The effects of amfonelic acid and some other central stimulants on mouse striatal tyramine, dopamine and homovanillic acid.

1 The concentrations of p- and m-tyramine, dopamine and homovanillic acid were measured in the mouse striatum following the subcutaneous administration of amfonelic acid, (+)-amphetamine or nomifensine.2 The administration of 2.5-25 mg/kg of amfonelic acid produced a reduction in p-tyramine that lasted at least 8 h. m-Tyramine was significantly increased and this was observed between 2 and 24 h after drug treatment. The levels of homovanillic acid were increased within 4 h after amfonelic acid administration.3 (+)-Amphetamine treatment (5 mg/kg) produced a reduction in p-tyramine observed up to 4 h after its administration and no significant changes in m-tyramine.4 The administration of 10 mg/kg of nomifensine produced no significant changes in p-tyramine, m-tyramine or homovanillic acid. By increasing the dose to 20 mg/kg, nomifensine produced an increase in p-tyramine and homovanillic acid.5 The present results support the view that amfonelic acid and (+)-amphetamine would respectively release granular or newly synthesized dopamine, both actions being accompanied by an increase in tyrosine hydroxylase activity and dopamine turnover which in turn reduces p-tyramine but produces no change or an increase in m-tyramine.6 The effects of nomifensine were observed after the administration of a relatively high dose (20 mg/kg), that was lethal to some mice (about 20%, at 2 h), and more likely to posses unspecific actions.