The effect of vitamin D on morphine preference in rats: Possible biochemical and DRD2-GDNF signaling

Abstract

Introduction: Despite half a century of research on vitamin D (Vit. D), its link to substance abuse and dependence has only been discussed in recent decades. Evidence also shows the involvement of Vit. D in the evolution of dopaminergic neurons in the nucleus accumbens, an increase in the expression of tyrosine hydroxylase, and the regulation of dopaminergic processes. The novel idea for this work is taken from a hypothesis given about the effectiveness of Vit. D on dopamine signaling pathway. It is therefore presumed that Vit. D can be considered an effective therapeutic approach for narcotic addiction and substance abuse.

Methods: The animals were assigned into six groups (control, vehicle, Morphine [Mor.], and Vit. D [250, 500, and 1000 IU/kg, i.p.]). Following each conditioning session in a conditioned place preference (CPP) model, the animals received Vit. D. Afterward, the locomotor activity of the animals was assessed using open-field apparatus. Malondialdehyde (MDA), nitric oxide (NO), catalase (CAT), superoxide dismutase (SOD), thiol, and total antioxidant capacity (TAC) were measured in the brain. The relative DRD2 and GDNF expressions (%) were also measured in the hippocampus.

Results: Vit. D administration after Mor. caused a significant increase in the place preference index in the acquisition phase (p < .05). Vit. D altered the oxidation/antioxidation profiles (CAT, SOD, MDA, NO, TAC, and Thiol). Vit. D was more effective than Mor. in the expression of GDNF (p < .0001); however, in the expression of DRD2, this was only the case for 1000 IU Vit. D (p < .0001).

Conclusions: Considering the increased place preference index induced by Mor., it can be concluded that Vit. D interacts via the oxidative pathway and DRD2-GDNF signaling to potentiate the Mor. effect.

Keywords: Condition place preference; Dopamine; Morphine; Rat; Vitamin D.

FIGURE 1

(a) The effects of different doses of Mor. administration on CPP for determining the effective dose of Mor. (b) The effect of treatment with different dose of Vit. D (250, 500, and 1000 IU/kg, i.p.) on the CPP in all groups. (c) The effect of treatment with different dose of Vit. D (250, 500, and 1000 IU/kg, i.p.) on locomotor activity in all groups. Ctl., Control; Veh., vehicle; Mor., Morphine; Vit. D, vitamin D; CPP, conditioned place preference. Data are expressed as mean ± SEM (n = 6 in each group). ^** p < .01 compared to Ctl. group. ^*** p < .001 compared to Ctl. group. ⁺ p < .05 compared to Mor. group. ⁺⁺⁺ p < .001 compared to Mor. group. ^&& p < .01 compared to Veh. group. Comparisons between different groups were made using one‐way analysis of variance (ANOVA) followed by Tukey's post hoc test

FIGURE 2

The activity of CAT (μM/mg protein) (a) and SOD (U/M) (b) in brain tissue after Vit. D treatment in all groups. Ctl., Control; Veh., vehicle; Mor., Morphine; Vit. D, vitamin D; CAT, catalase; SOD, superoxide dismutase. Data are expressed as mean ± SEM (n = 6 in each group). ⁺⁺⁺ p < .001 compared to Mor. group. ^** p < .01 compared to Ctl. group. ^&& p < .01 and ^&&& p < .001 compared to Veh. group. Comparisons between different groups were made using one‐way analysis of variance (ANOVA) followed by Tukey's post hoc test

FIGURE 3

The level of MDA (nmol/mg protein) (a) and NO (nmol/mg protein) (b) in brain tissue after Vit. D treatment in all groups. Ctl., Control; Veh., vehicle; Mor., Morphine; Vit. D, vitamin D; MDA, malondialdehyde; NO, nitric oxide. Data are expressed as mean ± SEM (n = 6 in each group). ^** p < .01 compared to Ctl. group. ^*** p < .001 compared to Ctl. group. ⁺ p < .05 compared to Mor. group. ⁺⁺ p < .01 compared to Mor. group. ⁺⁺⁺ p < .001 compared to Mor. group. ^& p < .05 compared to Veh. group. ^&& p < .01 and ^&&&& p < .0001 compared to Veh. group. Comparisons between different groups were made using one‐way analysis of variance (ANOVA) followed by Tukey's post hoc test

FIGURE 4

The level of TAC (nmol/mg protein) (a) and the level of Thiol (nmol/mg protein) (b) in brain tissue after Vit. D treatment in all groups (n = 10 in each group). Ctl., Control; Veh., vehicle; Mor., Morphine; Vit. D, vitamin D; TAC, total antioxidant capacity. Data are expressed as mean ± SEM (n = 6 in each group). ^* p < .05 compared to Ctl. group. ^** p < .01 compared to Ctl. group. ^*** p < .001 indicates significant difference compared to Ctl. group. ⁺⁺ p < .01 compared to Mor. group. Comparisons between different groups were made using one‐way analysis of variance (ANOVA) followed by Tukey's post hoc test

FIGURE 5

The effect of Mor. alone and Mor. + Vit. D (250, 500, and 1000 IU/kg, i.p.) on DRD2 expression (%). All animals received saline (1 ml/kg) or effective dose of Mor. (5 mg/kg, i.p.) per se or Mor. and different doses of Vit. D (250, 500, and 1000 IU/kg, i.p.). (a) The brain expression levels of DRD2, in Mor.‐induced CPP. The evaluation of DRD2 expression level was performed in six groups: Ctl. (group 1, no treatment and CPP); Veh. (group 2); (Mor. + almond oil) the Mor. (5 mg/kg) (groups 3); and Mor. + Vit. D groups (groups 4, 5, and 6) following CPP using western blotting (upper panel shows the immunoblotting profile). (b) The brain expression levels of DRD2, in CPP paradigm. The analysis indicated that DRD2 was significantly decreased (p < .001) in Veh. group and increased in Mor. + Vit. D groups as compared to Ctl. group. ^**** p < .0001 compared to the Ctl. group, ⁺⁺⁺ p < .001 and ⁺⁺⁺⁺ p < .0001 compared to the Mor. group. ^&&&& p < .0001 compared to Veh. group. Each value represents the mean ± SEM (n = 6 in each group). Comparisons between different groups were made using one‐way analysis of variance (ANOVA) followed by Tukey's post hoc test. Ctl., Control; Veh., vehicle; Mor., Morphine; Vit. D, vitamin D

FIGURE 6

The effect of Mor. alone and Mor. + Vit. D (250, 500, and 1000 IU/kg, i.p.) on GDNF expression (%). All animals received saline (1 ml/kg) or effective dose of Mor. (5 mg/kg, i.p.) per se or different doses of Vit. D (250, 500, and 1000 IU/kg, i.p.). (a) The brain expression levels of GDNF, in Mor.‐induced CPP. The evaluation of GDNF expression level was performed in six groups Ctl. (group 1, no treatment and CPP); Veh. (group 2); (Mor. + almond oil) the Mor. (5 mg/kg) (groups 3); and Mor. + Vit. D groups (groups 4, 5, and 6) following CPP using western blotting (upper panel shows the immunoblotting profile). (b) The brain expression levels of GDNF, in CPP paradigm. The analysis indicated that GDNF was significantly decreased (p < .001) in Veh. group and increased in Mor. + Vit. D groups as compared to Ctl. group. ^**** p < .001 compared to the Ctl. group. ⁺⁺⁺⁺ p < .001 compared to the Mor. group. ^&& p < .01 and ^&&&& p < .0001 compared to Veh. group. Each value represents the mean ± SEM (n = 6 in each group). Comparisons between different groups were made using one‐way analysis of variance (ANOVA) followed by Tukey's post hoc test. Ctl., Control; Veh., vehicle; Mor., Morphine; Vit. D, vitamin D