At. Loo et al., THE AGING OLFACTORY EPITHELIUM - NEUROGENESIS, RESPONSE TO DAMAGE, AND ODORANT-INDUCED ACTIVITY, International journal of developmental neuroscience, 14(7-8), 1996, pp. 881-900
Olfactory epithelium retains the capacity to recover anatomically afte
r damage well into adult life and perhaps throughout its duration. Non
e the less, olfactory dysfunctions have been reported widely for elder
ly humans. The present study investigates the effects of aging on the
neurophysiological and anatomical status of the olfactory epithelium i
n barrier-raised Fischer 344X Brown Norway F1 hybrid rats at 7, 10, 25
and 32/35 months old. The posterior part of the olfactory epithelium
in 32/35-month-old rats is well preserved. Globose basal cells are div
iding, and new neurons are being born even at this advanced age. None
the less, the numbers of proliferating basal cells and immature, GAP-4
3 (+) neurons are significantly decreased. Neurophysiological status w
as evaluated using voltage-sensitive dye techniques to assess inherent
patterns of odorant-induced activity in the epithelium lining the sep
tum and the medial surface of the turbinates. In middle and posterior
zones of the epithelium, there were neither age-related changes in ove
rall responsivity of this part of the olfactory epithelium to any of f
ive odorants, nor shifts in the location of the odorant-induced hotspo
ts. The inherent activity patterns elicited by the different odorants
do become more distinct as a function of age, which probably reflects
the decline in immature neurons and a slight, but not statistically si
gnificant, increase in mature neurons as a function of age. In contras
t with the excellent preservation of posterior epithelium, the epithel
ium lining the anterodorsal septum and the corresponding face of the t
urbinates is damaged in the 32/35-month-old animals: in this part, hor
izontal basal cells are reactive, more basal cells and sustentacular c
ells are proliferating than in younger animals or in posterior epithel
ium of the same animals, and the neuronal population is less mature on
average. Our findings indicate that degeneration of the olfactory epi
thelium is not an inevitable or preprogrammed consequence of the aging
process, since the posterior zone of the epithelium is very well pres
erved in these barrier-protected animals. However, the deterioration i
n the anterior epithelium suggests that environmental insults can accu
mulate or become more severe with age and overwhelm the regenerative c
apacity of the epithelium. Alternatively, the regenerative capacity of
the epithelium may wane somewhat with age. Either of these mechanisms
or some combination of them can account for the functional and anatom
ical deterioration of the sense of smell associated with senescence in
humans. Copyright (C) 1996 ISDN.