🎯 Nerve Growth Factor Pain Sensitization Mechanism Simulator

Tissue Injury Triggers an Inflammatory Cascade

Damaged cells and immune cells flood the wound with signaling molecules.

• 12+: Mediators released (cytokines, prostaglandins, NGF)
• Minutes: Mast cell response (after injury onset)
• 4: NGF source cells (fibroblasts, keratinocytes, immune cells)
• ↓ acidic: Local pH shift (sensitizes nerve endings)

Injury triggers a chemical alarm

Torn or infected tissue releases danger signals fast.

Mast cells and macrophages arrive

Immune cells amplify the response with more mediators.

NGF joins the inflammatory soup

Fibroblasts and keratinocytes start producing extra NGF.

NGF Concentration Rises Around Nerve Endings

Local NGF levels climb well above baseline near injured tissue.

• 10–50×: NGF increase (above healthy tissue baseline)
• ~mm: Diffusion radius (around injury site)
• Arthritis, cystitis: Detected in (chronic pain conditions)
• Hours: Half-life (sustained by ongoing inflammation)

NGF diffuses toward nociceptors

Molecules drift from inflamed tissue to nerve terminals.

Concentration tracks inflammation severity

Worse inflammation means more NGF reaching nerves.

Chronic conditions sustain the surge

Persistent inflammation keeps NGF elevated for weeks.

NGF Binds and Activates TrkA Receptors

TrkA on nociceptor terminals recognizes NGF and switches on.

• TrkA: Receptor (tyrosine kinase receptor)
• p75NTR: Co-receptor (modulates binding affinity)
• Dimerization: Activation trigger (auto-phosphorylation cascade)
• Seconds: Response time (to minutes for full activation)

NGF docks onto TrkA

Binding causes two receptors to pair up.

Kinase domains cross-phosphorylate

Paired receptors activate their internal signaling tails.

Downstream cascades switch on

MAPK and PI3K pathways begin propagating the signal.

Signaling Travels to the Nucleus and Rewrites Gene Expression

Activated TrkA signals retrogradely, boosting pain-channel gene transcription.

• Retrograde axonal: Transport route (endosome to soma)
• NaV1.8: Key channel (sodium channel upregulated)
• TRPV1: Key receptor (heat/capsaicin receptor upregulated)
• Hours–days: Onset (for new protein synthesis)

Signaling endosomes travel to soma

Active TrkA complexes ride the axon to the nucleus.

Transcription factors switch genes on

CREB and others boost channel gene expression.

New proteins reach the membrane

Newly made channels traffic back to nerve terminals.

Peripheral Sensitization Lowers the Pain Threshold

Extra channels make the nociceptor fire at weaker stimuli.

• ↓ 30–70%: Threshold shift (less stimulus needed to fire)
• Allodynia: Clinical term (pain from normally mild stimuli)
• Hyperalgesia: Related term (exaggerated pain response)
• Anti-NGF mAbs: Therapeutic target (tanezumab and similar drugs)

Channel density keeps rising

More NaV1.8 and TRPV1 sit on the membrane.

Firing threshold keeps falling

Light touch or warmth now triggers pain signals.

Chronic pain state consolidates

Sensitization can persist after the original injury heals.