Regional distribution of [3H]naloxone binding in the brain of a newborn rhesus monkey.

The distribution of opiate receptors in the brain of a newborn monkey (Macaca mulatta) was mapped by in vitro autoradiographic localization of [3H]naloxone binding to tissue sections. The autoradiographs of the newborn brain were compared to those from two adult brains. The distribution of opiate receptors appeared to be adult-like in subcortical structures (both limbic and nonlimbic) and allocortical areas. By contrast, all neocortical areas, except the primary visual cortex, lacked at birth the laminar specific patterns that characterize the adult. The results therefore suggest that, like many other aspects of neocortical maturation, such as dendritic growth, synaptogenesis, myelination and neurotransmitter concentrations, the distribution of opiate receptors continues to develop postnatally.