Endogenous release of gamma-aminobutyric acid from the medial preoptic area measured by microdialysis in the anaesthetised rat.
The characteristics of gamma-aminobutyric acid (GABA) release as monitored by microdialysis have been investigated in the chloral hydrate anaesthetised rat. The high outflow of GABA following insertion of the microdialysis probe (membrane 2 mm in length, 0.5 mm in diameter) into the medial preoptic area was found to decline to a stable baseline level after 2 h. After this time, perfusion with a medium containing 100 mM potassium ions evoked a 56-fold increase in GABA outflow. The addition of the calcium channel blocker verapamil (100 microM) to the perfusion medium induced significant 25 and 50% reductions in basal and potassium-stimulated GABA outflow, respectively. In the same animals, verapamil caused an 80% decrease in potassium-stimulated noradrenaline outflow. The glutamic acid decarboxylase inhibitors 3-mercaptopropionic acid and L-allylglycine added to the perfusion medium at a concentration of 10 mM reduced basal GABA release by approximately 50% with different time-courses of action. Ethanolamine-O-sulfate, a GABA-transaminase inhibitor, induced significant increases in basal GABA outflow 90 min after inclusion in the perfusion medium. These results demonstrate that microdialysis is a suitable technique with which to monitor extracellular levels of GABA and provide in vivo data on GABA release and degradation mechanisms.
Department of Neuroendocrinology, AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, England.
A E
AE
Herbison
R P
RP
Heavens
R G
RG
Dyer
D000612:4-Aminobutyrate Transaminase / Q000037:antagonists & inhibitors; D000818:Animals; D003956:Dialysis / Q000379:methods; D004983:Ethanolamines / Q000494:pharmacology; D005260:Female; D005968:Glutamate Decarboxylase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000378:metabolism; D010052:Ovariectomy; D011188:Potassium / Q000494:pharmacology; D011301:Preoptic Area / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D004983:Ethanolamines; D005680:gamma-Aminobutyric Acid; C020619:ethanolamine O-sulfate; D014700:Verapamil; D000612:4-Aminobutyrate Transaminase; D005968:Glutamate Decarboxylase; D011188:Potassium; D009638:Norepinephrine