ANALYSIS OF GLUTAMATE IN STRIATAL MICRODIALYSATES USING CAPILLARY ELECTROPHORESIS AND LASER-INDUCED FLUORESCENCE DETECTION

High-performance liquid chromatography (HPLC) with electrochemical detection has been used routinely to analyse the neurochemical constituents of brain microdialysates. However, conventional HPLC analysis requires large injection volumes and hence lengthy dialysis sampling times. Capillary electrophoresis (CE) is a rapid high-resolution separation technique with the ability to routinely handle very small sample volumes. If CE is coupled to a high-sensitivity detection system, such as laser-induced fluorescence (LIF), it becomes a powerful and rapid separation technique for the analysis of small-volume microdialysis samples. These preliminary studies report reduced separation times for the excitatory amino acid glutamate, prederivatised with naphthalene 2,3-dialdehyde, and demonstrate its detection within small-volume brain microdialysis samples. The limit of detection for this system was 10(-8) M. Characterisation of striatal microdialysis samples comprised infusions of Ca2+-free artificial cerebrospinal fluid (aCSF) and Tetrodotoxin (TTx) (10 mM) to demonstrate that the detected transmitter is of neuronal origin and released in a calcium-dependent manner. Removal of calcium from aCSF resulted in a decrease in glutamate in dialysis samples. Glutamate release significantly decreased (p < 0.05) to ca. 40% of preinfusion control levels after 60 min and this level was maintained throughout the sampling period. These data suggest that glutamate release is, to some degree, a calcium-dependent process. TTx infusion (10 mu M) produced a significant (p < 0.05) reduction in glutamate release to ca. 10% of preinfusion levels. It would therefore appear that glutamate release is dependent on neuronal activity. In summary, we have demonstrated the establishment of CE-LIF and microdialysis for the measurement of glutamate.