Behavioral and neurochemical changes following predatory stress in mice

This article had several objectives. First it aimed at investigating the an xiogenic-like behaviors elicited by unavoidable cat exposure and/or cat odo r across nine strains of mice (BALB/c, C57BL/6, OH, CBA, DBA/2, NMRI, NZB, SJL, Swiss) in a modified version of the free-exploration test. The second objective was to investigate possible neurochemical changes following cat e xposure in Swiss mice by measuring the turnover of dopamine (DA), noradrena line (NA) and serotonin (5-HT) in several brain re-ions known to be involve d in the modulation of emotional processes (hippocampus, hypothalamus and s triatum). Finally, the third objective was to examine the effects of anxiol ytic drug treatments on the anxiogenic responses elicited by a cat odor (i. e. a feces) in Swiss mice previously exposed to a cat using the free-explor ation test. Results from the strain comparison showed that mice could be di vided into three distinct groups: two non-reactive strains (NZB and SJL) wh ich were relatively insensitive to predatory exposure and/or odor; five int ermediate-reactive strains (Swiss, NMRI, CBA, C3H and BALB/c) which display ed clear anxiogenic-like responses only when exposed to both cat and, subse quently, to feces; and two high reactive strains (C57BL/6 and DBA/2) which showed anxiogenic-like reactions following cat exposure, regardless of the stimulus (clay or feces) present in the free-exploration cage. Neurochemica l data revealed that, while brain levels of NA, DA, 5-HT in cat exposed Swi ss mice were not significantly different from those of control animals, tur nover rates of these monoamines were increased in the hippocampus (NA and 5 -HT), hypothalamus and striatum (DA) after cat exposure. Results from pharm acological experiments indicated that repeated administration of the 5-HT r euptake inhibitor fluoxetine (5-20 mg/kg, twice a day, for 5 days) complete ly abolished avoidance of the cat feces in Swiss mice previously exposed to the predator. Neither acute nor repeated administration of the classical a nxiolytic diazepam was able to reduce avoidance behavior of the anxiogenic stimulus in the free-exploration test. Taken together, these findings indic ate that the exposure of mice to unavoidable predatory stimuli is associate d with behavioral and neurochemical changes consistent with increased anxie ty. (C) 2001 Elsevier Science Ltd. All rights reserved.