Beyond marbles buried: a comparative analysis of tests targeting restricted and repetitive behaviors in C57B6/J mouse strain

Restricted and repetitive behaviors (RRBs), referring to set of responses showed with high frequency and for unusually long periods, are defining features of autism and other psychiatric conditions. The study of RRBs in animal models plays an important role in elucidating the mechanisms underlying these conditions and in screening treatment response. Thus, the choice of reliable behavioral tests provides the foundation of such investigations.

One of the paradigms commonly used to analyze RRBs is the marble burying test (MBT) that allows to assess digging and burying behaviors showed by mice when they are introduced into a cage with marbles lined up on the surface of the bedding. The main outcome is the total number of marbles buried under the sawdust. However, it has not yet been established whether this parameter really reflects RRBs, or may be simply a proxy of digging behavior or anxiety-like response elicited by the presence of marbles.

In order to disentangle different behavioral responses underlying the marble burying behavior, the present study was aimed to: i) identify potential correlations between the number of marbles buried and behavioral responses showed by mice during the MBT and ii) perform a comparative analysis between MBT and other behavioral tasks targeting RRBs (i.e., hole board, grooming test and spontaneous alternation in Y-maze test) and anxiety-like behavior (i.e., Elevated Plus Maze) in adolescent C57B6J mice.

Our preliminary analyses revealed that the number of marbles buried did not correlate with anxiety-like behavior, whereas it was associated not only with digging in MBT, but also with number of head dipping in the Hole Board exploration and percentage of spontaneous alternation in Y-maze. These data indicate that the marble burying behavior is not simply a byproduct of digging behavior, and provides a useful tool to evaluate RRBs in murine models.