Analysis of GABA and glutamate in the mouse dorsal striatum

GABA and glutamate are the predominant inhibitory and excitatory amino acid neurotransmitters in the central nervous system (CNS), respectively. However, their altered levels cause several neurological diseases including Parkinson's and Huntington's disease, schizophrenia, and epilepsy. It is important to measure their levels in the extra- and intracellular environments to better understand and develop improved therapeutics that will treat these neurological disorders. The principle aim of this study is to study the impacts of different endogenous and exogenous factors on the striatal extracellular GABA and glutamate levels. The first objective was to develop a method to analyze GABA and glutamate using HPLC coupled to fluorescence detection. The second objective was to evaluate the effects of BDNF, age, ethanol, and Mn exposure on the striatal GABA and glutamate levels. Using a monolithic column, GABA and glutamate were separated in dialysis samples at 2 and 4.5 minutes, respectively. Low levels of endogenous BDNF, acute administration of ethanol (2 g/kg), and age differently affect the GABA and glutamate levels. In BDNF+/- mice potassium stimulated release of glutamate was significantly reduced while release of GABA was not different between wildtype and BDNF+/- mice. Administration of ethanol increased extracellular levels of GABA in both wildtype and BDNF+/- mice. The impact of age on striatal extracellular GABA and glutamate levels was evaluated in mice 3 and 18 months old. Aged mice showed a significant reduction in both high K+-stimulated GABA and glutamate release. The final study evaluated the effect of a sub-acute Mn treatment on striatal extracellular GABA levels, where a modest but significant increase in extracellular GABA was observed 2 days after Mn treatment. Taken together, these findings reveal that extracellular GABA and glutamate are differentially affected by BDNF, ethanol, age, and Mn.