Antinociceptive and hypothermic effects of trimethyltin

Trimethyltin (TMT) induced a dose-dependent antinociceptive and hypothermic effect in mice. Antinociception was not attenuated by naloxone but was reversed by atropine. TMT, however, was ineffective in displacing (³H)-QNB binding $\text{in vitro}$ and did not affect (³H)-QNB binding or acetylcholinesterase activity after $\text{in vivo}$ administration. The ethyl ester of nipecotic acid, a specific inhibitor of synaptosomal GABA uptake, exerted a similar antinociceptive effect that could be blocked by atropine. The GABA receptor antagonist bicuculline attenuated antinociception induced by TMT and nipecotic acid ethyl ester but not by morphine or oxotremorine. γ-Vinyl GABA, an irreversible inhibitor of GABA metabolism, prolonged TMT but not morphine-induced antinociception. In contrast, neither the dose-response nor the time course of TMT-induced hypothermia were affected by any of the drugs tested. The findings suggest that the GABAergic system may be involved in TMT induced antinociception; however, the mechanism responsible for the hypothermic effect of TMT is not apparent.