Abstract
Purpose: :
Rabbit ganglion cells have recently been classified by Rockhill et al. (2002) and Roska et al. (2006). These groups have identified one type of bistratified ganglion cell (G7; directionally selective) and a "partly bistratified" type called as G3. We have identified another type of bistratified ganglion cell in the rabbit retina. Here, we morphologically and physiologically study this ganglion cell.
Methods: :
Ganglion cells were visualized with acridine orange and stained via Neurobiotin injection following loose patch recording. Immunohistochemistry was performed to check stratification and possible synaptic inputs.
Results: :
This ganglion cell had the following morphogical characteristics: (1) The dendritic arbor in sublamina a was smaller than the arbor in sublamina b. (2) The OFF arbor had sparser, thicker dendrites with few spines, while the ON arbor had finer, more numerous dendrites with many spines. (3) The OFF dendritic arbor ramified distal to the cholinergic band in sublamina a, while the ON arbor ramified proximal to the cholinergic band in sublamina b. (4) The final segments of the dendrites in sublamina a often descended back into sublamina b. (5) This ganglion cell was Neurobiotin-coupled to two types of amacrine cell. One type was a polyaxonal amacrine cell whose somas were displaced to the ganglion cell layer. The other type was strongly positive for GABA. Additionally, double labeling with an antibody to calbindin indicated likely synaptic contacts from the calbindin positive bipolar cell. Stimulation with small spots of light showed an ON center response abolished by APB; a smaller OFF center response was augmented by APB. An antibody to melanopsin confirmed that this bistratified ganglion cell was not the photosensitive ganglion cell.
Conclusions: :
We have identified a bistratified ganglion cell in the rabbit retina distinct from the G7, G3 and melanopsin-containing ganglion cells that also branch in both sublaminae. This cell has morphological similarities to: (1) the uniformity detector of Amthor et al. (1989), but does not respond similarly to light stimulation; (2) an ON bistratified ganglion cell described by Roska et al. (2006), but has an OFF excitatory component not described by them.
Keywords: ganglion cells • gap junctions/coupling • retina: proximal (bipolar, amacrine, and ganglion cells)