title: Potentiation of amygdaloid and hippocampal auditory-evoked potentials in a discriminatory fear-conditioning task in mice as a function of tone pattern and context.
abstract: According to the local memory storage hypothesis, information about the tone-shock association in an auditory fear-conditioning paradigm is stored in synapses within the lateral amygdala. Thus, fear-conditioning-induced potentiation of auditory-evoked potentials in response to a conditioned stimulus (CS+, a series of short lasting tones; patterned tone) has been interpreted as an in vivo correlate of amygdaloid synaptic plasticity. Here, we re-examine the specificity of potentiation of auditory-evoked potentials in terms of (i) local confinement to the lateral amygdala, (ii) parameters of CS+ and (iii) influence of context, using a discriminatory fear-conditioning paradigm. Adult male C57BL/6J mice were implanted with recording electrodes aimed at the lateral amygdala, the CA1 region of the hippocampus and the neck muscles for simultaneous recordings of auditory-evoked potentials and startle responses. In a neutral context, auditory-evoked potentials within lateral amygdala and CA1 as well as startle and freezing responses to the CS+ were significantly potentiated following conditioning, as compared with pre-conditioning values and responses to a neutral stimulus (CSn; tone of different frequency). Potentiation was only evident if CS+ was presented as a uniform series but not if presented mixed with CSn. Accordingly, mice failed to show intensified freezing to a patterned tone if a single lasting tone of the same frequency served as CS+. Both CA1 and lateral amygdala auditory-evoked potentials were potentiated in response to CSn if presented in the conditioning context. These findings demonstrate that (i) potentiation of auditory-evoked potentials is not restricted to the lateral amygdala, (ii) both tone frequency and pattern of tone presentation are essential for proper CS+ recognition and (iii) contextual memory leads to a general potentiation of auditory-evoked potentials.
authors.affiliation: Zentrum für Molekulare Neurobiologie, Universität Hamburg, Hamburg, Germany.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Tang
authors.forename: Stefanie
authors.initials: S
authors.lastname: Wagner
authors.forename: Melitta
authors.initials: M
authors.lastname: Schachner
authors.forename: Alexander
authors.initials: A
authors.lastname: Dityatev
authors.forename: Carsten T
authors.initials: CT
authors.lastname: Wotjak
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000679:Amygdala / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D003213:Conditioning, Psychological / Q000502:physiology*; D004192:Discrimination, Psychological; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005239:Fear; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL