Noradrenaline enhances temporal auditory contrast and neuronal timing precision in the cochlear nucleus of the...

In the mustached bat, Pteronotus parnellii, noradrenaline (NA) was applied iontophoretically to single units in the anteroventral cochlear nucleus. NA suppressed tonic components of auditory responses and enhanced phasic onset responses to pure tone stimuli. The enhancement of onset activity was most pronounced in awake bats and was due to a decrease in the latency jitter of the first tone-evoked spikes from 0.55 msec in controls to 0.28 msec during NA application. In addition, NA reduced spontaneous neuronal activity. Noradrenergic antagonists suppressed phasic onset activity and increased the latency jitter of onset spikes. Opposite to the effect of NA, the tonic response component increased during application of the beta-antagonist propranolol but decreased during injection of the alpha 1-antagonist corynanthine. Other putative transmitter substances tested, nonselectively depressed both phasic and tonic response components (GABA, glycine) or increased both components either similarly or had more pronounced effects on the tonic response components (ACh, glutamate). Thus, NA specifically enhances auditory temporal contrast in favor of transients and improves neuronal timing precision, which may be of relevance for auditory tasks like passive sound localization, echolocation, and recognition of temporal patterns.