Nuclear envelope invaginations in hamster facial motor neurons during development and aging.

Morphometric measurements of nuclear envelope invaginations (NEI) in hamster facial motor neurons were made. These showed that the amount of NEI increased markedly between fetal life and birth to a high level that was maintained during the period of accelerated neuronal somal growth. Subsequently, the amount of NEI decreased to a plateau of low incidence that persisted through maturity and aging. This sequence of NEI formation and subsidence differs from that previously observed in a similar developing and aging series of pyramidal neurons in the same species. This may indicate, as discussed, that the presence of NEI reflects stage-specific functions that may differ depending on neuronal type.