On 2015 Aug 10, Simon Young commented:

In the article by Tiger et al the levels reported for both serotonin and 5-hydroxyindoleacetic acid (5-HIAA) in human cerebrospinal fluid (CSF) are not consistent with reports in the literature. Concerning serotonin they cite two references, to Anderson et al Anderson GM, 2002 and to Hubbard et al Hubbard KE, 2010. Anderson et al Anderson GM, 2002 report a mean level of serotonin in cisternal CSF of rhesus monkey of 87 pg/ml, which is well below the mean level reported by Tiger et al for human lumbar cerebrospinal fluid. However, the relevance of rhesus monkey cisternal CSF serotonin for human lumbar CSF levels is not clear. The paper by Hubbard et al Hubbard KE, 2010 describes a method for measuring human CSF serotonin. Fig. 2D in that paper shows a chromatogram obtained with a human CSF sample that has a very small peak at the same retention time as the serotonin standard. However, no information is give on the concentration of serotonin detected in CSF. The article which Tiger et al cite by Anderson et al Anderson GM, 2002 mentions that levels of serotonin in human lumbar CSF reported in the literature varied over several orders of magnitude. The paper reports an attempt to determine the true level. Human lumbar CSF from 25 participants was collected on ice and aliquots were frozen at -70C. Measurements were performed in two different laboratories using different HPLC columns and eluting buffers. One lab used an electrochemical detector (detection limit 7 – 8 pg/ml for serotonin) and the other a fluorometric detector (detection limit 7 – 15 pg/ml). In both labs N-methylserotonin was used as an internal standard and a sample was injected directly into the HPLC after removal of proteins. Neither system was able to detect serotonin in any CSF sample. The conclusion was that the real value was less than 10 pg/ml. Anderson et al Anderson GM, 2002 suggest that the higher values reported in the litterature can be attributed to some extent to a failure to carry out rigorous validation steps needed to insure that a peak in HPLC is in fact the analyte of interest and not another compound with a similar retention time and fluorescent or electrochemical properties. Given the rigor of the study of Anderson et al Anderson GM, 2002 the values reported by Tiger et al, which are in the range 400 – 800 pg/ml, must be considered with skepticism. The same is true for the CSF 5-HIAA values reported by Tiger et al which are in a range from less than 1 ng/ml to about 4 ng/ml. Other studies report lumbar CSF 5-HIAA levels in the range 10 – 30 ng/ml, e.g. Kishida I, 2007 Chotai J, 1999 Carpenter LL, 2003.

On 2015 Aug 10, Simon Young commented:

In the article by Tiger et al the levels reported for both serotonin and 5-hydroxyindoleacetic acid (5-HIAA) in human cerebrospinal fluid (CSF) are not consistent with reports in the literature. Concerning serotonin they cite two references, to Anderson et al Anderson GM, 2002 and to Hubbard et al Hubbard KE, 2010. Anderson et al Anderson GM, 2002 report a mean level of serotonin in cisternal CSF of rhesus monkey of 87 pg/ml, which is well below the mean level reported by Tiger et al for human lumbar cerebrospinal fluid. However, the relevance of rhesus monkey cisternal CSF serotonin for human lumbar CSF levels is not clear. The paper by Hubbard et al Hubbard KE, 2010 describes a method for measuring human CSF serotonin. Fig. 2D in that paper shows a chromatogram obtained with a human CSF sample that has a very small peak at the same retention time as the serotonin standard. However, no information is give on the concentration of serotonin detected in CSF. The article which Tiger et al cite by Anderson et al Anderson GM, 2002 mentions that levels of serotonin in human lumbar CSF reported in the literature varied over several orders of magnitude. The paper reports an attempt to determine the true level. Human lumbar CSF from 25 participants was collected on ice and aliquots were frozen at -70C. Measurements were performed in two different laboratories using different HPLC columns and eluting buffers. One lab used an electrochemical detector (detection limit 7 – 8 pg/ml for serotonin) and the other a fluorometric detector (detection limit 7 – 15 pg/ml). In both labs N-methylserotonin was used as an internal standard and a sample was injected directly into the HPLC after removal of proteins. Neither system was able to detect serotonin in any CSF sample. The conclusion was that the real value was less than 10 pg/ml. Anderson et al Anderson GM, 2002 suggest that the higher values reported in the litterature can be attributed to some extent to a failure to carry out rigorous validation steps needed to insure that a peak in HPLC is in fact the analyte of interest and not another compound with a similar retention time and fluorescent or electrochemical properties. Given the rigor of the study of Anderson et al Anderson GM, 2002 the values reported by Tiger et al, which are in the range 400 – 800 pg/ml, must be considered with skepticism. The same is true for the CSF 5-HIAA values reported by Tiger et al which are in a range from less than 1 ng/ml to about 4 ng/ml. Other studies report lumbar CSF 5-HIAA levels in the range 10 – 30 ng/ml, e.g. Kishida I, 2007 Chotai J, 1999 Carpenter LL, 2003.