A ganglion stimulating action of neostigmine.

The actions of neostigmine on transmission in the superior cervical ganglion have been investigated by means of the nictitating membrane preparation in the anaesthetized cat. Intravenous injections of neostigmine produced a rapid and often complete reversal of hexamethonium block, whereas eserine had no effect. This reversal by neostigmine was obtained regularly even after large doses of eserine or dyflos, but was sometimes brief. In ganglia perfused with heparinized plasma containing neostigmine (10(-8) to 10(-4)), there was no potentiation of the responses to maximal stimulation of the preganglionic nerve. Intra-arterial injections of neostigmine to both normal and preganglionically denervated ganglia produced first a potentiation of the responses to nicotine, then, with larger doses, a contraction of the nictitating membrane and, concurrently, a depression of the responses to nicotine. These results are consistent with the view that neostigmine exerts a direct stimulant action on the ganglion, which is distinct from its anticholinesterase action.