Comparison between dopaminergic and non-dopaminergic neurons in the VTA following chronic nicotine exposure during pregnancy

Abstract

Exposure to nicotine during pregnancy through maternal smoking or nicotine replacement therapy is associated with adverse birth outcomes as well as several cognitive and neurobehavioral deficits. Several studies have shown that nicotine produces long-lasting effects on gene expression within many brain regions, including the ventral tegmental area (VTA), which is the origin of dopaminergic neurons and the dopamine reward pathway. Using a well-established rat model for perinatal nicotine exposure, we sought to investigate altered biological pathways using mRNA and miRNA expression profiles of dopaminergic (DA) and non-dopaminergic (non-DA) neurons in this highly-valuable area. Putative miRNA-gene target interactions were assessed as well as miRNA-pathway interactions. Our results indicate that extracellular matrix (ECM) receptor interactions were significantly altered in DA and non-DA neurons due to chronic nicotine exposure during pregnancy. They also show that the PI3K/AKT signaling pathway was enriched in DA neurons with multiple significant miRNA-gene targets, but the same changes were not seen in non-DA neurons. We speculate that nicotine exposure during pregnancy could differentially affect the gene expression of DA and non-DA neurons in the VTA.

Investigating the influence of perinatal nicotine and alcohol exposure on the genetic profiles of dopaminergic neurons in the VTA using miRNA–mRNA analysis

“…Following perinatal nicotine–alcohol treatment contrasted against the alcohol group, 2,113 genes were upregulated and 1,836 were downregulated. Statistical analysis was done using Benjamini and Hochberg (BH) method with q value < 0.05 and an absolute log2 fold change > 1 as previously described in Keller et al 31 , 32 . Figure 1 illustrates the heatmaps of the top 50 significantly differentially expressed miRNAs (DEmiRs) following perinatal (a) alcohol and (b) nicotine–alcohol exposures compared to the saline control group, and (c) nicotine–alcohol exposure compared to the alcohol treatment group.…”

“…Following nicotine–alcohol exposure 5 miRNAs were upregulated and 8 were downregulated when compared to the alcohol treatment group. The BH method was used for the statistical analysis applying parameters of q value < 0.05 and an absolute log2 fold change > 0.5 as previously described in Keller et al 31 , 32 . Table 2 a–c list the most significant up and downregulated DEGs along with their description and predicted miRNA targets for perinatal alcohol, nicotine–alcohol and nicotine–alcohol vs. alcohol treatment groups, respectively.…”

“…Pregnant female SD rats purchased from Charles River (Charles River, Wilmington, MA, USA) were housed in the animal facility and were maintained at 22 ± 2 °C with 65% humidity, on a 12-h light/12-h dark cycle. The animal treatment method has been further detailed in Keller et al 31,32 . Briefly, rats were acclimated to the animal facility upon arrival for 72 h before the subcutaneous insertion of an osmotic pump (Alzet, Cupertino, CA, USA) containing either nicotine hydrogen tartrate (Sigma-Aldrich, St. Louis, MO, USA), which released nicotine at a rate of 6 mg/kg/day in order to simulate the nicotine plasma level found in moderate smokers 31,32 , or an equal volume of saline for control 126 .…”

“…The animal treatment method has been further detailed in Keller et al 31,32 . Briefly, rats were acclimated to the animal facility upon arrival for 72 h before the subcutaneous insertion of an osmotic pump (Alzet, Cupertino, CA, USA) containing either nicotine hydrogen tartrate (Sigma-Aldrich, St. Louis, MO, USA), which released nicotine at a rate of 6 mg/kg/day in order to simulate the nicotine plasma level found in moderate smokers 31,32 , or an equal volume of saline for control 126 . Liquid diet containing 36% kcal from ethanol F1265SP or F1264SP control, purchased from Lieber-DeCarli (Bio-Serv, Flemington, NJ, USA) was placed in Richter feeding tubes (Bio-Serv), and was gradually introduced to the pregnant mothers based on the protocol provided from Bio-Serv.…”

Investigating the effects of chronic perinatal alcohol and combined nicotine and alcohol exposure on dopaminergic and non-dopaminergic neurons in the VTA

“…We recently investigated the influence of maternal nicotine intake on genetic pathways of VTA DA and non-DA neurons in rat pups 33 . Our results showed that the extracellular matrix (ECM) receptor interactions were significantly altered in both DA and non-DA neurons.…”