[Variability in the morphofunctional differentiation of the CNS in a heterogeneous population of laboratory mice].

The psychomotor maturation rate was studied in a heterogeneous stock of laboratory mice. Mean ages of several innate reflexes formation were compared for two groups of animals which represented extreme variants of brain weight phenotypes when adult. Mice with measured brain weights, by least 0.67 standard deviation higher (H) or lower (L) than the average for the whole population, reveal substantially different psychomotor development, the H-group appearing to be more advanced. This observation is at variance with those obtained using the lines of laboratory mice selectively bred for high and low brain weight. The apparent inconsistency of the two experiments may reflect the relative dominance of environmental (heterogeneous stock) or genetic (selected lines) factors, as well as occasional fixing of certain alleles in process of selection.