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.
Herbison
A E
AE
Department of Neuroendocrinology, AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, England.
Heavens
R P
RP
Dyer
R G
RG
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