The effects of tramadol administration on hippocampal cell apoptosis, learning and memory in adult rats and neuroprotective effects of crocin

Abstract

Tramadol, a frequently used pain reliever drug, present neurotoxic effects associated to cognitive dysfunction. Moreover, crocin has been reported to have neuroprotective effects. The aim of this study was to assess crocin's capacity to protect learning, and memory abilities on tramadol-treated rats. A total of 35 rats were divided into five groups: Control, Saline, tramadol (50 mg/kg), tramadol + crocin(30 mg/kg), crocin groups and treated orally for 28 consecutive days. Morris water maze (MWM) and passive avoidance (PA) tests were done, followed by dissection of the rat's brains for toluidine blue and TUNEL staining. In MWM test, tramadol group spent lower time and traveled shorter distance in the target quadrant (Q1) (P < 0.05). On the other side, the traveled distance in tramadol-crocin group was higher than tramadol (P < 0.05). In PA test, both the delay for entering the dark, and the total time spent in the light compartment decreased in tramadol comparing to the control group (P < 0.05), while it increased in tramadol-crocin compared with the tramadol group (P < 0.05). In tramadol-treated animals, the dark neurons (DNs) and apoptotic cells in CA1, CA3 and DG increased (P < 0.05), while concurrent intake of crocin decreased the number of DNs and apoptotic cells in these areas (P < 0.05). Crocin was able to improve learning and memory of tramadol-treated rats and also decreased DNs and apoptotic cells in the hippocampus. Considering these results, the potential capacity of crocin for decreasing side effects of tramadol on the nervous system is suggested.

Keywords: Apoptosis; Crocin; Memory; Morris water maze; Passive avoidance; Tramadol.

Fig. 1

Comparison of (a) time spent and (b) the traveled distance in the MWM test between the five groups using repeated measures ANOVA. Data is expressed as mean ± SEM (n = 7 in each group)

Fig. 2

Comparison of (a) time spent and (b) the traveled distance in the MWM test in the target quadrant (Q1) and other quadrants between the five groups using repeated measures ANOVA. Data are expressed as mean ± SEM (n = 7 in each group). ^** P < 0.01 Tramadol group compared with Control group, ⁺⁺ P < 0.01 (a), ⁺⁺⁺ P < 0.001 (b) Tramadol group compared with Saline group, ^$$ P < 0.01 Crocin and Tramadol-Crocin groups compared with Tramadol group

Fig. 3

(a) Comparison of time delay for entering the dark compartment in the PA test at 3, 24 and 48 h after receiving the shock between the five groups using repeated measures ANOVA. Data is expressed as mean ± SEM (n = 7 in each group). ^** P < 0.01, ^*** P < 0.001 Crocin, Tramadol-Crocin and Tramadol groups compared with the Control group, ⁺⁺ P < 0.01, ⁺⁺⁺ P < 0.001 Crocin, Tramadol-Crocin and Tramadol groups compared with Saline group, ^$ P < 0.05, ^$$ P < 0.01 Crocin and Tramadol-Crocin groups compared with Tramadol group (b) Comparison of total time spent in the dark compartment in the PA test at 3, 24 and 48 h after receiving the shock between the five groups using repeated measures ANOVA. Data are expressed as mean ± SEM (n = 7 in each group). ^*** P < 0.001 Tramadol group compared with Control group, ⁺⁺⁺ P < 0.001 Tramadol group compared with Saline group, ^$ P < 0.05, ^$$ P < 0.01 Crocin and Tramadol-Crocin groups compared with Tramadol group (c) Comparison of the number of entries to the dark compartment in the PA test at 3, 24 and 48 h after receiving the shock between the five groups using repeated measures ANOVA. Data are expressed as mean ± SEM (n = 7 in each group). ^** P < 0.01 Tramadol group compared with Control group, ⁺⁺ P < 0.01 Tramadol group compared with Saline group (d) Comparison of total time spent in the light compartment in the PA test at 3, 24 and 48 h after receiving the shock between the five groups using repeated measures ANOVA. Data are expressed as mean ± SEM (n = 7 in each group). ^*** P < 0.001 Tramadol group compared with Control group, ⁺⁺⁺ P < 0.001 Tramadol group compared with Saline group, ^$ P < 0.05, ^$$ P < 0.01 Crocin and

Fig. 4

Photomicrographs of the adult rat’s hippocampus in the CA3 and DG. Administration of tramadol to adult rats increased formation of DNs in the hippocampus, while concurrent intake of crocin reduced formation of DNs

Fig. 5

Comparing of DNs mean per unit area (NA) in the CA1, CA2, CA3 and DG of the hippocampus between the five groups using one way ANOVA. Data are expressed as mean ± SEM (n = 7 in each group). ^** P < 0.01, ^*** P < 0.001 Tramadol group compared with Control group, ⁺ P < 0.05, ⁺⁺⁺ P < 0.001 Tramadol group compared with Saline group, ^$ P < 0.05, ^$$$ P < 0.001 Crocin and Tramadol-Crocin groups compared with Tramadol group

Fig. 6

Photomicrographs of the adult rat’s hippocampus in the CA1, CA3, and DG. Administration of tramadol to adult rats increased TUNEL positive cells in the hippocampus, while concurrent intake of crocin reduced TUNEL positive cells

Fig. 7

Comparing of TUNEL positive cells mean per unit area (NA) of the CA1, CA2, CA3 and DG of the hippocampus between the five groups using one way ANOVA. Data are expressed as mean ± SEM (n = 7 in each group). ^*** P < 0.001 Tramadol group compared with Control group, ⁺⁺⁺ P < 0.001 Tramadol group compared with Saline group, ^$ P < 0.05, ^$$$ P < 0.001 Crocin and Tramadol-Crocin groups compared with Tramadol group