Increased cortical synaptic activation of TrkB and downstream signaling markers in a mouse model of Down Syndrome.

Down Syndrome (DS), trisomy 21, is characterized by synaptic abnormalities and cognitive deficits throughout the lifespan and with development of Alzheimer's disease (AD) neuropathology and progressive cognitive decline in adults. Synaptic abnormalities are also present in the Ts65Dn mouse model of DS, but which synapses are affected and the mechanisms underlying synaptic dysfunction are unknown. Here we show marked increases in the levels and activation status of TrkB and associated signaling proteins in cortical synapses in Ts65Dn mice. Proteomic analysis at the single synapse level of resolution using array tomography (AT) uncovered increased colocalization of activated TrkB with signaling endosome related proteins, and demonstrated increased TrkB signaling. The extent of increases in TrkB signaling differed in each of the cortical layers examined and with respect to the type of synapse, with the most marked increases seen in inhibitory synapses. These findings are evidence of markedly abnormal TrkB-mediated signaling in synapses. They raise the possibility that dysregulated TrkB signaling contributes to synaptic dysfunction and cognitive deficits in DS.

Discoveries in Down syndrome: moving basic science to clinical care.

This review describes recent discoveries in neurobiology of Down syndrome (DS) achieved with use of mouse genetic models and provides an overview of experimental approaches aimed at development of pharmacological restoration of cognitive function in people with this developmental disorder. Changes in structure and function of synaptic connections within the hippocampal formation of DS model mice, as well as alterations in innervations of the hippocampus by noradrenergic and cholinergic neuromodulatory systems, provided important clues for potential pharmacological treatments of cognitive disabilities in DS. Possible molecular and cellular mechanisms underlying this genetic disorder have been addressed. We discuss novel mechanisms engaging misprocessing of amyloid precursor protein (App) and other proteins, through their affect on axonal transport and endosomal dysfunction, to "Alzheimer-type" neurodegenerative processes that affect cognition later in life. In conclusion, a number of therapeutic strategies have been defined that may restore cognitive function in mouse models of DS. In the juvenile and young animals, these strategists focus on restoration of synaptic plasticity, rate of adult neurogenesis, and functions of the neuromodulatory subcortical systems. Later in life, the major focus is on recuperation of misprocessed App and related proteins. It is hoped that the identification of an increasing number of potential targets for pharmacotherapy of cognitive deficits in DS will add to the momentum for creating and completing clinical trials.

Penetration, diffusion, and uptake of recombinant human alpha-L-iduronidase after intraventricular injection into the rat brain.

Central nervous system disease can have devastating consequences in the severe or Hurler form of mucopolysaccharisosis I (MPS I). Intravenously administered recombinant human alpha-L-iduronidase (rhIDU) is not expected to reach and treat the brain disease due to the blood-brain barrier. To determine whether administration of rhIDU into the cerebrospinal fluid could successfully treat the brain, we studied intraventricular administration of rhIDU in rats. RhIDU was stereotactically administered directly to the lateral ventricle of the intact rat brain and the brain tissues assessed by enzyme assays, immunofluorescence and confocal microscopy 30 min, 24 h, or 7 days later. Quantitation of activity revealed that rhIDU was widely distributed throughout the brain following injection into the lateral ventricle, with activities increased by a factor of 3.3 higher than control in most samples 30 min-24 h after injection and highest levels on the side of injection. The enzyme crossed the ependymal lining of the ventricle and entered neurons into lysosomal-like vesicles. The enzyme was able to diffuse through brain tissue as demonstrated by a decreasing signal gradient from 0.2 to 4.8 mm from the ventricle surface. The largest amount of rhIDU, as detected by immunostaining, was observed 24 h after injection and decreased approximately 50% during the first 7 days. Although the immunostaining decreased with time, specific vesicular staining was still detectable 28 days after injection. The data suggest that rhIDU given into the ventricle can diffuse, penetrate at least several millimeters of brain tissue and be taken up into neurons and glial cells.

[Structural changes in dendritic spines of the pyramidal neurons of layer III of the rat sensory-motor cortex during remote postischemic period]. / Strukturnye izmeneniia dendritnykh shipikov piramidnykh neironov sloia III sensomotornoi kory bol'shogo mozga krys v otdalennom postishemicheskom periode.

The combination of Golgi method with the lipid phosphorilate mark Dil (1,1'-dioctadecyl-3,3,3 cents, 3 cents-tetramethyl-indocarbocyanine perchlorate) and confocal laser scanning microscope for demonstration of the structure of dendritic tree and dendritic spines enables exact determination of spatial organization of small dendrites and their spines at significant distances in norm and especially in postischemic period. The regularities of dendritic spine reorganization in layer III pyramidal neurons of the cerebral sensory-motor cortex during 9 months after short-term (10 min) total brain ischemia were established.

Brain-directed autoantibodies levels in the serum of Rett syndrome patients.

Increased titer of brain-directed autoantibodies (AAB) may represent a risk for brain development in children with Rett syndrome (RTT). The aims of this work were to study the levels of brain-directed AAB, mainly nerve growth factor (NGF) and S-100 protein AAB, to analyze morphological features of brain labeling by AAB produced in RTT patients, and to correlate with clinical manifestation. The increased titer of anti-NGF AAB, but not of anti-S100 AAB has been determined in the blood of RTT patients. The blood from five RTT girls was investigated repeatedly (two to four times) within 0.5-3 years. In these RTT patients the level of anti-NGF AAB was stable, not depending on the stage of illness, so individual stability of anti-NGF AAB levels have been detected. However, the negative correlation between the level of these AAB and severity of disease has been found: girls with the milder course of illness (with relative preservation of speech and locomotor functions, later disease onset, and later development of regressive symptoms) were characterized by the higher levels of AAB. The study also revealed immunohistochemical labeling of neuronal population with serum from RTT patients. Serum AAB from RTT cases labeled the cytoplasm and apical dendrites of pyramidal neurons in the neocortex and hippocampus, neurons in basal ganglia and brain stem, but not in the cerebellum of rats. Our results show the presence of brain-directed AAB in blood serum of RTT patients, which suggests an autoimmune component in pathogenesis of RTT.

Failed retrograde transport of NGF in a mouse model of Down's syndrome: reversal of cholinergic neurodegenerative phenotypes following NGF infusion.

Age-related degeneration of basal forebrain cholinergic neurons (BFCNs) contributes to cognitive decline in Alzheimer's disease and Down's syndrome. With aging, the partial trisomy 16 (Ts65Dn) mouse model of Down's syndrome exhibited reductions in BFCN size and number and regressive changes in the hippocampal terminal fields of these neurons with respect to diploid controls. The changes were associated with significantly impaired retrograde transport of nerve growth factor (NGF) from the hippocampus to the basal forebrain. Intracerebroventricular NGF infusion reversed well established abnormalities in BFCN size and number and restored the deficit in cholinergic innervation. The findings are evidence that even BFCNs chronically deprived of endogenous NGF respond to an intervention that compensates for defective retrograde transport. We suggest that age-related cholinergic neurodegeneration may be a treatable disorder of failed retrograde NGF signaling.

Effect of transplantation of embryonic nervous tissue on reorganization of interneuronal relationships after mechanical damage to sensorimotor cortex.

The effect of implanted embryonic nervous tissue on restoration of axonal connections in the cerebral cortex after mechanical injury was studied on albino rats using fluorescent lipophilic probe DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate) and confocal laser scanning microscope. Implantation of embryonic tissue to damaged area promotes the growth of axons through the transplant to adjacent tissue. The damaged area is impenetrable for axons growing without implantation.

Guidelines for reporting clinical features in cases with MECP2 mutations.

An international group recommends that papers relating phenotypes to genotypes involving mutations in the X chromosome gene MECP2 should provide a minimum data set reporting the range of disturbances frequently encountered in Rett Syndrome. A simple scoring system is suggested which will facilitate comparison among the various clinical profiles. Features are described which should prompt screening for MECP2 mutations.

Neuronal and fibre organization in neocortical grafts placed in post-ischaemic adult rat brain: a three-dimensional confocal microscopy study.

The dendritic morphology in neocortical grafts was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer Yellow into individual cells. The grafts had been implanted into infarct cavities in the neocortex of hypertensive rats 46 weeks earlier. The carbocyanine dye method was used to identify afferent (host to transplant) and efferent (transplant to host) connections. Pyramidal, nonpyramidal and glial cells were present in the transplants. Some dendrites had an almost normal appearance, but abnormalities (atypical orientation of apical, basal or oblique apical dendrites) were observed. Some bi-apical pyramidal neurons and pyramidal neurons with obliquely oriented apical dendrites were also observed. Carbocyanine dye-labelled fibres of different diameter formed a dense network in the transplant, enabling the border between transplant and host tissue to be clearly recognized. No labelled fibres were observed to enter the host brain. Fibres with "boutons en passant" and no preferential orientation were noted. It is proposed that Lucifer Yellow microinjection may be a useful method in studies aimed at improving graft morphology. Failure to demonstrate host to transplant connections with the carbocyanine dye method was contrary to earlier studies in which tracers were applied in vivo. A combined use of in-vivo and post-mortem tracer techniques is needed to establish the reason for the discrepancy.

Dendritic and synaptic alterations of hippocampal pyramidal neurones in scrapie-infected mice.

Neurone damage and eventual loss may underlie the clinical signs of disease in the transmissible spongiform encephalopathies (TSEs). Although neurone death appears to be through apoptosis, the trigger for this form of cell death in the TSEs is not known. Using two different murine scrapie models, hippocampal pyramidal cells were studied through microinjection of fluorescent dye, and synaptic integrity, using p38-immunoreactivity (p38-IR), both visualized using confocal laser scanning microscopy. Intradendritic distensions and dendritic spine loss were found to co-localize to areas of vacuolar and prion protein pathology in the hippocampus of mice infected with ME7 or 87 V scrapie. A significant reduction in p38-IR was found concomitantly in the hippocampus in ME7 scrapie mice. These results indicate that both pre- and post-synaptic sites are altered by scrapie infection; this would disrupt neuronal circuitry and may initiate apoptotic cell death, giving rise to the neurological disturbances manifested in clinical TSE cases.

Early destruction of the extracellular matrix around parvalbumin-immunoreactive interneurons in Creutzfeldt-Jakob disease.

GABA-interneurons immunoreactive (IR) for the calcium-binding protein parvalbumin are lost during the early stages of Creutzfeldt-Jakob disease (CJD) and diminution in their number may partially account for the neurological disturbances manifested in patients suffering from this condition. The disease is characterized by a transformation of the prion protein, PrP(c)-a host-coded sialoglycoprotein-to its protease-resistant and putatively pathological form, PrP(CJD). And since this conversion is likely to take place at the cell surface, we were curious to know whether the "perineuronal net"-a characteristic accumulation of extracellular matrix in intimate contact with the surface of parvalbumin-IR neurons-is implicated in the early disappearance of the mantled cells. Using various lectins and antibodies as markers for the perineuronal net in brains of 21 CJD victims, we observed that this meshwork of extracellular matrix molecules is lost before the embraced parvalbumin-IR neurons themselves disappear. Hence, an interaction of PrP(c) and/or PrP(CJD) with components of the extracellular matrix around this subpopulation of nerve cells precipitates a sequence of as yet unknown events which culminates in the replacement of perineuronal nets by deposits of insoluble PrP(CJD). This change in the environment of the GABA-interneurons IR for parvalbumin may ultimately provoke their death.

Morphological study of the entorhinal cortex, hippocampal formation, and basal ganglia in Rett syndrome patients.

Entorhinal cortex (EC), fascia dentata (FD), hippocampus (HP), and basal ganglia (BG) were studied in Rett syndrome (RS) cases and compared with control brains and an autism case. Kluver-Barrera and Golgi methods were used. In RS most of the areas of EC, HP, and FD showed severe cell hypochromia. In the EC all cells of layer II and most in layer III were in a state of total chromatolysis or were "ghost" cells, but the cells of layers V and VI were preserved and moderately hyperchromic. In FD and HP the majority of the granular cells and cells of CA3 and CA4 fields were severely hypochromic, whereas in the CA1 field most cells were normal or slightly hypercaryochromic. In BG mostly mild or moderate aberration from normal cell structure was observed: in striatum, mild hypercaryochromia of small neurons and more expressive hyperchromia of large neurons were found; and in pallidum, mild or moderate hypercaryochromia to severe hyperchromia in pallidum internum was found. Degeneration of thick myelinated fibers was evident in pallidum. Large striatal and pallidal neurons showed signs of constructive changes in Golgi slices. These data allow the determination of the cause of the main symptoms of RS. The motor disorders, including specific stereotyped movements, could be related to the enhanced activity of BG cells due to their deafferentation from the side of the neocortex and to supposed hyperactivity of the EC-striatal pathway; the mental retardation and epileptic seizures could be due to FD-HP involvement.

The cellular distribution of GAP-43 immunoreactivity in human neocortical areas using immunofluorescence and confocal microscopy: post-ischemic influence.

The distribution of growth associated protein-43 (GAP-43) immunoreactive (IR) neurons were studied in human neocortical areas, using immunofluorescence and confocal microscopy. The GAP-43-IR cells were generally localised close to blood vessels, and contained fewer lipofuscin granules than GAP-43 negative cells. Quantification of the relative number of GAP-43-IR cells in control cases showed that the highest number of GAP-43-IR cells were present in layers III and V in the motor and visual cortices, fewer in the temporal cortex, and the lowest number in the frontal cortex. After general ischemia, GAP-43-IR cells were significantly reduced at various survival times, with the counts being lowest in the 1 week surviving case, and higher, but still subcontrol, in the 1 year post-ischemic case.

Quantitative analysis of synaptophysin immunoreactivity in human neocortex after cardiac arrest: confocal laser scanning microscopy study.

Transient global ischaemia caused by cardiac arrest results in lesions that involve all brain structures. The aim of this study was to investigate the condition of synapses in patients surviving, but remaining in a persistent vegetative state, following resuscitation after cardiac arrest. We performed a quantitative analysis of the distribution and density of elements containing a synaptic vesicle protein--synaptophysin (p38)--in human neocortex in cases which survived for 1 week, 2 months, and 1 year after the cardiac arrest. Neurologically healthy cases that died following an accident served as control. Dual-channel confocal laser scanning microscopy (CLSM) was used to image p38-immunoreactivity (IR) and lipofuscin autofluorescence. In control cases no statistically significant differences were found for p38-IR between layers II-III and V-VII. However, the temporal cortex had a higher density of p38-immunoreactive structures than the motor cortex. In postischaemic cases a reduction in the density of p38-IR elements was apparent, mainly in the frontal and motor cortices and less pronounced in the temporal cortex. The least decrease compared with controls was observed in the visual cortex. In the 1 week survival case, a maximal decrease in p38-IR (35% below control) was found. In this case, the number of p38-IR elements per visual field was decreased, and big aggregates of p38-IR structures were observed. In general, the amounts of p38-IR structures were higher in all of the control cases compared with the postischaemic cases.

Dendritic changes of the pyramidal neurons in layer V of sensory-motor cortex of the rat brain during the postresuscitation period.

Experiments were performed on 40 Wistar rats. Total brain ischemia was induced by 10 min clamping of the cardiac blood vessels. The brains were examined in control rats, after 90 min and after 1, 3, 7, 30 and 90 days during the postresuscitation period. Histological sections were stained with the Golgi method. Morphometrical parameters, 12, of dendritic changes of the pyramidal neurons in layer V of sensory motor cortex (SMC) in rat brain were studied at different intervals of the postresuscitation period. Reduction of the dendrites of the pyramidal neurons due to the loss of the terminal branches of the oblique apical dendrites in layer III-IV was detected from the first day after ischemia. The maximal dendritic change was detected 3 and 7 days after ischemia. Decrease the volume of dendritic territory (54, 4%), the total dendritic length of the whole dendritic territory (56, 0%) and branching of dendrites, and decrease in the number of dendritic spines on apical dendrites in layers I-II (46, 1%) were the main changes during this period. Reduction of the total length of dendrites occurred mostly due to disappearance of the 2nd and 3rd order branches of the apical and basal dendrites. The change of dendrites neurons had returned to control levels after 30 days. By that time the diameter of the dendrites had increased, the varicosities on oblique apical and basal dendrites had disappeared, and the number of 2nd and 3rd order dendrites and of dendritic spines had increased.

Morphological study of neocortical areas in Rett syndrome.

Various neocortical areas from four females aged 16-24 years with Rett syndrome (RS) were investigated and compared with brains of therapy-resistant partial epilepsy (TRPE) patients (18-25 years), infantile autism (IA), and control brains (24 and 58 years). The cytoarchitecture of area 10 (frontal), area 21 (temporal), area 4 (primary motor cortex), and area 17 (primary visual cortex) was studied by the combined Klüver-Barrera (luxol fast blue and cresyl violet) standard procedure. Autofluorescence of lipofuscin, immunofluorescence of synaptic vesicle proteins [synaptophysin (p38)] and lectin-stained (Wisteria floribunda agglutinin) perineuronal nets (PNs) were studied in the cortices using dual-channel confocal laser scanning microscopy. The brains of RS females show various types of morphological/cytoarchitectonical abnormalities of single pyramidal neurons in layers II-III, and V-VII of different cortical areas. The abnormalities include mild losses of pyramidal neurons, more pronounced in layers II and III than in layers V and VII, and more evident in frontal and temporal areas than in the visual cortex. Microdysgenesis, including abnormalities due to neuronal migration disorders, was not found in RS, in contrast to the observations in TRPE patients, strongly indicating that RS is not a neuronal migration disorder. Lipofuscin distribution was normal but amounts were lower in RS cases than in control and TRPE brains. PNs were less expressed in cortices of the IA case but were clearly overexpressed in the motor cortex of RS. Quantitative analysis of p38 showed a decrease in the area occupied by p38 immunoreactivity by 20-40% in RS compared with controls. It is concluded that RS could best be explained by a postnatal synaptogenic developmental deficiency; the basic defect, however, is still completely unknown.

HIV-I induced destruction of neocortical extracellular matrix components in AIDS victims.

Neurological dysfunction is not uncommon in patients suffering from acquired immunodeficiency syndrome (AIDS) and, when manifested, intimates involvement of the central nervous system. Here, the human immunodeficiency virus (HIV) infects preferentially microglial cells, which thereby release substances known to interfere with neuronal function. One class of agents set free in this manner are proteases; these degrade certain components within, and thereby undermine the integrity of, the extracellular matrix (ECM) compartment, which plays a vital role in cell-to-cell communication. We wished to ascertain whether the ECM compartment is indeed disrupted in the brains of AIDS victims. We examined the neocortical areas of 27 AIDS autopsy cases, including 9 with diagnosed HIV-encephalopathy (HIVE); 8 HIV-seronegative cases with various types of brain lesion, including viral infections, were also included in this study. HIV-antigens and DNA were identified by use of immunohistochemistry and in situ hybridization, and ECM components by lectin staining and immunohistochemistry. Of the 27 AIDS cases examined, each of the 9 with HIVE was completely devoid of labeled ECM components; 8 of the 18 without HIVE had incurred substantial losses, and only 2 manifested a normal complement of constituents within this compartment. With respect to stratal and topographic variations, layers II and III were less affected than layers V to VII, as was the frontal cortex relative to other areas. These findings confirmed our expectations of the brain's ECM undergoing degradation following HIV infection, and these changes may well underlie the neurological disturbances manifested in AIDS patients.

Relationship between oligodendrocytes and axons.

Oligodendrocytes can myelinate a variable number of axons in their surroundings; however, the mechanisms underlying axon-oligodendrocyte associations are unknown. We tested the hypothesis that single oligodendrocytes exclusively myelinate axons belonging to the same functional system. Carbocyanine dyes (DiI, FAST DiI) were applied to the sternomastoid muscle of the rat and allowed to transport retrogradely for 4 weeks within the motor axons. Using fluorescence microscopy and iontophoretic injection of Lucifer Yellow (LY), oligodendrocytes were injected in the proximity of retrogradely carbocyanine dye-labeled axons. Using dual channel confocal laser scanning microscopy (CLSM), the three-dimensional relationship between axons and glia was studied. The data indicate that a single oligodendrocyte can myelinate retrogradely labeled axons concomitantly with other, unlabeled axons belonging to apparently different functional systems.