has characteristic 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 Cajal-Retzius cells are unique, early-born neurons found within the developing cerebral cortex and hippocampus. They are named after Santiago Ramon y Cajal and Gustaf Retzius, who first discovered them independently in the late 19th century. These neurons are characterized by horizontally oriented bipolar or multipolar cell bodies, facilitating their function in structuring the architecture of the cortex. The primary role of Cajal-Retzius cells is to mediate the correct formation of the cortical layers in the developing brain. They accomplish this chiefly through the secretion of the extracellular matrix protein Reelin, which interacts with receptors on migrating neurons to control neuronal migration and position. The Reelin signal provided by Cajal-Retzius cells is essential to establish the cortical plate, where new neurons arising from the ventricular zone accumulate and form the recognizable layered structure of the cortical region. Disruptions in Reelin signaling can lead to reeler-like phenotypes characterized by inversion of cortical layers, demonstrating the importance of these cells during normal brain development. In addition to layer formation, Cajal-Retzius cells also play a role in synaptic plasticity, which is a key aspect of learning, memory, and cognitive function. It has been suggested that these cells are involved in establishing the first functional synapses in the developing cortex, providing initial neural network activity. Furthermore, they have been linked to the modulation of gamma-aminobutyric acid (GABA) trafficking, excitatory-inhibitory balance, and thus, the fine-tune of the neural network activity during early postnatal life. Despite their disappearance shortly after birth in rodents and during early adolescence in humans, Cajal-Retzius cells lay the groundwork for the structure and functionality of the brain's cortical region. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) https://cellxgene.cziscience.com/cellguide/CL_0000695 Horizontal cells of Cajal ZFA:0009300 neuron of the forebrain cortical bipolar morphology