Lactation exposure to BDE-153 damages learning and memory, disrupts spontaneous behavior and induces hippocampus neuron death in adult rats

Abstract

Objective: To study the effects of 2,2',4,4',5,5'-hexa-brominated diphenyl ether (BDE-153) exposure during lactation on the learning and memory abilities, spontaneous behavior and brain cells of adult rats and to elicit basic information on PBDE's developmental neurotoxicity.

Methods: Newborn male rat pups were randomly categorized into the following groups (15 pups per group), according to their weights and litters: a control group, and 1mg/kg, 5mg/kg and 10mg/kg BDE-153 groups. At postnatal day 10 (PND10), the pups in the BDE-153 groups were intraperitoneally injected once with BDE-153 plant oil solutions at 0.1ml/10g body weight, and the controls were injected with plant oil. Throughout the entire experiment, physiological measures were recorded, such as food and water consumption, body weight and clinical symptoms. At 1 month and 2 months after treatment, the learning and memory abilities of the rats were tested by the Morris water maze test, the step-down test, and the step-through test; spontaneous behavior was tested by the open-field test. After all tests were accomplished, rats were weighed and sacrificed, and the brain tissue was immediately isolated and divided into two parts. Sections were fabricated from one part, and changes in the morphology and ultrastructure in CA3 region of hippocampus were observed under an optical microscope and transmission electron microscope, along with the detection of apoptotic cells with the terminal-deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) method. The tissue of the second part was digested into single-cell suspension liquid, and the cell apoptosis was assayed with flow cytometry and the lactate dehydrogenase (LDH) leakage was detected with spectrophotometry.

Results: There was no obvious change in food and water consumption, body weight and the ratio of brain to body weight, or any overt clinical symptoms in the BDE-153-treated rats. Compared to the control group, rats' latency time in the test session (LT2) in the step-down test was significantly increased in the 10mg/kg BDE-153 group at 2 months after treatment (P<0.05), and the BDE-153-treated rats' swimming times and distances in the target quadrant were significantly decreased at 1 month and 2 months after treatment (P<0.05 or P<0.01). These parameters were also significantly increased in the opposite quadrant at 1 month after treatment (P<0.05 or P<0.01). The spontaneous behavior was significantly reduced in the treated groups compared to the controls (P<0.05 or P<0.01). The severity of neurobehavioral dysfunction was dependent on the exposure dose of BDE-153, and worsened with age. Under an optical microscope, the treated rats' neurons in the CA3 region of the hippocampus were observed to be reduced and disarranged, and the cell junctions were loosened and the intercellular spaces were enlarged. Under a transmission electron microscope, the cell nucleus was observed to shrink; the chromatin was condensed and gathered near the nuclear membrane, the Nissl bodies and other organelles in the perikaryon were reduced, and the vacuole was observed to degenerate and even disappear. Moreover, compared to the controls, the cell apoptosis rates were significantly increased in the 5 and 10mg/kg BDE-153 groups (P<0.05), and the LDH activity was significantly increased in the 10mg/kg BDE-153 groups (P<0.01).

Conclusion: Lactation exposure to BDE-153 damaged adult rats' learning and memory abilities, disrupted their spontaneous behavior (hypoactivity) and induced hippocampus neuron apoptosis.