Ontogenesis of the myenteric plexus in the cat gastro-intestinal sphincters. II. Axonal differentiation

The differentiation of the axons in the cat myenteric ganglia of the gastro-intestinal sphincters has been examined during pre- and postnatal development. The quantitative analysis has been also used. The differentiation of the axons was a prolonged process that advanced parallel to the maturation of the myenteric nerve perikarya and dendrites. The early fetal period was marked by axonal growth cones. Regardless of the fact that during the development their frequency decreased at the expense of axon varicosities, growth cones were also observed in the first postnatal month. The formation of the axon varicosities was intensive in the late fetal period and in the first weeks after birth. This was judged from the changes in the volume fraction of the varicosities to total neuropil and the number of the varicosities per 100 sp x micrometer of neuropil. The maturation of the varicosities exhibited a longer course which was evident from the changes in the number of the vesicles and in the varicosity area. The cholinergic varicosities differentiated first and most quickly. The so-called p-type varicosities appeared as early as the fetal period, but their number continued to increase after birth. The adrenergic varicosities developed most slowly, which was confirmed by the experiments with 6-OHDA. The axons differentiated with a different speed in the three sphincters examined.