Articles: itch.
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Neuroscience letters · Jan 2019
Randomized Controlled TrialDistinct behavioral response of primary motor cortex stimulation in itch and pain after burn injury.
It is still unclear whether chronic neuropathic pain and itch share similar neural mechanisms. They are two of the most commonly reported challenges following a burn injury and can be some of the most difficult to treat. Transcranial direct current stimulation (tDCS) has previously been studied as a method to modulate pain related neural circuits. ⋯ We did not find any treatment effects during Phase II. Based on these findings, it seems that an important placebo effect occurred during sham tDCS for itch, while active M1 tDCS seems to disrupt sensory compensatory mechanisms. We hypothesize that pain and itch are complementary but distinct mechanisms of adaptation after peripheral sensory injury following a burn injury and need to be treated differently.
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Uncontrollable itch-scratching cycles lead to serious skin damage in patients with chronic itch. However, the neural mechanism promoting the itch-scratching cycle remains elusive. Here, we report that tachykinin 1 (Tac1)-expressing glutamatergic neurons in the lateral and ventrolateral periaqueductal gray (l/vlPAG) facilitate the itch-scratching cycle. ⋯ Importantly, activation of Tac1-expressing neurons induced robust spontaneous scratching and grooming behaviors. The scratching behavior evoked by Tac1-expressing neuron activation was suppressed by ablation of spinal neurons expressing gastrin-releasing peptide receptor (GRPR), the key relay neurons for itch. These results suggest that Tac1-expressing neurons in the l/vlPAG promote itch-scratching cycles.
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Methylglyoxal (MGO), an endogenous reactive carbonyl compound, plays a key role in the pathogenesis of diabetic neuropathy. The aim of this study is to investigate the role of MGO in diabetic itch and hypoalgesia, two common symptoms associated with diabetic neuropathy. Methods: Scratching behavior, mechanical itch (alloknesis), and thermal hypoalgesia were quantified after intradermal (i.d.) injection of MGO in naïve mice or in diabetic mice induced by intraperitoneal (i.p.) injection of streptozotocin (STZ). ⋯ Thermal hypoalgesia was induced by intrathecal (i.t.) injection of MGO or in STZ-induced diabetic mice, which was abolished by MGO scavengers, intrathecal injection of TRPA1 blockers, and in Trpa1-/- mice. Conclusion: This study revealed that Nav1.7 and MGO-mediated activation of TRPA1 play key roles in itch and hypoalgesia in a murine model of type 1 diabetes. Thereby, we provide a novel potential therapeutic strategy for the treatment of itch and hypoalgesia induced by diabetic neuropathy.
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Frontiers in psychiatry · Jan 2019
ReviewPlacebo and Nocebo Effects Across Symptoms: From Pain to Fatigue, Dyspnea, Nausea, and Itch.
Placebo and nocebo effects are, respectively, the helpful and harmful treatment effects that do not arise from active treatment components. These effects have thus far been researched most often in pain. It is not yet clear to what extent these findings from pain can be generalized to other somatic symptoms. ⋯ Individual characteristics do not consistently predict placebo or nocebo effects across symptoms or studies. In sum, many conclusions deriving from placebo and nocebo pain studies do appear to apply to other somatic symptoms, but a number of important differences exist. Understanding what type of learning mechanisms for which symptom are most likely to trigger placebo and nocebo effects is crucial for generalizing knowledge for research and therapies across symptoms and can help clinicians to optimize placebo effects in practice.
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Frontiers in psychiatry · Jan 2019
Effects of Open- and Closed-Label Nocebo and Placebo Suggestions on Itch and Itch Expectations.
Placebo and nocebo effects have been shown to influence subjective symptoms such as itch. These effects can be induced by influencing outcome expectations through, for example, combining the application of an inert substance (e.g., a cream) with verbal suggestions on the anticipated effects of this substance. Interestingly, placebo effects also occur when it is known that a treatment is inert (i.e., open-label placebo). ⋯ In addition, a smaller increase in skin temperature was found in the positive compared with negative suggestion groups. The findings illustrate a potential role of (open- and closed-label) placebo for optimizing expectations and treatment effects for itch in clinical practice. Clinical Trial Registration: Netherlands Trial Register, trial number: NTR6530.