• ultrasonic vocalization;
  • isolation;
  • contact comfort;
  • fear;
  • rat;
  • development;
  • ambient temperature;
  • maternal potentiation


Sensory and temporal factors have been demonstrated to be involved in the regulation of isolation-induced ultrasonic vocalizations (USV) of young rats. Sensory cues include thermal, olfactory, and tactile modalities. Temporal factors include the time spent in isolation. The goal of the present research was to examine the interaction of these factors in both isolation-induced and maternally potentiated USV. Maternal potentiation of USV occurs when a brief interaction with the dam, even a passive (anesthetized) dam, elicits an augmented vocal response to a subsequent isolation, with rates of USV in rat pups well above those emitted in standard isolation tests. We found that passive maternal potentiation of USV did occur under all conditions tested. Neither a 30-min prior isolation nor high ambient temperature prevented an increase in USV rate over the rate of the original isolation. After 30-min isolation at warm temperatures when the rate of USV had fallen to zero, the pups increased vocalization in the presence of the dam as well as in the subsequent isolation. Temporal and thermal factors also interacted significantly in regulating the level of the USV emitted by the pups during the first isolation, in the presence of the anesthetized dam, and during the second isolation. © 2003 Wiley Periodicals, Inc. Dev Psychobiol 42: 206–222, 2003