Impaired social contacts with familiar anesthetized conspecific in CA3-restricted BDNF knockout mice

Familiarity is the vital characteristic conveyed by social cues to determine behaviors towards conspecific. Here we characterize social contacts to familiar vs unfamiliar male conspecific, anesthetized to eliminate inter-male aggression. During initial 10 min (phase-1), subjects contacted demonstrators vigorously regardless of familiarity. During subsequent 80 min (phase-2), however, they contacted more with familiar than unfamiliar conspecifics. Then, this test was applied on highly aggressive mice with hippocampal CA3-restricted BDNF knockout (KO), in which aggression may mask other behaviors. KO showed less preference to contacting familiar conspecific than wild type (WT) during phase-2 but no differences during phase-1. Among non-social behaviors, eating duration was shorter in the presence of familiar than unfamiliar conspecific in WT, but same in KO. Additionally, KO exhibited reduced pain sensitization. Altogether, these findings suggest that KO has deficits in circuits that process social cues from familiar conspecifics and pain and, possibly, underlie empathy-like behaviors.