The effects of chronic cobalt exposure on behavior and metallothionein levels in the adult rat

39 The Effects of Chronic Cobalt Exposure on Behavior and Metallothionein Levels in The Adult Rat k,ta;;,ifR6r /@~gp;& A.E., Clark, D.E., and Hare M. dSDA Agriculture Research Service Texas A&M University and College Station, Texas 77843 College Station, Texas 77843 Adult male rats fed daily rations on laboratory chow (control) or chow laced with cobalt chloride (either 5 or 2D mg/kg) were tested for operant (schedule-controlled) responding and conditioned suppression (CER). Determinations of tissue Co, level of metallothionein, and the ratio of Co in the tissue to the Co-binding capacity of metallothionein also were made. The results from a median test showed that animals ex- posed to 20 mg/kg Co, but not animals exposed to 5 mg/kg Co, lever pressed at a signifi- cantly slower rate on a variable interval two-min (VI-2) food reinforcement schedule than nontreated control subjects over the last 8 sessions of a 35 session operant testing phase (1 session/day). Tests for trend (orthogonal polynomials) revealed that, relative to controls, both dose levels resulted in greater lever press suppression when a tone predictive of forthcoming inescapable shock was introduced. There were no significant differences found on a test of mixed VI-2, differential reinforcement of other behavior (DRO) responding where subjects were required to lever press for reward during the first 15 min component and not lever oress during the last 15 min component of the schedule. Atomic absorption spectrophotowtric analyses revealed a positive correlation between dietary Co and tissue Co in blood, bone, brain, hair, small intestine, kidney, liver, and testes. Contrary to the biochemical pattern shown by some other heavy metals, prolonged Co exposure did not induce significant increases in metallothionein concentrations in the liver, kidney, or small intestine. The overall behavioral findings from this study conform to an emerging pattern evident among reports on heavy metal toxicity, i.e., chronic low level exposure leads to reduced operant response rates and heightened emotionality. Chronic Cadmium Exposure in the Adult Rat: Nation J.R Departknt of Psyc#o?og$ Bour e is A.E., Clark, D.E.. Texas A&M University and College Station, Texas 77843 Behavioral and Biochemical Interactions Baker, D.N USDA Agriculture Research Service College Station, Texas 77843 Adult male rats fed daily rations of laboratory chow laced with CdC12 were tested for schedule controlled responding in an operant chamber along with conditioned suppres- sion (ccnditioned emotional response-CER). Determinations of tissue Cd, levels of rnetallothionein. and the ratio of Cd in the tissue to the Cd-binding capacity of metallothionein also were made. Animals were exposed daily to either 5 mg/kg Cd (Group Cd-5), 1 mg/kg Cd (Group Cd-l), or no added Cd (Group Control). An initial phase of training on a variable interval 2 min (VI-2) food reinforcement schedule lasting 40 sessions (1 session/day) was followed by CER training and then an interpolated period (100 days) of continued exposure but with no training. Schedule retraining was intro- duced for 21 sessions (1 session/day). Parametric and nonparametric statistical analyses showed no group differences during original schedule training. On the CER test, a re- peated measures analysis of variance test indicated that Group Cd-l exhibited less sup- pression (defined in terms of operant lever press rates) than controls to preaversive stimuli. It was further revealed that Group Cd-5 showed significantly greater suppression to the primary aversive stimulus (shock) than the other two groups. Finally, a median test of operant responses following the 100 day rest interval showed that both treatment groups had significantly lower lever press rates than controls on the schedule retraining task. These behavioral pertubations occurred coincident with body burdens sufficient to overload the binding capacity of metallothionein in the liver, kidney, and small intestine. This study of the behavioral toxicity of cadmium suggests that chronic oral exposure to cadmium can occasion behavioral disturbances and enhance emotlonality in animals even in the absence of overt signs of toxicosis.