Effects of Nicotine on Chicken Embryonic Development

Abstract

A large proportion of the United States population has been exposed to maternal smoking in utero. Mounting data suggests that nicotine can have a negative impact on neural system development. The goal of this study was to evaluate effects of nicotine exposure on chicken neural system. The early chick embryo is an established model of the first month of embryonic development in mammals. Nicotine (nicotine hydrogen bitartrate) or vehicle (sodium bitartrate monohydrate) solutions were injected in eggs prior to incubation (300ng/ml). Three cohorts of 24 eggs distributed between treatment groups were generated. After injections, eggs were sealed and placed in the incubator. Embryos were harvested on day 5 after injections, evaluated and measured, embedded in paraplast, sectioned, and stained with hematoxylin and eosin for histological analysis. Our data indicates that the nicotine treatment does not affect viability, weight, or length of the embryos. Nonetheless, nicotine notably affects the axial rotation of the embryos (defined as a change in the dorsoventral orientation of the head during development). In this study, altered axial rotation was observed in nicotine treated groups 4 times more often than in controls (p<0.05). Microscopic analysis demonstrated that atypical axial rotation was associated with incomplete closing of the embryonic neural tube in the cervical region, but not in other areas of the tube. Further research is needed to evaluate the exact mechanisms of the developmental insult onto neural system development observed in the present study.

Effects of Nicotine on Chicken Embryo Development: A Review

“…Neural tube defects (NTD), which affect the brain and spinal cord, occur in approximately 3000 births in the US each year and correlate to an increase in child mortality within a year after birth [16]. Both passive and active smoking are risk factors associated with NTDs [16] as nicotine decreases growth rate or causes a retraction of neurites, inhibiting central nervous system development [49,50]. Nicotine-induced abnormal axial rotation, neural tube formation, and synaptic expression.…”

“…A chick embryo begins development with its head facing downward and as development progresses, the body follows the rotation of the head until the embryo is positioned on its left side [16]. Bohn et al [16] found that nicotine-treated embryos compared to the controls had four times as many occurrences of atypical rotation or excessive rotation and uneven cervical regions dorsally. The atypical rotation correlated to incomplete neural tube closure of the cervical region and other spinal cord developmental defects.…”

“…The atypical rotation correlated to incomplete neural tube closure of the cervical region and other spinal cord developmental defects. Treated embryos also had a lack of separation between the embryo's surface and the spinal cord roof [16]. Additionally, Dalgic et al [4], analyzed changes in stage 12 of development to observe the effects of cotinine, a major metabolite of nicotine, on neural tube closure.…”

“…Chicken embryos are common models for these teratogenic studies as they are sensitive to various chemical and physical manipulations that can be conducted at precise developmental stages [15]. Their parallel development of early stages to the beginning half of human pregnancy [16], easy accessibility, and inexpensiveness [15] also make them ideal model organisms to study the potential risks of nicotine in human embryos.…”