Wouterlood F G, Mugnaini E, Nederlof J
Brain Res. 1985 Sep 23;343(2):283-96. doi: 10.1016/0006-8993(85)90746-2.
Glutamic acid decarboxylase (GAD) immunoelectron microscopy in combination with anterograde degeneration was applied in rats to study the synaptic targets of olfactory bulb afferents to the lateral subdivision (LEA) of the entorhinal area (EA). Immunoreactive neurons and terminals are scattered throughout all layers of LEA. After olfactory bulb resection, terminal degeneration occurs in layer Ia of EA. Using the electron microscope we examined serial thin sections of 12 and 14 immunoreactive neurons sampled from layer Ia of the dorsal (DLEA) and ventral (VLEA) subdivisions of LEA, respectively. The morphology of all these neurons is similar: they are small (short axis 5-9 micron, long axis 7-12 micron) and possess eccentrically located, indented nuclei provided with filamentous nuclear rodlets. The immunoreactive neurons have thin, smooth dendrites which usually emerge abruptly from the somata. We observed a single cilium on 5 of the immunoreactive neurons. In layer Ia of both DLEA and VLEA, the somata of the immunoreactive neurons are contacted by degenerating, non-immunoreactive boutons showing asymmetric synaptic junctions. In addition to these boutons, 4 other categories of axo-somatic terminals can be distinguished: normal, non-immunoreactive boutons forming asymmetric synapses and containing spherical synaptic vesicles; normal, non-immunoreactive boutons with symmetric synapses and pleomorphic synaptic vesicles; normal, non-immunoreactive boutons with asymmetric synapses, containing dense-cored vesicles in addition to spherical synaptic vesicles; and normal, immunoreactive boutons with symmetric synapses and pleomorphic synaptic vesicles. It is suggested that the GAD-immunoreactive neurons which receive olfactory bulb input correspond to local circuit neurons with intralaminar axons which innervate each other as well as the distal segments of the apical dendrites of projection neurons with cell bodies in layers II and III. Thus, the olfactory input in EA seems to be wired not only for excitation of layers II and III pyramidal neurons but also for feed-forward inhibition using GABAergic intermediary neurons, strategically located in the area of termination of olfactory bulb fibers.
在大鼠中应用谷氨酸脱羧酶（GAD）免疫电子显微镜结合顺行性变性技术，研究嗅球传入纤维至内嗅区（EA）外侧亚区（LEA）的突触靶点。免疫反应性神经元和终末散在于LEA的所有层中。嗅球切除后，EA的Ia层出现终末变性。我们用电子显微镜分别检查了从LEA背侧（DLEA）和腹侧（VLEA）亚区的Ia层中选取的12个和14个免疫反应性神经元的连续超薄切片。所有这些神经元的形态相似：它们体积小（短轴5 - 9微米，长轴7 - 12微米），核偏心定位，有凹陷，核内有丝状核小体。免疫反应性神经元有细而光滑的树突，通常从胞体突然发出。我们在5个免疫反应性神经元上观察到一根纤毛。在DLEA和VLEA的Ia层中，免疫反应性神经元的胞体与退化的、非免疫反应性的终扣接触，呈现不对称突触连接。除了这些终扣外，还可区分出其他4类轴-体终末：形成不对称突触并含有球形突触小泡的正常非免疫反应性终扣；具有对称突触和多形性突触小泡的正常非免疫反应性终扣；具有不对称突触、除球形突触小泡外还含有致密核心小泡的正常非免疫反应性终扣；以及具有对称突触和多形性突触小泡的正常免疫反应性终扣。提示接受嗅球输入的GAD免疫反应性神经元对应于具有层内轴突的局部回路神经元，它们相互支配，也支配位于II层和III层的投射神经元顶树突的远端节段。因此，EA中的嗅觉输入似乎不仅用于兴奋II层和III层的锥体神经元，还用于利用战略性地位于嗅球纤维终末区域的GABA能中间神经元进行前馈抑制。
