Development of the human hypoglossal nucleus from mid-gestation to the perinatal period: A morphological study

The human hypoglossal nucleus (nXII) was morphologically examined from mid-gestation to the perinatal period.

Serial brain sections from 6 preterm and 4 perinatal infants aged 21-43 postmenstrual weeks (PW) were stained with the Klüver-Barrera method. Following microscopic observation, morphometric parameters (volume, neuronal number, and neuronal profile area [PA]) were analysed.

Two types of neurons, motor and non-motor neurons, were observed at 21 PW. The motor neurons were distributed into clusters, which were not completely separated. The non-motor neurons were dispersed among the motor neurons. Myelination of the hypoglossal nerve roots was noted at 21 PW, when degenerated neurons were sporadically encountered. To a lesser extent, they were seen until 35 PW. The nXII volume increased exponentially with age. Conversely, the neuronal numerical density decreased exponentially, while the total number remained relatively stable. The neuronal PA increased gradually, with a greater rate of increase measured in the caudal part.

In the human nXII, motor and non-motor neurons are distinguishable from mid-gestation. Then, while the nXII expands exponentially in volume, the two types of neurons change in number and PA almost in parallel during the second half of gestation. Natural neuronal death may also occur.