Muscarinic transmission decreases the number of SIF cells demonstrating catecholamine histofluorescence in rat superior cervical ganglia

Preganglionic electrical stimulation of the cervical sympathetic trunk to the rat superior cervical ganglia produced a mean reduction in the number of visible small intensely fluorescent (SIF) cells demonstrating catecholamine histofluorescence to 32% of the unstimulated contralateral control. The reduction in the number of catecholamine-positive SIF cells required the presence of specific blockers of catecholamine uptake and synthesis and was dependent on normal synaptic transmission. No change in the number of catecholamine-positive SIF cells was observed when ganglionic transmission occurred in solutions containing both hexamethonium and atropine or with atropine alone (97% of the unstimulated control). Furthermore, preganglionic stimulation in the presence of high magnesium/low calcium solutions, which effectively blocked synaptic transmission, prevented the stimulation-induced decrease in the number of catecholamine-positive SIF cells. Prolonged antidromic stimulation of the internal carotid nerve only reduced the number of catecholamine-positive SIF cells to 75% of the unstimulated contralateral control. These results suggest that preganglionic synaptic impulses can induce the release of catecholamines from SIF cells via muscarinic receptor activation. Furthermore, the necessity for pharmacological intervention of uptake and synthesis blockers of catecholamines in order to detect the synaptically-induced reduction in the number of catecholamine-positive SIF cells, suggests that synaptic transmission also modulates the synthesis of catecholamines in SIF cells within the rat superior cervical ganglia.