Influence of the anteromedial thalamus on social defeat-associated contextual fear memory

• Published in: Behavioural brain research 2018-02, Vol.339, p.269-277
• Main Authors: Rangel, Miguel J., Baldo, Marcus Vinicius C., Canteras, Newton Sabino
• Format: Article
• Language: English
• Subjects: Animals; Anterior Thalamic Nuclei - physiology; Behavior, Animal - physiology; Conditioning (Psychology) - physiology; Conditioning, Classical - physiology; Contextual fear; Fear - physiology; Hypothalamus - physiology; Male; Memory - physiology; Mental Processes - physiology; Neural Pathways - physiology; Periaqueductal Gray - physiology; Rats, Wistar; Resident intruder paradigm; Social defeat; Thalamic nuclei
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/j.bbr.2017.10.038

•We investigated the role of the ventral anteromedial thalamic nucleus (AMv) in both unconditioned and contextual social fear responses.•AMv cytotoxic lesions did not change unconditioned fear responses but reduced contextual fear responses to the social threat.•AMv is in a position to convey social threat information to the hippocampal circuits involved in the processing of contextual fear memory.•The study supports a role for anterior thalamic paths in emotional learning to social threats. The ventral part of the anteromedial thalamic nucleus (AMv) is heavily targeted by the dorsal premammillary nucleus (PMd), which is the main hypothalamic site that is responsive to both predator and conspecific aggressor threats. This PMd-AMv pathway is likely involved in modulating memory processing, and previous findings from our group have shown that cytotoxic lesions or pharmacological inactivation of the AMv drastically reduced contextual fear responses to predator-associated environments. In the present study, we investigated the role of the AMv in both unconditioned (i.e., fear responses during social defeat) and contextual fear responses (i.e., during exposure to a social defeat-associated context). We addressed this question by placing N-methyl-d-aspartate (NMDA) lesions in the AMv and testing unconditioned fear responses during social defeat and contextual fear responses during exposure to a social defeat-associated context. Accordingly, bilateral AMv lesions did not change unconditioned responses, but decreased contextual conditioning related to social defeat. Notably, our bilateral AMv lesions also included, to a certain degree, the nucleus reuniens (RE), but single RE lesions did not affect innate or contextual fear responses. Overall, our results support the idea that the AMv works as a critical hub, receiving massive inputs from a hypothalamic site that is largely responsive to social threats and transferring social threat information to circuits involved in the processing of contextual fear memories.