Effects of Piper nigrum fruit and Cinnamum zeylanicum bark alcoholic extracts, alone and in combination, on scopolamine-induced memory impairment in mice

Abstract

Background and purpose: Alzheimer's disease is a progressive brain disorder that is thought to be triggered via disruption of cholinergic neurons and enhanced oxidative stress. Therefore, antioxidant phytochemicals with the ability to fortify cholinergic function should help in preventing the progress of the disease. This study aimed at evaluating the combinational effects of two popular herbs one with anticholinesterase activity namely Piper nigrum and the other with antioxidant capacity, Cinnamomum zeylanicum.

Experimental approach: In this study, P. nigrum extract (PN) (50, 100 mg/kg, ip) and C. zeylanicum extract (CZ) (100, 200, 400 mg/kg, ip) and their combinations were administered for 8 days before the injection of scopolamine (1 mg/kg, ip). Mice were then tested for their memory using two behavioral models, namely the object recognition test and the passive avoidance task.

Findings/results: Administration of scopolamine significantly impaired memory performance in both memory paradigms. In the passive avoidance test (PAT) model, PN at doses up to 100 mg/kg and CZ at doses up to 400 mg/kg did not significantly alter the memory impairment induced by scopolamine. The combination of these two plant extracts did not change the PAT parameters. In the object recognition test (ORT) model, however, administration of 100 mg/kg CZ alone and a combination of PN (50 mg/kg) with CZ (400 mg/kg), significantly increased the recognition index (P < 0.05).

Conclusion and implications: Two plant extracts when administered alone or in combinations affected the memory performance differently in two memory paradigms. In the PAT model, the extracts did not show any memory improvement, in ORT, however, some improvements were observed after plant extracts.

Keywords: Alzheimer; Cinnamum zeylanicum; Piper nigrum; Scopolamine.

Fig. 1

Effects of Piper nigrum, Cinnamomum zeylanicum alcoholic extracts, and their combinations on memory performance in passive avoidance test. On days 8 and 9, memory deficit was induced by scopolamine (1 mg/kg, i.p.). Animals were tested after 24 h the training, for retention of memory. Cognitive performance was measured by (A) step-through latency time of entering the dark chamber for the first time, (B) total time spent in the dark chamber, and (C) the number of crossings between chambers and 24 h after train session. Results are expressed as mean ± SEM, n = 6. ^#P < 0.05 indicates significant differences compared with the control group, ***P < 0.001 versus the scopolamine group.

Fig. 2

Effects Piper nigrum, Cinnamomum zeylanicum alcoholic extracts, and their combinations on memory performance in the object recognition test. On days 8 and 9, memory deficit was induced by scopolamine (1.0 mg/kg, i.p.). Animals were tested after 24 h training, for retention of memory. Cognitive performance was expressed as (A) the percentage discrimination index and (B) the recognition index. Results are expressed as mean ± SEM, n = 6. ^#P < 0.01 indicates significant differences compared with the control group, *P < 0.05 and **P < 0.01 against scopolamine group.