Temporal features of pain evoked spike trains
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1
Freie Universität Berlin, Neuroinformatics & Theoretical Neuroscience, Institute of Biology, Germany
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2
Bernstein Center for Computational Neuroscience Berlin, Germany
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3
Max-Delbrück Center for Molecular Medicine, Molecular Physiology of Somatic Sensation, Germany
A large portion of peripheral nociceptors are unmyelinated C-fibers. Most C-fiber nociceptors are polymodal, responding to multiple noxious modalities such as thermal and mechanical stimuli. Nevertheless, distinct noxious modalities can be dissociated behaviorally [1], raising the question how the nervous system achieves to determine the modality of the stimulus.
To shed light on this question, we investigated the response of C-fiber nociceptors to noxious heat and mechanical stimulation at the earliest stage of sensory processing. We recorded the afferent responses of single-C-fiber receptive fields to both graded mechanical pain and heat stimulation in an in vitro mouse skin-nerve preparation. In accordance to previous reports, we could observe the cells roughly into three classes on the basis of their response characteristics: C-M, C-H and C-MH fibers [2]. C-M fibers responded to mechanical stimuli and not to heat, C-H fibers were sensitive mainly to heat but also responded with lower firing rates to mechanical stimulation, and C-MH fibers which appeared equally sensitive to both mechanical and heat stimuli. We found that each neuron class exhibited characteristic features in response to each modality. For example, the heat responses in C-H fibers exhibited a maximum response at a certain temperature, while heat responses in C-MH fibers were rather uniform during a heat ramp. Similarly, C-MH fibers mainly responded strongly during the onset and offset of mechanical stimulation with little response in between, while C-M fibers maintained their response during the stimulus duration, albeit with fluctuating firing rates.
These multimodal responses suggest that noxious stimuli may be encoded by a combinatorial code at the earliest stage of sensory processing, instead of having a “labeled line” for each modality. Downstream neurons might exploit the different response characteristics to determine the quality of the stimulus, or to resolve its temporal characteristics.
Acknowledgements
We thank Stephan Gabler for support and helpful comments on this work. This work is funded by Federal Ministry of Education and Research (BMBF), grant 01GQ1001D and 01GQ1001E to BCCN.
References
[1] Cavanaugh DJ, Lee H, Lo L, et al. Distinct subsets of unmyelinated primary sensory fibers mediate behavioral responses to noxious thermal and mechanical stimuli. PNAS 2009;106(22):9075-80.
[2] Zimmermann K, Hein A, Hager U, Kaczmarek JS, et al. Phenotyping sensory nerve endings in vitro in the mouse. nprot. 2009;4(2):174-96.
Keywords:
C-fibers,
Nociceptors,
Pain,
sensory neurons
Conference:
Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012.
Presentation Type:
Poster
Topic:
Sensory processing and perception
Citation:
Dezhdar
T,
Albert
T,
Lewin
GR and
Schmuker
M
(2012). Temporal features of pain evoked spike trains.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference 2012.
doi: 10.3389/conf.fncom.2012.55.00121
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Received:
11 May 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Ms. Tara Dezhdar, Freie Universität Berlin, Neuroinformatics & Theoretical Neuroscience, Institute of Biology, Berlin, Germany, t_dezhdar@yahoo.de