DIETARY-PROTEIN LEVELS ALTER RAT BEHAVIOR

The performance of rats in a battery of behavioral test systems following long-term, dietary protein manipulation was evaluated. Groups of rats were pair-fed with isocaloric diet containing low (8%), normal (20%) and high (50%) casein for 20 weeks. The high-casein group was more responsive compared to the normal- and low-casein groups in sensorimotor function, negative geotaxis, and spontaneous locomotor activity. In addition, the high-casein fed rats exhibited reduced aversion as measured by the elevated plus-maze test of anxiety, and hyperalgesia as shown by the tail-flick reaction time. Results from the animals which were fed the low-casein diet were not different from those fed the normal-casein diet in all of the behavioral tests employed except the tail-flick, in which the low-casein group exhibited hypoalgesia. These data suggest that consumption of a long-term, high-protein diet leads to hyperactivity, hyper-responsiveness, and anxiolysis in rats. Only the results of the tail-flick test were compatible with protein:carbohydrate ratio effect on behavior.