Exacerbation of harmaline-induced tremor by imipramine

Imipramine is a well-established tricyclic antidepressant which was first approved for the treatment of depression in the late fifties. Antidepressant effect of imipramine is attributed to inhibition of serotonin (5HT) and noradrenaline (NA) reuptake in brain. These monoamines have been implicated in a variety of neurological disorders including tremor. In the present investigation attempt was made to study the effect of imipramine on harmaline-induced tremor in rats. Male Sprague Dawley rats weighing 115+/-2.5 g were given harmaline (10 mg/kg, i.p.) alone or along with imipramine (30 min before harmaline) in doses of 60 and 90 mg/kg respectively. The latency of onset, intensity and duration of tremor and EMG were recorded. To substantiate the role of 5HT in aetiopathology of tremor the above experiment was repeated in the rats pretreated with P-chlorophenylalanine (PCPA), a potent 5HT depleter. The levels of 5HT and 5-hydroxyindole acetic acid (5HIAA) in the brain stem were measured using high performance liquid chromatography. Imipramine dose-dependently exacerbated the duration, intensity and amplitude of EMG following harmaline-induced tremor. Imipramine treatment further decreased harmaline-induced 5HT turnover in the brain stem. However, this was statistically insignificant. Depletion of 5HT produced a significant reduction in the intensity and duration of harmaline-induced tremor. In conclusion, this study suggests that imipramine exacerbates harmaline-induced tremor. Clinical use of imipramine for the treatment of depression in patients who also suffer from tremors may require a close monitoring.