Abstract
After lesions were placed in the hippocampal commissures, degenerating terminals could be localized above, inside and beneath the granule cell layer of the contralateral dentate gyrus. The terminals formed asymmetric synapses with spines, dendritic shafts and somata of granule cells. Degenerating terminals also formed synapses with dendrites and somata of basket cells identified by the Golgi-electron microscope technique. These basket cells were located either at the hilar border of the granule cell layer or in the molecular layer and each formed an axonal plexus around the somata and proximal dendrites of granule cells. These observations provide an anatomical basis for the recently described feed-forward inhibition in this brain region.
Highlights
The commissural pathway to the dentate gyrus arises from neurons in the contralateral hilus (Laurberg, 1979; West et al, 1979; Berger et al, 1981; Voneida et aI., 1981) and terminates both above and below the granule cell layer (Blackstad, 1965; Laatsch & Cowan, 1966; Gottlieb & Cowan, 1973; Hjorth-Simonsen & Laurberg, 1977; Kishi et al, 1980)
Degenerating commissural axon terminals Following either the two- or four-day survival periods, degenerating axon terminals were observed in the hippocampal dentate gyrus in the hemispheres contralateral to the cut hippocampal commissures
Axons of neurons in the contralateral hilus were lesioned as they passed through the hippocampal commis~ures causing their terminals to degenerate in the dentate gyrus
Summary
The commissural pathway to the dentate gyrus arises from neurons in the contralateral hilus (Laurberg, 1979; West et al, 1979; Berger et al, 1981; Voneida et aI., 1981) and terminates both above and below the granule cell layer (Blackstad, 1965; Laatsch & Cowan, 1966; Gottlieb & Cowan, 1973; Hjorth-Simonsen & Laurberg, 1977; Kishi et al, 1980). The terminals of this commissural pathway are found in the lowest one-third of the molecular layer and scattered diffusely throughout the hilus. These terminals form asymmetric synapses with spines and dendrites that are probably derived from granule cells and hilar neurons. Using a combined Golgi-electron microscopic method that utilizes gold
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