Antibiotics may affect neurogenesis directly, and not act only via the gut bacteria. (Representational Image)
Treatments involving long-term use of antibiotics may disrupt brain functions and affect the formation of new brain cells, a new study has claimed.
A special kind of immune cell serves as an intermediary between gut bacteria and the brain, according to Susanne Wolf from Max Delbruck Centre for Molecular Medicine in Germany.
The findings are of significance when it comes to the effects of using antibiotics in the long term, and could also help to alleviate the symptoms of mental disorders, researchers said.
The gut and the brain "talk" to one another via hormones, metabolic products or direct neural connections. A specific population of monocyte immune cells acts as a further link between the two, they said.
Researchers switched off the gut microbiome in mice, that is their intestinal bacteria, with a strong concoction of antibiotics.
Compared to the mice that had not undergone treatment, they subsequently observed significantly fewer newly formed nerve cells in the hippocampus region of the brain.
The memory of the treated mice also deteriorated because the formation of these new brain cells - a process known as neurogenesis - is important for certain memory functions.
As well as impaired neurogenesis, researchers also found that the population of a specific immune cell in the brain - the Ly6C(hi) monocytes - decreased significantly when the microbiota was switched off.
When they removed just these cells from the mice, neurogenesis declined and when they gave the cells to the mice that had been on antibiotics, neurogenesis increased once again, researchers said.
They cured the antibiotic-treated mice using two different strategies - the mice were either given a mixture of selected bacterial strains or had access to voluntary training in the running wheel, thus reversing the negative effects of the antibiotics.
The mice's number of monocytes increased and their memory performance and neurogenesis improved. However, it was not possible to restore the immune and brain functions using the microbiota of untreated mice, researchers said.
"With the Ly6C(hi) monocytes, we may have discovered a new general communication path from the periphery to the brain," said Ms Wolf.
Applied to humans, the findings do not show that all antibiotics disrupt brain function, as the combination of drugs used in the study was extremely potent, researchers said.
"It is possible, however, that similar effects could result from treatments involving long-term use of antibiotics," said Ms Wolf.
Researchers also found that the antibiotics may affect neurogenesis directly, and not act only via the gut bacteria.
The study is also of significance for treating people with mental disorders such as schizophrenia or depression, who also have impaired neurogenesis, said Wolf.
The findings were published in the journal Cell Reports.