Timing of neurogenesis is a determinant of olfactory circuitry.

An odorant receptor map in mammals that is constructed by the glomerular coalescence of sensory neuron axons in the olfactory bulb is essential for proper odor information processing. How this map is linked with olfactory cortex is unknown. Using a battery of methods, including various markers of cell division in combination with tracers of neuronal connections and time-lapse live imaging, we found that early- and late-generated mouse mitral cells became differentially distributed in the dorsal and ventral subdivisions of the odorant receptor map. In addition, the late-generated mitral cells extended substantially stronger projections to the olfactory tubercle than did the early-generated cells. Together, these data indicate that the odorant receptor map is developmentally linked to the olfactory cortices in part by the birthdate of mitral cells. Thus, different olfactory cortical regions become involved in processing information from distinct regions of the odorant receptor map.