The effects of noradrenergic neurotoxin, DSP-4, on the performance of young and aged rats in spatial navigation task.

The present study investigated whether an overactive noradrenergic system is related to the impairment in learning/memory in aged subjects. The effects of partial noradrenaline depletion (using the noradrenergic neurotoxin DSP-4) on the acquisition of a water maze task was investigated in young and aged rats, and hippocampal noradrenaline content was correlated with spatial learning performance in similar rats. DSP-4 treatment impaired markedly the acquisition of the water maze task in aged rats, but improved it slightly in young rats. DSP-4 treatment decreased swimming speed, and this effect tended to be more marked in young rats. In the group of control rats, hippocampal noradrenaline tended to correlate positively with spatial bias in aged rats (the rats with the highest noradrenaline content in the hippocampus tended to have the best spatial learning/memory), but negatively in young rats. These results do not support the hypothesis that spatial learning/memory impairment is due to an overactive noradrenergic system in aged rats. Further studies are needed to clarify the reasons of the marked age-related difference in the effects of DSP-4 on the performance of water maze task in rats.