Reliability of triggering postinhibitory rebound bursts in deep cerebellar neurons

Deep cerebellar nuclear (DCN) neurons exhibit distinct phenotypes of rebound discharge following current-evoked membrane hyperpolarizations that arise from specific CaV3 T-type Ca2+ channel isoforms and Ca2+-activated K+ channels. The probability of evoking rebound bursts following a brief train of GABAergic inhibitory synaptic input from cerebellar Purkinje cells was recently questioned for stimulus intensities adjusted to evoke a long post-stimulus pause in spike firing. We revisited this issue to examine the potential for generating rebound bursts in DCN cells in response to synaptic inputs in vitro. Both a Transient and Weak Burst phenotype could be distinguished in on-cell extracellular recordings or whole-cell recordings in response to inhibitory synaptic input. We found that the rebound burst response was a sensitive function of stimulus intensity, such that increasing stimulus intensity significantly raised the probability for evoking bursts while decreasing pause duration. The threshold for reliably generating rebound bursts was ~40 percent of maximum intensity, a level that evokes an IPSC corresponding to only a small number of the inhibitory terminals known to impinge on DCN cells. The probability for evoking rebound bursts is thus very high for moderate levels of stimulation in vitro, leaving the potential role for rebound discharge to contribute to signal processing in vivo an open question.