Brain Region-specific Changes in Oxidative Stress and Neurotrophin Levels in Autism Spectrum Disorders (ASD)

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders characterized by social and language deficits, stereotypic behavior, and abnormalities in motor functions. The particular set of behavioral impairments expressed in any given individual is variable across the spectrum. These behavioral abnormalities are consistent with our current understanding of the neuropathology of ASD which suggests abnormalities in the amygdala, temporal and frontal cortexes, hippocampus, and cerebellum. However, regions unrelated to these behavioral deficits appear largely intact. Both genetic predisposition and environmental toxins and toxicants have been implicated in the etiology of autism; the impact of these environmental triggers is associated with increases in oxidative stress, and is further exacerbated when combined with genetic susceptibility. We have previously reported increased levels of 3-nitrotyrosine (3-NT), a marker of oxidative stress, in ASD cerebella. We have also shown that this increase was associated with an elevation in neurotrophin-3 (NT-3) levels. The objectives of the current study were to determine whether the increase in oxidative stress in ASD is brain region-specific, to identify the specific brain regions affected by oxidative stress, and to compare brain region-specific NT-3 expression between ASD and control cases. The levels of 3-NT and NT-3 were measured with specific ELISAs in individual brain regions of two autistic and age- and postmortem interval (PMI)--matched control donors. In the control brain, the levels of 3-NT were uniformly low in all brain regions examined ranging from 1.6 to 12.0 pmol/g. On the other hand, there was a great variation in 3-NT levels between individual brain regions of the autistic brains ranging from 1.7 to 281.2 pmol/g. The particular brain regions with the increased 3-NT and the magnitude of the increase were both different in the two autistic cases. In the older autistic case, the brain regions with highest levels of 3-NT included the orbitofrontal cortex (214.5 pmol/g), Wernicke's area (171.7 pmol/g), cerebellar vermis (81.2 pmol/g), cerebellar hemisphere (37.2 pmol/g), and pons (13.6 pmol/g); these brain areas are associated with the speech processing, sensory and motor coordination, emotional and social behavior, and memory. Brain regions that showed 3-NT increase in both autistic cases included the cerebellar hemispheres and putamen. Consistent with our earlier report, we found an increase in NT-3 levels in the cerebellar hemisphere in both autistic cases. We also detected an increase in NT-3 level in the dorsolateral prefrontal cortex (BA46) in the older autistic case and in the Wernicke's area and cingulate gyrus in the younger case. These preliminary results reveal, for the first time, brain region-specific changes in oxidative stress marker 3-NT and neurotrophin-3 levels in ASD.