Investigation on cerebrospinal fluid opioids and neurotransmitters related to spinal cord stimulation

Involvement of Opioid Peptides in the Analgesic Effect of Spinal Cord Stimulation in a Rat Model of Neuropathic Pain

Spinal cord stimulation (SCS)-induced analgesia was characterized, and its underlying mechanisms were examined in a spared nerve injury model of neuropathic pain in rats. The analgesic effect of SCS with moderate mechanical hypersensitivity was increased with increasing stimulation intensity between the 20% and 80% motor thresholds. Various frequencies (2, 15, 50, 100, 10000 Hz, and 2/100 Hz dense-dispersed) of SCS were similarly effective. SCS-induced analgesia was maintained without tolerance within 24 h of continuous stimulation. SCS at 2 Hz significantly increased methionine enkephalin content in the cerebrospinal fluid. The analgesic effect of 2 Hz was abolished by μ or κ opioid receptor antagonist. The effect of 100 Hz was prevented by a κ antagonist, and that of 10 kHz was blocked by any of the μ, δ, or κ receptor antagonists, suggesting that the analgesic effect of SCS at different frequencies is mediated by different endorphins and opioid receptors.

Association of Acute Postoperative Pain and Cigarette Smoking With Cerebrospinal Fluid Levels of Beta-Endorphin and Substance P

Objectives: Cigarette smoking is associated with postoperative pain perception, which might be mediated by beta-endorphin and substance P. These effects on postoperative pain perception have never been investigated in human cerebrospinal fluid (CSF), which reflects biochemical alterations in the brain. Therefore, we investigated the associations among cigarette smoking, postoperative pain, and levels of beta-endorphin and substance P in human CSF.

Methods: We recruited 160 Chinese men (80 active smokers and 80 nonsmokers) who underwent lumbar puncture before anterior cruciate ligament reconstruction, and 5-ml CSF samples were collected. Pain visual analog scale (VAS) scores, post-anesthetic recovery duration (PARD), and smoking variables were obtained. CSF levels of beta-endorphin and substance P were measured.

Results: Compared to non-smokers, active smokers had significantly higher pain VAS (2.40 ± 0.67 vs. 1.70 ± 0.86, p < 0.001) and PARD scores (9.13 ± 2.11 vs. 7.27 ± 1.35, p = 0.001), lower CSF beta-endorphin (33.76 ± 1.77 vs. 35.66 ± 2.20, p = 0.001) and higher CSF substance P (2,124.46 ± 217.34 vs. 1,817.65 ± 302.14, p < 0.001) levels. Pain VAS scores correlated with PARD in active smokers (r = 0.443, p = 0.001).

Conclusions: Cigarette smoking is associated with increased postoperative pain intensity, shown by delayed pain perception, higher pain VAS scores, and lower beta-endorphin and higher substance P levels in the CSF of active smokers. The more extended postoperative pain perception is delayed, the more pain intensity increases.

Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action

Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain.

Do low levels of beta-endorphin in the cerebrospinal fluid indicate defective top-down inhibition in patients with chronic neuropathic pain? A cross-sectional, comparative study

OBJECTIVE

Pain medicine still lacks mechanism-specific biomarkers to guide diagnosis and treatment, and defective top-down modulation is an important factor in the pathophysiology of chronic pain conditions. Using modern analytical tools and advanced multivariate statistical analysis, the aim of this study was to revisit two classical potential biomarkers of pro- and anti-nociception in humans (substance P and beta-endorphin), focusing particularly on the cerebrospinal fluid (CSF).

DESIGN

Cross-sectional, comparative, observational study.

SUBJECTS

Patients with chronic, post-traumatic and/or post-surgical, neuropathic pain refractory to conventional treatment (N = 15) and healthy controls (N = 19) were included.

METHODS

Samples were taken from CSF and blood, and levels of substance P and beta-endorphin were investigated using a Luminex technology kit.

RESULTS

We found low levels of beta-endorphin in the CSF of neuropathic pain patients (66 ± 11 pcg/mL) compared with healthy controls (115 ± 14 pcg/mL) (P = 0.017). Substance P levels in the CSF did not differ (20 ± 2 pcg/mL, 26 ± 2, P = 0.08). However, our multivariate data analysis showed that belonging to the patient group was associated with low levels of both substances in the CSF. A higher correlation between the levels of beta-endorphin and substance P in CSF was found in healthy controls than in patients (rs  = 0.725, P < 0.001 vs. rs  = 0.574, P = 0.032).

CONCLUSIONS

Patients with chronic neuropathic pain due to trauma or surgery had low levels of beta-endorphin in the CSF. We speculate that this could indicate a defective top-down modulation of pain in chronic neuropathic pain. Our results also illustrate the importance of taking a system-wide, multivariate approach when searching for biomarkers.

The effect of physical therapy on beta-endorphin levels

Beta-endorphin (betaE) is an important reliever of pain. Various stressors and certain modalities of physiotherapy are potent inducers of the release of endogenous betaE to the blood stream. Most forms of exercise also increase blood betaE level, especially when exercise intensity involves reaching the anaerobic threshold and is associated with the elevation of serum lactate level. Age, gender, and mental activity during exercise also may influence betaE levels. Publications on the potential stimulating effect of manual therapy and massage on betaE release are controversial. Sauna, mud bath, and thermal water increase betaE levels through conveying heat to the tissues. The majority of the techniques for electrical stimulation have a similar effect, which is exerted both centrally and--to a lesser extent--peripherally. However, the parameters of electrotherapy have not yet been standardised. The efficacy of analgesia and the improvement of general well-being do not necessarily correlate with betaE level. Although in addition to blood, increased brain and cerebrospinal fluid betaE levels are also associated with pain, the majority of studies have concerned blood betaE levels. In general, various modalities of physical therapy might influence endorphin levels in the serum or in the cerebrospinal fluid--this is usually manifested by elevation with potential mitigation of pain. However, a causal relationship between the elevation of blood, cerebrospinal fluid or brain betaE levels and the onset of the analgesic action cannot be demonstrated with certainty.

Long-term follow-up of patients with cardiac syndrome X treated by spinal cord stimulation

OBJECTIVE

To assess the long-term effect of spinal cord stimulation (SCS) in patients with refractory cardiac syndrome X (CSX).

METHODS

A prospective, controlled, long-term follow-up was performed of 19 patients with CSX with refractory angina who underwent SCS (SCS group, 5 men, mean (SD) age 60.9 (8.5) years); 9 comparable patients with CSX who refused SCS treatment (3 men, mean (SD) age 60.9 (8.8) years) constituted the control group. Clinical and functional status were assessed at the time of screening for SCS indication (basal evaluation) and at a median (range) follow-up of 36 (15-82) months.

RESULTS

The two groups at baseline did not show any difference in clinical characteristics and angina status. All indicators of angina status (angina episode frequency, duration and short-acting nitrate use) improved significantly at follow-up in the SCS group (p<0.001) but not in controls. Functional status, as assessed by the Seattle Angina Questionnaire and a visual analogue scale for quality of life, improved at follow-up in the SCS group (p<0.001 for all scales) but not in controls. Exercise tolerance, exercise-induced angina and ST segment changes also significantly improved in the SCS group but not in controls.

CONCLUSIONS

Data show that SCS can be a valid form of treatment for long-term control of angina episodes in patients with refractory CSX.