Epileptogenesis is the gradual process through which a non-epileptic brain undergoes pathological changes that lead to the development of epilepsy. Epilepsy is a chronic neurological condition characterized by a predisposition to generate seizures, which are episodes of abnormal, hypersynchronous neuronal firing.
It involves the transformation of neuronal networks following an initial insult, such as trauma, infection, or prolonged seizures. This process is distinct from ictogenesis, which describes the mechanisms underlying the initiation of a seizure event.
Initiating events Epileptogenesis is typically triggered by an initial brain insult that disrupts normal neuronal networks and initiates a cascade of molecular and cellular events leading to epilepsy. A variety of conditions have been identified as initiating events, but their occurrence does not guarantee the development of epilepsy. Common initiating events include neurodegenerative diseases, traumatic brain injury (TBI), ischemic stroke, intracerebral hemorrhage, infections of the central nervous system (such as neurocysticercosis or encephalitis), brain tumors, and status epilepticus (a prolonged seizure or a series of seizures occurring in quick succession). The likelihood that an individual will develop epilepsy after an initiating event depends on multiple factors, including the type, location, and severity of the insult, the age at which the injury occurs, and genetic predisposition. Severe TBI involving intracranial bleeding carries a higher risk of subsequent epilepsy compared to milder forms of head trauma, and the risk of developing epilepsy following a stroke is higher in cases involving cortical involvement or hemorrhagic components.
Stages of epileptogenesis
Epileptogenesis typically involves three stages: an initial precipitating event, a seizure-free latent period, and the eventual onset of spontaneous recurrent seizures. These stages often overlap and vary depending on the type and severity of the initial injury.
Early pathophysiological events Epileptogenesis is initiated by a cascade of early pathological processes such as (a)excessive release of glutamate, leading to excitotoxic neuronal injury, (b)disruption of the blood–brain barrier, resulting in infiltration of serum proteins and immune cells, and (c)activation of neuroinflammatory pathways, particularly microglial activation and cytokine production.
Latent phase The latent phase of epileptogenesis refers to a clinically silent interval following the initial brain insult, during which no spontaneous seizures occur but extensive molecular, cellular, and network remodeling takes place. During this phase, pathological changes include synaptic reorganization, loss of inhibitory neurons, gliosis, neurogenesis, and altered gene expression and epigenetic modifications.
Chronic phase The chronic phase of epileptogenesis is marked by the clinical onset of epilepsy. At this stage, the brain has undergone sufficient pathological reorganization to sustain seizures without an external precipitant. Pathological changes may continue during the chronic phase.
Pathophysiology Key mechanisms implicated in epileptogenesis include neuroinflammation, disruption of the blood-brain barrier, aberrant synaptic reorganization such as mossy fiber sprouting, neuronal death, reactive gliosis, and altered neurogenesis. Brain regions that are highly sensitive to insults and can cause epileptogenesis include temporal lobe structures such as the hippocampus, the amygdala, and the piriform cortex. The precise sequence and interplay of pathological events remain incompletely understood. Biomarkers capable of predicting the development of epilepsy after an injury are under investigation, and no therapies have yet been proven to prevent the progression of epileptogenesis in clinical practice.
Glutamate receptor activation
Activation of glutamate receptors, including both ionotropic glutamate receptors (such as NMDA and AMPA receptors) and metabotropic glutamate receptors, is a major contributor to early epileptogenic processes. Injury-induced excessive release of glutamate results in overstimulation of these receptors, leading to excitotoxicity characterized by sustained neuronal depolarization and a sharp increase in intracellular calcium (Ca²⁺) concentrations.
Elevated intracellular Ca²⁺ levels activate signaling pathways involving kinases such as Src and Fyn, which are implicated in long-term modifications of neuronal excitability and network architecture. Persistent glutamate-mediated excitotoxicity can cause neuronal injury, cell death, and contribute to the disruption of normal synaptic balance. While excessive glutamatergic activity is prominent during the acute phase following brain injury, its role appears to diminish during the latent period of epileptogenesis, with other mechanisms, such as inflammatory and structural changes, becoming more predominant.
Epileptogenic insults induce long-lasting changes in the expression and function of neurotransmitter receptors and ion channels, contributing to network hyperexcitability. Alterations in inhibitory signaling are common, including the downregulation or subunit rearrangement of GABA A receptors, which weakens synaptic inhibition. Simultaneously, excitatory pathways are often enhanced, with upregulation and increased activation of glutamate receptors, particularly NMDA receptors, further promoting excitotoxicity and neuronal depolarization. In addition to changes in receptor subunit composition, a reduction in overall GABA levels and decreased sensitivity of GABA A receptors to the neurotransmitter have been observed, further weakening inhibitory control. Hyperexcitability also reflects an imbalance between increased glutamatergic excitation and diminished GABAergic inhibition, a characteristic feature of epileptic circuits.
Neuroinflammation Neuroinflammation is recognized as a critical contributor to the pathophysiology of epileptogenesis. Following a variety of brain insults, innate immune mechanisms are activated within the central nervous system, involving microglia, astrocytes, neurons, and vascular cells.
Among the molecular mediators implicated in this process are interleukin-1β (IL-1β), tumor necrosis factor (TNF), high mobility group box 1 (HMGB1), transforming growth factor-β (TGF-β), and prostaglandins. These factors alter neuronal excitability, glial function, and blood–brain barrier integrity through complex transcriptional and post-translational mechanisms. An important pathway is the activation of the interleukin-1 receptor (IL-1R) and Toll-like receptor 4 (TLR4) axis. IL-1β binds to IL-1R, while HMGB1 engages TLR4, both triggering inflammatory cascades that modulate synaptic function and lower seizure threshold.
If unresolved, neuroinflammation promotes neuronal hyperexcitability, seizure propagation, neuronal death, and maladaptive synaptic plasticity, thereby contributing to the transition from an initially injured brain to a chronically epileptic state. Inflammatory mediators measurable in the blood or detected by molecular imaging are being investigated as potential diagnostic, prognostic, and predictive biomarkers of epileptogenesis and pharmacoresistant epilepsy.
Blood–brain barrier disruption Disruption of the blood–brain barrier (BBB) is common consequence of brain insults such as stroke, traumatic brain injury, status epilepticus, brain tumors, and central nervous system infections, and represents a pivotal event in the pathogenesis of epileptogenesis. BBB disruption was shown to underlay epileptogenesis by several experimental models. Breakdown of the BBB is associated with the extravasation of serum proteins, immune cells, and inflammatory mediators into the brain parenchyma, contributing to neuroinflammation, oxidative stress, and ionic imbalances.
Among serum components, albumin is associated with epileptogenesis. Upon entering the brain, albumin activates transforming growth factor-β (TGF-β) signaling pathways in astrocytes, leading to disruption of potassium and glutamate homeostasis and promoting neuronal hyperexcitability. Further studies have confirmed that TGF-β signaling activation after BBB leakage promotes excitatory synaptogenesis and structural remodeling associated with epileptogenesis. Other blood-derived factors, such as iron released from hemoglobin after hemorrhage, may also exacerbate oxidative injury and contribute to epileptogenic processes.
Neuronal loss and gliosis Neuronal death is a pathological feature in the early stages of epileptogenesis, affecting inhibitory GABAergic interneurons. Loss of excitatory pyramidal neurons, especially within the hippocampus and neocortex, has been documented in both human and experimental models. The selective vulnerability and loss of interneurons disrupt inhibitory control within neural circuits, tipping the excitation–inhibition balance toward hyperexcitability. In models of temporal lobe epilepsy, neuronal loss is especially prominent in the hippocampus, including the CA1 region and the hilus of the dentate gyrus, both of which are critical for maintaining normal network stability.
Reactive gliosis develops, characterized by the proliferation and activation of astrocytes and microglia. Reactive astrocytes undergo morphological and functional changes that impair potassium and glutamate buffering, alter neurotransmitter homeostasis, and release proinflammatory cytokines. Activated microglia further contribute to the pro-inflammatory environment by releasing additional inflammatory mediators and promoting neuronal injury. Astrogliosis and microgliosis actively participate in circuit remodeling and the perpetuation of a hyperexcitable state.
Synaptic reorganization (mossy fiber sprouting) Following neuronal loss and gliosis, surviving neurons may undergo synaptic reorganization in an attempt to restore network connectivity. An example of such reorganization in temporal lobe epilepsy is mossy fiber sprouting (MFS), wherein dentate granule cell axons aberrantly project into the inner molecular layer of the dentate gyrus. This aberrant growth forms recurrent excitatory circuits among granule cells, potentially contributing to network hyperexcitability and the generation of spontaneous seizures. Factors promoting mossy fiber sprouting include the loss of target neurons in the hilus and CA3, activity-dependent release of growth factors such as brain-derived neurotrophic factor (BDNF), and downregulation of axonal guidance molecules like Sema3A.
Although MFS is a frequent histopathological finding in mesial temporal lobe epilepsy and various experimental models, its precise role remains controversial. Some studies have demonstrated robust mossy fiber sprouting in the absence of spontaneous seizures, while others have shown seizure activity without evident MFS. MFS is not considered strictly necessary nor sufficient for epileptogenesis. It has been proposed that mossy fiber sprouting may initially represent a compensatory or adaptive response to injury, aimed at restoring lost synaptic contacts, but may ultimately contribute to the emergence of aberrant excitatory networks. MFS remains an active area of investigation for its potential as a therapeutic target in epilepsy prevention and disease modification.
Altered neurogenesis