Examining object location and object recognition memory in mice

Abstract

This unit is designed to provide sufficient instruction for the setup and execution of tests for object location and object recognition in adult mice. This task is ideally suited for the study of a variety of mouse models that examine disease mechanisms and novel therapeutic targets. By altering several key parameters, the experimenter can investigate short-term or long-term memory and look for either memory impairments or enhancements. Object location and object recognition memory tasks rely on a rodent's innate preference for novelty, and can be conducted sequentially in the same cohort of animals. These two tasks avoid the inherent stress induced with other common measures of rodent memory such as fear conditioning and the Morris water maze. This protocol covers detailed instructions on conducting both tasks, as well as key points concerning data collection, analysis, and interpretation.

Keywords: memory disorders; object memory; spatial memory.

FIGURE 1

Object location and object recognition memory task design. (A) Experimental timeline for Object Location Memory (OLM) followed by Object Recognition Memory (ORM) in the same cohort of animals. (B) Diagrams of context and object placement for OLM and ORM. For OLM the right object is shown as the displaced object during testing. In actual experiments the left object is moved for half the animals and the right object is moved for the other half. Similarly, for ORM either the right or left object can be replaced with the novel object at test. The height of the contexts are 23 cm. (C) Images of the actual experimental setup for OLM and ORM. The mouse shown in the testing apparatus is a C57/Bl6J male mouse age 9 weeks. Note that the objects are all filled with gray cement. For ORM, the training condition uses two identical glass candle holders flipped upside down. In an actual experiment, half of the animals would be trained with two tins. For the ORM test, the animals receive one of each object with the location of the novel object counterbalanced across groups.

FIGURE 2

Anticipated results for a typical OLM and ORM sequential experiment. (A) Schematic of behavioral testing. OLM and ORM were then conducted sequentially, as described in the methods, for two independent groups of animals. (B) Total exploration (object 1 and 2) during a 10 min OLM training session (n = 10 animals per group). There was no difference between groups 1 and 2: t(18) = 0.84, p = 0.41. (C) Total exploration (object 1 and 2) duringa5minOLM testing session.Therewas no difference between groups 1 and 2: t(18)= 0.84, p = 0.41. (D) Discrimination Index (DI) for the 5 min OLM testing session. There was a significant difference between groups 1 and 2: t(18) = 2.49, p = 0.02. (E) Total exploration (object 1 and 2) during 10 min ORM training session (n = seven to nine animals per group). There was no difference between groups 1 and 2: t(14) = 0.73, p = 0.48. (F) Total exploration (object 1 and 2) during 5 min ORM testing session. There was no difference between groups 1 and 2: t(14) = 0.47, p = 0.64. (G) Discrimination Index (DI) for the 5 min ORM testing session. There was a significant difference between groups 1 and 2: t(14) = 2.94, p = 0.01. * indicates significant difference at p < 0.05. Portions of this data were previously included in Vogel-Ciernia et al. (2013). Reprinted with the author's permission.

Figure 3

Object preference testing for ORM. (A) Total exploration for the holder and tin for individual animals during a 10 min test for object preference. Preference testing was performed using the standard ORM paradigm described in the text with one alteration. In place of the typical ORM training session, the animals shown here were given one holder and one tin to explore for 10 min (instead of two identical objects). (B) Average exploration for the holder and tin for a 10 min session. As predicted the two objects are explored equally [paired t-test t(10) = 0.502, p = 0.627]. (C) Discrimination index (DI) for the holder compared to tin for a 10-min session. DI was calculated arbitrarily as if the holder was a novel object. There is no significant difference in the DI from zero [one-sample t-test t(10) = 0.582, p = 0.573].