Characterization of extracellular GABA in the substantia nigra reticulata by means of brain microdialysis

Naunyn Schmiedebergs Arch Pharmacol. 1992 Jun;345(6):661-5. doi: 10.1007/BF00164580.

Abstract

Brain microdialysis was used to characterize extracellular gamma-aminobutyric acid (GABA) in the substantia nigra reticulata (SNR) of freely moving rats. The extracellular GABA in the SNR was characterized using acutely implanted probes (4-8 h after surgery; day 1) and chronically implanted probes (24 h after surgery; day 2). 3-Mercaptopropionic acid, a glutamic acid decarboxylase inhibitor, was used to identify GABA. This drug induced an immediate decrease in the extracellular GABA levels to 40% of basal values, suggesting that the detected GABA is, at least in part, newly synthesized. The basal levels of extracellular GABA measured either on day 1 or day 2 were not affected by infusion of micromolar amounts of tetrodotoxin. Therefore, a direct coupling between GABA dialysate concentrations and nerve-impulse flow does not seem to exist. Infusion of the GABA uptake inhibitor nipecotic acid (0.5 mmol/l) resulted in a 4-fold increase in the dialysate levels of GABA lasting at least for 3 h on both days. K+ stimulation (60 mmol/l) increased extracellular GABA levels in the SNR to 450% of basal values. This effect again did not differ significantly on day 1 and day 2. The origin of the extracellular GABA in the SNR, as recorded by microdialysis under the two experimental conditions, is discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Mercaptopropionic Acid / pharmacology
  • Animals
  • Dialysis
  • Extracellular Space / drug effects
  • Extracellular Space / metabolism
  • Male
  • Potassium / pharmacology
  • Rats
  • Rats, Inbred Strains
  • Substantia Nigra / drug effects
  • Substantia Nigra / metabolism*
  • Tetrodotoxin / pharmacology
  • gamma-Aminobutyric Acid / metabolism*

Substances

  • Tetrodotoxin
  • gamma-Aminobutyric Acid
  • 3-Mercaptopropionic Acid
  • Potassium