No abstract

The open-field test is a commonly used apparatus in many behavioral studies. However, in most studies, temporal changes of details of behavior have been ignored. We thus examined open-field behavior as measured by both conventional indices and 12 ethograms supported by detailed temporal observation. To obtain a broader understanding, we used genetically diverse mouse strains: 10 wild-derived mouse strains (PGN2, BFM/2, HMI, CAST/Ei, NJL, BLG2, CHD, SWN, KJR, MSM), one strain derived from the so-called fancy mouse (JFI), and one standard laboratory strain, C57BL/6. Conventional measurements revealed a variety of relationships: some strains did not show the hypothesized association between high ambulation, longer stay in the central area, and low defecation. Our ethological approach revealed that some behaviors, such as freezing and jumping, were not observed in C57BL/6 but were seen in some wild-derived strains. Principal component analysis which included temporal information indicated that these strains had varied temporal patterns of habituation to novelty.

High aggression is often linked to lowered serotonin (5-HT) neurotransmission. Although this may hold for high aggression as a trait characteristic of an individual, serotonergic activity is probably increased during performance of aggressive behavior. To test this hypothesis, first, the 5-HT1A agonist alnespirone and gamma aminobutyric acid-A agonist muscimol were administered into the dorsal raphe nucleus. These treatments, which inhibit 5-HT neuronal activity, were shown to decrease performance of aggressive behavior. Second, after a resident-intruder test, the activation of 5-HT neurons (measured by c-fos expression) was increased in high-aggressive rats, compared with low-aggressive rats or control rats that were not subjected to a social confrontation. Results show that performance of aggressive behavior increases 5-HT neuronal activity and that preventing this activation inhibits expression of aggressive behavior.

No abstract

The present study investigated the effects of variations in maternal behavior on the development of maternal behavior of female offspring in BALB/c and CBA/Ca inbred mice. In Experiment 1, we conducted fostering within or between the two strains and observed the maternal behaviors of mothers and female offspring for 2 weeks postpartum. Although fostering changed the maternal behavior of mothers in both strains, CBA mothers generally showed greater frequency of nursing posture and pup licking than BALB mothers. BALB female offspring reared by CBA mothers showed more body licking than those reared by BALB mothers, whereas fostering did not affect the maternal behavior of CBA female offspring. In Experiment 2, we examined the maternal behavior of females of F1 hybrids derived from reciprocal crosses between the two strains to confirm the maternal effect demonstrated in Experiment 1. Female F1 hybrids from CBA mothers showed more arched-back nursing, body licking, and nest building than those from BALB mothers. These results suggested that maternal care affect the development of maternal behavior in inbred mice, though the contributions of genetic and prenatal factors cannot be ignored.