Rj. Rodgers et al., PLUS-MAZE RETEST PROFILE IN MICE - IMPORTANCE OF INITIAL-STAGES OF TRIAL-1 AND RESPONSE TO POSTTRIAL CHOLINERGIC RECEPTOR BLOCKADE, Pharmacology, biochemistry and behavior, 54(1), 1996, pp. 41-50
Recent research has shown that a single undrugged prior experience of
the elevated plus-maze produces significant behavioural changes upon 2
4-h retest in rats and mice. Typically, when reexposed to the maze, an
imals display an increased avoidance of the open arms and a correspond
ing preference for the enclosed sections of the apparatus. Using ethol
ogical analyses, the present series of experiments sought to further c
haracterize this phenomenon in mice and to determine whether or not it
involves cholinergic receptor mechanisms. Results confirmed that beha
viour during Trial 2 is markedly different to that seen on initial exp
osure, and that such changes are independent of the duration of Trial
1 (2 vs. 5 min). Retest behavioural changes included reduced entry lat
encies, reduced open arm entries, less time on the open arms and centr
e platform, lower levels of exploratory head-dipping, and increased en
tries into and time spent in the closed arms. The importance to the re
test phenomenon of the first few minutes of initial exposure was furth
er suggested by min-by-min analyses of the behaviour of animals naive
to the maze. Results showed that behaviour during the first min is cha
racterized by high levels of risk assessment from the centre platform
and relatively low, but equal, levels of open- and closed-arm explorat
ion. From min 2 onwards, however, behaviour showed a marked change wit
h increasing open arm/centre platform avoidance, increasing closed-arm
preference, and decreasing levels of risk assessment and exploratory
head-dipping. Thus, it would appear that this within-session aversive
learning transfers between sessions to account for behavioural profile
s on retest. Irrespective of the duration of Trial 1 (2 or 5 min), pos
ttrial administration of the muscarinic antagonist, scopolamine (0.1-1
.0 mg/kg), failed to significantly alter the behavioural changes seen
between trials. Data are discussed in relation to the apparent sensiti
zation of fear produced by plus-maze exposure, its possible relation t
o phobia acquisition, and the need for further research on underlying
mechanisms.