title: Characterization of basal and morphine-induced histamine release in the rat periaqueductal gray.
abstract: Previous studies have shown that antinociceptive doses of systemic morphine increase extracellular histamine (HA) levels in the rat periaqueductal gray (PAG), although the cellular origin of basal and morphine-induced HA release in the PAG is unknown. Treatment with alpha-fluoromethylhistidine (FMH; 100 mg/kg, i.p.), the irreversible inhibitor of histidine decarboxylase, decreased basal HA release by a maximum of 80% and prevented morphine-induced HA release in the PAG. In addition, perfusion of this area with the sodium channel blocker tetrodotoxin (10(-6) M) decreased basal HA release by a maximum of 57% from baseline levels. When the perfusion medium was modified by substitution of magnesium for calcium, extracellular HA levels in the PAG decreased by a maximum of 72%, and morphine-induced HA release was prevented. Thioperamide (5 mg/kg, i.p.), an H3 antagonist, increased HA release in the PAG to a maximum of 249% within the first 30-60-min period. Taken together, these results suggest that basal and morphine-induced HA release in the rat PAG have a neuronal origin.
authors.affiliation: Department of Pharmacology and Toxicology, Albany Medical College, NY 12208.
authors.forename: K E
authors.initials: KE
authors.lastname: Barke
authors.forename: L B
authors.initials: LB
authors.lastname: Hough
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D006636:Histamine Release / Q000187:drug effects*; D006640:Histidine Decarboxylase / Q000037:antagonists & inhibitors; D008297:Male; D008762:Methylhistidines / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000927:Anticonvulsants; D008762:Methylhistidines; D010880:Piperidines; D013779:Tetrodotoxin; C028309:alpha-fluoromethylhistidine; D009020:Morphine; D006640:Histidine Decarboxylase; C052075:thioperamide