Blood glucose level affects perceived sweetness intensity in rats

Electrophysiological data indicate that hyperglycemia is associated with decreased neural taste responsiveness to 1.0 M glucose, but not to 0.01 M quinine HCl, in the rat's hindbrain. The present behavioral experiment was conducted to determine whether this suppression of neural activity is manifested in a reduced intensity perception to glucose, but not quinine. Each rat learned to avoid 1.0 M glucose through development of a conditioned taste aversion. Perceived intensity was then measured in control and in hyperglycemic rats by the extent to which they generalized to each test concentration of glucose. Experimental subjects treated moderate glucose concentrations (0.6-2.0 M) as if their intensity perceptions were reduced by 47%. This is consistent with the mean reduction of 43% in taste-evoked neural activity associated with hyperglycemia. A corresponding experiment gave no indication of a change in intensity perception to quinine as a function of hyperglycemia, again in accord with earlier electrophysiological results. We conclude that nutritional state may selectively affect gustatory sensitivity in the rat.