EFFECTS OF AN INTRAHYPOTHALAMIC INJECTION OF ANTISENSE OLIGONUCLEOTIDES FOR PREPROENKEPHALIN MESSENGER-RNA IN FEMALE RATS - EVIDENCE FOR OPIOID INVOLVEMENT IN LORDOSIS REFLEX

Previous studies in female rats have shown that estrogen increases pre proenkephalin (PPE) mRNA levels in the ventrolateral part of the ventr omedial nucleus of the hypothalamus (VMHVL), an area implicated in the modulation of sexual behavior, In order to assess the physiological r ole of hypothalamic opioid expression in lordosis reflex 16-mer oligod eoxynucleotide (ODN) directed towards the PPE, mRNA were acutely micro injected above the VMH of estradiol-primed ovariectomized rats. Estrad iol-induced lordosis behavior was observed in response to a stud male 2 days thereafter. Antisense (without or with 4 mismatches) ODN inject ions near the VMHVL resulted in a significant reduction in lordosis qu otient compared to control (reverse sense) ODN treatment or to antisen se ODN injections targeted anterior or posterior to the VMHVL. In cont rast, locomotor activity of these animals in the open-field test was n ot affected by ODN treatments. Enkephalin immunoreactive levels were d etermined by radioimmunoassay in the preoptic area, a major terminal f ield of the VMHVL. Estradiol-induced enkephalin levels were greatly re duced in antisense-treated groups. Using the in situ hybridization tec hnique, PPE mRNA levels in the VMHVL were also determined. A 1.5-2-fol d increase in PPE mRNA levels was observed in estradiol-treated rats c ompared to ovariectomized rats as previously described. This increase in PPE mRNA levels was not affected by ODN treatment, suggesting that the reduction of enkephalin expression was mainly due to physical bloc kade of PPE mRNA translation and not to its degradation. Taken togethe r, these data further support the behavioral role of PPE expressing VM HVL neurons. They also highlight the in vivo potency of acute administ ration of antisense phosphorothioate ODNs in blocking neuronal target gene expression. (C) 1997 Elsevier Science B.V.