Motor learning deficits in aged rats are correlated with loss of cerebellar noradrenergic function.

We have demonstrated that aged rats show impairments in learning patterned motor movements. Similar behavioral impairment is observed in rats with noradrenergic lesions. Norepinephrine is known to act as a neuromodulator in the cerebellar cortex because it can augment the action of GABA and other neurotransmitters. This effect of NE to augment the signal to noise ratio of GABAergic inputs to cerebellar Purkinje neurons is a possible substrate for NE's effect on motor learning. Aged rats demonstrate deficits in the modulatory actions of NE to augment GABAergic inhibitions when both substances are locally applied onto cerebellar Purkinje neurons. In this report, we examined how motor learning and cerebellar noradrenergic function varied in individual young and 20-month-old Fischer 344 rats. There was a significant correlation between the loss of the neuromodulatory actions of norepinephrine (NE) in the cerebellar cortex and the rate of learning a novel motor task in individual rats. This report thus demonstrates for the first time a correlation between age-related impairments in motor plasticity and specific neurophysiological deficits in cerebellar Purkinje neurons in individual animals.