Pain
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Randomized Controlled Trial
Endogenous opioids mediate left dorsolateral prefrontal cortex rTMS-induced analgesia.
The concurrent rise of undertreated pain and opiate abuse poses a unique challenge to physicians and researchers alike. A focal, noninvasive form of brain stimulation called repetitive transcranial magnetic stimulation (rTMS) has been shown to produce acute and chronic analgesic effects when applied to dorsolateral prefrontal cortex (DLPFC), but the anatomical and pharmacological mechanisms by which prefrontal rTMS induces analgesia remain unclear. Data suggest that DLPFC mediates top-down analgesia via gain modulation of the supraspinal opioidergic circuit. ⋯ Naloxone pretreatment significantly reduced the analgesic effects of real rTMS. These results demonstrate that left DLPFC rTMS-induced analgesia requires opioid activity and suggest that rTMS drives endogenous opioidergic pain relief in the human brain. Further studies with chronic dosing regimens of drugs that block or augment the actions of opiates are needed to determine whether TMS can augment opiates in chronic or postoperative pain management.
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Randomized Controlled Trial Comparative Study
Placebo manipulations reduce hyperalgesia in neuropathic pain.
Several studies have shown that placebo analgesia effects can be obtained in healthy volunteers, as well as patients suffering from acute postoperative pain and chronic pain conditions such as irritable bowel syndrome. However, it is unknown whether placebo analgesia effects can be elicited in chronic pain conditions with a known pathophysiology such as a nerve injury. Nineteen patients who had developed neuropathic pain after thoracotomy were exposed to a placebo manipulation in which they received either open or hidden administrations of lidocaine. ⋯ No placebo effect was observed in relation to spontaneous pain or evoked pain, which is most likely due to low pain levels resulting in floor effects. This is the first study to demonstrate a placebo effect in neuropathic pain. The possible mechanisms underlying the placebo effects in hyperalgesia are discussed, and implications for treatment are outlined.
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Comparative Study
How efficient is the orienting of spatial attention to pain? An experimental investigation.
This study investigated how efficient spatial attention was oriented to pain in 2 experiments. Participants detected whether painful (pain group) or nonpainful (control group) somatosensory stimuli were delivered to the left or right hand. Each stimulus was preceded by a visual cue presented near to the stimulated hand (valid trial), the opposite hand (invalid trial), or centrally between hands. ⋯ This effect was due to faster responses on valid relative to baseline trials (engagement), rather than slower responses on invalid relative to baseline trials (disengagement), and was significantly correlated with self-reported bodily threat. In experiment 2, prioritization of the pain location was probably overridden by task strategies because it was advantageous for participants' task performance to attend to the cued location irrespective of whether stimulation was painful or not. Implications of these findings for theories of hypervigilance and attentional management of pain are discussed.
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Chronic low back pain (LBP) is a complex, multifactorial disorder with unclear underlying mechanisms. In humans and rodents, decreased expression of secreted protein acidic rich in cysteine (SPARC) is associated with intervertebral disc (IVD) degeneration and signs of LBP. The current study investigates the hypothesis that IVD degeneration is a risk factor for chronic LBP. ⋯ Morphine (6 mg/kg, i.p.) reduced cutaneous sensitivity and alleviated axial discomfort in SPARC-null mice. Ageing SPARC-null mice mirror many aspects of the complex and challenging nature of LBP in humans and incorporate both anatomic and functional components of the disease. The current study supports the hypothesis that IVD degeneration is a risk factor for chronic LBP.