Research reportThe effects of different basal levels of anxiety on the behavioral shift analyzed in the central platform of the elevated plus maze

- Wistar and DA/Han rats were studied in EPM.
- The study was focused on rat activity in the central platform of the EPM.
- A complex structure of rat behavior in central platform was identified.
- Different basal levels of anxiety influence the behavioral architecture.
- Analysis of transition matrix allows the study of behavioral shift.

The aim of the present research was to study the effects of different basal levels of anxiety on the behavioral shift studied in the central platform of the elevated plus maze. To this purpose, quantitative and multivariate analyses, the latter based on transition matrix elaboration, were carried out on Wistar and on DA/Han rats the latter belonging to a strain characterized by different reactivity to anxiogenic stimuli. Wistar rats spent 74.11 ± 5.11 s in the central platform, whereas DA/Han significantly more: 127.08 ± 9.87. Per cent distributions evidenced a clear-cut difference in walking activities (46.25% in Wistar, 28.4% in DA/Han rats) and in the sniffing activities (45.82% in Wistar, 62.54% in DA/Han). Mean frequencies of each behavioral element showed in DA/Han strain a value significantly lower than in Wistar for central-platform entry, open arm-entry and closed-arm entry and a significant higher value for central- platform sniffing, open-arm sniffing and corner-rearing. Moreover, the ratio open-arm entry/open-arm sniffing and closed-arm entry/closed-arm-sniffing showed significant higher values in the Wistar strain. Finally, by means of hierarchical clustering analysis, strong differences between the two strains were observed in the behavioral architecture: a cascade-shaped dendrogram, branching from Walking activities, indicates that Wistar rat behavior is oriented to cross the central platform so to rapidly reach an arm; on the contrary, the dendrogram of DA/Han rats displays a behavior heavily oriented toward the permanence in the central platform.The results show that different basal levels of anxiety provoke significant differences in the behavioral shift studied in the central platform of the elevated plus maze. Such differences, evidenced by means of transition matrices elaboration, might represent the behavioral expression of anxiety-induced modifications of decision making process underlying behavioral shift activities.

Wistar and Dark Agouti (DA/Han) rats are two strains characterized by a different reactivity to anxiogenic stimuli. Such a different level of reactivity can be detected in terms of objective behavioral measurements in the central platform of the elevated plus maze test. Silhouettes on the left side of the image indicate the behavioral components included in the analysis. Dendrograms on the right side present the results obtained by means of hierarchical clustering analysis. A cascade-shaped dendrogram, branching from Walking activities, indicates that Wistar rat behavior is oriented to cross the central platform so to rapidly reach an arm; the dendrogram of DA/Han rats displays a behavior heavily oriented toward the permanence in the central platform.242