Morphological differentiation of bipolar cells in the ferret retina

Abstract

Bipolar cells are not only important for visual processing but input from these cells may underlie the reorganization of ganglion cell dendrites in the inner plexiform layer (IPL) during development. Because little is known about the development of bipolar cells, here we have used immunocytochemical markers and dye labeling to identify and follow their differentiation in the neonatal ferret retina. Putative cone bipolar cells were immunoreacted for calbindin and recoverin, and rod bipolar cells were immunostained for protein kinase C (PKC). Our results show that calbindin-immunoreactive cone bipolar cells appear at postnatal day 15 (P15), at which time their axonal terminals are already localized to the inner half of the IPL. By contrast, recoverin-immunoreactive cells with terminals in the IPL are present at birth, but many of these cells may be immature photoreceptors. By the second postnatal week, recoverin-positive cells resembling cone bipolar cells were clearly present, and with increasing age, two distinct strata of immunolabeled processes occupied the IPL. PKC-containing rod bipolar cells emerged by the fourth postnatal week and at this age have stratified arbors in the inner IPL. The early bias of bipolar axonal arbors in terminating in the inner or outer half of the IPL is confirmed by dye labeling of cells with somata in the inner nuclear layer. At P10, several days before ribbon synapses have been previously observed in the ferret IPL, the axon terminals of all dye-labeled bipolar cells were clearly stratified. The results suggest that bipolar cells could provide spatially localized interactions that are suitable for guiding dendritic lamination in the inner retina.

Unique Functional Properties of On and Off Pathways in the Developing Mammalian Retina

“…In line with this idea, recent studies have shown that the axon terminals of On-and Off-cone bipolar cells form their stratified projection patterns in a remarkably precise manner, without any initial period of intermingling (Miller et al, 1999;Günhan-Agar et al, 2000). Moreover, electrophysiological recordings have reported that very few ganglion cells in the developing cat retina respond with On-Off discharges to flashing spots of light at a time when multistratified cells would be expected to be plentiful (Dubin et al, 1986;Tootle, 1993).…”

Retina-Driven Dephosphorylation of the NR2A Subunit Correlates with Faster NMDA Receptor Kinetics at Developing Retinocollicular Synapses

“…The biological mechanism had to be distinct from eye opening, which does not occur until P13. Several reports have suggested that the maturation of the photoreceptor-bipolarganglion cell pathway occurs close to P10 (Miller et al, 1999) and that glutamate receptors begin to play a prominent role in driving retinal activity by P11 (Bansal et al, 2000). To test whether this maturation of the glutamatergic pathway in the retina was necessary for the activation of CaN in the sSC, we reduced retinal glutamatergic activity in vivo and assayed the effects on NMDAR currents in sSC neurons.…”

The role of nAChR‐mediated spontaneous retinal activity in visual system development

“…Functional studies of the resulting mature visual system reveal that this pharmacologic manipulation leads to a dramatic increases in the number of RGCs that permanently exhibit both ON and OFF responses to light (Bisti et al, 1998). However, a significant percentage of RGCs stratify into ON/OFF sublaminae before bipolar cells-the source of glutamate to RGCs-have made functional synapses in the IPL (Miller et al, 1999). What then drives the initial RGC dendritic segregation?…”

“…At the earliest stages of development when processes can first be detected with immunohistochemical markers, both bipolar cell (Miller et al, 1999) and cholinergic amacrine cell (West Greenlee et al, 1998) processes appear stratified. A recent study in rats has also demonstrated that bipolar cell stratification is normal in the absence of RGCs (Gunhan-Agar et al, 2000).…”