Calcium and cAMP signaling induced by gamma-hydroxybutyrate receptor(s) stimulation in NCB-20 neurons

Successful Treatment of Severe Gamma-Hydroxybutyric Acid Withdrawal Syndrome With Dantrolene

The prevalence of gamma-butyrolactone/gamma-hydroxybutyric acid (GBL/GHB) use is increasing. The gravity and number of incidents with this drug are relatively high. A feared complication is addiction and its withdrawal syndrome, which can be life-threatening and is difficult to treat. We present the case of a 31-year-old man, admitted to the ICU because of accidental GBL withdrawal. The patient was tachycardic, sweaty, extremely agitated, and showed signs of psychosis. High doses of benzodiazepines, propofol, sufentanil, and quetiapine could not sedate the patient sufficiently. Dosing with pharmaceutical GHB was challenging due to severe gastric retention. As the patient developed hyperthermia and rhabdomyolysis, signs of a neuroleptic malignant syndrome (NMS), he was treated with dantrolene. After 14 days, the patient was discharged to a psychiatric clinic for further treatment. GHB affects multiple neurotransmitters and chronic use causes the up- or down-regulation of several receptors. During GHB withdrawal, the patient developed a hyperexcitable state, in which there was insufficient gamma-aminobutyric acid (GABA) (the most important inhibiting neurotransmitter) and an abundance of glutamate (the most important excitatory neurotransmitter). High-dose benzodiazepines are often advocated as the first-line treatment, but benzodiazepine resistance has frequently been reported. Therefore, treatment with pharmaceutical GHB is advised. Patients with GHB-withdrawal who have clinical signs of NMS can be treated with dantrolene because it regulates the distorted calcium secretion and affects the serotonin and cholinergic system.

Mechanisms for the Specific Properties of γ-Hydroxybutyrate in Brain

γ-Hydroxybutyrate (GHB) is both a natural brain compound with neuromodulatory properties at central GABAergic synapses (micromolar concentration range) and also a drug (Xyrem(R) ) clinically used for the treatment of various neurological symptoms (millimolar dose range). However, this drug has abuse potential and can be addictive for some patients. Here, we review the basic mechanistic role of endogenous GHB in brain as well as the properties and mechanisms of action for therapeutic clinical doses of exogenous GHB. Several hypotheses are discussed with a preference for a molecular mechanism that conciliates most of the findings available. This conciliatory model may help for the design of GHB-like drugs active at lower doses and devoid of major side effects.

Xanthurenic acid binds to neuronal G-protein-coupled receptors that secondarily activate cationic channels in the cell line NCB-20

Xanthurenic acid (XA) is a metabolite of the tryptophan oxidation pathway through kynurenine and 3-hydroxykynurenine. XA was until now considered as a detoxification compound and dead-end product reducing accumulation of reactive radical species. Apart from a specific role for XA in the signaling cascade resulting in gamete maturation in mosquitoes, nothing was known about its functions in other species including mammals. Based upon XA distribution, transport, accumulation and release in the rat brain, we have recently suggested that XA may potentially be involved in neurotransmission/neuromodulation, assuming that neurons presumably express specific XA receptors. Recently, it has been shown that XA could act as a positive allosteric ligand for class II metabotropic glutamate receptors. This finding reinforces the proposed signaling role of XA in brain. Our present results provide several lines of evidence in favor of the existence of specific receptors for XA in the brain. First, binding experiments combined with autoradiography and time-course analysis led to the characterization of XA binding sites in the rat brain. Second, specific kinetic and pharmacological properties exhibited by these binding sites are in favor of G-protein-coupled receptors (GPCR). Finally, in patch-clamp and calcium imaging experiments using NCB-20 cells that do not express glutamate-induced calcium signals, XA elicited specific responses involving activation of cationic channels and increases in intracellular Ca(2+) concentration. Altogether, these results suggest that XA, acting through a GPCR-induced cationic channel modulatory mechanism, may exert excitatory functions in various brain neuronal pathways.