Alterations in neurochemistry during retinal degeneration

Retinitis pigmentosa refers to a family of hereditary retinal degenerations that lead to photoreceptor death and vision loss. The underlying cause(s) are not known. In recent years there has been accumulating evidence of neur ochemical changes during degeneration. In particular, the amino acids gluta mate, GABA, and glycine show alterations in labelling intensity in subsets of neurons. Furthermore, there are differences in the labelling of the prec ursors, glutamine and aspartate, prior to, during, and following loss of ph otoreceptors, suggesting that the metabolic pathways involved in neurotrans mitter formation and degradation may be abnormal. In addition, there is an elevation in glutamine and arginine content within Muller cells prior to th e onset of photoreceptor death. Investigations evaluating Muller cell funct ion indicate that formation and degradation of glutamate, in particular, is abnormal in the degenerating retina from an early age. These studies sugge st that even though the primary genetic defect of the RCS rat is within the retinal. pigment epithelium, Muller cells develop abnormally, and may cont ribute to the observed photoreceptor loss. (C) 2000 Wiley-Liss, Inc.