In a recent study, Owen & Marsden (1965) have shown that adrenaline increases and that the adrenergic ft-receptor blocking drugs, pronethalol and propranolol, diminish tremor in patients with Parkinson's disease. Vas (1966), however, did not observe any effect of propranolol in Parkinsonian tremor.Friedman (1963) andFriedman, Aylesworth &Friedman (1963) have shown that tremorine lowers the noradrenaline levels in the brains of rats, mice and guinea-pigs but fails to do so in rabbits, which do not show tremor after the administration of tremorine.These findings indicate that brain catecholamines may have a role in causing tremor and the present work was undertaken to study their role in, and the effect of, a recent adrenergic f,-receptor blocking drug-namely, dextro-N-isopropyl-para-nitrophenylethanolamine (d-INPEA)-on tremorine and harmaline induced tremor in mice.
METHODSTremor was recorded by a modification of the method of Ahmed & Taylor (1959). A perforated plastic box 5 in x 3 in x 2 in was bolted to a 31 in brass rod (* in diameter), which in turn was fixed into the position of the stylus of a high impedance (6,000Q) electromagnetic gramophone pick-up. Lateral movements of the box were converted by the pick-up into electrical changes, which were amplified and recorded on one channel of a Grass four channel electroencephalograph. The amplification level was kept at a minimum. The paper speed was 15 mm/sec. The whole device was kept in a sound-proof booth. Sixty male mice, weighing between 22-27 g, fed in the morning on the day of experiment, were used. They were placed in the box, one at a time, for 10-15 min before each experiment, in order to acclimatize them. This ensured a very low baseline due to reduced spontaneous activity of the mice. After a control period, one of the two tremorogenic drugs was injected intraperitoneally (tremorine 20 mg/kg and harmaline 30 mg/kg) and movements were recorded every 5 min for 60 min. After establishing that in the doses given, all the mice showed tremor after the drugs, they were divided into six groups of 10 mice.The mice in each group received one of the drugs used in the present study, intraperitoneally, and each group then was further divided into two subgroups of five animals each, for challenging with tremorine and harmaline. The effects of these tremorogenic drugs were then followed for a period of 1 hr.The various drugs used for modifying tremor were: reserpine (Serpasil; Ciba), alpha-methylmeta-tyrosine (Merck, Sharp and Dohme), pargyline (Abbot), propranolol (I.C.I.), d-INPEA and I-INPEA (Selvi).