Potentiated amygdaloid auditory-evoked potentials and freezing behavior after fear conditioning in mice.

Elucidation of cellular and molecular mechanisms underlying fear-related memory would greatly benefit from the possibility of combined behavioral and electrophysiological recordings in genetically modified mice. As a first step to this goal, we implanted adult C57BL/6J mice with recording electrodes aimed at the basolateral amygdaloid complex and trained them in an auditory fear conditioning paradigm. After conditioning, animals with paired tone and footshock presentation showed not only intensified freezing behavior lasting for 2 days, but also increases, lasting 4 days, in slope and amplitude of the most negative component of auditory-evoked potentials triggered by the conditioned stimulus. These effects could not be observed in animals with unpaired tone and footshock presentation. Thus, our data show that a long-lasting association of a former neutral tone with an aversive situation is accompanied by a long-lasting increase of auditory-evoked potentials in freely moving mice. However, extinction of the potentiation of auditory-evoked potentials and freezing behavior followed different time courses, thus making a direct relationship between these responses unlikely.