Date of Award
8-2015
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Legacy Department
Environmental Toxicology
Committee Chair/Advisor
Stephen J Klaine
Committee Member
Joseph H Bisesi, Jr.
Committee Member
Lisa Bain
Committee Member
Thomas E Schwedler
Committee Member
Cindy M Lee
Abstract
Over 47 percent of Americans take at least one prescription drug per month and of these pharmaceuticals, antidepressants are the third most prescribed drug. Their widespread and prolonged use coupled with incomplete removal during wastewater treatment processes has made them one of the most commonly detected pharmaceuticals in the aquatic environment. Antidepressants are intended to modify human behavior by altering brain chemistry and the neurotransmitter receptor targets of these chemicals are highly conserved in many vertebrate species; thus, aquatic organisms may be at risk. Previous research in our lab has shown that exposure of hybrid striped bass (HSB) (Morone saxatilis x. M. chrysops) to serotonin targeting antidepressants causes decreased in brain serotonin concentrations that correlate with significant changes in time to capture prey. The goal of this dissertation was to gain a better understanding of how antidepressants alter brain chemistry and predatory behavior in the hybrid striped bass, and to utilize the information to develop a preliminary model to predict the effects of antidepressants on fish brain chemistry and behavior. Hybrid striped bass were exposed to bupropion, a norepinephrine and dopamine reuptake inhibitor antidepressant, to understand if alteration of the dopaminergic neurotransmitter concentrations in the HSB would alter a predator’s ability to capture prey. HSB were exposed to bupropion in a static system for 6 days, followed by a 6 day recovery period. Bupropion altered the concentration of dopamine and many of the dopaminergic neurotransmitter metabolite concentrations in the HSB brains on day 3 of the exposure, but it did not alter the HSB time to capture prey. The lack of effect on time to capture prey suggests that alteration of dopaminergic neurotransmitter concentrations in the HSB brain does not alter a predator’s ability to capture prey and led to focusing of future work on serotonin targeting antidepressants, such as the selective serotonin reuptake inhibitor (SSRI) class. The target of SSRI antidepressants is the serotonin reuptake transporter (SERT). The SERT transporter has been identified in a few fish species, but not the hybrid striped bass. I utilized recently sequenced striped bass and white bass transcriptomes as well as conserved sequences from aligned serotonin reuptake transporters of other vertebrate species to design primers for cloning. I was able to sequence roughly 80% of the SERT, compared to the striped bass sequence, and found that it had 72% identity to the human SERT. The functional domains identified in the human SERT were highly conserved with the amino acid residues in the hybrid striped bass. The binding affinity of SSRI antidepressants were quantified for the SERT in a HSB brain homogenate using competitive radioligand binding assays with [3H] citalopram, a tritium labeled SSRI. In general, the HSB antidepressant binding affinities were less potent than affinities observed for the human SERT. These results confirmed that the SERT is conserved and present in the HSB, and that antidepressants are binding to the SERT in the HSB brain. The bioavailability of two serotonin targeting antidepressants, fluoxetine and venlafaxine, was quantified by exposing HSB to each drug and quantifying antidepressant concentrations in HSB plasma and brains. Fluoxetine and venlafaxine brain concentrations strongly correlated with decreases in brain serotonin concentrations and time to capture prey, providing internal antidepressant concentrations that correspond to adverse effects on HSB brain serotonin and predatory behavior. Antidepressants are entering the aquatic environment in complex mixtures. In order to gain a better understanding of the effects of SSRI antidepressant mixtures on fish brain chemistry and behavior, HSB were exposed to a mixture of sertraline, citalopram, and fluoxetine for 6 days, followed by a 6 day recovery period. The antidepressants were detected in the brains of the HSB throughout the recovery period, and significant changes in all treatments were observed on day 12 of the experiment, which correlated with significant increases in time to capture prey. Further, greater than additive changes in brain serotonin were observed in the experiment. Overall, the results of this dissertation indicate that SSRI antidepressants are binding to the SERT in the HSB brain and causing adverse effects on brain serotonin and time to capture prey. I have quantified the partitioning of antidepressants from aqueous exposures, to plasma concentrations, to ultimately reaching the brain and exerting effects on brain serotonin. These drugs can remain in the brain of the HSB even after being in a clean system for 6 days, and can continue to exert greater than additive effects on brain serotonin and alter predatory behavior. The work has furthered our understanding on how antidepressants in the environment alter hybrid striped bass brain serotonin and predatory behavior.
Recommended Citation
Sweet, Lauren, "Antidepressant Effects in Hybrid Striped Bass: Moving from External Exposures to Internal Doses" (2015). All Dissertations. 1530.
https://open.clemson.edu/all_dissertations/1530