Effects of polybrominated biphenyl on a discrimination task in rats.

Learning or performance of an operant discrimination task by laboratory rats in Skinner boxes was studied as a function of subchronic treatment with polybrominated biphenyl (PBB) (1.0 mg/kg, 3.0 mg/kg or 6.0 mg/kg for 20 days). Acquisition of the discrimination task was similar for experimental and control rats at each dose level. Response times were slower for the 1.0 mg/kg rats but were like controls for the 3.0 and 6.0 mg/kg animals. Extra responses occurring in the absence of auditory discriminative stimuli increased significantly for the 1.0 mg/kg rats (hyperactivity), were no different from controls for the 3.0 mg/kg rats and decreased significantly for the 6.0 mg/kg animals (CNS depression). The weights of PBB animals did not differ significantly from controls. Analyses of brains and plasma by electron capture gas chromatography yielded detectable levels of PBB as long as 10 months following the last PBB administration. PBB in brains and plasma varied directly as a function of dose administered.