Braniste et al. recently reported in Science Translational Medicine (2014 Nov 19;6(263):263ra158. doi: 10.1126/scitranslmed.3009759) that the permeability of the mouse blood brain barrier (BBB) is influenced by the gut microbiome. They showed that germ-free mice, beginning in intrauterine life, displayed increased BBB permeability compared to mice of the same strain with normal gut flora. The increased BBB permeability was associated with reduced expression of specific tight junction proteins that regulate barrier function. Expression of these same  proteins could be upregulated by exposure of germ-free mice to gut microbiota.

Hilary Vernon, MD PhD