Taste responsiveness and diet preference in autoimmune MRL mice.
One of the most profound behavioural deficits in lupus-prone MRL-lpr mice is blunted responsiveness to sweet solutions. Given the systemic nature of autoimmune/inflammatory disease, it was not clear whether impaired taste sensitivity or motivated response to palatable food underlie this deficit. The present study compares response rates of MRL-lpr mice (which develop disease early), congenic MRL +/+ mice (which develop disease later in life) and non-autoimmune Swiss Webster (SW) mice to different tastes and diets. Healthy SW mice showed the highest responsiveness to palatable stimulation throughout the study. Conversely, the preference for palatable solutions progressively declined in MRL-lpr mice as the disease developed. No differences between the two MRL substrains were seen in responsiveness to quinine or saline, suggesting that blunted responsiveness to palatable solutions cannot be accounted for by reduced taste sensory function (hypogeusia). In addition, changes in response rates to palatable solutions were associated with systemic upregulation of pro-inflammatory cytokines. With a new cohort of mice fed on carbohydrate-rich and fat-rich diets, we also examined whether reduced sucrose intake in MRL-lpr mice can be accounted for by a reduced craving for carbohydrates. Contrary to this expectation, diseased MRL-lpr mice preferred carbohydrate-rich food while consuming a food mass comparable to controls. These results further support the hypothesis that the onset of lupus-like disease alters motivated behaviour, independent of changes in neurologic function and food metabolism.