Effects of amitriptyline and isocarboxazid on 5-hydroxytryptophan induced head twitches in mice.

Effects of amitriptyline and isocarboxazid on brain 5-HT and 5-HIAA were examined in relation to their action on 5-HTP induced head twitches. Amitriptyline reduced 5-HTP induced head twitches but isocarboxazid increased them. Both amitriptyline and isocarboxazid caused a significant increase of brain 5-HT concentration in 5-HTP treated mice. Amitriptyline also caused a significant increase of 5-HIAA concentration, while isocarboxazid reduced 5-HIAA concentration in the brains of 5-HTP treated mice. Probenecid, which significantly increased 5-HIAA concentration without affecting brain 5-HT concentration in 5-HTP treated mice, reduced 5-HTP induced heat twitches. These results suggest that 5-HTP induced head twitches might be induced by an increase of 5-HT concentration, and reduced by an increase of 5-HIAA or a decrease of 5-HT concentration in the brains of mice.