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GABA-ergic neurons and the neurobiology of schizophrenia and other psychoses.

There are a number of disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM IV) that are characterised by having psychotic symptoms as the defining feature [17]. The narrowest definition of psychosis is restricted to delusions or prominent hallucinations, with the hallucinations occurring in the absence of insight into their pathological nature. Schizophrenia is the most prevalent form of psychosis, but this may also occur due to other medical conditions (e.g., Prader-Willi syndrome, epilepsy), in the early post-partum period, at menopause, and as a result of drug use. This article attempts to draw together an underlying causation across the various forms of psychotic disorder and, by integrating this with what is known about the genetics, neuroanatomy and neuropharmacology of the positive symptoms in schizophrenia, produce a broader understanding. At the cellular level, gamma-aminobutyric acid (GABA)-ergic interneurons are a common feature in psychotic states, and are a principal focus for serotonin and dopamine innervations, as well as playing an important role in cortical development. At the systems level, prefrontal and medial temporal cortices are implicated with activity levels out of synchrony in schizophrenics. How these vast areas of disparately functioning cortical networks are "bound" together to provide coherent conscious experiences is again a function of GABA-ergic interneurons. These interneurons have highly divergent inhibitory projections to large numbers of pyramidal neurons and are themselves synchronised by the ascending dopamine and serotonin innervations.

Animals↗

Fungal auxin overproduction affects the anatomy of Hebeloma cylindrosporum-Pinus pinaster ectomycorrhizas.

We studied the effect of fungal auxin overproduction on the growth polarity of cortical cells in pine mycorrhizas by comparing the anatomy of Pinus pinaster (Ait.) Sol. mycorrhizas formed by an IAA-overproducing mutant of Hebeloma cylindrosporum Romagnesi or by the corresponding wild type with non-mycorrhizal short roots. Both wild- type and mutant strains induced an increase in root diameter that was mostly a result of the influence of the fungus on root cortical development. Both strains affected growth polarity of P. pinaster cortical cells and induced a change in their shape. The main modifications were a large reduction in axial diameter and an increase in the radial diameter of the cortical cells. The modifications were more marked with the mutant than with the wild type. The mutant induced a 43% reduction in cortical cell elongation and a 35% increase in radial diameter, whereas the corresponding changes induced by the wild type were 30 and 10%, respectively. The volume of cortical cells in mature mycorrhizas was generally lower than in uninoculated short roots indicating that wild-type and mutant strains induced a reorientation of cortical cell growth but did not induce an increase in turgor pressure of the cells. Immunolocalization allowed visualization of alpha-tubulin in root cortical cells, but no obvious modification in alpha-tubulin distribution was detected as a consequence of symbiosis establishment. Likewise, cytochemical localization of polysaccharides in cortical cell walls did not show significant modification following symbiosis establishment and Hartig net formation. The only noticeable modification was a reduction in cortical cell wall thickness in mycorrhizas compared with uninoculated short roots. The possible involvement of fungal auxin in the observed modifications is discussed.

Basidiomycota↗

[Case of cortical deafness sparing the music area].

A 33-year-old woman had developed cortical deafness with profound initial deafness lasting for eleven months after pneumococcal meningitis ten years previously. CT scan demonstrated bilateral temporal lobe lesions, predominantly on the left side where it extended into the adjacent parietal and frontal lobes. Audiometry suggested integrity of the internal ear and brain stem. Early auditory evoked potentials were present, while potentials of moderate latency and delayed potentials were abolished. Neuropsychological investigations demonstrated total absence of spoken language, contrasting with conservation of written language, though with agrammatism and an impossibility of identifying non-verbal noises, spoken language, and music. The patient could not identify rhythms, pitch, melodies or the different types of music. The musical quality of sound stimuli and musical pleasure were, however spared as shown by recognition of tape recorded sound stimuli with written denomination and designation of images in multiple choice tests. The relations between auditory agnosia, "pure" verbal deafness and cortical deafness are discussed. Reported cases are reviewed and an attempt is made to demonstrate the existence of several levels in the integration of musical stimuli, the most elementary of which could be the perception of the musical quality of sounds, as was the case in the present patient.

Adult↗

Expression of GABA and GABAA receptors by neurons of the subplate zone in developing primate occipital cortex: evidence for transient local circuits.

Several lines of evidence suggest that the transient subplate zone of the embryonic mammalian telencephalon could influence cortical development through synaptic or trophic interactions with growing cortical afferents and migrating neurons. Since such interactions may involve neurotransmitters and their receptor molecules, we have examined the expression of GABA and subunits of the GABAA/benzodiazepine receptor complex in the occipital lobe of embryonic rhesus monkeys by immunochemistry and in situ hybridization. We found that during the second half of gestation, when the subplate zone reaches peak maturity in this species, many neurons can be immunolabeled with both GABA antisera and monoclonal antibodies against GABAA receptor subunits. The most robust labeling occurs at approximately embryonic day (E)125 (birth is at E165). Electron microscopic observations of receptor subunit-immunolabeled material confirmed that subunits of the GABAA receptor are localized in the subplate neurons and their dendritic processes. In many instances the reaction product is associated with the plasma membranes of labeled processes, some of which form symmetrical synapses with small unlabeled axon terminals. The results of in situ hybridization are in accord with the results of receptor subunit immunochemistry. From E80 to E141, hybridization signal for GABAA receptor subunit mRNA occurs in the subplate zone and increases steadily to peak levels between E125 and E141. The present results reveal that all the elements necessary for the formation of functional GABAergic synaptic circuitry are present in the subplate zone. Further, the ages showing the most pronounced receptor and transmitter expression in this primate coincide with the ingrowth of major cortical afferent systems. Taken together, these findings suggest that GABAergic local neuronal circuits in the subplate may be involved in the development of long tract connections stationed in this zone prior to their transfer to the overlying cortical plate.

Animals↗

Dopamine agonists suppress visual-cortical reflex myoclonus.

Two patients with a diagnosis of olivo-ponto-cerebellar atrophy developed cortical reflex myoclonus to visual (flash) and somaesthetic stimuli. Oral treatment with levodopacarbidopa (1000/100 mg) or subcutaneous administration of apomorphine (1 mg) abolished the visually-triggered myoclonus, without modifying reflex myoclonus to electrical or tactile stimulation. Intravenous administration of lisuride (0.1 mg) produced a marked reduction in both types of reflex myoclonus. These results indicate a selective inhibitory effect of dopamine agonist drugs on visual reflex myoclonus of cortical origin.

Aged↗

Major events in the development of the forebrain.

The development of the central nervous system can be divided into a number of phases, each of which is characterized by particular developmental disorders. In recent years, much progress has been made in elucidating the mechanisms by which the forebrain develops and in our understanding of major developmental disorders such as holoprosencephaly and neuronal migration disorders. In this general introduction to this symposium the major stages in the development of the forebrain, its regionalization and the genes involved, and some of the developmental disorders derailing cortical development with subsequent damage to the main cortical fiber connections (pyramidal tract and corpus callosum) are discussed.

Brain↗

The specificity of interactions between the cortex and the thalamus.

The functioning of the adult mammalian cerebral cortex depends critically upon precise interconnections between specific thalamic nuclei and distinct cortical regions. Therefore, one central issue in understanding cortical development is determining the cellular and molecular strategies underlying the specification of thalamocortical projections. We address the role of axon-axon interactions and membrane-bound guidance molecules in the establishment of the development of layer-specific patterns of afferent and efferent cortical connections does not depend upon neuronal activity. We present evidence that activity conveyed by thalamic afferents is required for the elaboration of the columnar specificity of cortical circuits.

Animals↗

Distinct ontogenic and regional expressions of newly identified Cajal-Retzius cell-specific genes during neocorticogenesis.

Cajal-Retzius (CR) cells are early-generated transient neurons and are important in the regulation of cortical neuronal migration and cortical laminar formation. Molecular entities characterizing the CR cell identity, however, remain largely elusive. We purified mouse cortical CR cells expressing GFP to homogeneity by fluorescence-activated cell sorting and examined a genome-wide expression profile of cortical CR cells at embryonic and postnatal periods. We identified 49 genes that exceeded hybridization signals by >10-fold in CR cells compared with non-CR cells at embryonic day 13.5, postnatal day 2, or both. Among these CR cell-specific genes, 25 genes, including the CR cell marker genes such as the reelin and calretinin genes, are selectively and highly expressed in both embryonic and postnatal CR cells. These genes, which encode generic properties of CR cell specificity, are eminently characterized as modulatory composites of voltage-dependent calcium channels and sets of functionally related cellular components involved in cell migration, adhesion, and neurite extension. Five genes are highly expressed in CR cells at the early embryonic period and are rapidly down-regulated thereafter. Furthermore, some of these genes have been shown to mark two distinctly different focal regions corresponding to the CR cell origins. At the late prenatal and postnatal periods, 19 genes are selectively up-regulated in CR cells. These genes include functional molecules implicated in synaptic transmission and modulation. CR cells thus strikingly change their cellular phenotypes during cortical development and play a pivotal role in both corticogenesis and cortical circuit maturation.

Animals↗

GABA stimulates chemotaxis and chemokinesis of embryonic cortical neurons via calcium-dependent mechanisms.

During rat cortical development, when neurons migrate from the ventricular zone to the cortical plate, GABA localizes within the target destinations of migratory neurons. At this time, cells in germinal zones and along migratory pathways express GABA receptor subunit transcripts, implying that in vivo, GABA may be a chemoattractant. We used an in vitro strategy to study putative chemotropic effects of GABA on embryonic rat cortical cells. GABA stimulated neuronal migration in vitro at embryonic day 15 (E15). From E16 onward, two concentration ranges (fM and microM) induced motility. Femtomolar GABA primarily stimulated chemotaxis (migration along a chemical gradient), whereas micromolar GABA predominantly initiated chemokinesis (increased random movement). These effects were mimicked by structural analogs of GABA with relative specificity at GABAA (muscimol), GABAB (R-baclofen), and GABAC (trans- or cis-4-aminocrotonic acid) receptors. Antagonists of GABAB (saclofen) and GABAC (picrotoxin) receptors partially inhibited responses to both femto- and micromolar GABA; however, only responses to femtomolar GABA were partially blocked by bicuculline, a well established antagonist of GABA at GABAA receptors. Hence, chemotactic responses to femtomolar GABA seem to involve all three classes of GABA receptor proteins, whereas chemokinetic responses to micromolar GABA involve GABAB and GABAC receptor proteins. GABA-induced motility was blocked by loading the cells with the Ca(2+)-chelating molecule bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid, suggesting that intracellular Ca2+ mediates GABA-induced cell movement. Optical recordings of cells loaded with Ca2+ indicator dye revealed that both femto- and micromolar GABA evoked increases in intracellular Ca2+. Thus, GABA-stimulated increases in intracellular Ca2+ may mediate both chemotactic and chemokinetic responses in embryonic cortical cells.

Animals↗

Ancestry of the mammalian preplate and its derivatives: evolutionary relicts or embryonic adaptations?

Mammalian cortical development is preceded by the elaboration of a transient preplate, which is split into a superficial marginal zone and a deep subplate after the arrival of the cortical plate. There has been some controversy in the evolutionary interpretation of this transient structure, as some propose it to represent the ancestral cortex or pallium of non-mammals, while others consider it to be a phylogenetic novelty. The preplate and its derivatives contain components derived by both tangential and radial migration. Tangentially migrating elements include pioneer neurons and interneurons, both of subpallial origin, and Cajal-Retzius cells, mostly of pallial origin. Pioneer neurons were probably present in the ancestors of mammals, but may have changed their original superficial position to one below the developing cortex, thus attracting thalamic afferents in the subcortical white matter, and making them penetrate the cortex radially. In mammals, Cajal-Retzius cells appear to have increased both in number and on their level of reelin expression, perhaps in the context of controlling the final stages of migration in a radially expanding neoocortex. Radial-migrating cells are partly represented by the pyramidal-like cells of the subplate. These neurons resemble the excitatory elements of the adult reptilian cortex, but is not clear whether they are their true homologues. One possibility is that these cells appeared by virtue of a heterochronic process in which the earliest radial elements of the cortical plate began to be produced at progressively earlier developmental stages. Thus, we conclude that the mammalian preplate and its derivatives contain both ancestral and derived elements, all of which have been modified in the course of mammalian evolution to support an increasingly complex cortical plate development.

Animals↗

A role for subplate neurons in the patterning of connections from thalamus to neocortex.

During cerebral cortical development, ingrowing axons from different thalamic nuclei select and invade their cortical targets. The selection of an appropriate target is first evident even before thalamic axons grow into the cortical plate: initially axons accumulate and wait below their cortical target area in a zone called the subplate. This zone also contains the first postmitotic neurons of the cerebral cortex, the subplate neurons. Here we have investigated whether subplate neurons are involved in the process of target selection by thalamic axons by ablating them from specific cortical regions at the onset of the waiting period and examining the subsequent thalamocortical axon projection patterns. Subplate neurons were ablated at the onset of the waiting period by intracortical injections of kainic acid. The effect of the ablation on the thalamocortical projection from visual thalamus was examined by DiI-labeling of the LGN days to weeks following the lesion. At two to four weeks post-lesion, times when LGN axons would have normally invaded the cortical plate, the axons remained below the cortical plate and grew past their appropriate cortical target in an anomalous pathway. Moreover, examination of LGN axons at one week post-lesion, a time when they would normally be waiting and branching within the visual subplate, indicated that the axons had already grown past their correct destination. These observations suggest that visual subplate neurons are involved in the process by which LGN axons select and subsequently grow into visual cortex. In contrast, subplate neurons do not appear to play a major role in the initial morphological development of the LGN itself. Subplate ablations did not alter dendritic growth or shapes of LGN projection neurons during the period under study, nor did it prevent the segregation of retinal ganglion cell axons into eye-specific layers. However, the overall size of the LGN was reduced, suggesting that there may be increased cell death of LGN neurons in the absence of subplate neurons. To examine whether subplate neurons beneath other neocortical areas play a similar role in the formation of thalamocortical connections, subplate neurons were deleted beneath auditory cortex at the onset of the waiting period for auditory thalamic axons. Subsequent DiI labeling revealed that in these animals the majority of MGN axons had grown past auditory cortex instead of innervating it. Taken together these observations underscore a general requirement for subplate neurons throughout neocortex in the process of cortical target selection and ingrowth by thalamic axons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Changes in the CSF fluid pathways in the developing rat fetus with early onset hydrocephalus.

Interest in the factors involved in the abnormal cortical development of the HTx rat fetus have led us to re-examine the structural and morphological changes in the CSF pathways preceding constriction and blockage of the cerebral aqueduct. Histological analysis was carried out on coronal and sagittal sections from HTx and Wistar fetuses. The aqueduct is found to be a broad channel extending from the posterior end of the third ventricle that ends in a blind pouch above the developing cerebellum. The aqueduct drains into the fourth ventricle via a vertically orientated, narrow channel lying between the posterior aspect of the pontine flexure and the anterior surface of the cerebellum. On Day E18 the connecting channel between the aqueduct and the fourth ventricle is blocked by apposition of its walls. 24 hours later the lateral ventricles begin to dilate and the anterior end of the aqueduct is blocked and the connecting channel between the aqueduct and the fourth ventricle reopens. The cause of these sequential changes in the CSF fluid pathways remains speculative.

Animals↗

The structure of cerebral cortex in the rat following prenatal administration of 6-hydroxydopamine.

The early, prenatal formation of noradrenergic projections to the forebrain has led to the proposition that these axons exert a trophic influence on cerebral cortex during ontogeny. To test this hypothesis, we have examined a number of different structural features of cortical development following prenatal lesions of the ascending noradrenergic axons. The parameters that were analyzed include cytoarchitecture, dendritic morphology, and the distribution of monoaminergic and nonmonoaminergic cortical afferents. Rat fetuses were administered the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) by transuterine, intraperitoneal injection on embryonic day 17. Vehicle-injected controls and fetuses treated with the catecholamine uptake inhibitor desmethylimipramine (DMI) prior to 6-OHDA were prepared. After reaching maturity (200-300 g), the brain of treated and control rats were examined using Nissl and Golgi preparations (for cytoarchitecture and dendritic morphology), histofluorescence (for monoaminergic afferents, especially dopaminergic axons), and serotonin and dopamine-beta-hydroxylase (DBH) immunocytochemistry. Effective lesioning of the ascending noradrenergic system was confirmed in each case, using DBH immunocytochemistry. Prenatal treatment with 6-OHDA resulted in complete and long-lasting destruction of the noradrenergic innervation of the cerebral cortex, along with hyperinnervation of the diencephalon and brain stem. Despite the widespread denervation of cerebral cortex, no significant alterations in cytoarchitecture, dendritic morphology, or spine counts were found in treated brains. In particular, no abnormalities were observed in the apical dendrites of layer VI pyramidal cells, based on qualitative criteria. The distribution, density and morphology of serotonergic and dopaminergic afferents were unaffected. Thalamocortical afferents had developed normally as reflected by the cortical barrels. In 33% of the 6-OHDA-treated fetuses foci of ectopic neurons were found at the cortical surface. The ectopias contain neuronal processes, somata, and synapses interspersed with collagen and other connective tissue elements. While the ectopias may result from selective damage to the noradrenergic neurons, the finding of similar (but smaller) malformations in DMI-protected animals is equally consistent with a non-specific effect of 6-OHDA upon non-adrenergic cells. The examination of intervening stages will be needed to resolve this question. Based on the parameters of cortical structure analyzed in this study we conclude that the neocortex develops normally even in the absence of the noradrenergic system.

Afferent Pathways↗

Maternal Immune Activation Disrupts Epigenomic and Functional Maturation of Cortical Excitatory Neurons.

Elevated levels of maternal pro-inflammatory cytokines during gestation can disrupt offspring neural development, increasing the risk of neurodevelopmental disorders. We studied the effects of Poly(I:C)-induced maternal immune activation (PIC-MIA) during mid-gestation on developing cortical excitatory neurons' DNA methylation and transcriptome. PIC-MIA disrupted the developmental regulation of synapse-related genes and of genes implicated in autism spectrum disorders. Genomic regions that gain or lose DNA methylation during normal development were altered following PIC-MIA, including neurodevelopmental transcription factor binding sites. The DNA methylation and transcriptional changes were consistent with a delay in excitatory neuron maturation. Whole-cell recordings showed that PIC-MIA preferentially altered the physiological development of layer 5 excitatory neurons. Taken together, present results suggest that alterations in the epigenome, through the disruption of circuit formation, may drive the long-term consequences of maternal infection during gestation.

DNA methylation↗

Oxygen and glucose deprivation induces major dysfunction in the somatosensory cortex of the newborn rat.

The mechanisms and functional consequences of ischemia-induced injury during perinatal development are poorly understood. Subplate neurons (SPn) play a central role in early cortical development and a pathophysiological impairment of these neurons may have long-term detrimental effects on cortical function. The acute and long-term consequences of combined oxygen and glucose deprivation (OGD) were investigated in SPn and compared with OGD-induced dysfunction of immature layer V pyramidal cortical neurons (PCn) in somatosensory cortical slices from postnatal day (P)0-4 rats. OGD for 50 min followed by a 10-24-h period of normal oxygenation and glucose supply in vitro or in culture led to pronounced caspase-3-dependent apoptotic cell death in all cortical layers. Whole-cell patch-clamp recordings revealed that the majority of SPn and PCn responded to OGD with an initial long-lasting ischemic hyperpolarization accompanied by a decrease in input resistance (R(in)), followed by an ischemic depolarization (ID). Upon reoxygenation and glucose supply, the recovery of the membrane potential and R(in) was followed by a Na+/K+-ATPase-dependent postischemic hyperpolarization, and in almost half of the investigated SPn and PCn by a postischemic depolarization. Whereas neither a moderate (2.5 mm) nor a high (4.8 mm) increase in extracellular magnesium concentration protected the SPn from OGD-induced dysfunction, blockade of NMDA receptors with MK-801 led to a significant delay and decrease of the ID. Our data demonstrate that OGD induces apoptosis and a profound dysfunction in SPn and PCn, and underline the critical role of NMDA receptors in early ischemia-induced neuronal damage.

Animals↗

Bilateral frontoparietal polymicrogyria: clinical and radiological features in 10 families with linkage to chromosome 16.

Polymicrogyria is a common malformation of cortical development characterized by an excessive number of small gyri and abnormal cortical lamination. Multiple syndromes of region-specific bilateral symmetric polymicrogyria have been reported. We previously have described two families with bilateral frontoparietal polymicrogyria (BFPP), an autosomal recessive syndrome that we mapped to a locus on chromosome 16q12-21. Here, we extend our observations to include 19 patients from 10 kindreds, all linked to the chromosome 16q locus, allowing us to define the clinical and radiological features of BFPP in detail. The syndrome is characterized by global developmental delay of at least moderate severity, seizures, dysconjugate gaze, and bilateral pyramidal and cerebellar signs. Magnetic resonance imaging demonstrated symmetric polymicrogyria affecting the frontoparietal regions most severely, as well as ventriculomegaly, bilateral white matter signal changes, and small brainstem and cerebellar structures. We have refined our genetic mapping and describe two apparent founder haplotypes, one of which is present in two families with BFPP and associated microcephaly. Because 11 of our patients initially were classified as having other malformations, the syndrome of BFPP appears to be more common than previously recognized and may be frequently misdiagnosed.

Adolescent↗

Prevention of experimental diabetic cataract by Indian Ayurvedic plant extracts.

The efficacy of Momordica charantia (MC), Eugenia jambolana (EJ), Tinospora cordifolia (TC) and Mucuna pruriens (MP) was assessed in the prevention of murine alloxan dibetic cataract. Alloxan (120 mg/kg) was used as the diabetogenic agent. While controls and diabetic controls did not receive any plant extract, treated rats received lyophilized aqueous extract of MC and EJ (200 mg/kg p.o.), alcohol extract of TC (400 mg/kg) and MP (200 mg/kg p.o.) every day until 4 months. Serum glucose concentration was assessed and cataracts examined with both the naked eye and through a slit lamp. Of the eight animals in the diabetic control group, four developed cortical cataract (stage IV) by day 90 while the remaining four developed it by day 100. The incidence rate of cataract in MC, EJ, TC and MP treated groups at 120 days was only 0, 0, 1 and 2. Oral feeding of MC, EJ, TC and MP extracts for 1 month produced a fall of 64.33%, 55.62%, 38.01% and 40.17%, respectively, in the serum glucose levels in comparison with the 48 h level. After 2 months of treatment, the respective values were 66.96%, 59.85%, 40.41% and 45.63%. MC and EJ prevented the development of cataract while the protective effect was less with TC and MP along with a significant reduction of plasma glucose levels (p < 0.001).

Administration, Oral↗

Evidence of activated microglia in focal cortical dysplasia.

Focal cortical dysplasia (FCD), which is caused by malformations of cortical development, is known to be a major cause of intractable epilepsy. Cortical laminar disorganization and the presence of abnormal neuronal and astroglial cell types are histological characteristics of FCD. Though, little information is known about the microglia/macrophage cell system in FCD and its possible contribution to the high epileptogenesis of this disorder. In the present study, the distribution of cells of the microglia/macrophage lineage was studied in 20 specimens of FCD (type II) by immunocytochemistry for CD68 and human HLA-DR. A significant number of microglial cells and macrophages were observed within the dysplastic cortex. The mean number of CD68- and HLA-DR-positive cells was significantly higher in FCD specimens than in normal-appearing control cortex obtained at autopsy. HLA-DR-positive cells, which represent activated microglia, were localized around blood vessels and also clustered around dysplastic neuronal cells. The density of these activated HLA-DR-positive microglial cells correlated with the duration of epilepsy, as well as with the frequency of seizures prior to surgical resection. CD68-positive macrophages were mainly located around vessels and the number of these cells did not correlate with seizure frequency, neither with the duration of symptoms prior to surgical resection. In conclusion, our findings demonstrate a specific and persistent increase in the numerical density of HLA-DR-positive activated microglia within the dysplastic region, supporting the contribution of the inflammatory response and proinflammatory molecules to the epileptogenicity of FCD.

Adolescent↗