Assessing memory in zebrafish using the one-trial test

Pharmacological analyses of learning and memory in zebrafish (Danio rerio)

Over the last decade, zebrafish (Danio rerio) have become valuable as a complementary model in behavioral pharmacology, opening a new avenue for understanding the relationships between drug action and behavior. This species offers a useful intermediate approach bridging the gap between in vitro studies and traditional mammalian models. Zebrafish offer great advantages of economy compared to their rodent counterparts, their complex brains and behavioral repertoire offer great translational potential relative to in vitro models. The development and validation of a variety of tests to measure behavior, including cognition, in zebrafish have set the stage for the use of this animal for behavioral pharmacology studies. This has led to research into the basic mechanisms of cognitive function as well as screening for potential cognition-improving drug therapies, among other lines of research. As with all models, zebrafish have limitations, which span pharmacokinetic challenges to difficulties quantifying behavior. The use, efficacy and limitations associated with a zebrafish model of cognitive function are discussed in this review, within the context of behavioral pharmacology.

Using visual lateralization to model learning and memory in zebrafish larvae

Impaired learning and memory are common symptoms of neurodegenerative and neuropsychiatric diseases. Present, there are several behavioural test employed to assess cognitive functions in animal models, including the frequently used novel object recognition (NOR) test. However, although atypical functional brain lateralization has been associated with neuropsychiatric conditions, spanning from schizophrenia to autism, few animal models are available to study this phenomenon in learning and memory deficits. Here we present a visual lateralization NOR model (VLNOR) in zebrafish larvae as an assay that combines brain lateralization and NOR. In zebrafish larvae, learning and memory are generally assessed by habituation, sensitization, or conditioning paradigms, which are all representatives of nondeclarative memory. The VLNOR is the first model for zebrafish larvae that studies a memory similar to the declarative memory described for mammals. We demonstrate that VLNOR can be used to study memory formation, storage, and recall of novel objects, both short and long term, in 10-day-old zebrafish. Furthermore we show that the VLNOR model can be used to study chemical modulation of memory formation and maintenance using dizocilpine (MK-801), a frequently used non-competitive antagonist of the NMDA receptor, used to test putative antipsychotics in animal models.

Towards the characterization of short-term memory of zebrafish: effect of fixed versus random reward location

The zebrafish has been proposed as an efficient tool for the analysis of behavioral and neurobiological mechanisms of learning and memory. However, compared to traditional laboratory rodents, it is a relatively newcomer. In fact, only limited information on its mnemonic and cognitive abilities has been obtained, and only a small number of learning and memory paradigms have been available for its testing. Previously, we have shown that zebrafish are capable of learning the systematic alternating sequence of reward location in a shuttle box task in which we evaluated behavioral responses manually. Here, we employ a computerized, automated version of this task. We study whether zebrafish can remember the prior location of a reward (the sight of conspecifics) when the location is fixed (constant), or when the sequence of the location of presentation randomly changes between the left and the right side of the experimental tank. We also analyze performance features including the swim speed of experimental fish as well as the temporal changes of the position of fish when the reward (stimulus) is not presented. Our results show that under both the fixed and randomly changing reward location conditions zebrafish exhibit a significant preference for the prior location of reward, albeit the preference is stronger under the fixed location condition. We conclude that adult zebrafish have short-term associative memory that can be induced and quantified in an automated manner.