Involvement of Cajal-Retzius neurons in spontaneous correlated activity ofembryonic and postnatal layer 1 from wild-type and reeler mice

Cajal-Retzius (CR) cells are a transient population of neurons in developin g cortical layer 1 that secrete reelin, a protein necessary for cortical la mination. Combining calcium imaging of cortical hemispheres and cross-corre lation analysis, we previously found spontaneous correlated activity among non-CR neurons in postnatal rat layer 1. This correlated activity was block ed by GABAergic and glutamatergic antagonists, and we postulated that it wa s controlled by CR cells. We now investigate the correlated activity of emb ryonic and postnatal layer 1 in wild-type and reeler mice, mutant in the pr oduction of reelin. We find that mouse layer 1 also sustains patterned spon taneous activity and that CR cells participate in correlated networks. Thes e networks are present in embryonic marginal zone and are blocked by GABAer gic and glutamatergic antagonists. Surprisingly, network activity in reeler mice displays similar characteristics and pharmacological profile as in wi ld-type mice, although small differences are detected. Our results demonstr ate that the embryonic marginal zone has correlated spontaneous activity th at could serve as the scaffold for the development of intracortical connect ions. Our data also suggest that reelin does not have a major impact in the development of specific synaptic circuits in layer 1.