Induction of Fos expression in the rat brain after intragastric administration of dried bonito dashi

Increased functional connectivity following ingestion of dried bonito soup

Soup, including dried bonito broth, is customarily consumed as an umami taste during meals in Japan. Previous functional magnetic resonance imaging (fMRI) studies have investigated neuronal activation following human exposure to carbohydrates and umami substances. However, neuronal activity following ingestion of dried bonito soup has not been investigated. Additionally, recent progress in fMRI has enabled us to investigate the functional connectivity between two anatomically separated regions, such as the default mode network. In this study, we first investigated the altered functional connectivity after ingesting dried bonito soup in healthy volunteers. Functional connectivity in several brain regions, including the connection between the vermis, part of the cerebellum, and bilateral central opercular cortex, was markedly increased after ingesting dried bonito soup, compared to the ingestion of hot water. Physiological scaling showed that satiety was substantially increased by ingesting hot water rather than dried bonito soup. These results indicate that increased functional connectivity reflects the post-ingestive information pathway of dried bonito soup.

Enhanced preference for dried bonito dashi by prior experience with dashi and various taste substances in mice

Dried bonito dashi, a complex mixture of sour, bitter, and umami substances as well as over 400 odorants, is the most widely used Japanese fish broth that enhances palatability of various dishes. Recent studies have suggested that prior experience with dried bonito dashi produces strong enhancement of subsequent intake and preference for dried bonito dashi. The present study investigated taste substances in dried bonito dashi that enhance subsequent dashi preference by its prior exposure. Male C57BL/6N mice were initially exposed for 10 days to (1) dried bonito dashi, (2) a chemical mixture of taste substances identified in dried bonito dashi (artificially reconstituted dashi), or (3) individual chemical solutions such as NaCl, monosodium l-glutamate (MSG), inosine 5'-monophosphate (IMP), lactic acid, histidine, and glucose. Intakes of 0.01-100% dried bonito dashi with water were then measured using ascending concentration series of 2-day two-bottle choice tests. Prior exposure to 1-100% dashi enhanced subsequent dashi preference in a concentration-dependent manner and the greatest effects were attained with 10-100% dashi exposure. Exposure to the reconstituted dashi also enhanced subsequent dashi preference. Among individual chemical solutions, 0.1% IMP produced modest enhancement of subsequent dashi preference, but neither NaCl, MSG, histidine, lactic acid, nor glucose did. These results suggest that IMP is at least a key substance that produces experience-based enhancement of dried bonito dashi preference.

Intake and preference for dried bonito dashi in male Sprague-Dawley rats and C57BL/6 N mice

Dried bonito dashi is a traditional Japanese fish broth that enhances palatability of various dishes due to its specific flavor. The present study examined influences of dietary fat levels (10% vs. 45% fat), presentation order of dried bonito dashi (ascending vs. descending concentrations), and prior experience with dashi on subsequent dashi intake and preference using two-bottle choice tests in two rodent strains, Sprague-Dawley (SD) rats and C57BL/6 N (B6N) mice. In the ascending concentration tests, SD rats on a low fat diet preferred 10-100% dashi to water, whereas B6N mice showed a blunted preference for dashi. Consumption of a high fat diet reduced dashi preference in SD rats. The B6N mice on the high fat diet never preferred dashi at any concentration. In the descending concentration tests, SD rats on the low fat diet preferred dashi over a wide range (0.03-100% dashi). The B6N mice showed a trend similar to that of SD rats. Ingestion of the high fat diet in both strains reduced dashi preference in the descending concentration tests. However, introduction of the high fat diet to dashi experienced rats maintained on the low fat diet, reduced neither dashi intake nor dashi preference. Dashi intake affected neither high fat diet intake, caloric intake, nor preference for high fat diet. These results suggest that preference for dried bonito dashi is influenced at least by 1) dietary fat levels, 2) presentation order of dashi, and 3) prior experience with dashi.