Figure 4.

Pyridine analogs generate stress-related behaviors in mice. An open field exploration test is used to evaluate the innate fear reactions of mice. (A) The behavioral arena observed during nocturnal phase. The limits of the arena zone (black rectangle) and the central zone (red dashed rectangle) are shown. Mice are automatically tracked (yellow circle) in the presence of different tested cues deposited on a blotting paper (blue square). Scale bar, 5 cm in (A). (B) Representative tracking distances covered by the same mouse in the presence of a neutral cue (Water), pure mountain lion urine (Mt. Lion), a mix of pyrazines (Pyrazine mix; 2,6-DMP, 2-EDMP, 2,3,5-TMP; 1%), a mix of pyridines (Pyridine mix; 2,4-Lu, 3,4-Lu, 4-Pi; 1%) or 2,4-lutidine (2,4-Lu; 1%). (C–G) Stress-related behaviors are quantified according to the control session and displayed as indexes. Stress (red) or non-stress (blue) tendencies are displayed on graphics. The number of visits in the central zone of the arena (C), the total walking distance recorded during 5 min (D), the defecation (number of fecal pellets) (E), the risk assessment episodes (F) and the freezing behaviors (G) were quantified. Innate fear reactions were observed for the mountain lion urine, the mixes of pyrazines and pyridines and for the 2,4-lutidine. Seven adult male mice were used (C–G). Values are expressed as mean ± SEM; one-tailed paired t-test or w-test, ^*P < 0.05; ^**P < 0.01; ^***P < 0.001; ns, not significant.