Mechanisms for gravity stress-induced synaptic plasticity in rat hippocampus

我们测量了CA1区域的场电位，以响应Schaffer’s collateral的电刺激。与100和1Hz刺激相比，负偏转振幅的相对比例在2g切片中增加了40%。超重力增强了CA1区的单位活动和突触传递，这可能是大鼠重力反应机制的基础。在1G（基础水平）时，振幅的相对比值为1.3，在2G超重力时增加到1.8。2g暴露增加海马CA1区突触传递效率。超重力诱导的早期LTP（长期增强）可能反映了CA1区放电频率的增加。Ishii等人也报道了类似的数据，在暴露于4G 48小时的小鼠中诱导早期LTP， AMPA受体磷酸化增强。另一组报告了急性行为应激对海马LTP诱导的部位和时间依赖性调节。数据表明，海马LTP、谷氨酸受体、Ca ^<2+>、LTP的5-羟色胺（5-HT）强化和GABA抑制神经元对海马可塑性的影响，最终导致重力信息的学习和记忆紊乱的分子机制。海马、杏仁核和下丘脑是通过神经元回路相互连接的结构。这些区域的神经元活动的调节可能在引力改变反应的机制中起因果作用。

We measured the field potential in the CA1 region as responding to electrical stimulation of Schaffer's collaterals. The relative ratio of amplitude of the negative deflection, as compared between 100 vs. 1Hz stimulation, was 40% increased in the 2G-slices. Hypergravity enhanced unit activities and synaptic transmission in the CA1 region, which may underlie the gravity-response mechanism of rat. The relative ratio of amplitude was 1.3 at 1G (basal level), and increased to 1.8 at 2G hypergravity. The efficiency of synaptic transmission in the hippocampal CA1 region was increased by 2G-exposure. The hypergravity-induced early-phase LTP (long-term potentiation) might reflect the increase of firing frequency in the CA1 region. Similar data were reported by Ishii et al. in that early-phase LTP was induced in mice that were exposed to 4G for 48 hrs with enhancement of AMPA receptor phosphorylation. Another group reported the site and time-dependent modulation of acute behavioral stress on hippocampal LTP induction. Data suggest molecular mechanism for the hippocampal LTP, glutamate-receptor, Ca ^<2+>, serotonin (5-HT) enforcement of LTP, and GABA inhibitory neurons on hippocampal plasticity, which will finally result in disordered learning and memory of gravitational informations. Hippocampus, amygdala, and hypothalamus are interconnected structures by neuronal circuit. The modulation of neuronal activity in these areas might play causative roles in the mechanism underlying the response to gravitational alteration.