Aging results in reduced epidermal growth factor receptor signaling, diminished olfactory neurogenesis, and deficits in fine olfactory discrimination.
Previous studies demonstrating olfactory interneuron involvement in olfactory discrimination and decreased proliferation in the forebrain subventricular zone with age led us to ask whether olfactory neurogenesis and, consequently, olfactory discrimination were impaired in aged mice. Pulse labeling showed that aged mice (24 months of age) had fewer new interneurons in the olfactory bulb than did young adult (2 months of age) mice. However, the aged mice had more olfactory interneurons in total than their younger counterparts. Aged mice exhibited no differences from young adult mice in their ability to discriminate between two discrete odors but were significantly poorer at performing discriminations between similar odors (fine olfactory discrimination). Leukemia inhibitory factor receptor heterozygote mice, which have less neurogenesis and fewer olfactory interneurons than their wild-type counterparts, performed more poorly at fine olfactory discrimination than the wild types, suggesting that olfactory neurogenesis, rather than the total number of interneurons, was responsible for fine olfactory discrimination. Immunohistochemistry and Western blot analyses revealed a selective reduction in expression levels of epidermal growth factor (EGF) receptor (EGFR) signaling elements in the aged forebrain subventricular zone. Waved-1 mutant mice, which express reduced quantities of transforming growth factor-alpha, the predominant EGFR ligand in adulthood, phenocopy aged mice in olfactory neurogenesis and performance on fine olfactory discrimination tasks. These results suggest that the impairment in fine olfactory discrimination with age may result from a reduction in EGF-dependent olfactory neurogenesis.
Enwere
Emeka
E
Genes and Development Research Group, Department of Cell Biology and Anatomy, University of Calgary Faculty of Medicine, Calgary, Alberta T2N 4N1, Canada.
Shingo
Tetsuro
T
Gregg
Christopher
C
Fujikawa
Hirokazu
H
Ohta
Shigeki
S
Weiss
Samuel
S
D000375:Aging / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D002452:Cell Count; D049109:Cell Proliferation; D002478:Cells, Cultured; D004192:Discrimination, Psychological / Q000502:physiology*; D066246:ErbB Receptors / Q000378:metabolism*; D006579:Heterozygote; D007395:Interneurons / Q000166:cytology / Q000378:metabolism; D020547:Lateral Ventricles / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D053680:Leukemia Inhibitory Factor Receptor alpha Subunit; D051379:Mice; D008815:Mice, Inbred Strains; D008817:Mice, Mutant Strains; D009830:Olfactory Bulb / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D018121:Receptors, Cytokine / Q000235:genetics; D053606:Receptors, OSM-LIF; D015398:Signal Transduction / Q000502:physiology; D012903:Smell / Q000235:genetics / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology; D013268:Stimulation, Chemical; D016211:Transforming Growth Factor alpha / Q000235:genetics
D053680:Leukemia Inhibitory Factor Receptor alpha Subunit; C507841:Lifr protein, mouse; D018121:Receptors, Cytokine; D053606:Receptors, OSM-LIF; D016211:Transforming Growth Factor alpha; D066246:ErbB Receptors