CELLS OF ORIGIN OF HORIZONTAL AXONS IN THE MONKEY INFERIOR TEMPORAL CORTEX

Tanigawa, H., Fujita, I., Ojima, H.,Kato ,M.

Fourth IBRO World Congress of Neuroscience
9-14 July 1995, Kyoto Japan

  Area TE of the inferior temporal cortex of the macaque monkey contains an extensive network of intrinsic horizontal axons.  Horizontal axons run parallel to the pia mater over an extent of more than 4 mm within the TE and form patchy plexuses of terminal arborization at certain intervals.  The plexuses are columnar in shape and 0.5 mm wide on average which coincides with the size of functional columns of this area.  Horizontal axons thus enable distant columns to interact with each other. 
  To better understand the nature of this interaction, we examined the distribution and dendritic morphology of cells of origin of horizontal axons.  Fluorescent retrograde tracers, fast blue (FB) or diamidino yellow (DY), were injected into the TE of Japanese macaques.  The brains were fixed with 4% paraformaldehyde, and sliced to 200 or 300 m thickness.  We first analyzed the distribution of FB- or DY- labeled cells within the TE.  We then injected Lucifer Yellow intracellularly into randomly selected cells among the DY-labeled cells.  Because DY labeled only the nucleus of the cells, our sampling for Lucifer Yellow injections was unlikely to be biased to a particular type of cells. 
  Single injections of FB or DY, which covered all layers and were 0.2-0.4mm in tangential width, labeled more than 20 columnar clusters of cells as well as diffusely distributed cells in the TE.  The furthest cluster appeared at 7mm from the injection site.  In the clusters, labeled cells were found from layer 2 to 6 with much fewer labeled cells in layer 4 than in the other layers.  Although labeled cells in layers 2 and 3 were in vertical alignment with those in layers 5 and 6, the labeled cells in layers 2 and 3 tended to form more distinct clusters than those in layers 5 and 6.  The width of columnar clusters was typically 0.2-0.6 mm(0.3}0.1 mm, n=25).  Intracellular staining with Lucifer Yellow revealed that most of the cells of origin of horizontal axons were pyramidal cells of symmetrical type in both the supragranular and infragranular layers, although non-pyramidal cells such as fusiform cells and asymmetrical pyramidal cells were also labeled.  (Supported by the Uehara Memorial Foundation and the Ichiro Kanehara Foundation)


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