Graduation Date

Spring 2023

Document Type



Master of Arts degree with a major in Psychology, option Academic Research

Committee Chair Name

Ethan Gahtan

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Amanda Hahn

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Carrie Aigner

Third Committee Member Affiliation

HSU Faculty or Staff


ADHD, Zebrafish, Atomoxetine, Circadian rhythm, Attention-deficit hyperactivity disorder

Subject Categories



Background: Attention deficit hyperactivity disorder (ADHD) is a common neurological disorder characterized by inattention, hyperactivity, and impulsive behavior. Many people with ADHD who are taking pharmacological treatments also report having sleep problems, and both children and adults tend to fall asleep later than neurotypical people. Since diagnosis and treatment of ADHD are on the rise, understanding how the disorder and common medications influence circadian rhythms is becoming more important. Zebrafish are a common animal model that have been shown to reliably represent features of many human disorders, including ADHD. Hypothesis: The specific hypotheses tested were: (H1) that a common medication used to treat ADHD, atomoxetine (ATX), would disrupt circadian rhythms in developing zebrafish; (H2) that ATX will increase locomotor activity overall; (H3) that ATX would influence light-evoked startle swimming; (H4) that treatment with 6 mg/L of ATX would have a greater effect on behavioral measurements than treatment with 3 mg/L. Methods: Zebrafish were raised from day 0-7 under a standard light/dark cycle to entrain circadian rhythms. Separate groups (N = 24 per group) were treated with an ATX solution with a concentration of 3 mg/L or 6 mg/L, or a control solution during entrainment. On day 7, locomotor activity was recorded for 5 minutes per hour for 24 hours in constant low illumination, followed by two brief (30 second) light-dimming evoked startle trials. Results: The group treated with 6 mg/L showed altered circadian rhythms with higher overall activity levels across the entire recording period compared to the control group and the group treated with 3 mg/L. The group treated with 3 mg/L also showed significant differences when compared to the control group. All groups showed significant locomotor startle response to light dimming but startle response magnitude and duration were equivalent across groups. Implications: These results highlight the importance of understanding the effects of circadian disruption by ADHD medications. As a selective norepinephrine re-uptake inhibitor with no direct effects on brain dopamine levels, ATX is considered a non-stimulant, but it still increased activity levels. This could be harmful to humans through sleep loss or other mechanisms. Future studies should examine the possible dose-dependent response to ATX in both adult and larval zebrafish. These results also justify using zebrafish to investigate the biological mechanisms of these drug effects on circadian cycles.

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