Davis L, Vinsant S L, Steward O
Department of Neuroscience, University of Virginia School of Medicine, Charlottesville 22908.
J Comp Neurol. 1988 Jan 8;267(2):190-202. doi: 10.1002/cne.902670204.
The present study was undertaken to define the ultrastructure of synapses of the crossed temporodentate pathway from the entorhinal cortex to the contralateral dentate gyrus and to compare the synapses of the sparse crossed pathway with those of the massive ipsilateral temporodentate pathway. The synapses of the crossed pathway were identified by using EM degeneration and EM autoradiographic techniques. For the degeneration studies, adult male Sprague-Dawley rats were killed 1, 2, or 4 days following a unilateral entorhinal cortex lesion and prepared for electron microscopy. To identify the synapses by using autoradiographic techniques, four animals received injections of 3H-proline into the entorhinal cortex, were allowed to survive for 3 days, and were prepared for EM autoradiography. Degenerating synapses of the crossed pathway that were found in the molecular layer of the dentate gyrus contralateral to a lesion formed asymmetric synapses on spines and possessed presynaptic organelles indistinguishable from synapses of the ipsilateral temporodentate pathway. The number of degenerating synapses was very low at all survival intervals (14.80 degenerating synapses/10,000 microns2 at 1 day postlesion and 1.95 degenerating synapses/10,000 microns2 at 2 days postlesion); no degenerating synapses were found at 4 days postlesion. Ninety-eight percent of the degenerating synapses found at 1 day postlesion exhibited electron-lucent degeneration. At 2 days postlesion 83% of the degenerating synapses in the dorsal blade and 18% of those in the ventral blade showed lucent degeneration; the remainder were electron dense. EM autoradiography confirmed the degeneration studies in terms of the type of terminals that were labeled and suggested that the density of the crossed pathway was higher than the degeneration results implied. We conclude that synapses of the crossed temporodentate pathway have a similar ultrastructure to synapses of the ipsilateral temporodentate pathway but exhibit a rapid form of degeneration such that they disappear very rapidly following the lesion.
本研究旨在明确从内嗅皮质到对侧齿状回的交叉颞齿状通路突触的超微结构，并比较稀疏交叉通路的突触与大量同侧颞齿状通路的突触。通过电子显微镜下的变性和电子显微镜放射自显影技术来识别交叉通路的突触。对于变性研究，成年雄性Sprague-Dawley大鼠在单侧内嗅皮质损伤后1、2或4天处死，并制备用于电子显微镜观察。为了用放射自显影技术识别突触，给四只动物的内嗅皮质注射3H-脯氨酸，使其存活3天，然后制备用于电子显微镜放射自显影。在损伤对侧齿状回分子层中发现的交叉通路变性突触在棘上形成不对称突触，并且具有与同侧颞齿状通路突触难以区分的突触前细胞器。在所有存活时间间隔内，变性突触的数量都非常少（损伤后1天为14.80个变性突触/10,000平方微米，损伤后2天为1.95个变性突触/10,000平方微米）；损伤后4天未发现变性突触。损伤后1天发现的变性突触中有98%表现为电子透亮变性。损伤后2天，背侧叶片中83%的变性突触和腹侧叶片中18%的变性突触表现为透亮变性；其余为电子致密性。电子显微镜放射自显影在标记的终末类型方面证实了变性研究，并表明交叉通路的密度高于变性结果所暗示的。我们得出结论，交叉颞齿状通路的突触具有与同侧颞齿状通路突触相似的超微结构，但表现出快速的变性形式，使得它们在损伤后很快消失。
