Effects of neonatal thermal lesioning of the mesocortical dopaminergic projection on the development of the rat prefrontal cortex.

The role of dopamine (DA) in the development of the prefrontal cortex (PFC) was investigated by depleting the dopaminergic innervation of the PFC. A new stereotaxic procedure made it possible to produce small lesions in 1-day-old rats confined to the A10 group of dopaminergic cell bodies in the ventral tegmentum, from which the dopaminergic projection to the PFC originates. The variety in the lesions revealed a clear topographical organization of the efferent connections of the ventral tegmental area (VTA) to the prefrontal cortex. As far as we know from the literature the data presented in this study are a first direct indication of a neurotrophic role for dopamine in the development of the prefrontal cortex. When the prefrontal cortex was depleted of the dopaminergic innervation from birth on, by lesioning the cells of origin on postnatal day 1, the cortical thickness in the medial PFC was reduced by about 6%. Although coagulative lesions in the ventral tegmentum cause also a depletion of cortical serotonin, cortical reduction seems to be rather the result of the absence of dopamine during its development. This is indicated by the absence of a significant cortical thickness reduction in the dysgranular part of the first somatosensory cortex, which receives a serotonergic but no dopaminergic innervation.