Serotonin Syndrome and Seizures. The GABA and Glutamate Connection.

Kia ora team, Serotonin syndrome is a life-threatening toxidrome caused by excess serotonin activity in the central nervous system. This video explains exactly how it causes seizures, using the glutamate/GABA circuit as the foundation.

Serotonin syndrome occurs when excess serotonin accumulates in the CNS, most commonly from drug combinations such as SSRIs with tramadol or fentanyl, or MDMA toxicity. The seizures it produces result from a simultaneous failure of excitatory and inhibitory neurotransmitter balance across multiple brain regions.
The normal circuit:
Glutamatergic neurons are the brain's primary excitatory neurons. When stimulated — by serotonin (via 5-HT2A receptors), acetylcholine, noradrenaline, or other glutamatergic neurons — they release glutamate from their axon terminals onto a target neuron. Simultaneously, an axon collateral stimulates a nearby GABAergic interneuron to release GABA onto the same target neuron. Glutamate says fire; GABA says not too much. This feedforward inhibition keeps neuronal activity controlled and proportional. The glutamatergic neuron is the accelerator, glutamate is the petrol, the GABAergic interneuron is the brake, and GABA is the brake fluid.
What goes wrong in serotonin syndrome:
Excess serotonin floods 5-HT2A receptors on glutamatergic neurons, causing a massive glutamate flood — the accelerator is floored. Simultaneously, serotonin binds to 5-HT1A receptors on GABAergic interneurons, inhibiting them and reducing GABA release — the foot comes off the brake. The sheer volume of glutamate initially overrides this inhibition and some GABA is still released, but eventually the GABAergic interneuron becomes exhausted — we are out of brake fluid. Hyperthermia, generated by uncontrolled neuronal firing and hypothalamic thermostat disruption, then directly impairs GABA-A receptor function — the brake callipers melt. Even the small amount of GABA remaining cannot bind effectively.
The result is four simultaneous failures:

Accelerator floored — glutamate flood via 5-HT2A
Foot off the brake — GABA release reduced via 5-HT1A
Out of brake fluid — GABAergic interneuron exhausted
Brake callipers melted — hyperthermia impairs GABA-A receptors

Where this occurs:
This circuit failure occurs simultaneously across multiple brain regions, each producing specific clinical signs — seizures (cortex), confusion and excitotoxic damage (hippocampus), clonus and hyperreflexia (spinal cord), tachycardia and hypertension (brainstem), hyperthermia (hypothalamus), agitation and terror (limbic system/amygdala), and tremor and rigidity (basal ganglia).

Видео Serotonin Syndrome and Seizures. The GABA and Glutamate Connection. канала Ben Reynolds