MODULAR STRUCTURE AND CORTICAL HIERARCHY DISPLAYED BY DISTRIBUTION OF AMPA-TYPE GLUTAMATE RECEPTORS IN THE MONKEY VENTRAL VISUAL CORTICAL PATHWAY.

L.H.Xu, H.Tanigawa and I.Fujita

Society Chinese Neuroscience 1997

  Modular organization and hierarchically organized pathway are two important aspects of the primate visual cortex.  Here we report that the distribution pattern of ionotropic, -amino-3-hydroxy-5-methyl-4-isoxalone propionic acid (AMPA)-type glutamate receptors (GluR1 and GluR2/3) along the ventral visual cortical pathway is correlated with these aspects.  We determined the distribution of GluR1- and GluR2/3-like immunoreactivity using subtype-specific antibodies in Japanese monkeys(Macaqu fuscata).
  Each subtype of GluRs showed different cellular, laminar and regional distribution patterns.  In all areas we examined (primary visual cortex, V1; two extrastriate cortices, V2 and V4; the posterior and anterior inferior temporal cortex, areas TEO and TE), GluR1 moderately stained a group of neurons, most of which were of nonpyramidal types and were found in layers 2, 5, and 6, whereas GluR2/3-immunoreactive cells were distributed mainly in layers 2, 3, 5 and 6 as well as layer 4A in V1 and were mostly pyramidal cells.  When we compared the immunoreactivity among the areas, a distinct gradient existed in the distribution of both GluR1- and GluR2/3-positive cells along the pathway:  the number of immunoreactive cells in each layer increased from area V1 through areas V2, V4 and TEO to area TE.  Particularly, the number of GluR2/3-positive cells in layers 2 and 3 increased two-fold at the transition from V1 to V2, so that a sharp boundary can be seen at the border between the two areas.  We also noted that darkly stained GluR2/3-positive cells in V1 formed clusters in layers 2 and 3, which were in register with cytochrome oxidase blobs.  The specificity and diversity of the distribution patterns of AMPA receptors along the pathway may at least partially contribute to the functional diversity of specific neuronal circuits(e.g., blobs vs interblobs)or different visual areas.

  Supported by a grant to I.F from CREST of Japan Science Technology Corporation.


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