Ganglion blocking effects of streptomycin

The effects of streptomycin on the postganglionic compound action potential, presynaptic nerve terminal spike and preganglionic nerve action potnetial were studied in rabbit and rat superior cervical gnaglia. Streptomycin had a dose-dependent, blocking effect on the postganglionic action potential. The drug was found to have a preferential blocking effect on the first spike, S1, of the compound postganglionic action potential, but the second, S2, major spike was depressed at higher concentrations. At 1 mg/ml, streptomycin reduced the amplitude of the presynaptic nerve terminal action potential, but had no significant effect on the action potential recorded from the cervical sympathetic preganglionic nerve. Increasing the concentrations of Ca++ in the bathing solution antagonized the blocking effect of the antibiotic on the postganglionic action potential. The results are interpreted as indicating that ganglionic blockade by streptomycin is due, mainly, to a presynaptic effect which results in a decreased release of acetylcholine.