Role of PAG in the antinociception evoked from the medial or central amygdala in rats.
The effects of stimulating the periaqueductal gray (PAG) against the rat tail flick reflex (TFR) was not changed significantly by the microinjection of lidocaine (5%/0.5 microl) into the medial (ME) or central (CE) nuclei of the amygdala. In contrast, lidocaine into the PAG blocked the effects from the ME or CE. The microinjection of naloxone (1 microg), beta-funaltrexamine (2 microg), propranolol (1 microg), or methysergide (1 microg), but not atropine (1 microg) or mecamylamine (1 microg) into the PAG significantly reduced the effects from the CE. The effect from the ME was not altered significantly by microinjecting naloxone into the PAG. Therefore, the ME or CE are unlikely to be intermediary stations for depression of the TFR evoked by stimulating the PAG, but the PAG may be a relay station for the effects of stimulating the ME or CE. The circuitry activated from the CE, but not the ME, utilises opioid mediation in the PAG. The effect from the CE depends at least on mu-opioid, serotonergic, and probably beta-adrenergic mediation in the PAG.
Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, São Paulo, Brazil.
M A
MA
Oliveira
W A
WA
Prado
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004558:Electric Stimulation; D005730:Ganglionic Blockers / Q000494:pharmacology; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D008845:Microinjections; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000502:physiology*; D017288:Pain Threshold / Q000187:drug effects; D010276:Parasympatholytics / Q000494:pharmacology; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012702:Serotonin Antagonists / Q000494:pharmacology
D000319:Adrenergic beta-Antagonists; D000779:Anesthetics, Local; D005730:Ganglionic Blockers; D009292:Narcotic Antagonists; D010276:Parasympatholytics; D012702:Serotonin Antagonists; D009270:Naloxone; D009271:Naltrexone; D008464:Mecamylamine; C024524:beta-funaltrexamine; D001285:Atropine; D008012:Lidocaine; D011433:Propranolol; D008784:Methysergide