Several secreted proteins facilitate the growth and guidance of sympathetic axons to their target organs during development. Here we show that IL-1β, a key regulator of inflammation in the immune system, inhibits axonal growth and branching from cultured sympathetic neurons at a stage in development when their axons are ramifying within their targets in vivo. IL-1β is synthesised in sympathetic ganglia and its targets at this stage, and IL-1β protein is detectable in the axons and perikarya of the innervating neurons. It acts directly on developing axons to inhibit their growth via NF-κB signalling. These findings show that IL-1β is a novel locally, and target-derived factor that can regulate the extent of sympathetic axon growth during the late embryonic and early postnatal period in developing rat sympathetic neurons.
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