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Pain Autonomic NS

Research Projects

Transcriptomic patterns of dermal Schwann cell reactivity in neuropathic itch and pain

Neuropathic pruritus leads to significant impairment of life quality. During the first funding period, we recruited 245 patients with polyneuropathies (PNP): 24 reporting itch as only symptom and 58 reporting itch and pain. We defined a PNP subgroup characterized by high pain ratings upon electrical C fiber stimulation and mechanical hyperalgesia. In skin biopsies, we noted a pronounced loss of dermal nerve fibers paralleled by a strong branching of remaining C fibers in patients with itch. By RNA-sequencing (RNA-seq) and quantitative PCR, we found increased expression of IFI44L in skin biopsy samples from patients with itch only. We showed feasibility of subepidermal Schwann cell (SC) type mapping by immunohistochemistry. Utilizing single-nucleus RNA-seq (snRNA-seq), we could characterize SC subtypes and decode their subtype-specific transcriptomic signatures. Notably, IFI44L is a direct target of the microRNA let-7d, which we previously found to be increased in skin from patients with chronic pain, and let-7 represses netrin expression in SCs. Given that let-7 family members are strongly expressed in SCs, we postulate that SC expression of let-7-IFI44L-netrin pathway members might mediate itch and pain in a subgroup of PNP patients. Thus, we will investigate SC morphology and protein expression in itch and pain, aiming at a deeper understanding of SC related pathways in the skin of well-defined subgroups of patients. PNP patients with either pain or itch, will be recruited and carefully assessed by clinical measurements. For comparison, we will include patients with brachioradial pruritus and receive skin samples of patients with psoriasis from collaborating project #5. We will then identify and characterize groups of PNP patients with itch, pain and high pain sensitivity upon C fiber stimulation aiming at understanding their psychophysical characteristics and at selecting homogenous samples to be used in high-throughput transcriptomic technologies. Next, oligonucleotide-tagged antibody multiplex snRNA-seq will allow us to analyze cell type-specific gene expression from cryo-preserved skin biopsy samples obtained from large clinical cohorts. By bioinformatic analysis, we will be able to decode the transcriptomic profile of cutaneous SCs between different clinical entities and define molecular traits of homeostatic and reactive SCs. Multiplex RNA in situ mapping will enable us to map back levels of SC subtype reactivity to the underlying skin microenvironment. In summary, work with high-quality frozen skin biopsy samples from well-characterized patients with neuropathic pain and itch in combination with single-cell and spatial transcriptomic tools will allow us to identify novel cell-type specific targets and biomarkers for future interventional studies. We hypothesize that identification of novel SC characteristics relative to itch or pain will help better understand their role in relation to axon pathology and the clinical phenotype.

The neurogenic inflammation

In this project we study the function of thin A-and C-fibers. By chemical, mechanical or electrical stimulation, axon reflex is induced. This mechanism leads to neuropeptide release (CGRP, substance P) from peripheral nerve terminals, contributing to vasodilation, which as a flare reaction by means of a laser Doppler scanner (LDI) can be quantified.
In a part of this investigation, microdialysis membranes were placed intradermally in one hand, this way current or different substances or drugs can be administered. There are usually administered substances that affect the neuropeptide release of peripheral nerve endings. Aside from the analysis of flair up reaction, the LDI enables the investigation of the microdialysis eluate on the content of neuropeptides (CGRP, substance P) by ELISA. With this technique, we are currently investigating small-fiber neuropathy patients, migraine patients and patients with a specific reaction of the autonomic nervous system as well as healthy volunteers.

Neural mechanisms of sweat gland regulation

In this project, the regulation of sweat gland activity is investigated.
Preliminary tests showed that not only acetylcholine, the actual transmitter of sudomotor, but also nicotine and carbachol can cause sweat response to iontophoresis. This was triggered by microdialysis with nicotine sweat response. The sudometry shows that this welding answer is concentration dependent. In collaboration with the Institute of Pharmacology, we can measure whether it released acetylcholine in the skin. The first results show that this is the case. Furthermore a distinction should be made whether the acetylcholine is neuronal or non-neuronal origin. By welding the neural response is inhibited by injection of botulinum toxin and then the micro-dialysis is repeated with nicotine.
Another objective is to study the modulation of the response by neuropeptides such as welding CGRP and VIP. Another project investigates the distribution of the somatotopically sweat glands in the lower extremities. Here is the size of sweat glands is compared with the amount of sweat produced.

The modulation of pain by the autonomic nervous system

In this project the influence of the autonomic nervous system (ANS) was examined for the excitation of primary afferents. These controls are included in addition to various groups of patients in the study: patients after sympathectomy and patients with a Vagus stimulator as pain free controls, and patients with acute (complex regional pain syndrome, CRPS) and chronic neuropathic pain (polyneuropathy, PNP).
To define the sympathy part in pain generation can be quantified using a peripheral sympathetic innervation. This test system is validated by the study of pain-healthy patients before and after sympathectomy. Because the sympathetic nervous system can be strengthened by the provision of such prostaglandins from their nerve endings inflammation, bradykinin, in these patients at various concentrations added to the skin and quantify the inflammatory response with microdialysis and laser Doppler imaging.
Infections are probably influenced by the activity of the vagus nerve. Investigation of the peripheral portion of the Vagus effect is quantified in a group of healthy pain epilepsy patients before and during vagus stimulation of the neurogenic inflammation caused by tonic pressure, (LDI) and set in correlation with the pain rating.
In CRPS, there are striking sympathetic disorders. In these patients, the first peripheral sympathetic activity is examined (see above). In a second step noradrenaline is applied. It is similar to the investigations of receptor blockade. The sympathetic disturbance in CRPS also leads to disturbances of microcirculation, contributing to the hypoxia of the diseased tissue. The oxygen supply is measured in the side comparison with the aid of spectrophotometry, measurements are performed before and after sympathetic blockade.
Chronically painful PNP also maintains the hypothesis of a pathological interaction between sympathetic and afferent nerve fibers. We analyze sympathetic transmitters in the skin in patients with painful and non-painful PNP. In these patients is the functionally relevant portion of the sympathetic nervous determined. By measuring the sympathetic transmitters and by stimulation of the (inflammatory) response to norepinephrine competing hypotheses of pain origin during PNP will be verified or falsified.

Causes of pain and hyperalgesia in neuropathic pain syndromes

In this project, psychophysical and fMRI studies will be combined. Using various methods of stimulation, patients will be characterized in terms of hyperalgesia before and after lidocaine treatment. Lidocaine at different concentrations and application forms is administered in order to distinguish between central and peripheral effects. The comparison of fMRI and psychophysical data of patients and a control group will allow us to differentiate between peripheral and central causes of neuropathic pain.

Selected Publications

Birklein F, Schmelz M, Schifter S, Weber M. The important role of neuropeptides in complex regional pain syndrome. Neurology 2001; 57(12):2179-2184.

Birklein F, Walther D, Bigalke H, Winterholler M, Erbguth F. Sudomotor testing predicts the presence of neutralizing botulinum A toxin antibodies. Ann Neurol 2002; 52(1):68-73.

Eberle T, Doganci B, Kramer HH, Geber C, Fechir M, Magerl W, Birklein F. Warm and cold complex regional pain syndromes: differences beyond skin temperature? Neurology 2009; 72(6):505-512.

Sommer C, Birklein F. Fighting off pain with resolvins. Nat Med 2010; 16(5):518-520.

Rodriguez-Raecke R, Doganci B, Breimhorst M, Stankewitz A, Buchel C, Birklein F, May A. Insular cortex activity is associated with effects of negative expectation on nociceptive long-term habituation. J Neurosci 2010; 30(34):11363-11368.


Work Group
Pain - Autonomic NS

Group Leader
Prof. Frank Birklein
Klinik und Poliklinik für Neurologie
Langenbeckstr. 1
Mainz, 33121
Tel: +49(0)6131-17-5486