Programmed cell death enhances uniformity in rat cerebral hemispheres.

Programmed cell death (apoptosis) in rat cerebral hemispheres (CH) reportedly occurs around postnatal day 7 and kills 15-75% of all cells whose continuing presence would be of disadvantage for the organism: neurons erroneously connected, or supranumerary neurons that do not find targets and are not protected by neurotrophins. In the present paper we report that apoptosis (or a concomitant phenomenon) reduces also variability (coefficient of variation, CV) of CH parameters: weight, DNA content and protein content (presented here as a percent of the mean of each of these parameters). Postapoptotic brains have significantly lower CV of these parameters than the preapoptotic brains.

Quantitative study of DNA contents (cell numbers) in parts of the rat brain.

DNA contents (cell numbers) of rat brain parts were determined for cerebral hemispheres, cerebral cortex, cerebellum, and brain stems at postnatal ages 30, 60, 90, and 120 days. It was found that for all these parts these contents reach their maxima (maturation plateaux) at the same age (weaning; 30 days). Thus, cells in these brain parts attain mature numbers in concert.

Neonatal brain parameters: outstanding tails of normal distribution.

Previous studies were concerned with distribution curves of values of brain parameters (weight, DNA or cell number, and protein) in a population of 720 neonatal rats. These values followed normal distribution curves, and the tails of such curves, with values in excess of two standard deviations (SD) above (right hand) or below (left hand) the mean (X), were statistically significant. In the present work a larger sample (1,948) of neonatal rats, with particular reference to those whose brain parameters exceeded three SD above or below X, respectively, was examined.

Differential effects of chronic ingestion of tritiated water on prenatal brain development.

Female rats were given tritiated drinking water (3 microCi/ml) from 30 days before mating up to and throughout pregnancy. At this low dose, the course and the outcome of pregnancy were normal. The differences between newborn body and cerebral weights of the treated rats and those of control animals were on the borderline of significance.

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.