Early susceptibility for epileptiform activity in malformed cortex

The collaboration of Francis Forster and Wilder Penfield in the management of a girl with 'reflex epilepsy'

In the era after World War II, Francis (Frank) Forster (1912-2006) became a preeminent American neurologist and epileptologist, with international prominence in the study of reflex epilepsy. Forster's interest in reflex epilepsy began with a chance observation of the condition, in 1946, in a four-year-old girl. When medical measures failed to control her somatosensory-evoked seizures, Forster recommended surgery, and then facilitated transfer to Canadian neurosurgeon Wilder Penfield (1891-1976) at the Montreal Neurological Institute. Forster traveled to Montreal for the child's surgery. The surgery on February 27, 1948, proved to be curative for the child, and Forster's interactions with Penfield and epileptologist Herbert Jasper (1906-1999) made a lasting impression. This study reviews the medical and surgical history of this case, which strongly influenced Forster's career.

Altered excitatory and inhibitory neocortical circuitry leads to increased convulsive severity after pentylenetetrazol injection in an animal model of schizencephaly, but not of microgyria

OBJECTIVE

Malformations of the polymicrogyria spectrum can be mimicked in rodents through neonatal transcranial focal cortical freeze lesions. The animals presenting the malformations present both altered synaptic events and epileptiform activity in the vicinity of the microgyrus, but the comprehension of their contribution to increased predisposition or severity of seizures require further studies.

METHODS

In order to investigate these issues, we induced both microgyria and schizencephaly in 57 mice and evaluated: their convulsive susceptibility and severity after pentyleneterazol (PTZ) treatment, the quantification of their symmetric and asymmetric synapses, the morphology of their dendritic arbors, and the content of modulators of synaptogenesis, such as SPARC, gephyrin and GAP-43 within the adjacent visual cortex.

RESULTS

Our results have shown that only schizencephalic animals present increased convulsive severity. Nevertheless, both microgyric and schizencephalic cortices present increased synapse number and dendritic complexity of layer IV and layer V-located neurons. Specifically, the microgyric cortex presented reduced inhibitory synapses, while the schizencephalic cortex presented increased excitatory synapses. This altered synapse number is correlated with decreased content of both the anti-synaptogenic factor SPARC and the inhibitory postsynaptic organizer gephyrin in both malformed groups. Besides, GAP-43 content and dendritic spines number are enhanced exclusively in schizencephalic cortices.

SIGNIFICANCE

In conclusion, our study supports the hypothesis that the sum of synaptic alterations drives to convulsive aggravation in animals with schizencephaly, but not microgyria after PTZ treatment. These findings reveal that different malformations of cortical development should trigger epilepsy via different mechanisms, requiring further studies for development of specific therapeutic interventions.

Epilepsy and EEG Abnormalities in Congenital Zika Syndrome

SUMMARY

The congenital Zika syndrome is a new entity of a group of etiologies that can lead to microcephaly and other brain damages during pregnancy, such as toxoplasmosis, rubeola, cytomegalovirus, and herpes simplex. The Zika virus crosses the placental barrier and, predominantly, affects neuronal progenitor cells. This disruptive process results in severe cortical developmental disorder, calcifications, cortical and subcortical atrophies, and malformations of the cerebellum, brain stem, and spinal cord. Children with congenital Zika syndrome have a set of clinical findings, such as cerebral palsy, dysphagia, orthopedic deformities, visual and auditory impairment, and, rarely, hydrocephalus. Because of the severity of brain lesions, epilepsy is a common finding and a frequent cause of increased morbidity. The prevalence of epilepsy in different series of patients ranges from 37.7% to 71.4%. The aim of this study is to review the studies published so far regarding epilepsy and the EEG pattern in series of patients with congenital Zika syndrome.

Effect of Memantine on Pentylenetetrazol-induced Seizures and EEG Profile in Animal Model of Cortical Malformation

Developmental cortical malformations (DCM) are one of the main causes of refractory epilepsy. Many are the mechanisms underlying the hyperexcitability in DCM, including the important contribution of N-methyl-D-aspartate receptors (NMDAR). NMDAR blockers are shown to abolish seizures and epileptiform activity. Memantine, a NMDAR antagonist used to treat Alzheimeŕs disease, has been recently investigated as a possible treatment for other neurological disorders. However, the effects on preventing or diminishing seizures are controversial. Here we aimed to evaluate the effects of memantine on pentylenetetrazole (PTZ)-induced seizures in the freeze-lesion (FL) model. Bilateral cortical microgyria were induced (FL) or not (Sham) in male Wistar neonate rats. At P30, subdural electrodes were implanted and 7 days later, video-EEG was recorded in animals receiving either memantine (FL-M or Sham-M) or saline (FL-S or Sham-S), followed by PTZ. Seizures were evaluated by video-EEG during one hour and scored according to Racine scale. The video-EEG analyses revealed that the number of seizures and the total duration of stage IV-V seizures developed during the 1 h-period increased after memantine application in all groups. The EEG power spectral density (PSD) analysis showed an increased PSD of pre-ictal delta in Sham-M animals and increased PSD of slow, middle and fast gamma oscillations after memantine injection that persists during the pre-ictal period in all groups. Our findings suggested that memantine was unable to control the PTZ-induced seizures and that the associated enhancement of PSD of gamma oscillations may contribute to the increased probability of seizure development in these animals.

Continuous epileptiform discharges during sleep as an evolutionary pattern in patients with congenital Zika virus syndrome

Congenital Zika virus syndrome (CZVS) is associated with severe neurological deficits. Clinical characteristics of epilepsy and the electroencephalographic (EEG) pattern in CZVS were documented in infancy. In this study, we aimed to describe the EEG findings observed during the follow-up of children with CZVS. Seventy-six EEGs of 55 children (60% female; mean age = 50 months) with confirmed CZVS were analyzed, considering the background, interictal, and ictal epileptiform discharges. Continuous (or almost continuous) epileptiform discharges during non-rapid eye movement sleep were identified in 22 (40%) patients. In 20 (90.1%) patients, the pattern was symmetrical, with an anterior predominance of the epileptiform activity. All patients with this pattern had epilepsy, which was severe in 15 (68.2%) and demanded polytherapy in 19 (86.4%). Subcortical calcifications (77.3%) and multifocal EEGs (72.8%) in earlier ages occurred more often in patients with this pattern. Other unspecific interictal EEG patterns were focal epileptiform discharges in 23 (41.8%) and multifocal activity in six (10.9%). In CZVS, continuous (or almost continuous) epileptiform discharges during sleep emerge as a pattern after the second year of life. This was associated with severe and drug-resistant epilepsy, but not necessarily with an apparent regression. Subcortical calcifications and multifocal epileptiform discharges in infancy are associated with this pattern.

Laser-scanning astrocyte mapping reveals increased glutamate-responsive domain size and disrupted maturation of glutamate uptake following neonatal cortical freeze-lesion

Astrocytic uptake of glutamate shapes extracellular neurotransmitter dynamics, receptor activation, and synaptogenesis. During development, glutamate transport becomes more robust. How neonatal brain insult affects the functional maturation of glutamate transport remains unanswered. Neonatal brain insult can lead to developmental delays, cognitive losses, and epilepsy; the disruption of glutamate transport is known to cause changes in synaptogenesis, receptor activation, and seizure. Using the neonatal freeze-lesion (FL) model, we have investigated how insult affects the maturation of astrocytic glutamate transport. As lesioning occurs on the day of birth, a time when astrocytes are still functionally immature, this model is ideal for identifying changes in astrocyte maturation following insult. Reactive astrocytosis, astrocyte proliferation, and in vitro hyperexcitability are known to occur in this model. To probe astrocyte glutamate transport with better spatial precision we have developed a novel technique, Laser Scanning Astrocyte Mapping (LSAM), which combines glutamate transport current (TC) recording from astrocytes with laser scanning glutamate photolysis. LSAM allows us to identify the area from which a single astrocyte can transport glutamate and to quantify spatial heterogeneity in the rate of glutamate clearance kinetics within that domain. Using LSAM, we report that cortical astrocytes have an increased glutamate-responsive area following FL and that TCs have faster decay times in distal, as compared to proximal processes. Furthermore, the developmental shift from GLAST- to GLT-1-dominated clearance is disrupted following FL. These findings introduce a novel method to probe astrocyte glutamate uptake and show that neonatal cortical FL disrupts the functional maturation of cortical astrocytes.