The photoreceptor populations in the retina of the greater horseshoe bat Rhinolophus ferrumequinum.

Recently, we reported the existence of AII "rod" amacrine cells in the retina of the greater horseshoe bat Rhinolophus ferrumequinum (Jeon et al., 2007). In order to enhance our understanding of bat vision, in the present study, we report on a quantitative analysis of cone and rod photoreceptors. The average cone density was 9,535 cells/mm2, giving a total number of cones of 33,538 cells/retina. The average rod density was 368,891 cells/mm2, giving a total number of rods of 1,303,517 cells. On average, the total populations of rods were 97.49%, and cones were 2.51% of all the photoreceptors. Rod: cone ratios ranged from 33.85:1 centrally to 42.26:1 peripherally, with a mean ratio of 38.96:1. The average regularity index of the cone mosaic in bat retina was 3.04. The present results confirm the greater horseshoe bat retina to be strongly rod-dominated. The rod-dominated retina, with the existence of AII cells discovered in our previous study, strongly suggests that the greater horseshoe bat retina has a functional scotopic property of vision. However, the existence of cone cells also suggests that the bat retina has a functional photopic property of vision.

AII amacrine cells in the inner nuclear layer of bat retina: identification by parvalbumin immunoreactivity.

The purpose of this investigation is to characterize parvalbumin-immunoreactive (PV-IR) amacrine cells in bat retina through immunocytochemistry, quantitative analysis, and confocal microscopy. PV immunoreactivity was present in ganglion cell and inner nuclear layers. The regular distribution of PV-IR neurons, the inner marginal locations of their cell bodies in the inner nuclear layers, and the distinctive bilaminar morphologies of their dendritic arbors in the inner plexiform layers suggested that these PV-IR cells were AII amacrine cells. PV-IR neurons were double labeled forcalretinin, a marker for AII cells. These results indicate that PV antibodies can be used to label AII cells selectively in bats. The existence of AII cells suggests that bats have retinas involved in both rod-driven and cone-driven signals.

Ionotropic glutamate receptor GluR1 in the visual cortex of hamster: distribution and co-localization with calcium-binding proteins and GABA.

The subunit composition of the AMPA receptor is critical to its function. AMPA receptors that display very low calcium permeability include the GluR2 subunit, while AMPA receptors that contain other subunits, such as GluR1, display high calcium permeability. We have studied the distribution and morphology of neurons containing GluR1 in the hamster visual cortex with antibody immunocytochemistry. We compared this labeling to that for calbindin D28K, parvalbumin, and GABA. Anti-GluR1-immunoreactive (IR) neurons were located in all layers. The highest density of GluR1-IR neurons was found in layers II/III. The labeled neurons were non-pyramidal neurons, but were varied in morphology. The majority of the labeled neurons were round or oval cells. However, stellate, vertical fusiform, pyriform, and horizontal neurons were also labeled with the anti-GluR1 antibody. Two-color immunofluorescence revealed that many of the GluR1-IR neurons in the hamster visual cortex were double-labeled with either calbindin D28K (31.50%), or parvalbumin (22.91%), or GABA (63.89%). These results indicate that neurons in the hamster visual cortex express GluR1 differently according to different layers and selective cell types, and that many of the GluR1-IR neurons are limited to neurons that express calbindin D28K, parvalbumin, or GABA. The present study elucidates the neurochemical structure of GluR1, a useful clue in understanding the differential vulnerability of GluR1-containing neurons with regard to calcium-dependent excitotoxic mechanisms.