Long-duration spike afterhyperpolarizations in neurons from the guinea pig superior cervical ganglion.

Intracellular recordings from guinea pig superior cervical ganglia maintained in vitro have revealed a protracted spike afterhyperpolarization in approximately 18% of the principal neurons that is substantially longer (greater than 1 s duration) than those previously reported. This long afterhyperpolarization is distinct from shorter duration afterpotentials in these cells because it can be selectively and reversibly blocked by cooling and by bath applied histamine. Cellular excitability is increased when the long-duration afterhyperpolarization is abolished and thus it deserves consideration as a site for modulation of synaptic transmission through the superior cervical ganglion.