Pavlovian Avoidance Learning (mild electric shock)

Avoidance learning procedures involve subjects learning that certain aversive events are predicted by specific environmental stimuli. In the following zebrafish version of the task, fish must learn that a specified visual cue (e.g., blue light) predicts an aversive stimulus (e.g., mild electric shock) (Brock et al., 2017; Kenney et al., 2016). This type of task is a robust method which assesses associative learning and memory, and it is reported to be impaired in many psychiatric disorders, such as anxiety disorders and schizophrenia and in neurodegenerative disorders, such as Alzheimer’s disease.

Experimental setup

Pavlovian Avoidance learning (mild electric shock) with zebrafish
Pavlovian avoidance learning task inserts and stimulus in the Zantiks AD unit. A) shows the dividing inserts used to create 4 separate arenas. B) Overhead still image of the inserts in a testing tank captured from the Zantiks interface during the running of the experiment. Four fish are tracked in the separate arenas with two shocking plates, straddling all arenas placed at each end of the tank. C) Example of typical baseline and probe presentation of visual stimuli. Both CS+ and CS- are presented concurrently. D) Example of stimulus presentation during conditioning. One stimulus covers the entire testing environment.

The Zantiks AD unit is used for avoidance learning in zebrafish. The dividing inserts are used to create four separate testing compartments for tracking four fish in one unit (see image A above).

Metal “shock-plate” inserts are used to deliver the unconditioned stimulus (US+), a mild electric shock, through the water. The plates are placed at both ends of the tank and are designed to be present in each of the 4 arenas (as shown in image B above).

The visual stimuli are presented from the integrated screen below the testing tank (see images C and D). The stimuli can be comprised of colour, shapes, stripes, or bitmap images.

Experimental procedure

Experimental procedure for avoidance learning
Illustrated schema of experimental procedure for avoidance learning. 1) Fish are initially habituated to the tank, and then tracked to establish baseline preference for the environmental stimuli. Both stimuli are presented for baseline measures. 2) The conditioned stimulus is paired with a mild electric shock, 3) followed by presentation of the non-conditioned stimulus. 4) Stimulus preference is then measured in a probe period following conditioning.

Results/data output

The conditioned stimulus preference scores are the main behavioural endpoint analysed in this task. Preference towards the CS is determined in the same manner for both baseline and probe calculations. The proportion of time spent in the vicinity of the CS is calculated for the preference as: Total time in CS / (Time in CS + Time in non-CS).

A decrease in the time spent in the CS is interpreted that the fish has learned to avoid the environmental stimulus present during the electric shock conditioning. A learned association between the environmental stimulus and the electric shock results in the fish spending less time in that environmental stimulus. The Zantiks AD system can automatically track and provide data analysis on this variable.

The CS preference scores are frequently analysed with independent samples t-tests, one-way ANOVAs or two-way repeated measures ANOVAs, depending on the number of factors.

Avoidance learning results
Typical results when a change in preference following aversive conditioning is seen. Fish are initially measured for baseline preference. The decrease in time spent in the conditioned stimulus, following conditioning is observed in the trial.

References

Brock, A. J., Sudwarts, A., Daggett, J., Parker, M. O., & Brennan, C. H. (2017). A fully automated computer based Skinner box for testing learning and memory in zebrafish. bioRxiv, 110478.

Kenney, J. W., Scott, I. C., Josselyn, S. A., & Frankland, P. W. (2016). Contextual Fear Conditioning in Zebrafish. bioRxiv, 068833.

Valente, A., Huang, K. H., Portugues, R., & Engert, F. (2012). Ontogeny of classical and operant learning behaviors in zebrafish. Learning & Memory, 19(4), 170-177.