Significance of central noradrenergic system on harmaline induced tremor.

Since there is degeneration of substantia nigra concomitant with that of locus coeruleus (LC) in patients with Parkinson's disease, the study was performed to determine the role of central norepinephrine (NE) on harmaline induced tremor. The duration of harmaline (10 mg/kg IP) induced tremor was significantly reduced by intraventricular administration of L-thero-3,4-dihydroxyphenylserine (200 micrograms/rat) and 1-NE (50 micrograms/rat) was increased NE levels in the cerebral cortex, striatum, diencephalon, cerebellum and brain stem. Electrical stimulation of bilateral LC suppressed harmaline-induced 10-12/sec EMG activities in the neck muscle. Bilateral LC lesion upon electrocoagulation and 6-hydroxydopamine treatment resulted in a significant prolongation of the duration of harmaline induced tremor, reducing NE levels in the brain. These data suggest that central NE originating in the LC neurons has an inhibitory effect on the development of the tremor induced by harmaline.