Introduction of gloved hand to cage induces 22-kHz ultrasonic vocalizations in male albino rats

Abstract

Rodents emit ultrasonic vocalizations (USVs) above the human hearing threshold of ~ 20 kHz to communicate emotional states and to coordinate their social interactive behavior. Twenty-two kHz USVs emitted by adult rats have been reported in a variety of aversive social and behavioral situations. They occur not only under painful or restraining conditions but can also be evoked by gentle cutaneous touch or airflow. This study aimed to test if placement of a human hand in a cage can evoke 22-kHz USVs. It was found that 36% of the adult male Sprague-Dawley and 13% of the adult male Wistar Han rats emitted 22-kHz USVs when a gloved hand was introduced into the cages. Average vocalization onset latencies were 5.0 ± 4.4 s (Sprague-Dawley) and 7.4 ± 4.0 s (Wistar Han) and the USVs had a stable frequency (22 kHz) across the calls, ranging from 0.1 to 2.3 seconds in duration. Surprisingly, no 22-kHz USVs were found in any female Wistar Han rats tested. To further explore the mechanisms underlying this observation, we compared retinal function, basal serum corticosterone, and testosterone levels between the 22-kHz USV responders and non-responders. None of these parameters or endpoints showed any significant differences between the two cohorts. The results suggest that the introduction of a gloved-hand inside the cage can trigger adult male albino rats to emit 22-kHz ultrasonic vocalizations. This response should be considered in USV studies and animal welfare.

Sex-related differences in retinal function in Wistar rats: implications for toxicity and safety studies

“…The emissions were captured by the UltraSoundGate condenser ultrasonic microphone (CM16, Avisoft Bioacoustics, Berlin, Germany), which is sensitive to frequencies between 15 and 180 kHz and has a flat frequency response between 25 and 140 kHz (±6 dB). The microphone was connected to a computer via an UltraSoundGate IH8 (Avisoft Bioacoustics), and acoustic data were recorded by Avisoft Recorder software (version 2.95, Avisoft Bioacoustics), using a sampling rate of 250,000 Hz in 16-bit format and a recording range of 0–125 kHz ( Hwang et al, 2022 ). Fifty and 22 KHz signals were analyzed off-line.…”

Behavioral and biological regulators of hypervigilance following early life adversity

“…In late adolescent animals, the male startle response was enhanced by USV exposure, but females did not respond differently from baseline when the USV was played. In the USV literature, it is generally accepted that females emit fewer alarm calls than males when presented with aversive stimuli (Hwang et al, 2022;Willadsen et al, 2021). Although little work has attempted to determine why male and female USV emission patterns differ, the failure of 22kHz…”

“…Although 22kHz USVs serve as an alarm call, they may be perceived differently by males and females. Females are not known to reliably produce 22kHz USVs, even when a predator or aversive stimulus is present (Hwang et al, 2022).…”