Brauth Steven E, Liang Wenru, Tang YeZhong, Galdzicka Ewa, Hall William S
Department of Psychology, University of Maryland, College Park, MD 20742, USA.
Neurobiol Learn Mem. 2007 Jul;88(1):33-9. doi: 10.1016/j.nlm.2007.03.006. Epub 2007 Apr 20.
In situ hybridization histochemistry was used to assess the effect of auditory stimulation with natural contact calls on expression of NR2A and NR2B NMDA subunit mRNAs in neurons of the thalamic auditory relay nucleus ovoidalis (Ov) of a vocal learning parrot species, the budgerigar (Melopsittacus undulatus). The results showed that both the core (Ov) and ventromedial shell subdivisions (Ovm) of ovoidalis contained neurons expressing NR2A and NR2B mRNA in no-stimulation control subjects and that the distributions of neurons expressing these subunit mRNAs were very similar in both the core and shell of Ov. Contact call stimulation (5, 30 and 180 min) resulted in substantial increases of 50-60% in the number of neurons expressing NR2A and NR2B mRNAs in both the core and shell. Staining intensity, as measured by the optical density of stained somata approximately doubled compared to controls for both NR2 subunits in the 5 and 30 min conditions, but declined from 30 to 180 min. In all conditions, the density, but not staining intensity, of neurons expressing NR2B exceeded NR2A expression. Furthermore, the density of neurons expressing both subunit mRNAs in call stimulation conditions was greater in the core than in the shell despite the fact that total neuronal density was approximately 20% higher in the shell. Previous experiments have shown that call stimulation is more effective at inducing expression of the immediate early gene zenk in the Ov shell than core; however the present results do not indicate that either NR2A or NR2B mRNA expression mediates this effect since neither subunit exhibits greater expression in Ovm. Ca(++) release is needed for immediate early gene expression, however and, notably, Ovm contains large numbers of neurons containing CGRP, a peptide which has been shown to increase cytosolic Ca(++) levels.
采用原位杂交组织化学方法，评估了自然接触叫声的听觉刺激对一种能发声学习的鹦鹉——虎皮鹦鹉（Melopsittacus undulatus）丘脑听觉中继核卵圆核（Ov）神经元中NR2A和NR2B NMDA亚基mRNA表达的影响。结果显示，在无刺激对照实验对象中，卵圆核的核心区域（Ov）和腹内侧壳层亚区（Ovm）均含有表达NR2A和NR2B mRNA的神经元，且表达这些亚基mRNA的神经元在Ov的核心区域和壳层中的分布非常相似。接触叫声刺激（5、30和180分钟）导致核心区域和壳层中表达NR2A和NR2B mRNA的神经元数量大幅增加50 - 60%。在5分钟和30分钟的实验条件下，与对照组相比，通过染色胞体的光密度测量的染色强度，两种NR2亚基均增加了约一倍，但在30分钟至180分钟时下降。在所有实验条件下，表达NR2B的神经元密度高于NR2A表达，但染色强度并非如此。此外，尽管壳层中的总神经元密度比核心区域高约20%，但在叫声刺激条件下，核心区域中表达两种亚基mRNA的神经元密度仍高于壳层。先前的实验表明，叫声刺激在诱导Ov壳层而非核心区域中即早基因zenk的表达方面更有效；然而，目前的结果并未表明NR2A或NR2B mRNA表达介导了这种效应，因为这两种亚基在Ovm中均未表现出更高的表达。不过，即早基因表达需要Ca(++)释放，值得注意地是，Ovm含有大量含有降钙素基因相关肽（CGRP）的神经元，该肽已被证明可提高胞质Ca(++)水平。
