This study investigates, both behaviourally and biochemically, the action of 2-allophanyl-2-allyl-4-valerolactone (
Valofan) in the mouse, after acute or repeated administration. The exploratory behaviour was measured in different experimental conditions by a hole-board test modified in observation length: 10 min instead of original 5. The variations in
5-HT and
5-HIAA levels were measured in cortex and brainstem. Acute administration of
Valofan (50 to 500 mg/kg os) did not change exploration during the first 5 min period, while at higher doses (200-500 mg/kg) it did produce a significant increase in basal exploratory behaviour, measured by prolonging hole-board test to 10 min. These data were confirmed by the habituation test to he thole-board whereby, after three days of exposure, low exploratory baseline of mice was constant. The elevation of the exploration was consistant with a significant net increase in
5-HT levels (greater than 5-HT; less than 5-HIAA) in brainstem, and with a relative enhance in
amine levels (= 5-HT; less than 5-HIAA) in cortex for higher doses of the
drug. Modifications of
serotonin mechanisms positively affect behaviour in an unfamiliar environment. Surprisingly repeated treatment (for 8 days) with
Valofan did not change exploration in respect of controls. The biochemical pattern of repeated treatments showed that higher doses of
drug increased
5-HT without affecting
5-HIAA levels in brainstem and cortex. Repeatedly handheld mice showed control values significantly higher than those of acute treatment. This increase in activity corresponded to a biochemical pattern similar to that obtained after acute administration of 500 mg/kg
Valofan, indicating that handling affected the basal
5-HT content. Thus
Valofan could stimulate exploration in mice with a low baseline, while it did not change the activity of animals with a higher baseline. Further evidence for a possible involvement of
5-HT mechanisms in the action of
Valofan was given by the
fatigue test. Mice, submitted to hole-board after 24 h of forced walking, showed, with 500 mg/kg, a significant decrease in exploration: action of
Valofan seemed to potentiate the effects exerted by stress on
serotonin turnover.