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.

Abstract

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 time 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 surges that become apparent in middle-aged rats. We wished to determine whether suppression of VIP synthesis, through antisense oligonucleotides (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 LH and PRL. To test the specificity of antisense oligo treatment, rats were ovariectomized and treated with estradiol. Antisense or control random oligos were infused into the peri-SCN region through stereotaxically placed bilateral cannulas. Beginning at lights off, rats were maintained in constant dim red illumination throughout the remainder of the experiment. They were killed at specific times, brains were microdissected, and VIP concentrations in the SCN, paraventricular nuclei, and cortex were assayed. As a control for the specificity of antisense VIP treatment, we monitored the levels of arginine vasopressin in the SCN. To test the effects of antisense treatment on the pattern of plasma LH and PRL secretion, blood samples were collected from atrial catheters from 1200-2000 h, and plasma samples were assayed for LH and PRL. The results indicate that the effects of antisense treatment were discrete, as they suppressed VIP concentrations in the SCN, but had no effect on VIP concentrations in the paraventricular nuclei or cortex or on arginine vasopressin concentrations in the SCN. Peak LH levels during the surge were delayed and attenuated in antisense-treated animals compared to random oligo-treated control rats in a manner strikingly similar to that observed previously in middle-aged rats. Likewise, PRL, which was unaffected in middle-aged rats, was also unaffected by targeted suppression of VIP. In summary, our findings clearly demonstrate that antisense VIP oligos suppress VIP levels in the SCN and do not affect peptide concentrations in other regions of the brain or other neuropeptides in the SCN. Further, we show that suppression of a single neuropeptide in the SCN can mimic the effects of age on the estradiol-induced surges of LH and PRL. These data support a central role for suprachiasmatic VIP in the regulation of the LH surge and suggest that age-related perturbations in the integrity of this axis may account for alterations in the pattern of LH secretion observed during middle age.