Articles: neuralgia.
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Spinal mGluR5 is a key mediator of neuroplasticity underlying persistent pain. Although brain mGluR5 is localized on cell surface and intracellular membranes, neither the presence nor physiological role of spinal intracellular mGluR5 is established. Here we show that in spinal dorsal horn neurons >80% of mGluR5 is intracellular, of which ∼60% is located on nuclear membranes, where activation leads to sustained Ca(2+) responses. ⋯ Decreasing intracellular glutamate via blocking EAAT-3, mimics the effects of intracellular mGluR5 antagonism. These findings show a direct link between an intracellular GPCR and behavioural expression in vivo. Blockade of intracellular mGluR5 represents a new strategy for the development of effective therapies for persistent pain.
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Review
The Sphenopalatine Ganglion: Anatomy, Pathophysiology, and Therapeutic Targeting in Headache.
The sphenopalatine ganglion (SPG) has attracted the interest of practitioners treating head and face pain for over a century because of its anatomical connections and role in the trigemino-autonomic reflex. In this review, we discuss the anatomy of the SPG, as well as what is known about its role in the pathophysiology of headache disorders, including cluster headache and migraine. We then address various therapies that target the SPG, including intranasal medication delivery, new SPG blocking catheter devices, neurostimulation, chemical neurolysis, and ablation procedures.
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Small fiber neuropathies (SFNs) are a subgroup of sensory neuropathies that almost exclusively affect thinly myelinated A-delta or unmyelinated C-nerve fibers. Patients with SFN typically report acral burning pain, paresthesias, and dysesthesias, and sometimes itch manifesting particularly at toes and feet. ⋯ The diversity in clinical presentation, however, already implies that different pathophysiological mechanisms underlie small nerve fiber degeneration and regeneration in these disorders. This review aims at presenting current knowledge on small nerve fiber research and at intensifying the awareness for SFN vs small fiber pathology as a chance to learn about small nerve fiber pathophysiology.
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Targeting peripheral neuropathic pain at its origin may prevent the development of hypersensitivity. Recently we showed this can be mediated by opioid receptors at the injured nerve trunk. Here, we searched for the most relevant peripheral site to block transient receptor potential vanilloid 1 (TRPV1), and investigated analgesic interactions between TRPV1 and opioids in neuropathy. ⋯ Together, the identification of the primary action site in damaged nerves is crucial for effective pain control. Contrary to opioids, the TRPV1 blockade in the injured nerve peripheral terminals, rather than at the nerve trunk, appears promising against heat pain. Opioid/TRPV1 antagonist combinations at both locations partially reduced neuropathy-triggered heat and mechanical pain.
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Ocimum gratissimum is used in popular medicine to treat painful diseases. The antihypernociceptive properties of O. gratissimum essential oil and two of its active components (eugenol and myrcene) were tested in a model of neuropathic pain induced by a chronic constriction injury of the sciatic nerve. In tests to determine chronic antinociception, adult male C57BL/6 J mice were treated orally with corn oil (control group), O. gratissimum essential oil at doses of 10, 20, or 40 mg/kg or eugenol or myrcene at doses of 1, 5, or 10 mg/kg for 14 days after surgery. ⋯ The treatment with 20 and 40 mg/kg of O. gratissimum essential oil and at doses of 5 and 10 mg/kg of the active components were able to promote antihypernociception in both mechanical (von Frey) and thermal (hot plate) tests. The treatment with the essential oil of the plant or eugenol was effective in reducing the levels of interleukin-1β in the sciatic nerve. Our findings demonstrate that O. gratissimum essential oil and its isolated active components possess antihypernociceptive activity in neuropathic pain models.