Enhanced Excitability of Small Dorsal Root Ganglion Neurons in Rats with Bone Cancer Pain

Abstract

BackgroundPrimary and metastatic cancers that affect bone are frequently associated with severe and intractable pain. The mechanisms underlying the development of bone cancer pain are largely unknown. The aim of this study was to determine whether enhanced excitability of primary sensory neurons contributed to peripheral sensitization and tumor-induced hyperalgesia during cancer condition. In this study, using techniques of whole-cell patch-clamp recording associated with immunofluorescent staining, single-cell reverse-transcriptase PCR and behavioral test, we investigated whether the intrinsic membrane properties and the excitability of small-sized dorsal root ganglion (DRG) neurons altered in a rat model of bone cancer pain, and whether suppression of DRG neurons activity inhibited the bone cancer-induced pain.ResultsOur present study showed that implantation of MRMT-1 tumor cells into the tibial canal in rats produced significant mechanical and thermal hyperalgesia in the ipsilateral hind paw. Moreover, implantation of tumor cells provoked spontaneous discharges and tonic excitatory discharges evoked by a depolarizing current pulse in small-sized DRG neurons. In line with these findings, alterations in intrinsic membrane properties that reflect the enhanced neuronal excitability were observed in small DRG neurons in bone cancer rats, of which including: 1) depolarized resting membrane potential (RMP); 2) decreased input resistance (Rin); 3) a marked reduction in current threshold (CT) and voltage threshold (TP) of action potential (AP); 4) a dramatic decrease in amplitude, overshot, and duration of evoked action potentials as well as in amplitude and duration of afterhyperpolarization (AHP); and 5) a significant increase in the firing frequency of evoked action potentials. Here, the decreased AP threshold and increased firing frequency of evoked action potentials implicate the occurrence of hyperexcitability in small-sized DRG neurons in bone cancer rats. In addiotion, immunofluorescent staining and single-cell reverse-transcriptase PCR revealed that in isolated small DRG neurons, most neurons were IB4-positive, or expressed TRPV1 or CGRP, indicating that most recorded small DRG neurons were nociceptive neurons. Finally, using in vivo behavioral test, we found that blockade of DRG neurons activity by TTX inhibited the tumor-evoked mechanical allodynia and thermal hyperalgesia in bone cancer rats, implicating that the enhanced excitability of primary sensory neurons underlied the development of bone cancer pain.ConclusionsOur present results suggest that implantation of tumor cells into the tibial canal in rats induces an enhanced excitability of small-sized DRG neurons that is probably as results of alterations in intrinsic electrogenic properties of these neurons. Therefore, alterations in intrinsic membrane properties associated with the hyperexcitability of primary sensory neurons likely contribute to the peripheral sensitization and tumor-induced hyperalgesia under cancer condition.

Suppression of KCNQ/M Potassium Channel in Dorsal Root Ganglia Neurons Contributes to the Development of Osteoarthritic Pain

“…Clinical and experimental observations implicate the increased excitability of DRG neurons as a probable substrate of persistent neuropathic pain [22]. The excitability of small-sized DRG neurons was enhanced in neuropathic pain and bone cancer pain rats, whereas activation of KCNQ/M channels with retigabine significantly inhibited the hyperexcitability [23]. However, whether the excitability of small-sized DRG neurons was enhanced in the DRG neurons of osteoarthritic rats was not further studied.…”

BDNF contributes to the development of neuropathic pain by induction of spinal long-term potentiation via SHP2 associated GluN2B-containing NMDA receptors activation in rats with spinal nerve ligation

“…Mechanical allodynia, as a behavioral sign of neuropathic pain, was assessed by measuring 50% paw withdrawal threshold (PWT) as described in our previous reports (Liu et al, 2013;Zheng et al, 2012). The 50% PWT in response to a series of von Frey filaments (Stoelting, Wood Dale, IL) was determined by the Up and Down method (Chaplan et al, 1994).…”

RGD peptide conjugated liposomal drug delivery system for enhance therapeutic efficacy in treating bone metastasis from prostate cancer

“…A mice model of bone metastasis from prostate cancer was established by intra-tibia injection of RM-1 cells, as previously described [32,33]. Briefly, after anesthetized by intra-peritoneal injection of chloral hydrate, the tibia of right hind limb of C57BL/6 mice was carefully exposed, and a 23-gauge needle was inserted into the intramedullary canal of the bone, followed by injection of 20 μL of RM-1 cells (4 × 10 5 ).…”