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Normal development of the cerebral cortex is dependent upon reciprocal connections with the thalamus.The predominant thalamic input to the PFC is from the medial dorsal nucleus (MD: also known as medial thalamus), though medial prefrontal area 32 also makes extensive connections with the medial pulvinar.Afferents from the MD synapse on spines and dendritic shafts of pyramidal cells in the PFC.Developmental maturation of neurons is activity-dependent and an early lesion of the MD could therefore result in abnormal development of the PFC.In particular, a decrease in thalamic input to PFC may result in decrease of calcium-mediated stimulation of dendritic remodeling.We examined three rat prefrontal cortical regions at P60 that receive projections from the MD: prelimbic (homologous to human area 32) Dorsolateral Anterior cortex (homologous to Brodmann area 24b), and Cgl following a lesion at P4 to determine if an early developmental insult to the MD leads to altered development of cortical pyramidal cells.Our data suggest that the morphological alterations observed in the PFC may indeed be related to altered levels of excitatory input due to loss of projections from the MD.In addition the alterations in the prefrontal cortex appear to have an impact on development in the hippocampus in particular the dentate gyrus.Our data suggest the model as a useful too in understanding neuronal development in the prefrontal cortex and may shed light on the development of such psychiatric disorders like schizophrenia, autism and attention deficit disorder.