Synaptic alterations and neuronal firing in human epileptic neocortical excitatory networks.

Epilepsy is a prevalent neurological condition, with underlying neuronal mechanisms involving hyperexcitability and hypersynchrony. Imbalance between excitatory and inhibitory circuits, as well as histological reorganization are relatively well-documented in animal models or even in the human hippocampus, but less is known about human neocortical epileptic activity. Our knowledge about changes in the excitatory signaling is especially scarce, compared to that about the inhibitory cell population. This study investigated the firing properties of single neurons in the human neocortex in vitro, during pharmacological blockade of glutamate receptors, and additionally evaluated anatomical changes in the excitatory circuit in tissue samples from epileptic and non-epileptic patients. Both epileptic and non-epileptic tissues exhibited spontaneous population activity (SPA), NMDA receptor antagonization reduced SPA recurrence only in epileptic tissue, whereas further blockade of AMPA/kainate receptors reversibly abolished SPA emergence regardless of epilepsy. Firing rates did not significantly change in excitatory principal cells and inhibitory interneurons during pharmacological experiments. Granular layer (L4) neurons showed an increased firing rate in epileptic compared to non-epileptic tissue. The burstiness of neurons remained unchanged, except for that of inhibitory cells in epileptic recordings, which decreased during blockade of glutamate receptors. Crosscorrelograms computed from single neuron discharge revealed both mono- and polysynaptic connections, particularly involving intrinsically bursting principal cells. Histological investigations found similar densities of SMI-32-immunopositive long-range projecting pyramidal cells in both groups, and shorter excitatory synaptic active zones with a higher proportion of perforated synapses in the epileptic group. These findings provide insights into epileptic modifications from the perspective of the excitatory system and highlight discrete alterations in firing patterns and synaptic structure. Our data suggest that NMDA-dependent glutamatergic signaling, as well as the excitatory synaptic machinery are perturbed in epilepsy, which might contribute to epileptic activity in the human neocortex.

Changes in Presynaptic Gene Expression during Homeostatic Compensation at a Central Synapse.

Homeostatic matching of pre- and postsynaptic function has been observed in many species and neural structures, but whether transcriptional changes contribute to this form of trans-synaptic coordination remains unknown. To identify genes whose expression is altered in presynaptic neurons as a result of perturbing postsynaptic excitability, we applied a transcriptomics-friendly, temperature-inducible Kir2.1-based activity clamp at the first synaptic relay of the Drosophila olfactory system, a central synapse known to exhibit trans-synaptic homeostatic matching. Twelve hours after adult-onset suppression of activity in postsynaptic antennal lobe projection neurons of males and females, we detected changes in the expression of many genes in the third antennal segment, which houses the somata of presynaptic olfactory receptor neurons. These changes affected genes with roles in synaptic vesicle release and synaptic remodeling, including several implicated in homeostatic plasticity at the neuromuscular junction. At 48 h and beyond, the transcriptional landscape tilted toward protein synthesis, folding, and degradation; energy metabolism; and cellular stress defenses, indicating that the system had been pushed to its homeostatic limits. Our analysis suggests that similar homeostatic machinery operates at peripheral and central synapses and identifies many of its components. The presynaptic transcriptional response to genetically targeted postsynaptic perturbations could be exploited for the construction of novel connectivity tracing tools.SIGNIFICANCE STATEMENT Homeostatic feedback mechanisms adjust intrinsic and synaptic properties of neurons to keep their average activity levels constant. We show that, at a central synapse in the fruit fly brain, these mechanisms include changes in presynaptic gene expression that are instructed by an abrupt loss of postsynaptic excitability. The trans-synaptically regulated genes have roles in synaptic vesicle release and synapse remodeling; protein synthesis, folding, and degradation; and energy metabolism. Our study establishes a role for transcriptional changes in homeostatic synaptic plasticity, points to mechanistic commonalities between peripheral and central synapses, and potentially opens new opportunities for the development of connectivity-based gene expression systems.

Rapid Turnover of Cortical NCAM1 Regulates Synaptic Reorganization after Peripheral Nerve Injury.

Peripheral nerve injury can induce pathological conditions that lead to persistent sensitized nociception. Although there is evidence that plastic changes in the cortex contribute to this process, the underlying molecular mechanisms are unclear. Here, we find that activation of the anterior cingulate cortex (ACC) induced by peripheral nerve injury increases the turnover of specific synaptic proteins in a persistent manner. We demonstrate that neural cell adhesion molecule 1 (NCAM1) is one of the molecules involved and show that it mediates spine reorganization and contributes to the behavioral sensitization. We show striking parallels in the underlying mechanism with the maintenance of NMDA-receptor- and protein-synthesis-dependent long-term potentiation (LTP) in the ACC. Our results, therefore, demonstrate a synaptic mechanism for cortical reorganization and suggest potential avenues for neuropathic pain treatment.

Skilled Movements Require Non-apoptotic Bax/Bak Pathway-Mediated Corticospinal Circuit Reorganization.

Early postnatal mammals, including human babies, can perform only basic motor tasks. The acquisition of skilled behaviors occurs later, requiring anatomical changes in neural circuitry to support the development of coordinated activation or suppression of functionally related muscle groups. How this circuit reorganization occurs during postnatal development remains poorly understood. Here we explore the connectivity between corticospinal (CS) neurons in the motor cortex and muscles in mice. Using trans-synaptic viral and electrophysiological assays, we identify the early postnatal reorganization of CS circuitry for antagonistic muscle pairs. We further show that this synaptic rearrangement requires the activity-dependent, non-apoptotic Bax/Bak-caspase signaling cascade. Adult Bax/Bak mutant mice exhibit aberrant co-activation of antagonistic muscle pairs and skilled grasping deficits but normal reaching and retrieval behaviors. Our findings reveal key cellular and molecular mechanisms driving postnatal motor circuit reorganization and the resulting impacts on muscle activation patterns and the execution of skilled movements.

A comparative study of the dentate gyrus in hippocampal sclerosis in epilepsy and dementia.

AIMS: Hippocampal sclerosis (HS) is long-recognized in association with epilepsy (HSE ) and more recently in the context of cognitive decline or dementia in the elderly (HSD ), in some cases as a component of neurodegenerative diseases, including Alzheimer's disease (AD) and fronto-temporal lobe dementia (FTLD). There is an increased risk of seizures in AD and spontaneous epileptiform discharges in the dentate gyrus of transgenic AD models; epilepsy can be associated with an age-accelerated increase in AD-type pathology and cognitive decline. The convergence between these disease processes could be related to hippocampal pathology. HSE typically shows re-organization of both excitatory and inhibitory neuronal networks in the dentate gyrus, and is considered to be relevant to hippocampal excitability. We sought to compare the pathology of HSE and HSD , focusing on re-organization in the dentate gyrus. METHODS: In nine post mortem cases with HSE and bilateral damage, 18 HSD and 11 controls we carried out immunostaining for mossy fibres (dynorphin), and interneuronal networks (NPY, calbindin and calretinin) on sections from the mid-hippocampal body. Fibre sprouting (FS) or loss of expression in the dentate gyrus was semi-quantitatively graded from grade 0 (normal) to grade 3 (marked alteration). RESULTS: Significantly more re-organization was seen with all four markers in the HSE than HSD group (P < 0.01). Mild alterations were noted in HSD group with dynorphin (FS in 3 cases), calretinin (FS in 6 cases), NPY (FS in 11 cases) and calbindin (loss in 10 cases). In eight HSD cases, alteration was seen with more than one antibody but in no cases were the highest grades seen. We also noted NPY and, to a lesser extent, calretinin labelling of Hirano bodies in CA1 of AD cases and some older controls, but not in HSE . CONCLUSION: Reorganization of excitatory and inhibitory networks in the dentate gyrus is more typical of HSE . Subtle alterations in HSD may be a result of increased hippocampal excitability, including unrecognized seizure activity. An unexpected finding was the identification of NPY-positive Hirano bodies in HSD but not HSE , which may be a consequence of the relative vulnerabilities of interneurons in these conditions.

Semaphorins 3A and synaptophysin P38 expression induced by status epilepticus in hippocampus of developing rat / 中华行为医学与脑科学杂志

ObjectiveTo observe Semaphorins-3A and synaptophysin P38 expression in hippocampus of developing rat induced by status epilepticus.Methods 320 SD rats were divided into four groups (P7,P14,P21 and P28) according to day -old after birth (7d,14d,21d and 28d).Rats in each group were randomly divided into model group (SE group) and saline control group (NS group).SE was induced by Pentylenetetrazol (PTZ).Semaphorins-3A and synaptophysin P38 expression were determined by immunohistochemical staining on 1d,7d,14d,21d and 28d after SE in hippocampal CA1 of rats.ResultsSemaphorins-3A-positive cells could be seen in the hippocampal granule cell layer in all rats.Semaphorins-3A expression tended to decrease with the increasing of day-age,especially in P7 group(91 552.68 ± 4664.69 ).No matter how day-age,Semaphorins-3A expression was similar to that in NS group and was obvious reduced in 7d after SE(56 938.84 ± 5688.47 ).Meanwhile P38 expression in P7-day-age rats had had been gradually increasing between 1 day and 14d (5413.18 ±48.77,6223.40±29.19,6902.94 ±78.51 ) and then stabilized gradually on 21d(7523.42 ± 62.94) after rats were tested.P38 expression in other day-age rat was relatively stable on the same level in physiological state.On the other hand P38 expression in the hippocampal CA1 region of P7,P14,P21 and P28 rats was significantly higher than that in normal rats between 1day and 28day after SE episode(P＜ 0.05 ),and reached a peak on 14 day(8408.35 ± 55.73 ).ConclusionSemaphorins-3A and synaptophysin P38 involved in hippocampal synaptic plasticity of rat in developing stage and epilepsy.

Ultrastructure of Spike Focus of Temporal Lobe Cortexes and Hippocampus in Patients with Protopathic Intractable Temporal Lobe Epilepsy / 中国康复理论与实践

@#Objective To observe the pathology in temporal lobe cortexes and hippocampus in protopathic intractable temporal lobe epileptics.Methods The cortexes of spike foci in temporal lobe and hippocampus were obtained from 9 cases with protopathic intractable temporal lobe epilepsy who accepted operation.The samples were observed under the transmission electron microscope.Results The ultrastructure changes in spike focus of temporal lobe cortexes are similar to those in hippocampus.It is common that neurons were pycnotic and decreased.Astrocytes were hydropic and degenerative.Gliosis were found in some cases.The number of synapses increased or decreased in different cases and positions.Blood-brain barriers were destroyed because foot processes of astrocytes around capillaries were edematous.Conclusion Neuronal loss,gliosis and synaptic reorganization which occur in epileptic hippocampus and maybe also in epileptic temporal lobe cortexes destroy the balance between excitatory and inhibitory neurotransmission.The abnormalities probably associate with protopathic intractable temporal lobe epileptic seizures.

Synaptic Reorganization of Dentate Mossy Fibers and Expression of Calcium Binding Proteins in Hippocampal Sclerosis of Temporal Lobe Epilepsy

This study was designed to identify expression of calcium-binding proteins and synaptic reorganizations of dentate mossy fibers in hippocampal sclerosis of human temporal lobe epilepsy. Hippocampal neuronal density was quantitively analyzed in temporal lobe epilepsy group (n=50) to investigate the degree of hippocampal sclerosis and it was compared with that of autopsy control (n=3). To verify the distribution of calcium-binding proteins in neurons of epileptic hippocampi, the parvalbumin (PV)-immunoreactive and calbindin-D28K (CB)-immunoreactive neurons were quantitively analyzed in each area of Ammon's horn by immunohistochemical stain. Also, to clarify synaptic reorganizations of the dentate mossy fibers, a part of each hippocampus was examined under light microscopy and transmission electron microscopy using Timm sulphide silver method. In epileptic hippocampi, severity of hippocampal sclerosis (HS) was graded four, which consisted of 3 cases with no HS, 6 mild HS, 12 moderate HS, and 29 severe HS. The hippocampal neuronal loss was most prominent in CA1, followed by CA4 and CA2. Expression of calcium-binding proteins was more prevalent in CA2 of all groups. The proportion of PV-immunoreactive neurons in CA1 and CA4 significantly increased in the moderate and severe HS group, whereas the proportion of CB-immunoreactive neurons did not correlated with the severity of HS. Timm granules were noted in inner molecular supragranular layer of dentate gyrus of epileptic hippocampi and they tended to increase in proportion along with the severity of hippocampal sclerosis. Transmission electron microscopy showed that supragranular Timm granules corresponded to synaptic terminals of mossy fibers. These results suggest that parvalbumin appears to have more protective effect against neuronal loss and that mossy fiber synaptic reorganization seems to play a major role in pathogenesis of hippocampal sclerosis of human temporal lobe epilepsy.

Mossy fiber Synaptic Reorganization and the Pattern of Sprouting in the Pilocarpine Epilepsy Model

BACKGROUND: The purpose of this study is to evaluate the synaptic reorganization and pattern of mossy fiber sprouting as a pathologic mechanism of chronic seizure in pilocarpine epilepsy model through histological alterations of hippocampus. METHOD: Sprague-Dawley, a sensitively damaged by pilocarpine stimulation, served as a experimental group(n=20). And the same dose of saline injected rats were served as a control group(n=10). They were implanted depth electrode in the hippocampus by a stereotaxic surgery, and injected pilocarpine 300mg/Kg intraperitoneally. They produced status epilepticus and the survival rats were monitored by a video-EEG monitoring system whether the spontaneous recurrent seizures occurring for more than 4 weeks. If more than 3 times spontaneous recurrent seizures were identified, then the rat hippocampus was examined by light microscope. RESULT: The pilocarpine injected group produced acute limbic seizure and developed to status epilepticus. The survival rats(n=10) became to chronic epilepsy state after silent period of everage 16.5 days. H&E staining demonstrated that loss of hilar polymorphic cell with ischemic changes and destruction of CA1 with damages of pyramidal cells in hippocampal subfields. Timm stains showed mossy fiber synatic reorganization in the supragranular and intragranular layer of dentate gyrus and infrapyramidal layer of CA3 hippocampal subfieid in pilocarpine induce seizure rats. CONCLUSION: These results suggest that chronic seizures in the pilocarpine epilepsy model is largely due to mossy fiber synatic reorganization, a consequence of supragranular mossy fiber sprouting. But intragranular and infrapyramidal axonal sprouting might have parts of role in synaptic reorganization. Additional research is required to determine the various patterns of axonal sprouting.

A Morphological Study of Synaptic Reorganization in Mossy Fibers of the Dentate Gyrus according to Hippocampal Sclerosis in Temporal Lobe Epilepsy: A Comparison of Intraoperative ECoG Findings for Tailored Resection

This study was carried out to identify synaptic reorganization by mossy fibers of epileptic dentate gyrus by Timm sulphide silver histochemistry and to investigate degree of synaptic reorganization according to both hippocampal sclerosis and epileptiform discharge in human temporal lobe epilepsy(TLE). The control group was composed of two hippocampal tissues obtained from autopsied brain without neurological abnormalities. TLE group was composed of thirteen hippocampal tissues obtained from surgically resected temporal lobe. Among thirteen hippocampal tissues, five specimens were obtained both of two areas of each hippocampus with or without prominent epileptiform discharges on electrocorticogram(ECoG) for tailored hippocampal resection. Hippocampal cell density was quantitatively analyzed in TLE group and compared with that of control group. A portion of hippocampal tissue was observed under light microscopic and transmission electron microscopes after development with Danscher method. The results were as follows : Hippocampal cell loss was noted in all TLE group. Hippocampal cell loss greater than 30% of control values was found in 12 cases and average hippocampal cell loss was 70%(range 39-88%). The remaining 1 case had 13% hippocampal cell loss. The supragranular Timm granules were noted in inner molecular layer of dentate gyrus and tended to significantly increase in proportion as severity of hippocampal sclerosis. Average of hippocampal cell loss in two areas of five hippocampal tissues with or without prominent epileptiform discharge on ECoG was 73.6%(range 53-90%) and 66.4%(range 50-86%), which showed statistically significant (p<0.05) difference between these two areas and the supragranular Timm granules also tended to increase in the hippocampal tissue with epileptiform discharge. On transmission electron microscope, there showed distinct supragranular Timm granules correspond to mossy fiber synaptic terminals. The results of this study demonstrated that mossy fiber synaptic reorganization seems to play a major role in pathogenesis of human TLE and the development of mossy fiber synaptic reorganization is closely related to severity of hippocampal sclerosis. The result also support the rationale for tailoring the extent of hippocampal resection by intraoperative acute recording(ECoG) according to individual pathophysiology.