Cell death in the developing trigeminal nuclear complex of the rat

The time course and distribution of cell death in the trigeminal nuclear complex of the rat has been examined with the aid of sections stained for Nissl substance and succinic dehydrogenase activity. Pyknotic figure counts in the principal trigeminal nucleus and in each of the three spinal trigeminal subnuclei revealed that cell death commences at E19, in the region of the junction between the principal nucleus and the subnucleus oralis, close to the site of entry of trigeminal afferents into the brainstem. Cell death subsequently spreads rostrally and caudally into the rest of the principal and spinal trigeminal nuclei. Cell death ceases simultaneously, at about P10, in all parts of the trigeminal nuclear complex examined. Neurons could not be reliably distinguished from glial cells in prenatal animals, but data for neuronal numbers postnatally indicate that much of this cell death is indeed due to loss of neurons. The data suggest that, in the trigeminal nuclear complex, only half the number of neurons produced survive to maturity. These findings are of significance for those investigators using this system in studies of plasticity.