GENERALIZATION OF FEAR RESPONSES IN C57BL 6N MICE SUBJECTED TO ONE-TRIAL FOREGROUND CONTEXTUAL FEAR CONDITIONING/

C57BL/6N mice were trained in a foreground contextual fear conditionin g paradigm by a single exposure to a context (context 1) paired with a n electric shock. Conditioned mice exhibited a strong fear response, i ndicated by increased freezing and low locomotor activity after subseq uent re-exposure to context 1, which had been used for conditioning as well as in a novel context (context 2). The fear responses to context s 1 or 2 required the temporal sequence of the conditioned (CS) and un conditioned (US) stimuli and did not differ significantly. The intensi ty of the fear response was maximal 24 h after conditioning, when long -term memory was fully established. The response to context 2 was inte rpreted as conditioned generalization, which was also observed in the elevated plus-maze representing an environment which differed in its s patial design significantly from contexts 1 and 2. Contextual discrimi nation of C57BL/6N mice was enhanced after extinction of the generaliz ed fear. Strain studies employing C57BL/6J and Balb/c mice in addition to the C57BL/6N strain revealed that Balb/c and C57BL/6J mice acquire d significantly weaker conditioned fear and generalized significantly less than C57BL/6N mice. It was concluded that the intensities of the context-specific and generalized fear responses were interlinked in a strain-specific manner. (C) 1998 Elsevier Science B.V. All rights rese rved.