Zappone C A, Sloviter R S
Department of Pharmacology, University of Arizona College of Medicine, 1501 N. Campbell Avenue, Tucson, AZ 85724, USA.
J Comp Neurol. 2001 Dec 24;441(4):324-44. doi: 10.1002/cne.1415.
Improved methods for detecting neuronal markers and the retrograde tracer Fluoro-Gold (FG) were used to identify commissurally projecting neurons of the rat hippocampus. In addition to the dentate hilar mossy cells and CA3 pyramidal cells shown previously to transport retrograde tracers after injection into the dorsal hippocampus, FG-positive interneurons of the dentate granule cell layer and hilus were detected in numbers greater than previously reported. FG labeling of interneurons was variable among animals, but was as high as 96% of hilar somatostatin-positive interneurons, 84% of parvalbumin-positive cells of the granule cell layer and hilus combined, and 33% of hilar calretinin-positive cells. By comparison, interneurons of the dentate molecular layer and all hippocampal subregions were conspicuously FG-negative. Whereas hilar mossy cells and CA3 pyramidal cells were FG-labeled throughout the longitudinal axis, FG-positive interneurons exhibited a relatively homotopic distribution. "Control" injections of FG into the neocortex, septum, and ventral hippocampus demonstrated that the homotopic labeling of dentate interneurons was injection site-specific, and that the CA1-CA3 interneurons unlabeled by contralateral hippocampal FG injection were nonetheless able to transport FG from the septum. These data suggest a hippocampal organizing principle according to which virtually all commissurally projecting hippocampal neurons share the property of being monosynaptic targets of dentate granule cells. Because granule cells innervate their exclusively ipsilateral target cells in a highly lamellar pattern, these results suggest that focal granule cell excitation may result in commissural inhibition of the corresponding "twin" granule cell lamella, thereby lateralizing and amplifying the influence of the initiating discharge.
采用改进的检测神经元标志物和逆行示踪剂荧光金（FG）的方法，来鉴定大鼠海马中通过连合投射的神经元。除了先前已表明在将逆行示踪剂注入背侧海马后能运输示踪剂的齿状回门区苔藓细胞和CA3锥体细胞外，还检测到齿状颗粒细胞层和门区中FG阳性中间神经元，其数量比先前报道的更多。中间神经元的FG标记在不同动物之间存在差异，但高达门区生长抑素阳性中间神经元的96%、颗粒细胞层和门区合并的小白蛋白阳性细胞的84%，以及门区钙视网膜蛋白阳性细胞的33%。相比之下，齿状分子层和所有海马亚区的中间神经元明显为FG阴性。虽然门区苔藓细胞和CA3锥体细胞在整个纵轴上都有FG标记，但FG阳性中间神经元呈现出相对同位的分布。将FG“对照”注射到新皮层（大脑皮层）、隔区和腹侧海马表明，齿状回中间神经元的同位标记是注射部位特异性的，并且未被对侧海马FG注射标记的CA1 - CA3中间神经元仍然能够从隔区运输FG。这些数据表明了一种海马组织原则，即几乎所有通过连合投射的海马神经元都具有作为齿状颗粒细胞单突触靶点的特性。由于颗粒细胞以高度分层的模式仅支配其同侧的靶细胞，这些结果表明局部颗粒细胞兴奋可能导致相应“孪生”颗粒细胞层的连合抑制，从而使起始放电的影响侧向化并放大。
