title: A role for the anteromedial thalamic nucleus in the acquisition of contextual fear memory to predatory threats.
abstract: Previous studies from our group have shown that cytotoxic lesions in the ventral portion of the anteromedial thalamic nucleus (AMv), one of the main targets of the hypothalamic predator-responsive circuit, strongly impairs contextual fear responses to an environment previously associated with a predator. The AMv is in a position to convey information to cortico-hippocampal-amygdalar circuits involved in the processing of fear memory. However, it remains to be determined whether the nucleus is involved in the acquisition or subsequent expression of contextual fear. In the present investigation, we addressed this question by inactivating the rat AMv with muscimol either prior to cat exposure or prior to exposure to the cat-related context. Accordingly, AMv pharmacological inactivation prior to cat exposure did not interfere with innate fear responses, but it drastically reduced contextual conditioning to the predator-associated environment. On the other hand, AMv inactivation prior to exposure to the environment associated with the predator threat did not affect contextual fear responses. The behavioral results were further supported by the demonstration that AMv inactivation prior to cat exposure also blocked the activation of sites critically involved in the expression of anti-predatory contextual defensive responses (i.e., the dorsal premammillary nucleus and the dorsolateral periaqueductal gray) in animals exposed to the predator-associated context. The AMv projections were also examined, and the results of this investigation outline important paths that can influence hippocampal circuitry and raise new ideas for anterior thalamic-hippocampal paths involved in emotional learning.
authors.affiliation: Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, Av. Lineu Prestes, 2415, São Paulo, SP, 05508-000, Brazil.
authors.forename: Miguel Antonio Xavier
authors.initials: MA
authors.lastname: de Lima
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, 05508-000, Brazil.
authors.forename: Marcus Vinicius C
authors.initials: MV
authors.lastname: Baldo
authors.affiliation: Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, Av. Lineu Prestes, 2415, São Paulo, SP, 05508-000, Brazil. newton@icb.usp.br.
authors.forename: Newton Sabino
authors.initials: NS
authors.lastname: Canteras
mesh_terms: D000818:Animals; D020643:Anterior Thalamic Nuclei / Q000187:drug effects / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects; D002415:Cats; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D058785:GABA-A Receptor Agonists / Q000008:administration & dosage; D007034:Hypothalamus, Posterior / Q000187:drug effects / Q000502:physiology; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D009118:Muscimol / Q000008:administration & dosage; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology; D011235:Predatory Behavior; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D058785:GABA-A Receptor Agonists; D016760:Proto-Oncogene Proteins c-fos; D009118:Muscimol
keywords: Anterior thalamic nuclei; Defensive behavior; Fear conditioning; Hippocampus; Predator threat