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.