RELATIONSHIP BETWEEN FOS PRODUCTION AND CLASSICAL FEAR CONDITIONING -EFFECTS OF NOVELTY, LATENT INHIBITION, AND UNCONDITIONED STIMULUS PREEXPOSURE

The relationship between FOS production in the sensory cortex and limb ic system and the ability of C57BL/6N mice to acquire context- and ton e-dependent freezing were investigated after fear conditioning, which was achieved by exposure of mice to context only or context and tone ( 10 kHz, 75 dB) as conditioned stimuli (Cs) paired with an electric foo tshock (0.7 mA, constant) as unconditioned stimulus (Us). The effect o f preexposure to Cs or Cs paired with Us on FOS production and learnin g was also tested. It was demonstrated that high simultaneous FOS prod uction in the parietal cortex, hippocampus, and amygdala paralleled th e ability of mice to acquire strong freezing responses to novel Cs, Af ter contextual preexposure (latent inhibition), FOS production could b e elicited in the central amygdala only by shock and in the basolatera l amygdala only by tone. Under these conditions, the ability of mice t o acquire contextual freezing was almost abolished, whereas tone-depen dent freezing was reduced. Lacking FOS production in the central amygd ala after preexposure to context followed by shock (Us preexposure eff ect) paralleled the inability of mice to acquire tone-dependent freezi ng, although the tone elicited FOS production in the basolateral amygd ala. On the basis of these findings it was concluded that synchronous Cs- and Us-induced FOS production in several defined forebrain areas w as accompanied with associative learning of novel stimuli, and that a subsequent low level of FOS production might have been responsible or indicative for delayed conditioning to those stimuli.