Analyzing Branch‐specific Dendritic Spikes Using an Ultrafast Laser Scalpel

Abstract

Dendritic spikes facilitate neuronal computation and they have been reported to occur in various regions of the dendritic tree of cortical neurons. Spikes that occur only on a select few branches are particularly difficult to analyze especially in complex and intertwined dendritic arborizations where highly localized application of pharmacological blocking agents is not feasible. Here, we present a technique based on highly targeted dendrotomy to tease out and study dendritic spikes that occur in oblique branches of cortical layer five pyramidal neurons. We first analyze the effect of cutting dendrites in silico and then confirmed in vitro using an ultrafast laser scalpel. A dendritic spike evoked in an oblique branch manifests at the soma as an increase in the afterdepolarization (ADP). The spikes are branch-specific since not all but only a few oblique dendrites are observed to evoke spikes. Both our model and experiments show that cutting certain oblique branches, where dendritic spikes are evoked, curtailed the increase in the ADP. On the other hand, cutting neighboring oblique branches that do not evoke spikes maintained the ADP. Our results show that highly targeted dendrotomy can facilitate causal analysis of how branch-specific dendritic spikes influence neuronal output.

Glocal dendritic spikes: variation in branch activity during dendritic spiking indicates multiple functional units in the pyramidal neuron apical tuft

“…Studies of hippocampal PNs during navigation revealed that spiking activity of basal dendrites is highly variable and that dendrites can display place tuning independent of their soma 36 . In addition, variable spiking activity was also observed in oblique dendrites of L5 PNs 37 . Together, variable and dynamic dendritic activity is employed in all dendritic compartments, in many brain sites, and across a variety of behavioral states.…”