Effects of Apical Dendrite Integrity on Action Potential Properties in Layer 6 Corticothalamic Pyramidal Neurons: Evidence for Hemispheric Differences.

Hemispheric asymmetries in the cortical structure and function are well documented, but whether this asymmetry is reflected in the electrophysiological properties of the same neuron type remains unclear, particularly given the many factors that influence action potential (AP) generation. Among these factors, dendritic tree size plays a crucial role in AP generation and in forward and backward propagation, yet it is not well understood whether dendritic size affects spike generation similarly in the two hemispheres. Here, electrophysiological recordings of layer 6a corticothalamic (CT) pyramidal neurons from a mouse's left and right primary visual cortex were analyzed to examine how apical dendrite integrity influences somatic AP properties. Neurons were divided into four groups based on hemisphere and apical dendrite status (intact vs. truncated), and the AP shape parameters were quantified in response to current stimulation. Intact CT neurons showed similar AP rapidity and width across hemispheres but differed in AP threshold and amplitude. In contrast, a comparison of the intact and truncated neurons within each hemisphere revealed significant and opposing effects of apical dendrite truncation on all AP parameters. These results suggest that the coupling between dendritic morphology and somatic AP generation differs between hemispheres, implying distinct rules for integrating dendritic load in the left and right CT neurons.