Taurine activates excitatory non‐synaptic glycine receptors on dopamine neurones in ventral tegmental area of young rats

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Abstract
The physiological and pharmacological properties of taurine‐induced responses were investigated in dopaminergic (DA) neurones from the ventral tegmental area (VTA) of young rats aged 1–13 postnatal days, either in acute brain slices or acutely dissociated neurones. When whole‐cell responses were recorded from current‐clamped neurones using the gramicidin‐perforated technique, the application of taurine (0.01–30 mm) accelerated firings and induced membrane depolarization. In voltage‐clamped neurones, taurine induced a current which was antagonized by strychnine and by picrotoxin, but not by bicuculline. In addition, taurine‐induced current showed complete cross‐desensitization with glycine‐activated currents but not with γ‐aminobutyric acid (GABA)‐activated currents. Thus, taurine is a full agonist of the glycine receptors (GlyRs) in the VTA. Further studies found that taurine acted mainly on non‐synaptic GlyRs. The application of 20 μm bicuculline abolished the spontaneous inhibitory post‐synaptic currents (IPSCs) in 40/45 neurones, and 93% of the evoked IPSCs. The addition of 1 μm strychnine completely eliminated the remaining IPSCs. These results suggest that GABAergic IPSCs predominate, and that functional glycinergic synapses are present in a subset of the VTA neurones. The application of 1 μm strychnine alone induced an outward current, suggesting that these neurones were exposed to tonically released taurine/glycine. In conclusion, by activating non‐synaptic GlyRs, taurine may act as an excitatory extra‐synaptic neurotransmitter in the VTA during early development.

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