Sex differences in swallowing response to Gaussian stochastic surface electrical stimulation

Abstract

One of the rehabilitation methods in practical use for dysphagia is electrical stimulation therapy, usually by stimulating the anterior neck muscles via surface electrodes. Electrostimulation therapy does not directly induce swallowing, but is used as resistance training or to alter drive to swallow muscles. Techniques to stimulate the sensory nervous system have been investigated as possible rehabilitation methods to activate the entire swallowing reflex circuit (such as direct magnetic stimulation of the primary somatosensory cortex). We hypothesized that electrical stimulation of the posterior thoracic region using surface electrodes on the back could work in a similar way to magnetic stimulation therapy to improve swallowing movements. We placed stimulating electrodes at three different locations on the back, neck, and subclavian region of adult Sprague Dawley rats ( n = 18). Using a stochastic paradigm, Gaussian probability electrical stimulation was applied to each site at a median frequency of 300 Hz. Natural swallow was evoked by oral water infusion, and swallow activity was recorded with electromyogram (EMG) wires placed in three swallow-related muscles: mylohyoid (laryngeal elevator), thyroarytenoid (laryngeal adductor), and thyropharyngeus (pharyngeal constrictor). A total of four 120 second electrical stimulus trials were applied with a median frequency of 300 Hz in a Gaussian distribution. EMG amplitudes during swallows after each stimulus were compared to those generated during control swallows. Results showed stimulator placement on the back facilitated all three muscles (mylohyoid, thyroarytenoid, and thyropharyngeus) in all male rats, and in some female rats. Stimulation placed on the lateral neck affected only the thyropharyngeus in male rats, and only the thyroarytenoid in female rats. EMG amplitudes were unchanged following subclavian stimulation. In conclusion, our finding that Gaussian electrical stimulation of the back activated a complement of swallowing muscles in male rats suggests that this may represent a novel swallowing treatment method. Additionally, male and female rats responded differently to simulation, indicating that potential sex differences need to be further elucidated. This work was supported by NIH grants HL 111215, HL 103415 and OT20D001983, the Craig H. Neilsen Foundation Pilot Research Grant 546714, Kentucky Spinal Cord and Head Injury Research Trust, and the Commonwealth of Kentucky Challenge for Excellence. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.