DISINHIBITION FROM OPIOID INFLUENCE AUGMENTS HYPOTHALAMIC NEUROPEPTIDE-Y (NPY) GENE-EXPRESSION AND PITUITARY LUTEINIZING-HORMONE RELEASE - EFFECTS OF NPY MESSENGER-RIBONUCLEIC-ACID ANTISENSE OLIGODEOXYNUCLEOTIDES

It is well known that hypothalamic endogenous opioid peptides (EOP) ex ert an inhibitory influence on LH release, and that a restraint on thi s inhibitory tone triggers preovulatory LHRH and LH hypersecretion. Re cent evidence suggests that hypothalamic neuropeptide Y (NPY) is an im portant component of the neural circuitry that participates in inducti on of the LR surge. We have reported previously that blockade of EOP i nfluence by the opioid receptor antagonist, naloxone (NAL), stimulated NPY accumulation in the median eminence (ME) in association with incr eased LH release in estradiol-17 beta-primed ovariectomized rats. To e valuate whether a restraint on the EOP system will result in an increa se in NPY synthesis, the effects of NAL infusion on preproNPY messenge r RNA (mRNA) levels in the medial basal hypothalamus were studied by s olution hybridization/Nase protection assay and by in situ hybridizati on. NAL (2 mg/0.6 ml . h) or saline (SAL, 0.6 ml/h) was infused for 3 h (1100-1400 h) via an intrajugular cannula in estradiol-17 beta-prime d ovariectomized rats. In accord with previous studies, NAL infusion s ignificantly increased plasma LH levels at 1400 h. Concomitant with th is activation of LR release, NPY gene expression was also aug mented. As compared with initial control levels at 1100 h, preproNPY mRNA leve ls in the medial basal hypothalamus increased at 1400 h in SAL (106%)- and NAL (202%)-infused rats, and at this time, preproNPY mRNA levels were significantly higher in NAL-infused rats than in SAL-infused rats . In situ hybridization studies showed that NAL infusion significantly increased the preproNPY mRNA signal at 1400 h mainly in the rostral a nd middle regions of the arcuate nucleus (ARC) as compared with that s een at 1100 and 1400 h in SAL-infused rats. To examine further the rel ationship between the NAL-induced increase in LH release and increase in NPY gene expression, the effects of NPY mRNA antisense oligonucleot ides (oligos) on NPY levels in the ME-ARC and on plasma LH levels were studied in NAL-infused rats. In NAL-infused rats, intracerebroventric ular administration of a NPY antisense oligo (25 mu g/rat) at 1000, 12 00, and 1300 h decreased NPY levels in the ME-ARC and blocked the incr ease in plasma LH levels at 1500 h, whereas control missense oligos ha d no effect. Collectively, these results show that a decrease in opioi d influence rapidly augments NPY gene expression in a subpopulation of neurons in the ARC, and support the hypothesis that a disinhibition f rom opioid influence acutely promotes NPY synthesis and release, which is necessary for phasic LH discharge in rats.