Prenatal cigarette smoke exposure effects on apoptotic and nicotinic acetylcholine receptor expression in the infant mouse brainstem

Abstract

Infants exposed to cigarette smoked during pregnancy into infancy have increased respiratory and cardiac abnormalities. Nicotine, the major neurotoxic component of cigarette smoke, induces its actions by binding to nicotinic acetylcholine receptors (nAChR), with one downstream effect being increased apoptosis. Using a pre- into post- natal cigarette smoke exposure mouse model (SE), we studied the immunohistochemical expression of nAChR subunits α2, α3, α4, α5, α7, α9, β1 and β2 and two markers of apoptosis, active caspase-3 and TUNEL, in seven nuclei of the medulla and facial nucleus of the pons in male mice. Pups of dams exposed to two cigarettes (nicotine ≤1.2mg, CO ≤15mg) twice daily for six weeks prior to mating, during gestation and lactation (n=5; SE), were compared to pups exposed to air under the same condition (n=5; SHAM) at P20. Results showed that the hypoglossal nucleus had increased α3, α4, α7, α9, Casp-3 and TUNEL, dorsal motor nucleus of the vagus had increased α3, α5, α7, β1 and Casp-3, nucleus of the solitary tract had increased α3 but decreased α4, α5, β1 and apoptosis, cuneate nucleus had increased α3, β2 and Casp- 3, but decreased α5, nucleus of the spinal trigeminal tract had increased α3, α7, β1, lateral reticular nucleus had decreased β1, inferior olivary nucleus had increased β1 but decreased apoptosis, and the facial had increased α2, α3 and α7. This is the first study to demonstrate that nAChR subunits are affected following pre- into post-natal SE and that they simultaneously coincided with changes in apoptotic expression.

Cellular protein and mRNA expression of β1 nicotinic acetylcholine receptor (nAChR) subunit in brain, skeletal muscle and placenta

“…The results are presented with the sc‐11371 (rabbit polyclonal) β1 antibody being the main focus of this study. This was because it has been used previously in our published studies on the human placenta (Machaalani et al, 2014), piglet brain (Vivekanandarajah et al, 2015) and mouse brain (Vivekanandarajah et al, 2016). Comparison between the two β1 antibodies (sc‐11371 and sc‐1448) are made subsequently.…”

What lessons have we learnt about the impact of maternal cigarette smoking from animal models?

“…The chemicals in cigarette smoke inhaled by the mothers can clearly affect the cognitive development of the offspring. There are alterations in nicotinic acetylcholine receptors (nAChRs) across various brain regions, which has been linked to the inhibition of DNA synthesis and increased apoptosis . In offspring, dose‐dependent responses to the number of cigarettes smoked by the mothers have been observed in humans.…”

“…The high risk of neurological disorders in smokers may suggest that oxidative stress is more potent than nicotine to cause nAChR dysfunction. Indeed, changes in brain nAChRs have been observed in the offspring from SE mothers …”

“…There are alterations in nicotinic acetylcholine receptors (nAChRs) across various brain regions, which has been linked to the inhibition of DNA synthesis and increased apoptosis. 13,25 In offspring, dosedependent responses to the number of cigarettes smoked by the mothers have been observed in humans. For example, increased risk of internalizing behaviours (such as fear, anxiety and sudden change of mood) is prominent in 1.5 and 3 years old children if the mothers were heavy smokers (>20 cigarettes/day) during pregnancy.…”

“…Indeed, changes in brain nAChRs have been observed in the offspring from SE mothers. 25 In homeostatic conditions the cellular antioxidant defense system can scavenge excess free radicals using enzymes copper-zinc superoxide dismutase, manganese superoxide dismutase (MnSOD), catalase, and glutathione peroxidase. 73 However, the overproduction of oxidative molecules can exhaust these enzymes leading to oxidative stress-induced damage.…”