Abstract
In humans, experiments assessing threshold sensitivity have all demonstrated significant impairment in olfaction in old age. The causes for such age dependent decreases in olfactory sensitivity are not well understood. To test whether there are similar age related changes in olfactory sensitivity in rats, which might be used for further analyzing this open question, we established the thresholds
of six subadult (2 months old at the beginning of testing) and six old (19 months) male Wistar rats. Ethylacetate was used as the solvent. The experiments were performed in an olfactory skinner box using operant conditioning. Before testing for olfactory thresholds was started, all animals were first familiarized with the experimental procedure and the individual learning speeds in the olfactory skinner box was established. In an additional experiment the learning speeds of two 32-month-old rats were tested. These
additional experiments revealed no age related decrease in the learning ability. In initial training a 0.1\% (of vapor saturation) ethylacetate served as the positive stimulus, and air served as the negative stimulus. If performance accuracy was 85-100\% for each animal, subsequent dilutions were made between 0.5 and 0.1 log unit steps. The olfactory threshold was defined as the lowest concentration in which performance of at least 75\% correct responses was achieved.
In all six young rats (age at the time of threshold establishment: 5 months) thresholds showed little individual differences and ranged between 3 x 1CT6 vol\% and 2 x 10''6 vol\%. The thresholds for the old rats (age 31 months) were enormously wide spread ranging from 1 x 10-3 to 7.2 x 10-6 vol\%. The difference between the two groups is statistically significant with P < 0.001. We, therefore, not only found an age dependent decline in the olfactory sensitivity, but also an increased variability in the thresholds in the old aged
rats (similar to that described in humans).
