Trial 2 in the elevated plus-maze: a different form of fear?
A factor analysis of the scores from rats given two trials in the elevated plus-maze showed that four independent factors emerged. Measures of anxiolytic activity on trial 1 (number of open arm entries and time spent on open arms) loaded on factor 1, measures of anxiolytic activity on trial 2 loaded on factor 2, the measure of general activity (number of closed arm entries) on both trials loaded on factor 3, and a measure of decision time (time spent in central square) for both trials loaded on factor 4. The independence of trials 1 and 2 anxiety measures raises the possibility that the state of anxiety/fear on the second trial in the plus-maze is qualitatively different from that on trial 1. This difference is reflected in the loss of anxiolytic action of diazepam (2 mg/kg) on trial 2. However, this occurs only when the trials are short (5 min); when they are longer (10 min) diazepam retains anxiolytic efficacy. It is concluded that during a brief (5 min) trial in the plus-maze rats acquire a specific phobic anxiety, which is relatively resistant to benzodiazepines. With a longer exposure to the plus-maze this form of fear extinguishes.
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Psychopharmacology Research Unit, UMDS Division of Pharmacology, Guy's Hospital, London, UK.
Zangrossi
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Viana
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Graeff
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D000818:Animals; D001007:Anxiety / Q000523:psychology*; D003975:Diazepam / Q000008:administration & dosage / Q000494:pharmacology*; D005106:Exploratory Behavior / Q000187:drug effects; D005239:Fear / Q000187:drug effects*; D006234:Handling, Psychological; D008297:Male; D008960:Models, Psychological; D010698:Phobic Disorders / Q000523:psychology; D051381:Rats
D003975:Diazepam