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

High-performance liquid chromatography (HPLC) with electrochemical det ection has been used routinely to analyse the neurochemical constituen ts of brain microdialysates. However, conventional HPLC analysis requi res 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 volum es. If CE is coupled to a high-sensitivity detection system, such as l aser-induced fluorescence (LIF), it becomes a powerful and rapid separ ation technique for the analysis of small-volume microdialysis samples . These preliminary studies report reduced separation times for the ex citatory amino acid glutamate, prederivatised with naphthalene 2,3-dia ldehyde, and demonstrate its detection within small-volume brain micro dialysis samples. The limit of detection for this system was 10(-8) M. Characterisation of striatal microdialysis samples comprised infusion s of Ca2+-free artificial cerebrospinal fluid (aCSF) and Tetrodotoxin (TTx) (10 mM) to demonstrate that the detected transmitter is of neuro nal origin and released in a calcium-dependent manner. Removal of calc ium from aCSF resulted in a decrease in glutamate in dialysis samples. Glutamate release significantly decreased (p < 0.05) to ca. 40% of pr einfusion control levels after 60 min and this level was maintained th roughout the sampling period. These data suggest that glutamate releas e is, to some degree, a calcium-dependent process. TTx infusion (10 mu M) produced a significant (p < 0.05) reduction in glutamate release t o ca. 10% of preinfusion levels. It would therefore appear that glutam ate release is dependent on neuronal activity. In summary, we have dem onstrated the establishment of CE-LIF and microdialysis for the measur ement of glutamate.