Members of the fibroblast growth factor (FGF) family are involved in a variety of cellular processes. In the nervous system, they affect the differentiation and migration of neurons, the formation and maturation of synapses, and the repair of neuronal circuits following insults. Because of the varied yet critical functions of FGF ligands, their availability and activity must be tightly regulated for the nervous system, as well as other tissues, to properly develop and function in adulthood. In this regard, FGF binding proteins (FGFBPs) have emerged as strong candidates for modulating the actions of secreted FGFs in neural and non-neural tissues. Here, we will review the roles of FGFBPs in the peripheral and central nervous systems.

Familiarity is conveyed by social cues and determines behaviors toward conspecifics. Here, we characterize a novel assay for social behaviors in mice-contacts with anesthetized conspecific-which eliminates reciprocal interactions, including intermale aggression and shows behaviors that are independent of the demonstrator's activity. During the initial 10 minutes (phase-1), the wild-type (WT) subjects contacted the anesthetized conspecifics vigorously regardless of familiarity. During the subsequent 80 minutes (phase-2), however, they contacted more with familiar than unfamiliar conspecifics. We then applied this test to highly aggressive mice with a hippocampal CA3-restricted knockout (KO) of brain-derived neurotrophic factor (BDNF), in which aggression may mask other social behaviors. The KO mice showed less preference for contacting familiar conspecifics than did WT mice during phase-2 but no differences during phase-1. Among nonsocial behaviors, WT mice also spent less time eating in the presence of familiar than with unfamiliar conspecifics, which was not seen in KO mice. In addition, KO mice exhibited reduced pain sensitization. Altogether, these findings suggest that CA3-specific deletion of BDNF results in deficits in circuits that process social cues from familiar conspecifics as well as pain and may underlie empathy-like behaviors.

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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.