Relationships of open-field behaviour with anxiety in the elevated zero-maze test: Focus on freezing and grooming

Abstract

The National Institutes of\rHealth Genetically Heterogeneous Rat Stock (NIH-HS) is a unique tool for genetic\rstudies of complex traits due to its high genetic heterogeneity and to its high\rlevel of genetic recombinants accumulated along many outbreeding generations.\rIn the present study, 90 NIH-HS male rats were tested for anxiety/fearfulness\rin the elevated zero-maze and in the open-field test in order to investigate\rthe associations among defensive responses from both tests and, in particular,\rthose among open- field self-grooming and freezing. These associations were\revaluated by means of a correlational-factorial approach and an analysis of differences\rbetween sub- groups displaying extreme scores in representative variables. The\rfinal factor analysis revealed a first factor with high loadings of all\rvariables from the zero-maze (“Maze\rtimidity/conflict” factor), and a second (independent) factor dominated\rby open-field crossings (-0.74), rearings (-0.62) and freezing (0.65), with\rlower loadings of open-field grooming (-0.39) and stretched attend postures, as\rwell as of entries and time (loadings of -0.32 to -0.25) in the open sections\rof the zero-maze (“Open Behavior\rinhibition/ desinhibition” factor), suggesting that open-field self-grooming\ris a response associated to activity, in the present study, rather than to\rinhibition. Furthermore, the finding that grooming in the OF loaded negatively\rin a second factor supports a\rrelationship between grooming and dearousal. Present results, thus, are in\raccordance with the usefulness of these tests for the purposes they are\rcommonly employed and add new evidence supporting their concurrent validity, as\rindicated by the relationships observed among measures from both tests.