Development of ultrasonic vocalization responses in genetically heterogeneous National Institute of Health (N:NIH) rats. II. Associations among variables and behaviors

In this study, the first three generations of laboratory-reared, 10-day-old pups of the N:NIH strain were examined for ultrasonic vocalizations (USV) rates in response to 2 min of isolation. The purpose of the study was to determine baseline USV rates in these progenitor (PR1, PR2, PR3) generations prior to selective breeding for high and low rates of USV. In addition, this study aimed to detect sources of variation in USV between and within generations and sexes, and factors associated with USV during isolation across the generations. Data were collected from 532 10 day-old pups in 81 litters. Evaluation by principal component analyses revealed four factors corresponding roughly to constructs indicative of: thermoregulation; maturity and exploratory behavior; distress/anxiety, in which USV consistently appeared; and activity. Different component structures for each sex suggested that USV may represent different dimensions of anxiety for component structures for each sex suggested that USV may represent different dimensions of anxiety for the sexes, with some degree of overlap. Nonetheless, all variables measured during isolation testing accounted for only a small portion of the variance in individual pup USV (less than 9%) at 10 days of age, when the effects of intercorrelations among all variables were taken into account. This suggests that variables currently measured do not represent a comprehensive model for the control of USV.