Yvonne Schmidt

Immune cell-derived opioids protect against neuropathic pain in mice

The analgesic effects of leukocyte-derived opioids have been exclusively demonstrated for somatic inflammatory pain, for example, the pain associated with surgery and arthritis. Neuropathic pain results from injury to nerves, is often resistant to current treatments, and can seriously impair a patients quality of life. Although it has been recognized that neuronal damage can involve inflammation, it is generally assumed that immune cells act predominately as generators of neuropathic pain. However, in this study we have demonstrated that leukocytes containing opioids are essential regulators of pain in a mouse model of neuropathy. About 30%-40% of immune cells that accumulated at injured nerves expressed opioid peptides such as beta-endorphin, Met-enkephalin, and dynorphin A. Selective stimulation of these cells by local application of corticotropin-releasing factor led to opioid peptide-mediated activation of opioid receptors in damaged nerves. This ultimately abolished tactile allodynia, a highly debilitating heightened response to normally innocuous mechanical stimuli, which is symptomatic of neuropathy. Our findings suggest that selective targeting of opioid-containing immune cells promotes endogenous pain control and offers novel opportunities for management of painful neuropathies.

T lymphocytes containing β-endorphin ameliorate mechanical hypersensitivity following nerve injury ☆

Neuropathic pain is a debilitating consequence of nerve injuries and is frequently resistant to classical therapies. T lymphocytes mediate adaptive immune responses and have been suggested to generate neuropathic pain. In contrast, in this study we investigated T cells as a source of opioidergic analgesic β-endorphin for the control of augmented tactile sensitivity following neuropathy. We employed in vivo nociceptive (von Frey) testing, flow cytometry and immunofluorescence in wild-type and mice with severe combined immunodeficiency (SCID) subjected to a chronic constriction injury of the sciatic nerve. In wild-type mice, T lymphocytes constituted approximately 11% of all immune cells infiltrating the injury site, and they expressed β-endorphin and receptors for corticotropin-releasing factor (CRF), an agent releasing opioids from leukocytes. CRF applied at the nerve injury site fully reversed neuropathy-induced mechanical hypersensitivity in wild-type animals. In SCID mice, T cells expressing β-endorphin and CRF receptors were absent at the damaged nerve. Consequently, these animals had substantially reduced CRF-mediated antinociception. Importantly, the decreased antinociception was fully restored by transfer of wild-type mice-derived T lymphocytes in SCID mice. The re-established CRF antinociception could be reversed by co-injection of an antibody against β-endorphin or an opioid receptor antagonist with limited access to the central nervous system. We propose that, in response to CRF stimulation, T lymphocytes accumulating at the injured nerves utilize β-endorphin for activation of local neuronal opioid receptors to reduce neuropathy-induced mechanical hypersensitivity. Our findings reveal β-endorphin-containing T cells as a crucial component of beneficial adaptive immune responses associated with painful peripheral nerve injuries.

[Comparison of Aggressive Behavior, Compulsory Medication and Absconding Behavior Between Open and Closed door Policy in an Acute Psychiatric Ward].

Objective According to legal requirements coercive treatment must be limited to acts necessary for the protection of patients and cannot be used for institutional interests. Here, we aimed to test the hypothesis that opening psychiatric wards can reduce the number of aggressive assaults and of coercive treatment without increasing absconding rates. Methods Numbers of absconding, coercive medication, fixation and special security actions were collected retrospectively and compared between phases of closed (N total = 409; N legally committed = 64) and 90 % of daytime opened (N total = 571; N legally committed = 99) doors in an acute psychiatric ward. Results During the phase of opened doors we observed significantly reduced aggressive assaults (p < 0,001) and coercive medication (p = 0,006) compared to the closed setting, while the absconding rate did not change (p = 0,20). Limitation Given the retrospective non-experimental design, no causal interpretations can be drawn. Conclusion The results suggest that open door is associated with reduction of aggressive assaults and coercive medication without increasing absconding rates. This speaks for a stronger implementation of open door policies in acute wards in order to preserve human rights in psychiatry. To collect more robust evidence for this thesis, longer phases should be monitored and moderating variables such as atmosphere and social cohesion should be assessed.

Cutaneous nociceptors lack sensitisation, but reveal μ-opioid receptor-mediated reduction in excitability to mechanical stimulation in neuropathy.

BackgroundPeripheral nerve injuries often trigger a hypersensitivity to tactile stimulation. Behavioural studies demonstrated efficient and side effect-free analgesia mediated by opioid receptors on peripheral sensory neurons. However, mechanistic approaches addressing such opioid properties in painful neuropathies are lacking. Here we investigated whether opioids can directly inhibit primary afferent neuron transmission of mechanical stimuli in neuropathy. We analysed the mechanical thresholds, the firing rates and response latencies of sensory fibres to mechanical stimulation of their cutaneous receptive fields.ResultsTwo weeks following a chronic constriction injury of the saphenous nerve, mice developed a profound mechanical hypersensitivity in the paw innervated by the damaged nerve. Using an in vitro skin-nerve preparation we found no changes in the mechanical thresholds and latencies of sensory fibres from injured nerves. The firing rates to mechanical stimulation were unchanged or reduced following injury. Importantly, μ-opioid receptor agonist [D-Ala2,N-Me-Phe4,Gly5]-ol-enkephalin (DAMGO) significantly elevated the mechanical thresholds of nociceptive Aδ and C fibres. Furthermore, DAMGO substantially diminished the mechanically evoked discharges of C nociceptors in injured nerves. These effects were blocked by DAMGO washout and pre-treatment with the selective μ-opioid receptor antagonist Cys2-Tyr3-Orn5-Pen7-amide. DAMGO did not alter the responses of sensory fibres in uninjured nerves.ConclusionsOur findings suggest that behaviourally manifested neuropathy-induced mechanosensitivity does not require a sensitised state of cutaneous nociceptors in damaged nerves. Yet, nerve injury renders nociceptors sensitive to opioids. Prevention of action potential generation or propagation in nociceptors might represent a cellular mechanism underlying peripheral opioid-mediated alleviation of mechanical hypersensitivity in neuropathy.

Immunohistochemical Analysis of Opioid Receptors in Peripheral Tissues

Immunohistochemical staining is widely used to identify opioid receptors in specific cell types or anatomical structures throughout the nervous system. Opioid receptors are not restricted to the central nervous system, but are also present in peripheral sensory neurons, where their activation exerts analgesic effects without inducing centrally mediated side effects. Here, we describe immunohistochemical analysis of opioid receptors in the peripheral sensory neuron cell bodies, along the axons and their peripheral endings in the hind paw skin, as well as in the spinal cord, under naïve and sciatic nerve damage conditions in mice. Moreover, we consider the current debate on the specificity of antibodies.

Skin-nerve preparation to assay the function of opioid receptors in peripheral endings of sensory neurons.

This chapter describes the methodology of the in vitro skin-saphenous nerve preparation and its application to test for the modulatory effects of opioids on the function of cutaneous sensory neurons in experimental models of pain. We detail the skin-nerve setup requirements and the technique to record action potentials from single sensory fibers. We address how to test for inhibitory effects of opioid receptor activation on mechanical and thermal sensitivity of nociceptors and mechanoreceptors in the complete Freunds adjuvant-induced inflammation and the chronic constriction injury model of neuropathic pain.

105 T CELL-DERIVED AND EXOGENOUS OPIOIDS ACTING AT PERIPHERAL OPIOID RECEPTORS CONTROL NEUROPATHIC PAIN

This study investigated the influence of LFS on cerebral activation pattern by functional magnetic resonance imaging (fMRI). Methods: Thirty-four experiments were performed in 17 healthy male volunteers. Painful electrical test stimulation and conditioning LFS (1Hz, 1200 pulses, 4-fold pain threshold) were applied by a concentric electrode to right hand dorsum. Test stimulation series were performed before (Pre) and after LFS (Post) or no stimulation period (Control). Volunteers rated sensory and affective pain perception. Results: Before LFS, test stimulation produced activation in primary and secondary somatosensory cortex (S1, S2), insula, anterior cingulate cortex (ACC), temporal cortex, prefrontal cortex and right inferior parietal lobe. No difference was found between Pre LFS and Pre Control. Pre LFS-Post LFS contrast showed a significant activity decrease in bilateral S1, S2, ACC and ipsilateral posterior insula. Brain activation during Control did not change. Comparison of Post LFS and Post Control revealed reduced activity in bilateral ACC after LFS. Sensory and affective pain ratings solely decreased after LFS. Pain relief was correlated with increased activity after LFS in ACC, anterior insula, striatum. Conclusions: Results indicate LFS-induced LTD of brain areas involved in sensory (S1, S2) and affective (insula, ACC) pain processing. Ratings confirm reduction of pain after LFS. LTD effect might be enhanced by an increased activation of brain areas involved in endogenous descending systems.

291 Expression of peripheral opioid receptors and peptides in a neuropathic pain model

tested. In this trial’s open-label extension, patients received 150–600 mg/d pregabalin (BID), adjusted to optimize efficacy/tolerability, for up to 6 months. Patients (97%) received P 300 mg/d. Pregabalin was generally well tolerated: 70/104 patients completed 24 weeks of open-label treatment, while 15/104 withdrew because of AEs. Peripheral edema, dizziness, and somnolence were the most common AEs associated with treatment. Conclusions. During 13-week double-blind treatment, pregabalin 600 mg/d showed robust efficacy for improving pain and sleep with no meaningful effect on nerve conduction. Pregabalin was generally well tolerated during 13-week double-blind and 6-month open-label treatment.

279 Leukocyte-derived opioids produce peripheral antinociception in neuropathic pain

278 INTRAEPIDERMAL NERVE FIBER DENSITY IN PATIENTS WITH CHEMOTHERAPY-INDUCED NEUROPATHY: A PROSPECTIVE STUDY A-L. Kautio , M.K. Koskinen *, H.K. Haapasalo , P.-L. Kellokumpu-Lehtinen , T.H. Saarto , M.L. Haanpaa d,e a Department of Oncology, Tampere University Hospital, Tampere, Finland b Department of Pathology, Tampere University Hospital, Tampere, Finland c Department of Oncology, Helsinki University Hospital, Finland, Finland d Pain Clinic, Department of Anesthesiology and Intensive Care, Helsinki University Hospital, Finland e Department of Neurosurgery, Helsinki University Hospital, Finland

275 LEUKOCYTE-DERIVED OPIOIDS INHIBIT NEUROPATHIC PAIN BY ACTIVATING PERIPHERAL OPIOID RECEPTORS

Background and Aims: It is known that microwave therapy applied to the acupuncture loci is effective in patients with osteoarthrosis. The aim of our study was to determine whether a therapeutic intervention consisted of microwave therapy and acupuncture on the acupuncture loci including the pain points at affected joints is also effective in such patients. Methods: Eighteen subjects with osteoarthrosis (mainly of the knees) associated with moderate reactive synovitis were studied. Clinical examination had included quantitative assessment of pain intensity (in marks) using appropriate Tables and indices. Needle reflex therapy involved 2 to 4 pain acupuncture points of affected joints, 1 to 2 points within the same nervous metamere (as a rule, contralaterally) and 1 to 2 appropriate auricular loci. Influences of needles inserted into pain acupuncture points and microwave therapy (using the ‘Luch-II’ device, Russia; low-thermal doses) involving the affected joints were simultaneous. Results: In 94% of the patients, pain markedly relieved since the 2nd or 3rd procedure already what was accompanied with increased joint mobility. At the end of the treatment course, pain and symptoms of synovitis had fully been gone. This allowed a 1.5-fold decrease of doses of pain-relieving and anti-inflammatory drugs, and even to abolish them in several patients. Conclusions: The results show that a therapeutic intervention consisted of microwave therapy and acupuncture on the loci of relevance including the pain points at affected joints is effective, and can be recommended to be used in patients with joint diseases associated with pain syndrome and reactive synovitis.