Neurologic development of the song control circuit in zebra finches (Taeniopygia guttata): A new model for the evaluation of endocrine disruption by polychlorinated biphenyls (PCBs)

This study describes the endocrine disruptive effect of polychlorinated biphenyls (PCBs) on the development of song control nuclei in zebra finches.; Song is an observable behavior which depends on neural health. Any disruption of song (acquisition, production or perception), is likely to result in impaired bird behavior. The discrete network of brain song nuclei is regulated by steroids and undergoes major anatomical and neurochemical changes during development and post-hatch growth.; A study was conducted in order to assess the effect of PCBs on a steroid-modulated song system, and zebra finch reproductive behavior after exposure to PCBs. Embryos in ovo were exposed to Aroclor 1248 (40μg/bird). Chicks post-hatch were pulse exposed to PCBs IUPAC 52 and 77 (80 μg/bird). Birds were euthanized at 50 days of age. Song control nuclei were microscopically evaluated after Nissl staining using an image analysis system.; The median tissue concentration of control birds was lower than that of exposed birds (P < 0.05). The reproductive ability, estimated as clutches laid per breeding cycle, number of nests constructed, incubation time, and hatchling mortality was higher in exposed than in non-exposed birds (P < 0.05). Brain nuclei HVC and RA were smaller in all exposed birds. Zebra finches exposed to Aroclor 1248 showed a statistical significant decrease in the volume of RA (males and females). PCB 52-exposed birds showed a statistically significant decrease in RA and HVC (males and females). PCB 77-exposed birds showed a statistically significant decrease in RA (females) and HVC (males and females).; Findings support the hypothesis that both RA and HVC song nuclei are susceptible to PCB-mediated endocrine disruption, in spite of the fact that PCB concentrations used in this study were lower than those reported in field studies. These findings indicate that: (i) measures other than fertility such as neurologic/hormonal disruption is a variable of potential importance for the evaluation of environmental health; and (ii) the threshold of PCB concentrations associated with endocrine disruption may be lower than previously reported, or subjected to hormensis.; Unexplained microgeographic variations in song, could be associated with exposure to endocrine-disrupting chemicals. It is suggested that bird song might be a valid model to study endocrine disruption. A down-grading revision of PCB concentration thresholds associated with toxicity is recommended.