Research has shown that antibiotics strong enough to kill off gut bacteria can also stop the growth of new brain cells in the hippocampus . This also demonstrates how inextricable (connected) the gut and brain really are.
The study saw researchers give mice enough antibiotics to almost decimate their gut microbiota. Interestingly, those that lost their healthy gut bacteria were shown to perform worse in memory tests. They also showed a loss of new brain cell creation or neurogenesis in the hippocampus. Here’s where it gets interesting though:
The white blood cell link
“At the same time that the mice experienced memory and neurogenesis loss, the research team detected a lower level of white blood cells (specifically monocytes) marked with Ly6Chi in the brain, blood, and bone marrow. So researchers tested whether it was indeed the Ly6Chi monocytes behind the changes in neurogenesis and memory .”
Follow up studies further investigated the white blood cell link. Lead author, researcher Susanne Asu Wolf said, “For us, it was impressive to find these Ly6chi cells that travel from the periphery to the brain, and if there’s something wrong in the microbiome, Ly6chi acts as a communicating cell .” One investigation saw researchers compare untreated mice to mice with healthy gut bacteria levels but low Ly6chi levels for whatever reason. In both cases, mice with low ly6chi levels showed the same memory and neurogenesis insufficiencies .
Ly6Chi white blood cells are important in the body’s immune defence system.
An interesting dichotomy that indicates that antibiotics can actually depress the immune system as well as brain function! The researchers did assert that antibiotics are still remarkably useful but noted the adverse effects that can be tied up with prolonged use .
Concerningly, “reconstitution with normal gut flora (SPF) did not completely reverse the deficits in neurogenesis unless the mice, also had access to a running wheel or received probiotics .”
Wolf remarked, “We found prolonged antibiotic treatment might impact brain function. But probiotics and exercise can balance brain plasticity and should be considered as a real treatment option .”
To Your Health,
 Staff Writer Cell Press, 2016. “Antibiotics that kill gut bacteria also stop the growth of new brain cells.” Cell Reports via Science Daily https://www.sciencedaily.com/releases/2016/05/160519130105.htm retrieved 15 February 17
 Mohle L, Mattei D, Heimesaat M, Bereswill S, Fischer A, Alutis M, French T, Hambardzumyan D, Matzinger P, Dunay I and Wolf S. 2016. LY6Chi monocytes provide a link between antibiotic-induced changes in gut microbiota and adult hippocampal neurogenesis. Cell Press. Volume 15, Issue 9, p1945-1956 31 May 2016, http://www.cell.com/cell-reports/abstract/S2211-1247(16)30518-6?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2211124716305186%3Fshowall%3Dtrue retrieved 15 February 2017
 Gaidt M, Ebert T, Chauhan D, Schmidt T, Schmid-Burgk J, Rapino F, Robertson A, Cooper M, Graf T and Hornung V. 2016. Human monocytes engage an alternative inflammasome pathway. Immunity. Volume 44, Issue 4, p833-846 http://www.cell.com/immunity/fulltext/S1074-7613(16)00037-6 retrieved 15 February 2017