Age-related qualitative shift in emotional behaviour: Paradoxical findings after re-exposure of rats in the elevated-plus maze

Abstract

Several variables, including age, are known to influence anxiety. Previous exposure to the elevated-plus maze (EPM) is known to modify emotional behaviour as retesting in the EPM at a standard age of 3 months increases open-arm avoidance and attenuates the effects of anxiolytic drugs. This study analysed whether similar results are obtained when older animals are subjected to these experimental paradigms. Overall, increasing age was associated with more signs of anxiety. Additionally, we observed a paradoxical behaviour pattern in aged-subjects that were re-exposed to the EPM, with mid-aged and old rats failing to display open arm avoidance (OAA) in the second trial; this qualitative shift in emotional behaviour was not associated with decreased locomotion. An examination of how age influences responsiveness to anxiolytic drugs, with or without previous maze experience, was also conducted. Midazolam (0.5 and 1 mg/kg) proved anxiolytic in maize-naive young animals; in marked contrast, in older animals midazolam at 1 mg/kg resulted in sedation but not anxiolyis. One trial tolerance to midazolam was evident in animals of both ages that were subjected to a second EPM trial; the latter phenomenon was apparently accentuated in older animals as they do not show open arm avoidance upon re-exposure to the EPM. These data suggest that the age-associated 'resistance' to anxiolytic drugs might be related to a qualitative shift in emotional behaviour.

Lifelong environmental enrichment in rats: impact on emotional behavior, spatial memory vividness, and cholinergic neurons over the lifespan

“…In the plus-maze, our data suggest a decrease in anxiety-related behavior over aging, in agreement with previous studies (Pisarska et al 2000;Torras-Garcia et al 2005, but Boguszewski andZagrodzka 2002;Bessa et al 2005). As this decrease was not observed in middle-aged rats, it is probably not a phenomenon protracting over lifespan.…”

A hitchhiker's guide to behavioral analysis in laboratory rodents

“…In addition, the elevated plus maze yields data on locomotor activity, vertical activity and exploratory behavior and provides indices of risk assessment and decision making (Rodgers & Dalvi 1997). Recent studies have shown that age (Bessa et al 2005), familiarity with the experimenter (van Driel & Talling 2005) and the gradient of luminosity between open and closed arms (rather than the absolute illumination strength) (Pereira et al 2005) have an important influence on the outcome of the elevated plus maze test.…”

Elevated plus-maze performance of Fischer-344 rats as a function of age and of exposure to 56Fe particles

“…These factors include individual differences in overall anxiety levels (Ho et al, 2002), gender (Imhof et al, 1993), illumination levels (Garcia et al, 2005;Pereira et al, 2005), strain (Bert et al, 2001;Chaouloff et al, 1995;Ramos et al, 1997), and experience in the maze (Bessa et al, 2005;File, 1993;Gallagher and Pelleymounter, 1988). The specific factors that might have elicited the preference for the open arms of the maze in the younger rats in the present experiment cannot be determined.…”

“…Previous research has shown that there are consistent changes in the amount of time spent in the open arms of the maze as a function of age. As the age of the rats increases, there is a corresponding decrease in the amount of time spent exploring the open arms of the maze (Andrade et al, 2003;Baguszewski and Zagrodzka, 2002;Bessa et al, 2005;Imhof et al, 1993).…”