Olster D H
Department of Psychology, University of California, Santa Barbara 93106, USA.
Horm Behav. 1998 Apr;33(2):115-24. doi: 10.1006/hbeh.1998.1442.
Ovariectomized (OVX) juvenile guinea pigs (approximately 3 weeks old) rarely display steroid-induced sexual receptivity. Systemic administration of the opioid receptor antagonist naloxone enhances the display of progesterone-facilitated lordosis in prepubertal females, suggesting that endogenous opioids tonically inhibit the expression of sexual receptivity at this age. This study was designed to ascertain the neural site(s) at which naloxone injection would stimulate lordosis in juvenile guinea pigs. Hartley guinea pigs were OVX at 10-11 days of age and 2-6 days later implanted with bilateral cannulae aimed at the medial preoptic area/anterior hypothalamus (MPOA/AH), ventrolateral hypothalamus/ventromedial hypothalamus (VLH/VMH), or mesencephalic central gray (MCG). At 21-23 days of age, following administration of estradiol benzoate (10 microgram(s)) and progesterone (0.5 mg), naloxone (100 ng/side) or 0.9% saline was injected through the cannulae and the guinea pigs were tested for the display of lordosis. The MPOA/AH was the only site at which application of naloxone reliably elicited lordosis (87% positive response vs 12% for saline). Few females (< 17%) displayed lordosis following injections of naloxone or saline into the VLH/VMH or MCG. A second experiment demonstrated that the stimulation of lordosis following MPOA/AH naloxone application was prevented by prior injection of the opioid agonist morphine (500 ng/side) at the same site. These data support the hypothesis that endogenous opioids acting in the MPOA/AH, but not the VLH/VMH or MCG, tonically inhibit the display of progesterone-facilitated lordosis in prepubertal guinea pigs.
卵巢切除的（OVX）幼年豚鼠（约3周龄）很少表现出类固醇诱导的性接受能力。阿片受体拮抗剂纳洛酮的全身给药可增强青春期前雌性豚鼠孕酮促进的脊柱前凸表现，这表明内源性阿片类物质在这个年龄段持续抑制性接受能力的表达。本研究旨在确定在幼年豚鼠中注射纳洛酮会刺激脊柱前凸的神经部位。哈特利豚鼠在10 - 11日龄时进行卵巢切除，2 - 6天后双侧植入套管，目标分别为内侧视前区/下丘脑前部（MPOA/AH）、下丘脑腹外侧/腹内侧（VLH/VMH）或中脑中央灰质（MCG）。在21 - 23日龄时，给予苯甲酸雌二醇（10微克）和孕酮（0.5毫克）后，通过套管注射纳洛酮（100纳克/侧）或0.9%生理盐水，然后测试豚鼠的脊柱前凸表现。MPOA/AH是唯一应用纳洛酮能可靠诱发脊柱前凸的部位（阳性反应为87%，而生理盐水注射组为12%）。向VLH/VMH或MCG注射纳洛酮或生理盐水后，很少有雌性（<17%）表现出脊柱前凸。第二个实验表明，在MPOA/AH注射纳洛酮后刺激脊柱前凸的现象可被事先在同一部位注射阿片类激动剂吗啡（500纳克/侧）所阻断。这些数据支持这样的假说，即在MPOA/AH而非VLH/VMH或MCG中起作用的内源性阿片类物质持续抑制青春期前豚鼠孕酮促进的脊柱前凸表现。
