Neurogenesis in the olfactory bulb induced by paced mating in the female rat is opioid dependent

The possibility to control the rate of sexual stimulation that the female rat receives during a mating encounter (pacing) increases the number of newborn neurons that reach the granular layer of the accessory olfactory bulb (AOB). If females mate repeatedly, the increase in the number of neurons is observed in other regions of the AOB and in the main olfactory bulb (MOB). It has also been shown that paced mating induces a reward state mediated by opioids. There is also evidence that opioids modulate neurogenesis. In the present study, we evaluated whether the opioid receptor antagonist naloxone (NX) could reduce the increase in neurogenesis in the AOB induced by paced mating. Ovariectomized female rats were randomly divided in 5 different groups: 1) Control (not mated) treated with saline, 2) control (not mated) treated with naloxone, 3) females that mated without controlling the sexual interaction (no-pacing), 4) females injected with saline before pacing the sexual interaction and 5) females injected with NX before a paced mating session. We found, as previously described, that paced mating induced a higher number of new cells in the granular layer of the AOB. The administration of NX before paced mating, blocked the increase in the number of newborn cells and prevented these cells from differentiating into neurons. These data suggest that opioid peptides play a fundamental role in the neurogenesis induced by paced mating in female rats.

在交配互动中控制雌性大鼠所接受的性刺激速率（即节奏控制，pacing），可增加抵达副嗅球（accessory olfactory bulb, AOB）颗粒层的新生神经元数量。若雌性大鼠反复交配，则在副嗅球的其他区域以及主嗅球（main olfactory bulb, MOB）中均可观察到神经元数量的增加。另有研究证实，控制性交配可诱导由阿片类物质介导的奖赏状态；同时有证据表明，阿片类物质可调控神经发生。本研究旨在评估阿片受体拮抗剂纳洛酮（naloxone, NX）是否能够削弱控制性交配诱导的副嗅球神经发生增加效应。我们将去卵巢雌性大鼠随机分为5组：1）生理盐水处理的未交配对照组；2）纳洛酮处理的未交配对照组；3）未控制性互动交配（无节奏控制，no-pacing）的雌性大鼠组；4）在控制性交配前注射生理盐水的雌性大鼠组；5）在控制性交配环节前注射纳洛酮的雌性大鼠组。如既往研究所报道的，我们观察到控制性交配可使副嗅球颗粒层中的新生细胞数量显著升高。在控制性交配前给予纳洛酮，可阻断新生细胞数量的增加，并阻止这些细胞向神经元分化。上述数据表明，阿片肽在雌性大鼠控制性交配诱导的神经发生过程中发挥着关键性作用。