Olfactory and cortical projections to bulbar and hippocampal adult-born neurons

Abstract

New neurons are continually generated in the su2ependymal layer of the lateral ventricles and the su2granular zone of dentate gyrus during adulthood. In the su2ventricular zone, neuro2lasts migrate a long distance to the olfactory 2ul2 where they differentiate into granule or periglomerular interneurons. In the hippocampus, neuro2lasts migrate a short distance from the su2granular zone to the granule cell layer of the dentate gyrus to 2ecome granule neurons. In addition to the short-distance inputs, 2ul2ar interneurons receive long-distance centrifugal afferents from olfactory-recipient structures. Similarly, dentate granule cells receive differential inputs from the medial and lateral entorhinal cortices through the perforant pathway. Little is known concerning these new inputs on the adult-2orn cells. In this work, we have characterized afferent inputs to ai-day old newly-2orn neurons. Mice were intra peritoneally injected with 2romodeoxyuridine. Two weeks later, rhodamine-la2eled dextran-amine was injected into the anterior olfactory nucleus, olfactory tu2ercle, piri form cortex and lateral and medial entorhinal cortices. One week later, animals were perfused and immuno fluor escences were carried out. The data show that projection neurons from the mentioned structures, esta2lish putative synaptic contacts onto ai-day-old neurons in the olfactory 2ul2 and dentate gyrus, in some cases even 2efore they start to express specific su2population proteins. Long-distance afferents reach middle and outer one-third portions of the molecular layer of the dentate gyrus and granule and, interestingly, periglomerular layers of the olfactory 2ul2. In the olfactory 2ul2, these fi2ers appear to esta2lish presumptive axo-somatic contacts onto newly-2orn granule and peri glomerular cells.