Age- and region-specific imbalances of basal amino acids and monoamine metabolism in limbic regions of female Fmr1 knock-out mice

The Fragile X syndrome, a common form of mental retardation in humans, originates from the loss of expression of the Fragile X mental retardation gene leading to the absence of the encoded Fragile X mental retardation protein 1 (FMRP). A broad pattern of morphological and behavioral abnormalities is well described for affected humans as well as Fmr1 knock-out mice, a transgenic animal model for the human Fragile X syndrome. In the present study, we examined neurochemical differences between female Fmr1 knock-out and wildtype mice with particular focus on neurotransmission. Significant age- and region-specific differences of basal tissue neurotransmitter and metabolite levels measured by high performance liquid chromatography were found. Those differences were more numerous in juvenile animals (postnatal day (PND) 28-31) compared to adults (postnatal day 209-221). In juvenile female knock-out mice, especially aspartate and taurine were increased in cortical regions, striatum, cerebellum, and brainstem. Furthermore, compared to the wildtype animals, the juvenile knock-out mice displayed an increased level of neuronal inhibition in the hippocampus and brainstem reflected by decreased ratios of (aspartate + glutamate)/(taurine + GABA), as well as an increased dopamine (DA) turnover in cortical regions, striatum, and hippocampus. These results provide the first evidence that the lack of FMRP expression in female Fmr1 knock-out mice is accompanied by age-dependent, region-specific alterations in brain amino acids, and monoamine turnover, which might be related to the reported synaptical and behavioural alterations in these animals.