Effects of Hypotarurine on the Substantia Gelatinosa Neurons of the Trigeminal Subnucleus Caudalis in Young Mice

Objectives: The substantia gelatinosa (SG) of trigeminal subnucleus caudalis (Vc) receives and integrates the nociceptive information from orofacial region. Hypotaurine, the immediate precursor of taurine is biosynthesized from cysteine in astrocytes. The physiological role of hypotaurine in the central nervous system remains unclear
Methods: So, in this study, to elucidate the effect and action mechanism of hypotaurine on orofacial pain processing, a patch clamp technique was used to examine the direct effects and receptor types involved in hypotaurine-induced membrane currents and potential chances on SG neurons.
Results: The hypotaurine-induced inward currents showed clear concentration dependency at range of 30–3000 µM. Hypotaurine-induced currents were maintained in the presence of 0.5 µM tetrodotoxin, a Na⁺ channel blocker, 20 µM D,L-2-amino-5-phosphonopentanoic acid, an NMDA receptor antagonist and 10 µM 6-cyano-7-nitroquinoxaline-2,3-dione, a non-NMDA glutamate receptor antagonist, indicating direct postsynaptic action of hypotaurine on SG neurons. Further, hypotaurine-mediated responses were not affected by gabazine (3 µM), a synaptic GABA_A receptor blocker, but almost blocked by strychnine (2 µM), a glycine receptor antagonist suggesting that hypotaurine-induced inward currents were mediated by glycine receptor activation. In addition, the responses to hypotaurine (300 µM) and glycine (3 mM) were not additive indicating that they act on the same binding site i.e. glycine receptors. The hypotaurine- and glycine-induced currents were partially blocked by picrotoxin (50 µM) and bicuculline (10 μM) suggesting the involvement of both homo- and hetero-glycine receptor.
Conclusions: These results indicate that hypotaurine affects SG neuronal activities by glycine receptor activation on the SG neurons and hypotaurine can be a target molecule for orofacial pain modulation. This research was supported by Basic Research program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2015R1D1A3A01018700).