[Development of neuronal structure in the hippocampus during pre- and post-natal ontogenesis in the albino rat. III. Morphometric determination of ontogenetic changes in dendrite structure and spine distribution on pyramidal neurons (CA1) of the hippocampus].

Following GOLGI impregnation pyramidal neurons of the rat hippocampus (CA1) from four stages of age (E21, P5, P10, P20) were investigated by morphometric methods with regard to their dendritic structure and amount and distribution of spines. The daesults show, that during the ontogenesis until reaching adult values the determined parameters are strongly following in their expression the sequence: degree of ramification, length of dendrites, amount of spines, and in the development of the certain dendritic parts of the pyramid the sequence: main apical dendrite with end ramifications, basal dendrites, apical lateral dendrites. Along the main apical dendrite the pattern of spine distribution develops proceeding from the form of a reverse nearly plain parabola (P5, P10) to the curve known from other adult pyramides (P20) with a spine poor initial segment, then the rapid increase in the number of spines (maximum of spine density in the middle of the whole distance), followed by a subsequent slow decrease in the number of spines. The apical end ramifications are mostly developed in the degree of ramification and length of dendrites during the prenatal period and show postnatal only significant changes in the spine density without reaching the values of the other dendritic fields. At basal dendrites no further increase in the number of dendrites can be found after P10. In dendritic length and spine density they are reaching adult level about the 20th postnatal day. In comparison with that, apical lateral dendrites show at P20 their definitive amount and a further increase of the spine density must be expected. The single dendritic fields of apical lateral dendrites are in length and total amount of spines sometimes smaller than those of basal dendrites, but more abundant. In both cases the spine densities increase until the stage P20 but they are not differing. Caused by the further development of apical lateral dendrites to adultness a predominance of the spine density of this part of the neuron is known. The total length of the dendrites of one pyramidal neuron (CA1) increases from 1000 mum (E21) to 5600 mum (P20), while the total amount of visible spines and the spine density increase from 20 to 3000 spines resp. from 0,02 to 0,55 spines/mum. It is important that the portion of the apical lateral dendrites grows from 2 to 40%, the portion of basal dendrites only from 20 to 33%, while the importance of the apical end ramifications decreases from 60 to 20%. In the presented paper the comparisons of developmental stages of the most pyramidalized hippocampal neurons (CA1) with adult pyramids of this region and with cortical pyramidal neurons of different phylogenetic ages are discussed.