Review Paper:
Oral-Gut Dysbiosis:
Causative for the Initiation of Brain Cognitive Memory Decline
Murugan Mukilan
Res. J. Biotech.; Vol. 20(3); 254-262;
doi: https://doi.org/10.25303/203rjbt2540262; (2025)
Abstract
Oral passage and intestinal tract are some of the important microecosystems present
in humans. In these microecosystems, approximately 1014 bacterial colonies are present
with 2000 known bacterial species. These bacterial colonies are responsible for
the maintenance of normal oral and gut microbiota. The presence of these common
oral and gut microbiomes results in the regulation and development of cognitive
functions in the brain. Imbalance in this normal flora, results in the development
of impaired cognitive functions. In a healthy state, oral and gut microbiomes are
present in a balanced state (BS) and do not have any impact on cognitive functions.
Whenever this BS is affected by internal or external microorganisms, it may result
in the formation of dysbiosis in oral and gut microflora. Later on, it results in
the development of impaired cognitive functions.
In the present review, we presented the impact of normal oral and gut microflora
in the development of cognitive functions and discussed the reversal of oral and
gut dysbiosis-induced impaired cognitive functions with the help of probiotic microorganisms.
Recent research studies showed that oral beneficial flora plays a major role in
the reversal of impaired cognitive functions through the secretion of neurotransmitter
precursors chemical compounds (NPCs) (short-chain fatty acids [SCFAs], tyrosine,
levodopa [L-DOPA], tryptophan and 5-hydroxytryptophan [5-HTP]). Secreted NPCs are
further transmitted to the brain for the formation of neurotransmitters like dopamine,
glutamate, gamma-aminobutyric acid (GABA), serotonin and norepinephrine. Further,
these synthesized neurotransmitters result in the reversal of cognitive memory formation
by strengthening the synaptic connections present in the brain through the molecules
involved in neuronal signaling pathways.
