Development of spatial navigation following prenatal cocaine and malnutrition in rats: lack of additive effects.

ABSTRACT

The effects of prenatal cocaine exposure and protein malnutrition on the development of spatial navigation were assessed in rats. Sprague-Dawley dams were fed a low-protein (6% casein), adequate protein (25% casein), or a laboratory chow diet prior to mating and throughout pregnancy. Within each diet group, rats received either cocaine injections (30 mg/kg i.p. two times per week prior to mating and then 30 mg/kg s.c. daily from day 3 to 18 of pregnancy) or saline injections. All litters were fostered on the day of birth to saline-injected mothers fed either the 25% casein diet or the chow diet. Gestation length was decreased by prenatal cocaine exposure whereas litter size was reduced by prenatal malnutrition. On postnatal days 21, 25, 30, or 70, rats were tested for their ability to locate a submerged platform in a Morris water maze. In well-nourished rats, prenatal cocaine increased the mean distance swum during acquisition over days 21-30, a difference that was abolished in rats with prenatal malnutrition. In the absence of drug exposure (saline groups), prenatal malnutrition was itself associated with longer swim paths. Neither prenatal insult affected the accuracy of the spatial navigation at these ages, as determined by their search pattern when the platform was removed. On postnatal day 25, rats raised on the chow diet exhibited superior performance to that of rats raised on the 25% casein diet, but by day 30 these two well-nourished groups were comparable. At day 70, prenatal cocaine impaired spatial performance on the first session, in well-nourished rats only. Thus, these results provide no support for the hypothesis that prenatal cocaine and protein malnutrition combine to produce a greater effect on behavioral development than either insult alone.