Microdialysis study of amino acid neurotransmitters in the spinal dorsal horn of patients undergoing microsurgical dorsal root entry zone lesioning -Technical note

The aim of this study was to develop, for the first time in the human spina l dorsal horn (DH), an in vivo method for the study of amino acids (AAs). A microdialysis technique was used to sample AAs in the extracellular fluid of the DH apex in eight patients in whom surgery in the dorsal root entry zone (DREZ) was performed. Before making microsurgical lesions, specific co ncentric-type microdialysis probes were implanted over a 60-minute period i n the DREZ and directed to the DH apex (10 implantations). The AA concentra tions in the dialysates were determined using high-performance liquid chrom atography with fluorescence detection. The concentrations of excitatory AAs (glutamate and aspartate) and inhibitory AAs (gamma -aminobutyric acid and glycine) decreased and were stabilized by 45 minutes after probe implantat ion, whereas the levels of nonneurotransmitter AAs (alanine and threonine) were not stabilized at 60 minutes. The ability of the probe to track the ch anges of extracellular AAs was demonstrated. Neither intra- nor postoperati ve microdialysis-related complications were observed (with a follow up of 1 8 months). The present study demonstrates that microdialysis can be performed safely i n the human DH during DREZ lesioning. Despite technical and analytical limi tations related to the intraoperative conditions, this technique offers new possibilities for clinical research on neurotransmitters involved in some relevant pathological states, especially in chronic pain and spasticity.