Quantitative developmental studies of feline neostriatal spiny neurons.

This research documents aspects of the quantitative development of the 'medium' spiny neuron in the kitten from 2 to 143 days of age. Using material derived from 244 Golgi-impregnated neurons in 15 kittens and with computer assistance the changes in somatic, dendritic and spine development were quantified. Although mean somatic diameter increased only slightly from 2--3 to 8--10 days of age, the proportion of neurons with large diameters increased significantly during the developmental period. In addition, the radius of the dendritic field of caudate spiny neurons increased significantly over the age period examined. An unexpected finding was that the number of dendrites per neuron decreased with age, probably due to a decrease in the proportion of neurons with 6 or more dendrites in animals 90--143 days of age. Growth of dendritic segments occurred throughout the age period studied. This growth was apparently caused by lengthening of all dendritic segments and this resulting increase was proportional to the initial length of the individual branches. Number of branches per dendrite and frequency of dendritic branches with different orders remained constant across age indicating that the basic dendritic branching pattern is probably set for the cat before birth. With maturation the density of spines on distal dendritic branches increased while on proximal dendritic branches spine density decreased. The time course of these quantitative changes was related to alterations in synaptogenesis and physiological changes in caudate neurons.