NCAM deficiency in the mouse forebrain impairs innate and learned avoidance behaviours.

The neural cell adhesion molecule (NCAM) has been implicated in the development and plasticity of neural circuits and the control of hippocampus- and amygdala-dependent learning and behaviour. Previous studies in constitutive NCAM null mutants identified emotional behaviour deficits related to disturbances of hippocampal and amygdala functions. Here, we studied these behaviours in mice conditionally deficient in NCAM in the postmigratory forebrain neurons. We report deficits in both innate and learned avoidance behaviours, as observed in elevated plus maze and passive avoidance tasks. In contrast, general locomotor activity, trait anxiety or neophobia were unaffected by the mutation. Altered avoidance behaviour of the conditional NCAM mutants was associated with a deficit in serotonergic signalling, as indicated by their reduced responsiveness to (±)-8-hydroxy-2-(dipropylamino)-tetralin-induced hypothermia. Another serotonin-dependent behaviour, namely intermale aggression that is massively increased in constitutively NCAM-deficient mice, was not affected in the forebrain-specific mutants. Our data suggest that genetically or environmentally induced changes of NCAM expression in the late postnatal and mature forebrain determine avoidance behaviour and serotonin (5-HT)1A receptor signalling.

Environmental bias? Effects of housing conditions, laboratory environment and experimenter on behavioral tests.

Behavioral testing does not always yield similar results when replicated in different laboratories, and it usually remains unclear whether the variability in results is caused by different laboratory environments or different experimenters conducting the tests. In our study, we applied a systematic variation of housing conditions, laboratories and experimenters in order to test the influence of these variables on the outcome of behavioral tests. We wanted to know whether known effects of different housing conditions on behavior can be demonstrated regardless of the respective laboratory and experimenters. In this study, we compared the behavior of mice kept under enriched housing conditions with mice kept in unstructured cages regarding their exploratory, locomotor and anxiety-related behavior in the barrier test, in the open-field test and in the elevated plus-maze test. Experiments were conducted by six different persons in two different laboratories. In spite of an extensive protocol standardizing laboratory environment, animal maintenance and testing procedures, significant differences in absolute values between different laboratories as well as between different experimenters were noticed in the barrier test and in the elevated plus-maze test but not in the open-field test. However, with regard to the differences between enriched and unstructured housing conditions, overall consistent results were achieved by different experimenters in both laboratories. We conclude that the reliability of behavioral phenotyping is not challenged seriously by experimenter and laboratory environment as long as appropriate standardizations are met and suitable controls are involved.