Benes F M, Vincent S L, Molloy R
Department of Psychiatry, Harvard Medical School, Boston, Massachusetts 02115.
Synapse. 1993 Dec;15(4):285-95. doi: 10.1002/syn.890150405.
Recent postmortem studies have suggested that reduced gamma-aminobutyric acid (GABA)ergic activity in limbic cortex may be one component to the pathophysiology of schizophrenia. This hypothesis has underscored the importance of knowing whether midbrain dopamine afferents interact extensively enough with inhibitory interneurons to suggest a direct functional relationship. Toward this end, a double immunofluorescence approach combined with confocal laser scanning microscopy has been used to localize dopamine and GABA simultaneously in rat medial prefrontal cortex. The results confirm studies from other laboratories showing a rich network of dopamine-immunoreactive fibers forming a gradient across the cortical laminae, with deeper layers having the highest density. When viewed with oil immersion optics, dopamine-immunoreactive fibers were frequently found to be in close apposition with GABA-immunoreactive cell bodies. The percentage of GABA-containing neurons showing such contacts was highest in layer VI (65%) and progressively decreased toward layer I (9%). Varicose regions of the dopamine fibers were typically present at the point of contact with a GABA-immunoreactive cell body. Using an immunoperoxidase technique to localize dopamine fibers and cresyl violet staining to visualize neurons simultaneously, two separate statistical analyses were performed to assess whether the frequency of contacts between dopamine fibers and cell bodies in general may be due to random effects. In layer VI, a high percentage of both pyramidal and nonpyramidal neurons were found to be in contact with dopamine varicosities (71% and 76%, respectively), but these were not significantly different from that observed for GABA-containing cells (65%) in double-immunofluorescence specimens. A Chi-square statistical test was used to compare the observed and predicted number of varicosities forming cell body contacts. This analysis indicated that the percentage of dopamine varicosities (30%) that form appositions with cell bodies is much greater than would be expected if these appositions were due to random effects (15%). Moreover, using an estimate of intensity for a stationary Poisson process, it was again found that random effects can not account for these interactions (P = 0.01). Taken together with earlier electron microscopic studies from other laboratories, the present findings support the idea that GABAergic interneurons have extensive interactions with dopamine varicosities. While these interactions are not unique to GABAergic cell bodies, they suggest that inhibitory interneurons can play a direct role in mediating the effects of midbrain dopamine afferents in rat medial prefrontal cortex.
最近的尸检研究表明，边缘皮质中γ-氨基丁酸（GABA）能活性降低可能是精神分裂症病理生理学的一个组成部分。这一假说强调了了解中脑多巴胺传入纤维是否与抑制性中间神经元有足够广泛的相互作用以表明直接功能关系的重要性。为此，一种结合共聚焦激光扫描显微镜的双重免疫荧光方法已被用于在大鼠内侧前额叶皮质中同时定位多巴胺和GABA。结果证实了其他实验室的研究，显示出丰富的多巴胺免疫反应性纤维网络在皮质各层形成梯度，深层的密度最高。用油浸光学显微镜观察时，经常发现多巴胺免疫反应性纤维与GABA免疫反应性细胞体紧密并置。显示这种接触的含GABA神经元的百分比在VI层最高（65%），并向I层逐渐降低（9%）。多巴胺纤维的曲张区域通常出现在与GABA免疫反应性细胞体接触的部位。使用免疫过氧化物酶技术定位多巴胺纤维并同时用甲酚紫染色使神经元可视化，进行了两项单独的统计分析，以评估多巴胺纤维与细胞体之间接触的频率总体上是否可能是由于随机效应。在VI层，发现高比例的锥体神经元和非锥体神经元都与多巴胺曲张体接触（分别为71%和76%），但这些与双重免疫荧光标本中观察到的含GABA细胞的比例（65%）没有显著差异。使用卡方统计检验来比较观察到的和预测的形成细胞体接触的曲张体数量。该分析表明，与细胞体形成并置的多巴胺曲张体的百分比（30%）远高于如果这些并置是由于随机效应所预期的百分比（15%）。此外，使用固定泊松过程的强度估计，再次发现随机效应无法解释这些相互作用（P = 0.01）。与其他实验室早期的电子显微镜研究结果相结合，目前的发现支持GABA能中间神经元与多巴胺曲张体有广泛相互作用的观点。虽然这些相互作用并非GABA能细胞体所特有，但它们表明抑制性中间神经元在介导大鼠内侧前额叶皮质中脑多巴胺传入纤维的作用中可以发挥直接作用。
