GABA released from astrocytes is synthesized from putrescine. (A-B) Concentration of ornithine, putrescine and GABA in hippocampal slice tissues and in the bathing medium following one hour incubation normal ACSF (control) or in [Mg2+] = 1 μM ACSF in the absence (A) and presence (B) of 100 μM SNAP-5114 as determined by LC-MS. Asterisks represent significant change (P < 0.05). (C) Holding currents in [Mg2+] = 1 μM buffer in the presence of the monoamino oxidase inhibitor, deprenyl (10 μM) and the diamino oxidase inhibitor, aminoguanidine (100 μM). Left, baseline currents plotted at 1 s intervals during control condition (black), SNAP-5114 application (red) and washout (blue); right, box-chart representation of GABAergic baselines during control condition, SNAP-5114 application and washout. Box edges represent 25th, 50th and 75th percentile, open squares represent means, circles connected by lines represent paired individual baseline values. Average holding current in control: 74.8 ± 12.8 (N = 8 cells/6 animals). (D) Intracellular [Na+] in the soma of SR101 identified astrocytes measured by SBFI fluorescence during 100 μM SNAP-5114 applications with (black line) or without (red line) preceding activation of the Glu transporters by 200 μM t-PDC in [Mg2+] = 10 μM ACSF in the presence of deprenyl (10 μM) and aminoguanidine (100 μM) (average of N = 13 cells/2 animals).