Some evidence suggests that retinal pigment epithelium (RPE) can express nicotinic acetylcholine receptors (nAChRs) as described for other epithelial cells, where nAChRs have been involved in processes such as cell development, cell death, cell migration, and angiogenesis. This study is designed to determine the expression and activity of α7 nAChRs in RPE cells. Reverse transcriptase (RT)-PCR was performed to test the expression of nicotinic α7 subunit in bovine RPE cells. Protein expression was determined by Western blot and by immunocytochemistry. Expression of nicotinic α7 subunits was also analyzed in cryostat sections of albino rat retina. Changes in protein expression were tested under hypoxic conditions. Functional nAChRs were studied by examining the Ca2+ transients elicited by nicotine and acetylcholine stimulation in fura-2–loaded cells. Expression of endogenous modulators of nAChRs was analyzed by RT-PCR and Western blot in retina and RPE. Cultured bovine RPE cells expressed nicotinic receptors containing α7 subunit. RT-PCR amplified the expected specific α7 fragment. Western blotting showed expression at the protein level, with a specific band being found at 57 kDa in both cultured and freshly isolated RPE cells. Expression of nAChRs was confirmed for cultured cells by immunofluorescence. Immunohistochemistry confirmed α7 receptor expression in rat RPE retina. α7 receptor expression was down-regulated by long-term hypoxia. A small subpopulation of RPE cultured cells showed functional nAChRs, as evidenced by the selective response elicited by nicotine and acetylcholine stimulation. Expression of the endogenous nicotinic receptors’ modulator lynx1 was confirmed in bovine retina and RPE, and expression of lynx1 and other endogenous nicotinic receptor modulators (SLURP1 and RGD1308195) were also confirmed in rat retina. These results suggest that nAChRs could have a significant role in RPE, which may not be related to the traditional role in nerve transmission but could more likely be related to the nonneuronal cholinergic system in the eye.

Adenosine-to-inosine (A-to-I) RNA editing is a cotranscriptional or posttranscriptional gene regulatory mechanism that increases the diversity of the proteome in the nervous system. Recently, the transcript for GABA type A receptor subunit α3 was found to be subjected to RNA editing. The aim of this study was to determine if editing of the chicken α3 subunit transcript occurs in the retina and if the editing is temporally regulated during development. We also raised the question if editing of the α3 transcript was temporally associated with the suggested developmental shift from excitation to inhibition in the GABA system. The editing frequency was studied by using Sanger and Pyrosequencing, and to monitor the temporal aspects, we studied the messenger RNA expression of the GABAA receptor subunits and chloride pumps, known to be involved in the switch. The results showed that the chick α3 subunit was subjected to RNA editing, and its expression was restricted to cells in the inner nuclear and ganglion cell layer in the retina. The extent of editing increased during development (after embryonic days 8–9) concomitantly with an increase of expression of the chloride pump KCC2. Expression of several GABAA receptor subunits known to mediate synaptic GABA actions was upregulated at this time. We conclude that editing of the chick GABAA subunit α3 transcript in chick retina gives rise to an amino acid change that may be of importance in the switch from excitatory to inhibitory receptors.

Transient uniformity detectors (UDs) are a unique type of retinal ganglion cell (RGC) whose maintained firing is transiently suppressed by all types of visual stimuli. In this study, we have characterized the dendritic morphology and tracer-coupling pattern of UDs that were labeled by loose-seal electroporation of Neurobiotin following functional identification in the isolated rabbit retina. The UDs have a bistratified dendritic tree, branching near the margins of the inner plexiform layer in stratum 1 (part of the OFF sublamina) and stratum 4/5 (part of the ON sublamina). Characteristically, many of the distal dendrites in the OFF arbor do not terminate there but dive recurrently back to the ON arbor. As a consequence, the ON dendritic arbor is usually twice as large as the OFF dendritic arbor in area. The UDs sometimes show homologous tracer coupling to neighboring RGCs with the same morphology, and from this material, we estimate that the UDs have a threefold dendritic field overlap and a maximum density of ~100 cells/mm2 on the peak visual streak, accounting for ~2% of RGCs in rabbit retina. The UDs also show strong heterologous tracer coupling to a novel type of amacrine cell that costratifies with the ON arbor of the UD. Consistent with their unistratified medium-field morphology, these St4/5 amacrine cells appear to be GABAergic: their somata are immunopositive for GABA but immunonegative for glycine and glycine transporter 1. We compare the dendritic morphology of the UDs to that of other types of bistratified RGCs described in rabbit retina and note that the stratification levels and distinctive recurrent dendrites closely resemble those of the “ON bistratified diving” RGCs. This raises the possibility that there are two types of RGCs with distinctive physiological properties that have almost identical bistratified dendritic morphologies.

Even during active fixation, small eye movements persist that might be expected to interfere with vision. Numerous brain mechanisms probably contribute to discounting this jitter. Changes in the timing of responses in the visual thalamus associated with fixational saccades are considered in this study. Activity of single neurons in alert monkey lateral geniculate nucleus (LGN) was recorded during fixation while pseudorandom visual noise stimuli were presented. The position of the stimulus on the display monitor was adjusted based on eye position measurements to control for changes in retinal locations due to eye movements. A method for extracting nonstationary first-order response mechanisms was applied, so that changes around the times of saccades could be observed. Saccade-related changes were seen in both amplitude and timing of geniculate responses. Amplitudes were greatly reduced around saccades. Timing was retarded slightly during a window of about 200 ms around saccades. That is, responses became more sustained. These effects were found in both parvocellular and magnocellular neurons. Timing changes in LGN might play a role in maintaining cortical responses to visual stimuli in the presence of eye movements, compensating for the spatial shifts caused by saccades via these shifts in timing.

Nonarteritic anterior ischemic optic neuropathy (NAION) is associated with vascular risk factors and a genetic predisposition for NAION. In this study, we examined the potential association of endothelial nitric oxide synthase (eNOS) G894T polymorphism with NAION. For this, 45 patients (29 men and 16 women) and 193 controls (122 men and 71 women) were enrolled prospectively and genotyped for eNOS genes. Genotypes were determined by polymerase chain reaction and restriction enzyme analysis. The prevalence of eNOS polymorphisms was estimated in NAION patients and controls. Genotype frequencies were estimated with chi-square test, and odds ratios were calculated. We found that eNOS G894T polymorphism is not associated with NAION occurrence as the genotype and allele frequencies were not significantly different between the control and patient groups (TT vs. GG + GT: P = 0.646 and T vs. G: P = 0.86). The precise mechanism of NAION occurrence has not been elucidated yet; since NAION may occur when a compromised watershed microcirculation is combined with insufficient autoregulation of systematic circulation, other alterations in the eNOS gene or polymorphism of genes involved in systematic circulation may be associated with NAION occurrence.

Eye fixation–related potential (EFRP) measures electrical brain activity in response to eye fixations. The aim of the current study was to investigate whether the EFRPs vary during consecutive eye fixations while subjects were performing an object identification task. Eye fixations evoked P1 and N1 components at the occipital and parietal recording sites. The latency of P1 component increased during consecutive fixations. The amplitude of P1 increased and the amplitude of N1 decreased during consecutive fixations. The results indicate that EFRPs are modulated during consecutive fixations, suggesting that the current technique may provide a useful tool to study temporal dynamics of visual perception and processes underlying object identification.