Altered mRNA Levels of Stress-Related Peptides in Mouse Hippocampus and Caudate-Putamen in Withdrawal after Long-Term Intermittent Exposure to Tobacco Smoke or Electronic Cigarette Vapour

Abstract

Nicotine addiction is a severe public health problem. The aim of this study was to investigate the alterations in key neurotransmissions after 60 days of withdrawal from seven weeks of intermittent cigarette smoke, e-cigarette vapours, or an e-cigarette vehicle. In the nicotine withdrawal groups, increased depressive and anxiety/obsessive-compulsive-like behaviours were demonstrated in the tail suspension, sucrose preference and marble burying tests. Cognitive impairments were detected in the spatial object recognition test. A significant increase in Corticotropin-releasing factor (Crf) and Crf1 mRNA levels was observed, specifically after cigarette withdrawal in the caudate-putamen nucleus (CPu). The nociceptin precursor levels were reduced by cigarette (80%) and e-cigarette (50%) withdrawal in the CPu. The delta opioid receptor showed a significant reduction in the hippocampus driven by the exposure to an e-cigarette solubilisation vehicle, while the mRNA levels doubled in the CPu of mice that had been exposed to e-cigarettes. Withdrawal after exposure to e-cigarette vapour induced a 35% Bdnf mRNA decrease in the hippocampus, whereas Bdnf was augmented by 118% by cigarette withdrawal in the CPu. This study shows that long-term withdrawal-induced affective and cognitive symptoms associated to lasting molecular alterations in peptidergic signalling may determine the impaired neuroplasticity in the hippocampal and striatal circuitry.

Keywords: Bdnf; Crf; Crf receptors; addiction models; e-cigarette; nicotine addiction; nociceptin; opioid peptides; opioid receptors; orexin receptors.

Figure 1

Depressive-like behaviour evaluated in the cigarette (cig), e-cigarette (e-cig) and vehicle mice compared to the control group at 60 days of withdrawal: (a) immobility time evaluated for 6 min in the tail suspension test; (b) sucrose preference measured in terms of the percentage of the consumed sucrose solution to the total volume of liquid consumed. The evaluation of anxiety-like behaviour in the marble burying task as the total number of buried marbles (c) and latency to the first burial (d) evaluated within 15 min. Cognitive impairments evaluated in the spatial object recognition test as the discrimination index at a 24 h (e) or 48 h delay (f). n = 4–32 for each group. *** p < 0.001; ** p < 0.01, * p < 0.05 in the Planned Comparison vs. control.

Figure 2

Relative mRNA levels of Crf (a), Crf1 (b), or Crf2 (c,d) after e-cigarette (e-cig, downward triangle) or cigarette (cig, upward triangle) exposure with respect to the exposure to air (control, circle) or the e-cigarette administration vehicle (vehicle, square). The results displayed in panels (a, b, d) were obtained in the CPu, while panel c shows the results obtained in the hippocampus. The mice were exposed to cigarettes or e-cigarettes for 7 weeks, followed by a 60-day withdrawal. n = 4–6 for each group. *: p < 0.05 in the Planned Comparison vs. control. Hip: hippocampus, CPu: caudate-putamen.

Figure 3

Relative mRNA levels of Pdyn (a,c) or dynorphin receptor Kop (b,d) after e-cigarette (e-cig, downward triangle) or cigarette (cig, upward triangle) exposure with respect to exposure to air (control, circle) or the e-cigarette administration vehicle (vehicle, square). The results displayed in panels a and b were obtained in the hippocampus, while panels c and d show the results of the CPu. The mice were exposed to cigarettes or e-cigarettes for 7 weeks, followed by a 60-day withdrawal. n = 4–6 for each group. Hip: hippocampus; CPu: caudate-putamen.

Figure 4

Relative mRNA levels of Pnoc (a,c) or nociceptin receptor Nop (b,d) after e-cigarette (e-cig, downward triangle) or cigarette (cig, upward triangle) exposure with respect to exposure to air (control, circle) or an e-cigarette administration vehicle (vehicle, square). The results displayed in panels a and b were obtained in the hippocampus, while panels c and d show the results from the CPu. The mice were exposed to cigarettes or e-cigarettes for 7 weeks, followed by a 60-day withdrawal. n = 4–6 for each group. **: p < 0.01, *: p < 0.05 in the Planned Comparison vs. control. Hip: hippocampus; CPu: caudate-putamen.

Figure 5

Relative mRNA levels of Penk (a,c) or enkephalin receptor Dop (b,d) after e-cigarette (e-cig, downward triangle) or cigarette (cig, upward triangle) exposure with respect to exposure to air (control, circle) or an e-cigarette administration vehicle (vehicle, square). The results displayed in panels a and b were obtained in the hippocampus, while panels c and d show the results of the CPu. The mice were exposed to cigarettes or e-cigarettes for 7 weeks, followed by a 60-day withdrawal. n = 4–6 for each group. **: p < 0.01, *: p < 0.05 in the Planned Comparison vs. control. Hip: hippocampus; CPu: caudate-putamen.

Figure 6

Relative mRNA levels of orexin receptors Ox1 (a,c), or Ox2 (b,d) after e-cigarette (e-cig, downward triangle) or cigarette (cig, upward triangle) exposure, with respect to exposure to air (control, circle) or an e-cigarette administration vehicle (vehicle, square). The results displayed in panels (a,b) were obtained in the hippocampus, while panels (c,d) show the results of the CPu. The mice were exposed to cigarettes or e-cigarettes for 7 weeks, followed by a 60-day withdrawal. n = 4–6 for each group. Hip: hippocampus; CPu: caudate-putamen.

Figure 7

Relative mRNA levels of Bdnf after e-cigarette 8e-cig, downward triangle) or cigarette (cig, upward traingle) exposure with respect to exposure to air (control, circle) or an e-cigarette administration vehicle (vehicle, square). The results displayed in panel (a) were obtained in the hippocampus, while panel (b) show the results of the CPu. The mice were exposed to cigarettes or e-cigarettes for 7 weeks followed by a 60-day withdrawal. n = 4–6 for each group. *: p < 0.05 in the Planned Comparison vs. control. Hip: hippocampus; CPu: caudate-putamen.