Monitoring Dopamine Metabolism in the Brain of the Freely Moving Rat

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Abstract
Determination of DOPAC and HVA in cisternal CSF taken repeatedly from freely moving rats provides a useful means of monitoring central DA metabolism. A large proportion of both metabolites occurs in cisternal CSF as conjugates from which they are liberated by acid hydrolysis. The method enables DA turnover values to be determined for individual rats. Drug experiments indicate that these values reflect brain DA metabolism and that most of this occurs in extrastriatal DA neurons. Concurrent determination of 5HT turnover on the same CSF samples revealed a significant positive correlation between the turnovers of the two transmitters together with considerable inter-individual differences. The turnover method was particularly convenient when investigating daily variations of turnover. Repeated CSF withdrawal also appears to be useful in the analysis of stress-provoked changes of the metabolism of DA and other transmitters. For example, it was used to show that central DA metabolism becomes highly responsive to tyrosine availability if rats are subjected to immobilization stress. The method can also be used to compare the time dependencies of both metabolic and behavioral responses to the stress in the same animal. Preliminary results suggest that the increase of 5HT metabolism during immobilization (rather than that of DA) may oppose the suppression of open field activity that occurs 24 hr later.

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