Behavioural and biochemical effects of chronic reduction of cerebral noradrenaline receptor stimulation.

Mice were given various 7-day treatments designed to reduce cerebral noradrenergic function. Following these treatments, alterations in the sensitivity of limbic forebrain adenylate cyclase to noradrenaline (NA), and in the locomotor response of the mice to dopaminergic and noradrenergic agonists were studied. An enhanced response of the NA-sensitive adenylate cyclase to 1-NA(10-5 M), in comparison to control mice, was demonstrated after treatments producing a chronic reduction in stimulation of alpha-adrenergic receptors (phenoxybenzamine 10 mg/kg per day), beta-adrenergic receptors (propranolol, 0.05% diet), all noradrenergic receptors (reserpine 5 mg/kg, followed by FLA-63, 25 mg/kg per day), and dopaminergic as well as noradrenergic receptors (chlorpromazine, 5 mg/kg per day). Sensitivity of the NA-stimulated adenylate cyclase was not altered by chronic treatment with FLA-63 alone as a 0.05% diet. However, none of the chronic treatments except chlorpromazine administration increased the locomotor activity recorded for 2 h following apomorphine (1 mg/kg, s.c.) and none of the treatments altered the locomotor activity recorded in the 2 h following administration of the alpha-adrenergic agonist clonidine (1mg/kg, i.p.), or a combination of apomorphine (1 mg/kg, s.c.) plus clonidine (1 mg/kg, i.p.) The results support the hypothesis that noradrenergic stimulation plays a role secondary to that of dopamine in the production of locomotor activity.