The present study aimed to clarify the connection between immune responses and the administration frequency of methamphetamine (MAP) in

Ultrasonic vocalizations (USVs) are essential communicative sounds used between rodent pups and their mother. Rat pups emit USVs in stressful situations, such as when they are cold or separated from the nest. We verified the ontogenetic changes in USVs emitted by infant rats isolated from their mother during the pre-weaning period. The number of calls, and the median frequency and first peak of frequency of the calls were measured at 1, 3, 5, 7, 10, 12, and 14 days postnatal age in Wistar-Imamichi rats. Pups were placed in a cold glass beaker and USVs were recorded for 5 min. The number of calls increased to a peak on day 5 and then gradually decreased. The median frequency of calls decreased slowly during the first 12 days, and then increased slightly on day 14. Similarly, the first peak frequency of calls was the highest on day 1, and then decreased gradually by day 12. A small increase was observed on day 14. These changes in frequency were correlated with the physical development of the pups, whose body weights increased significantly with age except during postnatal days 7-10.

Ontogenetic changes of USVs were investigated to establish an index of stress in infant rats. The USVs were obtained by exposing infant rats to cold stress and were analyzed by real-time spectrography. USV waveforms consisted of four types, R-I, II, III and IV. These USVs were closely monitored at the age of 3-7 days in both sexes. From day 14, the frequency and incidence of USVs gradually decreased and had disappearedcompletely at the age of 21 days. Therefore, USVs should be useful in estimating the stress of infant rats between the ages of 3-7 days.

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