Researches on the retinal tissues Essay

Studies reporting the neurochemical and synaptic differentiation of retina revealed the existence of glutamate receptors in the embryonic retina (Bleckert et al 2013, Cases et al 2015). This shows that the tissue response to GABA and LGlu is maximally differentiated early in development (Bleckert et al 2013). The retinal tissues conserve a high grade of glicolytic metabolism (ZarainHerzberg et al, 2005). This was reported by a study by Odani and coworkers (2007) that the retinal tissues have the ability of endogenous activity to regulate glutamate and dopamine receptors. It was also reported in the studies conducted on chicks retina that active dopaminergic transmission develops in the embryonic retina which causes desensitization of these receptor system in the differentiating CNS cells (Odani et al, 2007).
The glutamate receptors are also associated with kinate receptors, which have a very important role in the differentiation of retinal cells during embryonic development (Stenkamp et al 2000). While the retina is developing, the LGlu induces depolarization through the kainate receptors at Offbipolar cell synapses (BenAri et al 2002). On the other hand, the kainate subunits and Onbipolar cells are articulated in the outer retina (Stenkamp,et al 2000). As the result, a different class of LGlu receptors is implicated in the expression of light perception by the retinal cells (Stenkamp et al 2000). Okada et al (1999) reported in their study that neurite retraction of some cells in fish retina (such as horizontal cells) are associated with dark adaptation. This adaptation to darker environment is regulated by calciumpermeable AMPA receptors (Okada et al, 1999). Stone and coworkers (2003) have noted that in chick retina AMPA/kainate receptors were located in the inner nuclear layer, ganglion cell layer and plexiforms layers. LGlu and Glu 17 are also reported to increase, same as kainate receptors during retinal developmental stages (Cases et al 2015).
Signaling by LGlu receptors pathway was broadly described in the nervous system producing changes and also excitotoxicity in differentiating cells of CNS via NMDA receptors (Okada et al 1999). The calcium influx induced by LGlu is reported to be associated with nitrous oxide activation in embryonic retinas in early stages of development (BenAri 2002). This activation of nitrous oxide is paused by the NMDA antagonist i.e., MK801 (BenAri 2002). Cheng and coworkers (2014) showed that the NMDA receptor expression is linked with the generation of synapse during retinal development. The stimulation with light prompts the down regulation of nitrous oxide subunits therefore inducing the cyclic trend of luminous stimuli (Cheng et al 2014). This finding correlates with the increase in the expression of LGlu transporter EAAT1 and downregulation of nr1 subunits in the glial cells responsible for retinal cells differentiation (Lamas et al, 2005). This corroborates a trophic and homeostatic role of LGlu in the development of retina. Studies conducted on chicks retina (Stone et al 20013) and rabbits (Zhou & Xu 2015) also show that retinospheroid cultures and functional expression of NMDA receptors is similar to that in the integral tissue during embryonic development of other vertebrates.