Department of Marine Biology and Ecology, University of Miami Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States of America.
Department of Biological Sciences, University of North Texas, Denton, TX, United States of America.
PLoS One. 2019 May 23;14(5):e0217300. doi: 10.1371/journal.pone.0217300. eCollection 2019.
The simplified nervous system of Aplysia californica (Aplysia) allows for detailed studies of physiological and molecular changes in small sets of neurons. Sensory neurons of the biting and tail withdrawal reflexes are glutamatergic and show reduced L-Glutamate current density in aged animals, making them a good candidate to study age-related changes in glutamatergic responses. To examine if changes in ionotropic L-Glu receptor (iGluR) transcription underlie reduced physiology, mRNA expression of iGluR was quantified in two sensory neuron clusters of two cohorts of Aplysia at both sexual maturity (8 months) and advanced age (12 months). Sensory neuron aging resulted in a significant overall decrease in expression of iGluR subunits in both sensory neuron clusters and cohorts. Although the individual subunits differentially expressed varied between sensory neuron clusters and different cohorts of animals, all differentially expressed subunits were downregulated, with no subunits showing significantly increased expression with age. Overall declines in transcript expression suggest that age-related declines in L-Glu responsiveness in Aplysia sensory neurons could be linked to overall declines in iGluR expression, rather than dysregulation of specific subunits. In both sensory neuron clusters tested the N-methyl-D-aspartate receptor subtype was expressed at significantly greater levels than other iGluR subtypes, suggesting an in vivo role for NMDAR-like receptors in Aplysia sensory neurons.
加利福尼亚海兔（Aplysia）简化的神经系统允许对少量神经元的生理和分子变化进行详细研究。咬和尾部退缩反射的感觉神经元是谷氨酸能的，并且在老年动物中显示出减少的 L-谷氨酸电流密度，这使它们成为研究谷氨酸能反应与年龄相关变化的良好候选物。为了检查离子型 L-Glu 受体（iGluR）转录的变化是否是生理学变化的基础，在两个性成熟（约 8 个月）和老年（约 12 个月）的 Aplysia 的两个感觉神经元簇中定量测定了 iGluR 的 mRNA 表达。感觉神经元老化导致两个感觉神经元簇和两个动物群体中的 iGluR 亚基的表达总体显著下降。尽管感觉神经元簇之间和不同动物群体之间的差异表达的各个亚基不同，但所有差异表达的亚基都下调，没有亚基的表达随年龄显著增加。转录物表达的总体下降表明，Aplysia 感觉神经元中与年龄相关的 L-谷氨酸反应性下降可能与 iGluR 表达的总体下降有关，而不是特定亚基的失调。在测试的两个感觉神经元簇中，N-甲基-D-天冬氨酸受体亚型的表达水平明显高于其他 iGluR 亚型，这表明 NMDAR 样受体在 Aplysia 感觉神经元中具有体内作用。
