Differential effects of noradrenaline on evoked, spontaneous and miniature IPSCs in rat cerebellar stellate cells

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Abstract
The modulation by noradrenaline (NA) of synapses among stellate cells was investigated in rat cerebellar slices by using presynaptic loose cell‐attached recording and postsynaptic whole‐cell recording. NA increased the frequency of spontaneous IPSCs recorded from stellate cells without changing their mean amplitude. NA increased the firing rate of stellate cells. This effect persisted after blocking ionotropic glutamate receptors and GABA receptors, indicating that it was independent of synaptic input. The effects of NA on action potential frequency were mimicked by the β‐receptor agonist isoprenaline but not by the α‐receptor agonist 6‐fluoro noradrenaline, and they were not blocked by the α‐receptor antagonist phentolamine, indicating that they were mediated by β‐receptors. In paired recordings of connected stellate cells, NA slightly decreased the success rate of synaptic transmission. A small decrease in mean IPSC amplitude (excluding failures) and a slight increase in latency were also observed in NA. These results show that, while NA increases the number of action potential‐dependent IPSCs by increasing the firing rate of stellate cells, it actually reduces the probability of evoked release. Since previous studies showed that NA increases the rate of miniature IPSCs in this preparation, we conclude that different mechanisms underly the modulation by NA of action potential‐dependent and action potential‐independent transmitter release.