Abstract
In the present study, newborn rats were implanted with corticosterone (CORT) containing polymers at postnatal day 0 (releasing rate 320-80 μg CORT/kg body weight and day). Controls received a CORT-free implant. All implants were removed at postnatal day 12. At the age of 16-20 weeks, these animals were tested for emotional behavior using an elevated plus-maze and fear-sensitized acoustic startle response. On the elevated plus-maze significant differences were found between hormone treated and control animals. The CORT-group demonstrated higher numbers of entries into closed arms and all arms, and the time spent in the center of the maze was significantly enhanced. Hormone-treated and control rats showed a significant fear sensitization of the acoustic startle response. However, no significant differences were observed between the two groups. The number of CRF-immunopositive neurons in the central nucleus of the amygdala was decreased after CORT treatment, whereas the number of NPY-immunopositive neurons and total number of neurons in the amygdala did not differ significantly between both groups. In conclusion, early postnatal stress induced by CORT administration in neonatal rats led to a higher locomotor activity correlated with changes in the number of CRF containing neurons in the central nucleus of the amygdala.