Correlation of serotonin levels in CSF, platelets, plasma, and urine

Background: Neurotransmitter levels are best measured in the cerebrospinal fluid (CSF), but that requires an invasive procedure. Methods: Samples were collected from humans and rats. Eighteen women age 38-51 years with fibromyalgia provided samples of CSF, plasma, platelets, and urine. Samples of CSF, plasma, platelets, and urine were also collected from Sprague-Dawley rats, adult male, 6 months old. One group of rats was treated with p-chlorophenylalanine to decrease their levels of serotonin, and another group of rats was treated with amphetamine to increase their levels of serotonin. Methodological improvements include: 1) the use of siliconized glassware, plasticware, and tubing to prevent adsorption of serotonin, 2) the extraction of serotonin from the CSF, plasma, and platelets, 3) repeated washing of the platelets with an improved buffer, and 4) early morning sample collection. HPLC/MS was used to measure serotonin after extraction. Results: For serotonin, the new method of measuring platelet levels resulted in a very high correlation with levels of serotonin in CSF in rats (r = 0.97) and humans (r = 0.97). There were lower correlations of levels of serotonin in CSF with levels in plasma (r = 0.77 for rats and r = 0.57 in humans) and urine (r =0.67 in rats and r = 0.62 in humans). General significance: This method of measuring serotonin levels in platelets results in a very strong correlation with levels in CSF, so in most cases platelet measurements will be preferable since it is much less invasive to collect. Levels of serotonin in plasma and urine are significantly but less strongly correlated with levels in CSF.