Increased Robustness and Adaptation of the Crab Pyloric Rhythm to Simultaneous Temperature and Elevated Extracellular Potassium

Academic Background

In nature, animals often face multiple simultaneous environmental perturbations, which may include temperature fluctuations, pH variations, salinity changes, and alterations in extracellular potassium concentrations. For marine organisms like the crab (Cancer borealis), these perturbations are particularly common. The crab’s pyloric rhythm, controlled by its stomatogastric ganglion (STG), is a rhythmic motor pattern that drives stomach muscle contractions. This rhythmic activity is crucial for the crab’s survival, making its adaptability under multiple perturbations a significant scientific inquiry.

Previous studies have shown that the pyloric rhythm exhibits a certain degree of adaptability to single environmental perturbations, such as temperature or elevated extracellular potassium. However, little research has explored how the adaptation mechanisms interact when these perturbations occur simultaneously. To address this, a team led by Prof. Margaret Lee and Prof. Eve Marder conducted a study to uncover the adaptability and robustness of the pyloric rhythm under dual perturbations of temperature and elevated extracellular potassium.

Source of the Paper

This paper was authored by Margaret Lee and Eve Marder, both affiliated with the Biology Department and Volen Center at Brandeis University in Massachusetts, USA. Published in the Journal of Neurophysiology (J Neurophysiol) in 2025, the paper is titled “Increased Robustness and Adaptation to Simultaneous Temperature and Elevated Extracellular Potassium in the Pyloric Rhythm of the Crab, Cancer borealis.”

Research Process

Subjects and Treatment

The study used 45 adult male Jonah crabs (Cancer borealis), purchased from a commercial lobster company in Boston between October 2023 and March 2024. Prior to experiments, the crabs were maintained in artificial seawater at temperatures between 9°C and 14°C, with a 12-hour light/dark cycle. For dissection, crabs were placed on ice for at least 30 minutes.

Methods

1. Dissection and Isolation of the Ganglion
   Researchers extracted the intact stomatogastric nervous system (STNS) from the crabs, which was pinned in a Sylgard-coated dish and continuously perfused with 11°C physiological saline. The STNS includes the stomatogastric ganglion (STG), esophageal ganglion (OG), and associated connecting and motor nerves.

2. Preparation of High-Potassium Solution
   The physiological saline (control) consisted of 440 mM NaCl, 11 mM KCl, 26 mM MgCl₂, 13 mM CaCl₂, 11 mM Trizma base, and 5 mM maleic acid, adjusted to pH 7.4–7.5 (23°C). High-potassium (2.5×[K⁺]) solution was prepared by adding more KCl to the control saline, achieving a final concentration of 27.5 mM.

3. Intracellular Recording and Electrophysiological Experiments
   Glass microelectrodes were used to record membrane potentials of pyloric rhythm neurons (e.g., pyloric dilator, PD). By injecting current ramps, researchers measured the action potential threshold and neuronal excitability under elevated extracellular potassium conditions. In the experiment, baseline activity of the STNS in physiological saline was recorded for 30 minutes, followed by high-potassium treatment at different temperatures (11°C and 20°C) for 60 minutes and a 30-minute wash with physiological saline.

Data Processing and Analysis

Data were processed using MATLAB 2023a, and a linear mixed-effects model was employed to analyze the interaction between temperature and time. The rhythmic activity of neurons was calculated using fast Fourier transform (FFT), with “rhythmicity” defined as power spectral density (PSD) in the low-frequency range (1 Hz to 5 Hz) accounting for over 70% of the total PSD.

Main Findings

1. Effect of Temperature on Adaptation to High Potassium
   At 11°C, the high-potassium solution depolarized pyloric rhythm neurons, causing a temporary cessation of rhythmic activity, which recovered within minutes. At 20°C, the depolarization of neurons under high potassium was less pronounced, and the recovery of rhythmic activity was significantly faster. Data showed that the latency to first spike decreased from 18.2 minutes at 11°C to 4.9 minutes at 20°C, indicating that high temperatures accelerated neuronal adaptation to elevated potassium.

2. Neuronal Excitability and Rhythmic Recovery
   At 20°C, neurons exhibited significantly enhanced excitability under high potassium, with both action potential thresholds and burst thresholds being more hyperpolarized compared to 11°C. At 20°C, all 26 experimental samples recovered rhythmic activity, whereas only 4 samples recovered at 11°C. This suggests that high temperatures not only accelerated neuronal adaptation to high potassium but also enhanced the recovery of rhythmic activity.

3. Memory Effects and Repeated High-Potassium Treatment
   Repeated application of high-potassium solution induced a “cryptic memory,” where neurons exhibited faster adaptation to subsequent high-potassium treatments. At both 11°C and 20°C, the latency to first spike was significantly reduced during the second high-potassium application, indicating that high temperatures do not affect the formation of this memory effect.

Conclusions and Significance

This study demonstrates that high temperatures significantly enhance the adaptability of crab pyloric rhythm neurons to elevated extracellular potassium and accelerate the recovery of rhythmic activity. These findings highlight the critical role of environmental temperature in regulating neuronal adaptability and provide new insights into how animals cope with multiple environmental perturbations.

Research Highlights

1. Adaptability Under Multiple Perturbations
   This study is the first to explore the adaptation mechanisms of the pyloric rhythm under dual perturbations of temperature and elevated extracellular potassium, addressing a gap in the field.

2. Innovative Methods and Data Analysis
   Novel electrophysiological techniques and a linear mixed-effects model were employed, offering new methodological tools for neuroscience research.

3. Potential Applications
   The findings not only hold significant scientific value for understanding the adaptability of animal nervous systems but also provide potential references for developing treatments for neurological disorders such as epilepsy and cardiovascular diseases.

Additional Insights

Experimental data and analysis code from this study are publicly available on the Marder Lab GitHub page. Furthermore, the study hints at the profound impact of long-term environmental changes (e.g., climate change) on the adaptability of animal nervous systems, opening new avenues for ecological and neuroscience research.