Marcus Schley

NGF induces non-inflammatory localized and lasting mechanical and thermal hypersensitivity in human skin

&NA; Nerve growth factor (NGF) modulates sensitivity and sprouting of nociceptors. We explored the spatial and temporal sensitization induced by NGF injection (1 &mgr;g) in human skin. Hyperalgesia was investigated in 16 volunteers (36 ± 9 years) at day 1, 3, 7, 21, and 49. Areas of mechanical (brush, pin‐prick) and heat (43 °C) sensitization were mapped and thermal (heat and cold) pain thresholds, mechanical (impact stimulation) and electrically evoked pain, and axon reflex flare were assessed. No spontaneous pain or local inflammation was recorded upon NGF injection and during 49 days. Sensitization to heat was maximum at day 3 and lasted 21 days. Hyperalgesia to cold was recorded at day 7 and 21. Hypersensitivity to mechanical impact stimuli developed delayed, reached maximum at day 21, and persisted throughout 49 days. Fifty percent of all volunteers reported a static allodynia to tonic pressure until day 21. Electrical stimulation at 7.5 mA was more painful at the NGF site at day 21, which correlated significantly to maximum impact pain. Axon reflex flare was unaffected by NGF. Sensitization was limited to the NGF injection site, no touch‐ or pin‐prick evoked secondary hyperalgesia was observed. Spatially restricted hyperalgesia indicates a peripheral rather than central mechanism. The temporal profile of lasting nociceptor sensitization suggests an altered peripheral axonal expression of sensory proteins specifically leading to mechanical and thermal sensitization. Intradermal NGF administration provokes a pattern of sensitization that can be used as experimental model for neuropathic pain.

Predominant CB2 receptor expression in endothelial cells of glioblastoma in humans.

BACKGROUND AND OBJECTIVES The most abundant malignant brain tumor in human is glioblastoma and patients with this type of tumor have a poor prognosis with high mortality. Glioblastoma are characterized particularly by fast growth and a dependence on blood vessel formation for survival. Cannabinoids (CBs) inhibit tumor growth by inducing apoptosis of tumor cells and impairing tumor angiogenesis. The distribution of CB1 and CB2 receptors in glioblastoma and associated endothelial vessels is still unknown. METHODS Tissue samples were collected consecutively after neurosurgery of 19 patients suspected glioblastoma and examined immunohistochemically for CB1 and CB2 receptor expression. Vessel endothelial cells of the sections were immunocytochemically identified by using a primary antibody against PECAM-1. Double labelling was performed for CB receptors and endothelial cells of the vessels by DAPI staining. RESULTS In endothelia of control tissue, about 24% and 45% of the cells were positive for CB1 and CB2 receptors. In glioblastoma endothelial cells, CB1 and CB2 receptors were present in about 38% and 54% of the cells respectively. In comparison to CB1, an elevated CB2 receptor expression was identified in glioblastoma. CONCLUSIONS The abundant expression and distribution of CB2 receptors in glioblastoma and particularly endothelial cells of glioblastoma indicate that impaired tumor growth in presence of CB may be associated with CB2 activation. Selective CB2 agonists might become important targets attenuating vascular endothelial growth factor (VEGF) signalling and thereby diminishing neoangiogenesis and glioblastoma growth.

Delta-9-THC based monotherapy in fibromyalgia patients on experimentally induced pain, axon reflex flare, and pain relief.

ABSTRACT Objective: Fibromyalgia (FM) is a chronic pain syndrome characterized by a distinct mechanical hyperalgesia and chronic pain. Recently, cannabinoids have been demonstrated as providing anti-nociceptive and anti-hyperalgesic effects in animal and human studies. Here, we explored in nine FM patients the efficacy of orally administered delta-9-tetrahydrocannabinol (THC) on electrically induced pain, axon reflex flare, and psychometric variables. Research design and methods: Patients received a daily dose of 2.5–15 mg of delta‐9-THC, with a weekly increase of 2.5 mg, as long as no side effects were reported. Psychometric variables were assessed each week by means of the West Haven-Yale Multidimensional Pain Inventory (MPI), Pittsburgh Sleep Quality Index (PSQI), Medical outcome survey-short form (MOS SF‐36), the Pain Disability Index (PDI), and the Fibromyalgia Impact Questionnaire (FIQ). In addition, patients recorded daily, in a diary, their overall pain intensity on a numeric scale. Each week, pain and axon reflex flare was evoked experimentally by administration of high intensity constant current pulses (1 Hz, pulse width 0.2 ms, current increase stepwise from 2.5–12.5 mA every 3 minutes) delivered via small surface electrodes, attached to the volar forearm skin. Main outcome measures: Daily pain recordings by the patient, experimentally induced pain, and axon reflex flare recorded by a laser Doppler scanner. Results: Five of nine FM patients withdrew during the study due to adverse side effects. Delta‐9-THC had no effect on the axon reflex flare, whereas electrically induced pain was significantly attenuated after doses of 10–15 mg delta‐9-THC ( p < 0.05). Daily-recorded pain of the FM patients was significantly reduced ( p < 0.01). Conclusions: This pilot study demonstrated that a generalized statement that delta‐9-THC is an analgetic drug cannot be made. However, a sub-population of FM patients reported significant benefit from the delta‐9-THC monotherapy. The unaffected electrically induced axon reflex flare, but decreased pain perception, suggests a central mode of action of the cannabinoid.

Nociceptor sensitization to mechanical and thermal stimuli in pig skin in vivo

Primary hyperalgesia to mechanical and thermal stimuli are major clinical symptoms of inflammatory pain and can be induced experimentally by ultraviolet‐B (UV‐B) irradiation in humans. We set‐up a pig model in order to have more options for pharmacological intervention on primary hyperalgesia.

Rapid flare development evoked by current frequency-dependent stimulation analyzed by full-field laser perfusion imaging.

We analyzed, with a new imaging technique, the rapid axon reflex flare responses in human skin upon transcutaneous delivery of electrical stimuli at 1, 5, 10 and 50 Hz in single bursts of five pulses each. Two-dimensional perfusion images covering an area of 8×8 cm2 were captured at 25 Hz and their averages saved at 0.5 Hz. The stimulation caused an axon reflex flare (maximum 3 cm2, 20 s after stimulation) that gradually resolved within 2 min. Maximum flare responses developed at 5 Hz, whereas pain ratings increased with stimulation frequency. The highest neuropeptide release at 5 Hz correlates to the discharge characteristics of mechanoinsensitive C-fibers, whereas the maximum pain intensity at 50 Hz may be attributed to the activation of A-delta fibers.

Skin innervation at different depths correlates with small fibre function but not with pain in neuropathic pain patients

Neuropathy can lead not only to impaired function but also to sensory sensitization. We aimed to link reduced skin nerve fibre density in different levels to layer‐specific functional impairment in neuropathic pain patients and tried to identify pain‐specific functional and structural markers.

Treatment-related changes in brain activation in patients with fibromyalgia syndrome

Little is known about the effects of successful treatment on brain function in chronic pain. This study examined changes in pain-evoked brain activation following behavioral extinction training in fibromyalgia patients. Using functional magnetic resonance imaging, brain activation to painful mechanical stimuli applied to the 2nd phalanx of the left 2nd digit (m. flexor digitorum) was assessed in 10 patients with fibromyalgia syndrome (FM) before and after behavioral extinction training. The behavioral treatment significantly reduced interference from pain in the FM patients. Mechanical pain threshold and pain tolerance increased significantly after treatment. Activation in the insula shifted bilaterally from a more anterior site before treatment to a more posterior location after treatment. The pre- to post-treatment reduction in both interference related to pain and pain severity were significantly associated with bilateral activation in pain-evoked activity in the posterior insula, the ipsilateral caudate nucleus/striatum, the contralateral lenticular nucleus, the left thalamus and the primary somatosensory cortex contralateral to the stimulated side. These data show a relation between successful behavioral treatment and higher activation bilaterally in the posterior insula and in the contralateral primary somatosensory cortex. Future studies should compare responders and non-responders for differential treatment effects and examine in more detail the mechanisms underlying these changes.

NGF enhances electrically induced pain, but not axon reflex sweating.

&NA; High‐affinity receptors for nerve growth factor (NGF) are found on nociceptors and sympathetic efferents. NGF is known to sensitize nociceptors, increase innervation density, and fire frequency of sympathetic fibers. We explored axonal sensitization of afferent and efferent fibers following intracutaneous injection of NGF in human and pig skin. In humans, frequency‐dependent (5, 20, 100 Hz) electrically induced pain was assessed 1, 3, 7, 21, and 49 days post injection. Sweat output was recorded in parallel using the quantitative sudomotor axon reflex test (QSART). Electrically induced pain ratings (7.5 mA for 30 s) significantly increased at the NGF sites for 5 Hz (numeric rating scale [NRS] 6 ± 0.5 vs 3.7 ± 0.4), 20 Hz (NRS 7.2 ± 0.4 vs 5 ± 0.5), and 100 Hz stimulation (NRS 6.9 ± 0.4 vs 5.4 ± 0.3) at day 21, and also for 5 Hz at day 49 (NRS 5.4 ± 0.4 vs 3.8 ± 0.3). Electrically evoked QSART increased frequency dependent, but was not altered by NGF throughout the entire observation period (average QSART at 5 Hz: 3 mL/h/m2, 20 Hz: 9 mL/h/m2, 100 Hz: 10 mL/h/m2). Similarly, NGF did not change the activity‐dependent slowing of conduction of sympathetic efferents (6 ± 2% vs 5.1 ± 1.5%, for 3 minutes, 2 Hz) in pig single‐fiber recordings. In parallel to the increased pain ratings recorded in humans, activity‐dependent slowing of mechano‐insensitive nociceptors was reduced by NGF (18.1 ± 2% vs 29 ± 1.4%). In summary, axonal sensitization of nociceptors by NGF could underlie the hyperalgesia to electrical stimulation. Enhanced responses were limited to nociceptors, as no sensitization was found in sympathetic efferent neurons. NGF administration increased electrically induced pain, decreased activity‐dependent slowing of mechano‐insensitive nociceptors, but did not affect sympathetic efferents. Axonal sensitization could underlie the NGF‐evoked hyperalgesia.

Differential central pain processing following repetitive intramuscular proton/prostaglandin E2 injections in female fibromyalgia patients and healthy controls

BACKGROUND While the etiology of fibromyalgia syndrome (FMS) remains unclear, it is assumed that both peripheral and central components are involved. AIMS/METHODS To investigate central activation patterns following chemically-induced muscle pain we repetitively injected protons (low pH) and prostaglandin E(2) (PGE(2)) in isotonic solution into the left extensor carpi radialis brevis muscle of female FMS patients and female healthy control subjects (HC). The injection of protons/PGE(2) has the advantage that it is not prone to tachyphylaxis compared to capsaicin and hypotonic saline solution. During the repetitive injections continuous pain ratings were recorded and functional magnetic resonance imaging measurements were conducted. RESULTS Injection of protons/PGE(2) led to activation of the anterior and medial cingulate cortices, contralateral primary sensory cortex, bilateral insula and thalamus, left basal ganglia, left orbitofrontal cortex and the cerebellum in FMS patients. In HC, activations were found only in the anterior, medial, and posterior cingulate cortices, and the primary somatosensory cortex. The contrast between the groups revealed significantly stronger activation for FMS patients in the left anterior insula. Peak pain ratings were comparable between HC and FMS patients, but pain duration (sustained pain) was prolonged in FM. CONCLUSION Repetitive proton/PGE(2)-induced excitation of muscle tissue led to a more prolonged perception of pain and more wide-spread activation in pain-related brain areas in FMS, especially in the left (ipsilateral) insula, whereas acute protons/PGE(2)-induced pain processing was similar in the two groups. These data provide further evidence for enhanced central pain processing in FMS patients.Background: While the etiology of fibromyalgia syndrome (FMS) remains unclear, it is assumed that both peripheral and central components are involved.

Tetrahydrocannabinol (Delta 9-THC) Treatment in Chronic Central Neuropathic Pain and Fibromyalgia Patients: Results of a Multicenter Survey

Central neuropathic pain is difficult to treat, but delta 9-Tetrahydrocannabinol (delta 9-THC) may be a promising therapeutic agent. We administered in 172 patients on average 7.5 mg delta 9-THC over 7 months. Of these, 48 patients prematurely withdrew due to side effects, insufficient analgesia, or expense of therapy. Thus, 124 patients were assessed retrospectively in a multicenter telephone survey. Reported changes in pain intensity, recorded on a numeric rating scale (NRS), Pain Disability Index (PDI), Medical Outcomes Short-Form (SF-12), Quality of Life Impairment by Pain (QLIP), Hospital Anxiety Depression Scale (HADS), and amount of concomitant pain medication were recorded. Psychometric parameters (PDI, SF-12, QLIP, HADS) and pain intensity improved significantly during delta 9-THC treatment. Opioid doses were reduced and patients perceived THC therapy as effective with tolerable side effects. About 25% of the patients, however, did not tolerate the treatment. Therapy success and tolerance can be assessed by a transient delta 9-THC titration and its maintained administration for several weeks. The present survey demonstrates its ameliorating potential for the treatment of chronic pain in central neuropathy and fibromyalgia. A supplemental delta 9-THC treatment as part of a broader pain management plan therefore may represent a promising coanalgesic therapeutic option.