Altricial mammals

The newborns of birds including chickens and of some mammals such as guinea pigs and sheep can open their eyes, eat, and exhibit sleep-wake cycles similar to those found in adulthood (1—4) these animals are precocial species. The newborns of other mammals such as those of rats, cats, and rabbits are not able to open their eyes at birth and have very different sleep-wake states from their adulthood (4,5). These species are altricial mammals. There are also a variety of developmental and anatomical brain differences in altricial and precocial species that appear to relate to learning and experiential development (1). 

Considering the fact that an increase in the percentage of wake parallels the decrease of REM sleep, the wake/REM (W/R) ratio might be an important index to describe the developmental levels in altricial mammals. This ratio is about 0.4 (28%/72%) in the first 10 days of life in the rat (4), dramatically increases to 1.77 at PN 21, 3.99 at PN 26 (9), and 8.1 in adulthood (calculated from Ref. 152). This ratio is 1.0 in the human newborn and is 2.6,10.3, and 11 at PN 1, PN 14-18, and adult, respectively (calculated from Ref. 12). The developmental features of sleep-wake states suggest that the strong REM sleep propensity in neonates is progressively suppressed or that a REM sleep inhibitory process is immature in neonatal rats. 

The early VN neurones migrate by various routes and in mammals become organised into two layers, each with distinct functional attributes (Chaps. 2 and 6). Amongst marsupials, the sensory cells of an opossum appear at about one-week post-conception (Jia and Halpem, 1998). Despite their extremely altricial developmental pattern, the bandicoots dendrites produce sensory processes (Fig. 4.5) on the lumenal border of the VNO at 35 days postnatal, which in the Northern Bandicoot (Isoodon macrourus) is about 50% of pouch life (Kratzing, 1986). 

Rosenblatt l.S. (1983). Olfaction mediates developmental transition in the altricial newborn of selected species of mammals. Dev Psychobiol 16, 347-375. 

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