Abstract. We analyzed the expression of 5-HT 2 receptors and proteins related to inactivation of 5-HT in primary cultures of mouse osteoblasts. The mRNA for the 5-HT 2A receptor was detectable in anaplastic osteoblasts as well as in differentiated and matured osteoblasts. The mRNA for the 5-HT 2B receptor and 5-HT transporter was undetectable in anaplastic osteoblasts and became detectable in differentiated and matured osteoblasts. It was suggested that 5-HT might regulate the proliferation of anaplastic osteoblasts through the 5-HT 2A receptor without control by 5-HT-inactivating mechanisms. The differentiation and maturation of osteoblasts might be regulated by the activation of the 5-HT 2B receptor under the control of 5-HT inactivation.

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We evaluated the effects of sound noise or forced swim stress applied to pregnant mice or to neonatal mice on the anxiety-related behavior using the elevated plus-maze test performed during the age of 5 weeks. The forced swim stress applied at the late gestation period, days 10-18 of pregnancy, caused a significant reduction of the body weight gain of the dams. However, the anxiety-related behavior of the male and female offspring were not affected by the antenatal stress treatment. When the forced swim stress was applied to the neonatal mice during the late lactation period, 14-18 days after birth, the male mice showed an elevated level of anxiolytic behavior accompanying the reduction of the emotion-related motor activity. The anxiety-related behavior of the female mice was not affected by the stress treatment. Furthermore, we applied the sound noise or forced swim stress to the neonatal mice immediately after the weaning, 21-25 days after birth. The stress applied after the weaning period had no effect on the anxiety-related behavior. These results suggested that the stress applied during the lactation period, but not that during the antenatal period, nor after the weaning period, might have gender-dependently reduced the anxiety level of the male mouse. It was shown that the effects of perinatal stress on the anxiety-related behavior of the adolescent mouse varied according to the period of application and gender. The hypothesis that gender-dependent abnormalities in neurodevelopment might be caused by the excess stress applied to the breast-fed infant is of importance in elucidating the relationship between the psychoneurotic disorder in childhood and the environment stress of the breast-fed infant.

We examined the effects of perinatal stress on the emotion-related behavior of the mouse during their adolescent period. Firstly, we applied the sound noise and/or the forced swim stress to the maternal pregnant mice in the pregnant mice at 10 to 18 d gestation. The stress applied during the fetal period did affect neither the spontaneous locomotor activity of the offspring mice in a new environment at an age of 4 weeks, nor those soundinduced changes in the locomotor activity. Secondly, we applied the stress to the neonatal mouse during the late lactation period, 14 to 18 d after birth. The mice that underwent the forced swim stress accompanied by the sound noise stress showed a significant reduction of the locomotor activity. On the other hand, the mice that underwent the forced swim stress during the lactation period showed a significant increase in the locomotor activity after the stimulation by the sound noise. Lastly, we applied the stress to the neonatal mouse immediately after the weaning period, 21 to 25 d after birth. The spontaneous locomotor activity of the mice was not changed compared to that of the non-stressed group. Thus, it was found that the stress applied to the mice during the lactation period, thought to be the critical period of mouse brain development, selectively influenced the emotion-related behavior in the subsequent adolescent period. These results suggested that second postnatal week may be the critical period for establishing proper behavioral responses to emotional stress in the adolescent mouse.