Postnatal development of quantitative morphological parameters in the lateral geniculate nucleus of the marmoset monkey.

Quantitative morphological parameters were studied in the lateral geniculate nucleus (LGN) of the marmoset monkey (Callithrix jacchus) during development, using a series of 14 animals, at ages from birth to adulthood. They include the volume of the LGN and of its layers and interlaminar zones, their neuronal content expressed as numerical density and total number, and the density and number of glial cells in the nucleus as a whole. The volume of the LGN increases rapidly after birth, reaches a maximum at 6 months of age, and then decreases to its adult value of about 11 mm3. Neuronal density follows a reciprocal curve, reaching an adult value of about 41,000 neurons/mm3, so that the total number of about 440,000 neurons per LGN remains constant throughout life although large interindividual variations, especially in juveniles, do not allow unequivocal statements about total neuronal number to be made. Parvocellular layers occupy most of the geniculate volume, and contain about 74% of its neurons in the adult. We found no difference in their development pattern compared with the magnocellular component. The 'superficial' layers and interlaminar zones contain more than 15% of the geniculate neurons, and they could therefore play an important functional role in the primary visual pathway of New World primates. The number of glial cells nearly triples during the first 6 weeks and stabilizes around 800,000 in the LGN of one hemisphere. As the same brains were used as in a previous study on the area 17 of the marmoset (Dev. Brain Res., 29 (1986) 173-188) direct comparisons of the development of cortex and thalamus can be made. Their development is parallel in time, and in both cases the adult values for volume, neuronal density and glial numbers are reached several months postnatally.