This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g., "glutamate_excitotoxicity#Excitotoxic Neuronal Death", the key conformance target). It models the conserved excitotoxic cascade shared across amyotrophic lateral sclerosis (impaired astrocytic glutamate clearance; the antiglutamate drug riluzole is a partial validation), the cyanobacterial-toxin disorders (BMAA acting at AMPA/kainate and NMDA/mGluR5 receptors in Guam ALS-PDC), methylmercury poisoning (NMDA-receptor-mediated injury), Huntington disease, and epilepsy-associated neuronal injury. It is intentionally distinct from the epilepsy_excitation_inhibition_imbalance module, which models hyper-synchronous network firing producing seizures rather than the receptor-overactivation calcium-overload cell-death cascade modeled here. Conforming nodes may be partial where excitotoxicity is one of several parallel injury mechanisms (e.g., the oxidative-stress-dominant methylmercury and BMAA mechanisms).
Excessive Glutamatergic Stimulation and Impaired Glutamate Clearance
trigger
The shared initiating condition is a pathological rise in glutamatergic receptor stimulation. This arises from impaired astrocytic glutamate clearance (loss of the EAAT2/GLT-1 transporter), increased presynaptic glutamate release, or exogenous excitotoxins — including BMAA, which additionally inhibits the cystine/glutamate antiporter (system xc-) to raise extracellular glutamate and deplete glutathione.
Downstream
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Glutamate Receptor Overactivation and Calcium Overload
Elevated glutamatergic stimulation overactivates ionotropic glutamate receptors and drives pathological calcium entry.
Glutamate Receptor Overactivation and Calcium Overload
central effector
Sustained overactivation of NMDA, AMPA, and kainate glutamate receptors opens cation channels and produces pathological intracellular calcium influx and overload. The calcium overload is the proximate injurious signal that couples excessive receptor activation to downstream organelle dysfunction and death. Motor neurons are selectively vulnerable owing to their calcium-permeable AMPA-receptor complement.
Downstream
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Mitochondrial Dysfunction and Oxidative Stress
Calcium overload disrupts mitochondrial function and generates reactive oxygen species.
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Excitotoxic Neuronal Death
Calcium overload activates calcium-dependent death effectors.
Mitochondrial Dysfunction and Oxidative Stress
amplifier
Calcium overload is taken up by mitochondria, impairing oxidative phosphorylation, collapsing membrane potential, and generating reactive oxygen species. Excitotoxins compound this directly: BMAA and methylmercury both induce neuronal oxidative stress. The resulting bioenergetic failure and ROS burden amplify the injury and lower the threshold for neuronal death.
Downstream
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Excitotoxic Neuronal Death
Bioenergetic failure and oxidative damage drive neuronal death.
Excitotoxic Neuronal Death
effector
The convergent endpoint is death of the selectively vulnerable neuronal population through calcium- and ROS-dependent effectors (calpains, nitric oxide synthase, mitochondrial permeability transition) producing apoptotic and necrotic neuronal loss. This is the key conformance target: disorders substitute their specific glutamatergic insult and vulnerable neurons while sharing this excitotoxic death.