Geometrical and topological characteristics in the dendritic development of cortical pyramidal and non-pyramidal neurons.

Publisher Summary This chapter deals with regression or reduction in the size of dendritic fields in some cell types during normal development, while the general developmental characteristics of cortical neurons are also discussed. Developmental characteristics are illustrated using data from layer II/III pyramidal neurons, layer IV multipolar non-pyramidal neurons, small layer V pyramidal neurons and large layer V pyramidal neurons in rat visual cortex. These neurons show some different developmental characteristics. The data available concerning cortical dendrite development describe that, irrespective of birth date or an earlier start of dendritic maturation, the phase of rapid dendritic growth ends around the same age for all types of cortical pyramidal and non-pyramidal neurons. In general, the mode of branching appears to be the same for all the types of cortical neurons examined at the various ages studied, i.e. mainly random branching at the terminal segments. However, the branching probability per dendritic unit of length is lower in non-pyramidal neurons, resulting in fewer bifurcations per dendrite. The results indicate the occurrence of some regression in the basal dendrites of pyramidal cell types during normal development and puberty. The major part of dendritic development appears to follow an intrinsic ‘program’ which can be modified, however, by environmental influences without altering the mode of branching.