Nov, 2007
Differential presynaptic effects of opioid agonists on a delta and C-afferent glutamatergic transmission to the spinal dorsal horn
ANESTHESIOLOGY
- ,
- ,
- Volume
- 107
- Number
- 5
- First page
- 807
- Last page
- 812
- Language
- English
- Publishing type
- DOI
- 10.1097/01.anes.0000286985.80301.5e
- Publisher
- LIPPINCOTT WILLIAMS & WILKINS
Background: Although intrathecal administration of opioids produces antinociceptive effects in the spinal cord, it has not been established whether intrathecal opioid application more effectively terminates C fiber-mediated pain than A fiber-mediated pain. Here, the authors focus on the differences in opioid actions on A delta- and C-afferent responses.
Methods: Using the whole cell patch clamp technique, the authors investigated the presynaptic inhibitory actions of mu-, delta-, and K-opioid receptor agonists on primary afferent-evoked excitatory postsynaptic currents (EPSCs) in substantia gelatinosa neurons of adult rat spinal cord slices.
Results: The mu agonist DAMGO (0.1, 1 mu m) reduced the amplitude of glutamatergic monosynaptic A delta- or C fiber-evoked EPSCs. C fiber-evoked EPSCs were inhibited to a greater extent than AS fiber-evoked EPSCs. The 5 agonist DPDPE (1, 10 mu m) produced modest inhibition of A delta- or C fiber-evoked EPSCs. In contrast, the K agonist U69593 (1 mu m) did not affect the amplitude of either A delta or C fiber-evoked EPSCs.
Conclusions: These results indicate that opioids suppress excitatory synaptic transmission mainly through activation of mu receptors on primary afferent C fibers. Given that the substantia gelatinosa is the main termination of A delta and C fibers transmitting nociceptive information, the current findings may partially explain the different potency of opioid agonists.
Methods: Using the whole cell patch clamp technique, the authors investigated the presynaptic inhibitory actions of mu-, delta-, and K-opioid receptor agonists on primary afferent-evoked excitatory postsynaptic currents (EPSCs) in substantia gelatinosa neurons of adult rat spinal cord slices.
Results: The mu agonist DAMGO (0.1, 1 mu m) reduced the amplitude of glutamatergic monosynaptic A delta- or C fiber-evoked EPSCs. C fiber-evoked EPSCs were inhibited to a greater extent than AS fiber-evoked EPSCs. The 5 agonist DPDPE (1, 10 mu m) produced modest inhibition of A delta- or C fiber-evoked EPSCs. In contrast, the K agonist U69593 (1 mu m) did not affect the amplitude of either A delta or C fiber-evoked EPSCs.
Conclusions: These results indicate that opioids suppress excitatory synaptic transmission mainly through activation of mu receptors on primary afferent C fibers. Given that the substantia gelatinosa is the main termination of A delta and C fibers transmitting nociceptive information, the current findings may partially explain the different potency of opioid agonists.
- Link information
- ID information
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- DOI : 10.1097/01.anes.0000286985.80301.5e
- ISSN : 0003-3022
- Web of Science ID : WOS:000250457400017