Introduction: Alzheimer's disease is the most common neurodegenerative disorder. Due to the neurodegenerative effect of fennel (Foeniculum vulgare) this study aimed at investigating the effect of this plant on the improvement of learning and memory in rat models of Alzheimer's disease. 

Material & Methods: The male Wistar rats were assigned into six groups, namely the control group (no injection), sham group (saline injection), experimental group (injection of beta-amyloid (40-1). The other three groups received 75, 140, and 250 ml/kg of fennel extract intraperitoneally 7 days before and 3 weeks after bilateral intraventricular beta-amyloid injection. Shuttle box was used to study the learning and memory behavior of the rats; moreover hematoxylin-eosin staining was conducted for histological studies.

Findings: According to the results, fennel extract at a dose of 140 mg/kg increased behavioral indicators in measuring the passive avoidance memory in the Alzheimer's group, compared to the sham group (P<0.001). Moreover, optical microscopy studies showed a significant decrease in tissue damage and an increase in the number of Nissl bodies stained in CA1 hippocampal region, especially in pyramidal layer, in Alzheimer's disease-induced rats treated with fennel extract at a dose of 140 mg/kg.

Discussion & Conclusions: In this study, fennel extract shows the neuroprotective effect against Alzheimer’s disease induced by beta-amyloid (40-1). the observed improvements are probably related with antioxidant, anti-inflammatory, and pseudo-estrogenic properties of this plant.