Nanoprobe NMR spectroscopy and in vivo microdialysis: new analytical methods to study brain neurochemistry.

Nuclear magnetic resonance (NMR) spectroscopy was used to study the chemical composition of cerebrospinal fluid (CSF) microdialysate from the rat brain. In vivo microdialysis techniques were used in several brain regions including the frontal cortex, amygdala, striatum, nucleus accumbens and third ventricle and dialysate samples (20microl) were subsequently analyzed by one and two-dimensional 1H NMR experiments using a Varian nanoprobe. Neurochemical resonances were assigned on the basis of published chemical shifts [Lindon et al., Ann. Rep. NMR Spectrosc. 38 (1999) 1-88], correlation experiments and addition of standard compounds. Glucose, lactate, formate, pyruvate, creatinine, gamma-hydroxybutyrate, acetate, glutamate, glycine, tyrosine, isoleucine, leucine, alanine and choline were some of the neurochemicals unambiguously assigned. Additional studies in the frontal cortex showed that amino acids such as glutamate, alanine and isoleucine were sensitive to local tetrodotoxin (TTX) infusion. The NMR spectra were also subjected to multivariate statistical methods to compare the different brain regions examined. To our knowledge, the present experiments are the first to describe the combination of nanoprobe NMR technology with in vivo microdialysis for the analysis of brain neurochemistry in freely-moving rats.