James C. Smith - US grants

The long-term objective of this research is to develop an animal model for the study of age-related decrements in the sense of taste. There currently exists a paucity of research on changes in taste as a function of aging in all sub-human species, and, indeed, there is little known about such changes in humans. The specific aim of this project will be to study age-related changes in the sweet taste in the Fischer 344 rat. Since it has been shown that aged humans exhibit significant decrements in sweet sensitivity, the tastants to be used in this project will be sucrose, saccharin and glucose + saccharin mixtures. The Fischer 344 rat was chosen because of the extensive literature on all aspects of aging, particularly pathology, which is available for this strain. Both cross sectional and longitudinal studies will be conducted using rats from 150 to 900 days of age. Taste perception in the rat will be measured in two ways: 1. Detailed records of licking and drinking bouts together with day-night fluid and food consumption will be made on a 24-hr basis using a computer-monitored living cage. 2. Short-term drinking tests will be conducted with rats which have been implanted with a gastric cannula. This will allow for sham feeding tests where only oropharyngeal factors will operate since no postingestinal feedback is possible. These sham feeding rats can be used as their own controls in subsequent short-term drinking tests where the screw which closed the cannula is left in place. The age-related changes observed in the rat model will contribute to the understanding of the known decreases in taste sensitivity in the elderly human. These age-related taste changes undoubtedly contribute to the frequent loss of palatability and subsequent nutritional deficits in the older person.

The long term objective of the research is to continue developing an animal model using the Fischer-344 laboratory rat for the study of the effects of age on the sense of taste. Special attention will be given to behavioral studies of the taste of sucrose. Since it has been shown that the palate of the rat, more so than the tongue, is of particular importance in mediating the taste of sucrose, the distribution and density of palatal taste buds will be studied in the Fischer-344 rat. The unique aspect of this description of palatal tastes buds will be that it will be made from rats with a known history of sucrose preference and sucrose thresholds, yielding a correlation between sucrose avidity and thresholds and density or distribution of palatal taste buds. Since the palatal taste buds are supported by the greater superficial petrosal nerve, a series of experiments will be conducted investigating the role of this nerve in the perception of sucrose by the rat. Finally, it will be observed if long term experience with sucrose in younger rats effects the avidity or thresholds for sucrose in older age. Emphasis will be placed on longitudinal rather than cross-sectioanl studies. The effects of age on taste in humans is not understood and the literature is filled with controversies in both psychophysical and anatomical studies. There is little literature on the changes in the palate with age. This may be very important especially for denture wearers. Variability is so large within age groups that without longitudinal studies changes occuring with age are obscured.

The long term objective of the research is to continue developing an animal model using the Fischer-344 laboratory rat for the study of the effects of age on the sense of taste. Special attention will be given to behavioral studies of the taste of sucrose. Since it has been shown that the palate of the rat, more so than the tongue, is of particular importance in mediating the taste of sucrose, the distribution and density of palatal taste buds will be studied in the Fischer-344 rat. The unique aspect of this description of palatal tastes buds will be that it will be made from rats with a known history of sucrose preference and sucrose thresholds, yielding a correlation between sucrose avidity and thresholds and density or distribution of palatal taste buds. Since the palatal taste buds are supported by the greater superficial petrosal nerve, a series of experiments will be conducted investigating the role of this nerve in the perception of sucrose by the rat. Finally, it will be observed if long term experience with sucrose in younger rats effects the avidity or thresholds for sucrose in older age. Emphasis will be placed on longitudinal rather than cross-sectioanl studies. The effects of age on taste in humans is not understood and the literature is filled with controversies in both psychophysical and anatomical studies. There is little literature on the changes in the palate with age. This may be very important especially for denture wearers. Variability is so large within age groups that without longitudinal studies changes occuring with age are obscured.