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，尚未确定这两种神经递质是否定位于从腹侧被盖区到前额叶皮层的哪种类型的轴突末梢。为了解决由突触后前额叶皮质结构和利用GABA或多巴胺的中前额叶纤维形成的突触特征，我们进行了电子显微镜的双重标记方法，结合了顺行束的过氧化物酶标记物，用植入后免疫金标记追踪酪氨酸羟化酶（TH）、多巴胺和GABA。顺行追踪的研究表明，从腹侧被盖皮质纤维终止为对称和不对称的轴突终末与主要的对称突触类型在前额叶皮层的大鼠。此外，一项使用顺行束追踪和植入后免疫细胞化学的联合研究表明，形成对称突触的被盖皮质轴突终末是GABA能或多巴胺能的，这些结果表明，中脑被盖皮质向PFC的投射不仅通过对称性突触对多巴胺产生抑制作用，和GABA对PFC中细胞自发活动的影响，但也有未知的影响，通过不对称突触使用其他神经递质。

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.