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, 90 (4), 753-7

Low Dose MK-801 Reduces Social Investigation in Mice

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Low Dose MK-801 Reduces Social Investigation in Mice

Hong Zou et al. Pharmacol Biochem Behav.

Abstract

To characterize MK-801's effect on social behavior in mice, we examined adult male ICR mice for interaction with companion mice (juvenile male). Test mice were injected with either saline or MK-801 (0.1 mg/kg), and were tested 30 min later for their social behavior during a 5-min session. A second encounter took place 30 min later, with either a familiar companion mouse (the same as in the initial encounter) or a novel mouse. In saline controls, second encounter with a familiar companion mouse showed reduced social investigative behaviors (anogenital sniffing and staying together), indicating habituation toward a familiar mouse. Second encounter with a novel companion mouse did not show habituation in social investigative behaviors. Pretreatment with MK-801 reduced anogenital sniffing during the first encounter. At the second encounter, these mice displayed non-discriminative habituation of social investigative behaviors, with reduced anogenital sniffing and staying together, regardless of whether the companion mouse was a familiar or a novel one. These results indicate that MK-801 affected exploratory activities of mice, resulting in both reduced social investigative behaviors during first encounter with a companion mouse, and diminished discriminative capacities for a familiar vs. a novel companion mouse during subsequent encounter.

Figures

Figure 1
Figure 1
First-encounter social investigative behaviors in mice and the impact of MK-801. Test mice (adult male ICR) were placed in the testing arena to acclimate for 15 min, followed by i.p. injection of either saline or MK-801 (0.1 mg/kg), and placed in home cage for 30 min. First encounter began when a test mouse and a companion mouse (juvenile male ICR) were placed into the test arena at the same time. Animals were allowed to move and interact freely, and were videotaped for 5 min. The video was analyzed offline for various behaviors of the test mouse only. Data are shown as mean ± SEM (n = 12 – 13). Open boxes: saline-injected control mice. Closed boxes: MK-801-injected mice. *, significant difference (p < 0.05) between MK-801 mice and saline controls (Student's un-paired t-test). Top row: individual-oriented behaviors; bottom row: social behaviors.
Figure 2
Figure 2
Second-encounter social investigative behaviors and the impact of MK-801. After the first-encounter social interaction described in Figure 1, mice were returned to their home cage for 30 min. Second-encounter testing began when a test mouse was placed in the same testing arena as before, and a companion mouse was also placed in the arena at the same time. The companion mouse was either the same as in the first encounter (“familiar”), or different (“novel”). Animals were allowed to move and interact freely, and were videotaped for 5 min. The video was analyzed offline for various animal behaviors of the test mouse only. Data are shown as mean ± SEM (n = 12 – 13). Open bars: first-encounter behaviors. Closed bars: second-encounter behaviors with a familiar companion mouse. Hatched bars: second-encounter behaviors with a novel companion mouse. *, significant difference (p < 0.05) between the first- and the second-encounter behaviors (Wilcoxon test). Top row: individual-oriented behaviors; bottom row: social behaviors.

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