Selective Toxicity of Opiate Competitors in Embryonic Avian Brain Development

Serotonin (5-hydroxytryptamine) is a central nervous system neurotransmitter important in embryonic development. It has been determined to be an important factor in cell migration initiation in the early phases of development. Six-day old white leghorn chick embryos were incubated for 20 days. Methadone doses were dissolved in PBS and injected in-ova on days 8 to 15 of the incubation period. Low, medium, and high methadone doses were comparable to human doses. Ten replicates for each treatment were used. The control injections consisted of 0.5 ml of only PBS. All treatments were injected directly into the air sac using a hypodermic needle. On the 20^th day of incubation, embryos were sacrificed and brain tissue was harvested for further analysis. The Elisa immunoassay was used to determine serotonin concentrations in the brain tissue.  DNA damage was determined using single cell gel electrophoresis (comet assay). The SPSS Statistical Program One-Way ANOVA multiple comparison Student-Newman-Keuls analysis was used to test for variation of serotonin levels. There was a statistically significant difference of serotonin responses in all methadone treatments in comparison to the controls. The highest concentration of 3.0 ng/ml was observed at the low methadone dose. There was a decrease in concentration of serotonin at the medium dose at 1.7 ng/ml and increase at the high dose to 2.9 ng/ml. Our data suggests that an increase of serotonin in the experimental organisms was a response to stress caused by the methadone injection. Exposure to methadone was correlated with increased brain DNA damage.