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Abstract
Behavioral categories were measured in rats left on an elevated plus-maze for 5 min,
in addition to the traditional measures. Four independent factors emerged from a factor
analysis. The variables that loaded highly and positively on Factor 1, seemingly related
with anxiety, were: number of entries onto open arms, time spent on open arms, percentage
of open/total arm entries, percentage of time on open arms, scanning over the edge
of an open arm, and open arm end-exploring. The time spent on enclosed arms loaded
highly, but negatively on the same factor. Risk-assessment from an enclosed arm also
loaded negatively on Factor 1. Number of enclosed arm entries, total number of arm
entries and rearing loaded highly on Factor 2, probably related to motor activity.
However, the total number of entries also loaded on Factor 1, being thus a mixed index.
Similarly, the number of open arm entries loaded on both Factors 1 and 2. As expected,
the variables having high loads on Factor 1 were changed to one direction by administration
of two anxiolytics (nitrazepam and midazolam) and to the opposite direction by two
anxiogenic drugs (pentylenetetrazol and FG 7142). Such pattern of drug effects was
not observed with the remaining variables.