Electrical stimulation of the superior cervical ganglia causes a rapid increase in the concentration ofcyclic AMP in the pineal gland of rats. This effect is dependent upon the frequency, voltage, and duration of the stimulus and is markedly potentiated by pretreating the animals with desmethylimipramine. The increase in cyclic AMP is blocked by prior treatment of the rats with reserpine, bretylium, or propanolol but not with phentolamine. These results provide direct evidence that electrical stimulation ofsympathetic nerves increases cyclic AMP in a target organ through the release ofnorepinephrine from presynaptic terminals acting on postsynaptic P-adrenergic receptors. (3)(4)(5). In those cases in which cyclic AMP was increased, the changes were small and inconsistent and were not totally or specifically inhibited by ,-adrenergic blocking drugs (4).The recent finding that the in vivo administration of norepinephrine to rats failed to increase the concentration ofcyclic AMP in pineal gland except when given after the tricyclic antidepressant drug desmethylimipramine (6), which prevents the reuptake ofthe catecholamine into sympathetic nerve terminals (7), suggested that one may be able to demonstrate an increase ofcyclic AMP induced by nerve stimulation more readily in rats pretreated with desmethylimipramine.The pineal gland should be a good model for demonstrating whether direct sympathetic nerve stimulation does increase the concentration ofcyclic AMP in tissues supplied by these nerves. This gland is richly innervated by sympathetic fibers originating exclusively from the superior cervical ganglia (8), it contains a high density of &adrenergic receptors coupled to adenylate cyclase (9), and it possesses an adenylate cyclase system which, when activated by catecholamines (10), results in a marked increase in the intracellular concentration of cyclic AMP (11).The present results demonstrate that electrical stimulation of the superior cervical ganglia produces a rapid and marked increase in the concentration of cyclic AMP in rat pineal gland of animals treated with desmethylimipramine.
METHODSMale Sprague-Dawley rats (300-500 g), purchased from Zivic Miller Laboratories (Allison Park, PA), were allowed free access to food and water. They were housed in an environmental chamber (Hotpack, Philadelphia, PA) and were kept in constant light for at least 6 days prior to the experiment, a procedure which increases the sensitivity of the catecholamine-sensitive adenylate cyclase system of pineal gland (12). Either saline or desmethylimipramine was given intraperitoneally 1 hr prior to stimulation of the superior cervical ganglia. Unless otherwise indicated, desmethylimipramine was given at a dose of38 Zmol/ kg (10 mg/kg).To stimulate the superior cervical ganglia, the animals were decapitated, the head was washed with cold saline to remove excess blood, and both superior cervical ganglia were isolated and attached to platinum bipolar electrodes connected to Grass SD-9 square-wave stimulators. Stimulation be...