The genetically inbred Balb/c mouse strain shows evidence of impaired sociability in a standard paradigm. For example, relative to 8-week-old male outbred Swiss-Webster mice, 8 week-old male Balb/c mice spend less time sniffing and in the vicinity of an enclosed 4 week-old male ICR stimulus mouse and, when allowed to interact freely with the stimulus mouse for five minutes, make fewer discrete episodes of social approach and show suppression of locomotor activity. We explored the effect of D-cycloserine (320mg/kg, intraperitoneally), a partial glycine agonist that binds to the obligatory co-agonist glycine binding site on the NMDA receptor, on the sociability of the Balb/c and Swiss-Webster mouse strains in a standard paradigm. The results show that treatment with D-cycloserine increased the locomotor activity of the Balb/c mouse strain in the presence of an enclosed social stimulus mouse and when these mice were allowed to interact freely with each other. Also, D-cycloserine increased the number of discrete episodes of social approach when Balb/c mice were allowed to interact freely with social stimulus mice. However, D-cycloserine had similar effects on measures of sociability in the Swiss-Webster mouse, raising the possibility that the positive effects on the sociability of the Balb/c mouse strain may be mediated by indirect effects on locomotion, arousal, and anxiety.
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