Ontogeny of open field activity in rats after neonatal lesioning of the mesocortical dopaminergic projection.

In order to examine the effect of neonatal depletion of the dopaminergic mesocortical projection on the development of a prefrontal cortex-mediated behaviour the ontogeny of open field behaviour was studied after neonatal depletion of cortical dopamine. Cortical dopamine was depleted by neonatal thermal lesions of the ventral tegmental area (VTA). Medial VTA lesions caused a moderate dopamine depletion in the prefrontal cortex and an almost complete cortical serotonin depletion, and resulted in transient hyperactivity in the open field at postnatal day 25. More extensive VTA lesions produced an almost complete depletion of dopamine in the prefrontal cortex, but also affected the dopaminergic innervation of the nucleus accumbens, and resulted in a permanent hypoactivity in locomotor and exploratory behaviour in the open field. The effects of neonatal lesions of the mesolimbocortical projection are quite different from those made in adulthood. These results indicate in addition that, apart from the dopamine/noradrenaline balance, the serotonin/dopamine interactions in the frontal cortex may also be of importance in regulating open field activity.