Evidence of beta-adrenergic involvement in forced swimming-induced behavioural despair of mice

Modulation of forced swimming-induced immobility by beta-adrenoceptor activation was investigated in mice. Isoprenaline prolonged the immobility duration of mice in a dose-related manner when the animals were forced to swim for 6 min periods. On the other hand, salbutamol (a beta 2-agonist) reduced the immobility duration of mice. Pretreatment with propranolol (1,2,4,8 and 16 mg/kg, ip), atenolol (10 mg/kg, ip) and metoprolol (10 mg/kg, ip) antagonized the immobility-enhancing effect of isoprenaline. Chronic administration (10 mg/kg/day) for 8 days of propranolol and imipramine protected the animals from isoprenaline-evoked prolongation of immobility. These findings suggest that central beta 1- and beta 2-subtypes of adrenoceptors may be acting in opposite directions to modify the immobility duration of mice. Activation of central beta 1-adrenoceptors may lead to enhanced behavioural despair, whereas a reverse effect may be observed on beta 2-adrenoceptor activation.