Continual Trials Spontaneous Recognition Tasks in Mice: Reducing Animal Numbers and Improving Our Understanding of the Mechanisms Underlying Memory

Abstract

Spontaneous recognition tasks are widely used as a laboratory measure of memory in animals but give rise to high levels of behavioral noise leading to a lack of reliability. Previous work has shown that a modification of the procedure to allow continual trials testing (in which many trials are run concurrently in a single session) decreases behavioral noise and thus significantly reduces the numbers of rats required to retain statistical power. Here, we demonstrate for the first time that this improved method of testing extends to mice, increasing the overall power of the approach. Moreover, our results show that the new continual trials approach provides the additional benefits of heightened sensitivity and thus provides greater insight into the mechanisms at play. Standard (c57) and transgenic Alzheimer model (TASTPM) mice were tested both at 7 and 10 months of age in both object recognition (OR) and object-location (OL) spontaneous recognition tasks using the continual trials methodology. Both c57 and TASTPM mice showed age-dependent changes in performance in OR. While c57 mice also showed age-related changes in performance of OL, TASTPM mice were unable to perform OL at either age. Significantly, we demonstrate that differences in OL performance in c57s and TASTPM animals is a result of proactive interference rather than an absolute inability to recognize OL combinations. We argue that these continual trials approaches provide overall improved reliability and better interpretation of the memory ability of mice, as well as providing a significant reduction in overall animal use.

The NMDA receptor antagonist MK-801 fails to impair long-term recognition memory in mice when the state-dependency of memory is controlled

“…In the present study, we tested whether MK-801 induced a state that affected performance of memory by testing long-term object recognition memory in mice. Mice were tested using a procedure that allows for multiple tests of object recognition memory, which increases the overall sensitivity of the measure (Ameen-Ali et al, 2012, Chan et al, 2018). Mice were exposed to eight different objects on day 1 and then on day 2 received a series of novelty preference tests, one for each of the eight familiar objects, in which they were allowed to explore a familiar object and a novel object.…”

Dissociating the effects of distraction and proactive interference on object memory through tests of novelty preference

“…Of note, the same effect was seen but to a much-reduced extent in the vehicle group. Whilst we used dietary restriction to promote conNOR performance (Chan et al, 2018), in practice many pellets were either not collected or left unconsumed by rats during the task, so we feel performance would be equally good in future studies without prior food restriction. Overall, these observations strongly support the presence of two separable deficits of cognitive control in the scPCP rat; distraction and proactive interference.…”

“…Rats were first habituated to the conNOR arena over four days, during which timed dispensing of food pellets encouraged shuttling between holding and experimental chambers (Chan et al, 2018). On day 1, cage groups were placed into the arena with the central door open for 30min to explore freely, encouraged by single pellet dispensing into both chambers every minute.…”

“…For analyses the DI metric was again used for each trial where exploration times were summed for all trials to that point. For example, for conNOR trial 3 the sum of exploration durations for familiar objects on trials 1 to 3 was subtracted from the sum of novel object exploration over the same trials, the result divided by the sum of these two measures (Chan et al, 2018).…”

“…Whilst this demonstrates the cross-species validation of a simple and fast means to measure distraction susceptibility, this effectively precludes stNOR as a probe for disease-relevant memory deficits. However, recent developments allow NOR to be probed in a continuous trials design (conNOR); allowing the sequential performance of 10 or more object preference trials in a single session, all with minimal distraction between task phases (Albasser et al, 2010;Ameen-Ali et al, 2012;Chan et al, 2018). Using such an approach provides a promising means to probe object memory deficits independent of distraction in the scPCP and other models of human neuropsychiatric conditions.…”