Stimulus-seeking in rats is accompanied by increased c-Fos expression in hippocampal CA1 as well as short 22 kHz and flat 50 kHz calls

Abstract

We determined CA1 hippocampal field to be involved in self-exposure, a type of novelty-seeking behaviour that has also been associated with short 22 kHz and flat 50 kHz ultrasonic vocalizations (USV) in adult male Long-Evans rats. Rats were habituated for three days to a self-exposure cage with two nose-poke holes. On day four, the animals from the experimental group were allowed to turn the cage light off for 5 s with a nose-poke (test/self-exposure session), while rats from control-yoked group had changing light conditions coupled and identical to the experimental animals. The experimental rats performed more nose-pokes during self-exposure session than animals from the control group. This effect was accompanied by a higher density of c-Fos-positive nuclei in the hippocampal CA1. There were no significant group differences in c-Fos expression in other brain regions analysed. However, possible involvement of several other structures in self-exposure (i.e., CA3, the dentate gyrus, amygdala, prefrontal cortex, and nucleus accumbens) is also discussed, as their correlational activity, reflected by c-Fos immunoactivity, was observed in the experimental rats. During test sessions, there were more nose-pokes accompanied by short 22 kHz calls and 50 kHz calls performed by the rats of the experimental group than of the control group. The CA1 region has previously been associated with novelty; short 22 kHz USV and flat 50 kHz USV could be associated with self-exposure, also they appear to be emitted correlatively.

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

“…In a recent experiment in a semi-novel environment, i.e., in a cage that had holes in the walls and was familiar to the rats but the lighting was changed so that the illumination of the cage had a novel element, rat ultrasonic vocalizations were recorded. Any time the experimental animal nose-poked the hole, the light was switched off for 5 s. The yoked control group was unable to switch the light off, but the on–off lights were controlled by the experimental group of animals [ 97 ]. It was found that rats that could control lighting performed more nose-pokes and emitted more vocalizations than the yoked rats.…”

“…10–20 ms in duration) as compared to the control yoked group. Although the behavioral situation was not a typical novel environment, there was an element of novelty and novel exploration, and it was associated with calling [ 97 ]. It was concluded that 50 kHz calls and short 22 kHz calls could be associated with the investigative function and novelty seeking.…”

Response Calls Evoked by Playback of Natural 50-kHz Ultrasonic Vocalizations in Rats

“…Interestingly, it was shown that rats emit 22-kHz as well as 50-kHz USV during neutral situations and not only aversive ones (Robakiewicz et al, 2019). The study by Robakiewicz et al (2019) also showed that both call types and hence presumably both emotional states can be present during an emotional neutral task of performing nose pokes in order to change the light of the experimental apparatus. Both call types were also found in a cocaine self-administration task (Barker et al, 2010), where animals received either high or low doses of cocaine.…”

“…This is also reminiscent of an approach/avoidance conflict, i.e., a situation characterized by choices leading to either reward or punishment (Aupperle et al, 2015). Interestingly, it was shown that rats emit 22-kHz as well as 50-kHz USV during neutral situations and not only aversive ones (Robakiewicz et al, 2019). The study by Robakiewicz et al (2019) also showed that both call types and hence presumably both emotional states can be present during an emotional neutral task of performing nose pokes in order to change the light of the experimental apparatus.…”

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

“…The other system responsible for the stress response is the autonomic nervous system (especially the sympathetic branches). In future experiments, it would be interesting to compare the neuronal structure or activities in the relevant brain areas, eg, the basolateral amygdala [35,36], perirhinal cortex [37], or hippocampus [38], etc. One weakness of this study is that the WH rats were significantly older than the SD rats.…”