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Phasic and tonic serotonin modulate alarm reactions and post-exposure behavior in zebrafish
Monica Lima-Maximino1, Maryana Pereira Pyterson2, Rhayra Xavier do Carmo Silva2,3
1Laboratório de Neurofarmacologia e Biofísica, Centro de Ciências Biológicas e da Saúde, Departamento de Morfologia e Ciências Fisiológicas, Universidade do Estado do Pará, Marabá, Brazil.
Journal of Neurochemistry
|February 8, 2020
Summary
Serotonin (5-HT) plays a dual role in defensive behaviors, potentially encoding an aversive expectation. This study in zebrafish suggests 5-HT shifts behavior toward anxiety when threats are absent.
Area of Science:
- Neuroscience
- Behavioral Biology
- Pharmacology
Background:
- Serotonin (5-HT) is theorized to have a dual role in vertebrate defensive behaviors, increasing anxiety while decreasing fear.
- This dual role suggests a tonic 5-HT level inhibits fear, while acute increases induce anxiety, but evidence for tonic 5-HT has been lacking.
- Investigating the role of phasic and tonic serotonin in fear-like behaviors and post-exposure responses is crucial for understanding its complex functions.
Purpose of the Study:
- To investigate the participation of phasic and tonic serotonin levels in zebrafish fear-like behavior and post-stimulation responses.
- To explore the effects of pharmacological manipulations on serotonin pathways and their impact on defensive behaviors.
- To determine if serotonin encodes an aversive expectation value influencing cautious behavior.
Main Methods:
- Zebrafish were exposed to Conspecific Alarm Substance (CAS) to elicit alarm responses.
- Pharmacological agents including clonazepam, fluoxetine, metergoline, and para-chlorophenylalanine were used to modulate serotonin activity.
- Behavioral analyses included bottom-dwelling, erratic swimming, freezing, and assessment of monoamine oxidase activity post-exposure.
Main Results:
- CAS exposure increased bottom-dwelling and erratic swimming; post-exposure, increased bottom-dwelling and freezing were observed.
- Acute fluoxetine decreased fear-like behavior but increased post-exposure freezing, while metergoline and para-chlorophenylalanine blocked CAS effects on post-exposure behavior.
- CAS exposure decreased monoamine oxidase activity, suggesting a role for serotonin in modulating this enzyme.
Conclusions:
- Phasic and tonic serotonin levels appear to encode an aversive expectation value in zebrafish.
- Serotonin signaling shifts behavior towards cautious exploration, risk assessment, and anxiety when an aversive stimulus is no longer present.
- These findings provide evidence for the complex, context-dependent role of serotonin in regulating defensive behaviors.
