BDNF and Cognitive impairment: In rats, L. helveticus NS8 improved the behavioural and cognitive impairment induced by chronic stress, decreased the plasma concentrations of corticosterone (CORT) and adrenocorticotropic hormone (ACTH), restored the hippocampal levels of 5-hydroxytryptamine (5-HT) and norepinephrine (NE), and increased hippocampal expression of the gene encoding brain-derived neurotrophic factor (BDNF) [10].