PubMed · 11752563
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B Richmond. 2001-12-21. Neuroscience. Information coding.. https://doi.org/10.1126/science.1067928
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We investigated the effect of morphological differences on neuronal firing behavior within the hippocampal CA3 pyramidal cell family by using three-dimensional reconstructions of dendritic morphology in computational simulations of electrophysiology. In this paper, we report for the first time that differences in dendritic structure within the same morphological class can have a dramatic influence on the firing rate and firing mode (spiking versus bursting and type of bursting). Our method consisted of converting morphological measurements from three-dimensional neuroanatomical data of CA3 pyramidal cells into a computational simulator format. In the simulation, active channels were distributed evenly across the cells so that the electrophysiological differences observed in the neurons would only be due to morphological differences. We found that differences in the size of the dendritic tree of CA3 pyramidal cells had a significant qualitative and quantitative effect on the electrophysiological response. Cells with larger dendritic trees: (1) had a lower burst rate, but a higher spike rate within a burst, (2) had higher thresholds for transitions from quiescent to bursting and from bursting to regular spiking and (3) tended to burst with a plateau. Dendritic tree size alone did not account for all the differences in electrophysiological responses. Differences in apical branching, such as the distribution of branch points and terminations per branch order, appear to effect the duration of a burst. These results highlight the importance of considering the contribution of morphology in electrophysiological and simulation studies.
BACKGROUND: Despite extensive proximal ablation, all potentials frequently cannot be eliminated from the left pulmonary veins (PV). Methods and Results- PV electrograms were analyzed during sinus rhythm, coronary sinus, and left atrial appendage (LAA) pacing, and PV and LAA angiography performed. During pacing, an initial low-amplitude slow potential was recorded on the anterior aspect of the left superior PV and anticipated with shortest activation time by LAA pacing. Its timing coincided with posterior LAA activation, shown to be immediately adjacent to the left superior PV by angiography. In the left inferior PV, the first potential was smaller and less sharp, coinciding with adjacent low LA activation. Angiographically, the LAA was at least 15 mm from the left inferior PV. The second sharper potential in both left PVs was eliminated by proximal ablation. CONCLUSION: Far field LAA activity consistently adds to PV myocardial electrograms in the left superior PV whereas lower, less sharp extravenous potentials in the left inferior PV originate from the inferior LA. They can be identified by LAA and coronary sinus pacing.
We evaluated by morphologic and functional analysis the regeneration of peripheral nerve fibers through polyimide regenerative-type electrodes over long-term implantation. Polyimide sieve electrodes were placed in silicone chambers and implanted between the severed ends of the sciatic nerve in rats. The sieve part had 281 round via holes of 40 microm in diameter, with nine integrated recording-stimulating electrodes arranged around the via holes. The degree of axonal regeneration was examined at 2, 7, and 12 months postimplantation (mpi). Regeneration was successful in 12 of the 13 animals implanted. Reinnervation of distal muscle and nerves increased with time, reaching a plateau about 7 mpi. The number of myelinated fibers increased from 2 to 7 months, at which time it was similar to control values. With time the myelinated fibers matured, with significant increases in axon diameter and myelin thickness. Only 0.6% of the regenerated axons showed evidence of compression near the implanted electrode. The majority of the myelinated fibers that crossed the via holes and had been regenerated through the distal nerve had a normal appearance. Sieve electrodes were useful for nerve stimulation at postimplantation. Stimulation through different active electrodes excited nerve bundles, evoking compound muscle action potentials of varying shape and amplitude, indicative of selective axonal stimulation.