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.