Wigger A, Neumann I D
Max Planck Institute of Psychiatry, Kraepelinstrasse 2, 80804 Munich, Germany.
Neuroscience. 2002;112(1):121-9. doi: 10.1016/s0306-4522(02)00068-4.
Oxytocin secretion into blood in response to swim stress is differentially regulated by endogenous opioids in virgin and pregnant rats. Here, the influence of endogenous opioids on oxytocin release within the hypothalamic paraventricular and supraoptic nuclei was investigated using microdialysis in virgin and pregnant (day 19-21) rats. Rats fitted with a U-shaped microdialysis probe 3 days before testing were injected with naloxone (5 mg/kg body weight, s.c.) or vehicle (sterile saline) and, 3 min later, were forced to swim (10 min at 19 degrees C). Within the paraventricular nucleus, basal and stimulated oxytocin release did not significantly differ between vehicle-treated virgin and pregnant rats. After naloxone, local oxytocin release in response to swimming was lowered in virgin rats (P<0.01), whereas it was further increased in pregnant rats (P<0.01). Within the supraoptic nucleus, basal oxytocin release was significantly lower in pregnant compared to virgin rats (P<0.01). Forced swimming induced a similar rise in intranuclear oxytocin release in both vehicle-treated virgin and pregnant rats, but peak levels were still higher in the virgin controls. In contrast to the paraventricular nucleus, naloxone did not alter swim-induced oxytocin release within the supraoptic nucleus either in virgin or pregnant rats. Vasopressin release in the paraventricular nucleus was also increased by forced swimming but there was no effect of pregnancy or naloxone on it. In summary, in pregnancy, basal and stress-induced oxytocin release within the paraventricular nucleus was not changed, whereas it was blunted within the supraoptic nucleus. Further, within the paraventricular nucleus the excitatory effect of endogenous opioids on local oxytocin release seen in virgins was switched into an inhibitory action in pregnancy. In contrast, endogenous opioids were evidently not involved in the regulation of swim-induced oxytocin release within the supraoptic nucleus either in virgin or pregnant rats. Thus, pregnancy-related neuroendocrine plasticity also includes site-specific functional alterations in opioid receptor-mediated actions in the hypothalamus.
未孕和怀孕大鼠对游泳应激的催产素分泌进入血液的过程受到内源性阿片类物质的不同调节。在此，我们使用微透析技术研究了内源性阿片类物质对未孕和怀孕（第19 - 21天）大鼠下丘脑室旁核和视上核内催产素释放的影响。在测试前3天安装了U形微透析探针的大鼠，皮下注射纳洛酮（5毫克/千克体重）或溶剂（无菌生理盐水），3分钟后，强迫其游泳（在19摄氏度下游10分钟）。在室旁核内，溶剂处理的未孕和怀孕大鼠的基础催产素释放和刺激后的催产素释放没有显著差异。注射纳洛酮后，未孕大鼠游泳引起的局部催产素释放降低（P<0.01），而怀孕大鼠的催产素释放进一步增加（P<0.01）。在视上核内，怀孕大鼠的基础催产素释放显著低于未孕大鼠（P<0.01）。强迫游泳在溶剂处理的未孕和怀孕大鼠中引起了类似的核内催产素释放增加，但未孕对照组的峰值水平仍然更高。与室旁核不同，纳洛酮在未孕或怀孕大鼠中均未改变视上核内游泳诱导的催产素释放。强迫游泳也增加了室旁核内的加压素释放，但怀孕或纳洛酮对其没有影响。总之，在怀孕期间，室旁核内的基础和应激诱导的催产素释放没有变化，而视上核内的催产素释放则减弱。此外，在室旁核内未孕大鼠中内源性阿片类物质对局部催产素释放的兴奋作用在怀孕时转变为抑制作用。相反，内源性阿片类物质显然不参与未孕或怀孕大鼠视上核内游泳诱导的催产素释放的调节。因此，与怀孕相关的神经内分泌可塑性还包括下丘脑阿片受体介导作用的位点特异性功能改变。
