toxicity in mice: the mouse i.v. LD50 for muscarine chloride was calculated to be 0.23 mg/kg and for acetylcholine chloride 33.05 mg/kg, thus muscarine was 143 times more toxic than acetylcholine. Signs of poisoning were similar, acetylcholine being lethal almost immediately and muscarine after 3 to 10 min. Death never occurred later than 10 min after the injection.

Muscarine (1-30 microM) produced a dose-dependent hyperpolarization in a subpopulation of the nucleus raphe magnus (NRM) cells that contain 5-hydroxytryptamine (5-HT). In voltage clamp, the muscarine-induced outward current reversed polarity at the potassium equilibrium potential and was characterized by strong inward rectification. The concentration-response curve for muscarine (EC50 = 2.7 microM) was shifted in a parallel manner to the right by increasing concentrations of pirenzepine (300 nM to 3 microM) and methoctramine (50-200 nM).