Role of glutathione in schizophrenia? The effect of brain glutathione depletion on prepulse inhibition (PPI) in rats and mice

Reductions in brain glutathione (GSH) levels have been reported in schizophrenia. We investigated the effects of brain GSH depletion on prepulse inhibition (PPI), a model of sensorimotor gating which is disrupted in individuals with schizophrenia. It was hypothesized that GSH depletion would lead to disruption of PPI similar to that seen in schizophrenia and enhance the effect of increased dopamine release by amphetamine. Sprague-Dawley rats and C57Bl/6 mice were treated with saline or 2-cyclohexene-1-one (CHX, 75 mg/kg and 120 mg/kg respectively) to deplete brain GSH. 225 minutes later the animals were injected with amphetamine (2.5 mg/kg in rats and 25 mg/kg in mice). Total brain GSH levels were measured using an enzymatic recycling assay. Surprisingly, in rats CHX treatment prevented the disruption of PPI by amphetamine. Thus, while there was the expected disruption of PPI caused by amphetamine on its own (average %PPI reduced from 58 ± 5 to 44 ± 4), in combination with CHX, amphetamine had no significant effect (67 ± 4 vs. 63 ± 3, respectively). In contrast to rats, in mice CHX had no effect on PPI. Thus, amphetamine similarly disrupted PPI after saline (41 ± 5 vs. 28 ± 5) and CHX pretreatment (45 ± 6 vs. 26 ± 5). There were significant 40-63% depletions of GSH in frontal cortex and striatum of CHX-treated rats and mice. These data show that GSH depletion in the brain by CHX treatment did not induce the expected decrease in PPI. Because the levels of GSH depletion in this study were similar to those found in schizophrenia, these results cast doubt on a direct interaction between brain GSH levels and PPI disruption in this illness. In rats, CHX treatment prevented the disruption of PPI caused by amphetamine. We have observed that resting levels of GSH are lower in rats than in mice. It is plausible that some oxidative damage may occur after amphetamine treatment alone, which induces marked release of the electroactive species, dopamine. In mice with their higher levels of GSH (either with or without CHX treatment) and in control rats, this does not cause functional effects. However, in CHX-treated rats GSH levels are reduced to a point where amphetamine-induced dopamine release may cause increased metabolism and lipid peroxidation inducing a decrease in postsynaptic dopamine receptor function and consequently leading to an apparent inhibition of the disruption of PPI. In conclusion, while individuals with schizophrenia show disruption of PPI and reduced brain GSH levels, in rats and mice brain GSH depletion alone does not impact on PPI. In combination with a hyperdopaminergic state, functional effects on PPI regulation were found. These effects warrant further investigation.<br />