Boophone disticha attenuates five day repeated forced swim-induced stress and adult hippocampal neurogenesis impairment in male Balb/c mice

Abstract

Depression is one of the most common neuropsychiatric disorders and is associated with dysfunction of the neuroendocrine system and alterations in specific brain proteins. Boophone disticha (BD) is an indigenous psychoactive bulb that belongs to the Amaryllidacae family, which is widely used in Southern Africa to treat depression, with scientific evidence of potent antidepressant-like effects. The present study examined the antidepressant effects of BD and its mechanisms of action by measuring some behavioural parameters in the elevated plus maze, brain content of corticosterone, brain derived neurotropic factor (BDNF), and neuroblast differentiation in the hippocampus of Balb/c mice exposed to the five day repeated forced swim stress (5d-RFSS). Male Balb/c mice were subjected to the 5d-RFSS protocol to induce depressive-like behaviour (decreased swimming, increased floating, decreased open arm entry, decreased time spent in the open arms and decreased head dips in the elevated plus maze test) and treated with distilled water, fluoxetine and BD. BD treatment (10 mg/kg/p.o for 3 weeks) significantly attenuated the 5d-RFSS-induced behavioural abnormalities and the elevated serum corticosterone levels observed in stressed mice. Additionally, 5d-RFSS exposure significantly decreased the number of neuroblasts in the hippocampus and BDNF levels in the brain of Balb/c mice, while fluoxetine and BD treatment attenuated these changes. The antidepressant effects of BD were comparable to those of fluoxetine, but unlike fluoxetine, BD did not show any anxiogenic effects, suggesting better pharmacological functions. In conclusion, our study shows that BD exerted antidepressant-like effects in 5d-RFSS mice, mediated in part by normalizing brain corticosterone and BDNF levels.

Keywords: Antidepressant agents; Corticosterone; Depression; Fluoxetine; Hippocampus.

Fig. 1

Spectrum view of LC-MS chromatogram, acquired in the positive-ion mode, from an extract of the bulb of BD. LC-MS, liquid chromatography-mass spectrometry; BD, boophone disticha.

Fig. 2

Graphic representation of changes in swimming times after 21 days of treatment. (A) Significant differences in swimming time across different groups were observed in ANOVA test (P=0.04). (B) The post-hoc test showed that in day 14 of treatment, the swimming time for the fluoxetine treated animals was significantly higher (P=0.0012) compared to the distilled water and BD treated animals, while BD treated animals only showed a significant increase by day 21, whereby the fluoxetine group had reached a plateau of increase in swimming time. (C) In day 21, immobility times were significantly different across the treatment groups as demonstrated in ANOVA test (P=0.029). (D) A significant time dependant steady reduction in immobility time from day 5 to day 21 was observed in the BD treated animals (P=0.004), whereas a steady reduction was observed in fluoxetine treated group from day 5 to day 14 and plateaued between day 14 to day 21. The immobility time for distilled water treated group remained high throughout the treatment period (P=0.001). Error bars correspond to the standard error of the mean, **indicates significant changes due to treatments. BD, boophone disticha.

Fig. 3

Graphic representation of the elevated plus maze results. (A) The time spent in the open arms was significantly different across the groups in ANOVA test (P=0.0001). Bonferroni’s post-hoc test revealed that the time spent in the open arms was significantly higher in the control group compared to experimental groups (P<0.05). BD treated group recorded significantly high time in the open arms compared to both distilled water and fluoxetine groups (P<0.05). The time spent in the open arms for fluoxetine and distilled water group was not significantly different (P>0.05). (B) The time spent in the closed arms was not significantly different across the groups (P=0.195). The control group recorded the lowest time in closed arms though non-significant in the ANOVA test when compared with the treatment groups. Both fluoxetine and BD recorded low time in the closed arms as compared to the distilled water group. (C) The number of head dips was significantly different across the groups as shown by ANOVA test (F=6.122, P=0.0105). Bonferroni’s post-hoc test showed that the BD group had significantly high number of head dips compared to distilled water and fluoxetine treated groups both of which scored the lowest number of head dips (P<0.05). Both the control and BD treated groups recorded high frequency of open arm entries compared to both distilled water and fluoxetine treated groups (P<0.05). (D) Both the control and BD treated groups recorded high frequency of open arm entries when compared to both distilled water and fluoxetine treated groups (P<0.05). (E) BD treated group had significantly low frequency of closed arm entries compared to distilled water and fluoxetine treated groups (P<0.05). Error bars correspond to the standard error of the mean, **indicates significant changes due to treatments. BD, boophone disticha.

Fig. 4

Graphic representation of the volumes of the dentate gyrus and hippocampus across the groups. (A) The ANOVA test did not detect any significant differences in the volume of the dentate gyrus (F=0.3083, P=0.8190), (B) whole hippocampus (F=3.110, P=0.1101), and (C) granule cell layer of the dentate gyrus (F=1.501, P=0.2955) across all the groups. There was a slight reduction of the dentate gyrus volume in the experimental groups compared to the control group. A slight reduction in the hippocampal volume of the experimental groups as compared to the control group was also observed. The same observation was also noted in the volume of the granule cell layer of the experimental groups compared to the control group. Error bars correspond to the standard error of the mean, **indicates significant changes due to treatments.

Fig. 5

Photomicrographs showing DCX immunoreactive cells in the SGZ of the dentate gyrus of the hippocampus of the normal (control) (A) and treated (B–D) groups. The black arrows are showing the cell bodies of the neuroblasts and the white arrows are showing the dendritic spines. Poorly developed dendritic spines can be seen in the distilled water treated group B. The oval circle in group B shows one of the patches in the lower limb of the dentate gyrus where DXC immunoreactive cells were absent leading to low cell count in this group. The magnified areas on the top right of each micrograph represent the areas indicated by the black rectangles. DCX, doublecortin; SGZ, subgranular zone; GCL, granule cell layer; ML, molecular layer.

Fig. 6

Graphic representation of the expression of DCX-ir and biochemical analyses of BDNF and corticosterone. (A) The expression of DCX-ir was significantly different across the groups (P=0.0005). DCX-ir expression was significantly lower in the distilled water treated group when compared to both fluoxetine and BD treated groups as shown by the post-hoc test (P<0.05). Post-hoc analyses further showed that the counts of DCX-ir cells in both fluoxetine and BD groups were significantly higher than the distilled water group (P>0.05). (B) The expression of BDNF was significantly different across the groups (P=0.0026). BDNF expression was significantly lower in the distilled water treated group when compared to the control, fluoxetine and BD treated groups in the post-hoc test (P<0.05). The post-hoc test further showed that fluoxetine and BD treatment significantly increased the expression of BDNF when compared to the distilled water group (P<0.05). (C) The expression of corticosterone was significantly different across the groups (P=0.001). The post-hoc test showed that corticosterone levels remained significantly high in the distilled water treated group when compared to the control group (P<0.05). On the contrary, treatment with either fluoxetine or BD significantly reduced corticosterone levels (P<0.05). The levels of corticosterone in the fluoxetine and BD treated groups were not significantly different from that of the control group (P>0.05). Error bars correspond to the standard error of the mean, **indicates significant changes due to treatments. BDNF, brain derived neurotropic factor; DCX-ir, doublecortin immunoreactive cells; BD, boophone disticha.