Neurons are classified according to action potential firing in response to current injection. While such
firing patterns are shaped by the composition and distribution of ion channels, modelling studies
suggest that the geometry of dendritic branches also influences temporal firing patterns. Verifying
this link is crucial to understanding how neurons transform their inputs to output but has so far been
technically challenging. Here, we investigate branching-dependent firing by pruning the dendritic tree
of pyramidal neurons. We use a focused ultrafast laser to achieve highly localized and minimally invasive
cutting of dendrites, thus keeping the rest of the dendritic tree intact and the neuron functional.
We verify successful dendrotomy via two-photon uncaging of neurotransmitters before and after
dendrotomy at sites around the cut region and via biocytin staining. Our results show that significantly
altering the dendritic arborisation, such as by severing the apical trunk, enhances excitability in layer V
cortical pyramidal neurons as predicted by simulations. This method may be applied to the analysis of
specific relationships between dendritic structure and neuronal function. The capacity to dynamically
manipulate dendritic topology or isolate inputs from various dendritic domains can provide a fresh
perspective on the roles they play in shaping neuronal output.