Objective: Circulating estrogen influences fluid regulation, but the functional effects of estrogen loss with and without induced systemic vocal fold dehydration remain unclear. This study investigated the temporal effects of dehydration on rat ultrasonic vocalizations (USVs) in the condition of reduced circulating estrogen simulating menopause.

Methods: USVs from eight ovariectomized (OVX) seven-month-old Long-Evans rats were elicited using an anticipatory food reward paradigm. USVs were recorded consecutively across five days of baseline followed by random assignment to 15 days of dehydration induced by water restriction (N = 3) or euhydration (n = 5). USV recordings were collected individually in a sound isolation chamber using an ultrasonic microphone and analyzed with specialized software (Sonotrack, Metris b.v.). USV measures included total call number, average duration (s), maximum intensity (dB), and frequency range (kHz).

Results: During the initial review of the data one rat in the euhydrated group was determined to be an outlier and was removed from the analysis. With the outlier removed, water-restriction (N = 3); euhydration (n = 4), there were no significant differences in any of the USV measures between groups at any time point.

Conclusion: The temporal impact of dehydration on rat USVs was similar to euhydration in a reduced circulating estrogen state. This was surprising considering prior literature shows biological changes within the rat larynx due to systemic dehydration. The small sample size and/or functional resilience of the vocal folds to mild system dehydration may be the reason for these unexpected findings. Future larger-scale studies will help to clarify the impact of dehydration in the context of reduced circulating estrogen.