Mice lacking Dlx1 show subtype-specific loss of interneurons, reduced inhibition and epilepsy

Dlx homeodomain transcription factors are essential during embryonic development for the production of forebrain GABAergic interneurons. Here we show that Dlx1 is also required for regulating the functional longevity of cortical and hippocampal interneurons in the adult brain. We demonstrate preferential Dlx1 expression in a subset of cortical and hippocampal interneurons which, in postnatal Dlx1 mutants, show a time-dependent reduction in number. This reduction preferentially affects calretinin(+) (bipolar cells) and somatostatin(+) subtypes (for example, bitufted cells), whereas parvalbumin(+) subpopulations (basket cells and chandelier cells) seem to be unaffected. Cell transplantation analysis demonstrates that interneuron loss reflects cell-autonomous functions of Dlx1. The decrease in the number of interneurons was associated with a reduction of GABA-mediated inhibitory postsynaptic current in neocortex and hippocampus in vitro and cortical dysrhythmia in vivo. Dlx1 mutant mice show generalized electrographic seizures and histological evidence of seizure-induced reorganization, linking the Dlx1 mutation to delayed-onset epilepsy associated with interneuron loss.

Cux1 and Cux2 regulate dendritic branching, spine morphology, and synapses of the upper layer neurons of the cortex

Dendrite branching and spine formation determines the function of morphologically distinct and specialized neuronal subclasses. However, little is known about the programs instructing specific branching patterns in vertebrate neurons and whether such programs influence dendritic spines and synapses. Using knockout and knockdown studies combined with morphological, molecular, and electrophysiological analysis, we show that the homeobox Cux1 and Cux2 are intrinsic and complementary regulators of dendrite branching, spine development, and synapse formation in layer II-III neurons of the cerebral cortex. Cux genes control the number and maturation of dendritic spines partly through direct regulation of the expression of Xlr3b and Xlr4b, chromatin remodeling genes previously implicated in cognitive defects. Accordingly, abnormal dendrites and synapses in Cux2(-/-) mice correlate with reduced synaptic function and defects in working memory. These demonstrate critical roles of Cux in dendritogenesis and highlight subclass-specific mechanisms of synapse regulation that contribute to the establishment of cognitive circuits.

Cortical inhibition modified by embryonic neural precursors grafted into the postnatal brain

Embryonic medial ganglionic eminence (MGE) cells transplanted into the adult brain can disperse, migrate, and differentiate to neurons expressing GABA, the primary inhibitory neurotransmitter. It has been hypothesized that grafted MGE precursors could have important therapeutic applications increasing local inhibition, but there is no evidence that MGE cells can modify neural circuits when grafted into the postnatal brain. Here we demonstrate that MGE cells grafted into one location of the neonatal rodent brain migrate widely into cortex. Grafted MGE-derived cells differentiate into mature cortical interneurons; the majority of these new interneurons express GABA. Based on their morphology and expression of somatostatin, neuropeptide Y, parvalbumin, or calretinin, we infer that graft-derived cells integrate into local circuits and function as GABA-producing inhibitory cells. Whole-cell current-clamp recordings obtained from MGE-derived cells indicate firing properties typical of mature interneurons. Moreover, patch-clamp recordings of IPSCs on pyramidal neurons in the host brain, 30 and 60 d after transplantation, indicated a significant increase in GABA-mediated synaptic inhibition in regions containing transplanted MGE cells. In contrast, synaptic excitation is not altered in the host brain. Grafted MGE cells, therefore, can be used to modify neural circuits and selectively increase local inhibition. These findings could have important implications for reparative cell therapies for brain disorders.

Dysfunction of synaptic inhibition in epilepsy associated with focal cortical dysplasia

Focal cortical dysplasia (FCD) is a common and important cause of medically intractable epilepsy. In patients with temporal lobe epilepsy and in several animal models, compromised neuronal inhibition, mediated by GABA, contributes to seizure genesis. Although reduction in GABAergic interneuron density has been reported in FCD tissue samples, there is little available information on the resulting physiological changes in synaptic inhibition and the potential contribution of these changes to epileptogenesis in the dysplastic human brain. Using visualized whole-cell patch-clamp recordings from identified neurons in tissue slices obtained from patients with FCD, we demonstrate that GABAA-receptor-mediated inhibition is substantially altered in regions of dysplasia. These alterations include a significant reduction in IPSC frequency and a potentially compensatory decrease in transporter-mediated GABA reuptake function; the latter is marked by a significant increase in the decay-time constant for evoked and spontaneous IPSCs and a lack of effect of the GABA transport-inhibitor 1-[2([(diphenylmethylene)imino]oxy)ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride on IPSC kinetics. Immunohistochemical staining revealed a scattering of GABAergic interneurons across dysplastic cortex and striking reductions in GABA transporter expression. Together, these results suggest that profound alterations in GABA-mediated synaptic inhibition play an essential role in the process of epileptogenesis in patients with FCD.

Neocortical hyperexcitability in a human case of tuberous sclerosis complex and mice lacking neuronal expression of TSC1

OBJECTIVE

To identify brain regions, cell types, or both that generate abnormal electrical discharge in tuberous sclerosis complex (TSC). Here we examined excitatory and inhibitory synaptic currents in human tissue samples obtained from a TSC patient with no discernible cortical tubers and acute neocortical brain slices from a mouse featuring synapsin-driven conditional deletion of a TSC1 gene. These studies were designed to assess whether TSC gene inactivation alters excitability.

METHODS

We used visualized patch-clamp (human and mouse) and extracellular field (mouse) recordings. Additional mice were processed for immunohistochemistry or Western blot analysis.

RESULTS

Detailed anatomic studies in brain tissue sections from synapsin-TSC1 conditional knock-out mice failed to uncover gross anatomic defects, loss of lamination, or frank tuber formation. However, regions of abnormal and potentially activated neocortex were shown using antibodies to nonphosphorylated neurofilaments (SMI-311) and immediate early genes (c-Fos). Extracellular recordings from neocortical slices, examining synaptic activity in these regions, demonstrated clear differences in excitability between conditional knock-out and age-matched control mice. Whole-cell patch-clamp recordings demonstrated excitatory synaptic currents with strikingly long duration and epileptiform discharge patterns, similar to waveforms observed in our human tissue samples. These events were 1-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor mediated and were most prominent in neocortex. Normal-appearing inhibitory postsynaptic currents (human) and intrinsic neuronal firing patterns (mouse) were also recorded.

INTERPRETATION

This combination of human and mouse tissue studies suggests, for the first time, that synaptic excitation is altered in a direction that favors seizure generation in TSC brain tissue regardless of cortical tubers.

Cortical Malformations: Lessons in Human Brain Development

Creating a functional cerebral cortex requires a series of complex and well-coordinated developmental steps. These steps have evolved across species with the emergence of cortical gyrification and coincided with more complex behaviors. The presence of diverse progenitor cells, a protracted timeline for neuronal migration and maturation, and diverse neuronal types are developmental features that have emerged in the gyrated cortex. These factors could explain how the human brain has expanded in size and complexity. However, their complex nature also renders new avenues of vulnerability by providing additional cell types that could contribute to disease and longer time windows that could impact the composition and organization of the cortical circuit. We aim to discuss the unique developmental steps observed in human corticogenesis and propose how disruption of these species-unique processes could lead to malformations of cortical development.

High-pass filtering of corticothalamic activity by neuromodulators released in the thalamus during arousal: in vitro and in vivo

The thalamus is the principal relay station of sensory information to the neocortex. In return, the neocortex sends a massive feedback projection back to the thalamus. The thalamus also receives neuromodulatory inputs from the brain stem reticular formation, which is vigorously activated during arousal. We investigated the effects of two neuromodulators, acetylcholine and norepinephrine, on corticothalamic responses in vitro and in vivo. Results from rodent slices in vitro showed that acetylcholine and norepinephrine depress the efficacy of corticothalamic synapses while enhancing their frequency-dependent facilitation. This produces a stronger depression of low-frequency responses than of high-frequency responses. The effects of acetylcholine and norepinephrine were mimicked by muscarinic and alpha(2)-adrenergic receptor agonists and blocked by muscarinic and alpha-adrenergic antagonists, respectively. Stimulation of the brain stem reticular formation in vivo also strongly depressed corticothalamic responses. The suppression was very strong for low-frequency responses, which do not produce synaptic facilitation, but absent for high-frequency corticothalamic responses. As in vitro, application of muscarinic and alpha-adrenergic antagonists into the thalamus in vivo abolished the suppression of corticothalamic responses induced by stimulating the reticular formation. In conclusion, cholinergic and noradrenergic activation during arousal high-pass filters corticothalamic activity. Thus, during arousal only high-frequency inputs from the neocortex are allowed to reach the thalamus. Neuromodulators acting on corticothalamic synapses gate the flow of cortical activity to the thalamus as dictated by behavioral state.

GABAergic interneurons in epilepsy: More than a simple change in inhibition

The pathophysiology of epilepsy has been historically grounded on hyperexcitability attributed to the oversimplified imbalance between excitation (E) and inhibition (I) in the brain. The decreased inhibition is mostly attributed to deficits in gamma-aminobutyric acid-containing (GABAergic) interneurons, the main source of inhibition in the central nervous system. However, the cell diversity, the wide range of spatiotemporal connectivity, and the distinct effects of the neurotransmitter GABA especially during development, must be considered to critically revisit the concept of hyperexcitability caused by decreased inhibition as a key characteristic in the development of epilepsy. Here, we will discuss that behind this known mechanism, there is a heterogeneity of GABAergic interneurons with distinct functions and sources, which have specific roles in controlling the neural network activity within the recruited microcircuit and altered network during the epileptogenic process. This article is part of the Special Issue "NEWroscience 2018.

Neuroprotective effects of guanosine administration on behavioral, brain activity, neurochemical and redox parameters in a rat model of chronic hepatic encephalopathy

It is well known that glutamatergic excitotoxicity and oxidative stress are implicated in the pathogenesis of hepatic encephalopathy (HE). The nucleoside guanosine exerts neuroprotective effects through the antagonism against glutamate neurotoxicity and antioxidant properties. In this study, we evaluated the neuroprotective effect of guanosine in an animal model of chronic HE. Rats underwent bile duct ligation (BDL) and 2 weeks later they were treated with i.p. injection of guanosine 7.5 mg/kg once a day for 1-week. We evaluated the effects of guanosine in HE studying several aspects: a) animal behavior using open field and Y-maze tasks; b) brain rhythm changes in electroencephalogram (EEG) recordings; c) purines and glutamate levels in the cerebral spinal fluid (CSF); and d) oxidative stress parameters in the brain. BDL rats presented increased levels of glutamate, purines and metabolites in the CSF, as well as increased oxidative damage. Guanosine was able not only to prevent these effects but also to attenuate the behavioral and EEG impairment induced by BDL. Our study shows the neuroprotective effects of systemic administration of guanosine in a rat model of HE and highlights the involvement of purinergic system in the physiopathology of this disease.

B, Cristina G. M, Guimarães AO, Calcagnotto ME, Pesquero JB, Mello LE. Effects of FGF-2 and EGF removal on the differentiationof mouse neural precursor cells

Cell therapy for neurological disorders has advanced, and neural precursor cells (NPC) may become the ideal candidates for neural transplantation in a wide range of diseases. However, additional work has to be done to determine either the ideal culture environment for NPC expansion in vitro, without altering their plasticity, or the FGF-2 and EGF mechanisms of cell signaling in neurospheres growth, survival and differentiation. In this work we evaluated mouse neurospheres cultured with and without FGF-2 and EGF containing medium and showed that those growth factors are responsible for NPC proliferation. It is also demonstrated that endogenous production of growth factors shifts from FGF-2 to IGF-1/PDGFb upon EGF and FGF-2 withdrawal. Mouse NPC cultured in suspension showed different patterns of neuronal localization (core versus shell) for both EGF and FGF-2 withdrawal and control groups. Taken together, these results show that EGF and FGF-2 removal play an important role in NPC differentiation and may contribute to a better understanding of mechanisms of NPC differentiation. Our findings suggest that depriving NPC of growth factors prior to grafting might enhance their chance to effectively integrate into the host.

Value of immunologic testing in stroke patients. A prospective multicenter study

BACKGROUND AND PURPOSE

The aims of this prospective and multicenter study were to determine the frequency of anticardiolipin and antinuclear antibodies in an unselected ischemic and hemorrhagic stroke population and to evaluate the clinical significance of these autoantibodies.

METHODS

Over a 1-year period, we collected plasma from 481 consecutive patients with ischemic or hemorrhagic stroke attending four different hospitals. Blood (10 mL) was drawn from each subject into a citrated glass tube. Plasma was obtained immediately by centrifugation and was stored at -70 degrees C until use. Concentrations of IgM and IgG anticardiolipin antibodies were measured at room temperature in normal (not heat-treated) plasma by standardized enzyme-linked immunosorbent assay. All sera were treated by indirect immunofluorescence on mouse liver and kidney sections for antinuclear antibodies.

RESULTS

A total of 481 patients (325 men, 156 women) 16 to 90 years in age (mean age, 61 years) were studied. Anticardiolipin antibodies were present in 5 of 481 (1.04%) patients. One patient was IgG positive and four patients were IgM positive. Of 481 patients, 35 (7.2%) were positive for antinuclear antibodies. Anti-DNA antibodies were not demonstrable in any patient.

CONCLUSIONS

The frequency of anticardiolipin antibodies in a heterogeneous stroke population is possibly lower than reported. The routine screening of anticardiolipin and antinuclear antibodies in a stroke population is of questionable value.

Frequency of the different mutations causing spinocerebellar ataxia (SCA1, SCA2, MJD/SCA3 and DRPLA) in a large group of Brazilian patients

Spinocerebellar ataxia type 1 (SCA1), spinocerebellar ataxia type 2 (SCA2) and Machado-Joseph disease or spinocerebellar ataxia type 3 (MJD/SCA3) are three distinctive forms of autosomal dominant spinocerebellar ataxia (SCA) caused by expansions of an unstable CAG repeat localized in the coding region of the causative genes. Another related disease, dentatorubropallidoluysian atrophy (DRPLA) is also caused by an unstable triplet repeat and can present as SCA in late onset patients. We investigated the frequency of the SCA1, SCA2, MJD/SCA3 and DRPLA mutations in 328 Brazilian patients with SCA, belonging to 90 unrelated families with various patterns of inheritance and originating in different geographic regions of Brazil. We found mutations in 35 families (39%), 32 of them with a clear autosomal dominant inheritance. The frequency of the SCA1 mutation was 3% of all patients; and 6% in the dominantly inherited SCAs. We identified the SCA2 mutation in 6% of all families and in 9% of the families with autosomal dominant inheritance. The MJD/SCA3 mutation was detected in 30% of all patients; and in the 44% of the dominantly inherited cases. We found no DRPLA mutation. In addition, we observed variability in the frequency of the different mutations according to geographic origin of the patients, which is probably related to the distinct colonization of different parts of Brazil. These results suggest that SCA may be occasionally caused by the SCA1 and SCA2 mutations in the Brazilian population, and that the MJD/SCA3 mutation is the most common cause of dominantly inherited SCA in Brazil.

Prolonged NMDA-mediated responses, altered ifenprodil sensitivity, and epileptiform-like events in the malformed hippocampus of methylazoxymethanol exposed rats

Cortical malformations are often associated with refractory epilepsy and cognitive deficit. Clinical and experimental studies have demonstrated an important role for glutamate-mediated synaptic transmission in these conditions. Using whole cell voltage-clamp techniques, we examined evoked glutamate-mediated excitatory postsynaptic currents (eEPSCs) and responses to exogenously applied glutamate on hippocampal heterotopic cells in an animal model of malformation i.e., rats exposed to methylazoxymethanol (MAM) in utero. Analysis revealed that the late N-methyl-D-aspartate (NMDA) receptor-mediated eEPSC component was significantly increased on heterotopic cells compared with age-matched normotopic pyramidal cells. At a holding potential of +40 mV, heterotopic cells also exhibited eEPSCs with a slower decay-time constant. No differences in the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) component of eEPSCs were detected. In 23% of heterotopic pyramidal cells, electrical stimulation evoked prolonged burst-like responses. Focal application of glutamate (10 mM) targeted to different sites near the heterotopia also evoked epileptiform-like bursts on heterotopic cells. Ifenprodil (10 microM), an NR2B subunit antagonist, only slightly reduced the NMDA receptor (NMDAR)-mediated component and amplitude of eEPSCs on heterotopic cells (MAM) but significantly decreased the late component and peak amplitude of eEPSCs in normotopic cells (control). Our data demonstrate a functional alteration in the NMDA-mediated component of excitatory synaptic transmission in heterotopic cells and suggest that this alteration may be attributable, at least in part, to changes in composition and function of the NMDAR subunit. Changes in NMDAR function may directly contribute to the hyperexcitability and cognitive deficits reported in animal models and patients with brain malformations.

Modeling epileptogenesis and temporal lobe epilepsy in a non-human primate

Here we describe a new non-human primate model of temporal lobe epilepsy (TLE) to better investigate the cause/effect relationships of human TLE. Status epilepticus (SE) was induced in adult marmosets by pilocarpine injection (250mg/kg; i.p.). The animals were divided in 2 groups: acute (8h post-SE) and chronic (3 and 5 months post-SE). To manage the severity of SE, animals received diazepam 5min after the SE onset (acute group: 2.5 or 1.25mg/kg; i.p.; chronic group/; 1.25mg/kg; i.p). All animals were monitored by video and electrocorticography to assess SE and subsequent spontaneous recurrent seizures (SRS). To evaluate brain injury produced by SE or SRS we used argyrophil III, Nissl and neo-Timm staining techniques. Magnetic resonance image was also performed in the chronic group. We observed that pilocarpine was able to induce SE followed by SRS after a variable period of time. Prolonged SE episodes were associated with brain damage, mostly confined to the hippocampus and limbic structures. Similar to human TLE, anatomical disruption of dentate gyrus was observed after SRS. Our data suggest that pilocarpine marmoset model of epilepsy has great resemblance to human TLE, and could provide new tools to further evaluate the subtle changes associated with human epilepsy.

Hippocampus-entorhinal cortex loop and seizure generation in the young rodent limbic system

Application of the convulsant 4-aminopyridine (4AP, 50 microM) to adult mouse combined hippocampus-entorhinal cortex (EC) slices induces interictal and ictal discharges originating from CA3 and EC respectively. In this model of limbic seizures, ictal discharges disappear over time and are reestablished after Schaffer collateral cut, a procedure that blocks interictal propagation from CA3 to EC. Here we tested whether this form of network plasticity is operant in hippocampus-EC slices obtained from young (10-25 day-old) mice. In these experiments 4AP elicited interictal (duration = 100-250 ms; interval = 0.7 +/- 0.2 s, mean +/- SD, n = 20) and ictal (duration = 267 +/- 37 s; interval = 390 +/- 37 s, n = 20) discharges in both CA3 and EC. However, in young mouse slices the ictal events occurred throughout the experiment, whereas Schaffer collateral cut abolished CA3-driven interictal discharges in EC without influencing ictal activity (n = 10). Perforant path lesion prevented the spread of EC-driven ictal events to CA3, where interictal and short ictal discharges (duration = 32 +/- 11 s; interval = 92 +/- 9.7 s, n = 8) continued to occur. Hence, two independent forms of ictal activity were seen in CA3 and in EC after separation of these structures. In intact hippocampus-EC slices, ictal discharges were reduced by an N-methyl-D-aspartate receptor antagonist (n = 10). Under these conditions, Schaffer collateral cut abolished ictal activity in EC, not in CA3 (n = 6). Thus the young mouse hippocampus-EC loop has different properties as compared with adult tissue. These differences, which include the inability of hippocampal outputs to control ictal discharge generation in EC and the ability of the loop to sustain ictal activity, may contribute to the low-seizure threshold seen in young individuals.

Short post-weaning social isolation induces long-term changes in the dopaminergic system and increases susceptibility to psychostimulants in female rats

Childhood and adolescence are sensitive periods of development, marked by high brain maturation and plasticity. Exposure to early life stress, such as social isolation, is able to prompt changes in sensitive brain circuitries, essentially in the mesolimbic dopaminergic system and increase the risk for addictive behaviors later in life. Post-weaning social isolation can stimulate the consumption of rewarding substances, like drugs of abuse and palatable foods. However, most studies analyze long periods of social isolation and very little is known about the effects of a brief social isolation in a sensitive period of development and its association with palatable food on the reward system sensitization. Furthermore, females are more susceptible to the reinforcing effect of drugs than males. Therefore, the aim of this study was to analyze the effects of a short post-weaning social isolation combined with a free access to a chronic high sugar diet (HSD) on the dopaminergic system, oxidative status and behavioral response to an amphetamine-like drug in adulthood. We used female Wistar rats that were socially isolated from post-natal days (PD) 21 to 35 and received free access to a HSD until PD 60. On PD 65, animals were submitted to a challenge with diethylpropion (DEP), an amphetamine-like drug and different responses were analyzed: locomotor activity, immmunocontent of dopamine related proteins, and the oxidative status in the striatum, before and after the DEP challenge. We showed that a short post-weaning social isolation (SI) increased the locomotor response to DEP, when compared with previous saline administration. Social isolation also increased dopamine transporter, tyrosine hydroxylase, and decreased dopamine D2 receptor immunocontent. Additionally, SI increased the overall oxidative status parameters after the challenge with DEP. Interestingly, the exposure to a HSD prevented the SI effects on locomotor response, but did not interfere in the dopaminergic parameters evaluated, despite having modified some oxidative parameters. This study showed for the first time that a short post-weaning social isolation was able to induce long-term changes in the striatal dopaminergic system and increased the response to psychostimulants. These results emphasize the importance of stressful experiences during a short period of development on programming susceptibility to psychostimulants later in life.

The Subcortical-Allocortical- Neocortical continuum for the Emergence and Morphological Heterogeneity of Pyramidal Neurons in the Human Brain

Human cortical and subcortical areas integrate emotion, memory, and cognition when interpreting various environmental stimuli for the elaboration of complex, evolved social behaviors. Pyramidal neurons occur in developed phylogenetic areas advancing along with the allocortex to represent 70-85% of the neocortical gray matter. Here, we illustrate and discuss morphological features of heterogeneous spiny pyramidal neurons emerging from specific amygdaloid nuclei, in CA3 and CA1 hippocampal regions, and in neocortical layers II/III and V of the anterolateral temporal lobe in humans. Three-dimensional images of Golgi-impregnated neurons were obtained using an algorithm for the visualization of the cell body, dendritic length, branching pattern, and pleomorphic dendritic spines, which are specialized plastic postsynaptic units for most excitatory inputs. We demonstrate the emergence and development of human pyramidal neurons in the cortical and basomedial (but not the medial, MeA) nuclei of the amygdala with cells showing a triangular cell body shape, basal branched dendrites, and a short apical shaft with proximal ramifications as "pyramidal-like" neurons. Basomedial neurons also have a long and distally ramified apical dendrite not oriented to the pial surface. These neurons are at the beginning of the allocortex and the limbic lobe. "Pyramidal-like" to "classic" pyramidal neurons with laminar organization advance from the CA3 to the CA1 hippocampal regions. These cells have basal and apical dendrites with specific receptive synaptic domains and several spines. Neocortical pyramidal neurons in layers II/III and V display heterogeneous dendritic branching patterns adapted to the space available and the afferent inputs of each brain area. Dendritic spines vary in their distribution, density, shapes, and sizes (classified as stubby/wide, thin, mushroom-like, ramified, transitional forms, "atypical" or complex forms, such as thorny excrescences in the MeA and CA3 hippocampal region). Spines were found isolated or intermingled, with evident particularities (e.g., an extraordinary density in long, deep CA1 pyramidal neurons), and some showing a spinule. We describe spiny pyramidal neurons considerably improving the connectional and processing complexity of the brain circuits. On the other hand, these cells have some vulnerabilities, as found in neurodegenerative Alzheimer's disease and in temporal lobe epilepsy.

Neuronal types of the human cortical amygdaloid nucleus

The human cortical amygdaloid nucleus (CoA) receives exteroceptive sensory stimuli, modulates the functions coded by the intrinsic amygdaloid circuit, and constitutes the beginning of the limbic lobe continuum with direct and indirect connections toward subcortical, allocortical, and higher order neocortical areas. To provide basic data on the human CoA, we characterized and classified the neurons using the thionin and the "single-section" Golgi method adapted for postmortem brain tissue and light microscopy. We found 10 different types of neurons named according to the morphological features of the cell body, dendritic branches, and spine distribution. Most cells are multipolar spiny neurons with two or more primary dendrites, including pyramidal-like ones. Three-dimensional reconstructions evidenced the types and diversity of the dendritic spines in each neuron. The unlike density of spines along dendritic branches, from proximal to distal ones, indicate that the synaptic processing and plasticity can be different in each CoA neuron. Our study provides novel data on the neuronal composition of the human CoA indicating that the variety of cells in this region can have phylogenetic, ontogenetic, morphological, and likely functional implications for the integrated human brain function. This can reflect both a more complex subcortical synaptic processing of sensory and emotional information and an adaptation for species-specific social behavior display.

A new device for step-down inhibitory avoidance task--effects of low and high frequency in a novel device for passive inhibitory avoidance task that avoids bioimpedance variations

Background

Step-down inhibitory avoidance task has been widely used to evaluate aversive memory, but crucial parameters inherent to traditional devices that may influence the behavior analysis (as stimulus frequency, animal’s bioimpedance) are frequently neglected.

New Method

We developed a new device for step-down inhibitory avoidance task by modifying the shape and distribution of the stainless steel bars in the box floor where the stimuli are applied. The bars are 2mm wide, with rectangular shape, arranged in pairs at intervals of 1cm from the next pairs. Each pair makes an electrical dipole where the polarity inverts after each pulse. This device also presents a component that acquires and records the exact current received by the animal foot and precisely controls the frequency of stimulus applied during the entire experiment.

Result

Different from conventional devices, this new apparatus increases the contact surface with bars and animal´s paws, allowing the electric current pass through the animal´s paws only, drastically reducing the influence of animal’s bioimpedance. The analysis of recorded data showed that the current received by the animal was practically the same as applied, independent of the animal´s body composition. Importantly, the aversive memory was observed at specific stimuli intensity and frequency (0.35 or 0.5 mA at 62 and 125Hz but not at 0.20 mA or 20 Hz). Moreover, with this device it was possible to observe the well-known step-down inhibitory avoidance task memory impairment induced by guanosine.

Conclusion

This new device offers a substantial improvement for behavioral analysis in step-down inhibitory avoidance task and allows us to precisely compare data from different animals with distinct body composition.

Sexual dimorphism, estrous cycle and laterality determine the intrinsic and synaptic properties of medial amygdala neurons in rat

The posterodorsal medial amygdala (MePD) is a sex steroid-sensitive area that modulates different social behavior by relaying chemosensorial information to hypothalamic nuclei. However, little is known about MePD cell type diversity and functional connectivity. Here, we have characterized neurons and synaptic inputs in the right and left MePD of adult male and cycling female (in diestrus, proestrus or estrus) rats. Based on their electrophysiological properties and morphology, we found two coexisting subpopulations of spiny neurons that are sexually dimorphic. They were classified as Class I (predominantly bitufted-shaped neurons showing irregular spikes with frequency adaptation) or Class II (predominantly stellate-shaped neurons showing full spike frequency adaptation). Furthermore, excitatory and inhibitory inputs onto MePD cells were modulated by sex, estrous cycle and hemispheric lateralization. In the left MePD, there was an overall increase in the excitatory input to neurons of males compared to cycling females. However, in proestrus, the MePD neurons received mainly inhibitory inputs. Our findings indicate the existence of hemispheric lateralization, estrous cycle and sexual dimorphism influences at cellular and synaptic levels in the adult rat MePD.

Impairment of GABAergic system contributes to epileptogenesis in glutaric acidemia type I

OBJECTIVES

Glutaric acidemia type I (GA-I) is an inherited neurometabolic disorder caused by deficiency of glutaryl-CoA dehydrogenase (GCDH) and characterized by increased levels of glutaric, 3-OH-glutaric, and glutaconic acids in the brain parenchyma. The increment of these organic acids inhibits glutamate decarboxylase (GAD) and consequently lowers the γ-aminobutyric acid (GABA) synthesis. Untreated patients exhibit severe neurologic deficits during development, including epilepsy, especially following an acute encephalopathy outbreak. In this work, we evaluated the role of the GABAergic system on epileptogenesis in GA-I using the Gcdh^-/- mice exposed to a high lysine diet (Gcdh^-/- -Lys).

METHODS

Spontaneous recurrent seizures (SRS), seizure susceptibility, and changes in brain oscillations were evaluated by video-electroencephalography (EEG). Cortical GABAergic synaptic transmission was evaluated using electrophysiologic and neurochemical approaches.

RESULTS

SRS were observed in 72% of Gcdh^-/- -Lys mice, whereas no seizures were detected in age-matched controls (Gcdh^+/+ or Gcdh^-/- receiving normal diet). The severity and number of PTZ-induced seizures were higher in Gcdh^-/- -Lys mice. EEG spectral analysis showed a significant decrease in theta and gamma oscillations and predominant delta waves in Gcdh^-/- -Lys mice, associated with increased EEG left index. Analysis of cortical synaptosomes revealed a significantly increased percentage of glutamate release and decreased GABA release in Gcdh^-/- -Lys mice that were associated with a decrease in cortical GAD immunocontent and activity and confirmed by reduced frequency of inhibitory events in cortical pyramidal cells.

SIGNIFICANCE

Using an experimental model with a phenotype similar to that of GA-I in humans-the Gcdh^-/- mice under high lysine diet (Gcdh^-/- -Lys)-we provide evidence that a reduction in cortical inhibition of Gcdh^-/- -Lys mice, probably induced by GAD dysfunction, leads to hyperexcitability and increased slow oscillations associated with neurologic abnormalities in GA-I. Our findings offer a new perspective on the pathophysiology of brain damage in GA-I.

Guanosine Exerts Neuroprotective Effect in an Experimental Model of Acute Ammonia Intoxication

The nucleoside guanosine (GUO) increases glutamate uptake by astrocytes and acts as antioxidant, thereby providing neuroprotection against glutamatergic excitotoxicity, as we have recently demonstrated in an animal model of chronic hepatic encephalopathy. Here, we investigated the neuroprotective effect of GUO in an acute ammonia intoxication model. Adult male Wistar rats received an intraperitoneal (i.p.) injection of vehicle or GUO 60 mg/kg, followed 20 min later by an i.p. injection of vehicle or 550 mg/kg of ammonium acetate. Afterwards, animals were observed for 45 min, being evaluated as normal, coma (i.e., absence of corneal reflex), or death status. In a second cohort of rats, video-electroencephalogram (EEG) recordings were performed. In a third cohort of rats, the following were measured: (i) plasma levels of glucose, transaminases, and urea; (ii) cerebrospinal fluid (CSF) levels of ammonia, glutamine, glutamate, and alanine; (iii) glutamate uptake in brain slices; and (iv) brain redox status and glutamine synthetase activity in cerebral cortex. GUO drastically reduced the lethality rate and the duration of coma. Animals treated with GUO had improved EEG traces, decreased CSF levels of glutamate and alanine, lowered oxidative stress in the cerebral cortex, and increased glutamate uptake by astrocytes in brain slices compared with animals that received vehicle prior to ammonium acetate administration. This study provides new evidence on mechanisms of guanine-derived purines in their potential modulation of glutamatergic system, contributing to GUO neuroprotective effects in a rodent model of by acute ammonia intoxication.

Effective recommendations towards healthy routines to preserve mental health during the COVID-19 pandemic

Objective:

To assess the adherence to a set of evidence-based recommendations to support mental health during the coronavirus disease 2019 (COVID-19) pandemic and its association with depressive and anxiety symptoms.

Methods:

A team of health workers and researchers prepared the recommendations, formatted into three volumes (1: COVID-19 prevention; 2: Healthy habits; 3: Biological clock and sleep). Participants were randomized to receive only Volume 1 (control), Volumes 1 and 2, Volumes 1 and 3, or all volumes. We used a convenience sample of Portuguese-speaking participants over age 18 years. An online survey consisting of sociodemographic and behavioral questionnaires and mental health instruments (Patient Health Questionnaire-9 [PHQ-9] and Generalized Anxiety Disorder-7 [GAD-7]) was administered. At 14 and 28 days later, participants were invited to complete follow-up surveys, which also included questions regarding adherence to the recommendations. A total of 409 participants completed the study – mostly young adult women holding university degrees.

Results:

The set of recommendations contained in Volumes 2 and 3 was effective in protecting mental health, as suggested by significant associations of adherence with PHQ-9 and GAD-7 scores (reflecting anxiety and depression symptoms, respectively).

Conclusion:

The recommendations developed in this study could be useful to prevent negative mental health effects in the context of the pandemic and beyond.