The acoustic startle reflex as a tool for assessment of odor environment effects on affective states in laboratory mice.

Apart from self and conspecific odors, odors from other species also influence the affective states in laboratory mice (Mus musculus musculus) in their home cages and during experimental procedures, possibly inducing confusion and inconsistency in experimental data. Thus, it is important to detect the types of animal odors associated with housing, husbandry, and laboratory practice that can arouse different types of affective changes in mice. Here, we aimed to test the effectiveness of the acoustic startle reflex (ASR) in detecting changes in the affective states of laboratory mice due to animal-derived-odor as it has a non-zero baseline, and can be enhanced or attenuated by positive or negative affective shifts, respectively. We used ASR to examine the affective changes in mice that were induced by bedding odors and an alarm pheromone. The odor of bedding obtained from the mice' home cages significantly attenuated the ASR, suggesting positive affective shifts in the test mice, whereas that from bedding obtained from rat cages significantly enhanced the ASR, suggesting negative affective shifts. No significant changes in ASR were observed in mice presented with the odor of bedding obtained from cages of unfamiliar conspecifics. In contrast, there was significant ASR enhancement in mice exposed to volatile components of alarm pheromones trapped in water, suggesting negative affective shifts. Thus, our findings show that ASR may be a valuable tool in assessing the effects of odors on the affective states in laboratory mice.

Rodent models of depression: forced swimming and tail suspension behavioral despair tests in rats and mice.

Rodents forced to swim in a narrow space from which there is no escape will, after an initial period of vigorous activity, adopt a characteristic immobile posture, making only those movements necessary to keep their heads above the water. It was hypothesized that immobility reflected the animals' having learned that escape was impossible and their having given up hope. Immobility was therefore given the name "behavioral despair". Immobility was subsequently found to be reduced by a wide range of clinically active antidepressant drugs. This simple behavioral procedure has since become a useful test for screening novel antidepressants in rats and is presented in this unit. An equivalent procedure in the mouse is also described along with a "dry" version of the test where immobility is induced simply by suspending the mouse by the tail.