Fishing for the mechanisms causing febrile seizures: employing a novel model to uncover the physiological generators of seizures with fever

Thermoregulation in epilepsy

Several aspects of thermoregulation play a role in epilepsy. Circuitries involved in thermoregulation are affected by seizures and epilepsy, hyperthermia may be both cause and result of seizures, and hypothermia may prevent or abort seizures. Autonomic manifestations of seizures including thermoregulatory disturbances are common in a variety of clinical epilepsy syndromes. Experimental hyperthermia has been studied extensively, predominantly to investigate febrile seizures of childhood. In particular prolonged or complex febrile seizures have been associated with the later development of epilepsy in adulthood and the pathophysiology of how febrile seizures cause epilepsy is of tremendous interest. Febrile seizures represent an opportunity to potentially intervene early in life in susceptible individuals and affect epileptogenesis. The pathophysiologic underpinnings of how hyperthermia induces seizures and how this in turn results in epilepsy are controversial, but likely involve multiple factors. Both glutamatergic and GABAergic neurotransmission is affected, and numerous mutations in genes encoding ion channels have been identified. Cytokines such as interleukin-1β have been implicated in febrile seizures as well as susceptibility to provoked seizures later in life. Hyperthermia is a common feature of generalized convulsive status epilepticus, but may also be seen with nonconvulsive seizures, indicating involvement of thermoregulatory centers.

Pharmacological characterization of an antisense knockdown zebrafish model of Dravet syndrome: inhibition of epileptic seizures by the serotonin agonist fenfluramine

Dravet syndrome (DS) is one of the most pharmacoresistant and devastating forms of childhood epilepsy syndromes. Distinct de novo mutations in the SCN1A gene are responsible for over 80% of DS cases. While DS is largely resistant to treatment with existing anti-epileptic drugs, promising results have been obtained in clinical trials with human patients treated with the serotonin agonist fenfluramine as an add-on therapeutic. We developed a zebrafish model of DS using morpholino antisense oligomers (MOs) targeting scn1Lab, the zebrafish ortholog of SCN1A. Zebrafish larvae with an antisense knockdown of scn1Lab (scn1Lab morphants) were characterized by automated behavioral tracking and high-resolution video imaging, in addition to measuring brain activity through local field potential recordings. Our findings reveal that scn1Lab morphants display hyperactivity, convulsive seizure-like behavior, loss of posture, repetitive jerking and a myoclonic seizure-like pattern. The occurrence of spontaneous seizures was confirmed by local field potential recordings of the forebrain, measuring epileptiform discharges. Furthermore, we show that these larvae are remarkably sensitive to hyperthermia, similar to what has been described for mouse models of DS, as well as for human DS patients. Pharmacological evaluation revealed that sodium valproate and fenfluramine significantly reduce epileptiform discharges in scn1Lab morphants. Our findings for this zebrafish model of DS are in accordance with clinical data for human DS patients. To our knowledge, this is the first study demonstrating effective seizure inhibition of fenfluramine in an animal model of Dravet syndrome. Moreover, these results provide a basis for identifying novel analogs with improved activity and significantly milder or no side effects.