The noradrenergic system influences the fate of Cajal-Retzius cells in the developing cerebral cortex.

Cajal-Retzius cells are neurons prominently located in layer I of the developing cerebral cortex. They are the first neurons to be born in the cortex reaching maturity long before any other cortical neuronal cell type; later in development they degenerate and/or change phenotype. The noradrenergic system, which originates in the locus coeruleus in the brain stem, is one of the earliest axonal systems to enter the cortex forming contacts with Cajal-Retzius cells in layer I. Here we followed the course of development of the Cajal-Retzius cells in postnatal life in animals depleted of noradrenaline in the cortex. We found that removal of this system after birth resulted in significantly more Cajal-Retzius cells during the first 2 weeks of life. This may be due to the observed decline in the number of dying cells in layer I of these animals during the same period. We speculate that the noradrenergic system regulates the development of Cajal-Retzius cells which have been implicated in neuronal migration and laminar formation in the cerebral cortex.