Effects of hydroalcoholic, methanolic, and hexane extracts of brown algae Sargassum angustifolium on scopolamine-induced memory impairment and learning deficit in rodents

Abstract

Background and purpose: Properties of Alzheimer's disease, can be caused by several reasons and there is no definite treatment for it. We aimed to study the effect of the hydroalcoholic extract, methanolic and n-hexane fractions of brown algae Sargassum angustifolium on memory impairment in mice and rats.

Experimental approach: Hydroalcoholic extract (25, 50, 100, 200 mg/kg), methanolic (20 and 40 mg/kg) and n-hexane (40 and 60 mg/kg) fractions of S. angustifolium were administered for 21 days intraperitoneally before scopolamine injection (2 mg/kg) on day 21. Rivastigmine was administered for 3 weeks intraperitoneally as well. Then, cognitive function was evaluated by three behavioral tests: passive avoidance, object recognition, and the Morris Water Maze test.

Findings/results: Scopolamine induced memory impairment and rivastigmine significantly reversed the memory dysfunction in all three tests. Hydroalcoholic extract and methanolic fraction significantly reversed scopolamine-induced memory impairment in passive avoidance by 64% and 55% and enhanced the recognition index in the object recognition test. In the Morris water maze test probe trial and training session, on days 3 and 4, the hydroalcoholic extract showed a significant decrease in time spent in the target quadrant and path length, respectively. Also, hydroalcoholic extract and methanolic fraction decreased escape latency time in training sessions on days 3 and 4, by 50% and 31% in comparison to scopolamine. N-hexane fractions had no significant effect on scopolamine-induced cognitive impairment.

Conclusion and implications: Although the n-hexane fraction wasn't effective, the administration of hydroalcoholic extract and the methanolic fraction of S. angustifolium enhanced scopolamine-induced memory impairment.

Keywords: Alzheimer; Morris water maze test; Object recognition; Passive avoidance; Sargassum angustifolium; Scopolamine.

Fig. 1

Standard curve of gallic acid. Results were calculated according to a linear gallic acid regression and expressed as milligrams of gallic acid per liter.

Fig. 2

Effect of Sargassum angustifolium extracts on step-through latency time (train) in the passive avoidance task. Step-through latency time in training and test trials was calculated according to the time required for the mouse to enter the dark compartment when the door is opened. Six animals were used per treatment group. Scopolamine was injected 30 min after the last dose of extracts on day 21. Data represent means ± SEM. HA, Hydroalcoholic extract (25, 50, 100, and 200 mg/kg); Met, methanolic extract (20 and 40 mg/kg); Hex, hexane extract (40 and 60 mg/kg).

Fig. 3

Effect of Sargassum angustifolium extracts on step-through latency time (test) in the passive avoidance task. Step-through latency time in training and test trials was calculated according to the time required for the mouse to enter the dark compartment when the door is opened. Six animals were used per treatment group. Scopolamine was injected 30 min after the last dose of extracts on day 21. Data represent means ± SEM. HA, Hydroalcoholic extract (25, 50, 100, and 200 mg/kg); Met, methanolic extract (20 and 40 mg/kg); Hex, hexane extract (40 and 60 mg/kg). ^###P < 0.001 Indicates significant differences compared to control group; *P < 0.05, **P < 0.01, and ***P < 0.001 versus scopolamine group.

Fig. 4

Effect of Sargassum angustifolium extracts on recognition index in the object recognition test. HA: hydroalcoholic extract (25, 50, 100, and 200 mg/kg); Met: methanolic extract (20 and 40 mg/kg); Hex: hexane extract (40 and 60 mg/kg). Six animals were used per treatment group. Data represent means ± SEM. HA, Hydroalcoholic extract (25, 50, 100, and 200 mg/kg); Met, methanolic extract (20 and 40 mg/kg); Hex, hexane extract (40 and 60 mg/kg). ^###P < 0.001 Indicates significant differences compared to control group; **P < 0.01 and ***P < 0.001 versus scopolamine group.

Fig. 5

Effect of Sargassum angustifolium extracts on escape latency time in Morris water maze Test. Six animals were used per treatment group. Scopolamine was injected 30 min after the last dose of extracts on day 21. Data represent means ± SEM. ^#P < 0.05, ^##P < 0.01 indicate significant differences compared to the control group in each day; *P < 0.05 and **P < 0.01 versus corresponding scopolamine group in each day; ^$$$P < 0.001 versus corresponding rivastigmine group in each day.

Fig. 6

Effect of Sargassum angustifolium extracts on path length in Morris water maze test. Six animals were used per treatment group. Scopolamine was injected 30 min after the last dose of extracts on day 21. Data represent means ± SEM. ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 indicate significant differences compared to the control group in each day; *P < 0.05, **P < 0.01, ***P < 0.001 versus corresponding scopolamine group in each day; ^$P < 0.05 versus corresponding rivastigmine group in each day.

Fig. 7

Effect of Sargassum angustifolium extracts on swimming speed in Morris water maze test. Six animals were used per treatment group. Scopolamine was injected 30 min after the last dose of extracts on day 21. Data representmeans ± SEM.

Fig. 8

The effect of administration of scopolamine, rivastigmine, and extracts on the time spent in the target zone during probe trial in Morris water maze test. Data represent means ± SEM. HA, Hydroalcoholic extract (25, 50, 100, and 200 mg/kg); Met, methanolic extract (20 and 40 mg/kg); Hex, hexane extract (40 and 60 mg/kg). ^##P < 0.01 Indicates significant differences compared to the control group; **P < 0.01 and ***P < 0.001 versus scopolamine group.