Disruptions in the development of normal microflora have also been associated with alterations in stress reactivity that continue into later life. For example, various metabolic pathways, such as those involving bile acids and steroid hormone synthesizers, that are necessary for bodily functions depend on a healthy microbiome (Antunes, Han, Ferreira, Lolic, Borchers, & Finlay, 2011). Research shows that antibiotic use early in life leads to a reduction in intestinal flora and diversity and may be involved in causing a physiological state of alert, akin to a trait known as "anxiety sensitivity". Anxiety sensitivity refers to a tendency in some individuals to monitor their physiological state continuously and misinterpret normal fluctuations in homeostasis as life threatening events. In animal studies, consumption of probiotics leads to reductions in anxiety-related behaviours as well as alterations in the GABA receptors that mediate stress-related hormones (Bravo, Forsythe, Chew, Escaravage, Savignac, Dinan, Bienenstock, & Cryan, 2011). The beneficial effects of gut microbiota on stress and anxiety have also been evidenced when comparing germ-free mice (i.e., mice with no microbiome) to mice with rich intestinal microflora. Mice with rich intestinal microflora show less stress reactivity than germ-free mice.