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Psychiatric disorders like schizophrenia or autism are thought to result from disruption of the normal pattern of brain development. Abnormalities in the amygdaloid complex and hippocampus have been reported in these disorders. In the present study rats were lesioned in the amygdala or ventral hippocampus on day 7 of life (immature brain) or day 21 of life (almost mature brain) and open field behaviour was determined later in life before and after puberty. Lesioning on day 7 resulted in behavioural changes, interpreted as locomotor stereotypy and decreased anxiety in case of amygdala or hippocampus, respectively. These effects were more profoundly present after puberty. Lesioning on day 21 did not result in these behavioural changes, which subscribes to the importance of the stage of brain maturation on functional development. The results suggest that the behavioural changes in rats lesioned on day 7 may due to a malfunctioning of structures connected to the amygdala or ventral hippocampus. Brain lesions made on day 7 of life may serve as a potential model of psychopathological neurodevelopmental disorders. [Copyright &y& Elsevier]