Marble burying behavior is prevented by anxiolytics as well as by motorstimulants

Marble burying is used for characterizing potential anxiolytic drugs. Clinically used anxiolytics as diazepam reduce the number of marbles which are buried by an animal in a given time interval. We tested the effects of the anxiolytics diazepam (0.1–3mpk) and buspirone (1–10mpk) as well as the effects of the motorstimulants methamphetamine (0.1–3 mpk), cocaine (1–10mpk), MK–801 (0.003–0.3mpk) and phencyclidine (0.3–3mpk). Male NMRI mice (17–32g) received saline or drugs 0.5h before the test and were transferred into new cages, which were filled with sawdust of 5cm height. On top 24 glass marbles were placed. After 30min the number of buried marbles was counted. Both anxiolytics diazepam (ED₅₀=1.4mpk) and buspirone (ED₅₀=6.7mpk) reduced the number of buried marbles in a dose-related manner; all psychostimulants also reduced this number. The ED₅₀s were 0.03mpk for MK–801, 0.3mpk for methamphetamine and 1.1mpk for PCP and 2.5mpk for cocaine. At the highest dose tested all psychostimulants led to a nearly full blockade of burying. So far, compounds inducing hypolocomotion were considered as the only false positives. Here we demonstrate for the first time that psychostimulants also produce false positive effects by inducing hyperlocomotion. We conclude that marble burying is a model not only sensitive to anxiolytics, but also to a variety of compounds interfering with motor activity.