Adaptation and habituation to an open field and responses to various stressful events in animals with neonatal lesions in the amygdala or ventral hippocampus

A rat model of neurodevelopmental psychopathological disorders, designed to determine neurodevelopmental deficits following damage to the brain early in life, was used to investigate behavioural changes in adaptation and habi tuation to an open field and responses to different kinds of stressful even ts. Animals with bilateral ibotenic acid lesions in the amygdala or ventral hippocampus on day 7 or 21 of life were compared to sham-operated animals. According to the model it was assumed that behavioural changes in animals lesioned on day 7, but not in animals lesioned on day 21 of life, were caus ed by maldevelopment of one or more structures connected to the damaged are a. Animals lesioned in the amygdala or ventral hippocampus on day 7, but no t animals lesioned in these structures on day 21 of life, displayed decreas ed (within-session) adaptation and (between-session) habituation to the ope n field and a decrease in immobility in the forced swim test, whereas only animals lesioned in the amygdala displayed enhanced general activity. These results were indicative of neurodevelopmental deficits. No changes in stre ss-induced hyperthermia were found, while animals lesioned in the amygdala both on day 7 or 21 of life exhibited decreased conditioned ultrasonic voca lizations. These latter results suggest that the amygdala is implicated in the conditioned stress-induced response. The contribution of the present fi ndings to the animal model of neurodevelopmental disorders like schizophren ia and possible brain structures and neurotransmitter systems involved in t he neurodevelopmental deficits are discussed. (C) 2001 Elsevier Science B.V . All rights reserved.