It has previously been shown that the consumption of probiotics may have beneficial effects not only on peripheral tissues but also on the central nervous system and behavior via the microbiota–gut–brain axis, raising the possibility that treatment with probiotics could be an effective therapeutic strategy for managing neurodegenerative disorders. In this study, we investigated the effects of oral administration of Bifidobacterium breve strain A1 (B. breve A1) on behavior and physiological processes in Alzheimer’s disease (AD) model mice. We found that administration of B. breve A1 to AD mice reversed the impairment of alternation behavior in a Y maze test and the reduced latency time in a passive avoidance test, indicating that it prevented cognitive dysfunction. We also demonstrated that non-viable components of the bacterium or its metabolite acetate partially ameliorated the cognitive decline observed in AD mice. Gene profiling analysis revealed that the consumption of B. breve A1 suppressed the hippocampal expressions of inflammation and immune-reactive genes that are induced by amyloid-β. Together, these findings suggest that B. breve A1 has therapeutic potential for preventing cognitive impairment in AD.

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Vertebrates receive tastants, such as sugars, amino acids, and nucleotides, via taste bud cells in epithelial tissues. In mammals, two families of G protein-coupled receptors for tastants are expressed in taste bud cells-T1Rs for sweet tastants and umami tastants (l-amino acids) and T2Rs for bitter tastants. Here, we report two families of candidate taste receptors in fish species, fish T1Rs and T2Rs, which show significant identity to mammalian T1Rs and T2Rs, respectively. Fish T1Rs consist of three types: fish T1R1 and T1R3 that show the highest degrees of identity to mammalian T1R1 and T1R3, respectively, and fish T1R2 that shows almost equivalent identity to both mammalian T1R1 and T1R2. Unlike mammalian T1R2, fish T1R2 consists of two or three members in each species. We also identified two fish T2Rs that show low degrees of identity to mammalian T2Rs. In situ hybridization experiments revealed that fish T1R and T2R genes were expressed specifically in taste bud cells, but not in olfactory receptor cells. Fish T1R1 and T1R2 genes were expressed in different subsets of taste bud cells, and fish T1R3 gene was co-expressed with either fish T1R1 or T1R2 gene as in the case of mammals. There were also a significant number of cells expressing fish T1R2 genes only. Fish T2R genes were expressed in different cells from those expressing fish T1R genes. These results suggest that vertebrates commonly have two kinds of taste signaling pathways that are defined by the types of taste receptors expressed in taste receptor cells.

A large-scale mutagenesis screen was performed in Medaka to identify genes acting in diverse developmental processes. Mutations were identified in homozygous F3 progeny derived from ENU-treated founder males. In addition to the morphological inspection of live embryos, other approaches were used to detect abnormalities in organogenesis and in specific cellular processes, including germ cell migration, nerve tract formation, sensory organ differentiation and DNA repair. Among 2031 embryonic lethal mutations identified, 312 causing defects in organogenesis were selected for further analyses. From these, 126 mutations were characterized genetically and assigned to 105 genes. The similarity of the development of Medaka and zebrafish facilitated the comparison of mutant phenotypes, which indicated that many mutations in Medaka cause unique phenotypes so far unrecorded in zebrafish. Even when mutations of the two fish species cause a similar phenotype such as one-eyed-pinhead or parachute, more genes were found in Medaka than in zebrafish that produced the same phenotype when mutated. These observations suggest that many Medaka mutants represent new genes and, therefore, are important complements to the collection of zebrafish mutants that have proven so valuable for exploring genomic function in development.

Previous studies have identified many cDNA species that encode a variety of G protein alpha-subunits occurring in taste buds. These include the cDNA encoding a taste-bud-specific Galpha, gustducin (G(gust)). Here we carried out comprehensive analyses of Galpha species that occur in the taste buds of rat circumvallate papillae and also in their single cells isolated from the taste buds. Reverse transcriptase-polymerase chain reaction showed the presence of 10 kinds of Galpha cDNAs, including a splice variant of Galphas, among which G(gust), Galphas, Galphai2 and Galphai3 cDNAs were shown to be major species. In situ hybridization and immunohistochemistry showed that Galphai2, as well as G(gust), expressed in a subset of taste bud cells, and the frequency of Galphai2-expression appears to be higher than that of G(gust). Southern analyses of the amplified cDNA from single cells showed that each taste bud cell expresses multiple Galpha mRNA species. For example, some Galphai2-positive cells also express one or more other Galpha species, including Galphas, Galphai3 and G(gust), and there is no apparent correlation in expression among the three Galpha species.