Strain-and context-based 50 kHz ultrasonic vocalizations and anxiety behaviour in the Wistar-Kyoto rat

Abstract

Rodent ultrasonic vocalizations (USVs) are influenced by immediate, prior contexts and have emerged as important indicators that monitor an individual's 'state'. They also index direct reflections of inherent 'trait' and are suggested to constitute non-invasive read-outs of pathological conditions. Analysis of USVs emitted under particular contexts could help discern strain-specific differences and existence of individual USV profiles. USVs of the Wistar-Kyoto (WKY) strain, a putative model of depression, could indicate social communication deficits. In the cage, USV emission was significantly reduced in WKYs. An elevated plus maze exposure led to no change in USV emission in WKYs, while it significantly reduced USVs in Wistars. Re-exposure induced strain-specific differences in behaviour and total calling time. Sonographic patterns indicated that the predominant USV subtype were flat 50 kHz USVs. EPMexposure induced a reduction in peak amplitude in WKY USVs and in USV length in both strains. USV peak frequency and amplitude, genetically determined spectral features, were strain-specific, while bandwidth and temporal features such as total calling time and USV duration were context-dependent. WKY USVs demonstrated characteristic spectral structures such as increased call length and reduced peak frequency while other parameters were not quantitatively different, reflecting the shared phylogeny between Wistars and WKYs.