Behavioral phenotyping of oxytocin deficient mice exposed to acute shaker stress

M. Mach^1,2, M. Morris¹, M. Dubovicky², E. Ujhazy² and J.B. Lucot¹

¹Department of Pharmacology/Toxicology School of Medicine, Wright State University, Dayton,OH, USA
²Laboratory of Teratology Institute of Experimental Pharmacology, Slovak Academy of Sciences, Bratislava, Slovakia

When the targeted gene is not expressed in the brain, the behavioral phenotype of the mutant mice may reveal genetic mechanisms underlying normal behavior and may increase our knowledge of genetic factors in neuropsychiatric disorders. Reliable phenotyping methods are of great importance in understanding the influence of genetic or pharmacological interference on a complex organism. Therefore, it is necessary to develop behavioral tests that enable to obtain a differential, and thus a reliable image of the phenotype of an animal. Oxytocin (OT) is a stress-responsive hormone which has behavioral actions, including antidepressive, sedative and anxiolytic effects. Behavioral performance assessment was conducted after acute shaker stress in male and female OT knockout (OT -/-) and wild type (OT +/+). A standard battery of behavioral tests using Hamilton-Kinder measuring system was used including measuring anxiety (elevated plus maze), locomotor activity (open field test) and sensorimotor function (acoustic startle response and pre-pulse inhibition). Moreover, the plasma corticosterone level was established after the stress. Stress significantly impaired all measures observed in the open field test. However, the decrease in basic and fine movements in male OT -/- was significantly lower than in OT +/+ (p<0.001) and the total time spent in the periphery tended to be higher in OT -/- (p<0.09). The elevated plus maze showed a decrease in basic movements after stress with a greater decrement in OT -/- males. Stress also increased total time in the closed arms for both genders and genotypes. Acoustic startle response and pre-pulse inhibition were not altered by stress, genotype or gender. We conclude:

1. There is a gender specific role for OT in the behavioral response to stress.
2. OT attenuates the locomotor response to stress in males.

This work was funded by USA Department of Defense contract # DAMD 17-00-C-0020 and supported by the grant VEGA 2/5052/25 Bratislava, Slovakia.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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