Fucoidan prevents depression-like behavior in rats exposed to repeated restraint stress.

Previous studies have demonstrated that repeated restraint stress in rodents increased depression-like behavior and altered the expression of corticotrophin-releasing factor in the hypothalamus. The current study focused on verifying the impact of fucoidan (FCN) administration on repeated restraint stress-induced behavioral responses using the forced swimming test (FST). Additionally, we examined the effect of FCN on the central noradrenergic system by observing changes in neuronal tyrosine hydroxylase (TH) immunoreactivity and brain-derived neurotrophic factor (BDNF) mRNA expression in the rat brains. Male rats received 10, 20, or 50 mg/kg FCN (i.p.) 30 min before daily exposures to repeated restraint stress (2 h/day) for 14 days. Repeated restraint stress increased immobility in the FST. Daily administration of FCN during the repeated restraint stress period significantly inhibited the stress-induced behavioral deficits in this behavioral test. Administration of FCN also significantly blocked the increase in TH expression in the locus coeruleus and the basolateral nucleus of the amygdala, and the decrease in BDNF mRNA expression in the hippocampus. Taken together, these findings indicate that administration of FCN prior to restraint stress significantly improved helpless behavior in rats, possibly through modulating the central noradrenergic system. Therefore, FCN may be a useful agent for treating complex symptoms of depression disorder.