There are many discrepancies between sensory neuron thresholds reported by experimental studies. Furthermore, no studies seem to be available to compare the stimulus-response function of noxious and non-noxious afferents. I strongly believe that the alterations in physiological pain threshold are associated with variations in the stimulus-response functions exhibited by the neurons involved in pain networks, as has been shown for inflammatory and neuropathic states (Ahlgren et al., 1997).
Hi Erick, try the following papers:
Lu Y et al, 2005. Stapp Car Crash Journal 49: 291-322.
Chen et al, 2006. Journal of Bone and Joint Surgery (American) 88(8):1807-16.
John Cavanaugh's lab at Wayne State University has done a lot of work characterizing the neural response to facet joint capsule stretch, and some of their earlier work examined the response under conditions of inflammation.
Hope that helps!
Thank you Nadia!
Now I have two questions for you:
1. Could you please provide me the titles? it will be easier for me...
2. Are those papers indexed in this database (ResearchGate)?
Again, thank you very much!
Nadia, I just found the second paper ("Distribution of A-delta and C-fiber receptors in the cervical facet joint capsule and their response to stretch", Chen et al, 2006), but I'm still looking for the first one.
Unfortunately, this characterization is restricted to nociceptors (i.e., Adelta- and C-fibers), just as was done in earlier studies (Van Hees & Gybels, 1981; Slugg et al, 2000; Slugg et al, 2004, Levy & Strassman, 2002). Cain et al, (2001) characterized the response properties of Abeta-, Adelta and C-fibers with regard to their mechanical thresholds (mN) and Conduction velocities, but they do not compare the stimulus-response functions of these three types of primary afferents (They study the variation of the firing frequency in response to thermal stimuli, only for Adelta and C-fibers).
I think this is a very important aspect that has been underestimated for many years, and this could give us some insight about physiological pain thresholds.
Regards!
Erick
Hi Erick,
Not sure if this is what you are looking for, but have you looked into the microneurography literature? Jordi Serra and G Iannetti both use this technique to look at C fibres etc... and if I'm not mistaken, Line Lokken has also done some work looking at non-noxious sensory receptors in which she determined the optimal 'touch velocity' for pleasant touch.
I'll dig out more detailed references if you think this is of interest?
Thank you Rosie!
I just attached one picture to illustrate my point (adapted from Slugg et al., 2000; 2004).
As shown, the response from Adelta- and C-fibers increases monotonically with the intensity of the stimulus, although the latter exhibit a steeper response than the one exhibited by the Adelta-fibers... But, what about mechanoreceptors (Abeta-fibers)? So far, no studies seem to be avalilable to compare this feature of primary afferents...
Hi Erick,
The Lu et al. paper is called "Neural Response of Cervical Facet Joint Capsule to Stretch: A Study of Whiplash Pain Mechanism". However, they also did not examine the response of A-beta fibres.
Best of luck with your quest!
Hi Erick,
I might be able to help you with some papers and techniques, but I am not entirely clear by what you mean when you say 'stimulus-response', so before I try to help.
Are you interested in whether the peripheral Dorsal Root Ganglion neurons (in this case, non-nociceptors, such as low-threshold mechanoreceptors vs nociceptors, such as high-threshold mechanoreceptors) show different changes in the mechanical force required to activate these neurons? I.e. the von Frey filaments required to activate individual neurons from these different types both before and after insult?
Finally, so I know where to try and point you, are you interested in designing a study, or data that has already been obtained examining this?
Thanks,
Trevor
Thank you very much Trevor!
I recently published an article about the implementation of the Neuroid, a novel neuron-model which emphasizes the functional rather than the physiological features of the nerve cells, such as the activation threshold and the FI-curves, (also known as the stimulus-response function). I strongly believe that these curves could give us an useful criterium to classify primary afferents, specifically, DRG-neurons, as well as give us some insight about how somatic sensations are codified.
In this study, I assumed (because the lack of experimental studies) that the response (firing frequency) of the Low-threshold primary afferents (A-beta fibers) increases vigorously with amplitudes barely above the threshold value, but it reaches a plateau with greater (noxious?) amplitudes. On the contrary, if the A-beta fiber response increases monotonically with the stimulus intensity, we will not perceive pain at all. In fact, I think that the perceptual physiological threshold is given by the interaction of these curves (please, see the attachment). Summarizing, I would like to verify this hypothesis with experimental evidence, and also, use the experimental results to characterize noxious and non-noxious primary afferents, with regard to their activation thresholds and FI-curves, such that I can replicate them using my neuron-model, the Neuroid.
If you have any questions about this matter, please do not hesitate to contact me
Best regards!
Erick
Hi Trevor!
Perhaps I did not make myself clear. I am very interested in experimental data to support (or to discard) my hypothesis about the differences between the FI-curves exhibited by both, mechanoreceptors and nociceptors.
Any help with this regard will be well received.
Erick
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