Prevention of the convulsant and hyperalgesic action of strychnine by intrathecal glycine and related amino acids.

Intrathecal administration of 25 micrograms strychnine induced consistent sensory and motor behavioral events in rats. Sensory events included scratching and biting the lower half of the body, spontaneous vocalizations and skin hyperalgesia, evidenced by vocalization and reflex scratching in response to stimulation with a 5.5 g von Frey fiber. This mild stimulus failed to elicit vocalizations in the preinjection condition. Strychnine induced two types of motor seizures: (1) falling over with tail whipping and (2) convulsions. The effect of equimolar doses of glycine (G) and some related amino acids: beta-alanine (A), taurine (T) and betaine (B) on the strychnine syndrome was tested by administering them (intrathecal route) along with strychnine. T and G but not B significantly decreased most of the sensory events triggered by strychnine. All amino acids significantly decreased the incidence and duration of convulsions; T and B abolished them. A decreased vocalizations and skin hyperalgesia but synergized with strychnine to facilitate scratching and self biting. These results are consistent with findings that G, A and T displace strychnine from its binding sites in the CNS.