Color information encoded by the spatiotemporal patterns of light response in ganglion cells of chick retina

Color Processing in Zebrafish Retina

Zebrafish (Danio rerio) is a model organism for vertebrate developmental processes and, through a variety of mutant and transgenic lines, various diseases and their complications. Some of these diseases relate to proper function of the visual system. In the US, the National Eye Institute indicates >140 million people over the age of 40 have some form of visual impairment. The causes of the impairments range from refractive error to cataract, diabetic retinopathy and glaucoma, plus heritable diseases such as retinitis pigmentosa and color vision deficits. Most impairments directly affect the retina, the nervous tissue at the back of the eye. Zebrafish with long or short-wavelength color blindness, altered retinal anatomy due to hyperglycemia, high intraocular pressure, and reduced pigment epithelium are all used, and directly applicable, to study how these symptoms affect visual function. However, many published reports describe only molecular/anatomical/structural changes or behavioral deficits. Recent work in zebrafish has documented physiological responses of the different cell types to colored (spectral) light stimuli, indicating a complex level of information processing and color vision in this species. The purpose of this review article is to consolidate published morphological and physiological data from different cells to describe how zebrafish retina is capable of complex visual processing. This information is compared to findings in other vertebrates and relevance to disorders affecting color processing is discussed.

Contribution of the GABAergic pathway(s) to the correlated activities of chicken retinal ganglion cells

In the present study, the spatiotemporal pattern of chicken retinal ganglion cells' firing activity in response to full-field white light stimulation was investigated. Cross-correlation analysis showed that ganglion cells of sustained subtype fired in precise synchrony with their adjacent neurons of the same subtype (delay lag within 2 ms, narrow correlation). On the other hand, the activities of neighboring ganglion cells of transient subtype were correlated with distributed time lags (10-30 ms, medium correlation). Pharmacological studies demonstrated that the intensity of the medium correlations could be strengthened when exogenous GABA was applied and attenuated when GABA receptors were blocked by picrotoxin. Meanwhile, the GABAergic modulation on the narrow correlations was not consistent. These results suggest that, in the chicken retina, GABAergic pathway(s) are likely involved in the formation of medium correlations between ganglion cells. Neurons might fire at a lower rate but with higher level of synchronization to improve the efficiency of information transmission, with the mechanism involving the GABAergic inhibitory input.

The dual-peak light response of ganglion cells in chicken retina

In the present study, a particular temporal pattern of the ganglion cells' light response specified as "dual-peak" was observed. In the chicken retina (N=15), about 37.5% (174 out of 464) of the ganglion cells showed such special temporal property in response to the onset of light flash. These neurons responded to light stimulus with two successive components: a transient increase of firing rate which lasted for less than 100 ms, and another prolonged light response appeared in about 100 ms after the first transient response. Moreover, our data demonstrated a temporal adaptation process in the later phase of firing activities when repeated flashes were applied. Meanwhile, the earlier phase had a more stable latency in response to the stimulus. Application of picrotoxin could evoke the dual-peak responses in transient ganglion cells. These results suggest that the origination of the two response components might be distinct and the later one is likely related to GABAergic pathways.