Distribution of calcium binding proteins in the lateral geniculate nucleus of the megachiropteran bat, Pteropus poliocephalus

Purpose. It has been proposed that megachiropteran and microchiropteran bats (megabats and microbats) evolved independently from primate-like and early insectivore ancestors, respectively. A major piece of evidence offered in support of a megabat-primate link is the highly developed visual system of the megabats which is theorized to be primate-like. Because the calcium binding proteins parvalbumin (PV) and calbindin (CB) show distinct and consistent distributions in the primate lateral geniculate nucleus (LGN), we examined the distribution of these same proteins in the megabat LGN. Methods. Standard immunocytochemical techniques were used to reveal PV and CB expression. Fluorescent double labeling techniques were also employed to examine the colocalization of these proteins. Results. The optic nerve and optic tract contained no staining for either antibody. In the LGN, CB labeling was profuse with cells labeled within all layers throughout the nucleus. PV labeling was sparse with clearly labeled cells located only within the "S" layer, which is located adjacent to the optic tract. Double labeling studies revealed that all PV positive cells also contained CB, but most CB positive cells did not contain PV. Conclusions. The distribution of calcium binding proteins in the megabat LGN is unlike the pattern found in primates where PV and CB staining is layer specific and complementary. These results do not support the proposal that the visual systems of megabats and primates derived from a common megabat-primate ancestor.