Amitriptyline sensitization of a serotonin-mediated behavior depends on the passage of time and not repeated...

Daily treatment for 10 days with either amitriptyline or the tricyclic muscle relaxant, cyclobenzaprine, increased the incidence of head-twitch behavior in response to 5-hydroxytryptophan (5-HTP) when this was examined two days later. Only one day of amitriptyline treatment followed by an 11-day hiatus before administration of 5-HTP also sensitized the head-twitch response whereas similar amitriptyline treatment followed by 5-HTP one hour later failed to do so. These data provide the first evidence for time-dependent sensitization of brain serotonin systems.