Early postnatal development of open field behaviour is changed by single doses of fenfluramine or p-chloroamphetamine

Three groups of 8 male hooded rats were treated with 50 mumol/kg fenfluramine (FF) or 50 mumol/kg p-chloroamphetamine (PCA) or the same amount of vehicle solution (NaCl) i.p. on postnatal day 8. Each rat was exposed to a 60 X 75 X 22 cm open field (OF) for 30 min from the 10th to the 30th postnatal day (pd) at the same time. FF and PCA enhanced the ambulatory activity on 11-14th pd between 200 and 1000%. Several parameters of the exploratory activity and grooming were also significantly increased in this period (p less than 0.01). Habituation to the OF was weakened. The differences disappeared during eye opening. Exploratory activity was significantly diminished in the fourth week. Most of the changes were similar after both drugs, some of them point to different actions of FF and PCA. The timing of the qualitative behavioral development was influenced by both drugs. The results demonstrate the important role of the serotoninergic system in behaviour development. Serotoninergic neurons are postulated to participate in certain forms of response inhibition. Some of the deficits may be compensated during early development.