glutamatergic neuron Cajal-Retzius cell A type of transient, early-born glutamatergic neuron located primarily in the marginal zone (future layer I) of the developing cerebral cortex and hippocampus in vertebrates. it is characterized by a bipolar morphology with an elongated soma, a single thick dendrite oriented toward the pial surface, and a long, thin axon that extends tangentially to form horizontal plexuses across the cortical surface. It is important for the multiple developmental processes including migration, dendritogenesis and synaptogenesis. It typically undergoes programmed cell death following cortical maturation with species- and region specific patterns of survival. In mice, it is predominantly observed in the hippocampal formation, particularly in the stratum lacunosum-moleculare and outer molecular layer of the dentate gyrus (van Bruggen et al., 2023). In contrast, in humans, a second morphologically distinct subpopulation emerges mid-gestation and persists postnatally, with surviving cells observed in the cortical sulci and the hippocampus. While previously called 'pioneer neurons' of the marginal zone, Cajal-Retzius cells are differentiated from pioneer neurons (which are Reln-negative) by their Reln-immunoreactivity. CR cells Horizontal cells of Cajal neuron of the forebrain