Effect of stimulation intensity of a differential target multiplexed SCS program in an animal model of neuropathic pain.

Abstract

Spinal cord stimulation (SCS) has been proven to be an effective treatment for patients suffering from intractable chronic neuropathic pain. Recent advances in the field include the utilization of programs that multiplex various signals to target different neural structures in the dorsal spinal cord associated with the painful area. Preclinical studies have been fundamental in understanding the mechanism by which this differential target multiplexed programming (DTMP) SCS approach works. Transcriptomic- and proteomic-based studies demonstrated that DTMP can modulate expression levels of genes and proteins involved in pain-related processes that have been affected by a neuropathic pain model. This work studied the effect of the intensity of DTMP signals on mechanical hypersensitivity and cell-specific transcriptomes. The spared nerve injury model (SNI) of neuropathic pain was induced in 20 animals which were 1:1 randomized into two SCS groups in which the intensity of the DTMP was adjusted to either 70% or 40% of the motor threshold (MT). SCS was applied continuously for 48 h via a quadripolar lead implanted in the dorsal epidural space of animals. Controls, which included a group of implanted SNI animals that received no SCS and a group of animals naive to the SNI, were assessed in parallel to the SCS groups. Mechanical hypersensitivity was assessed before SNI, before SCS, and at 48 h of SCS. At the end of SCS, the stimulated segment of the dorsal spinal cord was dissected and subjected to RNA sequencing to quantify expression levels in all experimental groups. Differential effects were assessed via fold-change comparisons of SCS and naive groups versus the no-SCS group for transcriptomes specific to neurons and glial cells. Standard statistical analyses were employed to assess significance of the comparisons (p < 0.05). SCS treatments provided significant improvement in mechanical sensitivity relative to no SCS treatment. However, the change in the intensity did not provide a significant difference in the improvement of mechanical sensitivity. DTMP regulated expression levels back toward those found in the naive group in the cell-specific transcriptomes analyzed. There were no significant differences related to the intensity of the stimulation in terms of the percentage of genes in each transcriptome in which expression levels were reversed toward the naive state. DTMP when applied at either 40% MT or 70% MT provided similar reduction of pain-like behavior in rats and similar effects in neuron- and glia-specific transcriptomes.