Noradrenaline modifies sympathetic preganglionic neuron spike and afterpotential.

Sympathetic preganglionic neurons were antidromically identified in the slice of the upper thoracic spinal cord of the adult cat, maintained in vitro. In normal Krebs solution, spikes evoked by intracellular stimulation had a marked 'hump' on the repolarization phase and were followed by an afterhyperpolarization of 2.8 s duration and 16.6 mV peak amplitude. Superfusion with Krebs solution containing noradrenaline 10-50 micron reversibly abolished the 'hump' of the spike and the late component of the afterhyperpolarization. In addition, it caused the appearance of a depolarizing afterpotential of 100-600 ms duration. This depolarization could result in repetitive firing of the neuron in response to a single intracellular current pulse.