Divergent pattern of development in rats and humans.

Rattus norvegicus is the second most used laboratory species and the most widely used model in neuroscience. Nonetheless, there is still no agreement regarding the temporal relationship of development between humans and rats. We addressed this question by examining the time required to reach a set of homologous developmental milestones in both species. With this purpose, a database was generated with data collected through a bibliographic survey. This database was in turn compared with other databases about the same topic present in the literature. Finally, the databases were combined, covering for the first time the entire development of the rat including the prenatal, perinatal, and postnatal periods. This combined database includes 497 individual dates for both species. The developmental relationship between humans and rats was better fit by a logarithmic function than by a linear function. Also, an inflection point close to birth becomes evident after the logarithmic transformation of the data. The predictions of the proposed model were compared with other estimators historically used to calculate developmental relationships, such as growth in brain weight, finding a notorious discrepancy. As development progresses, an increase in the dispersion of the data is observed. Until now, developmental relationships have been interpreted as a univocal equivalence. In this work, is proposed an alternative interpretation where the age of one species is translated into a range of ages in the other.