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. Presumably, this trend toward uniformity offers selective advantages (for rat) and established itself during evolution. The mechanisms and the control of this phenomenon are at present largely unknown.