Figure 5.

Adaptation to high potassium can be erased by a hyperpolarizing stimulus

(A and B) PD neurons were exposed to two 20-min high potassium (2.5x[K⁺]) saline exposures, followed by a hyperpolarizing stimulus, then two more high potassium exposures. All perturbations were interspersed with 20-mintue washes in control saline. All activity traces are taken from 15 min into each perturbation. For all panels, gray boxes indicate time of hyperpolarizing stimulus. (A) Three-second segments of a PD neuron’s activity in all high potassium applications and the low potassium (0.4x[K⁺]) perturbation. (B) Three-second segments of another PD neuron in all high potassium applications and during direct hyperpolarization by injected current.

(C) Raster plots of spiking activity in high potassium saline for nine PD neurons (21–30) exposed to the same four repeated exposures, with a hyperpolarizing stimulus between the second and third high potassium exposure. For all rasters, bursting activity is plotted in a darker shade and tonic firing in a lighter shade. Animals 21–25 were exposed to low potassium and animals 26–30 had the PD neuron directly hyperpolarized with injected current.

(D) Low potassium experiments: latency to recovery of the first action potential for each PD neuron across all high [K⁺] applications.

(E) Direct hyperpolarization experiments: latency to recovery of the first action potential for each PD neuron across all high [K⁺] applications. ∗p < 0.02, ∗∗p < 0.01, ∗∗∗p < 0.0001.