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Periaqueductal gray-evoked dorsal root reflex is frequency dependent
Yuan Bo Peng1, Daniel R Kenshalo, Richard H Gracely
1Pain and Neurosensory Mechanisms Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, 20892-4410, Bethesda, MD, USA. ypeng@uta.edu
Brain Research
|May 24, 2003
Summary
The periaqueductal gray (PAG) descending system modulates dorsal root reflexes (DRRs). Both PAG and peripheral nerve stimulation influence DRRs in a frequency-dependent manner, with stimulus intensity having no significant effect.
Area of Science:
- Neuroscience
- Spinal Cord Physiology
- Pain Modulation
Background:
- The dorsal root reflex (DRR) is an antidromic action potential originating in the spinal cord.
- GABA(A) and 5-HT(3) receptors are implicated in DRR generation.
- The periaqueductal gray (PAG) influences spinal GABA and serotonin release.
Purpose of the Study:
- To investigate the modulation of DRRs by the PAG descending system.
- To determine the effects of PAG and peripheral stimulation on DRRs.
- To analyze the frequency and intensity dependence of these modulations.
Main Methods:
- Single fiber recording of DRRs from the L5 dorsal root in Sprague-Dawley rats.
- Stimulation of the PAG, ipsilateral, and contralateral sciatic nerves.
- Stimulation across hindpaws transcutaneously.
- Assessment of DRR ratios across varying stimulus frequencies and intensities.
Main Results:
- PAG stimulation induced DRRs in a frequency-dependent manner.
- Ipsilateral and contralateral peripheral nerve stimulation also produced frequency-dependent DRRs.
- Stimulus intensity did not significantly affect DRR generation.
- Thoracic spinal transection abolished PAG-induced DRRs.
Conclusions:
- The PAG descending system plays a significant role in modulating DRRs.
- DRR generation is frequency-dependent for both central (PAG) and peripheral stimuli.
- These findings elucidate novel pathways for spinal reflex modulation.