Paradoxical rate-dependent effect of fluoxetine on captivity-induced stereotypies in bank voles.

Treatment of stereotypies in human and animal clinics is still empirical due to our incomplete understanding of underlying mechanisms. As a consequence, experimental studies in controlled laboratory conditions are necessary. Bank voles (Clethrionomys glareolus), housed in barren laboratory cages, often develop stereotyped up-and-down jumping even before the age of 1 month. The aim of this study was to investigate how captivity-induced stereotypies respond to fluoxetine (Prozac), a selective serotonin reuptake inhibitor. During a control period of 10 days saline was administered daily s.c. to 6-month-old bank voles (n=24). In the subsequent 30 days, 16 animals received a dose of 10-mg/kg s.c. daily while 8 other animals were injected a dose of 20-mg/kg fluoxetine. Stereotypies, general activity, food intake and body weight were measured. Dose-related and paradoxical rate-dependent effects were found on stereotypies. After 10 days of treatment, the stereotypy levels of the animals with high pre-drug stereotypy rates decreased in contrast with those of low stereotypers which increased. No effect was found on general activity and food intake. Weekly weighing revealed an increase of weight during the total drug period and a return to pre-drug levels during the week thereafter.