ABSTRACT
RATIONALE: The adenosine A3 receptor and the nitric oxide (NO) pathway regulate the function and localization of serotonin transporters (SERTs). These transporters regulate extracellular serotonin levels, which are correlated with defensive behavior. OBJECTIVE: The purpose of this study was to understand the role of the A3AR on anxiety and arousal models in zebrafish, and whether this role is mediated by the nitrergic modulation of serotonin uptake. METHODS: The effects of IB-MECA (0.01 and 0.1 mg/kg) were assessed in a series of behavioral tasks in adult zebrafish, as well as on extracellular serotonin levels in vivo and serotonin uptake in brain homogenates. Finally, the interaction between IB-MECA and drugs blocking voltage-dependent calcium channels (VDCCs), NO synthase, and SERT was analyzed. RESULTS: At the lowest dose, IB-MECA decreased bottom dwelling and scototaxis, while at the highest dose, it also decreased shoaling, startle probability, and melanophore responses. These effects were accompanied by an increase in brain extracellular serotonin levels. IB-MECA also concentration-dependently increased serotonin uptake in vitro. The effects of IB-MECA on extracellular 5-HT, scototaxis, and geotaxis were blocked by L-NAME, while only the effects on 5-HT and scototaxis were blocked by verapamil. In vitro, the increase in 5-HT uptake was dependent on VDCCs and NO. Finally, fluoxetine blocked the effect of IB-MECA on scototaxis, but not geotaxis. CONCLUSION: These results suggest that the effect of IB-MECA on scototaxis are mediated by a VDCC-NO-SERT pathway. While NO seems to mediate the effects of IB-MECA on geotaxis, neither VDCCs nor SERT seems to be involved in this process.
Subject(s)
Adenosine/analogs & derivatives , Anxiety/metabolism , Motor Activity/drug effects , Nitric Oxide/physiology , Serotonin Plasma Membrane Transport Proteins/metabolism , Serotonin/metabolism , Adenosine/pharmacology , Adenosine/therapeutic use , Animals , Anxiety/drug therapy , Dose-Response Relationship, Drug , Male , Motor Activity/physiology , Nitric Oxide Synthase/metabolism , Signal Transduction/drug effects , Signal Transduction/physiology , ZebrafishABSTRACT
A major hindrance for the development of psychiatric drugs is the prediction of how treatments can alter complex behaviors in assays which have good throughput and physiological complexity. Here we report the development of a medium-throughput screen for drugs which alter anxiety-like behavior in adult zebrafish. The observed phenotypes were clustered according to shared behavioral effects. This barcoding procedure revealed conserved functions of anxiolytic, anxiogenic and psychomotor stimulating drugs and predicted effects of poorly characterized compounds on anxiety. Moreover, anxiolytic drugs all decreased, while anxiogenic drugs increased, serotonin turnover. These results underscore the power of behavioral profiling in adult zebrafish as an approach which combines throughput and physiological complexity in the pharmacological dissection of complex behaviors.
Subject(s)
Anti-Anxiety Agents/pharmacology , Anxiety/drug therapy , Animals , Buspirone/pharmacology , Caffeine/pharmacology , Diazepam/pharmacology , Drug Evaluation, Preclinical , Freezing Reaction, Cataleptic/drug effects , Serotonin/metabolism , Swimming , ZebrafishABSTRACT
Serotonin (5-HT) is a neurotransmitter that is involved in many behavioral functions, including the organization of defense, and its putative pathological correlate, anxiety and stress disorders. Recently, behavioral tests for anxiety have been proposed in zebrafish. Exposure to the novel tank test or to the light/dark test increased extracellular fluid 5-HT content in the brain; anxiety-like behavior correlated positively with 5-HT content in the novel tank test, while the correlation was negative in the light/dark test. Acute treatment with a low dose of fluoxetine was anxiolytic in the geotaxis test and anxiogenic in the scototaxis test, while treatment with a higher dose produced a hyperlocomotor effect in both tasks. Buspirone and WAY 100635 were anxiolytic in both tests, while SB 224289 was anxiolytic in the geotaxis and slightly anxiogenic in the scototaxis test. Serotonin depletion with pCPA was anxiogenic in the geotaxis and anxiolytic in scototaxis. These results underline the differential sensitivity of these tasks to assess serotonergic agents; alternatively, serotonin might regulate zebrafish behavior differently in the novel tank test and in the light/dark test.
