Nerve Growth Factor (NGF), a neurotrophin that is essential for the development, survival, and function of sensory and sympathetic neurons. In the context of chronic pain conditions like osteoarthritis, NGF is upregulated in inflamed and damaged tissues (e.g., synovium, intervertebral discs). It binds to its high-affinity receptor TrkA and the lower-affinity p75NTR on nociceptive (pain-sensing) neurons.