EFFECTS OF ELECTRICAL STIMULATION, -METHYLTYROSINE AND DESMETHYLIMIPRAMINE ON THE NOREPINEPHRINE CONTENTS OF NEURONAL CELL BODIES AND TERMINALS

¹ Department of Pharmacology, Michigan State University, East Lansing, Michigan

The contents of norepinephrine (NE) in superior cervical ganglia, which represent cell bodies, and in submaxillary salivary glands and nictitating membranes, which contain nerve terminals of postganglionic sympathetic neurons, were determined in cats after various treatment schedules. In decentralized, nonstimulated preparations three hours of -methyltyrosine (-MT) infusion reduced the NE content in the cell bodies but not in the terminals. The -MT-induced depletion of NE in cell bodies was retarded if a ligature was tied around the axon. Intravenous injections of desmethylimipramine did not alter the NE content in cell bodies or terminals. Decentralized preganglionic fibers were stimulated (10 Hz for 30 sec/min) for three hours. The NE content in the cell bodies was not altered by stimulation alone, or in combination with desmethylimipramine or -MT. On the other hand, stimulation alone partially depleted NE in the terminals, and the administration of desmethylimipramine and -MT enhanced this depletion. The -MT-induced depletion did not result from the replacement of NE by -methylnorepinephrine. Preganglionic stimulation had little effect upon the conversion of ¹⁴C-tyrosine to ¹⁴C-NE in cell bodies, but increased (3- to 22-fold) the formation of ¹⁴C-NE in the terminals. -MT reduced the synthesis of ¹⁴C-NE in all tissues. These results suggest that in cell bodies synthesis of NE proceeds at a rapid rate that is independent of nerve activity, and levels of NE are maintained only by synthesis. In terminals synthesis of NE proceeds at a slow rate in the absence of nerve activity; with stimulation levels of NE are partially maintained by both synthesis and reuptake.