DISTRIBUTION OF CALCIUM-BINDING PROTEINS WITHIN THE PARALLEL VISUAL PATHWAYS OF A PRIMATE (GALAGO-CRASSICAUDATUS)

Bush babies possess three distinct parallel pathways to striate cortex (V1 or area 17). The calcium-binding proteins parvalbumin (PV) and ca lbindin (CB) typically show complementary regional distributions in th e brain, often associated with specific aspects of functionally relate d groups of cells. We asked whether PV+ and CB+ immunoreactivity diffe rentiate central visual parallel pathways in this species. Results sho w that PV and CB cell and neuropil staining is strongly complementary in the lateral geniculate nucleus (LGN) and is associated with separat e parallel pathways. CB+ immunoreactivity is dense, but cytochrome oxi dase (CO) staining is light in the paired koniocellular layers. PV+ an d CO+ immunoreactivity is most dense in the parvocellular and magnocel lular layers. Combined analyses of cell size, retrograde labeling, and double labeling have confirmed that all PV+ and CB+ LGN cells are gen iculocortical relay cells; none was found to be gamma-aminobutyric aci d (GABA)ergic. In V1, dense PV+ neuropil closely matches the expressio n of CO in layer 4 and in the blobs of layer 3. CB+ staining is most d ense in layers 2 and 3A and is not strongly expressed within the CO in terblobs. Finally, PV and CB are not found in related parallel pathway components in the LGN and V1 (e.g., in V1, CO blobs exhibit dense PV neuropil, yet they are targets of the small K geniculocortical relay cells that are CB+ in the LGN). Our findings support the view that thr ee functionally distinct visual pathways project to V1 from the LGN. H owever, the differences in the patterns of localization of PV and CB i n the LGN and in V1 suggest that these proteins may be utilized in dif ferent ways in these two visual areas. (C) 1995 Wiley-Liss, Inc.