title: Prenatal methylmercury exposure increases responding under clocked and unclocked fixed interval schedules of reinforcement.
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 microg/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)x3 (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.
authors.affiliation: Department of Psychology, Thach Hall, Auburn University, Alabama 36830, United States. reedmir@auburn.edu
authors.forename: Miranda N
authors.initials: MN
authors.lastname: Reed
authors.forename: M Christopher
authors.initials: MC
authors.lastname: Newland
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D000975:Antioxidants; D001522:Behavior, Animal / Q000187:drug effects*; D003216:Conditioning, Operant / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008767:Methylmercury Compounds / Q000633:toxicity*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced* / Q000503:physiopathology*; D051381:Rats; D020318:Rats, Long-Evans; D012055:Reinforcement Schedule; D012643:Selenium / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D008767:Methylmercury Compounds; D012643:Selenium