Figure 9: Cholinergic signalling positively gates terminal dendritic spike generation.

(a) Light spot-evoked terminal dendritic (marked by *) and large-amplitude dendritic spike generation were powerfully attenuated by nAChR antagonism (upper traces, hexamethonium; Hex). This reduction could be rescued by pairing light stimuli with sub-threshold dendritic depolarization (lower left traces). The insets show light spot-evoked dendritic spikes (blue traces) and somatically recorded activity (black traces). A section of the ON-DSGC morphology, the placement of electrodes, and the position of the light spot stimuli are also shown. (b) Peri-stimulus time histogram of light spot-evoked (ON time=0–0.5 s) action potential (AP) output under the indicated conditions. (c) Amplitude distribution of dendritically recorded spikes under the indicated conditions. Note that pairing of light spot stimuli with dendritic depolarization increased the generation of both terminal and large-amplitude dendritic spikes. (d) Number of terminal and large-amplitude dendritic spikes evoked by light spot stimuli under the indicated conditions (data represent mean±s.e.m). (e) When presynaptic ACh release was depleted (vesamicol), the pairing of light spot stimuli with the local dendritic iontophoretic delivery of ACh augmented dendritic spike generation. The insets show overlain spikes, a section of the ON-DSGC morphology, the placement of recording and iontophoresis electrodes, and the position of light spot stimuli. (f) Number of terminal and large-amplitude dendritic spikes evoked by light spot stimuli per trial under the indicated conditions (data represent mean±s.e.m).