Soc. Neurosci. Abstr. 1995.11

NEURONS MEDIATING HORIZONTAL INTERACTIONS IN THE MONKEY INFERIOR TEMPORAL CORTEX.

I. Fujita1,2*, H. Tanigawa1, H. Ojima3 and M. Kato1. 1Dept. Cognitive Neuroscience, Osaka Univ. Medical School; 2PRESTO, JRDC, Osaka 565; 3Dept. Anatomy, Toho Univ., Tokyo 143, Japan.

In area TE of the monkey inferior temporal cortex, horizontal axons run parallel to the pial surface and mediate interaction between distant sites. Distribution and type of horizontally projecting neurons determine the nature of the interaction. In this study, fluorescent retrograde tracers, fast blue (FB) or diamidino yellow (DY), were injected into the TE of Japanese macaques. The distribution of retrogradely labeled cells was analyzed in fixed slices. Lucifer Yellow was then intracellularly injected into DY-labeled cells, and their dendritic morphology was examined by confocal laser scanning microscopy. Single injections of FB or DY, which covered all layers and were 0.2-0.4 mm wide, labeled more than 20 columnar clusters of cells as well as cells diffusely scattered between the clusters. In the clusters, labeled cells were found in layers 2 to 6 with a few labeled cells in layer 4. The clustering of labeled cells in layers 5 and 6 tended to be looser than that in layers 2 and 3. In layers 2 and 3, all the cells so far injected with Lucifer Yellow were symmetrical pyramidal cells (120/120). A few cells labeled in layer 4 were also pyramidal cells (4/4). In layers 5 and 6, asymmetrical pyramidal cells and fusiform cells (36/88) and nonpyramidal interneurons (9/88) were labeled in addition to symmetrical pyramidal cells (43/88). No difference was detected in the laminar distribution and type of labeled cells between the clusters and interclusters. The results suggest that horizontal interactions in the TE are predominantly mediated by standard pyramidal cells, and contribution of other types of cells may differ between the supragranular and infragranular layers.

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