Maternal oral consumption of morphine increases Bax/Bcl-2 ratio and caspase 3 activity during early neural system development in rat embryos

Abstract

Maternal morphine consumption has been shown to result in physical and neurobehavioral defects in fetus and offspring, but the underlying molecular mechanisms of these defects remain unclear. Regarding the critical role of apoptosis in normal development of central nervous system, the present study was designed to investigate the effect of intrauterine morphine exposure on programmed cell death of neuroblasts during the early development of neural system. Pregnant Wistar rats received morphine sulfate through drinking water at the concentration of 0.01 mg/ml (20 ml water per day for each rat) from the first day of gestation to the time of sampling. Control groups received tap water. Control and morphine-treated pregnant rats, each in five separated groups, were killed on gestational days 9.5 to 13.5, and the embryos were taken out, fixed, and embedded in paraffin. Immunohistochemical assay was used to reveal the protein expression of Bax, Bcl2, and the activation of caspase 3. The results showed a significant increase in Bax immunoreactivity in all of the mentioned embryonic days (E9.5 to E13.5) and a significant decrease in Bcl-2 immunoreactivity at days E10.5 and E12.5 in morphine-treated groups compared with control. Data analysis revealed that Bax/Bcl2 ratio was increased in all of the morphine-exposed groups. Consistent with these results, immunostaining of cleaved caspase 3 showed a significant increase at days E11.5 to E13.5. These findings suggest that morphine exposure during the first embryonic days may enhance the susceptibility of neuroblasts to apoptosis by upregulating the ratio of Bax to Bcl-2 protein expression and increasing downstream caspase-3 activity. The increased probability of neuroblast apoptosis may be the cause of morphine-induced defects in the central nervous system development and its structural and neurobehavioral consequences.