of the ovariectomized rats were i mplanted 1 week later (day 0) with SILASTIC brand (Dow Coming) capsule s of estradiol. On the morning of day 2, half of the estradiol-treated rats were injected with 5 mg progesterone. All animals were killed at approximately 1530 h on day 2. We found that cells expressing mu, kap pa, and delta opiate receptor mRNAs were in all sections that also con tained LHRH neurons. In every case, LHRH neurons were seen to be surro unded by or in close proximity to cells containing mu, kappa, or delta mRNAs. However, regardless of steroid treatment, we found no neurons containing both LHRH mRNA and mRNAs encoding any of the three receptor subtypes. These results support the hypothesis that LHRH neurons are regulated indirectly by opiatergic neurons.