The mesolimbic dopamine (DA) system, extending from the ventral tegmental area (VTA) to the nucleus accumbens (nAcc), is involved in reward-dependent behaviors and addictive processes such as alcoholism and drug addiction.
Recently, it was proposed that strychnine-sensitive glycine receptors (GlyR) in the nAcc regulate both basal and ethanol-induced mesolimbic DA activity via a neuronal loop involving endogenous activation of nicotinic acetylcholine receptors (nAChR) in the VTA. However, because the nAcc appears to contain few glycine-immunoreactive cell bodies or fibers, the question remains as to what the endogenous ligand for GlyRs in this brain region might be.
Here, we investigated whether the amino acid taurine could serve this purpose using in vivo microdialysis in awake, freely moving male Wistar rats. Local perfusion of taurine (1, 10, or 100 mm in the perfusate) increased DA levels in nAcc. The taurine (10 mm)-induced DA increase, similar to that previously observed after ethanol, was completely blocked by (i) perfusion of the competitive GlyR antagonist strychnine in the nAcc, (ii) perfusion of the nAChR antagonist mecamylamine (100 microm) in the VTA, and (iii) systemic administration of the acetylcholine-depleting drug vesamicol (0.4 mg/kg, i.p).
The present results suggest that taurine may be an endogenous ligand for GlyRs in the nAcc and that the taurine-induced increase in DA levels in this area, similar to that observed after local ethanol, is mediated via a neuronal loop involving endogenous activation of nAChRs in the VTA.
Eur J Neurosci.: Taurine elevates dopamine levels in the rat nucleus accumbens; antagonism by strychnine
