[Development of neuronal structure in the hippocampus during pre- and post-natal ontogenesis in the albino rat. II. Neurohistological demonstration of the development of interneurons and of the relationship between long- and short-axonal neurons].

In this paper qualitative results are presented from GOLGI preparations by light microscopic evaluation about the appearance and the ontogenetic changes on GOLGI-II-type neurons of the rat hippocampus from 15 stages of age between the 20th embryonic and the 20th postnatal day. Interneurons are already detectable in all the hippocampal regions in the prenatal period. Their postnatal growth expresses above all in lengthening rather than in multiplication of the amount of dendrites. Cells predetermined for developing spines show already early in the postnatal period a rather large amount of spines. The further multiplication of the spine density remains minimal that never values of adult pyramids will be reached. The form of the dendritic and axonic fields of neurons with short axons is very variable. Nevertheless three main categories of GOLGI-II-type neurons can be distinguished: 1. neurons, the axonic and dendritic ramifications of which strongly remain within the layer (do not exist within the stratum pyramidale), 2. neurons, which are able to contact afferent fibres in other layers by means of ascending and/or descending dendrites, 3. basket cells, the axons of which have direct influence on the perikarya of pyramidal neurons. Within the region CA4b interneurons of the 2nd group could be found, dendrites of which penetrate into layers of the fascia dentata. Such a fact does not exist at the multipolare, efferent neurons of the same region and could never be seen at any axonic ramification. In the presented paper aspects of influencing the maturation of pyramides by interneurons are discussed. Also has been tried to summarize the results about the neuronal structure of the rat hippocampus by schemes of frontal sections from four selected stages of age.