Developmental and age-related changes in morphometry and cellular density of the vestibular ganglion in the chick

Vestibular ganglia at different stages of development in the chick and that of the adult were fixed in formal-saline. Serial sections were taken and stained by cresyl fast violet to analyze the results. Cells were categorized and counted. Ganglionic volume is the greatest on E18 during the whole ontogeny even though its rostrocaudal length is the greatest in the adult. This is quite different from that observed in other ganglia studied where the ganglionic volume is the greatest in the adult situation. The increased size of the ganglion on E18 might be related to the increased size of the cells, increased size of the neuropil (network of neuronal processes and neuroglia) and to the effects of tissue reactions resulting from the toxic substances of the dead cells. The loss of cells in the adult in comparison to that observed on the day of hatching might indicate a functional reduction as a result of aging process. The fluctuation in the number of cells during development might be considered as a normal process for the purpose of re- arrangement for better organization in order to perform an efficient function. The cell-loss has essentially ended around E15 by the time the ganglion begins to show its greatest expansion so as to reach its maximum size on E18. The appearance of a few light cells in the vestibular ganglion on E6 might indirectly indicate the beginning of an early establishment of a functional connection. This might possibly mean that an early development of functional organization of the vestibular ganglion is an important factor for the proper development of other organs and systems during embryonic development. The appearance of an increased number of tiny cells in the adult ganglion is peculiar from that observed in other ganglia studied; possibly these tiny cells, by their growth, maturation and establishment of functional connections, replace those inactive (or dead) cells, during ageing process. Possibly, continuation of an efficient vestibular function is important for the normal behaviour of the animal.