Thalamic projections to the hippocampal formation in the cat.

The thalamo-hippocampal projections in the cat were studied by anterograde and retrograde tracing methods. Injections of horseradish peroxidase (HRP) into the hippocampus and dentate gyrus led to retrograde labeling of cells in the nucleus reuniens of the ipsilateral thalamus throughout almost its entire anteroposterior extent. The labeled cells were found mostly in the parvocellular ventral part, but a few cells were labeled in the dorsal part at anterior levels. Anterograde transport following injections of wheat germ agglutinin conjugated to HRP into the nucleus reuniens resulted in terminal labeling in the subicular area, the neighboring parts of the hippocampus (CA1) and the border zone of the dentate gyrus with the hippocampus.