Protective effect of fennel, and its major component trans-anethole against social isolation induced behavioral deficits in rats.

Social isolation damages the nervous system by weakening the antioxidant system and leading to behavioral disorders. Fennel (Foeniculum vulgare Mill.) is an herbal plant that has antioxidant and neuroprotective properties. The objective of this study was to evaluate the effect of fennel methanol extract and its major component trans-anethole on spatial learning and memory, anxiety and depression in male rats exposed to social isolation stress.Rats were divided into six groups of Control (C), Fennel (F), trans-Anethole (A), Isolation, Isolation-F and Isolation-A. The rats were kept in the cage alone for 30 days to induce isolation. Fennel extract (150 mg/kg) and trans-anethole (80 mg/kg) were also gavaged during this period. At the end of the course, spatial learning and memory, anxiety and depression were measured by Morris water maze (MWM), elevated plus maze (EPM) and forced swimming test (FST), respectively.Learning and memory were impaired in isolated rats. Swimming time and distance to reach the hidden platform in these animals increased compared with controls (P < 0.05). In the EPM test, the percentage of open arm entries and open arm time also decreased significantly in the Isolation group (P < 0.01). The immobilization time in FST also increased significantly in these animals compared with the Control group (P < 0.001). Fennel and trans-anethole were both able to eliminate these changes in isolated rats.It is concluded that fennel and its major component, trans-anethole are suitable candidates for the prevention and treatment of stress-induced neurological disorders.