Response to urinary volatiles and chemosensory function decline with age in a prosimian primate.

The age-related decline in olfaction is well documented in humans. However, no data are available to date on changes in olfactory sensitivity with age in nonhuman primates. In the male gray mouse lemur (Microcebus murinus), a prosimian primate, the sense of smell is of high relevance for the modulation of both behavioral and physiological functions. We first assessed the effect of aging on physiological responses to urinary cues by measuring reproductive function in adult and aged males exposed to urine odor of preoestrous females. We then evaluated the effect of aging on chemosensory function using a discrimination test in freely behaving animals. Our results indicate that whereas adult animals show a clear increase in testosterone levels when exposed to female urine odor, this effect is lacking in aged animals. In addition, chemosensory function shows a progressive decline with age. Using both physiological responses to urinary volatiles and spontaneous behavior, this study provides the first data set on the effect of aging on chemosensory responsiveness in a nonhuman primate.