Stress-induced changes in trigeminal ganglion excitability in a mouse migraine model

Editor’s note: The research described below comes from a recipient of a 2024 MSC Travel Grant supporting travel to the 66th Annual Scientific Meeting of the American Headache Society. These grants reimburse travel expenses for those who have had their abstract for a presentation or poster accepted at a meeting.

By Mandee Schaub, PhD student, University of Texas at Dallas, US.

What is the research gap that your study addresses?

Migraine is the second leading cause of disability in the United States, and stress is the most common trigger associated with migraine, but the mechanism of stress in migraine is unknown. This study investigates the role stress in neuronal function in mouse trigeminal ganglion (TG). We chose to conduct this study in TG neurons as the TG is the location of the cell bodies of neurons innervating the dura, an anatomical location thought to contribute to migraine pain. To our knowledge, this is the first study investigating neuronal implications of stress in a model of migraine.

What is your research hypothesis?

We hypothesized that both 3 days of repeated restraint stress and corticosterone injections would induce hyperexcitability in trigeminal ganglion neurons in culture.

What methodology did you use to address your research hypothesis?

We used complex animal behavior and electrophysiological techniques to assess functional properties of primary TG neurons in culture. Whole-cell patch-clamp electrophysiology was used to assess functional properties of neurons cultured from TG of mice after repeated restraint stress. Repeated restraint stress consists of 3-5 days of animal handling and baseline periorbital withdrawal threshold testing before animals are placed in tail vein injection tubes for 2 hours, for 3 consecutive days. 24 hours after the third day of stress, animals have their periorbital withdrawal thresholds tested again to ensure migraine-like behavior was induced. Then their TGs were harvested and cultured for patch-clamp where they were assessed for rheobase, spontaneous activity, and hyperexcitability with both ramp and step current injections to the cell. In addition, we conducted a second study using 3 days of corticosterone injections instead of restraint stress to assess the role of corticosterone in stress-induced hyperexcitability, and conducted the patch-clamp experiments as described.

What are the main results of your study?

Cells from animals having undergone restraint stress had a lower rheobase than cells from control animals. In addition, in protocols assessing hyperexcitability, cells from restraint stress animals fired more action potentials in a stimulus injecting current ramping from 0-100 pA, and in a step protocol at 50, 150, 200, and 250 pA than their respective controls. Lastly, more cells from restraint stress conditions fired action potentials in the ramp protocol than the controls. Cells from animals that received corticosterone injections showed no increased excitability but distinct functional differences in action potential shape.

What conclusions did you reach based on your results?

Repeated restraint stress induces hyperexcitability in mouse TG neurons, and three days of repeated corticosterone injections induces differential functional changes in TG neurons.

What are the limitations of your study?

There are many types of neurons in the TG that yield different results on excitability and there may be neuronal subtypes that do not live through the culture process. In the restraint stress procedure, an animal may not be as restrained as another based on their size; while we try to control for that by using animals that are the same weight, we can’t quantify the degree of restraint for the animals. The way we sacrifice the animals for tissue harvest may activate the HPA axis, as well as the corticosterone injections themselves, which could confound corticosterone or stress effects.

What is the relevance of your study to migraine?

This study informs on a potential contributor to the mechanism of stress-induced migraine, which is the most reported trigger for migraine patients. Understanding the underlying mechanism for stress-induced migraine will inform on therapeutic targets to more efficiently and effectively treat migraine. Further, with patch-clamp electrophysiology, we can design experiments to further assess channel conductance and the membrane receptors that contribute to the hyperexcitability and functional changes that occur after restraint stress in mice.