Analgesia induced by 2- or 100-Hz electroacupuncture in the rat tail-flick test depends on the anterior pretectal nucleus.
AIMS
The anterior pretectal nucleus (APtN) and electroacupuncture (EA) activate descending mechanisms to modulate nociceptive inputs in the spinal dorsal horn. This study examines qualitatively whether mechanisms in the APtN participate in the EA-induced analgesia in rats.


MAIN METHODS
The tail-flick test was utilized to examine the changes produced by non-selective antagonists of serotonergic (methysergide, 37 pg), muscarinic (atropine, 10 ng) and opioid (naloxone, 10 ng) receptors; selective antagonists against μ (CTOP, 6.4 μg), δ (ICI174,864, 6.9 μg) or κ (nor-BNI, 7.3 μg); 5HT1 (methiothepin, 0.47 μg), 5HT2 (ketanserin, 5.4 μg), or 5HT3 (MDL 72222, 15.7 μg); and GABAA (bicuculline, 150 ng) receptors injected into the dorsal (d) or ventral (v) APtN on the antinociception induced by a 20-min EA applied at 2- or 100-Hz frequency to the Zusanli and Sanyinjiao acupoints.


KEY FINDINGS
The 2-Hz EA-induced analgesia was blocked by naloxone, CTOP or atropine, was less intense after bicuculline, was shorter after methysergide or methiothepin in dAPtN, and was less intense after methysergide, methiothepin and bicuculline in vAPtN. The 100-Hz EA-induced analgesia was less intense after methysergide, methiothepin and CTOP in vAPtN, and remained unchanged after injection of the antagonists into the dAPtN.


SIGNIFICANCE
The 2-Hz EA-induced analgesia utilizes cholinergic muscarinic, μ-opioid, GABAA and 5-HT1 mechanisms in the dAPtN and μ-opioid and 5-HT1 mechanisms in the vAPtN, while 100-Hz EA-induced analgesia utilizes μ-opioid and 5-HT1 mechanisms in the vAPtN but does not utilize them in the dAPtN.
['Silva|Marcelo L|ML|', 'Silva|Josie R T|JR|', 'Prado|Wiliam A|WA|']
D000698:Analgesia D000818:Animals D001285:Atropine D001640:Bicuculline D015671:Electroacupuncture D058787:GABA-A Receptor Antagonists D008297:Male D008636:Mesencephalon D008719:Methiothepin D008784:Methysergide D018727:Muscarinic Antagonists D009270:Naloxone D009271:Naltrexone D009292:Narcotic Antagonists D059408:Pain Management D051381:Rats D017208:Rats, Wistar D012702:Serotonin Antagonists D013004:Somatostatin
Analgesia Electroacupuncture Tail-flick test Anterior pretectal nucleus Descending pain control