text: Pretreatment with tropisetron (1 microM), a 5-HT3 antagonist, ketanserin (10 microM), a 5-HT2 antagonist, << thioperamide >> (10 microM), a [[ histamine H3 ]] antagonist, or phentolamine (10 microM), an alpha-adrenergic antagonist, however, had no effect.