Long-term hyperglycaemia induces qualitative and quantitative changes in rat ultrasonic vocalizations

Diabetes mellitus (DM) is currently considered a global epidemic. Recently, the relation between diabetes and mood disorders has been established, as well as a link with altered behavioural traits, that may depend on changes in the emotional state. To further elucidate the interplay between DM and changes in the emotional state, we evaluated in long-term diabetic hyperglycaemic (HG) or in control (CTRL) male rats the emission of ultrasonic vocalizations (USVs), a behavioural marker that may express the emotional states of rats and their changes. Rats were exposed to a conspecific matched for condition (i.e. HG or CTRL), to elicit calling behaviour; then, the numbers and acoustic parameters (duration, maximum frequency, minimum frequency, bandwidth) were scored for the 50-kHz USVs (appetitive) and 22-kHz USVs (aversive) emitted. Dyads of HG rats emitted higher numbers of 50-kHz USVs, compared with dyads of CTRL rats. Moreover, differences in acoustic parameters were detected between the 50-kHz USVs emitted by HG and CTRL rats. These effects were observed for the total 50-kHz USVs emitted, as well as for the flat and frequency modulated categories of 50-kHz calls. Finally, HG rats (30% of dyads) but not CTRL rats also emitted 22-kHz USVs. These findings demonstrate that long-term diabetic hyperglycaemia causes qualitative and quantitative changes in ultrasonic calling behaviour in male rats. Moreover, they suggest that measuring the emission of USVs may become an informative approach to study the effects of hyperglycaemia in rat models of DM.