Free operant and discrete trial performance of mice in the nine-hole box apparatus: validation using amphetamine and scopolamine.

RATIONALE

To determine the suitability of the nine-hole box to characterise mouse performance on a free operant task and a discrete trials task, and to validate the tests by probing whether d-amphetamine and scopolamine modify performance of the task as predicted.

OBJECTIVES

To demonstrate the functionality and efficiency of the mouse nine-hole box for the evaluation of performance under fixed- (FR) and progressive-ratio (PR) operant schedules, as well as under a three-choice visual discrimination task and subsequent reversals of the task. In addition, sensitivity of the apparatus was assessed using pharmacological challenges.

METHODS

C57BL/6J were tested on CRF, FR5, FR10, FR20, and a modified PR3 schedule. Behavioural response to d-amphetamine sulphate (0.1, 0.3, and 2.0 mg/kg for FR and 0.1, 0.3, and 1.0 mg/kg for PR) was assessed. In a separate group of mice trained on a three-choice visual discrimination task, the task was reversed (light+, dark+, light+, dark+) 3 times to determine acquisition and reversal of the visual discrimination rule. Scopolamine hydrobromide was examined in this paradigm with the reversal task, and was used to determine learning acquisition and rule reversal learning.

RESULTS

Mice rapidly acquired the FR and PR schedules, as well as both three-choice visual discrimination procedures in the nine-hole box. d-Amphetamine significantly reduced performance on the FR5 and FR10 schedules as shown by the reduction in the number of rewarded responses and the increases in various latency measurements. As expected, d-amphetamine induced an increase in the break point and eliminated the pauses that occurred on high ratio schedules under the PR3 paradigm. Pretreatment of scopolamine decreased accuracy in the three-choice visual discrimination task.

CONCLUSIONS

The nine-hole box is an effective tool to assess operant behaviours in mice following pharmacological manipulation validating the utility of this apparatus for the behavioural evaluation of drug-induced and transgenic models of neurodegenerative disorders.