Vertes Robert P, Hoover Walter B, Szigeti-Buck Klara, Leranth Csaba
Center for Complex Systems and Brain Sciences, Florida Atlantic University, Boca Raton, FL 33431, United States.
Brain Res Bull. 2007 Mar 30;71(6):601-9. doi: 10.1016/j.brainresbull.2006.12.002. Epub 2007 Jan 3.
The medial prefrontal cortex and the hippocampus serve well recognized roles in memory processing. The hippocampus projects densely to, and exerts strong excitatory actions on, the medial prefrontal cortex. Interestingly, the medial prefrontal cortex, in rats and other species, has no direct return projections to the hippocampus, and few projections to parahippocampal structures including the entorhinal cortex. It is well established that the nucleus reuniens of the midline thalamus is the major source of thalamic afferents to the hippocampus. Since the medial prefrontal cortex also distributes to nucleus reuniens, we examined medial prefrontal connections with populations of nucleus reuniens neurons projecting to hippocampus. We used a combined anterograde and retrograde tracing procedure at the light and electron microscopic levels. Specifically, we made Phaseolus vulgaris-leuccoagglutinin (PHA-L) injections into the medial prefrontal cortex and Fluorogold injections into the hippocampus (CA1/subiculum) and examined termination patterns of anterogradely PHA-L labeled fibers on retrogradely FG labeled cells of nucleus reuniens. At the light microscopic level, we showed that fibers from the medial prefrontal cortex form multiple putative synaptic contacts with dendrites of hippocampally projecting neurons throughout the extent of nucleus reuniens. At ultrastructural level, we showed that medial prefrontal cortical fibers form asymmetric contacts predominantly with dendritic shafts of hippocampally projecting reuniens cells. These findings indicate that nucleus reuniens represents a critical link between the medial prefrontal cortex and the hippocampus. We discuss the possibility that nucleus reuniens gates the flow of information between the medial prefrontal cortex and hippocampus dependent upon attentive/arousal states of the organism.
内侧前额叶皮质和海马体在记忆处理中发挥着广为人知的作用。海马体密集地投射到内侧前额叶皮质，并对其施加强烈的兴奋性作用。有趣的是，在大鼠和其他物种中，内侧前额叶皮质没有直接返回海马体的投射，并且对包括内嗅皮质在内的海马旁结构的投射也很少。众所周知，中线丘脑的 reunien 核是丘脑传入海马体的主要来源。由于内侧前额叶皮质也投射到 reunien 核，我们研究了内侧前额叶与投射到海马体的 reunien 核神经元群体之间的连接。我们在光镜和电镜水平上使用了顺行和逆行追踪相结合的方法。具体而言，我们将菜豆白细胞凝集素（PHA-L）注射到内侧前额叶皮质，并将荧光金注射到海马体（CA1/下托），然后检查顺行 PHA-L 标记纤维在逆行 FG 标记的 reunien 核细胞上的终末模式。在光镜水平上，我们发现来自内侧前额叶皮质的纤维在整个 reunien 核范围内与投射到海马体的神经元的树突形成多个假定的突触接触。在超微结构水平上，我们发现内侧前额叶皮质纤维主要与投射到海马体的 reunien 细胞的树突干形成不对称接触。这些发现表明，reunien 核代表了内侧前额叶皮质和海马体之间的关键联系。我们讨论了 reunien 核根据生物体的注意力/觉醒状态控制内侧前额叶皮质和海马体之间信息流的可能性。
