Bressler S C, Baum M J
Department of Biology, Boston University, MA 02215, USA.
Neuroscience. 1996 Apr;71(4):1063-72. doi: 10.1016/0306-4522(95)00493-9.
In rodents, reproductively relevant pheromonal cues are detected by receptors in the vomeronasal organ, which in turn transmit this information centrally via the accessory olfactory bulb, the medial nucleus of the amygdala, the posterior medial bed nucleus of the stria terminalis and the medial preoptic area. In the rat, more neurons are present in males than in females at virtually every relay in this vomeronasal projection circuit. Using Fos immunoreactivity as a marker of neuronal activation, we compared the ability of pheromonal cues derived from the urine and feces of estrous or anestrous female rats to activate neurons in this vomeronasal projection circuit in sexually experienced, gonadectomized male and female rats which were chronically treated in adulthood with a high dose of testosterone propionate (5 mg/kg). When compared with rats killed after 2 h of exposure to clean bedding, male and female subjects exposed for 2 h to bedding from estrous females had similar and significant increments in the number of Fos-immunoreactive neurons at each level of the vomeronasal projection circuit, including the granular layer of the accessory olfactory bulb, the posterior dorsal portion of the medial amygdaloid nucleus, the posterior medial portion of the bed nucleus of the stria terminalis and the medial preoptic area. Exposure to bedding from anestrous females stimulated similar and significant increments in Fos immunoreactivity in most of these same brain regions. Chemosensory stimulation failed to augment Fos immunoreactivity in neurons located in the ventrolateral subregion of the ventromedial nucleus of the hypothalamus or in the midbrain central tegmental field, sites at which mating has previously been shown to augment Fos immunoreactivity in both sexes. Finally, chemosensory stimulation augmented Fos immunoreactivity in the nucleus accumbens shell and core, two regions receiving dopaminergic afferents which have been implicated in sexual reward. On two occasions all subjects were given simultaneous access to bowls containing bedding from estrous versus anestrous females. Both males and females spent significantly more time investigating the estrous bedding, although the total time spent investigating either type of bedding was significantly greater in males. The results suggest that the previously established sexual dimorphism in the morphology of the rat's vomeronasal projection circuit is not reflected in the functional responsiveness of neurons in this circuit to chemosensory cues emitted by female conspecifics.
在啮齿动物中，与生殖相关的信息素线索由犁鼻器中的受体检测到，这些受体进而通过副嗅球、杏仁核内侧核、终纹床核后内侧核和内侧视前区将此信息传递至中枢。在大鼠中，在这个犁鼻投射回路的几乎每一个中继点上，雄性的神经元都比雌性多。我们以Fos免疫反应性作为神经元激活的标志物，比较了来自发情期或非发情期雌性大鼠尿液和粪便的信息素线索激活性经验丰富、性腺切除的雄性和雌性大鼠犁鼻投射回路中神经元的能力，这些大鼠在成年后长期接受高剂量丙酸睾酮（5毫克/千克）治疗。与暴露于干净垫料2小时后处死的大鼠相比，暴露于发情期雌性大鼠垫料2小时的雄性和雌性受试者，在犁鼻投射回路的各个水平，包括副嗅球颗粒层、杏仁核内侧核后背部、终纹床核后内侧部和内侧视前区，Fos免疫反应性神经元数量都有相似且显著的增加。暴露于非发情期雌性大鼠的垫料也能刺激这些相同脑区中大多数区域的Fos免疫反应性有相似且显著的增加。化学感觉刺激未能增强位于下丘脑腹内侧核腹外侧亚区或中脑中央被盖区的神经元的Fos免疫反应性，此前已表明交配能增强这两个区域两性的Fos免疫反应性。最后，化学感觉刺激增强了伏隔核壳部和核心区的Fos免疫反应性，这两个区域接受多巴胺能传入纤维，与性奖励有关。有两次，所有受试者都同时有机会接触装有发情期与非发情期雌性大鼠垫料的碗。雄性和雌性花在探究发情期垫料上的时间都显著更多，不过雄性探究两种垫料的总时间显著更长。结果表明，先前确立的大鼠犁鼻投射回路形态上的性二态性，并未体现在该回路中神经元对同种雌性发出的化学感觉线索的功能反应性上。
