Synaptic characteristics between cortical cells in the rat prefrontal cortex and axon terminals from the ventral tegmental area that utilizes different neurotransmitters

来自腹侧被盖区（VTA）的投射已被证明终止于前额叶皮层（PFC）作为多巴胺能和/或gaba能，形成涉及某些记忆和认知过程的神经回路。然而，目前还不确定这两种神经递质是否定位于从VTA到pfc的轴突末端。为了解决突触后前额叶皮层结构和中前额叶纤维利用GABA或多巴胺形成的突触特征，我们在电镜下采用了双标记方法，将用于顺行束示踪的过氧化物酶标记与酪氨酸羟化酶（TH）的包埋后免疫金标记结合起来。多巴胺和伽马氨基丁酸顺行束示踪研究表明，大鼠前额叶皮层的被盖皮层纤维以对称和不对称轴突终末终止，对称突触类型占主导地位。此外，一项使用顺行束示踪和包埋后免疫细胞化学的联合研究表明，形成对称突触的被盖皮层轴突末端要么是GABA能的，要么是多巴胺能的，而形成不对称突触的一小部分被盖皮层末端对多巴胺或GABA没有免疫反应。这些发现表明，被盖皮层对PFC的投射不仅通过多巴胺和GABA对称突触对PFC细胞的自发活动产生抑制作用，而且通过不对称突触使用其他神经递质对PFC细胞的自发活动产生未知的影响。

Projections from the ventral tegmental area (VTA) have been demonstrated to terminate in the prefrontal cortex (PFC) as dopaminergic and/or GABAergic, forming a neural circuit implicated in certain memory and cognitive processes. However, it has not been determined if these two neurotransmitters are localized in what types of axon terminals from the VTA to the PFC. In order to address synaptic characteristics made by postsynaptic prefrontal cortical structures and mesoprefrontal fibers utilizing either GABA or dopamine, we performed a double labeling method for electron microscopy that combined peroxidase markers for anterograde tract-tracing with postembedding immunogold labeling for tyrosine hydroxylase (TH), dopamine and GABA. The anterograde tract-tracing studies showed that tegmentocortical fibers from the VTA terminated as both symmetric and asymmetric axon terminals with the predominant symmetric synaptic type in the prefrontal cortex of the rat. Further, a combined study that used anterograde tract-tracing and postembedding immunocytochemistry indicated that tegmentocortical axon terminals forming symmetric synapses were either GABAergic or dopaminergic, while a small fraction of tegmentocortical terminals ending as asymmetric synapses was not immunoreactive for dopamine or GABA.These findings indicate that the tegmentocortical projections to the PFC exerts not only an inhibitory influence via symmetric synapses using dopamine and GABA on spontaneous activity of cells in the PFC but also unknown effects via asymmetric synapses using other neurotransmitters on that.