Differential effects of prenatal protein malnutrition and prenatal cocaine on a test of homing behavior in rat pups

The effects of prenatal cocaine exposure and protein malnutrition on orientation to home nest material was assessed in rat pups. Sprague-Dawley dams were fed a diet of low protein content (6% casein), an isocaloric diet of adequate protein content (25% casein, control), or a laboratory chow diet prior to mating and throughout pregnancy. Within each diet group, rats received either cocaine injections (30 mg/kg IP 2 times per week prior to mating and then 30 mg/kg SC daily from day 3 to 18 of pregnancy) or saline injections. All litters were fostered on the day of birth to control mothers fed an adequate diet. On postnatal days 7, 9, and 11, a single pup from each litter ( n = 11–15 per treatment) was tested repeatedly in a clean test cage for the rapidity of approach, and level of attraction to their own home (nest) bedding compared with fresh bedding. Prenatal malnutrition and prenatal cocaine exposure each gave rise to independent effects on performance, based upon factor analysis. Prenatal malnutrition, but not prenatal cocaine, increased the time taken for rat pups to approach their nest bedding, reduced the time spent on this bedding, decreased the number of entries into the sector containing the home bedding and reduced pup weight. Prenatal cocaine, but not prenatal malnutrition, produced a reduction in activity, but had no effect on pup weight. The lower activity level was most pronounced on postnatal day 7. Surprisingly, interactive effects of prenatal cocaine and prenatal malnutrition were not observed on any behavior examined. Nevertheless, the co-existence of drug addiction and malnutrition in human populations raises the possibility that some of the effects generally attributed to drug exposure may, in fact, be due to malnutrition.