IN-VIVO ANTISENSE ANTAGONISM OF VASOACTIVE-INTESTINAL-PEPTIDE IN THE SUPRACHIASMATIC NUCLEI CAUSES AGING-LIKE CHANGES IN THE ESTRADIOL-INDUCED LUTEINIZING-HORMONE AND PROLACTIN SURGES

In mammals, the suprachiasmatic nuclei (SCN) regulate the timing of LH surges. Recent evidence suggests that vasoactive intestinal peptide ( VIP), an abundantly expressed neuropeptide of the SCN, communicates ti me of day information from the SCN to GnRH neurons. VIP levels in the SCN decrease with age and may be responsible for alterations in LH sur ges that become apparent in middle-aged rats, We wished to determine w hether suppression of VIP synthesis, through antisense oligonucleotide s (oligos) directed at the SCN, results in 1) selective suppression of VIP levels in the SCN and 2) aging-like changes in the secretion of L H and PRL. To test the specificity of antisense oligo treatment, rats were ovariectomized and treated with estradiol. Antisense or control r andom oligos were infused into the peri-SCN region through stereotaxic ally placed bilateral cannulas. Beginning at lights off, rats were mai ntained in constant dim red illumination throughout the remainder of t he experiment. They were killed at specific times, brains were microdi ssected, and VIP concentrations in the SCN, paraventricular nuclei, an d cortex were assayed. As a control for the specificity of antisense V IP treatment, we monitored the levels of arginine vasopressin in the S CN. To test the effects of antisense treatment on the pattern of plasm a LH and PRL secretion, blood samples were collected from atrial cathe ters from 1200-2000 h, and plasma samples were assayed for LH and PRL. The results indicate that the effects of antisense treatment were dis crete, as they suppressed VIP concentrations in the SCN, but had no ef fect on VIP concentrations in the paraventricular nuclei or cortex or on arginine vasopressin concentrations in the SCN. Peak LH levels duri ng the surge were delayed and attenuated in antisense-treated animals compared to random oligo-treated control rats in a manner strikingly s imilar to that observed previously in middle-aged rats. Likewise, PRL, which was unaffected in middle-aged rats, was also unaffected by targ eted suppression of VIP. In summary, our findings clearly demonstrate that antisense VIP oligos suppress VIP levels in the SCN and do not af fect peptide concentrations in other regions of the brain or other neu ropeptides in the SCN. Further, we show that suppression of a single n europeptide in the SCN can mimic the effects of age on the estradiol-i nduced surges of LH and PRL. These data support a central role for sup rachiasmatic VIP in the regulation of the LH surge and suggest that ag e-related perturbations in the integrity of this axis may account for alterations in the pattern of LH secretion observed during middle age.