A comparative study of myelination in precocial and altricial murid rodents

The development of myelin staining was compared in two closely related rodent species, the precocial Acomys cahirinus and altricial Rattus norvegicus. While the progression of myelin staining was similar in both species (motor tracts myelinated before sensory systems, which were followed by forebrain fiber systems), the timing of maturation differed considerably: (1) at the same postconception age (PC38) Rattus was substantially more mature than Acomys, suggesting a relatively earlier onset of myelination in Rattus; although (2) from PC38-PC45, Acomys exhibited much more rapid growth than Rattus, indicating divergence in the rate of myelination. Both species appeared to reach maturity at a common postconception age corresponding to the time of weaning (PC45).