Quantitative analysis of neurotransmitters in fish brain: A tool to assess neurochemical effects of psychoactive pollutants.

Psychoactive drugs in fish act through mechanisms similar to those in humans because their main neurotransmitter (NT) systems are analogous. Psychoactive drugs are ubiquitous in aquatic environments, having negative effects on fish and other aquatic organisms. To understand the neurochemical changes underlying the effects, studying neurotransmitter levels is essential. The detection of NTs and their metabolites in biological samples may be challenging. A new analytical method using hydrophilic interaction liquid chromatography coupled to high-resolution mass spectrometry was developed. The method includes simple extraction and 17 min analytical run and enables reliable quantification of a wide range of NTs from different classes, including their precursors and metabolites: acetylcholine, choline, citrulline, 3,4-dihydroxyphenylacetic acid, dopamine, dopamine-3-O-sulfate, epinephrine, gamma-aminobutyric acid, gamma-hydroxybutyric acid, glutamate, glutamine, α-glycerophosphorylcholine, guanidine, histamine, histidine, levodopa, melatonin, norepinephrine, normetanephrine, octopamine, phenylalanine, phosphocholine, serotonin, 5-hydroxyindoleacetic acid, synephrine, tryptophan, 5-hydroxytryptophan, tyramine, 3-methoxytyramine, and tyrosine. The method was validated with highly satisfying performance parameters regarding sensitivity, repeatability and trueness. Under optimized conditions, recoveries from 55 to 130 % were obtained, while intra-day and inter-day RSD never exceeded 24 and 29 %, respectively. LOQs between 0.0012 and 25 μg/g d.w. were achieved. Finally, the optimized method was applied to analyze NTs in the brains of two fish species: European perch and rainbow trout. Proposed method will help to obtain fundamental information on NTs content in fish brain and on their changes in response to the exposure to psychoactive drugs.