Effects of caloric restriction and aging on the auditory function of rhesus monkeys (Macaca mulatta): The University of Wisconsin Study.

The present study is part of a larger project that investigates the effect of caloric restriction on longevity in the rhesus monkey. The purpose of the present study was to document presbycusis and the effect of caloric restriction on presbycusis in monkeys. The control group had 35 monkeys allowed to eat freely and the caloric-restricted group (CR) had 33 monkeys with a 30% reduction in caloric intake. Monaural and binaural auditory brainstem response (ABR) and middle latency response (MLR) were obtained from 27 female and 41 male monkeys that were 11-23 years of age and had been in the study for 102, 42, or 36 months when tested. Significant findings were the following: (1) wave I amplitudes were larger for females and for younger monkeys, and amplitudes decreased in aging males but not in aging females; (2) wave IV amplitudes were larger for females than males, and amplitudes for CR females were larger than for female controls, whereas the amplitudes from control and CR males were not different; (3) wave Pa latencies were shorter for females, and shorter latencies were maintained for aging females but not for aging males; (4) interwave interval IV-Pa was shorter for females, and intervals lengthened for aging males but not aging females; (5) binaural wave IV amplitude decreased faster with age for control monkeys than for CR monkeys, and the L+R Pa amplitude decreased with age. Additional trends were identified for longitudinal monitoring as monkeys enter old age.