Neuroscience letters
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Microneurography of human skin nerves has recently contributed detailed information on the peripheral input leading to itch sensations. In this context it has been demonstrated that itch induced by different agents activates different neuronal populations in the PNS. Histamine acts on a specific subgroup of mechano-insensitive C-fibers which are also sensitive to other endogenous mediators, e.g. prostaglandine E2 and acetylcholine, and to capsaicin. ⋯ Experimentally, the spicules of mucuna pruriens (cowhage) induce strong non-histaminergic itch. It turned out that they excite an entirely different population of C-fibers, namely mechano-responsive polymodal nociceptor units (CMH) and Adelta units. The neuronal mechanisms of clinically important pruritic states, e.g. in uremia are still unexplored.
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Neuroscience letters · Feb 2010
ReviewMicroneurographic single-unit recordings to assess receptive properties of afferent human C-fibers.
Action potentials in unmyelinated peripheral axons can be recorded in awake humans by microneurography with small electrodes placed in a peripheral nerve. This technique provides extracellular recordings of single C-fibers and thus enables characterization of their sensory and axonal properties. By using microneurographical basic properties of afferent C-fibers such as conduction velocities, innervation territories, sensory thresholds and chemical responsiveness were measured. ⋯ Based on those specific properties, unitary functional classes of nociceptors (such as polymodal nociceptors and mechano-insensitive nociceptors) and non-nociceptors (such as tactile afferents and warm fibers) were classified. With normal data available, sensitization and desensitization of afferent fibers have been found in pathophysiologic states as detected in chronic pain patients. As subjects and patients are awake during the recording, microneurography provides a unique tool to correlate the discharge behaviour of afferent nerve fibers with the sensation evoked by certain stimuli.
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Neuroscience letters · Feb 2010
ReviewMicroneurography in rats: a minimally invasive method to record single C-fiber action potentials from peripheral nerves in vivo.
Microneurography is a method suitable for recording intraneural single or multiunit action potentials in conscious subjects. Microneurography has rarely been applied to animal experiments, where more invasive methods, like the teased fiber recording technique, are widely used. We have tested the feasibility of microneurographic recordings from the peripheral nerves of rats. ⋯ Also, single C units can be functionally identified by their changes in latency to natural stimuli, and insensitive units can be recognized as 'silent' nociceptors or sympathetic efferents by their distinctive profiles of activity-dependent slowing during repetitive electrical stimulation, or by the effect on spontaneous efferent activity of a proximal anesthetic block. Moreover, information about the biophysical properties of C axons can be obtained from their latency recovery cycles. Finally, we show that this preparation is potentially suitable for the study of C-fiber behavior in models of neuropathies and nerve lesions, both under resting conditions and in response to drug administration.
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Neuroscience letters · Feb 2010
Microneurographic findings of relevance to pain in patients with erythromelalgia and patients with diabetic neuropathy.
Mechanisms responsible for neuropathic pain are still unclear. By using microneurography we have been able to record from single C-nociceptive and sympathetic fibers in patients and attempted to uncover possible abnormal functional properties of these fibers of relevance for pain. ⋯ Although some degree of spontaneous activity and sensitization also was found in patients without pain, these mechanisms may still be of importance for the development and maintenance of neuropathic pain. A change in the distribution of C-nociceptive fibers in the skin as shown in the patients with diabetic neuropathy may help to reveal mechanisms responsible for small-fiber dysfunction.