Hyperthermia-induced seizures modify the GABA(A) and benzodiazepine receptor binding in immature rat brain

Na+/K+- and Mg2+-ATPases and Their Interaction with AMPA, NMDA and D2 Dopamine Receptors in an Animal Model of Febrile Seizures

Febrile seizures (FS) are one of the most common seizure disorders in childhood which are classified into short and prolonged, depending on their duration. Short FS are usually considered as benign. However, epidemiological studies have shown an association between prolonged FS and temporal lobe epilepsy. The development of animal models of FS has been very useful to investigate the mechanisms and the consequences of FS. One of the most used, the "hair dryer model", has revealed that prolonged FS may lead to temporal lobe epilepsy by altering neuronal function. Several pieces of evidence suggest that Na⁺/ K⁺-ATPase and Mg²⁺-ATPase may play a role in this epileptogenic process. In this work, we found that hyperthermia-induced seizures (HIS) significantly increased the activity of Na⁺/ K⁺-ATPase and Mg²⁺-ATPase five and twenty days after hyperthermic insult, respectively. These effects were diminished in response to AMPA, D₂ dopamine A₁ and A_2A receptors activation, respectively. Furthermore, HIS also significantly increased the protein level of the AMPA subunit GluR1. Altogether, the increased Na⁺/ K⁺-ATPase and Mg²⁺-ATPase agree well with the presence of protective mechanisms. However, the reduction in ATPase activities in the presence of NMDA and AMPA suggest an increased propensity for epileptic events in adults.

Nucleus accumbens shell: A potential target for drug-resistant epilepsy with neuropsychiatric disorders

The nucleus accumbens (NAc) is an important component of the ventral striatum, involving motivational and emotional processes, limbic-motor interfaces. Recently, experimental and clinical data have shown that NAc, particularly NAc shell (NAcs), participates in ictogenesis and epileptogensis in drug-resistant epilepsy (DRE). Therefore, we summarize the existing literature on NAcs and potential role in epilepsy, from the bench to the clinic. Connection abnormalities between NAcs and remainings, degeneration of NAc neurons, and an aberrant distribution of neuroactive substances have been reported in patients with DRE. These changes may be underlying the pathophysiological mechanism of the involvement of NAcs in DRE. Furthermore, alterations in NAcs may also be involved in neuropsychiatric disorders in patients with DRE. These observational studies demonstrate the multiple properties of NAcs and the complex relationship between the limbic system and DRE with neuropsychiatric disorders. NAcs can be a potential target for DBS and stereotactic lesioning to manage DRE with neuropsychiatric disorders. Future studies are warranted to further clarify the role of NAcs in epilepsy.

Early-life febrile seizures worsen adult phenotypes in Scn1a mutants

Mutations in the voltage-gated sodium channel (VGSC) gene SCN1A, encoding the Na_v1.1 channel, are responsible for a number of epilepsy disorders including genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (DS). Patients with SCN1A mutations often experience prolonged early-life febrile seizures (FSs), raising the possibility that these events may influence epileptogenesis and lead to more severe adult phenotypes. To test this hypothesis, we subjected 21-23-day-old mice expressing the human SCN1A GEFS+ mutation R1648H to prolonged hyperthermia, and then examined seizure and behavioral phenotypes during adulthood. We found that early-life FSs resulted in lower latencies to induced seizures, increased severity of spontaneous seizures, hyperactivity, and impairments in social behavior and recognition memory during adulthood. Biophysical analysis of brain slice preparations revealed an increase in epileptiform activity in CA3 pyramidal neurons along with increased action potential firing, providing a mechanistic basis for the observed worsening of adult phenotypes. These findings demonstrate the long-term negative impact of early-life FSs on disease outcomes. This has important implications for the clinical management of this patient population and highlights the need for therapeutic interventions that could ameliorate disease progression.

Developmental pharmacology of benzodiazepines under normal and pathological conditions

Benzodiazepines are allosteric agonists of GABAA receptors (GABAAR), pentameric ligand-gated Cl(-) channels, which serve both an important neurodevelopmental role but are also the principal inhibitory system in the brain. However, their subunit composition, channel properties, and function, as well as their region-specific expression patterns, change through development. These processes have been extensively studied in rodents and to some extent confirmed in higher species. Specifically, GABAARs acquire faster kinetics with age and their pharmacology changes rendering them more sensitive to drugs that have higher affinity for α1 subunit-containing GABAARs, such as benzodiazepines, but also, their inhibitory function becomes more potent as they shift from having depolarising to hyperpolarising responses due to a shift in Cl(-) gradient and cation chloride cotransporter expression. Concerns have been raised about possible pro-apoptotic and paradoxical effects of benzodiazepines in the neonatal normal rat brain, although it is unclear, as yet, whether this extends to brains exposed to seizures. Growing evidence indicates that the pharmacology and physiology of GABAARs may be altered in the brain of rats or humans with seizures or epilepsy, or different aetiologies that predispose to epilepsy. These changes follow different paths, depending on sex, age, region, cell type, aetiology, or time-point specific factors. Identification of dynamic biomarkers that could enable these changes in vivo to be monitored would greatly facilitate the selection of more effective agonists with fewer side effects.

Experimental early-life febrile seizures induce changes in GABA(A) R-mediated neurotransmission in the dentate gyrus

PURPOSE

  Febrile seizures (FS), the most frequent seizure type during childhood, have been linked to temporal lobe epilepsy (TLE) in adulthood. Yet, underlying mechanisms are still largely unknown. Altered γ-aminobutyric acid (GABA)ergic neurotransmission in the dentate gyrus (DG) circuit has been hypothesized to be involved. This study aims at analyzing whether experimental FS change inhibitory synaptic input and postsynaptic GABA(A) R function in dentate granule cells.

METHODS

  We applied an immature rat model of hyperthermia (HT)-induced FS. GABA(A) R-mediated neurotransmission was studied using whole-cell patch-clamp recordings from dentate granule neurons in hippocampal slices within 6-9 days post-HT.

KEY FINDINGS

  Frequencies of spontaneous inhibitory postsynaptic currents (sIPSCs) were reduced in HT rats that had experienced seizures, whereas sIPSC amplitudes were enhanced. Whole-cell GABA responses revealed a doubled GABA(A) R sensitivity in dentate granule cells from HT animals, compared to that of normothermic (NT) controls. Analysis of sIPSCs and whole-cell GABA responses showed similar kinetics in postsynaptic GABA(A) Rs of HT and NT rats. quantitative real-time polymerase chain reaction (qPCR) experiments indicated changes in DG GABA(A) R subunit expression, which was most pronounced for the α3 subunit.

SIGNIFICANCE

  The data support the hypothesis that FS persistently alter neuronal excitability.

Febrile seizures: current views and investigations

Febrile seizures (FSs) are seizures that occur during fever, usually at the time of a cold or flu, and represent the most common cause of seizures in the pediatric population. Up to 5% of children between the ages of six months and five years-of-age will experience a FS. Clinically these seizures are categorized as benign events with little impact on the growth and development of the child. However, studies have linked the occurrence of FSs to an increased risk of developing adult epileptic disorders. There are many unanswered questions about FSs, such as the mechanism of their generation, the long-term effects of these seizures, and their role in epileptogenesis. Answers are beginning to emerge based on results from animal studies. This review summarizes the current literature on animal models of FSs, mechanisms underlying the seizures, and functional, structural, and molecular changes that may result from them.

Long-term behavioral outcome after early-life hyperthermia-induced seizures

Febrile seizures (FS) are among the most common types of seizures in the developing brain. It has been suggested that FS cause cognitive deficits that proceed into adulthood, but the information is conflicting. The aim of the present study was to determine whether experimental FS have long-term cognitive or behavioral deficits. FS were induced by hyperthermia (30 minutes, approximately 41 degrees C) in 10-day-old rat pups, and behavioral testing was performed. Hippocampus-dependent water maze learning, locomotor activity, and choice reaction time parameters (e.g., reaction time) were generally not affected by FS. However, more detailed analysis revealed that reaction times on the right side were slower than those on the left in controls, whereas this was not observed after FS. Early-life experimental FS did not cause overt cognitive and behavioral deficits, which is in line with previous work, but eliminated the lateralization effect in reaction time known to occur in normal controls, an effect that may be due to the combination of FS and kainic acid or to FS alone.

Injection of muscimol, a GABAa agonist into the anterior thalamic nucleus, suppresses hippocampal neurogenesis in amygdala-kindled rats

The relationship between neurogenesis and epilepsy remains to be solved so far, although aberrant electric circuit recognized in epilepsy might be involved in neurogenesis. In this study, neurogenesis and the proliferation of astrocytes in the subgranular zone of the hippocampus were explored using unilateral amygdala-kindled rats with or without muscimol, a gamma-aminobutyric acid a (GABAa) agonist injection into the bilateral anterior thalamic nuclei (AN). Muscimol injection significantly ameliorated the behavioral scores of epilepsy without any significant alteration on the electroencephalography recorded at the stimulated basolateral amygdala, thus suggesting that muscimol injection might affect the secondary generalization, but not the initial discharge itself. The number of bromodeoxyuridine (BrdU), BrdU/doublecortin and BrdU/glial fibrillary acidic protein-positive cells in the subgranular zone of kindled animals increased markedly. Muscimol injection significantly suppressed neurogenesis, but not the proliferation of astrocyte, in the subgranular zone of the non-stimulated side, probably through the suppression of secondary generalization via AN. The results might indicate the underlying relationships between neurogenesis and epilepsy, that epileptic propagation in unilateral amygdala-kindled rats might go through AN into the contralateral side with subsequent neurogenesis, although further studies need to clarify the hypothesis.

Modulation of synaptic GABAA receptor function by zolpidem in substantia nigra pars reticulata

AIM

The substantia nigra pars reticulata (SNr) constitutes one of the output centers of the basal ganglia, and its abnormal activity is believed to contribute to some basal ganglia motor disorders. Different lines of evidence revealed a major contribution of GABAA receptor-mediated synaptic inhibition in controlling the activity of SNr. The benzodiazepine binding site within the GABAA receptor is a modulation site of significant clinical interest. A high density of benzodiazepine binding sites has been reported in the rat SNr. In the present study, we investigate the effects of activating benzodiazepine binding sites in the SNr.

METHODS

Whole-cell patch-clamp recordings and motor behavior were applied.

RESULTS

Superfusion of zolpidem, a benzodiazepine binding agonist, at 100 nmol/L significantly prolonged the decay time of GABAA receptor-mediated postsynaptic currents. The prolongation on decay time induced by zolpidem was sensitive to the benzodiazepine antagonist flumazenil, confirming the specificity on the benzodiazepine site. Zolpidem at 1 micromol/L exerted a stronger prolongation on the decay time. A further experiment was performed on behaving rats. A unilateral microinjection of zolpidem into the rat SNr caused a robust contralateral rotation, which was significantly different from that of control animals receiving the vehicle injection.

CONCLUSION

The present in vitro and in vivo findings that zolpidem significantly potentiated GABA currents and thus inhibited the activity of the SNr provide a rationale for further investigations into its potential in the treatment of basal ganglia disorders.