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.