Suppression of GABAB receptor function in vivo by disulfide reducing agent, dl-dithiothreitol (DTT)

Rationale A recent in-vitro study demonstrated that the potent disulfide reducing agent, dl-dithiothreitol (DTT), may alter the structural stability of the GABA_B receptor, probably inactivating the disulfide bonds between four cysteine residues located in the GABA_B1(a) receptor structure.Objectives The present study was designed to evaluate whether DTT treatment was capable of antagonizing some behavioral effects of pharmacological stimulation of the GABA_B receptor.Methods Experiments on sedation/hypnosis induced by the GABA_B receptor agonists baclofen, SKF 97541, CGP 44532 and -hydroxybutyric acid (GHB) in DBA mice and selectively bred GHB-sensitive (GHB-S) rats, and a GHB drug discrimination study in Long Evans rats were conducted. Specificity of the DTT action on the GABA_B receptor was investigated by assessing its effect on the sedative/hypnotic effect induced by diazepam, ketamine and ethanol.Results DTT prevented the sedative/hypnotic effect of all GABA_B receptor agonists tested and also reversed baclofen-induced sedation/hypnosis. In contrast, DTT had no effect on, or even potentiated, sedation/hypnosis produced by diazepam, ketamine or ethanol. DTT completely blocked the discriminative stimulus effects of GHB.Conclusions These results are discussed in terms of DTT altering the stability of the binding domain of the GABA_B receptor, hindering the drug-receptor interaction.