Reduction of cerebellar norepinephrine alters climbing fiber enhancement of mossy fiber input to the Purkinje cell

Extra-cellular simple and complex spike activity from 58 Purkinje cells were recorded in cats that previously received an intracisternal injection of 6-OHDA which depletes brain catecholamines. The severest catecholamine depletion was noted for cerebellar norepinephrine (21.1% of controls). Less depletion occureed in the brainstem and the visual cortex. Past studies have shown that in normal non-depleted cats, somatosensory stimuli (forepaw tap) evoke both complex and simple spike responses. On those trials where complex spike or climbing fiber responses are evoked, there is an enhancement or increase in responsiveness in the majority of excitatory and inhibitory simple spike responses. In the norepinephrine depleted animal, there is a significant decrease in this climbing fiber enhancement only for the excitatory response components. Furthermore, on those trials where no complex spikes are evoked, there is a significant firing rate is also observed in the depleted animals. Thus, depletion of norepinephrine is associated with a reduction of both response amplitude and climbing fiber induced enhancement of excitatory simple spike responses. The inhibitory responses in these same cells are unchanged when compared to those recorded in the normal non-depleted animals.