Does taurine play an osmolarity role during ethanol intoxication?

Separate mechanisms regulating accumbal taurine levels during baseline conditions and following ethanol exposure in the rat

Ethanol-induced dopamine release in the nucleus accumbens (nAc) is associated with reward and reinforcement, and for ethanol to elevate nAc dopamine levels, a simultaneous increase in endogenous taurine is required within the same brain region. By employing in vivo microdialysis in male Wistar rats combined with pharmacological, chemogenetic and metabolic approaches, our aim with this study was to identify mechanisms underlying ethanol-induced taurine release. Our results demonstrate that the taurine elevation, elicited by either systemic or local ethanol administration, occurs both in presence and absence of action potential firing or NMDA receptor blockade. Inhibition of volume regulated anion channels did not alter the ethanol-induced taurine levels, while inhibition of the taurine transporter occluded the ethanol-induced taurine increase, putatively due to a ceiling effect. Selective manipulation of nAc astrocytes using Gq-coupled designer receptors exclusively activated by designer drugs (DREADDs) did not affect ethanol-induced taurine release. However, activation of Gi-coupled DREADDs, or metabolic inhibition using fluorocitrate, rather enhanced than depressed taurine elevation. Finally, ethanol-induced taurine increase was fully blocked in rats pre-treated with the L-type Ca2+-channel blocker nicardipine, suggesting that the release is Ca2+ dependent. In conclusion, while astrocytes appear to be important regulators of basal taurine levels in the nAc, they do not appear to be the main cells underlying ethanol-induced taurine release.

Differential increase in taurine levels by low-dose ethanol in the dorsal and ventral striatum revealed by microdialysis with on-line capillary electrophoresis

Ethanol increases taurine efflux in the nucleus accumbens or ventral striatum (VS), a dopaminergic terminal region involved in positive reinforcement. However, this has been found only at ethanol doses above 1 g/kg intraperitoneally, which is higher than what most rats will self-administer. We used a sensitive on-line assay of microdialysate content to test whether lower doses of ethanol selectively increase taurine efflux in VS as opposed to other dopaminergic regions not involved in reinforcement (e.g., dorsal striatum; DS). Adult male rats with microdialysis probes in VS or DS were injected with ethanol (0, 0.5, 1, and 2 g/kg intraperitoneally), and the amino acid content of the dialysate was measured every 11 sec using capillary electrophoresis and laser-induced fluorescence detection. In VS, 0.5 g/kg ethanol significantly increased taurine levels by 20% for 10 min. A similar increase was seen after 1 g/kg ethanol, which lasted for about 20 min after injection. A two-phased taurine efflux was observed with the 2.0 g/kg dose, where taurine was increased by 2-fold after 5 min but it remained elevated by 30% for at least 60 min. In contrast, DS exhibited much smaller dose-related increases in taurine. Glycine, glutamate, serine, and gamma-aminobutyric acid were not systematically affected by lower doses of ethanol; however, 2 g/kg slowly decreased these amino acids in both brain regions during the hour after injection. These data implicate a possible role of taurine in the mechanism of action of ethanol in the VS. The high sensitivity and time resolution afforded by capillary electrophoresis and laser-induced fluorescence detection will be useful for detecting subtle changes of neuronally active amino acids levels due to low doses of ethanol.