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Vol. 305, Issue 2, 668-674, May 2003
-Hydroxybutyrate in Rats: Time Course and
Antagonism Studies
Departments of Pharmacology (L.P.C., L.R.F., A.W.U., C.P.F) and
Psychiatry (C.P.F.), The University of Texas Health Science Center at
San Antonio, San Antonio, Texas, and Department of Pharmaceutical
Sciences (H.W., W.C., A.C.), University of Maryland, Baltimore,
Maryland
-Hydroxybutyrate (GHB) is a neurotransmitter in brain and an
emerging drug of abuse, although its mechanism of action is poorly
understood. This study characterized the role of GABAA, GABAB, and other receptors in the discriminative stimulus
effects of GHB. Eight rats reliably discriminated 200 mg/kg GHB from
saline after a median of 35 (range: 23-41) training sessions. GHB, a metabolic precursor 1,4-butanediol (1,4-BDL), and the GABAB
agonist (±)baclofen all occasioned greater than 83% responding on the GHB lever. The onset of action was similar for GHB and 1,4-BDL; however, 1,4-BDL exhibited a longer duration of action than GHB. The
GHB precursor
-butyrolactone, the benzodiazepine diazepam, the
neuroactive steroid pregnanolone, the opioid agonist morphine, and the
N-methyl-D-aspartate antagonist ketamine
elicited substantial GHB-appropriate responding, although none
occasioned greater than 66% drug-lever responding. The barbiturate
pentobarbital and the GABAA receptor agonist muscimol did
not occasion greater than 17% drug-lever responding at any dose
tested. The benzodiazepine antagonist flumazenil attenuated GHB-lever
responding occasioned by diazepam, but not GHB. The GABAB
receptor antagonist CGP 35348 antagonized GHB-lever responding
occasioned by baclofen or GHB. Small doses of the purported GHB
receptor antagonist
(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene ethanoic acid (NCS-382) attenuated partially the effects of GHB, whereas larger doses of NCS-382 alone occasioned partial GHB-lever responding. These results implicate GABAB mechanisms in the
discriminative stimulus effects of GHB and further suggest that the
effects of 1,4-BDL under these conditions result from its conversion to
GHB. That NCS-382 shares effects with GHB could explain the lack of antagonism reported for NCS-382 in some studies.
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