Aged animals typically show less alertness, arousal and activity than younger animals and thus it was thought that amphetamine might benefit the aged mice. It has been hypothesized that because amphetamine causes an overall increase in activity in many animals, the same should happen in the mice tested in the present experiment. Subjects were run on a computer controlled program which measured acoustic startle response, the startle being preceded by a prestimulus gap of varied duration time. The effect of amphetamine depends on dose level. While low doses of amphetamine may improve performance in disorders such as Attention Deficit Disorder, high doses of amphetamine often cause psychotic behavior similar to that seen in schizophrenic patients.
Schizophrenic patients display a lower level of prepulse inhibition than normal subjects.
It is also the case that high levels of amphetamine decrease prepulse inhibition in rats as well as increase startle behavior. However, there are no data indications that low doses of amphetamine might increase prepulse inhibition. In the low dose experiment, under the control condition of no amphetamine, startle response and inhibition caused by the gap prestimulus were highest in the eight month old mice and lowest in the twenty eight month old mice. When mice were given the very low dose injections, their startle and inhibitory responses were not significantly different from those obtained with the NaCl injection. Under the higher dose conditions, the control showed that startle response and inhibition were again highest in the eight month old mice and lowest in the twenty eight month old mice, and longer gaps led to inhibition in all groups.