Abstract
Central pattern generators (CPGs) are ubiquitous in biology and create the rhythmic motor patterns that allow animals to walk, fly, run, chew, breathe, digest, swim, hop, swallow, crawl and more. Thus, these neuronal circuits must function reliably over an animal’s lifetime. Furthermore, both theoretical and experimental evidence suggest that robust networks with similar activity patterns can ha¬ve widely variable underlying cell intrinsic and synaptic conductances. This thesis explores how diverse neuronal circuits respond and adapt to global perturbation. To address these questions, I studied the pyloric CPG of the stomatogastric ganglion of the crab Cancer borealis, a well-defined motor circuit with predictable behavioral outputs and can be easily recorded from in vitro. Pyloric neurons rapidly adapt when perturbed by elevated extracellular potassium. Moreover, the changes in circuit robustness are maintained after the perturbation is removed; pyloric neurons are more robust to subsequent potassium perturbations even after several hours of wash. Despite these long-term changes in circuit robustness, we observe no differences in neuronal activity under control conditions. These studies indicate that individual pyloric rhythms can adapt to global perturbation while maintaining rhythmic outputs. I also observed longer-term shifts in population resilience. Pyloric circuit robustness to high potassium saline, but not acute temperature, shifts depending on the month in which experiments were performed. Disconcertingly, in 2021 we recorded pyloric rhythms with extremely high temperature tolerances. Compared to crabs from five years earlier, we found that recent crabs were significantly more robust to extreme temperatures. Based on local sea temperatures, we believe this trend may be due to long-term acclimation to warmer sea temperatures resulting from climate change. Again, we observed no differences in control activity that predicted an animal’s temperature sensitivity. Therefore, within-species and within-animal changes in neuronal states can be hidden under normal conditions and may only be revealed by extreme perturbation.