Diminished interaction of norepinephrine with climbing fiber inputs to cerebellar Purkinje neurons in aged Fischer 344 rats.

The ability of norepinephrine (NE) to modulate climbing fiber activation of complex spike discharge in cerebellar Purkinje neurons was compared in young (3-6 months) and aged (18-20 months) Fischer 344 rats. In young rats, NE selectively inhibits spontaneous activity while climbing fiber evoked activity remains intact or increased. NE also increases the probability of observing 4 bursts of full-sized action potentials rather than partially inactivated action potentials in the complex spike. In older rats, both of these modulatory actions of NE on climbing fiber complex spike activation are markedly diminished. These data support the concept that age-related reductions in catecholamine modulation of synaptic inputs may contribute to CNS dysfunction found in senescence.