Alterations in Endogenous Opioid Functional Measures in Chronic Back Pain

Abstract

The absence of consistent end organ abnormalities in many chronic pain syndromes has led to a search for maladaptive CNS mechanisms that may explain their clinical presentations and course. Here, we addressed the role of brain regional -opioid receptor-mediated neurotransmission, one of the best recognized mechanisms of pain regulation, in chronic back pain in human subjects. We compared -opioid receptor availability in vivo at baseline, during pain expectation, and with moderate levels of sustained pain in 16 patients with chronic nonspecific back pain (CNBP) and in 16 age-and gender-matched healthy control subjects, using the -opioid receptor-selective radioligand [ 11 C]carfentanil and positron emission tomography. We found that CNBP patients showed baseline increases in thalamic -opioid receptor availability, contrary to a previously studied sample of patients diagnosed with fibromyalgia. During both pain expectation and sustained pain challenges, CNBP patients showed regional reductions in the capacity to activate this neurotransmitter system compared with their control sample, further associated with clinical pain and affective state ratings. Our results demonstrate heterogeneity in endogenous opioid system functional measures across pain conditions, and alterations in both receptor availability and endogenous opioid function in CNBP that are relevant to the clinical presentation of these patients and the effects of opioid analgesics on -opioid receptors.

Simultaneous fMRI–PET of the opioidergic pain system in human brain

“…The fMRI-PET activations overlapping in the medial thalamic sub-region, which has been reported previously for pain induced opioid release (Scott et al, 2007). The thalamus is important for sensory discrimination, transmission/modulation of painful stimuli, and is also a key structure associated with chronic pain development (Tracey and Bushnell, 2009) and pathology of different chronic pain conditions (Martikainen et al, 2013). An earlier study showed that opioid receptor activation (as measured by changes in BP ND ) in the thalamus is associated with sensory and affective response attenuation to sustained pain (Zubieta et al, 2001).…”

Endogenous Opioid Inhibition of Chronic Low-Back Pain Influences Degree of Back Pain Relief After Morphine Administration

“…Whether there would be correspondence across the acute and chronic pain contexts was unclear, given conflicting findings regarding the impact of chronic pain on endogenous opioid function. [7][8][9] If findings for chronic pain were consistent with findings for brief evoked pain outcomes, 6 we expected that greater endogenous opioid inhibition of chronic pain intensity would be associated with smaller acute analgesic effects of morphine on chronic pain intensity.…”

Nociception, Pain, Negative Moods, and Behavior Selection

“…The latter spatial shift seems to occur even though these subjects judge their back pain as essentially unchanged over the one-year monitoring period. Thus, it seems that chronification of pain, accompanied by gray matter and functional connectivity reorganization, and also accompanied with reduced capacity to activate central opioid neurotransmission (Martikainen et al, 2013), renders the pain to become more subjective/intrapersonal and more emotional.…”