Comparison of neurotransmitters concentration in canine cerebrospinal fluid, blood, and urine samples measured via highperformance liquid chromatography

The coordinated interplay between neurotransmitters is crucial for
the physiological functioning of the central nervous system. It is
thought that neurotransmitter do not penetrate the blood brain barrier.
However, in humans, urinary neurotransmitter analysis for mood
disorders like anxiety and depression is used in practice. The aim of the
current study was to compare neurotransmitter concentrations across
body fluids. This is the first canine study evaluating how neurotransmitter
concentrations in cerebrospinal fluid (CSF), serum, and urine are associated
with each other, providing new insights into the canine
neurotransmitter metabolism. CSF, serum, and urine were collected from
8 beagle dogs at three different time points (2weeks apart) under general
anesthesia. The samples were stored at -80C before high-performance
liquid chromatography was performed for analysis. Significant neurotransmitters
from the group of amino acids and catecholamines were
measured. Twenty-four CSF, blood, and urine samples were collected.
Concentrations of serine, glycine, and norepinephrine were significantly
positively correlated between all assessed body fluids. Aspartate concentrations
only correlated positively in CSF and serum. No significant negative
correlations were revealed. The mirroring of concentration profiles
of neurotransmitters in different body fluids offers new opportunities to
study non-invasively behavioural disorders which have recently gained
great importance in veterinary medicine. However, it is important to
state that neurotransmitters can also be produced by peripheral organ
systems and the microbiome, which makes further research necessary.