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 conditioning paradigm by a single exposure to a context (context 1) paired with an electric shock. Conditioned mice exhibited a strong fear response, indicated by increased freezing and low locomotor activity after subsequent re-exposure to context 1, which had been used for conditioning as well as in a novel context (context 2). The fear responses to contexts 1 or 2 required the temporal sequence of the conditioned (CS) and unconditioned (US) stimuli and did not differ significantly. The intensity of the fear response was maximal 24 h after conditioning, when long-term memory was fully established. The response to context 2 was interpreted as conditioned generalization, which was also observed in the elevated plus-maze representing an environment which differed in its spatial design significantly from contexts 1 and 2. Contextual discrimination of C57BL/6N mice was enhanced after extinction of the generalized 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 acquired 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.
Radulovic
J
J
Department of Molecular Neuroendocrinology, Max Planck Institute for Experimental Medicine, Goettingen, Germany. radulovic@mail.mpiem.gwdg.de
Kammermeier
J
J
Spiess
J
J
D000818:Animals; D003213:Conditioning, Psychological / Q000502:physiology*; D005108:Extinction, Psychological; D005239:Fear / Q000502:physiology*; D005793:Generalization, Psychological / Q000502:physiology*; D008297:Male; D008568:Memory / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D013045:Species Specificity; D013997:Time Factors