Involvement of α- and β1-adrenergic mechanisms in the immobility-reducing action of desipramine in the forced swimming test

Abstract

The influences of various monoaminergic agents on the immobility-reducing action of desipramine (DMI) in the forced swimming test were examined. 5-Methoxy- N, N-dimethyltryptamine and methysergide, a serotonin agonist and antagonist, respectively, did not affect the duration of immobility. Pimozide, a dopamine antagonist, prolonged the duration of immobility at a dose of 0.5 mg/kg. However, at the doses tested, these drugs had no effect on the action of desipramine. Phenoxybenzamine, an α-adrenergic antagonist, prolonged the duration of immobility only with the largest dose (20 mg/kg), but the action of desipramine was completely blocked by this drug at all doses tested. Intracerebroventricular injection of a β-adrenergic agonist, isoproterenol (ISO), and two selective β 1-adrenergic antagonists, atenolol (ATE) and practolol, dose-dependently diminished and potentiated, respectively, the action of desipramine although these drugs had no effect on the duration of immobility when given alone. A β 2-adrenergic antagonist derived from oximino-9-fluorene, (IPS 339) did not influence the duration of immobility or affect the action of desipramine. The effect of isoproterenol was almost completely blocked by the pretreatment with atenolol and practolol but not by IPS 339. Subcutaneously-injected isoproterenol did not affect the action of desipramine. Isoproterenol and atenolol had no effect on the concentration of desipramine in brain regions. Phenylephrine, a postsynaptic α-adrenergic agonist, reduced the duration of immobility as did desipramine, but this action was not affected by isoproterenol and atenolol. These results indicate that an activation of central α-adrenergic, but not of central serotonergic and dopaminergic systems, is a mechanism involved in the action of desipramine. It is also suggested that central β 1-adrenergic mechanisms have an inhibitory effect on the action of desipramine by reducing the activity of presynaptic noradrenaline neurons in the rat brain.