Infusion of Antisense Oligo-deoxynucleotides to the Oxytocin Receptor in the Ventromedial Hypothalamus Reduces Estrogen-Induced Sexual Receptivity and Oxytocin Receptor Binding in the Female Rat

Abstract

Exogenous administration of the neuropeptide oxytocin reliably facilitates sexual behavior in the female rat and exposure to estrogen increases oxytocin receptor (OTR) binding in the ventromedial nucleus (VMN) of the hypothalamus. We have used a novel approach to investigate the role of hypothalamic OTR in controlling behavior by infusing antisense oligodeoxy-nucleotides (oligo) to the 5’-region of the human OTR mRNA into the VMN of hormonally primed rats. Control infusions consisted of a scrambled-sequence oligo that had little or no homology to known mRNAs. OTR antisense oligo infusion significantly reduced lordosis frequency and intensity in females primed with estrogen. There was also a significantly greater number of rejection behaviors exhibited by antisense-oligo-infused estrogen-treated females versus controls and no evidence of decreased locomotion by either treatment. In contrast to the effects in estrogen-primed-females, when females were primed to be sexually receptive with estrogen plus progesterone, OTR antisense-oligo infusion had no effect on sexual behavior. The lack of effectiveness of OTR antisense oligo in females primed with progesterone may be the result of the action of this steroid on other neurotransmitter systems that also facilitate lordosis and thereby override a deficit in oxytocin binding. Alternatively, via previously described mechanisms, progesterone may enhance the effectiveness of oxytocin binding at its receptor. In vitro receptor autoradiography in estrogen-primed females indicated a 31% reduction in VMN OTR binding in the vicinity of the cannula tip in antisense-oligo-infused females compared to controls. There was no significant difference in the level of OTR binding in the central nucleus of the amygdala. In addition, OTR antisense-oligo-infused females exhibited a significant reduction in food intake as demonstrated by weight loss and a reduced appetite for sweetened milk compared to scrambled-oligo-infused controls. Since VMN damage results in increased food intake, these results indicate a lack of damage to the VMN as a result of the OTR antisense infusions.

Naturally occurring variations in maternal behavior in the rat are associated with differences in estrogen-inducible central oxytocin receptors

“…These findings belie an impressive level of regional specificity in the effect of maternal care on estrogen sensitivity in the female offspring. Oxytocin receptor activation in the ventromedial n. of the hypothalamus has been linked to sexual, and not maternal, behavior (35). It is possible, therefore, that the specificity in estrogen sensitivity is associated with selective functional outcomes, influencing maternal, but not sexual, behavior.…”

Antisense Oligonucleotides in the Study of Neuroendocrine Systems

“…vasopressin and oxytocin. Differentiation can be achieved using antisense oligonucleotides, as shown for the receptor subtypes for dopamine, acetylcholine, glutamate, angiotensin and NPY (16,25,28,39,40,43,46,57,58) and for the neuropeptides, vasopressin and oxytocin (37,45). Results demonstrate that in vitro or in vivo administration of an angiotensin AT-, antisense produced a reduction in the density of AT-, receptors, but no change in the AT-, population (39,43).…”

“…Likewise, in rats, the clearance rate for a PS oligomer followed a two-compartment model with an initial phase of 23 min and a into one side of the striatum produced a reduction in fos response on only that side and a behavioral rotation directed toward the treated side (49). When antisense oligomers to the oxytocin receptor were infused into the ventromedial nucleus, there were discrete reductions in receptor binding within this region (40).…”

“…The antisense sequence generally chosen is one which targets the region containing or adjacent to the start codon (AUG) for the protein. This type of construct is effective in reducing the synthesis of neuropeptides and receptors for steroids, proteins and neurotransmitters (17,25,(27)(28)(29)(37)(38)(39)(40)(41)(42)(43)(44)(45). While the DNA sequence can be logically selected on the basis of the known gene structure and the absence of other genetic homologies, the correct choice can only be ascertained empirically.…”

Sex, parturition and motherhood without oxytocin?

“…In the rat, oxytocin, produced and acting in the brain, is important in stimulating the expression of female receptive behaviour (Caldwell et al 1990) and in penile erection in the male (Melis et al 1994); in particular, centrally administered oxytocin facilitates lordosis by acting in the ventromedial nucleus of the hypothalamus, through specific oxytocin receptors positively regulated by oestrogen or testosterone ( Johnson 1992, McCarthy et al 1994, Bale & Dorsa 1995. By contrast, in the normal (and homozygous oxytocin knockout) mouse, there is a low density of oxytocin receptors in the ventromedial nucleus (Nishimori et al 1996), and in the male mouse testosterone negatively regulates oxytocin receptor binding in the ventromedial nucleus, the reverse of the effects of gonadal steroid in the rat (Insel et al 1993).…”