Mauritio
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- Feb 26, 2018
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This study says:
Beyond the gut, germ free mice also display an increased turnover rate of dopamine and norepinephrine (as well as serotonin) in the brain (Diaz Heijtz et al., 2011), which could generally reduce pools in systemic circulation independent of microbial production (although factors influencing that increased turnover rate remain to be determined). " (1)
This study refers to another one, that mentions that germ free mice experience less anxiety and more activity in general:
"Using measures of motor activity and anxiety-like behavior, we demonstrate that germ free (GF) mice display increased motor activity and reduced anxiety, compared with specific pathogen free (SPF) mice with a normal gut microbiota. " (2)
The first study only looked at the brain turnover of the monoamines, whereas this study looked at various serotonin values in different places in the body.
Germ free mice had lower serotonin values in the colon, large intestine platelet rich plasma and fecal matter ,while also showing lower TPH( tryptophan hydroplase) activity!
Plus the activity of the of the serotonin transporter was increased 1,75 fold .
For some reason they showed higher 5ht levels in the small intestines. (3):
"Consistent with the understanding that much of the body’s 5-HT derives from the GI tract, we find that GF mice exhibit significantly decreased levels of colonic and fecal 5-HT compared to SPF controls (Figures 1B and S1A, and Table S1). This deficit in 5-HT is observed broadly across the distal, medial and proximal colon (Figure S1D), but not in the small intestine (Figures S1A, S2A and S2B), suggesting a specific role for the microbiota in regulating colonic 5-HT."
"GF mice also display elevated colonic expression of the 5-HT transporter SLC6A4"
They also show that germ free mice excrete higher amounts of tryptophan,possibly resulting from less conversion to serotonin:
".. GF mice exhibit significantly increased levels of the Tph substrate, tryptophan (Trp), in both feces (Table S1) and serum..."
Next they mention that theres actually a subsetof bacteria that does not produce or increase the serotonin levels of mice:
"Mice monocolonized with Bacteroides fragilis or Segmented Filamentous Bacteria (SFB) display deficits in serum 5-HT that are comparable to those seen in GF mice (Figure 3A). Moreover, postnatal colonization (P42) with Bacteroides uniformis, altered Schaedler flora (ASF), an eight-microbe consortium known to correct gross intestinal pathology in GF mice (Dewhirst et al., 1999), or with cultured Bacteroides spp. from the SPF mouse microbiota, has no significant effect on the 5-HT deficiency seen in GF mice (Figures 3A and 3B)."
They also found out that inhibiting TPH TPH decreases serotonin ,although there was a compensatory increase in TPH and decrease in serotonin transporter by the body. So even with a TPH-inhibitot you might not fully get rid of serotonin as the body adapts to it:
"Interestingly, inhibiting Tph activity with PCPA results in a compensatory increase in colonic TPH1 and decrease in SLC6A4 (Figures 3D and S2D)"
Beyond the gut, germ free mice also display an increased turnover rate of dopamine and norepinephrine (as well as serotonin) in the brain (Diaz Heijtz et al., 2011), which could generally reduce pools in systemic circulation independent of microbial production (although factors influencing that increased turnover rate remain to be determined). " (1)
This study refers to another one, that mentions that germ free mice experience less anxiety and more activity in general:
"Using measures of motor activity and anxiety-like behavior, we demonstrate that germ free (GF) mice display increased motor activity and reduced anxiety, compared with specific pathogen free (SPF) mice with a normal gut microbiota. " (2)
The first study only looked at the brain turnover of the monoamines, whereas this study looked at various serotonin values in different places in the body.
Germ free mice had lower serotonin values in the colon, large intestine platelet rich plasma and fecal matter ,while also showing lower TPH( tryptophan hydroplase) activity!
Plus the activity of the of the serotonin transporter was increased 1,75 fold .
For some reason they showed higher 5ht levels in the small intestines. (3):
"Consistent with the understanding that much of the body’s 5-HT derives from the GI tract, we find that GF mice exhibit significantly decreased levels of colonic and fecal 5-HT compared to SPF controls (Figures 1B and S1A, and Table S1). This deficit in 5-HT is observed broadly across the distal, medial and proximal colon (Figure S1D), but not in the small intestine (Figures S1A, S2A and S2B), suggesting a specific role for the microbiota in regulating colonic 5-HT."
"GF mice also display elevated colonic expression of the 5-HT transporter SLC6A4"
They also show that germ free mice excrete higher amounts of tryptophan,possibly resulting from less conversion to serotonin:
".. GF mice exhibit significantly increased levels of the Tph substrate, tryptophan (Trp), in both feces (Table S1) and serum..."
Next they mention that theres actually a subsetof bacteria that does not produce or increase the serotonin levels of mice:
"Mice monocolonized with Bacteroides fragilis or Segmented Filamentous Bacteria (SFB) display deficits in serum 5-HT that are comparable to those seen in GF mice (Figure 3A). Moreover, postnatal colonization (P42) with Bacteroides uniformis, altered Schaedler flora (ASF), an eight-microbe consortium known to correct gross intestinal pathology in GF mice (Dewhirst et al., 1999), or with cultured Bacteroides spp. from the SPF mouse microbiota, has no significant effect on the 5-HT deficiency seen in GF mice (Figures 3A and 3B)."
They also found out that inhibiting TPH TPH decreases serotonin ,although there was a compensatory increase in TPH and decrease in serotonin transporter by the body. So even with a TPH-inhibitot you might not fully get rid of serotonin as the body adapts to it:
"Interestingly, inhibiting Tph activity with PCPA results in a compensatory increase in colonic TPH1 and decrease in SLC6A4 (Figures 3D and S2D)"