Beta and Gamma Range EEG Power-Spectrum Correlation with Spiking Discharges in DBA/2J Mice Absence Model: Role of GABAB Receptors

Gene therapy for Lafora disease in the Epm2a-/- mouse model

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy typically occurring early in adolescence. The disease results from mutations in the EPM2A gene, encoding laforin, or the EPM2B gene, encoding malin. Laforin and malin work together in a complex to control glycogen synthesis and prevent the toxicity produced by misfolded proteins via the ubiquitin-proteasome system. Disruptions in either protein cause alterations in this complex, leading to the formation of Lafora bodies containing abnormal, insoluble, and hyperphosphorylated forms of glycogen. We used the Epm2a-/- knockout mouse model of Lafora disease to apply gene therapy by administering intracerebroventricular injections of a recombinant adeno-associated virus carrying the human EPM2A gene. We evaluated the effects of this treatment through neuropathological studies, behavioral tests, video-electroencephalography, electrophysiological recordings, and proteomic/phosphoproteomic analysis. Gene therapy ameliorated neurological and histopathological alterations, reduced epileptic activity and neuronal hyperexcitability, and decreased the formation of Lafora bodies. Moreover, differential quantitative proteomics and phosphoproteomics revealed beneficial changes in various molecular pathways altered in Lafora disease. Our results represent proof of principle for gene therapy with the coding region of the human EPM2A gene as a treatment for EPM2A-related Lafora disease.

Gene replacement therapy for Lafora disease in the Epm2a -/- mouse model

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy typically occurring early in adolescence. Common symptoms include seizures, dementia, and a progressive neurological decline leading to death within 5-15 years from onset. The disease results from mutations transmitted with autosomal recessive inheritance in the EPM2A gene, encoding laforin, a dual-specificity phosphatase, or the EPM2B gene, encoding malin, an E3-ubiquitin ligase. Laforin has glucan phosphatase activity, is an adapter of enzymes involved in glycogen metabolism, is involved in endoplasmic reticulum-stress and protein clearance, and acts as a tumor suppressor protein. Laforin and malin work together in a complex to control glycogen synthesis and prevent the toxicity produced by misfolded proteins via the ubiquitin-proteasome system. Disruptions in either protein can lead to alterations in this complex, leading to the formation of Lafora bodies that contain abnormal, insoluble, and hyperphosphorylated forms of glycogen called polyglucosans. We used the Epm2a -/- knock-out mouse model of Lafora disease to apply a gene replacement therapy by administering intracerebroventricular injections of a recombinant adeno-associated virus carrying the human EPM2A gene. We evaluated the effects of this treatment by means of neuropathological studies, behavioral tests, video-electroencephalography recording, and proteomic/phosphoproteomic analysis. Gene therapy with recombinant adeno-associated virus containing the EPM2A gene ameliorated neurological and histopathological alterations, reduced epileptic activity and neuronal hyperexcitability, and decreased the formation of Lafora bodies. Differential quantitative proteomics and phosphoproteomics revealed beneficial changes in various molecular pathways altered in Lafora disease. Improvements were observed for up to nine months following a single intracerebroventricular injection. In conclusion, gene replacement therapy with human EPM2A gene in the Epm2a -/- knock-out mice shows promise as a potential treatment for Lafora disease.

MicroRNA-218 instructs proper assembly of hippocampal networks

The assembly of the mammalian brain is orchestrated by temporally coordinated waves of gene expression. Post-transcriptional regulation by microRNAs (miRNAs) is a key aspect of this program. Indeed, deletion of neuron-enriched miRNAs induces strong developmental phenotypes, and miRNA levels are altered in patients with neurodevelopmental disorders. However, the mechanisms used by miRNAs to instruct brain development remain largely unexplored. Here, we identified miR-218 as a critical regulator of hippocampal assembly. MiR-218 is highly expressed in the hippocampus and enriched in both excitatory principal neurons (PNs) and GABAergic inhibitory interneurons (INs). Early life inhibition of miR-218 results in an adult brain with a predisposition to seizures. Changes in gene expression in the absence of miR-218 suggest that network assembly is impaired. Indeed, we find that miR-218 inhibition results in the disruption of early depolarizing GABAergic signaling, structural defects in dendritic spines, and altered intrinsic membrane excitability. Conditional knockout of Mir218-2 in INs, but not PNs, is sufficient to recapitulate long-term instability. Finally, de-repressing Kif21b and Syt13, two miR-218 targets, phenocopies the effects on early synchronous network activity induced by miR-218 inhibition. Taken together, the data suggest that miR-218 orchestrates formative events in PNs and INs to produce stable networks.

Pallidal GABA B receptors: involvement in cortex beta dynamics and thalamic reticular nucleus activity

The external globus pallidus (GP) firing rate synchronizes the basal ganglia-thalamus-cortex network controlling GABAergic output to different nuclei. In this context, two findings are significant: the activity and GABAergic transmission of the GP modulated by GABA B receptors and the presence of the GP-thalamic reticular nucleus (RTn) pathway, the functionality of which is unknown. The functional participation of GABA B receptors through this network in cortical dynamics is feasible because the RTn controls transmission between the thalamus and cortex. To analyze this hypothesis, we used single-unit recordings of RTn neurons and electroencephalograms of the motor cortex (MCx) before and after GP injection of the GABA B agonist baclofen and the antagonist saclofen in anesthetized rats. We found that GABA B agonists increase the spiking rate of the RTn and that this response decreases the spectral density of beta frequency bands in the MCx. Additionally, injections of GABA B antagonists decreased the firing activity of the RTn and reversed the effects in the power spectra of beta frequency bands in the MCx. Our results proved that the GP modulates cortical oscillation dynamics through the GP-RTn network via tonic modulation of RTn activity.

A versatile system for neuromuscular stimulation and recording in the mouse model using a lightweight magnetically coupled headmount

Neural stimulation and recording in rodents are common methods to better understand the nervous system and improve the quality of life of individuals who are suffering from neurological disorders (e.g., epilepsy), as well as for permanent reduction of chronic pain in patients with neuropathic pain and spinal-cord injury. This method requires a neural interface (e.g., a headmount) to couple the implanted neural device with instrumentation system. The size and the total weight of such headmounts should be designed in a way to minimize its effect on the movement of the animal. This is a crucial factor in gait, kinematic, and behavioral neuroscience studies of freely moving mice. Here we introduce a lightweight 'snap-in' electro-magnetic headmount that is extremely small, and uses strong neodymium magnetics to enable a reliable connection without sacrificing the lightweight of the device. Additionally, the headmount requires minimal surgical intervention during the implantation, resulting in minimal tissue damage. The device has demonstrated itself to be robust, and successfully provided direct electrical stimulation of nerve and electrical muscle stimulation and recording, as well as powering implanted LEDs for optogenetic use scenarios.

Fatty Acid Amides Synthesized from Andiroba Oil (Carapa guianensis Aublet.) Exhibit Anticonvulsant Action with Modulation on GABA-A Receptor in Mice: A Putative Therapeutic Option

Epilepsy is a chronic neurological disease characterized by excessive neuronal activity leading to seizure; about 30% of affected patients suffer from the refractory and pharmacoresistant form of the disease. The anticonvulsant drugs currently used for seizure control are associated with adverse reactions, making it important to search for more effective drugs with fewer adverse reactions. There is increasing evidence that endocannabinoids can pharmacologically modulate action against seizure and antiepileptic disorders. Therefore, the objective of this study is to investigate the anticonvulsant effects of fatty acid amides (FAAs) in a pentylenetetrazole (PTZ)-induced seizure model in mice. FAAs (FAA1 and FAA2) are obtained from Carapa guianensis oil by biocatalysis and are characterized by Fourier Transform Infrared Analysis (FT-IR) and Gas Chromatography-Mass Spectrometry (GC-MS). Only FAA1 is effective in controlling the increased latency time of the first myoclonic jerk and in significantly decreasing the total duration of tonic-clonic seizures relative to the pentylenetetrazol model. Also, electrocortical alterations produced by pentylenetetrazol are reduced when treated by FAA1 that subsequently decreased wave amplitude and energy in Beta rhythm. The anticonvulsant effects of FAA1 are reversed by flumazenil, a benzodiazepine antagonist on Gamma-Aminobutyric Acid-A (GABA-A) receptors, indicating a mode of action via the benzodiazepine site of these receptors. To conclude, the FAA obtained from C. guianensis oil is promising against PTZ-induced seizures.

GABAergic inhibitory neurons as therapeutic targets for cognitive impairment in schizophrenia

Schizophrenia is considered primarily as a cognitive disorder. However, functional outcomes in schizophrenia are limited by the lack of effective pharmacological and psychosocial interventions for cognitive impairment. GABA (gamma-aminobutyric acid) interneurons are the main inhibitory neurons in the central nervous system (CNS), and they play a critical role in a variety of pathophysiological processes including modulation of cortical and hippocampal neural circuitry and activity, cognitive function-related neural oscillations (eg, gamma oscillations) and information integration and processing. Dysfunctional GABA interneuron activity can disrupt the excitatory/inhibitory (E/I) balance in the cortex, which could represent a core pathophysiological mechanism underlying cognitive dysfunction in schizophrenia. Recent research suggests that selective modulation of the GABAergic system is a promising intervention for the treatment of schizophrenia-associated cognitive defects. In this review, we summarized evidence from postmortem and animal studies for abnormal GABAergic neurotransmission in schizophrenia, and how altered GABA interneurons could disrupt neuronal oscillations. Next, we systemically reviewed a variety of up-to-date subtype-selective agonists, antagonists, positive and negative allosteric modulators (including dual allosteric modulators) for α5/α3/α2 GABA_A and GABA_B receptors, and summarized their pro-cognitive effects in animal behavioral tests and clinical trials. Finally, we also discuss various representative histone deacetylases (HDAC) inhibitors that target GABA system through epigenetic modulations, GABA prodrug and presynaptic GABA transporter inhibitors. This review provides important information on current potential GABA-associated therapies and future insights for development of more effective treatments.

GABA-B Agonist Baclofen Normalizes Auditory-Evoked Neural Oscillations and Behavioral Deficits in the Fmr1 Knockout Mouse Model of Fragile X Syndrome

Fragile X syndrome is a genetic condition resulting from FMR1 gene mutation that leads to intellectual disability, autism-like symptoms, and sensory hypersensitivity. Arbaclofen, a GABA-B agonist, has shown efficacy in some individuals with FXS but has become unavailable after unsuccessful clinical trials, prompting interest in publicly available, racemic baclofen. The present study investigated whether racemic baclofen can remediate abnormalities of neural circuit function, sensory processing, and behavior in Fmr1 knockout mice, a rodent model of fragile X syndrome. Fmr1 knockout mice showed increased baseline and auditory-evoked high-frequency gamma (30-80 Hz) power relative to C57BL/6 controls, as measured by electroencephalography. These deficits were accompanied by decreased T maze spontaneous alternation, decreased social interactions, and increased open field center time, suggestive of diminished working memory, sociability, and anxiety-like behavior, respectively. Abnormal auditory-evoked gamma oscillations, working memory, and anxiety-related behavior were normalized by treatment with baclofen, but impaired sociability was not. Improvements in working memory were evident predominantly in mice whose auditory-evoked gamma oscillations were dampened by baclofen. These findings suggest that racemic baclofen may be useful for targeting sensory and cognitive disturbances in fragile X syndrome.

Classifying amygdala kindling stages using quantitative assessments of extracellular recording of EEG in rats

PURPOSE

Determining different seizure stage specific features in a kindling model is a crucial step in developing efficient objective techniques for early prediction and treatment of seizures. This study identified and categorized kindling stages based on their electrophysiological features through processing extracellular field potentials of Amygdala rapid kindling.

METHODS

Thirteen Wistar rats (200±10g) were divided into 2 groups including kindle (n=7) and sham (n=6) and respectively underwent an amygdala rapid kindling and placebo stimulation. EEG signals in each stage were classified into 7 bands: delta (0-4Hz), theta (4-8Hz), alpha (8-12Hz), low beta (12-16Hz), mid beta (16-20Hz), high beta (20-28Hz) and gamma (28-40Hz). Spectral power and power of sub bands of stage 3 (localized seizure stage (SS)) and stages 4 and 5 (generalized SSs) were compared between kindling and sham groups.

RESULT

Spectral analyses showed larger spikes in delta and theta subbands in the stages of 3, 4, and 5 of kindling, compared with sham animals. Generalized SSs contained more spikes than the localized SS in the kindling. Kindling process was accompanied by reduction in high beta and gamma oscillations and increase in delta sub band power which were significant in the generalized SSs. The theta/alpha ratio in the localized SS was higher than the generalized SSs and sham group, but the difference with the sham group was statistically significant.

CONCLUSION

Our results showed that reduced high beta and gamma and increased delta oscillations power are associated with behavioral seizure progression.

Anticonvulsant effects of structurally diverse GABA(B) positive allosteric modulators in the DBA/2J audiogenic seizure test: Comparison to baclofen and utility as a pharmacodynamic screening model

The GABA(B) receptor has been indicated as a promising target for multiple CNS-related disorders. Baclofen, a prototypical orthosteric agonist, is used clinically for the treatment of spastic movement disorders, but is associated with unwanted side-effects, such as sedation and motor impairment. Positive allosteric modulators (PAM), which bind to a topographically-distinct site apart from the orthosteric binding pocket, may provide an improved side-effect profile while maintaining baclofen-like efficacy. GABA, the major inhibitory neurotransmitter in the CNS, plays an important role in the etiology and treatment of seizure disorders. Baclofen is known to produce anticonvulsant effects in the DBA/2J mouse audiogenic seizure test (AGS), suggesting it may be a suitable assay for assessing pharmacodynamic effects. Little is known about the effects of GABA(B) PAMs, however. The studies presented here sought to investigate the AGS test as a pharmacodynamic (PD) screening model for GABA(B) PAMs by comparing the profile of structurally diverse PAMs to baclofen. GS39783, rac-BHFF, CMPPE, A-1295120 (N-(3-(4-(4-chloro-3-fluorobenzyl)-6-methoxy-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide), and A-1474713 (N-(3-(4-(4-chlorobenzyl)-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide) all produced robust, dose-dependent anticonvulsant effects; a similar profile was observed with baclofen. Pre-treatment with the GABA(B) antagonist SCH50911 completely blocked the anticonvulsant effects of baclofen and CMPPE in the AGS test, indicating such effects are likely mediated by the GABA(B) receptor. In addition to the standard anticonvulsant endpoint of the AGS test, video tracking software was employed to assess potential drug-induced motor side-effects during the acclimation period of the test. This analysis was sensitive to detecting drug-induced changes in total distance traveled, which was used to establish a therapeutic index (TI = hypoactivity/anticonvulsant effects). Calculated TIs for A-1295120, CMPPE, rac-BHFF, GS39783, and A-1474713 were 5.31x, 5.00x, 4.74x, 3.41x, and 1.83x, respectively, whereas baclofen was <1. The results presented here suggest the DBA/2J mouse AGS test is a potentially useful screening model for detecting PD effects of GABA(B) PAMs and can provide an initial read-out on target-related motor side-effects. Furthermore, an improved TI was observed for PAMs compared to baclofen, indicating the PAM approach may be a viable therapeutic alternative to baclofen.

CNF1 Enhances Brain Energy Content and Counteracts Spontaneous Epileptiform Phenomena in Aged DBA/2J Mice

Epilepsy, one of the most common conditions affecting the brain, is characterized by neuroplasticity and brain cell energy defects. In this work, we demonstrate the ability of the Escherichia coli protein toxin cytotoxic necrotizing factor 1 (CNF1) to counteract epileptiform phenomena in inbred DBA/2J mice, an animal model displaying genetic background with an high susceptibility to induced- and spontaneous seizures. Via modulation of the Rho GTPases, CNF1 regulates actin dynamics with a consequent increase in spine density and length in pyramidal neurons of rat visual cortex, and influences the mitochondrial homeostasis with remarkable changes in the mitochondrial network architecture. In addition, CNF1 improves cognitive performances and increases ATP brain content in mouse models of Rett syndrome and Alzheimer's disease. The results herein reported show that a single dose of CNF1 induces a remarkable amelioration of the seizure phenotype, with a significant augmentation in neuroplasticity markers and in cortex mitochondrial ATP content. This latter effect is accompanied by a decrease in the expression of mitochondrial fission proteins, suggesting a role of mitochondrial dynamics in the CNF1-induced beneficial effects on this epileptiform phenotype. Our results strongly support the crucial role of brain energy homeostasis in the pathogenesis of certain neurological diseases, and suggest that CNF1 could represent a putative new therapeutic tool for epilepsy.

Evidence for inhibitory deficits in the prefrontal cortex in schizophrenia

Abnormal gamma-aminobutyric acid inhibitory neurotransmission is a key pathophysiological mechanism underlying schizophrenia. Transcranial magnetic stimulation can be combined with electroencephalography to index long-interval cortical inhibition, a measure of GABAergic receptor-mediated inhibitory neurotransmission from the frontal and motor cortex. In previous studies we have reported that schizophrenia is associated with inhibitory deficits in the dorsolateral prefrontal cortex compared to healthy subjects and patients with bipolar disorder. The main objective of the current study was to replicate and extend these initial findings by evaluating long-interval cortical inhibition from the dorsolateral prefrontal cortex in patients with schizophrenia compared to patients with obsessive-compulsive disorder. A total of 111 participants were assessed: 38 patients with schizophrenia (average age: 35.71 years, 25 males, 13 females), 27 patients with obsessive-compulsive disorder (average age: 36.15 years, 11 males, 16 females) and 46 healthy subjects (average age: 33.63 years, 23 females, 23 males). Long-interval cortical inhibition was measured from the dorsolateral prefrontal cortex and motor cortex through combined transcranial magnetic stimulation and electroencephalography. In the dorsolateral prefrontal cortex, long-interval cortical inhibition was significantly reduced in patients with schizophrenia compared to healthy subjects (P = 0.004) and not significantly different between patients with obsessive-compulsive disorder and healthy subjects (P = 0.5445). Long-interval cortical inhibition deficits in the dorsolateral prefrontal cortex were also significantly greater in patients with schizophrenia compared to patients with obsessive-compulsive disorder (P = 0.0465). There were no significant differences in long-interval cortical inhibition across all three groups in the motor cortex. These results demonstrate that long-interval cortical inhibition deficits in the dorsolateral prefrontal cortex are specific to patients with schizophrenia and are not a generalized deficit that is shared by disorders of severe psychopathology.

Hidden in plain sight: spike-wave discharges in mouse inbred strains

Twenty-seven inbred strains of mice were tested for spike-wave discharge (SWD) activity by video-electroencephalographic recordings over a 24-h recording period. Eight strains had reproducible, frequent SWDs, including five strains (C57BLKS/J, CBA/J, DBA/1J, NOR/LtJ, SM/J) previously undiagnosed for this distinctive phenotype. Eighteen other strains exhibited no such activity. Spike-wave discharges usually occurred while the subject was motionless, and in a significant number of annotated instances coincided with an arrest of the subject's relatively unrestrained locomotor activity, which resumed immediately after the discharge ended. In all five new strains, SWDs were suppressed by ethosuximide administration. From the genealogy of inbred strains, we suggest that two ancestors, A and DBA, transmitted genotypes required for SWD in all positive strains. Together these strains with SWDs provide new opportunities to understand the genetic core susceptibility of this distinctive electroencephalographic activity and to explore its relationship to absence epilepsy, a human disorder for which few genes are known.

Early deficits in social behavior and cortical rhythms in pilocarpine-induced mouse model of temporal lobe epilepsy

Many patients with epilepsy are afflicted with psychiatric comorbidities including social dysfunction. However, although social deficits have been a major concern in epilepsy treatment, the relationship between social behavioral pathogenesis and the time course of epileptogenesis is not well defined. To address this, we investigated social behavioral alterations and cortical rhythms during two distinct periods in a mouse model of temporal lobe epilepsy (TLE): 1) a seizure-free, latent period after status epilepticus and 2) the subsequent, chronic period characterized by spontaneous recurrent seizures (SRSs). We found that severe social impairments, such as reduced sociability/social novelty preference, social interaction, social learning, and enhanced defensiveness, appeared during the latent period in mice with TLE. The social dysfunctions in the latent-period mice were nearly comparable to those in the chronic-period mice. We also found that both the latent- and chronic-period mice showed similar aberrant neural activities. They showed enhanced delta-band (1-4 Hz) activity and reduced alpha- (8.5-12 Hz) and gamma-band (30-55 Hz) activity during baseline behavior. Interestingly, concomitant increases in alpha- and gamma-band activities during social behavior, which were characteristic in control mice, were not observed in either latent- or chronic-period mice. Our results indicate that social deficits and abnormal neural activities appear at an earlier stage in epileptogenesis regardless of SRS occurrence. These findings may help to understand behavioral pathogenesis in patients with TLE and at-risk patients with initial insults that develop into TLE.

Human brain cortical correlates of short-latency afferent inhibition: a combined EEG–TMS study

When linking in time electrical stimulation of the peripheral nerve with transcranial magnetic stimulation (TMS), the excitability of the motor cortex can be modulated to evoke clear inhibition, as reflected by the amplitude decrement in the motor-evoked potentials (MEPs). This specific property, designated short-latency afferent inhibition (SAI), occurs when the nerve–TMS interstimulus interval (ISI) is approximately 25 ms and is considered to be a corticothalamic phenomenon. The aim of the present study was to use the electroencephalographic (EEG) responses to navigated-TMS coregistration to better characterize the neuronal circuits underlying SAI. The present experimental set included magnetic resonance imaging (MRI)–navigated TMS and 60-channel TMS-compatible EEG devices. TMS-evoked EEG responses and MEPs were analyzed in eight healthy volunteers; ISIs between median nerve and cortical stimulation were determined relative to the latency of the individual N20 component of the somatosensory-evoked potential (SEP) obtained after stimulation of the median nerve. ISIs from the latency of the N20 plus 3 ms and N20 plus 10 ms were investigated. In all experimental conditions, TMS-evoked EEG responses were characterized by a sequence of negative deflections peaking at approximately 7, 44, and 100 ms alternating with positive peaks at approximately 30, 60, and 180 ms post-TMS. Moreover, ISI N20+3 ms modulated both EEG-evoked activity and MEPs. In particular, it inhibited MEP amplitudes, attenuated cortical P60 and N100 responses, and induced motor cortex beta rhythm selective decrement of phase locking. The findings of the present experiment suggest the cortical origin of SAI that could result from the cortico–cortical activation of GABAergic-mediated inhibition onto the corticospinal neurons modulated by cholinergic activation able to reducing intralaminar inhibition and promoting intracolumnar inhibition.

Quantitative trait locus on distal chromosome 1 regulates the occurrence of spontaneous spike-wave discharges in DBA/2 mice

PURPOSE

Most common forms of human epilepsy result from a complex combination of polygenetic and environmental factors. Quantitative trait locus (QTL) mapping is a first step toward the nonbiased discovery of epilepsy-related candidate genes. QTL studies of susceptibility to induced seizures in mouse strains have consistently converged on a distal region of chromosome 1 as a major phenotypic determinant; however, its influence on spontaneous epilepsy remains unclear. In the present study we characterized the influence of allelic variations within this QTL, termed Szs1, on the occurrence of spontaneous spike-wave discharges (SWDs) characteristic of absence seizures in DBA/2 (D2) mice.

METHODS

We analyzed SWD occurrence and patterns in freely behaving D2, C57BL/6 (B6) and the congenic strains D2.B6-Szs1 and B6.D2-Szs1.

KEY FINDINGS

We showed that congenic manipulation of the Szs1 locus drastically reduced the number and the duration of SWDs in D2.B6-Szs1 mice, which are homozygous for Szs1 from B6 strain on a D2 strain background. However, it failed to induce the full expression of SWDs in the reverse congenic animals B6.D2-Szs1.

SIGNIFICANCE

Our results demonstrate that the occurrence of SWDs in D2 animals is under polygenic control and, therefore, the D2 and B6 strains might be a useful model to dissect the genetic determinants of polygenic SWDs characteristic of typical absence seizures. Furthermore, we point to the existence of epistatic interactions between at least one modifier gene within Szs1 and genes within unlinked QTLs in regulating the occurrence of spontaneous nonconvulsive forms of epilepsies.

Cortical and hippocampal EEG effects of neurotransmitter agonists in spontaneously hypertensive vs. kainate-treated rats

To analyze mediatory mechanisms underlying attention-deficit hyperactivity disorder (ADHD) and their association with epilepsy, the electroencephalogram (EEG) responses to various centrally applied neurotransmitter agonists were studied in spontaneously hypertensive (SH), kainate-treated (KA), and normotensive (control) rats, with chronically implanted electrodes into the frontal cortex and hippocampus and a cannula into the lateral cerebral ventricle. In SH rats, the baseline EEG showed increased delta and beta2 activity in the hippocampus and decreased alpha/beta1 activity in both brain areas. In KA rats, these delta and alpha/beta1 effects were observed 2 weeks post-kainate, while the beta2 activity increase occurred after 5 weeks in the hippocampus and, to a greater extent, 9 weeks post-injection in both brain areas. In SH rats, NMDA increased delta and decreased alpha/beta1 activity, similar to KA rats 5 weeks post-injection. In SH rats, clonidine augmented theta/beta2 increase in the cortex and alpha suppression in both brain areas, in parallel with induction of beta2 activity in the hippocampus. These beta2 effects were observed 5 and 9 weeks post-kainate. In SH rats, baclofen produced robust delta/theta enhancement and alpha/beta1 suppression in both brain areas, with additional beta2 activity increase in the hippocampus, while muscimol was ineffective in both groups of rats. In KA rats, EEG responses to GABA agonists were similar to those in control. Our results demonstrate sensitization of NMDA receptors and α2-adrenoceptors both in SH and KA rats and that of GABAb receptors specifically in SH rats.

Evidence for excessive frontal evoked gamma oscillatory activity in schizophrenia during working memory

Gamma (gamma) oscillations (30-50 Hz) elicited during working memory (WM) are altered in schizophrenia (SCZ). However, the nature of the relationship between evoked frontal oscillatory activity, WM performance and symptom severity has yet to be ascertained. This study had two objectives. First, to extend previous studies by examining delta, theta, alpha, beta, and gamma (delta, theta, alpha, beta, and gamma) oscillatory activities during the N-back task in SCZ patients compared to healthy subjects; second, to evaluate the relationship between oscillatory activities elicited during the N-back, performance, and clinical symptoms in SCZ patients. Patients with SCZ elicited excessive frontal gamma oscillatory activity that was most pronounced in the 3-back condition compared to healthy subjects. Reduced frontal beta activity at all WM loads was also observed in patients with SCZ compared to healthy subjects. Task performance was inversely correlated with negative symptoms but not with positive symptoms. Our findings suggest that evoked frontal oscillatory activities during WM are selectively altered in the gamma and beta frequency bands that may contribute to WM impairment in SCZ patients. These findings may provide important insights into the pathophysiology underlying WM deficits, its relationship to negative symptoms and may represent a potential neurobiological marker for cognitive enhancing strategies in SCZ.

Suppression of gamma-oscillations in the dorsolateral prefrontal cortex following long interval cortical inhibition: a TMS-EEG study

Gamma (gamma)-oscillations (30-50 Hz) represent important electrophysiological measures, which are generated through the execution of higher order cognitive tasks (eg, working memory) in the dorsolateral prefrontal cortex (DLPFC). By contrast, cortical inhibition (CI) refers to a neurophysiological process in which GABAergic inhibitory interneurons selectively suppress the activation of other neurons in the cortex. Recently, abnormalities in both CI and gamma-oscillations have been associated with various neuropsychiatric disorders including schizophrenia. Animal research suggests that suppression of gamma-oscillations is, in part, mediated through GABAergic inhibitory neurotransmission. However, no such evidence has been demonstrated in human, largely because of technological limitations. Recently, we reported on novel methods permitting the recording of CI from the DLPFC through transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG). The aim of this study was to examine the effects of GABAergic inhibitory neurotransmission on gamma-oscillations by combining TMS with EEG. Long interval cortical inhibition (LICI), a paired TMS paradigm, was used to index GABA(B) receptor mediated inhibitory neurotransmission in the motor cortex and DLPFC of healthy individuals. Gamma-oscillations were significantly inhibited by LICI (38.1+/-26.5%; p< or =0.013) in the DLPFC but not in the motor cortex. These results provide neurophysiological evidence to demonstrate gamma-oscillations are inhibited by LICI in the DLPFC but not in the motor cortex. Such specificity suggests that the modulation of gamma-oscillations may represent an important neurophysiological process that may, in part, be responsible for optimal DLPFC functioning in healthy human subjects.

A glue-based, screw-free method for implantation of intra-cranial electrodes in young mice

Intra-cranial electroencephalographic recordings are increasingly employed in mice because of the availability of genetically manipulated mouse models. Currently, dental acrylic and anchoring screws are used to cement implanted electrodes. This technique works well for adult animals but often encounters difficulty when employed in young mice because their skulls are not strong enough to bear the anchoring screws. Here we describe a novel method favorable for implantation of intra-cranial electrodes in mice as young as postnatal 18 days and suitable for long-term intra-cranial electroencephalographic recordings. Our approach is to construct a multi-electrode assembly according to the desired stereotaxic coordinates of intra-cranial recordings and to secure the implanted electrode assembly to the skull via glue rather than dental acrylic/anchoring screws. The surgical operation for such electrode implantation is relatively quick and rarely associated with complications such as infection, bleeding, neurological deficits, spontaneous seizures or behavioral disturbances. The implanted electrodes are stable, allowing repeated monitoring for several months. Data obtained by simultaneous intra-hippocampal and intra-cortical recordings indicate that our method is suitable for the examination of behaviorally related electroencephalographic activities and experimentally induced seizures. Technical aspects of our methods are discussed, and the procedures for constructing the electrode assembly are presented in detail.

Activation of GABA(B) receptors reverses spontaneous gating deficits in juvenile DBA/2J mice

RATIONALE

Gamma-amino-butyric acid (GABA)(B) receptors play a key role in the pathophysiology of psychotic disorders. We previously reported that baclofen, the prototypical GABA(B) agonist, elicits antipsychotic-like effects in the rat paradigm of prepulse inhibition (PPI) of the startle, a highly validated animal model of schizophrenia.

OBJECTIVES

We studied the role of GABA(B) receptors in the spontaneous PPI deficits displayed by DBA/2J mice.

MATERIALS AND METHODS

We tested the effects of baclofen (1.25-5 mg/kg, intraperitoneal [i.p.]) in DBA/2J and C57BL/6J mice, in comparison to the antipsychotic drugs haloperidol (1 mg/kg, i.p.) and clozapine (5 mg/kg, i.p.). Furthermore, we investigated the expression of GABA(B) receptors in the brain of DBA/2J and C57BL/6J mice by quantitative autoradiography.

RESULTS

Baclofen dose-dependently restored PPI deficit in DBA/2J mice, in a fashion similar to the antipsychotic clozapine (5 mg/kg, i.p.). This effect was reversed by pretreatment with the GABA(B) antagonist SCH50211 (50 mg/kg, i.p.). In contrast, baclofen did not affect PPI in C57BL/6J mice. Finally, quantitative autoradiographic analyses assessed a lower GABA(B) receptor expression in DBA/2J mice in comparison to C57BL/6J controls in the prefrontal cortex and hippocampus but not in other brain regions.

CONCLUSIONS

Our data highlight GABA(B) receptors as an important substrate for sensorimotor gating control in DBA/2J mice and encourage further investigations on the role of GABA(B) receptors in sensorimotor gating, as well as in the pathophysiology of psychotic disturbances.

Levetiracetam attenuates spontaneous spike-and-wave discharges in DBA/2J mice

Recent evidence highlights levetiracetam (LEV) as an advantageous treatment of absence epilepsy (AE). Thus, we investigated the effects of this drug in DBA/2J mice, a murine model of AE. Similarly to ethosuximide (200 mg/kg, intraperitoneal, i.p.) and sodium valproate (250 mg/kg, i.p.), two classic antiabsence agents, LEV (50-200 mg/kg, i.p.) reduced the occurrence of spike-and-wave discharges, AE's typical electroencephalographic patterns. Our results confirm LEV's efficacy in AE treatment.

Correlations between acetylcholinesterase inhibition, acetylcholine levels and EEG changes during perfusion with neostigmine and N6-cyclopentyladenosine in rat brain

Organophosphate poisoning can result in seizures and subsequent neuropathology. In order to improve treatment strategies in organophosphate intoxication, the relationship between acetylcholinesterase inhibition, extracellular levels of acetylcholine, and electroencephalogram (EEG) changes was investigated during local perfusion of the reversible acetylcholinesterase inhibitor neostigmine in the hippocampus and striatum of freely moving rats. Acetylcholinesterase activity and acetylcholine levels were measured by microdialysis, and EEG signals were recorded from an electrode placed near the microdialysis probe. A non-linear relationship between the acetylcholinesterase activity and the extracellular amount of acetylcholine was found, the latter being approximately three times higher in the striatum than in the hippocampus upon infusion with 10(-4) M neostigmine. Highly accumulated extracellular acetylcholine significantly correlated with significant relative power increases of the EEG-gamma2-band and a significant relative power decrease in the beta2-band. Co-infusion of the adenosine A1 agonist N6-cyclopentyladenosine partly prevented acetylcholine accumulation, rendered both powers towards control values, and abolished the acetylcholine-EEG correlation. In view of the latter relationship, it is concluded that prevention of acetylcholine accumulation as a concept for neuroprotection in case of organophosphate poisoning, is worth to be further investigated.

Neural Synchrony in Brain Disorders: Relevance for Cognitive Dysfunctions and Pathophysiology

Following the discovery of context-dependent synchronization of oscillatory neuronal responses in the visual system, novel methods of time series analysis have been developed for the examination of task- and performance-related oscillatory activity and its synchronization. Studies employing these advanced techniques revealed that synchronization of oscillatory responses in the beta- and gamma-band is involved in a variety of cognitive functions, such as perceptual grouping, attention-dependent stimulus selection, routing of signals across distributed cortical networks, sensory-motor integration, working memory, and perceptual awareness. Here, we review evidence that certain brain disorders, such as schizophrenia, epilepsy, autism, Alzheimer's disease, and Parkinson's are associated with abnormal neural synchronization. The data suggest close correlations between abnormalities in neuronal synchronization and cognitive dysfunctions, emphasizing the importance of temporal coordination. Thus, focused search for abnormalities in temporal patterning may be of considerable clinical relevance.