The Journal of Neurophysiology Effect of Common Anesthetics on Dendritic Properties in Layer 5 Neocortical Pyramidal Neurons

Understanding the impact of active dendritic properties on network activity in vivo has so far been restricted to studies in anesthetized animals. However, to date no study has been made to determine the direct effect of the anesthetics themselves on dendritic properties. Here, we investigated the effects of three types of anesthetics commonly used for animal experiments (urethane, pentobarbital and ketamine/xylazine). We investigated the generation of calcium spikes, the propagation of action potentials along the apical dendrite and the somatic firing properties in the presence of anesthetics in vitro using dual somato-dendritic whole-cell recordings. Calcium spikes were evoked with dendritic current injection and high-frequency trains of action potentials at the soma. Surprisingly, we found that the direct action of anesthetics on calcium spikes were very different. Two anesthetics (urethane and pentobarbital) suppressed dendritic calcium spikes in vitro whereas a mixture of ketamine and xylazine enhanced them. Propagation of spikes along the dendrite was not significantly affected by any of the anesthetics but there were various changes in somatic firing properties that were highly anesthetic dependent. Lastly, we examined the effects of anesthetics on calcium spike initiation and duration in vivo using high-frequency trains of APs generated at the cell body. We found the same anesthetic-dependent direct effects in addition to an overall reduction in dendritic excitability in anesthetized rats with all three anesthetics compared to the slice preparation.