Abstract
For decades, elevated potassium ion (K+) concentrations have been used in experiments to increase excitability in neurons and networks, by shifting the potassium equilibrium potential (EK) and consequently, the resting potential. In this study, we studied the effects of increased extracellular [K+] on the well-described pyloric circuit of the crab, Cancer borealis through extracellular recordings recording pyloric network activity and intracellular recordings of the Pyloric Dilator (PD) neuron’s activity. Extracellular recordings revealed concentration-dependent changes in PD neurons’ responses and the variability in the time course and nature of the adaptive responses is closely associated with the time of year. Specifically, a 2.5-fold increase in extracellular [K+] (2.5x[K+]) depolarized PD neurons, led to an unexpected short-term loss of normal bursting activity, and was followed by recovery of spiking and/or bursting activity. In contrast, when pyloric presynaptic inputs to the PD neurons were blocked, PD neurons exhibited no loss of spiking activity in 2.5x[K+]. Over the course of exposure to 2.5x[K+], the action potential threshold in PD neurons decreased in control conditions but remained the same in PD neurons with presynaptic inputs blocked. Additionally, removal of neuromodulatory input did not decrease the robustness of PD neurons’ responses to the perturbation. This study illustrates a case of rapid adaptation to a global perturbation, and the evidence presented underscores the importance of circuit interactions in modulation of the adaptive response.