Retrograde double-labeling study of retinal ganglion cells from the ipsilateral vLGN and SC in the albino rat

Dorsal raphe nucleus projecting retinal ganglion cells: Why Y cells?

Retinal ganglion Y (alpha) cells are found in retinas ranging from frogs to mice to primates. The highly conserved nature of the large, fast conducting retinal Y cell is a testament to its fundamental task, although precisely what this task is remained ill-defined. The recent discovery that Y-alpha retinal ganglion cells send axon collaterals to the serotonergic dorsal raphe nucleus (DRN) in addition to the lateral geniculate nucleus (LGN), medial interlaminar nucleus (MIN), pretectum and the superior colliculus (SC) has offered new insights into the important survival tasks performed by these cells with highly branched axons. We propose that in addition to its role in visual perception, the Y-alpha retinal ganglion cell provides concurrent signals via axon collaterals to the DRN, the major source of serotonergic afferents to the forebrain, to dramatically inhibit 5-HT activity during orientation or alerting/escape responses, which dis-facilitates ongoing tonic motor activity while dis-inhibiting sensory information processing throughout the visual system. The new data provide a fresh view of these evolutionarily old retinal ganglion cells.

Types of parvalbumin-containing retinotectal ganglion cells in mouse

The calcium-binding protein parvalbumin (PV) occurs in the retinal ganglion cells (RGCs) of various vertebrate species. In the present study, we aimed to identify the types of PV-containing RGCs that project to the superior colliculus (SC) in the mouse. We injected retrograde tracer dextran into the mouse SC to label RGCs. PV-containing RGCs were first identified by immunocytochemistry and then neurons double-labeled with dextran and PV were iontophoretically injected with a lipophilic dye, DiI. Subsequently, confocal microscopy was used to characterize the morphologic classification of the PV-immunoreactive (IR) retinotectal ganglion cells on the basis of dendritic field size, branching pattern, and stratification within the inner plexiform layer. Among the 8 different types of PV-containing RGCs in the mouse retina, we found all 8 types of RGCs projecting to the SC. The RGCs were heterogeneous in morphology. The combined approach of using tracer injection and a single cell injection after immunocytochemistry on a particular protein will provide valuable data to further understand the functional features of the RGCs which constitute the retinotectal pathway.

Retinal ischemic injury rescued by sodium 4-phenylbutyrate in a rat model

Retinal ischemia is a common cause of visual impairment for humans and animals. Herein, the neuroprotective effects of phenylbutyrate (PBA) upon retinal ischemic injury were investigated using a rat model. Retinal ganglion cells (RGCs) were retrograde labeled with the fluorescent tracer fluorogold (FG) applied to the superior collicoli of test Sprague-Dawley rats. High intraocular pressure and retinal ischemia were induced seven days subsequent to such FG labeling. A dose of either 100 or 400 mg/kg PBA was administered intraperitoneally to test rats at two time points, namely 30 min prior to the induction of retinal ischemia and 1 h subsequent to the cessation of the procedure inducing retinal ischemia. The test-rat retinas were collected seven days subsequent to the induction of retinal ischemia, and densities of surviving RGCs were estimated by counting FG-labeled RGCs within the retina. Histological analysis revealed that ischemic injury caused the loss of retinal RGCs and a net decrease in retinal thickness. For PBA-treated groups, almost 100% of the RGCs were preserved by a pre-ischemia treatment with PBA (at a dose of either 100 or 400 mg/kg), while post-ischemia treatment of RGCs with PBA did not lead to the preservation of RGCs from ischemic injury by PBA as determined by the counting of whole-mount retinas. Pre-ischemia treatment of RGCs with PBA (at a dose of either 100 or 400 mg/kg) significantly reduced the level of ischemia-associated loss of thickness of the total retina, especially the inner retina, and the inner plexiform layer of retina. Besides, PBA treatment significantly reduced the ischemia-induced loss of cells in the ganglion-cell layer of the retina. Taken together, these results suggest that PBA demonstrates a marked neuroprotective effect upon high intraocular pressure-induced retinal ischemia when the PBA is administered prior to ischemia induction.

Retinal ganglion cells projecting to the dorsal raphe and lateral geniculate complex in Mongolian gerbils

Injections of rhodamine-B into the dorsal raphe nucleus (DRN) and Fluoro-Gold into the lateral geniculate nucleus (LGN) revealed double-labeled retinal ganglion cells (DL RGCs) projecting to both nuclei. The soma-size distribution of DL RGCs was compared with three other distributions: DRN-projecting RGCs, LGN-projecting RGCs, and a large sample of RGCs labeled via the optic nerve with DiI. DL RGC soma diameters fell primarily within the mid-to-upper size range of all three distributions. DL RGCs may provide information to both nuclei concerning comparable aspects of light and visual stimulation via collateralized axons.

Conceptual issues related to the role of the superior colliculus in the control of gaze

Various conceptual issues have been brought into focus by recent experiments studying the role of the superior colliculus in the control of coordinated movements of the eyes and head, the interaction of saccadic and vergence movements, and cognitive processes influencing the initiation and execution of saccades.