Prenatal methylmercury exposure increases responding under clocked and unclocked fixed interval schedules of reinforcement

• Published in: Neurotoxicology and teratology 2007-07, Vol.29 (4), p.492-502
• Main Authors: Reed, Miranda N, Newland, M. Christopher
• Format: Article
• Language: English
• Subjects: Age Factors; Analysis of Variance; Animals; Animals, Newborn; Antioxidants; Behavior, Animal - drug effects; Biological and medical sciences; Chemical and industrial products toxicology. Toxic occupational diseases; Conditioning, Operant - drug effects; Developmental; Dose-Response Relationship, Drug; Emergency; Female; Fixed interval; Medical Education; Medical sciences; Metals and various inorganic compounds; Methylmercury; Methylmercury Compounds - toxicity; Operant behavior; Pregnancy; Prenatal Exposure Delayed Effects - chemically induced; Prenatal Exposure Delayed Effects - physiopathology; Rats; Rats, Long-Evans; Reinforcement Schedule; Selenium; Selenium - pharmacology; Toxicology
• ISSN: 0892-0362; 1872-9738
• DOI: 10.1016/j.ntt.2007.03.002

Abstract Recent experiments have suggested that developmental methylmercury exposure produces perseverative behavior in adulthood. In the present experiment, interactions between developmental low-level methylmercury (MeHg) and nutritionally relevant dietary selenium (Se) on operant behavior and its persistence were examined in aged animals. Female rats were exposed, in utero , to 0, 0.5, or 5 ppm mercury as MeHg via drinking water, approximating mercury exposures of 0, 40, and 400 μg/kg/day. They also received both pre- and chronic post-natal exposure to a diet that was marginal (0.06 ppm) or rich (0.6 ppm) in Se, a nutrient believed to protect against MeHg's toxicity. This created a 2 (chronic Se) × 3 (gestational MeHg) full factorial design, with 6–8 female rats per cell. At eleven months of age, a multiple schedule consisting of alternating fixed interval (FI) and clocked FI (CFI) components was arranged. The CFI component was divided into 5, 24-second bins, each associated with a different auditory stimulus, providing a “clock.” Low and high response rates were evaluated using the initial 40% (bins 1 and 2) and last 20% (bin 5) of the FI and CFI components, respectively. Rats exposed to 5 ppm Hg made more responses than the other two groups during the last 20% of the intervals, regardless of selenium exposure or presence of the clock stimuli. They did not differ from the other groups during the initial 40% of the FI and CFI components. Following reinforcement omission for half of the intervals at 21 months of age, the 5 ppm Hg group continued to respond at higher rates than the other groups in both components.