Playback of ultrasonic vocalisations (38-48 kHz) communicates the state of stress and impaired context episodic memory in adolescent rats.

BACKGROUND AND AIM: Maternal isolation induces ultrasonic vocalisations (USVs), and playback of these USVs can elicit response calls in receivers. In this study, we investigated whether playback of USVs (38-48 kHz) transmits a state of stress and impairs memory in receivers.

METHOD: Rat pups were exposed to playback of USVs or modified USVs on postnatal day (PND) 12, and their response calls were recorded. On PND-34, control (Ctrl), maternally separated (MS), USV playback (PB), and modified USV playback (MPB) groups were tested for context-dependent episodic memory. Additionally, molecular markers involved in synaptic plasticity were assessed.

RESULTS

Playback receivers emitted specific response calls: female pups responded with step-up frequencies (39.0-49.7 kHz) to playback of USVs and with downward trills (32-39 kHz) to modified USVs. Rats in the MS and PB groups made more incorrect choices in odour-associated context transitions and long-term memory assessments than those in the Ctrl and MPB groups. Furthermore, corticosterone (CORT) levels were elevated, whereas phosphorylation of extracellular signal-regulated kinase (ERK1/2), N-methyl-D-aspartate (NMDA) receptor subunits (NR2A,2B), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits (GLUR1, GLUR2), postsynaptic density protein 95 (PSD-95), and mature brain-derived neurotrophic factor (mBDNF) were reduced in the MS and PB groups.

CONCLUSION

USV playback can transmit stress to receivers, alter molecular signalling pathways (pERK1/2, NR2A, NR2B, pGluR1, pGluR2, pPSD95, and BDNF), and impair episodic memory. This model may help identify the neuropathology of early-life stress and the development of behavioural disorders later in life.