Antinociceptive effects of intrathecal taurine and calcium in the mouse

Taurine (Tau), calcium (Ca⁺²) and opiates each produce antinociception when injected i.t. in mice. This study was initiated to determine whether there is a common mechanism underlying their antinociceptive effects. Using the abdominal stretch assay, the antinociceptive effects of both Tau (12 nmol) and Ca⁺² (72 nmol) were antagonized by i.t. TAG (4.4 nmol), a Tau antagonist, but not by i.p. injection of the opiate antagonist naloxone (5 mg/kg). The antinociceptive effects of Tau and Ca⁺² correlated with their ability to inhibit the intensity of caudally-directed biting and scratching behaviors produced by i.t. NMDA or kainic acid. The inhibitory effects of both Tau and Ca⁺² on the biting and scratching behaviors behaviors induced by substance P or excitatory amino acids were reversed by TAG, suggesting a common mediation by Tau. These data indicate that the antinoceptive effects of both Tau and Ca⁺² appear to be mediated, at least in part, by Tau but not by the release of endogenous opioid compounds. In addition, inhibition of chemical irritant-induced nociception may be produced by a simple blockade of excitatory amino acid activity.