The Digester

A new mouse study maps a gut–brain pathway linking age-associated microbiome changes to memory decline: expansion of Parabacteroides species raises medium-chain fatty acids that activate GPR84 on peripheral myeloid cells, provoke local inflammation, impair vagal sensory signalling and reduce hippocampal memory encoding, and several peripheral treatments restore cognition.

Transferring the gut microbiome from aged to young mice reproducibly impaired short-term object recognition and spatial memory in multiple models.
The bacterium Parabacteroides goldsteinii increased with age and its colonization reproduced the memory deficits.
Culture supernatants and oral administration of medium-chain fatty acids including 3-hydroxyoctanoic acid recapitulated vagal and hippocampal dysfunction and memory loss.
MCFA action required the fatty-acid receptor GPR84 on peripheral myeloid cells and triggered TNF and IL-1β inflammatory responses.
Inflammation reduced activity of gut-innervating vagal sensory neurons, blunted hippocampal immediate-early gene activation and impaired memory encoding.
Multiple peripheral interventions reversed deficits, including antibiotics, vagal stimulants (capsaicin, CCK, GLP1 agonist), GPR84 inhibition (PBI-4050), myeloid depletion, anti-TNF or anti-IL-1β antibodies, and selected bacteriophage treatment.
Effects were demonstrated across co-housing, faecal microbiota transfer and germ-free models, and vagal nodose imaging showed reduced neuronal responsiveness after acquiring an aged microbiome.
Authors highlight a gut–myeloid–vagus–hippocampus pathway as a modifiable mechanism for age-associated cognitive decline in mice but note that relevance to humans remains to be tested.

Gut microbiome and immune signals cause age-related memory loss in mice

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