Further evidence of central muscle relaxant activity of imipramine, desmethylimipramine and amitriptyline.

* Present address : Pharmacology Division , Central Drug Research Institute, Chatter Manzil Palace, Lucknow, India. Hafliger (1) synthesized a series of iminodibenzyl compounds which were found to possess antihistaminic, anticholinergic, sedative and analgesic properties. It was only after a clinical trial by Kuhn (2) that G 22355 (imipramine) "emerged as an antidepres sant". The exact mechanism of the antidepressant action of imipramine (IMI), its deriva tive desmethylimipramine (DMI) and its analogue amitriptyline (AMI) is not yet estab lished. These agents have been shown to antagonise reserpine induced muscular rigidity and this effect has been attributed to their central cholinolytic activity (3, 4). Another structurally related antidepressant, orphenadrine, has been reported to possess both central (5) and peripheral (6) muscle relaxant properties. We have, earlier, reported the inhibi tion of myoneural transmissson by IMI, DMI and AMI (7). Prolonged inhibition of linguomandibular reflex by low doses of these agents as compared to short lived action of mephenesin (8) prompted us to find out if these agents fulfill all the criteria essential for a central muscle relaxant. Accordingly, these drugs were subjected to various test procedures like effect on behaviour, effect on polysynaptic linguomandibular reflex, effect on facilitatory influence of reticular formation on patellar reflex and the effect on dece rebrate muscular rigidity in cat.