Structural characteristics of neurons in the feline hippocampus during postnatal ontogenesis

Abstract

Golgi studies of pyramidal and nonpyramidal neurons of the kitten hippocampus were carried out to determine the maturational status of these elements in the neonatal period and the essential morphological changes observed postnatally. Hippocampal pyramidal neurons exhibit well developed apical and basilar dendrites as well as numerous spines and axon collaterals in the newborn kitten. Nonpyramidal neurons are also well developed in all layers of the hippocampus in the neonatal period. Modified basket pyramid cells of the stratum radiatum are commonly observed in the neonatal period. These elements have extensive dendritic systems which distribute in all layers. Their axons descend to the stratum pyramidale, bifurcate, and distribute among the basilar and apical dendrites of pyramidal neurons. The multilaminate characteristics of the stratum pyramidale in the neonatal kitten are clearly revealed in Golgi studies. Cell bodies of pyramidal neurons are frequently located at a level corresponding to elaborate dendritic systems of nonpyramidal neurons, whose cell bodies may be among the largest encountered in the immature hippocampus. Wide variations in dendritic morphology are evident in pyramidal neurons of neonatal and young kittens. This is particularly evident in relationships between soma and primary dendritic branch points. These and other observations are relevant to problems of the organization of inhibitory pathways and properties of neurons in immature hippocampus as discussed in the two succeeding reports of this series.