Molecular basis of synaptic plasticity

雄性大鼠球海绵体脊髓核的运动神经元支配着与阴茎相连的会阴横面肌球海绵体和提肛肌。它们在交配行为中起着重要作用，这对循环中雄激素水平的变化很敏感。雄激素在雄激素敏感的SNB运动神经元突触连接的重组中也起着至关重要的作用。为了阐明雄激素影响突触可塑性的分子机制，我们采用免疫组化方法研究了雄激素对成年雄性大鼠与SNB运动神经元突触接触的轴突末端谷氨酸、γ -氨基丁酸（GABA）、酪氨酸羟化酶、脑啡肽和P物质等神经递质或神经调节剂表达的调控作用。酪氨酸羟化酶、脑啡肽或p物质免疫反应性轴突末端与完整雄性大鼠的SNB运动神经元发生突触接触，尽管这些末端的发生率很低。相比之下，检测到许多gaba免疫反应性轴突终末与SNB运动神经元突触接触。通过去势去除雄激素可显著减少gaba免疫反应性轴突末端的数量，而睾酮治疗可阻止这种变化。这些结果表明，雄激素调节gaba免疫反应性轴突末端突触到SNB运动神经元的发生率，并可能为激素诱导SNB运动神经元突触可塑性的分子机制提供证据。

Motoneurons of the spinal nucleus of the bulbocavernosus (SNB) of male rats innervate the perineal striated muscles bulbocavernosus and levator ani that attach to the penis. They have an important role in copulatory behavior, which is sensitive to alterations in circulating levels of androgen. Androgen is also known to play a crucial role in reorganizing synaptic connections in androgen-sensitive SNB motoneurons. To clarify molecular mechanisms of androgen for synaptic plasticity, we examined androgenic regulation of the expression of several kinds of neurotransmitters or neuromodulators such as glutamic acid, gamma-aminobutyric acid (GABA), tyrosine hydroxylase, enkephalin and substance P in the axon terminals making synaptic contact with SNB motoneurons of adult male rats by immunohistochemical analysis. Tyrosine hydroxylase-, enkephalin- or substance P-immunoreactive axon terminals were found to make synaptic contact with SNB motoneurons of intact male rats although the incidence of these terminals was very low. In contrast, a number of GABA-immunoreactive axon terminals making synaptic contact with SNB motoneurons were detected. Removal of androgen by castration significantly reduced the number of GABA-immunoreactive axon terminals, whereas the change was prevented by testosterone treatment. These results suggest that androgen regulates the incidence of GABA-immunoreactive axon terminals that synapse onto SNB motoneurons and may provide evidence for the molecular mechanisms of hormonally-induced synaptic plasticity in the SNB motoneuron.