Stroking stimulation of the skin elicits 50-kHz ultrasonic vocalizations in young adult rats

Abstract

The present study aimed to clarify if stroking stimulation of the skin produces positive emotion in rats. 50-kHz ultrasonic vocalizations (USVs) were recorded as an index of the positive emotion. Stroking stimulation was applied to the ventral, dorsal, or head region of the body while the rat was in a vertical holding condition. Rats emit abundant 50-kHz USVs in response to stroking, and the number of the USVs was not different among these three stimulated regions. Other stimulations, such as light touching of the abdominal area, swinging of the body back and forth, or stroking of the external genitalia under vertical holding condition, produced significantly less 50-kHz USVs. Furthermore, different call subtypes were observed during and after stroking of the ventral region. In particular, “Trill” calls, a representative index of positive emotion, were dominant after stimulation. These results suggest that stroking of the skin induces positive emotional states.

Biological Functions of Rat Ultrasonic Vocalizations, Arousal Mechanisms, and Call Initiation

“…Although adults rarely play, the appetitive value of light tactile stimulation, which only partially resembles rough-and-tumble play, still retained rewarding play value in young adults, and tactile stimulation induced emission of 50 kHz calls in habituated animals [ 60 ]. Interestingly, other forms of tactile stimulation by human hand in different parts of the rat’s body, which had low resemblance to natural rough-and-tumble play, or were entirely unnatural to rats (e.g., holding rats in a vertical position and touching their flanks), also induced the emission of 50 kHz calls, although at a lower rate than during natural play [ 60 , 112 ].…”

Activation of the rostral nucleus accumbens shell by optogenetics induces cataplexy-like behavior in orexin neuron-ablated mice

“…The NAc plays roles in positive emotional behavior such as motivation, drug abuse, alcohol, and rewards 15 , 16 . Blockade of dopamine receptors in the NAc reduces 50-kHz USVs as a marker of positive emotion induced by tactile stimulation of the skin 17 , 18 . The dorsal NAc shell activation of dynorphinergic neurons drives reward behavior and the ventral NAc shell drive aversion in mice 19 .…”

Rats emit aversive 44-kHz ultrasonic vocalizations during prolonged Pavlovian fear conditioning

“…On one hand, long (or not that long 16 ), frequency-stable high-pitch vocalizations have been reported before (e.g. 17,18 ), notably as caused by intense cholinergic stimulation 19 or higher shock-dose fear conditioning 20 . However, they have not been systematically defined, described or demonstrated to be a separate type of vocalization.…”

“…While they wrote in the introduction that "high-pitch (>32 kHz), long and monotonous ultrasonic vocalizations have not yet been described", they wrote in the discussion that "long (or not that long (Biały et al, 2019)), frequency-stable high-pitch vocalizations have been reported before (e.g. Sales, 1979;Shimoju et al, 2020), notably as caused by intense cholinergic stimulation (Brudzynski and Bihari, 1990) or higher shock-dose fear conditioning (Wöhr et al, 2005)" (and I wish to add that to my knowledge this list provided by the authors is incomplete). Therefore, I believe, the strong claims made in abstract ("we are the first to describe a new-type..."), introduction ("have not yet been described"), and results ("new calls") are not justified.…”