When administered to rats in a cold environment, 3,4-methylenedioxymethamphetamine reduces brown adipose tissue thermogenesis and increases tail blood flow: effects of pretreatment with 5-HT1A and dopamine D2 antagonists.
When given in a warm environment MDMA (3,4-methylenedioxymethamphetamine, ecstasy) causes hyperthermia by increasing interscapular brown adipose tissue (iBAT) heat production and decreasing heat loss via cutaneous vasoconstriction. When given in a cold environment, however, MDMA causes hypothermia by an unknown mechanism. This paper addresses these mechanisms and in addition examines whether antagonists at 5-HT(1A) and D(2) receptors reduce the hypothermic action of MDMA. Male Sprague-Dawley rats instrumented with a Doppler probe for measuring tail blood flow, and probes for measuring core and iBAT temperatures, were placed in a temperature-controlled chamber. The chamber temperature was reduced to 10 degrees C and vehicle (0.5 ml Ringer), the 5-HT(1A) antagonist WAY 100635 (0.5 mg/kg), the D(2) antagonist spiperone (20 mug/kg), or the combination of Way 100635 and spiperone were injected s.c. Thirty minutes later the antagonists were injected again along with MDMA (10 mg/kg) or vehicle. MDMA reduced core body temperature by preventing cold-elicited iBAT thermogenesis and by transiently reversing cold-elicited cutaneous vasoconstriction. Pretreatment with WAY 100635 prevented MDMA induced increases in tail blood flow, and briefly attenuated MDMA's effects on iBAT and core temperature. While spiperone alone failed to affect any of the parameters, the combination of spiperone and WAY 100635 decreased MDMA-mediated hypothermia by attenuating both the effects on tail blood flow and iBAT thermogenesis. MDMA's prevention of cold-induced iBAT thermogenesis appears to have a central origin as it rapidly reverses cold-induced increases in iBAT sympathetic nerve discharge in anesthetized rats. Our results demonstrate that MDMA in a cold environment reduces core body temperature by inhibiting iBAT thermogenesis and tail artery vasoconstriction and suggest that mechanisms by which this occurs include the activation of 5-HT1A and dopamine D2 receptors.
Departments of Emergency Medicine and Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, USA. drusynia@iupui.edu
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D002001:Adipose Tissue, Brown / Q000187:drug effects*; D000818:Animals; D003080:Cold Temperature; D018492:Dopamine Antagonists / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D007035:Hypothermia / Q000139:chemically induced / Q000503:physiopathology; D008297:Male; D018817:N-Methyl-3,4-methylenedioxyamphetamine / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects; D058829:Serotonin 5-HT1 Receptor Antagonists; D018490:Serotonin Agents / Q000633:toxicity*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013623:Tail / Q000098:blood supply / Q000187:drug effects; D022722:Thermogenesis / Q000187:drug effects*
D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D058829:Serotonin 5-HT1 Receptor Antagonists; D018490:Serotonin Agents; D012702:Serotonin Antagonists; D018817:N-Methyl-3,4-methylenedioxyamphetamine