Fig. 1

Behavioral sensitization (A) and CPP (B) protocols. A Five days after rats were weaned from their mother, they received a daily oil or nandrolone injection for ten consecutive days (PN-28 to 37). For the behavioral sensitization experiments, rats were habituated to the locomotor activity chamber for 1 h (2 days post-nandrolone treatment, PN-39). The data obtained from the first ten minutes of habituation (Day 39 and Day 40 was used as the data for the open field test (Fig. 2B and C). From days 40 through 44, on day 52, and on day 62, rats were injected with saline or with cocaine (15 mg/kg). Rats were injected in the locomotor activity chamber (days 40,44, 52, and 62) or in their home cage (days 41, 42, and 43) (see the context of injection). From days 45 through 51 and from days 53 through day 61, rats remained undisturbed in their home cages. B. Five days after rats were weaned from their mother, they received a daily oil or nandrolone injection for ten consecutive days (PN-28 to 37). On day 38, a second group of rats were tested in the elevated plus maze (EPM). These same rats were used for the CPP experiments. To determine the rat’s preference for a particular CPP chamber, rats were allowed to roam freely through both chambers for 3 days (Days 40–42: pre-conditioning). The amount of time spent in each chamber was calculated to determine which side it preferred. For the following 10 days (days 43–52, conditioning days), rats were injected daily, alternating between saline and cocaine (15 mg/kg) injections. Rats received cocaine in the non-preferred chamber and saline in the preferred chamber. Saline animals received saline in both chambers. After the injection, rats were confined for 30 min in the chamber where they received the injection. On the last day (day 53: post-conditioning day), the animals were placed in the activity chamber and allowed to roam freely between the two chambers for 30 min. The amount of time spent in each chamber was recorded and compared to that spent in pre-conditioning.