Showing papers on "Rhinal sulcus published in 1989"

Topographical organization of the entorhinal projection to the dentate gyrus of the monkey

Abstract: The topographic organization of the projections from the entorhinal cortex to the dentate gyrus in the macaque monkey was studied with anterograde and retrograde tracing methods. Injections of WGA-HRP or the fluorescent retrograde tracers, Fast blue and Diamidino yellow, were placed at various levels along the rostrocaudal axis of the dentate gyrus and hippocampus. In 5 experiments the fluorescent dyes were injected at 2 rostrocaudal levels of the same dentate gyrus. Labeled neurons were observed mainly in layers II and III of the entorhinal cortex, though some were also seen in layers V and VI. The labeled layer II cells resulting from each of the tracer injections were located throughout much of the rostrocaudal extent of the entorhinal cortex, though they tended to have a more limited distribution in the transverse or mediolateral axis. Injections of retrograde tracers located caudally in the dentate gyrus resulted in a rostrocaudally oriented zone of labeled cells that was situated laterally in the entorhinal cortex adjacent to the rhinal sulcus. The zone of labeled cells was not oriented strictly parallel to the rhinal sulcus since at caudal levels it extended medially to encompass the full transverse extent of the most caudal portion of the entorhinal cortex. When injections were placed more rostrally in the dentate gyrus and hippocampus, the rostrocaudally oriented zone of labeled cells was situated more medially in the entorhinal cortex. Anterograde tracing experiments using 3H-amino acid injections into different rostrocaudal and mediolateral positions of the entorhinal cortex confirmed the organization demonstrated by the retrograde tracers and further indicated that the entorhinal fibers terminate in the outer two-thirds of the molecular layer of the dentate gyrus. Unlike in the rat, where the entorhinal termination zone in the molecular layer is clearly bilaminate, projections from all portions of the entorhinal cortex appeared to terminate more diffusely throughout the outer two-thirds of the molecular layer. The results of the present study indicate that rostrocaudally oriented zones of cells that cut across several cytoarchitectonic subdivisions of the entorhinal cortex give rise to topographically organized projections to the dentate gyrus. Cells located laterally in the entorhinal cortex project to caudal levels of the dentate gyrus, whereas progressively more medially situated cells project to progressively more rostral parts of the dentate gyrus.

Differential projection from the motor and limbic cortical regions to the mediodorsal thalamic nucleus in the dog.

Abstract: The cortical afferents to the mediodorsal thalamic nucleus in the dog were studied by using horseradish peroxidase. Small injections allowed to establish two specific projection zones connected separately with the lateral and medial segments of the nucleus. The lateral segment received the major projection from the dorsal half of the hemisphere. It included premotor and part of the motor cortices in the anterior sigmoid gyrus and precruciate areas as well as the presylvian cortex. The medial segment of the nucleus was innervated by the limbic areas of the ventral half of the hemisphere. These areas included the medioventrally located genual, subcallosal and piriform cortices, as well as the cortex of the ventral bank of the anterior rhinal sulcus and the caudal part of the orbital gyrus. The cortical fields situated between these two main cortical zones, both on the lateral and medial surfaces (rhinal and sylvian sulci and anterior cingular gyrus, respectively) sent projections to both medial and lateral segments of the nucleus. These results indicate that in the mediodorsal thalamic nucleus may take place the integration of information from two functionally defined systems, the motor and limbic ones.