M1 and M2 receptors mediate different effects on synaptically evoked potentials of the rat superior cervical ganglion.

The application of muscarine, carbachol or methylfurmethide to the rat superior cervical ganglion in vitro resulted in a complex mixture of effects as recorded from the internal carotid nerve using a greased-gap technique. In addition to the previously described depolarizing and hyperpolarizing responses, increases and decreases in the amplitudes of the synaptically evoked compound action potential and its related afterhyperpolarization were observed. The depolarization and the enhancing effects of the agonists were selectively antagonized by pirenzepine (0.3 microM) whereas the hyperpolarization and depressant effects were antagonized by gallamine (10 microM). Methylfurmethide only induced the pirenzepine-sensitive effects. It is concluded that M1 and M2 (cardiac-like) receptors exert different effects on the synaptically evoked potentials of this preparation.