Methylmercury Exposure in Adolescence: Effects on Delay Discounting and Sensitivity to d-Amphetamine in Mice
Type of DegreeMaster's Thesis
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Methylmercury (MeHg) is an environmental neurotoxicant that can be used to study how cortical damage during early development affects behavior later in life. The consequences of MeHg exposure in adolescence, a developmental period in which the brain and behavior may be especially vulnerable to MeHg, is unknown. The current experiments were designed to assess the effects of low-level MeHg exposure during adolescence on delay discounting (i.e., preference for small, immediate reinforcers over large, delayed ones) and sensitivity to d-amphetamine (a dopamine agonist) using a mouse model. Thirty-six male C57BL/6n mice were exposed to 0, 0.3, or 3.0 ppm mercury (as MeHg) via drinking water from postnatal day 21 through 59, the murine adolescent period. As adults, mice lever-pressed for a 0.01-cc droplet of milk solution delivered immediately and four 0.01-cc droplets delivered after a series of delays for 35 sessions. A dose-response determination of d-amphetamine (i.p.; 0.1 – 1.7 mg/kg) followed. An information-theoretic analysis, which does not rely on traditional null-hypothesis testing, was employed to determine the most parsimonious model of the generalized matching equation to describe the data collected. Magnitude-sensitivity estimates were lower for mercury-exposed mice relative to controls, and delay-sensitivity estimates were reduced in the 0.3-ppm group compared to controls and the 3.0-ppm group. Further, d-amphetamine dose-dependently reduced delay-sensitivity estimates in all groups but decreased magnitude-sensitivity estimates only in the mercury-exposed groups. Adolescence is a developmental period during which the brain and behavior may be vulnerable to MeHg exposure.
- Steven's thesis_MeHg Exposure in Adolescence.pdf