Schwerdtfeger W K, Buhl E H, Germroth P
Max-Planck-Institut für Hirnforschung, Frankfurt, Federal Republic of Germany.
J Comp Neurol. 1990 Feb 8;292(2):163-77. doi: 10.1002/cne.902920202.
Electrophysiological and anatomical studies indicate functional relationships between the olfactory bulb and the hippocampus, mediated by the lateral olfactory tract and perforant path. Fibres from the lateral olfactory bulb terminate in the molecular layer of the lateral entorhinal cortex, which contains stellate and pyramidal cells that project to the hippocampus. Therefore this study was performed to analyze whether a trineuronal, disynaptic chain connects the olfactory bulb and the hippocampus. In adult rats, Fast Blue was unilaterally injected into the septal hippocampus to label cells of origin of the entorhinohippocampal pathway. Lesions of the ipsilateral olfactory bulb induced anterograde terminal degeneration in the entorhinal cortex of the same animals. Fast Blue labelled, and thus hippocampally projecting entorhinal neurones in fixed vibratome slices of the operated brains were injected with Lucifer Yellow. Most of these neurones were stellate layer II and pyramidal layer III cells; in addition there were some sparsely spinous multipolar cells in layers II and III and sparsely spinous horizontal cells at the layer I/II border. Injected cells were photoconverted and processed for electron microscopy. Olfactory bulb lesions resulted in electron-dense degeneration of abundant terminal boutons in the outer zone of entorhinal layer I. The relative frequency of degenerating boutons decreased towards deeper zones of the layer. In the outer zone, degenerated terminals predominantly contacted dendritic spines. These contacts could be seen on injected stellate cells but not on pyramidal cells. This study shows that the area dentata of the rat is reached by disynaptic afferent input from the olfactory bulb and thus is likely to process olfactory information. Oligosynaptic pathways might provide the hippocampus also with visual and auditory inputs; such fast transmitted polysensory information could be essential for the proposed participation of the hippocampus in attention-related mechanisms.
电生理和解剖学研究表明，嗅球与海马体之间存在功能联系，由外侧嗅束和穿通通路介导。来自外侧嗅球的纤维终止于外侧内嗅皮质的分子层，该层包含投射至海马体的星状细胞和锥体细胞。因此，本研究旨在分析是否存在一条三神经元、双突触链连接嗅球和海马体。在成年大鼠中，将快蓝单侧注射到隔区海马体中，以标记内嗅海马通路的起源细胞。同侧嗅球损伤导致同一只动物内嗅皮质出现顺行性终末变性。在手术大脑的固定振动切片中，对用快蓝标记且因此向海马体投射的内嗅神经元注射路西法黄。这些神经元大多数是II层星状细胞和III层锥体细胞；此外，在II层和III层有一些稀疏棘状多极细胞，在I/II层边界有稀疏棘状水平细胞。对注射的细胞进行光转换并处理用于电子显微镜观察。嗅球损伤导致内嗅I层外层大量终末小体出现电子致密变性。变性小体的相对频率向该层较深区域降低。在外侧区域，变性终末主要与树突棘接触。这些接触在注射的星状细胞上可见，但在锥体细胞上未见。本研究表明，大鼠的齿状回通过来自嗅球的双突触传入输入到达，因此可能处理嗅觉信息。少突触通路也可能为海马体提供视觉和听觉输入；这种快速传递的多感觉信息对于海马体参与注意力相关机制的假设可能至关重要。
