Quantitative changes in morphological parameters in the developing visual cortex of the marmoset monkey.

Several quantitative morphological parameters were measured during postnatal development in area 17 of the marmoset monkey (Callithrix jacchus). In a series of 14 animals, at ages from birth to adulthood, we studied changes in the thickness, surface area and volume of area 17, as well as the neuronal and glial numerical densities, and total numbers. We found evidence for a rapid increase in thickness, area and volume, culminating between 6 weeks and 6 months postnatally, and then decreasing. The adult values are close to those observed in one-month-old animals. The overshoot in thickness and volume is greatest in layers II, III, IVa and IVc. The neuronal density shows a trend which is opposite to that of volume, and therefore the total number of neurons is constant postnatally, ca. 38 million neurons in area 17 of one hemisphere. The number of glial cells approximately doubles during the first postnatal month and remains stable afterwards, so that in the adult, there is one glial cell for two neurons. Morphological development of area 17 in this New World monkey is similar to that reported in Old World monkeys, as are the adult values for neuronal and glial densities.