Does the visual system of the flying fox resemble that of primates? the distribution of calcium-binding proteins in the primary visual pathway of Pteropus poliocephalus

It has been proposed that flying foxes and echolocating bats evolved indepe ndently from early mammalian ancestors in such a way that flying foxes form one of the suborders most closely related to primates. A major piece of ev idence offered in support of a flying fox-primate link is the highly develo ped visual system of flying foxes, which is theorized to be primate-like in several different ways. Because the calcium-binding proteins parvalbumin ( PV) and calbindin (CB) show distinct;md consistent distributions in the pri mate visual system, the distribution of these same proteins was examined in the flying fox (Pteropus poliocephalus) visual system. Standard immunocyto chemical techniques reveal that PV labeling within the lateral geniculate n ucleus (LGN) of the flying fox is sparse, with clearly labeled cells locate d only within layer 1, adjacent to the optic tract. CB labeling in the LGN is profuse, with cells labeled in all layers throughout the nucleus. Double labeling reveals that all PV+ cells also contain CB, and that these cells are among the largest in the LGN. In primary visual cortex (V1) PV and CB l abel different classes of nonpyramidal neurons. PV+ cells are found in all cortical layers, although labeled cells are found only rarely in layer I. C BS cells are found primarily in layers II and III. The density of PV+ neuro pil correlates with the density of cytochrome oxidase staining; however, no CO+ or PV+ or CB+ patches or blobs are found in V1. These results show tha t the distribution of calcium-binding proteins in the flying fox LGN is unl ike that found in primates, in which antibodies for PV and CB label specifi c separate populations of relay cells that exist in different layers. Indee d, the pattern of calcium-binding protein distribution in the flying fox LG N is different; from that reported in any other terrestrial mammal. Within V1 no PV+ patches, CO blobs, or patchy distribution of CB+ neuropil that mi ght reveal interblobs characteristic of primate V1 are found; however, PV a nd CB are found in separate populations of non-pyramidal neurons, The types of V1 cells labeled with antibodies to PV and CB in all mammals examined i ncluding the flying fox suggest that the similarities in the cellular distr ibution of these proteins in cortex: reflect the fact that this feature is common to all mammals. J. Comp. Neurol. 417:73-87, 2000. (C) 2000 Wiley-Lis s, Inc.