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IntroductionWe recently showed that sub-kilohertz electrical stimulation of the afferent somata in the dorsal root ganglia (DRG) reversibly blocks afferent transmission. Here, we further investigated whether similar conduction block can be achieved by stimulating the nerve trunk with electrical peripheral nerve stimulation (ePNS). MethodsWe explored the mechanisms and parameters of conduction block by ePNS via ex vivo single-fiber recordings from two somatic (sciatic and saphenous) and one autonomic (vagal) nerves harvested from mice. Action potentials were evoked on one end of the nerve and recorded on the other end from teased nerve filaments, i.e., single-fiber recordings. ePNS was delivered in the middle of the nerve trunk using a glass suction electrode at frequencies of 5, 10, 50, 100, 500, and 1000 Hz. ResultsSuprathreshold ePNS reversibly blocks axonal neural transmission of both thinly myelinated Aδ-fiber axons and unmyelinated C-fiber axons. ePNS leads to a progressive decrease in conduction velocity (CV) until transmission blockage, suggesting activity-dependent conduction slowing. The blocking efficiency is dependent on the axonal conduction velocity, with Aδ-fibers efficiently blocked by 50–1000 Hz stimulation and C-fibers blocked by 10–50 Hz. The corresponding NEURON simulation of action potential transmission indicates that the disrupted transmembrane sodium and potassium concentration gradients underly the transmission block by the ePNS. DiscussionThe current study provides direct evidence of reversible Aδ- and C-fiber transmission blockage by low-frequency (<100 Hz) electrical stimulation of the nerve trunk, a previously overlooked mechanism that can be harnessed to enhance the therapeutic effect of ePNS in treating neurological disorders.
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This content will become publicly available on July 24, 2026
Sensory-selective peripheral and neuraxial nerve blockade with 2',6'-pipecolylxylidine
Background.Safe sensory-selective local anesthetics would be a major advance in the management of acute and chronic pain. Here we describe the sensory-selective local anesthetic properties and the toxicity profile of a known metabolite of amino-amide local anesthetics,2',6'-pipecolylxylidine (PPX). Methods.PPX was synthesized and made into its hydrochloride salt. PPX or ropivacaine (ROP) were injected at the sciatic nerve or intrathecally in rats, who then underwent modified hotplate (sensory) testing and weight-bearing (motor) testing. Rats injected with PPX or ROP were assessed for clinical toxicity endpoints. Conduction blockade was studied with single-unit recordings in mice. Biocompatibility was assessed histologically. Results.In male rats, sciatic sensory and motor block from 15 mM ROP lasted ~150 min; sensory nerve block from 30 mM PPX lasted 67.4 ± 17.4 min without motor block. Addition of chemical permeation enhancers to 30 mM PPX abolished sensory selectivity. Intrathecal 15 mM ROP produced sensory and motor block lasting ~15 min; sensory block from 30 mM PPX lasted 24.8 ± 8.7 min without motor block; repeated injection caused continuous sensory-selective block. In female rats, sciatic nerve blocks with ROP were similar to blocks in males, while blocks with PPX were sensory-selective but higher PPX concentrations were required. Ex vivo, 1.5 mM ROP caused reversible block of Aδ and C-fibers; 15 mM PPX blocked Aδ- but not C-fibers. Systemic 39.0 ± 1.8 mg/kg ROP caused severe clinical toxicity; 75.3 ± 3.2 mg/kg PPX caused none. Tissue reaction to PPX was benign, comparable to that of ROP. Conclusions.PPX provides sensory-selective local and neuraxial anesthesia with a good safety profile. The sensory selectivity may be attributable to the particular hydrophilic-hydrophobic balance of PPX.
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- Award ID(s):
- 1844762
- PAR ID:
- 10628345
- Publisher / Repository:
- Ovid
- Date Published:
- Journal Name:
- Anesthesiology
- ISSN:
- 0003-3022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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