Spinal NKCC1 blockade inhibits TRPV1-dependent referred allodynia.
BACKGROUND
The Na+, K+, 2Cl- type I cotransporter (NKCC1) and TRPV1 receptors, at the level of the dorsal horn, have been implicated in mediating allodynia in response to an inflammatory insult. The NKCC1 cotransporter regulates intracellular [Cl-] and thus the magnitude and polarity of GABAA receptor responses in neurons. TRPV1 receptors transduce diverse chemical and natural stimuli in nociceptors and are critical for inflammatory hyperalgesia.


RESULTS
Here we have tested the role of spinal NKCC1 cotransporters and TRPV1 receptors in referred allodynia in a model of visceral hyperalgesia in mice. Intrathecal (IT) injection of the NKCC1 inhibitor bumetanide (BUM, 1 nmol) inhibited referred, abdominal allodynia evoked by an intracolonic capsaicin injection. BUM was effective when injected IT either before or up to 4 hrs after the establishment of referred allodynia. The TRPV1 antagonist AMG 9810 (1 nmol) also inhibited referred allodynia in this model suggesting the involvement of an endogenous TRPV1 agonist in the dorsal horn in referred allodynia. In support of this suggestion, the endovanilloid TRPV1 agonist, narachidonoyl- dopamine (NADA, 1 or 10 nmol, IT) evoked stroking allodynia in the hindpaw that was blocked by co-treatment with AMG 9810 (1 nmol). The TRPV1-dependent stroking allodynia caused by NADA appeared to be functionally linked to NKCC1 because BUM (1 nmol) also inhibited NADA-evoked stroking allodynia.


CONCLUSIONS
Our findings indicate that spinal NKCC1 and TRPV1 are critical for referred allodynia mediated by a painful visceral stimulus. Moreover, they suggest that endogenous TRPV1 agonists, released in the CNS in painful conditions, might stimulate TRPV1 receptors on primary afferents that, in turn, play a role in increasing NKCC1 activity leading to allodynia.
Pitcher
Mark H
MH
McGill University, Anesthesia Research Unit, Faculty of Medicine, Faculty of Dentistry and McGill Centre for Research on Pain, Montreal, QC, Canada. mark.pitcher@mail.mcgill.ca
Price
Theodore J
TJ
Entrena
Jose M
JM
Cervero
Fernando
F
D000005:Abdomen / Q000473:pathology*; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D053591:Referred Pain / Q000139:chemically induced / Q000188:drug therapy*; D049994:Sodium Potassium Chloride Symporter Inhibitors; D064506:Solute Carrier Family 12, Member 2; D050916:TRPV Cation Channels / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000502:physiology*
D000613:Aminobutyrates; C401954:N(gamma)-acetyl-2,4-diaminobutyric acid; C578877:SLC12A2 protein, human; C578878:Slc12a2 protein, mouse; D049994:Sodium Potassium Chloride Symporter Inhibitors; D064506:Solute Carrier Family 12, Member 2; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; D002211:Capsaicin