Development of the alpha7 nicotinic cholinergic receptor in rat hippocampal formation

The alpha7 nicotinic receptor has been implicated in the regulation of a variety of developmental processes. The goal of the present study was to assess whether the alpha7 receptor might participate in the regulation of hippocampal ontogeny by describing the spatiotemporal development of alpha7 mRNA and alpha-bungarotoxin binding in rat hippocampal formation. Message for the alpha7 receptor was initially observed in the hippocampal neuroepithelium at embryonic day 13 and in the anlage of the hippocampal formation on embryonic day 14. Binding of alpha-bungarotoxin was initially seen on embryonic day 15 in the dorsal portion of the anlage of stratum oriens and stratum radiatum-lacunosum moleculare, but was never observed in the neuroepithelium. Dramatic elevations in both alpha7 mRNA and alpha-bungarotoxin binding were observed in most regions of the hippocampal formation neonatally. The levels of both alpha7 message and protein gradually decreased during the first three postnatal weeks to adult levels in most regions. The lack of alpha-bungarotoxin binding in the neuroepithelium suggests that the alpha7 receptor does not influence neurogenesis. The early appearance and complex, prolonged pattern of development of the alpha7 receptor suggest that it may influence processes as diverse as cell migration, dendritic elaboration and apoptosis during hippocampal maturation.