Dorsal Column Stimulation Induces Release of Serotonin and Substance P in the Cat Dorsal Horn:

Implantable, Programmable, and Wireless Device for Electrical Stimulation of the Dorsal Root Ganglion in Freely-Moving Rats: A Proof of Concept Study

Objective

This was a proof of concept study, based on systematic reviews of the efficacy and safety of the dorsal root ganglion (DRG) stimulation. The main objective was to develop an implantable, programmable, and wireless device for electrical stimulation of DRG and a methodology that can be used in translational research, especially to understand the mechanism of neuromodulation and to test new treatment modalities in animal models of pain.

Methods

We developed and tested a stimulator that uses a battery-powered microelectronic circuit, to generate constant current square biphasic or monophasic pulsed waveform of variable amplitudes and duration. It is controlled by software and an external controller that allows radio frequency communication with the stimulator. The stimulator was implanted in Sprague–Dawley (SD) rats. The lead was positioned at the L5 DRG level, while the stimulator was placed in the skin pocket at the ipsilateral side. Forty-five animals were used and divided into six groups: spinal nerve ligation (SNL), chronic compression injury of the DRG (CCD), SNL + active DRG stimulation, intact control group, group with the implanted sham stimulator, and sham lead. Behavioral testing was performed on the day preceding surgery and three times postoperatively (1st, 3rd, and 7th day).

Results

In animals with SNL, neurostimulation reduced pain-related behavior, tested with pinprick hyperalgesia, pinprick withdrawal test, and cold test, while the leads per se did not cause DRG compression. The rats well tolerated the stimulator. It did not hinder animal movement, and it enabled the animals to be housed under regular conditions.

Conclusion

A proof-of-concept experiment with our stimulator verified the usability of the device. The stimulator enables a wide range of research applications from adjusting stimulation parameters for different pain conditions, studying new stimulation methods with different frequencies and waveforms to obtain knowledge about analgesic mechanisms of DRG stimulation.

[Spinal cord stimulation in the treatment of chronic pain]

Despite the numerous analgesic drugs, the prevalence of intractable neuropathic pain remains high making up about 5%. Intervention methods, including methods of chronic electrostimulation, are used to treat these patients. Spinal cord stimulation (SCS) is the most common surgical method worldwide that replaced destructive and ablation procedures. Currently, common tonic SCS, HF-10 stimulation and burst SCS are applied, and the choice of method is based on clinical and neurophysiological data. Also, the introduction of nanomaterial-enabled neural stimulation could significantly minimize surgery risk.

Decreased intracellular GABA levels contribute to spinal cord stimulation-induced analgesia in rats suffering from painful peripheral neuropathy: the role of KCC2 and GABA(A) receptor-mediated inhibition

Elevated spinal extracellular γ-aminobutyric acid (GABA) levels have been described during spinal cord stimulation (SCS)-induced analgesia in experimental chronic peripheral neuropathy. Interestingly, these increased GABA levels strongly exceeded the time frame of SCS-induced analgesia. In line with the former, pharmacologically-enhanced extracellular GABA levels by GABA(B) receptor agonists in combination with SCS in non-responders to SCS solely could convert these non-responders into responders. However, similar treatment with GABA(A) receptor agonists and SCS is known to be less efficient. Since K⁺ Cl⁻ cotransporter 2 (KCC2) functionality strongly determines proper GABA(A) receptor-mediated inhibition, both decreased numbers of GABA(A) receptors as well as reduced KCC2 protein expression might play a pivotal role in this loss of GABA(A) receptor-mediated inhibition in non-responders. Here, we explored the mechanisms underlying both changes in extracellular GABA levels and impaired GABA(A) receptor-mediated inhibition after 30 min of SCS in rats suffering from partial sciatic nerve ligation (PSNL). Immediately after cessation of SCS, a decreased spinal intracellular dorsal horn GABA-immunoreactivity was observed in responders when compared to non-responders or sham SCS rats. One hour later however, GABA-immunoreactivity was already increased to similar levels as those observed in non-responder or sham SCS rats. These changes did not coincide with alterations in the number of GABA-immunoreactive cells. C-Fos/GABA double-fluorescence clearly confirmed a SCS-induced activation of GABA-immunoreactive cells in responders immediately after SCS. Differences in spinal dorsal horn GABA(A) receptor-immunoreactivity and KCC2 protein levels were absent between all SCS groups. However, KCC2 protein levels were significantly decreased compared to sham PSNL animals. In conclusion, reduced intracellular GABA levels are only present during the time frame of SCS in responders and strongly point to a SCS-mediated on/off GABAergic release mechanism. Furthermore, a KCC2-dependent impaired GABA(A) receptor-mediated inhibition seems to be present both in responders and non-responders to SCS due to similar KCC2 and GABA(A) receptor levels.

Spinal Cord Stimulation for Chronic Pain

Spinal cord stimulation (SCS) is one of the most effective modalities for management of re- fractory neuropathic pain unresponsive to conservative therapies. The SCS has been successful in providing analgesia, improving function, and enhancing quality of life for patients suffering from chronic pain conditions such as failed back surgery syndrome, complex regional pain syndrome, ischaemic and phantom limb pain, and coronary artery disease. This technique has proven to be cost effective in the long term despite its high initial cost. In this review article, we discuss the history of SCS development, mechanism of action, and indications for SCS. Key words: Failed back surgery syndrome, Ischaemic pain, Neuropathic pain

Spinal cord stimulation in the treatment of chronic critical limb ischemia

This paper reviews the clinical experience and proposed working mechanisms of spinal cord stimulation (SCS) in the treatment of chronic critical limb ischemia (CCLI). SCS appears to provide a significant long-term relief of ischemic pain and to improve healing of small ulcers, most likely due to effects on the nutritional skin blood flow. Despite these observations, randomized trials were not able to show limb salvage. Assessment of the microcirculatory skin blood flow, by means of transcutaneous oxygen pressure measurements and videocapillaromicroscopy, is necessary to evaluate the remaining microcirculatory reserve capacity likely to be exploited by SCS and to help identify patients that will benefit most from this treatment and in whom stimulation could lead to limb salvage.

Drug-enhanced spinal stimulation for pain: a new strategy

Neuropathic pain is notoriously difficult to manage and only a few classes of drugs may provide adequate benefits. Thus, in many cases spinal cord stimulation (SCS) is considered; however, in this group of patients, between 30-50% of the cases offered a percutaneous SCS trial may fail to obtain a satisfactory effect. Additionally, a certain number of patients with a good initial effect, report that after a period the benefits are reduced necessitating additional peroral drug therapy. Based on animal studies of transmitters and receptors involved in the effects of SCS in neuropathic pain, the GABA-B receptor seems to play a pivotal role for the effect and, moreover, the agonist baclofen injected intrathecally in rats potentiated the SCS effect in animals not responsive to SCS per se. Based on these and further studies, 48 patients with neuropathic pain and inadequate response to SCS were given intrathecal (i.t.) baclofen (ITB) in bolus doses as an adjuvant. In this group 7 patients enjoyed such a good effect that they were implanted with both SCS and drug delivery systems for ITB. Four additional cases received baclofen pumps alone. Some other patients were given intrathecal (i.t.) adenosine in combination with SCS and initially preferred this to baclofen. The chronic use of this drug in a pump however proved to be technically problematic and all the adenosine cases were eventually terminated. At follow-ups, in average 32 and 67 months after start of SCS + baclofen therapy, more than 50% still enjoy a very good effect. The daily dose of baclofen needed to maintain the effects was approximately doubled during the observation period. There were few and mild side-effects. However, in a group of three patients with peroral baclofen therapy and SCS, complaints of side-effects were common and this therapy was terminated. Informal reports from collegues support the negative experience with additional peroral baclofen. In conclusion, in patients with neuropathic pain demonstrating inadequate response to SCS (small VAS reduction; short duration) a trial of intrathecal baclofen in combination with SCS may be warranted.

Spinal cord stimulation: indications and outcomes

✓Spinal cord stimulation (SCS) is the most commonly used implantable neurostimulation modality for management of pain syndromes. In this paper the authors describe the current indications for SCS and its efficacy in the treatment of those diseases. Specifically, the literature on patient selection and outcomes after SCS for failed–back surgery syndrome (FBSS), refractory angina pectoris, peripheral vascular disease, and complex regional pain syndrome (CRPS) Type I was reviewed. Effective pain relief was obtained in 60 to 80% of patients with FBSS and CRPS Type I. Furthermore, these patients had significant improvements in quality of life (QOL) and a significantly greater chance of returning to work than patients who did not undergo SCS. The use of SCS in patients with inoperable angina (that is, refractory angina pectoris) resulted in significant decreases in chest pain and hospital admissions as well as increased exercise duration, with less morbidity than with open procedures that were performed for pain control only. Patients with inoperable PVD also demonstrated significant improvements in pain relief, QOL, and limb mobility. Reported complications were mostly related to hardware and were relatively minor. Review of randomized controlled studies supports the use of SCS as an effective treatment modality for pain associated with FBSS, refractory angina pectoris, peripheral vascular disease, and CRPS Type I.

Chronic daily headache: a scientist's perspective

Certain features of chronic daily headache, namely, increased headache frequency, expansion of headache area, and cutaneous allodynia, may imply sensitization of central nociceptive neurons in the trigeminal pathway. Repetitive activation of the trigeminal nerve can lead to a biologic and functional change in trigeminal nucleus caudalis neurons, characterized by a decrease in nociceptive threshold and receptive field expansion. Suppression of the endogenous pain control system can facilitate the process of central sensitization. Evidence of such suppression in patients with chronic daily headache includes decreased platelet serotonin, up-regulation of 5-HT2A receptors, increased platelet nitric oxide production, and increased levels of substance P and nerve growth factor in the cerebrospinal fluid. Results from a number of animal experiments have indicated that chronic analgesic exposure leads to changes in serotonin content and density of 5-HT2A receptors in the central nervous system. This plasticity of the serotonin-dependent pain control system may accelerate the process of sensitization; a biologic outcome that is expressed clinically by the development of chronic daily headache associated with analgesic overuse.

Pathophysiology of chronic daily headache

Despite no clear explanation of the mechanism underlying chronic daily headache, sensitization of central nociceptive neurons is one possibility. Either prolonged activation of peripheral nociceptors or any factors that can alter the endogenous pain control system can trigger this process. A decrease in platelet serotonin has been observed in patients with chronic tension-type headache as well as migraine patients with medication-induced headache. It was also shown that chronic analgesic exposure led to changes in the serotonin content and the density of the 5-HT(2A) receptor in the cerebral cortex. The plasticity of the serotonin-dependent pain control system may facilitate the process of sensitization and results in the development of chronic daily headache.