Early postnatal development of EEG and sleep-waking cycle in two inbred mouse strains.

The postnatal maturation of brain electrical activity and sleep-waking cycle were studied in two inbred mouse strains (C57BL and BALBc), previously differentiated in their sleep patterns at adult age. Genetic differences are evident during the first postnatal period (until day 12) in the maturation of electrical activity which is both earlier and slower in C57BL than in BALBc. On the other hand, from day 12 onwards, as soon as the sleep-waking cycle can be defined by using EEG morphology to select quiet sleep (QS) and active sleep (AS) C57BL is characterized by a higher amount of AS and a lower amount of waking (W) than BALBc, as found in juvenile and adult mice. These differences appear a little later when the recordings are performed on animals which are isolated instead of being left with the rest of the litter.