Structure of rat behavior in hole-board: II) multivariate analysis of modifications induced by diazepam

In our previous study we suggested that multivariate analysis could improve hole-board test reliability providing a more useful tool to determine behavioral effects of anxiolytic drugs. To support this hypothesis, a multivariate analysis of rat behavior in hole-board, following administration of the reference anxiolytic drug diazepam, was carried out. Four groups, each composed of thirty male Wistar rats, were used: one saline and three diazepam injected (0.25, 0.5 and 2 mg/kg IP). Rat behavior was recorded for 10 min through a digital videocamera. Descriptive and multivariate analyses were carried out. In all groups, more than 80% of whole behavioral structure encompassed walking, climbing, rearing, immobile-sniffing, edge-sniff and head-dip. Moreover, modifications observed of a specific index, represented by edge-sniff/head-dip ratio, were correlated to diazepam-induced modifications of anxiety level. Cluster analysis showed that diazepam at 0.5 and 2 mg/kg induced important changes for [edge-sniff/head-dip] cluster. In addition, in all diazepam groups a [walking/climbing] cluster appeared. Path diagrams showed close relationships among different patterns both in saline and diazepam injected animals. Also, significant changes were detected following diazepam for transitions encompassing both general exploratory patterns (walking, climbing) and the specific ones (head-dip and edge-sniff). Adjusted residuals confirmed in all groups patterns relationships and, where present, significant behavioral associations. Results demonstrate that an anxiolytic activity can be revealed by head-dip/edge-sniff association weakening and by the addressing of behavioral structure toward general exploratory activity. Improvement of hole-board test reliability in behavioral study of anxiety, following multivariate analysis, is emphasized.