Gamma hydroxybutyrate distribution and turnover rates in discrete brain regions of the rat

Gamma-hydroxybutyric acid and trans-gamma-hydroxycrotonic acid levels have been determined in 24 regions of the rat brain after sacrifice by microwave irradiation. Concentration ranges are from 4 pmol/mg protein (frontal cortex) to 46 pmol/mg protein (substantia nigra) for gamma-hydroxybutyric acid and from 0.4 pmol/mg protein (striatum) to 11 pmol/mg protein (hypothalamus) for trans-gamma-hydroxycrotonic acid. It appears that gamma-hydroxybutyric acid levels correlate well with GABA distribution in the same region. However this correlation is not evident with regard to the distribution of the gamma-hydroxybutyric acid synthesizing enzyme, specific succinic semialdehyde reductase. Using the antiepileptic drug, valproate which strongly inhibits gamma-hydroxybutyric acid release and degradation, we estimated the turnover rate of this compound in six regions of the rat brain. Turnover numbers ranged from 6.5 h(-1) in hippocampus to 0.76 h(-1) in cerebellum.