Structure of the mouse behaviour on the elevated plus-maze test of anxiety.

The elevated-plus maze is an animal model where the behavioural repertoire of rodents is used to detect effects on anxiety. However, the structure of behaviour has not been duly discerned. The objective was to perform descriptive, sequential and principal components analyses to discern the overall structure of the mouse behaviour on the elevated plus-maze test. Behaviour was videotaped and later analyzed. Behavioural elements were encoded from an ethological point of view, being employed an 8-pattern ethogram. Stretched attend posture (SAP) and head-dippings (Dip) were split into protected (pSAP, pDip) and unprotected (uSAP, uDip) behaviours. Markovian sequential analysis revealed that sniffing is the main pattern, pSAP and pDip are highly linked 'anxiety-related' responses, and uSAP is an 'approach-avoid conflict' response usually followed by either sniffing on an open arm or closed arm entry. Principal component analysis allowed obtaining four components: (i) anxiolysis-open arm entry, pSAP, pDip and uDip; open arm entry and uDip were positively loaded, in contrast to pSAP and pDip, which were oppositely related to them; (ii) motor activity-closed arm entry, sniffing, rearing, and total arm entries; (iii) approach-avoid conflict-uSAP and negatively loaded, closed arm return; and (iv) displacement-grooming and rearing. Results suggested that open arm entry, pSAP, pDip, and uDip are the best indicators of anxiety on the elevated plus-maze. Closed arm return and uSAP are independent anxiety-related patterns, reflecting an approach-avoid conflict dimension. Results should be taken into account if the effects of drugs or CNS manipulations on Swiss mouse behaviour on the elevated plus-maze are analyzed.