Spinogenesis and pruning in the primary auditory cortex of the macaque monkey (Macaca fascicularis): An intracellular injection study of layer III pyramidal cells

Recently we demonstrated that neocortical pyramidal cells in visual, visual association and prefrontal cortex of the macaque monkey are characterised by different growth, branching, spinogenesis and pruning during development. Some neurons, such as those in the primary visual area, prune more spines than they grow following sensory onset, while others such as those in area TE grow more than they prune. To what extent these different neuronal growth profiles may vary among cortical areas remains to be determined. To better comprehend the nature and extent of these regional differences in pyramidal cell growth profiles we expanded the bases for comparison by studying neurons in the primary auditory cortex (A1). We found that pyramidal cells in A1 continue to grow their basal dendritic trees beyond the peak period of spinogenesis (3¹/₂ months) up until at least 7 months of age. Likewise, the most prolific branching patterns were observed in the dendritic trees of pyramidal cells at 7 months of age. These data reveal that the basal dendritic trees of cells in A1 continue to grow for a much longer period, and attain almost double the number of spines, as compared with those in V1. Such differences in the growth profiles of neocortical pyramidal cells among cortical areas may influence therapeutic outcomes when applying new technologies such as neurotrophic delivery devices or stem cell therapy.