Neurochemical architecture of the normal and degenerating rat retina

Abstract

We used post-embedding immunocytochemistry to determine the cellular localization of glutamate, gamma-amino butyric acid (GABA), glycine, aspartate, glutamine, arginine, and taurine in the normal and degenerating rat retina. Müller's cell function was also evaluated by determining the uptake and degradation characteristics for glutamate. Immunocytochemical localization of amino acids in adult Royal College of Surgeons (RCS) and control rat retinas were similar with respect to cell classes. Differences in the intensity of labelling for glutamate, aspartate, glutamine, and glycine were observed in several classes of neurons, but the most prominent differences were shown by bipolar cells of the adult RCS rat retina. In addition, glutamine labelling within Müller's cells was higher in the RCS rat than the control. These changes may have occurred because of alterations in the glutamate production or degradation pathways. We tested this hypothesis by determining Müller's cells glutamate uptake and degradation characteristics in adult and postnatal day 16 RCS retinas. High affinity uptake of 3[H]-glutamate revealed an accumulation of grains over Müller's cell bodies in the adult RCS retina implying glutamate degradation anomalies. We confirmed anomalies in glutamate metabolism in RCS Müller's cells by showing that exogenously applied glutamate was degraded over a longer time course in postnatal day 16 RCS retinas, compared to control retinas. Differences in arginine immunoreactivity in adult and immature RCS retinas conform to the presumed dysfunction of Müller's cells in these degenerating retinas. The anomalies of amino acid localization, uptake and degradation lead us to conclude that Müller's cells in the RCS retina show abnormal function by postnatal day 16; an earlier time to previously reported anatomical and functional changes in this animal model of retinal degeneration.

Neurotransmitter contents in the retina of RCS rat

“…In the present study, however, the GABA content in the retina of RCS rats was not affected even at 23 weeks postnatally. This finding corresponded well with that obtained in RCS rats by Fletcher and Kalloniatis [7]. These discrepancies may be due to differences in experimental methods, animal species and stages of retinal degeneration.…”

“…The inner segments of photoreceptors are abundant in glutamate [7]. This amino acid is considered to be a neurotransmitter in the retinal pathway as well as a precursor for GABA production [11,15,16].…”

Glutamate uptake in retinal glial cells during diabetes

“…D-aspartate labelled Müller cell somata in the inner nuclear layer (INL), their end feet and processes extending radially throughout the outer nuclear layer (ONL) and inner plexiform layer (IPL). This is a similar pattern of immunoreactivity to that previously described [30,37]. By contrast, D-aspartate immunoreactivity was immunonegative in tissue that had been incubated in no D-aspartate (data not shown).…”

“…D-Aspartate is a non-metabolisable substrate for GLAST. Quantification of the level of D-aspartate taken up by glial cells is a well established method for examining the function of glutamate transporters [30,31,37]. We evaluated glutamate uptake in Müller cells, by examining the level of uptake of D-aspartate in Müller cells.…”

The significance of neuronal and glial cell changes in the rat retina during oxygen-induced retinopathy

“…In order to better characterize neuronal changes in the inner retina, neurochemical analysis has been performed [50]. It is well recognized that one or more of the amino acid neurotransmitters, glutamate, GABA and glycine are localized in virtually every neuronal subclass in the mammalian retina ( [51][52][53][54]; summarized in Fig. 5).…”