Specific gamma-hydroxybutyrate-binding sites but loss of pharmacological effects of gamma-hydroxybutyrate in GABA(B)(1)-deficient mice.
gamma-Hydroxybutyrate (GHB), a metabolite of gamma-aminobutyric acid (GABA), is proposed to function as a neurotransmitter or neuromodulator. gamma-Hydroxybutyrate and its prodrug, gamma-butyrolactone (GBL), recently received increased public attention as they emerged as popular drugs of abuse. The actions of GHB/GBL are believed to be mediated by GABAB and/or specific GHB receptors, the latter corresponding to high-affinity [3H]GHB-binding sites coupled to G-proteins. To investigate the contribution of GABAB receptors to GHB actions we studied the effects of GHB in GABAB(1)-/- mice, which lack functional GABAB receptors. Autoradiography reveals a similar spatial distribution of [3H]GHB-binding sites in brains of GABAB(1)-/- and wild-type mice. The maximal number of binding sites and the KD values for the putative GHB antagonist [3H]6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene acetic acid (NCS-382) appear unchanged in GABAB(1)-/- compared with wild-type mice, demonstrating that GHB- are distinct from GABAB-binding sites. In the presence of the GABAB receptor positive modulator 2,6-di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol GHB induced functional GTPgamma[35S] responses in brain membrane preparations from wild-type but not GABAB(1)-/- mice. The GTPgamma[35S] responses in wild-type mice were blocked by the GABAB antagonist [3-[[1-(S)-(3,4dichlorophenyl)ethyl]amino]-2-(S)-hydroxy-propyl]-cyclohexylmethyl phosphinic acid hydrochloride (CGP54626) but not by NCS-382. Altogether, these findings suggest that the GHB-induced GTPgamma[35S] responses are mediated by GABAB receptors. Following GHB or GBL application, GABAB(1)-/- mice showed neither the hypolocomotion, hypothermia, increase in striatal dopamine synthesis nor electroencephalogram delta-wave induction seen in wild-type mice. It, therefore, appears that all studied GHB effects are GABAB receptor dependent. The molecular nature and the signalling properties of the specific [3H]GHB-binding sites remain elusive.
Kaupmann
Klemens
K
Novartis Institutes for BioMedical Research, WKL-125.7.42, Novartis Pharma AG, CH-4002 Basel, Switzerland. klemens.kaupmann@pharma.novartis.com
Cryan
John F
JF
Wellendorph
Petrine
P
Mombereau
Cedric
C
Sansig
Gilles
G
Klebs
Klaus
K
Schmutz
Markus
M
Froestl
Wolfgang
W
van der Putten
Herman
H
Mosbacher
Johannes
J
Bräuner-Osborne
Hans
H
Waldmeier
Peter
P
Bettler
Bernhard
B
D015107:4-Butyrolactone / Q000493:pharmacokinetics; D000759:Adjuvants, Anesthesia / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000493:pharmacokinetics; D001345:Autoradiography; D001418:Baclofen / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects; D001567:Benzocycloheptenes / Q000493:pharmacokinetics; D001667:Binding, Competitive; D001835:Body Weight / Q000187:drug effects; D001921:Brain / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004563:Electrochemistry; D004569:Electroencephalography; D058786:GABA-B Receptor Agonists; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000493:pharmacokinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009043:Motor Activity / Q000187:drug effects; D009943:Organophosphorus Compounds / Q000493:pharmacokinetics; D010636:Phenols / Q000493:pharmacokinetics; D011869:Radioligand Assay; D018080:Receptors, GABA-B / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012978:Sodium Oxybate / Q000494:pharmacology*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
C438607:2,6-di-tert-butyl-4-(3-hydroxy-2,2-dimethylpropyl)phenol; D000759:Adjuvants, Anesthesia; D000927:Anticonvulsants; D001567:Benzocycloheptenes; D058786:GABA-B Receptor Agonists; D009943:Organophosphorus Compounds; D010636:Phenols; D018080:Receptors, GABA-B; C066471:NCS 382; C107353:CGP 54626; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D005680:gamma-Aminobutyric Acid; D004295:Dihydroxyphenylalanine; D012978:Sodium Oxybate; D001418:Baclofen; D015107:4-Butyrolactone