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Reactive Oxygen Species Donors Increase the Responsiveness of Dorsal Horn Neurons and Induce Mechanical Hyperalgesia in Rats.

Kim HY, Lee I, Chun SW, Kim HK - Neural Plast. (2015)

Bottom Line: The studies suggest that superoxide in spinal cord is one of important mediators of persistent pain.The responses of wide dynamic range neurons to mechanical stimuli increased after a local application of t-BOOH.The t-BOOH increased the frequency and the amplitude of excitatory postsynaptic potentials, depolarized membrane potential in SG neurons, and increased the frequency of action potentials evoked by depolarizing current pulses.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience and Cell Biology, 301 University Boulevard, University of Texas Medical Branch, TX 77555-1069, USA ; Department of Physiology, College of Korean Medicine, Daegu Haany University, Daegu 706-060, Republic of Korea.

ABSTRACT
Our previous studies suggest that reactive oxygen species (ROS) scavengers have analgesic effect on neuropathic pain through spinal mechanisms in the rat. The studies suggest that superoxide in spinal cord is one of important mediators of persistent pain. To test the hypothesis that increase of superoxide-derived intermediates leads to central sensitization and pain, the effects of an intrathecal injection of chemical ROS donors releasing either OH(∙), OCl(-), or H2O2 were examined on pain behaviors. Following treatment with t-BOOH (OH(∙) donor), dorsal horn neuron responses to mechanical stimuli in normal rats and the changes of neuronal excitability were explored on substantia gelatinosa (SG) neurons using whole-cell patch clamping recordings. Intrathecal administration of t-BOOH or NaOCl (OCl(-) donor), but not H2O2, significantly decreased mechanical thresholds of hind paws. The responses of wide dynamic range neurons to mechanical stimuli increased after a local application of t-BOOH. The t-BOOH increased the frequency and the amplitude of excitatory postsynaptic potentials, depolarized membrane potential in SG neurons, and increased the frequency of action potentials evoked by depolarizing current pulses. These results suggest that elevated ROS, especially OH(∙), in the spinal cord sensitized dorsal horn neurons and produced hyperalgesia in normal rats.

No MeSH data available.


Related in: MedlinePlus

Effects of t-BOOH on membrane potential and EPSP in a patch clamp recording of SG neurons. (a) Original amplitude traces of EPSP in an SG neuron show that t-BOOH (2 mM, 7 min) increased the amplitude and frequency of EPSPs. The lower traces show EPSP at an expanded time scale. Normalized cumulative distribution analysis of EPSP amplitude and frequency (lower panels) showed that t-BOOH caused a significant shift toward higher frequency (left) and amplitude (right) in the neuron. (b) Average EPSP frequency (left) and amplitude (right). After application of t-BOOH, both the frequency and the amplitude increased significantly (P < 0.05, asterisks) from pre-t-BOOH levels as determined by a paired t-test. The data are mean with standard errors of the mean.
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fig3: Effects of t-BOOH on membrane potential and EPSP in a patch clamp recording of SG neurons. (a) Original amplitude traces of EPSP in an SG neuron show that t-BOOH (2 mM, 7 min) increased the amplitude and frequency of EPSPs. The lower traces show EPSP at an expanded time scale. Normalized cumulative distribution analysis of EPSP amplitude and frequency (lower panels) showed that t-BOOH caused a significant shift toward higher frequency (left) and amplitude (right) in the neuron. (b) Average EPSP frequency (left) and amplitude (right). After application of t-BOOH, both the frequency and the amplitude increased significantly (P < 0.05, asterisks) from pre-t-BOOH levels as determined by a paired t-test. The data are mean with standard errors of the mean.

Mentions: Because the SG is a major termination site for unmyelinated afferents and plays an important role in pain mechanisms [18], we obtained whole-cell patch clamp recordings to investigate whether t-BOOH could change the excitability of SG neurons in spinal cord slices. Only SG neurons with a resting membrane potential more negative than −50 mV were examined. The resting membrane potential was −56.0 ± 1.1 mV (n = 26). When the cell was held at −60 mV, the application of t-BOOH (2 mM) for 7 min induced a 3.1 ± 0.5 mV depolarization, which was maintained for up to about 30 min after washout and which then recovered to baseline (Figure 3(a)). For measurement of spontaneous EPSPs of SG neurons, the baseline (control) was recorded for at least 10 min in ACSF after the whole-cell recording configuration, and the samples were superfused with t-BOOH (2 mM in the ACSF solution) for 7 min and then washed out for 15 min. Superfusion with t-BOOH significantly increased EPSP frequency (1.1 ± 0.3 versus 0.3 ± 0.1 Hz, P < 0.05) and amplitude (2.1 ± 0.2 versus 1.8 ± 0.1 mV, P < 0.05) (n = 26) over the baseline (Figure 3). These data suggest that an increase in the level of hydroxyl radicals in the SG neurons affected both presynaptic and postsynaptic mechanisms of excitatory transmission in the rats.


Reactive Oxygen Species Donors Increase the Responsiveness of Dorsal Horn Neurons and Induce Mechanical Hyperalgesia in Rats.

Kim HY, Lee I, Chun SW, Kim HK - Neural Plast. (2015)

Effects of t-BOOH on membrane potential and EPSP in a patch clamp recording of SG neurons. (a) Original amplitude traces of EPSP in an SG neuron show that t-BOOH (2 mM, 7 min) increased the amplitude and frequency of EPSPs. The lower traces show EPSP at an expanded time scale. Normalized cumulative distribution analysis of EPSP amplitude and frequency (lower panels) showed that t-BOOH caused a significant shift toward higher frequency (left) and amplitude (right) in the neuron. (b) Average EPSP frequency (left) and amplitude (right). After application of t-BOOH, both the frequency and the amplitude increased significantly (P < 0.05, asterisks) from pre-t-BOOH levels as determined by a paired t-test. The data are mean with standard errors of the mean.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4592728&req=5

fig3: Effects of t-BOOH on membrane potential and EPSP in a patch clamp recording of SG neurons. (a) Original amplitude traces of EPSP in an SG neuron show that t-BOOH (2 mM, 7 min) increased the amplitude and frequency of EPSPs. The lower traces show EPSP at an expanded time scale. Normalized cumulative distribution analysis of EPSP amplitude and frequency (lower panels) showed that t-BOOH caused a significant shift toward higher frequency (left) and amplitude (right) in the neuron. (b) Average EPSP frequency (left) and amplitude (right). After application of t-BOOH, both the frequency and the amplitude increased significantly (P < 0.05, asterisks) from pre-t-BOOH levels as determined by a paired t-test. The data are mean with standard errors of the mean.
Mentions: Because the SG is a major termination site for unmyelinated afferents and plays an important role in pain mechanisms [18], we obtained whole-cell patch clamp recordings to investigate whether t-BOOH could change the excitability of SG neurons in spinal cord slices. Only SG neurons with a resting membrane potential more negative than −50 mV were examined. The resting membrane potential was −56.0 ± 1.1 mV (n = 26). When the cell was held at −60 mV, the application of t-BOOH (2 mM) for 7 min induced a 3.1 ± 0.5 mV depolarization, which was maintained for up to about 30 min after washout and which then recovered to baseline (Figure 3(a)). For measurement of spontaneous EPSPs of SG neurons, the baseline (control) was recorded for at least 10 min in ACSF after the whole-cell recording configuration, and the samples were superfused with t-BOOH (2 mM in the ACSF solution) for 7 min and then washed out for 15 min. Superfusion with t-BOOH significantly increased EPSP frequency (1.1 ± 0.3 versus 0.3 ± 0.1 Hz, P < 0.05) and amplitude (2.1 ± 0.2 versus 1.8 ± 0.1 mV, P < 0.05) (n = 26) over the baseline (Figure 3). These data suggest that an increase in the level of hydroxyl radicals in the SG neurons affected both presynaptic and postsynaptic mechanisms of excitatory transmission in the rats.

Bottom Line: The studies suggest that superoxide in spinal cord is one of important mediators of persistent pain.The responses of wide dynamic range neurons to mechanical stimuli increased after a local application of t-BOOH.The t-BOOH increased the frequency and the amplitude of excitatory postsynaptic potentials, depolarized membrane potential in SG neurons, and increased the frequency of action potentials evoked by depolarizing current pulses.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience and Cell Biology, 301 University Boulevard, University of Texas Medical Branch, TX 77555-1069, USA ; Department of Physiology, College of Korean Medicine, Daegu Haany University, Daegu 706-060, Republic of Korea.

ABSTRACT
Our previous studies suggest that reactive oxygen species (ROS) scavengers have analgesic effect on neuropathic pain through spinal mechanisms in the rat. The studies suggest that superoxide in spinal cord is one of important mediators of persistent pain. To test the hypothesis that increase of superoxide-derived intermediates leads to central sensitization and pain, the effects of an intrathecal injection of chemical ROS donors releasing either OH(∙), OCl(-), or H2O2 were examined on pain behaviors. Following treatment with t-BOOH (OH(∙) donor), dorsal horn neuron responses to mechanical stimuli in normal rats and the changes of neuronal excitability were explored on substantia gelatinosa (SG) neurons using whole-cell patch clamping recordings. Intrathecal administration of t-BOOH or NaOCl (OCl(-) donor), but not H2O2, significantly decreased mechanical thresholds of hind paws. The responses of wide dynamic range neurons to mechanical stimuli increased after a local application of t-BOOH. The t-BOOH increased the frequency and the amplitude of excitatory postsynaptic potentials, depolarized membrane potential in SG neurons, and increased the frequency of action potentials evoked by depolarizing current pulses. These results suggest that elevated ROS, especially OH(∙), in the spinal cord sensitized dorsal horn neurons and produced hyperalgesia in normal rats.

No MeSH data available.


Related in: MedlinePlus