Abstracts

Rationale: Rationale: Vigabatrin (VGB) was recently approved by the FDA for the treatment of infantile spasms and refractory seizures. However, a major limiting factor to its use is the high incidence of retinal toxicity and bilateral visual field deficits in approximately 30% of treated patients. Human studies and rat models of VGB toxicity show that the retinal injury involves ganglion cell death (Duboc et al, Ann Neurol, 20 2004;55:695-705). The mechanism of this toxicity is poorly understood. Given that VGB increases retinal and brain GABA concentrations, we hypothesized that retinal injury might occur secondary to the presence of depolarizing GABA receptor responses and subsequent excitotoxic ganglion cell death. The presence of the NKCC1 chloride co-transporter is necessary for the paradoxical depolarizing GABA receptor mediated responses. As ganglion cells have GABA receptors, we hypothesized that NKCC1 may be expressed on ganglion cells in rat and human retina. Methods: Methods: We examined whether NKCC1 is expressed in rat and human retina using immunocytochemistry with NKCC1 antibody (Aviva Systems Biol., 1:300; Developmental Studies Hybridoma Bank, 1:500) and KCC2 (Upstate/Millipore, 1:500). Adult Long Evans rats were perfused with 4% PFA and the eyes (n=4) processed for cryosectioning. Human retinas (n=10) were fixed in formalin and embedded in paraffin and antigen retrieval was performed with citrate buffer. 20 m sections were stained for anti-NKCC1 and anti-KCC2 antibodies. Results: Results: In rat, NKCC1 expression was seen in horizontal, amacrine and ganglion cell somas as well as in the OPL in the synaptic terminal region. KCC2 expression was present in amacrine cells, horizontal and bipolar cells and ganglion cells as well as in OPL in the terminal processes and intense labeling in the entire neuropil area of the IPL. Similar patterns were observed in the human retina: NKCC1 was present in horizontal, amacrine cells and ganglion cell somas. KCC2 present in horizontal, amacrine and bipolar cells and ganglion cells as well as in the IPL. Conclusions: Conclusion: Taken together, these data suggest that NKCC1 is present in both rat and human eyes in a cell population that has been previously shown to be vulnerable to vigabatrin toxicity. In addition, human eye immunocytochemistry suggesting that depolarizing GABA responses may play a role in retinal toxicity due to VGB. Future studies will test the efficacy of bumetanide, an NKCC1 inhibitor, in preventing VGB induced retinal toxicity in a rat VGB model.(Supported by grants #:1RC1NS068938-01 and P3O HD 18655)