A comparison of cyclic guanosine 3':5'-monophosphate and muscarinic excitatory responses in the superior cervical ganglion of the rat

Abstract

The relationship between the magnitude of atropine-sensitive afterdischarge (AD), which is generated from slow excitatory postsynaptic potentials and the ganglionic cyclic guanosine 3':5'-monophosphate (cGMP) concentration was investigated in the rat superior cervical ganglion in vitro. Parallel increases in the magnitude of atropine-sensitive AD and cGMP concentration occurred with increasing frequency of preganglionic nerve stimulation up to 40 Hz for 10 sec. However, AD was completely antagonized by atropine, 0.1 to 1 microM, whereas the cGMP response was not significantly affected by up to 25 microM atropine. Although bethanechol, 0.5 mM, causes an asynchronous firing which can be recorded from the postganglionic nerve, bethanechol had no effect on the ganglionic cGMP concentration even in ganglia preincubated with the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, 1 mM. The methylxanthine did increase the resting cGMP concentration and the concentration of cGMP immediately after stimulation of the preganglionic nerve. It is concluded that muscarinic AD and the slow excitatory postsynaptic potentials of rat sympathetic ganglia are not generated by a mechanism involving an increase in ganglionic cGMP.