Differences in action potential propagation speed and axon initial segment plasticity between neurons from Sprague-Dawley rats and C57BL/6 mice

Action potentials(APs)in neurons are generated at the axon initial segment(AIS).AP dynamics,including initiation and propagation,are intimately associated with neuronal excitability and neurotransmitter release kinetics.Most learning and memory studies at the single-neuron level have relied on the use of animal models,most notably rodents.Here,we studied AP initiation and propagation in cultured hippocampal neurons from Sprague-Dawley(SD)rats and C57BL/6(C57)mice with genetically encoded voltage indicator(GEVI)-based voltage imaging.Our data showed that APs traveled bidirectionally in neurons from both species;forward-propagating APs(fpAPs)had a different speed than backpropagating APs(bpAPs).Additionally,we observed distinct AP propagation characteristics in AISs emerging from the somatic envelope compared to those originating from dendrites.Compared with rat neurons,mouse neurons exhibited higher bpAP speed and lower fpAP speed,more distally located ankyrin G(AnkG)in AISs,and longer Nav1.2 lengths in AISs.Moreover,during AIS plasticity,AnkG and Nav1.2 showed distal shifts in location and shorter lengths of labeled AISs in rat neurons;in mouse neurons,however,they showed a longer AnkG-labeled length and more distal Nav1.2 location.Our findings suggest that hippocampal neurons in SD rats and C57 mice may have different AP propagation speeds,different AnkG and Nav1.2 patterns in the AIS,and different AIS plasticity properties,indicating that comparisons between these species must be carefully considered.

3D Hessian deconvolution of thick light-sheet z-stacks for high-contrast and high-SNR volumetric imaging

Due to its ability of optical sectioning and low phototoxicity,z-stacking light-sheet microscopy has been the tool of choice for in vivo imaging of the zebrafish brain.To image the zebrafish brain with a large field of view,the thickness of the Gaussian beam inevitably becomes several times greater than the system depth of field(DOF),where the fluorescence distributions outside the DOF will also be collected,blurring the image.In this paper,we propose a 3D deblurring method,aiming to redistribute the measured intensity of each pixel in a light-sheet image to in situ voxels by 3D deconvolution.By introducing a Hessian regularization term to maintain the continuity of the neuron dis-tribution and using a modified stripe removal algorithm,the reconstructed z stack images exhibit high contrast and a high signal-to-noise ratio.These performance characteristics can facilitate subsequent processing,such as 3D neuron registration,segmentation,and recognition.

Dendritic Morphology Affects the Velocity and Amplitude of Back-propagating Action Potentials

The back-propagating action potential(bpAP)is crucial for neuronal signal integration and synaptic plasticity in dendritic trees.Its properties(velocity and amplitude)can be affected by dendritic morphology.Due to limited spatial resolution,it has been difficult to explore the specific propagation process of bpAPs along dendrites and examine the influence of dendritic morphology,such as the dendrite diameter and branching pattern,using patch-clamp recording.By taking advantage of Optopatch,an all-optical electrophysiological method,we made detailed recordings of the real-time propagation of bpAPs in dendritic trees.We found that the velocity of bpAPs was not uniform in a single dendrite,and the bpAP velocity differed among distinct dendrites of the same neuron.The velocity of a bpAP was positively correlated with the diameter of the dendrite on which it propagated.In addition,when bpAPs passed through a dendritic branch point,their velocity decreased significantly.Similar to velocity,the amplitude of bpAPs was also positively correlated with dendritic diameter,and the attenuation patterns of bpAPs differed among different dendrites.Simulation results from neuron models with different dendritic morphology corresponded well with the experimental results.These findings indicate that the dendritic diameter and branching pattern significantly influence the properties of bpAPs.The diversity among the bpAPs recorded in different neurons was mainly due to differences in dendritic morphology.These results may inspire the construction of neuronal models to predict the propagation of bpAPs in dendrites with enormous variation in morphology,to further illuminate the role of bpAPs in neuronal communication.