Learning performances of honeybees (Apis mellifera L) are differentially affected by imidacloprid according to the season.

To establish the sublethal concentrations domain, acute and chronic oral tests were conducted on caged honeybee workers (Apis mellifera L) using imidacloprid and a metabolite, 5-OH-imidacloprid, under laboratory conditions. The latter showed a 48-h oral LD50 value (153 ng per bee) five times higher than that of imidacloprid (30 ng per bee). Chronic feeding tests indicated that the lowest observed effect concentrations (LOEC) of imidacloprid and of 5-OH-imidacloprid on mortality of winter bees were 24 and 120 microg kg(-1) respectively. Behavioural effects of imidacloprid and 5-OH-imidacloprid were studied using the olfactory conditioning of proboscis extension response at two periods of the year. Winter bees surviving chronic treatment with imidacloprid and 5-OH-imidacloprid had reduced learning performances. The LOEC of imidacloprid was lower in summer bees (12 microg kg(-1)) than in winter bees (48 microg kg(-1)), which points to a greater sensitivity of honeybees behaviour in summer bees, compared to winter bees.

Effect of fenfluramine on caloric intake and macronutrient selection in Lou/c rats during aging.

Previous studies have shown a shift of preferences from carbohydrate to fat and a decrease in protein intake in self-selected Lou/c rats with advancing age. This study investigated a potential neurochemical mechanism underlying age-related modifications by evaluating the effects of fenfluramine (dl-F), a drug that enhances 5-HT release and blocks its re-uptake by presynaptic terminals, on macronutrient selection. The drug dl-F (1.5 and 3mg/kg s.c.) induces a dose-related hypophagia with the oldest animals being the most sensitive. The main decrease is in fat consumption with minor changes in carbohydrate and protein consumptions. Young, but not old animals, compensate during the day the nocturnal intake decrease induced by dl-F. The plasma concentration of dexfenfluramine (d-F) was higher as the rats aged. The icv administrations of dl-F induced a caloric intake decrease in the oldest groups and a differential effect on protein intake between old and young rats. Metergoline induced a partial reversion of dl-F effect on food intake but this effect was not age related. These data suggest a possible implication of serotoninergic system in modifications of food behavior during aging. However, further studies are needed.