Thalamus and pain

Pain and pain management in haemophilia

Joint pain is common in haemophilia and may be acute or chronic. Effective pain management in haemophilia is essential to reduce the burden that pain imposes on patients. However, the choice of appropriate pain-relieving measures is challenging, as there is a complex interplay of factors affecting pain perception. This can manifest as differences in patients’ experiences and response to pain, which require an individualized approach to pain management. Prophylaxis with factor replacement reduces the likelihood of bleeds and bleed-related pain, whereas on-demand therapy ensures rapid bleed resolution and pain relief. Although use of replacement or bypassing therapy is often the first intervention for pain, additional pain relief strategies may be required. There is an array of analgesic options, but consideration should be paid to the adverse effects of each class. Nevertheless, a combination of medications that act at different points in the pain pathway may be beneficial. Nonpharmacological measures may also help patients and include active coping strategies; rest, ice, compression, and elevation; complementary therapies; and physiotherapy. Joint aspiration may also reduce acute joint pain, and joint steroid injections may alleviate chronic pain. In the longer term, increasing use of prophylaxis or performing surgery may be necessary to reduce the burden of pain caused by the degenerative effects of repeated bleeds. Whichever treatment option is chosen, it is important to monitor pain and adjust patient management accordingly. Beyond specific pain management approaches, ongoing collaboration between multidisciplinary teams, which should include physiotherapists and pain specialists, may improve outcomes for patients.

Pilot Study of Functional Magnetic Resonance Imaging Responses to Somatic Pain Stimuli in Youth With Functional and Inflammatory Gastrointestinal Disease

BACKGROUND

Brain-gut axis signaling modifies gastrointestinal symptomatology. Altered neural processing of intestinal pain signals involves interoceptive brain regions in adults with functional and inflammatory gastrointestinal disorders. Although these disorders frequently present in childhood, there are no published studies in youth. We determined whether neural processing of somatic pain stimuli differs in adolescents and young adults (AYA) with irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), as compared to healthy controls (HC).

METHODS

IBS and IBD AYA (16-20 years) underwent anticipated and thermal pain stimuli of low and high intensity on their forearm and simultaneous blood oxygen level-dependent functional magnetic resonance imaging. Data from adult HC were used for comparison. Subjects answered surveys evaluating alexithymia, anxiety, depression, and pain catastrophizing. Group data were compared using linear mixed effects and analysis of variance.

RESULTS

Study groups were similar by sex but not age. Significant group by pain condition interactions were observed in interoceptive brain regions during pain anticipation, and within perceptual brain regions during perceived pain. Higher activation within interoceptive brain regions during anticipated pain was observed in IBS compared with IBD and HC subjects. IBD patients demonstrated increased activation in perceptual brain regions during experienced pain as compared to IBS and HC.

CONCLUSIONS

IBS and IBD AYA demonstrate altered neural processing of somatic pain compared with each other and with HC. Our results suggest that neuromodulatory interventions targeting interoceptive brain circuits in IBS and perceptual brain regions in IBD may be effective.

Presence of Spontaneous Pain and Comorbid Pain Conditions Identifies Vulvodynia Subgroups

OBJECTIVE

The aims of the study were to define the heterogeneity of vulvodynia by determining data-driven subgroups within the vulvodynia diagnosis using exploratory cluster analysis and to characterize the subgroups identified.

MATERIALS AND METHODS

Included were participants in the longitudinal population-based study of vulvodynia in southeast Michigan who screened positive for vulvodynia at least once during the study. A cluster analysis using variables reflecting vulvar pain characteristics and comorbid pain conditions was conducted. Variables reflecting best separation of clusters were used to assign participants to subgroup categories. Demographic, psychiatric, general health, and other vulvar pain characteristics were summarized for each subgroup, followed by multinomial regression and pairwise comparisons of subgroups on these factors.

RESULTS

Of 441 women screening positive for vulvodynia during the course of the study, 393 were eligible on the basis of data requirements. Cluster analysis suggested that best subgroup separation was based on the following 2 variables: (1) presence or absence of spontaneous vulvar pain and (2) presence or absence of other comorbid pain conditions. Subgroups did not differ by age or ethnicity. The subgroup having spontaneous pain and other comorbid conditions demonstrated greatest morbidity in general health measures, psychiatric disorders, and other vulvar pain measures. Primary versus secondary vulvodynia did not vary between subgroups and did not assist in subgroup separation in the cluster analysis.

DISCUSSION

Subgroups based on exploratory cluster analysis demonstrated that presence of spontaneous pain and the presence of comorbid pain conditions resulted in best separation of groups. Presence of both spontaneous pain and other comorbid pain conditions identified the group with greatest morbidity.

Elevated Neurosteroids in the Lateral Thalamus Relieve Neuropathic Pain in Rats with Spared Nerve Injury

Neurosteroids are synthesized in the nervous system from cholesterol or steroidal precursors imported from peripheral sources. These compounds are important allosteric modulators of γ-aminobutyric acid A receptors (GABAARs), which play a vital role in pain modulation in the lateral thalamus, a main gate where somatosensory information enters the cerebral cortex. Using high-performance liquid chromatography/tandem mass spectrometry, we found increased levels of neurosteroids (pregnenolone, progesterone, deoxycorticosterone, allopregnanolone, and tetrahydrodeoxycorticosterone) in the chronic stage of neuropathic pain (28 days after spared nerve injury) in rats. The expression of the translocator protein TSPO, the upstream steroidogenesis rate-limiting enzyme, increased at the same time. In vivo stereotaxic microinjection of neurosteroids or the TSPO activator AC-5216 into the lateral thalamus (AP -3.0 mm, ML ±3.0 mm, DV 6.0 mm) alleviated the mechanical allodynia in neuropathic pain, while the TSPO inhibitor PK 11195 exacerbated it. The analgesic effects of AC-5216 and neurosteroids were significantly attenuated by the GABAAR antagonist bicuculline. These results suggested that elevated neurosteroids in the lateral thalamus play a protective role in the chronic stage of neuropathic pain.

Normothermic Mouse Functional MRI of Acute Focal Thermostimulation for Probing Nociception

Combining mouse genomics and functional magnetic resonance imaging (fMRI) provides a promising tool to unravel the molecular mechanisms of chronic pain. Probing murine nociception via the blood oxygenation level-dependent (BOLD) effect is still challenging due to methodological constraints. Here we report on the reproducible application of acute noxious heat stimuli to examine the feasibility and limitations of functional brain mapping for central pain processing in mice. Recent technical and procedural advances were applied for enhanced BOLD signal detection and a tight control of physiological parameters. The latter includes the development of a novel mouse cradle designed to maintain whole-body normothermia in anesthetized mice during fMRI in a way that reflects the thermal status of awake, resting mice. Applying mild noxious heat stimuli to wildtype mice resulted in highly significant BOLD patterns in anatomical brain structures forming the pain matrix, which comprise temporal signal intensity changes of up to 6% magnitude. We also observed sub-threshold correlation patterns in large areas of the brain, as well as alterations in mean arterial blood pressure (MABP) in response to the applied stimulus.

The neurobiology of pain perception in normal and persistent pain

SUMMARY 

Pain is a significant national burden in terms of patient suffering, expenditure and lost productivity. Understanding pain is fundamental to improving evaluation, treatment and innovation in the management of acute and persistent pain syndromes. Pain perception begins in the periphery, and then ascends in several tracts, relaying at different levels. Pain signals arrive in the thalamus and midbrain structures which form the pain neuromatrix, a constantly shifting set of networks and connections that determine conscious perception. Several cortical regions become active simultaneously during pain perception; activity in the cortical pain matrix evolves over time to produce a complex pain perception network. Dysfunction at any level has the potential to produce unregulated, persistent pain.

Role of the thalamic submedius nucleus histamine H1 and H 2 and opioid receptors in modulation of formalin-induced orofacial pain in rats

Histamine and opioid systems are involved in supraspinal modulation of pain. In this study, we investigated the effects of separate and combined microinjections of agonists and antagonists of histamine H1 and H2 and opioid receptors into the thalamic submedius (Sm) nucleus on the formalin-induced orofacial pain. Two guide cannulas were implanted into the right and left sides of the Sm in ketamine- and xylazine-anesthetized rats. Orofacial formalin pain was induced by subcutaneous injection of a diluted formalin solution (50 μl, 1.5%) into the vibrissa pad. Face rubbing durations were recorded at 3-min blocks for 45 min. Formalin produced a biphasic pain response (first phase: 0-3 min and second phase: 15-33 min). Separate and combined microinjections of histamine H1 and H2 receptor agonists, 2-pyridylethylamine (2-PEA) and dimaprit, respectively, and opioid receptor agonist, morphine, attenuated the second phase of pain. The analgesic effects induced by 2-PEA, dimaprit, and morphine were blocked by prior microinjections of fexofenadine (a histamine H1 receptor antagonist), famotidine (a histamine H2 receptor antagonist), and naloxone (an opioid receptor antagonist), respectively. Naloxone also prevented 2-PEA- and dimaprit-induced antinociception, and the analgesic effect induced by morphine was inhibited by fexofenadine and famotidine. These results showed the involvement of histamine H1 and H2 and opioid receptors in the Sm modulation of orofacial pain. Opioid receptor might be involved in analgesia induced by activation of histamine H1 and H2 receptors and vice versa.

Prolonged repeated acupuncture stimulation induces habituation effects in pain-related brain areas: an FMRI study

Most previous studies of brain responses to acupuncture were designed to investigate the acupuncture instant effect while the cumulative effect that should be more important in clinical practice has seldom been discussed. In this study, the neural basis of the acupuncture cumulative effect was analyzed. For this experiment, forty healthy volunteers were recruited, in which more than 40 minutes of repeated acupuncture stimulation was implemented at acupoint Zhusanli (ST36). Three runs of acupuncture fMRI datasets were acquired, with each run consisting of two blocks of acupuncture stimulation. Besides general linear model (GLM) analysis, the cumulative effects of acupuncture were analyzed with analysis of covariance (ANCOVA) to find the association between the brain response and the cumulative duration of acupuncture stimulation in each stimulation block. The experimental results showed that the brain response in the initial stage was the strongest although the brain response to acupuncture was time-variant. In particular, the brain areas that were activated in the first block and the brain areas that demonstrated cumulative effects in the course of repeated acupuncture stimulation overlapped in the pain-related areas, including the bilateral middle cingulate cortex, the bilateral paracentral lobule, the SII, and the right thalamus. Furthermore, the cumulative effects demonstrated bimodal characteristics, i.e. the brain response was positive at the beginning, and became negative at the end. It was suggested that the cumulative effect of repeated acupuncture stimulation was consistent with the characteristic of habituation effects. This finding may explain the neurophysiologic mechanism underlying acupuncture analgesia.