Risperidone counteracts lethality
in an animal model of the serotonin syndrome

Nisijima K, Yoshino T, Ishiguro T
Department of Psychiatry,
Jichi Medical School,
Psychopharmacology (Berl) 2000 May; 150(1):9-14


RATIONALE: The serotonin (5-HT) syndrome is the most serious side effect of antidepressants, and pharmacologic treatment should be offered in severe cases. OBJECTIVE: In the present study, the effects of risperidone, ketanserin, and haloperidol on an animal model of the serotonin (5-HT) syndrome were evaluated. METHODS: Intraperitoneal administration of 100 mg/kg 5-hydroxy-L-tryptophan (5-HTP) (a precursor of 5-HT) and 2 mg/kg clorgyline (a monoamine oxidase type-A inhibiting antidepressant) induced the 5-HT syndrome in rats. The rectal temperature of the rats was measured, and the microdialysis method was used to measure noradrenaline (NA) levels in the anterior hypothalamus. RESULTS: In the group pre-treated with saline, the NA concentration increased to 13 times the pre-administration level, rectal temperature increased to more than 40 degrees C, and all of the animals died 75 min later. In the group pre-treated with risperidone (0.5 mg/kg), the 5-HT syndrome was completely inhibited, and the NA level increased to 6.5 times the pre-administration level. Ketanserin, a selective 5-HT2A antagonist (5 mg/kg) also inhibited the 5-HT syndrome. In contrast, all of the rats in the group pre-treated with haloperidol (0.5 mg/kg) died earlier than in the saline group. CONCLUSIONS: These results suggest that strong 5-HT2A antagonists such as risperidone, but not dopamine D2 antagonists, counteract lethality due to 5-HT syndrome, and that not only does enhancement of 5-HT activity occur in the 5-HT syndrome, but NA activity also increases.
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The serotonin syndrome
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