Post-train depression of ganglionic transmission in the presence of d-amphetamine

Repetitive stimulation (30 Hz, 20 sec) of the preganglionic nerve to the hamster isolated stellate ganglion in a control solution had only small effects on the compound action potentials of the postganglionic nerve (0.2 Hz) after the train. When 10(-5) M d-amphetamine was added to the superfusing solution, the repetitive stimulation induced a post-train depression of the postganglionic compound action potential. The mean reduction of the compound action potential during the post-train depression in d-amphetamine was 37 +/- 15% and the duration was from 60 to 120 sec. Post-train depression only occurred after long conditioning trains and was never observed with less than 100 stimuli in the conditioning train. A post-train depression (45 +/- 8%) was also observed in the presence of 10(-5) M cocaine. The post-train depression in d-amphetamine was significantly reduced by the alpha-adrenoceptor antagonist, phentolamine (10(-5) M) and by the alpha 2-adrenoceptor antagonist, yohimbine (10(-6) M), but not by the alpha 1-adrenoceptor antagonist, prazosin (10(-5) M). There was no post-train depression in the presence of d-amphetamine in ganglia from five hamsters that were pretreated with reserpine (6 mg/kg, i.p., 4 hr). Atropine (10(-6) M) increased and prolonged the post-train depression in the presence of d-amphetamine. These results indicate that repetitive stimulation in the presence of d-amphetamine leads to a post-train depression of the postganglionic compound action potential that is mediated by an action of endogenous catecholamines at alpha 2-adrenoceptors. Muscarinic cholinoceptors do not appear to be involved in the generation of the post-train depression.