Abstract
Active dendrites impact sensory processing and behaviour. However, it remains unclear how active dendritic integration relates to somatic output in vivo. We imaged semi-simultaneously GCaMP6s signals in the soma, trunk and distal tuft dendrites of layer 5 pyramidal neurons in the awake mouse primary visual cortex. We found that apical tuft signals were dominated by widespread, highly correlated calcium transients throughout the tuft. While these signals were highly coupled to trunk and somatic transients, the frequency of calcium transients was found to decrease in a distance-dependent manner from soma to tuft. Ex vivo recordings suggest that low-frequency back-propagating action potentials underlie the distance-dependent loss of signals, while coupled somato-dendritic signals can be triggered by high-frequency somatic bursts or strong apical tuft depolarization. Visual stimulation and locomotion increased neuronal activity without affecting somato-dendritic coupling. High, asymmetric somato-dendritic coupling is therefore a widespread feature of layer 5 neurons activity in vivo.
Highlights
Active dendritic conductances impact the integration of synaptic inputs and its effect on somatic output (Grienberger, Chen and Konnerth, 2015; Stuart and Spruston, 2015)
Given that electrical signals are known to attenuate in a distant dependent manner, we tested whether the correlation of calcium transients between apical tuft branches decreased with distance from the apical trunk
In addition to the global, widespread calcium transients, we observed in individual spines, calcium signals that were not correlated with dendritic signals (Figure 1- figure supplement 1), indicating that we could resolve spine calcium signals in our experimental conditions
Summary
Active dendritic conductances impact the integration of synaptic inputs and its effect on somatic output (Grienberger, Chen and Konnerth, 2015; Stuart and Spruston, 2015). In cortical layer 5 excitatory neurons, nonlinear dendritic spikes have been reported in the long apical dendrite and tuft, both in vitro and in vivo (Grienberger, Chen and Konnerth, 2015; Stuart and Spruston, 2015). These dendritic events are generally associated with calcium influx both locally and globally in the apical tuft (Xu et al, 2012; Hill et al, 2013; Palmer et al, 2014; Cichon and Gan, 2015; Manita et al, 2015; Takahashi et al, 2016). The coincident occurrence of back-propagating action potentials and tuft depolarization was shown to generate widespread calcium transients in the apical tuft dendrites (Spruston et al, 1995; Magee and Johnston, 1997; Svoboda et al., 1997; Helmchen et al, 1999; Larkum, Zhu and Sakmann, 1999; Waters et al, 2003; Manita et al, 2015)
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