The effect of 1, 1-dimethyl-4-phenylpiperazinium iodide on transmission in the superior cervical ganglion of the cat

DMPP administered intrarterially in doses of 1–2 μg produced a short biphasic ganglionic demarcation potential consisting of an initial period of depolarization with a subsequent phase of hyperpolarization. During depolarization, ganglionic action potentials were increased whereas during hyperpolarization the amplitude of the action potentials rapidly diminshed.

DMPP administered in the 5–20 μg doses evoked a biphasic blockade of transmission in the superior cervical ganglion of the cat. The first period of blockade was associated with the ganglionic depolarization and its magnitude and duration were dose-dependent. During the falling phase of depolarization, a partial recovery of ganglionic transmission occured, but after larger doses of DMPP (20–100 μg) this effect was not observed. The second period of blockade coincided with ganglionic hyperpolarization. This period was characterized by a strong increase of the negative after potentials while the spikes and positive after potentials were completely or partially blocked.

After 5–20 μg i.a. DMPP, asynchronous postganglionic firing of high amplitude was observed. Repetitive preganglionic stimulation markedly increased the postganglionic firing produced by DMPP, while hexamethonium (2 mg) and Ecolid (0·5 mg) abolished it almost completely.

Ganglionic depolarization evoked by ACh administered 15–60 min after DMPP was slightly diminished, whereas the postganglionic firing produced by ACh was strongly enhanced.

It is concluded that DMPP is a potent ganglionic stimulating agent actiing on the “nicotinic cholinoceptive sites” in the superior cervical ganglion of the cat.