Stability of GABA levels in CSF under various conditions of storage

Measurement of GABA in human lumbar CSF specimens stored under various conditions showed that the concentrations remained stable in untreated frozen specimens stored at -20 degrees C and at -70 degrees C. In untreated liquid specimens the GABA concentrations approximately doubled during 2 h at room temperature but did not change significantly during 10 min at room temperature or 2 h at 2-4 degrees C. The GABA level was stable at -70 degrees C in deproteinized specimens but doubled during 11 months of storage at -20 degrees C. The level was stable in liquid deproteinized samples for 49 h at room temperature but increased 1.3-fold and 2.0-fold in deproteinized specimens stored for 3 weeks at 2-4 degrees C and room temperature, respectively. Amino acid analyses of homocarnosine standards in 0.1 N HCl revealed a similar increase of GABA during storage at room temperature and at -20 degrees C, suggesting that at least part of the increase seen in CSF specimens might result from breakdown of GABA containing peptides. This instability of GABA level may account for some of the discrepancies among the reports of CSF GABA levels.