Involvement of the periaqueductal gray in the effect of motor cortex stimulation
Ruei-Jen Chiou1, Chen-Wei Chang, Chung-Chih Kuo
1Department of Anatomy, School of Medicine, College of Medicine, Taipei Medical University, 250 Wu-Hsing Street, Taipei City 10031, Taiwan, ROC.
Abstract:
Several clinical and animal studies of different pain models reported that motor cortex stimulation (MCS) has an antinociceptive effect. In our previous study, the response of the primary somatosensory cortex (SI) to peripheral stimuli decreased after MCS. The aim of the present study was to investigate involvement of the periaqueductal gray (PAG) in this inhibitory effect of MCS. Responses of the SI to electrical stimuli applied to both forepaws of anesthetized rats were monitored to evaluate the effect of MCS. After sensory-evoked potentials (SEPs) were stable, either saline, opioid, or dopamine receptor antagonists were locally microinjected into the PAG. After drug or saline administration, MCS was applied to the forepaw area of the right motor cortex. SEPs after MCS were compared to those before MCS. In the saline group, SEPs ipsilateral to MCS decreased, but SEPs contralateral to MCS did not. The decrease in SEPs was prevented by pretreatment of the PAG with naloxone. Application of a nonspecific dopamine receptor antagonist (α-flupenthixol) to the PAG also blocked the inhibition of SEPs after MCS. Inhibition of SEPs after MCS was blocked by local application of a D1 antagonist (SCH-23390) in the PAG, but not by a D2 antagonist (eticlopride). These results suggest that the PAG participates in the inhibitory effect of MCS, and this effect of MCS may be mediated by opioid and dopamine D1 receptors within thePAG.
Insights
Motor cortex stimulation (MCS) reduces pain by affecting the periaqueductal gray (PAG). This inhibitory effect involves opioid and dopamine D1 receptors in the PAG, modulating sensory responses.
Area of Science:
- Neuroscience
- Pain Research
- Neurophysiology
Background:
- Motor cortex stimulation (MCS) has demonstrated antinociceptive effects in various pain models.
- Previous research indicated MCS reduces primary somatosensory cortex (SI) responses to peripheral stimuli.
Purpose of the Study:
- To investigate the role of the periaqueductal gray (PAG) in the inhibitory effects of MCS.
- To elucidate the neurochemical mechanisms underlying MCS-induced inhibition in the PAG.
Main Methods:
- Recorded SI responses to forepaw electrical stimuli in anesthetized rats.
- Administered saline, opioid, or dopamine receptor antagonists into the PAG before MCS.
- Compared sensory-evoked potentials (SEPs) before and after MCS.
Main Results:
- MCS decreased ipsilateral SEPs, an effect blocked by naloxone (opioid antagonist) and α-flupenthixol (dopamine antagonist) in the PAG.
- Dopamine D1 antagonist (SCH-23390) blocked MCS inhibition, while D2 antagonist (eticlopride) did not.
- Contralateral SEPs were unaffected by MCS.
Conclusions:
- The PAG is involved in the antinociceptive effect of MCS.
- Opioid and dopamine D1 receptor pathways within the PAG mediate the inhibitory influence of MCS on sensory processing.
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