Assessment of nicotine withdrawal-induced changes in sucrose preference in mice

Abstract

Anhedonia, induced by nicotine withdrawal, may serve as an important affective sign that reinforces tobacco use and smoking relapse rates in humans. Animal models provide a way to investigate the underlying neurobiological factors involved in the decrease in responding for positive affective stimuli during nicotine withdrawal and may aid in drug development for nicotine dependence. Thus, we explored the use of the sucrose preference test to measure nicotine withdrawal-induced reduction in response for positive affective stimuli in mice. C57BL/6J and knockout (KO) mice were chronically exposed to different doses of nicotine through surgically implanted subcutaneous osmotic minipumps for 14days and underwent spontaneous nicotine withdrawal on day 15. A sucrose preference time course was performed and the results were compared to another well-established affective sign of nicotine withdrawal, the reduction in time spent in light side, using the Light Dark Box test. Subsequently, our results demonstrated a time-dependent and dose-related reduction in sucrose preference in nicotine withdrawn male C57BL/6J mice, indicative of a decrease in responding for positive affective stimuli. Furthermore, the sucrose preference reduction during nicotine withdrawal was consistent with decrease in time spent in the light side of the Light Dark Box test. We also found the reduction for positive affective stimuli and time spent in the light side was not present in nicotine withdrawn β2 and α6 KO mice, suggesting that these nicotinic subunits are involved in the affective signs of nicotine withdrawal. Thus, this report highlights the potential utility of the sucrose preference test as a useful measure of the decrease in responding for positive affective stimuli during spontaneous nicotine withdrawal.

Keywords: Light Dark Box; Nicotine; Sucrose preference test; Withdrawal.

Figure 1.. Sucrose preference test during spontaneous nicotine withdrawal in C57BL/6J mice.

C57BL/6J male mice were exposed to two sipper tubes, one containing normal drinking water and the other containing a 2% sucrose solution, for 24 hrs per day. Sucrose preference was determined as the percentage of 2% sucrose volume consumed over the total fluid intake volume. Mice were chronically exposed to nicotine (12 and 24 mg/kg/day) via osmotic minipumps then the sucrose preference was measured for 9 consecutive days after removal of minipumps. Sucrose preference deficit was observed in nicotine withdrawn groups when compared to saline group. Also, there was a dose dependent effect in nicotine treated groups at days 1, 2 and 4 during nicotine withdrawal. Each point represents the mean ± S.E.M. of 11 mice per group. *Denotes P < 0.05 from saline group; # Denotes P < 0.05 from nicotine 12 mg/kg/day treated-group.

Figure 2.. Measurement of sucrose preference after induction of nicotine withdrawal in nicotinic KO mice.

β2 and α6 KO and WT mice were chronically infused with nicotine (24 mg/kg/day) for 14 days. Minipumps were removed from mice on day 15, and sucrose preference (2%) was performed 48 hrs later. A) Sucrose preference test of β2 WT and KO mice at day 2 after removal of minipumps. B) Sucrose preference results of α6 WT and KO mice. Each point represents the mean ± S.E.M. of 8 mice per group. * Denotes p < 0.05 vs. Saline groups, # Denotes p < 0.05 vs. nicotine withdrawn WT mice.

Figure 3.. Time course of time spent in the light side of nicotine-dependent mice in the LDB test.

Mice were chronically infused with saline or nicotine (12 or 24 mg/kg/day) for 14 days. On day 15 mice underwent spontaneous nicotine withdrawal and the LDB test was performed at days 1, 2 and 5 after removal of minipumps. Each point represents the mean ± S.E.M. of 10 mice per group. *Denotes P < 0.05 from vehicle control, # Denotes from 12 mg/kg/day nicotine withdrawn group.

Figure 4.. Time spent in the light side of LDB in nicotinic KO mice during nicotine withdrawal.

β2 and α6 KO/WT mice were chronically infused with nicotine (24 mg/kg/day) for 14 days. Minipumps were removed from mice on day 15, and the LDB test was performed 48 h later. A) Nicotine withdrawn β2 WT mice exhibited an attenuation of time spent in the light side on day 2 after removal of minipumps. But this effect was not seen in β2 KO mice. B) Similarly, α6 WT mice displayed a reduction in the time spent in the light side on day 2 that was not observed in α6 KO mice. Each point represents the mean ± S.E.M. of 8 mice per group. * Denotes p < 0.05 vs. Saline groups, # Denotes p < 0.05 vs. nicotine withdrawn WT mice.