Abstract
- Several developmental disabilities are characterized by the presence of perseverative behaviors. It has recently been demonstrated that developmental exposure to methylmercury (MeHg) is associated with perseveration on operant tasks. An evaluation of the mechanisms underlying this behavior may provide insight regarding the behavioral and neural mechanisms of perseveration in individuals with developmental disabilities. Rats were exposed gestationally to 0, 0.5 or 5 ppm mercury as MeHg via maternal drinking water. They also received a diet during gestation and throughout life that was marginal (0.06 ppm) or rich (0.6 ppm) in selenium (Se), a nutrient believed to protect against MeHg's toxicity. Reinforcer efficacy was evaluated using a progressive ratio schedule of reinforcement during adulthood. Maximum ratio obtained (MRO) was determined using 20 or 60 mg sucrose pellets and with ratio requirements that increased at 5% or 20% per reinforcer. MRO was related to MeHg exposure, and this was modified by the rate at which the ratio increased, reinforcer magnitude, gender, and Se exposure. This implies that developmental MeHg exposure enhances reinforcer efficacy, an effect that could be related to other reports of perseveration.