[Selection for the predisposition to catalepsy enhances depressive-like traits in mice]

Immobility reaction or catalepsy is a natural passive defensive (lurking) behavioral response to the appearance of a predator. Selection for high predisposition to catalepsy has been performed in a population of (CBA x (CBA x AKR)) backcrosses of the crossing between mouse lines sensitive and resistant to catalepsy (VBA and AKR, respectively). A rapid increase in the number of animals with catalepsy has been observed: from 23% in backcrosses to 71% in the S3 generation. Selection for catalepsy does not affect mouse anxiety in the open field and plus-maze tests. However, S8 and S9 mice are characterized by a decreased motor activity in the open-field test and an increased immobility in the forced swim and tail suspension tests, which is interpreted as an increase in "depressiveness." The results indicate that genetically determined catalepsy is related to depressive-like characteristics of defensive behavior.