Analysis of mechanisms of pheromonal memory formation

当雌性小鼠交配时，它们会对交配雄性的信息素形成嗅觉记忆。这种记忆的神经变化发生在副嗅球(AOB)，依赖于交配诱导的去甲肾上腺素(NA)在AOB的释放，并涉及二尖瓣和颗粒细胞之间相互突触的变化。在本研究中，我们获得了以下结果。结论：1.原位杂交实验表明，在记忆形成过程中，AOB中存在信息素特异性激活的神经元型一氧化氮合酶基因，可能调节中间突触过程。利用小鼠AOB的切片，我们证明了N-甲基-D-天冬氨酸受体和II组代谢性谷氨酸受体在AOB二尖瓣细胞树突状反馈抑制中的相反作用。体内电生理实验表明，阴道刺激通过减少树突状细胞的相互抑制来增强AOB二尖瓣细胞的活性。行为学和免疫组织化学分析表明，神经胶质细胞在信息素记忆的形成中起着重要作用。此外，我们还显示了小鼠嗅球中谷氨酰胺合成酶和小胶质细胞特异性离子钙结合蛋白(IBA1)的免疫组织化学表达模式。为了进一步探索信息素记忆的详细机制，我们通过在原代分离的AOB神经元培养中重建二尖瓣和颗粒细胞之间的树突突触，简化了神经元回路的分析。利用该体外系统，我们证明NA通过突触前机制减少二尖瓣细胞GABA能抑制性突触后电流。体内和体外电生理实验表明，神经类固醇脱氢表雄酮和催产素对嗅球内二尖瓣和颗粒细胞之间的突触传递具有调制作用。

When female mice were mated, they form an olfactory memory to the pheromones of the mating male. The neural changes underlying this memory occur in the accessory olfactory bulb (AOB), depend upon mating-induced release of noradrenaline (NA) in the AOB and involve changes at the reciprocal synapses between mitral and granule cells. In this study we have obtained the following results.1. In situ hybridization experiments suggest that there is a pheromone-specific activation of neuronal nitric oxide synthase mRNA in the AOB during memory formation which may regulate intermediate synaptic processes.2. Using slices of the mouse AOB, we demonstrated opposite roles for N-methyl-D-aspartate receptors and group II metabotropic glutamate receptors in the dendrodendritic feedback inhibition of AOB mitral cells.3. In vivo electrophysiological experiments showed that vaginocervical stimulation enhances the activity of AOB mitral cells through a reduction in reciprocal dendrodendritic inhibition.4. Behavioural and immunohistochemical analyses demonstrated an important role for glial cells in the formation of pheromonal memory. In addition, we showed immunohistochemical expression patterns of glutamine synthetase and microglia-specific ionized calcium binding adaptor protein (Iba 1) in the mouse olfactory bulb.5. As a further step in exploring the detailed mechanisms underlying the pheromonal memory, we have simplified the analysis of neuronal circuit by reconstituting the dendrodendritic synapse between mitral and granule cells in primary dissociated cultures of AOB neurons. Using this in vitro system, we demonstrated that NA reduces GABAergic inhibitory postsynaptic currents in mitral cells by a presynaptic mechanism.6. In vivo and in vitro electrophysiological experiments demonstrated modulatory actions of the neurosteroid dehydroepiandrosterone and oxytocin on synaptic transmission between mitral and granule cells in the olfactory bulb.