Abstract
Tricyclic antidepressants like imipramine (IMI), desmethylimipramine (DMI) and amitriptyline (AMI) have been shown to antagonise muscle rigidity in experimental reserpine depressive syndrome (1-4) as well as in clinical depressive states. Imipramine also abolishes the rigidity associated with parkinsonism (5). We have earlier reported that these agents possess a potent central muscle relaxant activity of longer duration (6-8). Orphenadrine another structurally similar antidepressant has been reported to possess both central and peripheral muscle relaxant activity (9-11). Chlorpromazine, a tranquillizer causes skeletal muscle re l a xation in certain spastic disorders. Both supraspinal (12) and spinal (13) components have been reported for such activity. Preferential blockade of monosynaptic reflexes has been reported for major tranquillizers (14). Chlorpromazine has been shown to have less potent antistrychnine activity than mephenesin. Bhargava and Srivastava (15) also reported that chlorpromazine is less potent than mephenesin in antagonizing strychnine induced potentiation of linguomandibular polysynaptic reflex. Like tricyclic antidepressants, MAO inhibitors also antagonize reserpine induced muscular rigidity. However, no report regarding the central muscle relaxant activity of these agents is available in the literature. The commonly employed group of drugs in the treatment of psychic disorders are antidepressants, tranquillizers and stimulants. We have earlier suggested that the central muscle relaxant activity of imipramine and allied drugs, plays an important role in their antidepressant action. The present study was undertaken with two aims; firstly to find out a potent central muscle relaxant of longer duration than mephenesin secondly to explore the role of such an inhibitory activity (central muscle relaxant activity) in the antidepressive, tranquillizing and stimulant action of the drugs.
