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Ultrastructural characterization of the synapses of the crossed temporodentate pathway in rats
Author(s) -
Davis Lauren,
Vinsant Sharon L.,
Steward Oswald
Publication year - 1988
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902670204
Subject(s) - entorhinal cortex , biology , synapse , lesion , dentate gyrus , hippocampus , dendritic spine , ultrastructure , neuroscience , anatomy , degeneration (medical) , cortex (anatomy) , postsynaptic potential , hippocampal formation , pathology , medicine , biochemistry , receptor
Abstract 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 3 H‐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/10,000μm 2 at 1 day postlesion and 1.95 degenerating synapses/10,000μm 2 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.