Synaptic and non-synaptic components of the dorsal horn potential in isolated hamster spinal cord

Slow negative potentials, evoked by stimulation of the lumbar dorsal roots, have been demonstrated in the dorsal horn of an isolated, hemisected spinal cord preparation from golden hamsters. Paired stimuli revealed a period of partial suppression of this slow potential persisting for up to 2 s following the conditioning stimulus, but with high stimulation frequencies this effect was masked and above 20 Hz a tetanic train of stimuli produced a smoothly rising potential. The response evoked by tetanic stimulation was shown to consist of two components, a manganese-sensitive, synaptically generated component, and a manganese-resistant, frequency-dependent element. Treatment with 10⁻⁴ M 4-aminopyridine blocked the manganese-resistant tetanic response but did not reduce the manganese-sensitive component. Bicuculline, picrotoxin and tubocurare had little effect upon the tetanic response, but 10⁻³ M procaine blocked it completely. The possibility that the manganese-resistant response was due to the release of potassium ions is considered.