graph TD
    A["Tryptophan Dietary Intake"] -->|"substrate"| B["Gut Microbiome Metabolism"]
    B -->|"produces"| C["Indole-3-Propionic Acid"]
    C -->|"crosses BBB via MCT1/MCT2"| D["CNS Entry"]
    D -->|"ligand binding"| E["AHR Activation"]
    E -->|"transcriptional regulation"| F["IL10 Gene Expression"]
    E -->|"transcriptional regulation"| G["TGFB1 Gene Expression"]
    F -->|"anti-inflammatory"| H["Microglial M2 Polarization"]
    G -->|"immunosuppressive"| H
    H -->|"reduces"| I["Neuroinflammation"]
    I -->|"prevents"| J["Synaptic Loss"]
    I -->|"prevents"| K["Neuronal Death"]
    L["Dysbiosis"] -->|"reduces"| B
    M["Probiotic Therapy"] -->|"restores"| B
    N["AHR Agonists"] -->|"activates"| E
    O["Neuroprotection"]

    J -->|"maintains"| O
    K -->|"maintains"| O

    classDef mechanism fill:#4fc3f7,color:#0d0d1a
    classDef pathology fill:#ef5350,color:#0d0d1a
    classDef therapy fill:#81c784,color:#0d0d1a
    classDef outcome fill:#ffd54f,color:#0d0d1a
    classDef genetics fill:#ce93d8,color:#0d0d1a

    class A,C,D,E mechanism
    class L,I,J,K pathology
    class M,N therapy
    class O outcome
    class B,F,G,H genetics