Characterization of cerebrospinal fluid (CSF) and plasma NPY levels in normal volunteers over a 24-h timeframe

Neuropeptide Y (NPY) is abundant in mammals, where it contributes to diverse behavioral and physiological functions, centrally and peripherally, but little information is available in regard to NPY cerebrospinal fluid (CSF)/plasma concentration relationships and dynamics. Since plasma NPY levels are commonly used as proxy "biomarkers" for central NPY activity in stress and mental health research in humans this study aims to better characterize the CSF/plasma NPY relationships. Subjects were eleven healthy male volunteers, admitted to the clinical research center for placement of an indwelling CSF catheter, as well as venous catheter, for 24-h collection of CSF NPY (cNPY) and plasma NPY (pNPY) samples. As observed in prior studies, group mean (SE) cNPY concentrations [792.1 (7.80) pg/mL] were higher than pNPY concentrations [220.0 (3.63) pg/mL]. For the eleven normal volunteers who had sufficient common (hourly) pNPY and cNPY data points, analysis of pNPY/cNPY concentration ratios and lagged cross-correlation analysis was completed. Average pNPY/cNPY concentration ratios ranged from .20 to .40 across study subjects, with a mean of .29. pNPY/cNPY cross correlation analyses, computed at varying time lags, were non-significant. An attempt was made to analyze the circadian rhythmicity of NPY secretion, but circadian components were not detectable. Using 24-h data collection, we characterized CSF/plasma NPY relationships, including presentation of evidence of weak CSF and plasma correlations, an important consideration for study design of NPY in stress or mental health.