The Rat as a Potential Animal Model for Dysphonia

Abstract

Objectives: Dysphonia, or hoarseness, is the primary complaint of patients with unilateral vocal-fold paralysis due to damage to the recurrent laryngeal nerve (RLN). Animal models for RLN injury exist but are generally limited to histological, endoscopic, and electrophysiological approaches. As a step towards using the rat as a model system for dysphonia, we have characterized ultrasonic vocalizations in healthy adult animals. Methods: Ultrasonic vocalizations were evoked individually from adult male Sprague-Dawley rats by manual stroking on two different days one month apart. The vocalizations were visualized and recorded by using an ultrasound microphone attached to a computer. Parameters such as duration, amplitude, pitch, and entropy were measured for each vocalization as well as the preceding silent period with Sound Analysis Pro 2011 software. Results: For a total of 980 vocalizations from five rats, the following parameter values (mean ± standard deviation) were obtained: duration, 14 ± 10 msec; amplitude, 13 ± 6 relative units; pitch, 57 ± 7 kHz; and entropy, -3.9 ± 1.0. No differences were noticed among animals or days. However, the vocalizations were distinct from the background noise during the preceding silent period: amplitude, -1.4 ± 2.9 relative units; pitch, 42 ± 6 kHz; and entropy, -1.2 ± 0.9. Virtually none of the vocalizations were located in the 20-kHz band associated with distress. Conclusions: Ultrasound vocalizations can be recorded from adult rats easily and reliably. The features of the vocalizations are consistent among individuals and over time. Experiments with RLN-lesioned animals are now underway.