Development of the brain stem reticular core: an assessment of dendritic state and configuration in the perinatal rat.

The brain stems of normal newborn, 11- and 20-day-old rats were examined using Golgi techniques in the light and electron microscope. Patterns of dendritic branching and growth of brain stem reticular core neurons were analyzed by projection drawing and quantitative methods. The number of protospines and dendritic varicosities was counted on proximal and distal dendritic segments. The amount of DNA and protein in the brain stem was determined using colorimetric methods. During the course of early development, the sparsely branched reticular core dendrites extend rapidly into the neuropil. The dendritic branching of these neurons increases slightly but the number of primary dendrites remains constant. Protospine development follows a regular progression increasing in number to 11 days, then declining to 20 days as protospines are resorbed onto the dendritic surface. Dendritic varicosities often contain additional vesicles as a source of dendritic membrane and subsequent preterminal dendritic growth. The gradual decline of dendritic varicosities, first proximally then distally, indicates a shift of growth toward the distal extreme of the dendrite.