Articles: itch.
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We investigated roles for substance P (SP), gastrin-releasing peptide (GRP), and glutamate in the spinal neurotransmission of histamine-dependent and -independent itch. In anesthetized mice, responses of single superficial dorsal horn neurons to intradermal (i.d.) injection of chloroquine were partially reduced by spinal application of the α-amino-3-hydroxy-5-methyl-4-isoxazole proprionate acid (AMPA)/kainate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Co-application of CNQX plus a neurokinin-1 (NK-1) antagonist produced stronger inhibition, while co-application of CNQX, NK-1, and GRP receptor (GRPR) antagonists completely inhibited firing. ⋯ These results indicate that SP, GRP, and glutamate each partially contribute to histamine-independent itch. Histamine-evoked itch is mediated primarily by glutamate, with GRP playing a lesser role. Co-application of NK-1, GRP, and AMPA receptor antagonists may prove beneficial in treating chronic itch.
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Dermatologic therapy · Jan 2014
Case ReportsItch in familial lichen amyloidosis: effective treatment with amitriptyline in two cases.
Itch is a characteristic feature of lichen amyloidosis and the symptom can be debilitating. Treatments, however, are generally not effective. We report amitriptyline as a novel therapy in treating itch in two patients with familial lichen amyloidosis who did not respond to prior potent topical corticosteroids and antihistamines. ⋯ In the latter, his DLQI concurrently reduced from 14 to 6 of 30. Pathophysiology of itch in lichen amyloidosis may involve both cutaneous and neural components and amitriptyline is known to be useful for neuropathic itch. Low-dose amitriptyline poses little risk of side effects and may offer an effective and safe alternative for the treatment of itch in familial cutaneous amyloidosis.
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While considerable effort has been made to investigate the neural mechanisms of pain, much less effort has been devoted to itch, at least until recently. However, itch is now gaining increasing recognition as a widespread and costly medical and socioeconomic issue. This is accompanied by increasing interest in the underlying neural mechanisms of itch, which has become a vibrant and rapidly-advancing field of research. The goal of the present forefront review is to describe the recent progress that has been made in our understanding of itch mechanisms.
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Scratching inhibits pruritogen-evoked responses of neurons in the superficial dorsal horn, implicating a spinal site for scratch inhibition of itch. We investigated if scratching differentially affects neurons depending on whether they are activated by itchy vs. painful stimuli, and if the degree of inhibition depends on the relative location of scratching. We recorded from rat lumbar dorsal horn neurons responsive to intradermal (id) microinjection of serotonin (5-hydroxytryptamine, 5-HT). ⋯ These results indicate that scratching exerts a state-dependent inhibitory effect on responses of spinal neurons to pruritic but not algesic stimuli. Moreover, on-site scratching first excited neurons followed by inhibition, while off-site scratching immediately evoked the inhibition of pruritogen-evoked activity. This accounts for the suppression of itch by scratching at a distance from the site of the itchy stimulus.
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Experimental dermatology · Aug 2013
Sensitivity to itch and pain in patients with psoriasis and rheumatoid arthritis.
Symptoms of itch and pain in chronic inflammatory conditions of psoriasis (PS) and rheumatoid arthritis (RA) can highly affect patients' quality of life. Studies in other patient groups indicate that sensitivity to itch and pain is altered in line with the patient's main symptom of either chronic itch or pain, as a result of sensitization processes. This study directly compared whether patients with chronic inflammatory conditions associated with chronic itch or pain display a heightened sensitivity to itch and pain, respectively. ⋯ Levels of itch and pain evoked by the QST stimuli as well as the tolerance to the stimuli were determined. Patients with PS reacted to the stimuli with a higher itch response (histamine), while the patients with RA displayed a lowered tolerance to the stimuli (cold pressor test and mechanical stimulation) in comparison with the other patient group. In line with previous studies in other patient groups with chronic itch or pain, further support was found that somatosensory stimuli are processed in line with the patients' main symptom through generic sensitization processes, also in chronic inflammatory conditions such as PS and RA.