title: The lateral parabrachial nucleus is actively involved in the acquisition of fear memory in mice.
abstract: BACKGROUND
  Pavlovian fear conditioning is a form of learning accomplished by associating a conditioned stimulus (CS) and an unconditioned stimulus (US). While CS-US associations are generally thought to occur in the amygdala, the pathway mediating US signal processing has only been partially identified. The external part of the pontine lateral parabrachial nucleus (elPB) is well situated for providing US nociceptive information to the central amygdala (CeA), which was recently revealed to play a primary role in fear acquisition. Therefore, we manipulated the elPB activity to examine its role in the regulation of fear learning.
  
  
  RESULTS
  First, we transiently inactivate the elPB during the acquisition of fear memory. Mice received bilateral elPB injections of the GABAA agonist muscimol (MUS) or phosphate-buffered saline (drug control), with bilateral misplacement of MUS defined as a placement control group. After the injection, mice were conditioned with a pure tone and foot-shock. On a memory retrieval test on day 2, the freezing ratio was significantly lower in the MUS group compared with that in the drug control or placement control groups. A second retrieval test using a pip tone on day 4 following de novo training on day 3, resulted in significant freezing with no group differences, indicating integrity of fear learning and a temporary limited effect of MUS. Next, we examined whether selectively activating the elPB-CeC pathway is sufficient to induce fear learning when paired with CS. Mice with channelrhodopsin2 (ChR2) expressed in the elPB received a pure tone (CS) in association with optical stimulation in the CeA (CS-LED paired group). On the retrieval test, CS-LED paired mice exhibited significantly higher freezing ratios evoked by CS presentation compared with both control mice receiving optical stimulation immediately after being placed in the shock chamber and exposed to the CS much later (immediate shock group) and those expressing only GFP (GFP control group). These results suggest that selective stimulation of the elPB-CeC pathway substitutes for the US to induce fear learning.
  
  
  CONCLUSIONS
  The elPB activity is necessary and sufficient to trigger fear learning, likely as a part of the pathway transmitting aversive signals to the CeA.
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. mas_sato@jikei.ac.jp.|Department of Anesthesiology, Jikei University School of Medicine, Tokyo, 105-8461, Japan. mas_sato@jikei.ac.jp.
authors.forename: Masaru
authors.initials: M
authors.lastname: Sato
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. m-ito@jikei.ac.jp.|Department of Anesthesiology, Jikei University School of Medicine, Tokyo, 105-8461, Japan. m-ito@jikei.ac.jp.
authors.forename: Mariko
authors.initials: M
authors.lastname: Ito
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. m.nagase@jikei.ac.jp.
authors.forename: Masashi
authors.initials: M
authors.lastname: Nagase
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. sugimurayae@jikei.ac.jp.
authors.forename: Yae K
authors.initials: YK
authors.lastname: Sugimura
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. yukaritakahashi@jikei.ac.jp.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. awatabe@jikei.ac.jp.|Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi, Saitama, 332-0012, Japan. awatabe@jikei.ac.jp.|Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan. awatabe@jikei.ac.jp.
authors.forename: Ayako M
authors.initials: AM
authors.lastname: Watabe
authors.affiliation: Department of Neuroscience, Jikei University School of Medicine, Tokyo, 105-8461, Japan. fusao@jikei.ac.jp.|Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan. fusao@jikei.ac.jp.
authors.forename: Fusao
authors.initials: F
authors.lastname: Kato
mesh_terms: D000818:Animals; D003213:Conditioning, Psychological / Q000187:drug effects; D004597:Electroshock; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005239:Fear / Q000502:physiology*; D007103:Immobilization; D007267:Injections; D008568:Memory / Q000502:physiology*; D051379:Mice; D009118:Muscimol / Q000494:pharmacology; D065823:Parabrachial Nucleus / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D013997:Time Factors; D014275:Trigeminal Caudal Nucleus / Q000502:physiology
chemical_list: D009118:Muscimol