FURTHER STUDIES ON THE SUPPRESSING EFFECT OF ISOPROTERENOL ON THE IMMOBILITY-REDUCING ACTION OF DESIPRAMINE IN THE FORCED SWIMMING TEST

Abstract

The present study was undertaken to examine whether the suppressing effect of intracerebroventricular (i.c.v.) administration of isoproterenol (ISO) on the immobility-reducing action of desipramine (DMI) in the forced swimming test was mediated through the presynaptic noradrenaline (NA) neurons and presynaptic α₂-adrenoceptors in rat brain. As in the case of DMI, phenylephrine (i.c.v.) and yohimbine (i.p.) reduced the duration of immobility. The actions of DMI and yohimbine but not that of phenylephrine were diminished and potentiated by i.c.v. administration of ISO and atenolol, respectively. The suppressing effects of ISO were almost completely blocked by the pretreatment with atenolol. On the other hand, clonidine (s.c.) diminished the action of DMI as did ISO, although clonidine had no effect on the duration of immobility when given alone. The suppressing effect of clonidine was antagonized by the pretreatment with yohimbine at a dose which did not affect the duration of immobility, when given alone, nor influenced the action of DMI, whereas the effect of ISO was not affected by the same dose of yohimbine. These results suggest that the suppressing effect of ISO on the immobility-reducing action of DMI in the forced swimming test is mediated through the presynaptic NA neurons, and ISO acts through the presynaptic β₁- but not α₂-adrenoceptors.