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Brain Sci. 2015, 5(4), 400-418; doi:10.3390/brainsci5040400

Hemodynamic and Light-Scattering Changes of Rat Spinal Cord and Primary Somatosensory Cortex in Response to Innocuous and Noxious Stimuli

1,2,†,* , 3,†
and
1
1
Departments of Psychology, University of Texas at Arlington, Arlington, TX 76019, USA
2
Department of Neurological Surgery, University of California San Francisco, 1700 Owens Street, San Francisco, CA 94158, USA
3
Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editor: Patrick W. Stroman
Received: 2 July 2015 / Revised: 20 September 2015 / Accepted: 24 September 2015 / Published: 29 September 2015
(This article belongs to the Special Issue Functional Neuroimaging of Pain)
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Abstract

Neuroimaging technologies with an exceptional spatial resolution and noninvasiveness have become a powerful tool for assessing neural activity in both animals and humans. However, the effectiveness of neuroimaging for pain remains unclear partly because the neurovascular coupling during pain processing is not completely characterized. Our current work aims to unravel patterns of neurovascular parameters in pain processing. A novel fiber-optic method was used to acquire absolute values of regional oxy- (HbO) and deoxy-hemoglobin concentrations, oxygen saturation rates (SO2), and the light-scattering coefficients from the spinal cord and primary somatosensory cortex (SI) in 10 rats. Brief mechanical and electrical stimuli (ranging from innocuous to noxious intensities) as well as a long-lasting noxious stimulus (formalin injection) were applied to the hindlimb under pentobarbital anesthesia. Interhemispheric comparisons in the spinal cord and SI were used to confirm functional activation during sensory processing. We found that all neurovascular parameters showed stimulation-induced changes; however, patterns of changes varied with regions and stimuli. Particularly, transient increases in HbO and SO2 were more reliably attributed to brief stimuli, whereas a sustained decrease in SO2 was more reliably attributed to formalin. Only the ipsilateral SI showed delayed responses to brief stimuli. In conclusion, innocuous and noxious stimuli induced significant neurovascular responses at critical centers (e.g., the spinal cord and SI) along the somatosensory pathway; however, there was no single response pattern (as measured by amplitude, duration, lateralization, decrease or increase) that was able to consistently differentiate noxious stimuli. Our results strongly suggested that the neurovascular response patterns differ between brief and long-lasting noxious stimuli, and can also differ between the spinal cord and SI. Therefore, a use of multiple-parameter strategy tailored by stimulus modality (brief or long-lasting) as well as region-dependent characteristics may be more effective in detecting pain using neuroimaging technologies. View Full-Text
Keywords: pain; oxygenated hemoglobin; deoxygenated hemoglobin; oxygen saturation; neurovascular coupling; light scattering pain; oxygenated hemoglobin; deoxygenated hemoglobin; oxygen saturation; neurovascular coupling; light scattering
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

He, J.-W.; Liu, H.; Peng, Y.B. Hemodynamic and Light-Scattering Changes of Rat Spinal Cord and Primary Somatosensory Cortex in Response to Innocuous and Noxious Stimuli. Brain Sci. 2015, 5, 400-418.

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