Abstract
Behavioral pharmacological properties of mianserin (1, 2, 3, 4, 10, 14b-hexahydro-2-methyldibenzol[c, f]pyrazino [1, 2-a]azepine monohydrochloride) were investigated in comparison with imipramine (IMP) and amitriptyline (ATP). Mianserin antagonized reserpine-induced hypothermia but to a much lesser extent than IMP or ATP, and did not block the ptosis evoked by reserpine or tetrabenazine. Amphetamine-induced stereotyped behavior was significantly enhanced by both IMP and ATP, but not by mianserin. Unlike IMP or ATP, haloperidol-induced catalepsy in the rat was not blocked by mianserin. Like IMP or ATP, mianserin did not suppress the convulsions induced by bemegride or strychnine in the mouse, and or emetic action of apomorphine in the dog, while only mianserin did not block the convulsions evoded by electric shocks. Mianserin more strongly potentiated the anesthetic action of thiopental than did IMP. ATP showed strong muscle relaxant action and the impairment of coordinated motor activities both in mice and rats, in the inclinated screen test and rotarod test, while, like IMP, these actions of mianserin were significant only in the rat. Catalepsy was not induced nor was the righting reflex suppressed by mianserin. In the low spinal cat, mianserin did not depress the amplitude of extensor MSR. Moreover, the MSR inhibition induced by conditioning stimulation of ipsilateral cutaneous afferents and the MSR potentiation evoked by conditioning stimulation of contralateral saphenous nerve were unaffected by mianserin. The curious behavior of mice and rats was significantly and dose-dependently suppressed by mianserin, and tended to be suppressed by ATP, while an enhancement was seen with IMP in large doses. Mianserin was the most potent in suppressing the fighting behavior induced by long-term isolation of the mouse, and was the weakest in suppressing electric-stimulation-induced fighting behavior, compared with IMP and ATP. Mianserin showed no significant suppression of the muricide behavior of the olfactory bulbectomized rat, while IMP significantly suppressed it. No significant differences were observed among mianserin, IMP and ATP as to their actions on the conflict behavior and the shuttle-box type conditioned avoidance behavior of the rat. These results indicate that behavioral pharmacological actions of mianserin were not always the same as those of IMP and ATP. Therefore, mianserin may be a new antidepressant with mechanisms of action which differ from that of the usual tricyclic antidepressants.
