Embryonic and postnatal development of afferent innervation in cat vestibular receptors.

The maturing process of afferent innervation of the vestibular sensory cells in the cat was studied during both the fetal and postnatal stages. Although the type II cells from the 36th day of gestation already have an innervation similar to that found in the adult, it is not the same for the type I receptor cells. Only 75% have a complete innervation from the 7th postnatal day onwards. Most often, the formation of a continuous nerve calyx is caused by the fusion of the neighbouring membranes of the different dendritic elements belonging to the same neuron. Following the polyneuronal innervation of certain type I cells, numerous competition phenomena can be seen between the fibre endings coming from different neurons. The hypothesis that, during ontogenesis, type I cell innervation passes through a stage which corresponds to type II cell innervation is presented in the Discussion.