Quantitative studies of mitoses: hippocampus of neonatal rat

In continuation of our quantitative studies of mitoses in 15-day fetal rat brain, we have now studied mitoses in hippocampus of neonatal rat. In contrast to cortex in which neuroblast mitoses terminate prenatally, hippocampus in rodents has been known to exhibit mitoses well past birth. Our present study suggests that at birth (rat) 61% of these mitoses are situated in the medioventral tip of the germinal (ventricular and sub-ventricular) zone of lateral ventricle. However, the remaining 39% of mitoses may not be neural but represent mitoses of brain capillaries, similar to "deep mitoses" which we reported in 15-day fetuses. Like these, some of the neonatal mitoses are situated not in the germinal layer of the ventricle, but 44 +/- 21 microns deeper, near Ammon's horn or dentate gyrus; also, as in these previous studies, the spindles of all deep mitoses are not parallel to ventricular or hippocampal structures but perpendicular, presumably to promote their radial expansion known for capillaries at that age. Possibilities are considered that capillary cells are produced in excess and eventually undergo natural "capillary death", to follow natural "neuronal death".