Distinct classes of low frequency ultrasonic vocalizations in rats during sexual interactions relate to different emotional states

Abstract

This study examined low‑frequency ultrasonic vocalizations (lUSVs) in rats during two types of sexual interactions; postejaculatory interval (PEI) and barrier – noncontact (NC) test. We report distinct classes of lUSVs that can be assigned to different emotional states; relaxation vs. frustration. Totally flat, 22‑kHz calls (Class A), were observed during the relaxation state following ejaculation; characterized by immobilization or grooming during the PEI. On the other hand, two‑three component lUSVs (Class B) that start at a higher frequency (45‑kHz: flat, upward or short signal) and then shift to 35–23‑kHz (mostly to 28‑23‑kHz), correspond as we assume, to arousal and frustration – active states associated with sniffing a hole or exploration during the NC test. We suggest that momentary, abrupt decreases of arousal during the frustration state correspond to Class B lUSVs. The detailed spectral analysis of the high‑frequency component of two‑component lUSVs is crucial for establishing the relationship between such lUSVs and the corresponding behavior and emotional states. Our studies indicate that while the two‑component Class B 22‑kHz lUSVs may relate to the frustration state, a single component, flat, Class A lUSV relates to the relaxation state. The results of these studies support a notion that rats emit distinct vocalization patterns, reflecting their emotional states.