Aging effects on the startle response and startle plasticity in Fischer F344 rats

The effects of aging on acoustic and airpuff startle reactivity, acoustic and airpuff startle habituation, acoustic and cross-modal (light-acoustic) prepulse inhibition (PPI), and fear-potentiated startle (FPS) were examined using 3- (Y: young), 11- (AD: adult), 17- (MA: middle-aged), and 22- (O: old) month-old Fischer F344 rats. AD rats had the highest acoustic startle reactivity with the Y and MA rats showing smaller and comparable startle levels. The O rats had diminished startle reactivity, with over a 65% reduction in responding. Airpuff startle reactivity was comparable in the Y and AD groups, while the MA and O groups had 40% and 80% reductions in airpuff startle respectively. There was an age-related increase in airpuff startle habituation. Acoustic and cross-modal PPI were reduced significantly in O rats when compared to other age groups. Finally, there were no effects of age on FPS. In summary, these studies suggest that in Fischer F344 rats, there are age-associated differences in startle reactivity, startle habituation, and PPI, but no aging effect on FPS.