Remote effects on the striatal dopamine system after fluid percussion injury.

PURPOSE: To investigate the effects of traumatic brain injury (TBI) on the dopamine system in the brain at different distances from the impaction site, we compared the release, reuptake, metabolism, and release probability of dopamine on the sides of the brain ipsilateral and contralateral to the injury at different time points after varying severities of fluid percussion injuries.

MATERIALS AND METHODS: Tonic (1-pulse evoked) and bursting (10-pulse evoked) dopamine release changes in the ipsilateral and contralateral sides of the striatum resulting from mild (2-Pa) and severe (6-Pa) levels of fluid percussion injury were analyzed at the acute (2h and 24h), subacute (1 and 2 weeks), and chronic stages (4, 6, and 8 weeks) after injury by using fast scan cyclic voltammetry to measure brain slices. The metabolic rate of striatal dopamine was surveyed using high-performance liquid chromatography. The microglia reaction was analyzed using immunohistochemistry at each stage.

RESULTS: In 6-Pa injured animals, for both tonic and bursting dopamine release, reuptake and release probability were suppressed on both the ipsilateral and contralateral sides of the striatum from the acute to the chronic stage. These neuronal activities were also affected at the subacute stage on both sides of the striatum in 2-Pa injured animals. The turnover rate of dopamine was not affected in the 2-Pa injured animals but increased gradually during the chronic stage in the 6-Pa injured group.

CONCLUSION: TBI suppresses dopamine release and reuptake and affects the metabolic rate and release probability of dopamine on the sides of the nigrostriatal system both ipsilateral and contralateral to the injury during both the acute and subacute stages after the injury.