Axon Initial Segment Structural Plasticity is Involved in Seizure Susceptibility in a Rat Model of Cortical Dysplasia

Projection-Specific Heterogeneity of the Axon Initial Segment of Pyramidal Neurons in the Prelimbic Cortex

The axon initial segment (AIS) is a highly specialized axonal compartment where the action potential is initiated. The heterogeneity of AISs has been suggested to occur between interneurons and pyramidal neurons (PyNs), which likely contributes to their unique spiking properties. However, whether the various characteristics of AISs can be linked to specific PyN subtypes remains unknown. Here, we report that in the prelimbic cortex (PL) of the mouse, two types of PyNs with axon projections either to the contralateral PL or to the ipsilateral basal lateral amygdala, possess distinct AIS properties reflected by morphology, ion channel expression, action potential initiation, and axo-axonic synaptic inputs from chandelier cells. Furthermore, projection-specific AIS diversity is more prominent in the superficial layer than in the deep layer. Thus, our study reveals the cortical layer- and axon projection-specific heterogeneity of PyN AISs, which may endow the spiking of various PyN types with exquisite modulation.

Refractory psychiatric symptoms and seizure associated with Dandy-Walker syndrome: A case report and literature review

BACKGROUNDS

Dandy-Walker syndrome (DWS) is a group of brain malformations which occasionally accompanied by psychotic symptoms. The co-occurrence of DWS and epilepsy in children is quite rare.

CASE DESCRIPTION

We reported a 14-year-old male who presented with a 8-month history of inconsistent upper limb tremor and accidental seizure. The MRI showed the typical alterations of DWS: cystic dilatation of the fourth ventricle, vermian hypoplasia, enlarged posterior fossa. He received the ventriculoperitoneal shunting (VPS) placement for hydrocephalus and had a symptom-free period for 8 days. Then he experienced a recurrence of involuntary upper limb tremor and behavior disturbance after decreasing the pressure of cerebrospinal fluid (CSF) from 150 to 130 mm Hg. After being treated with Olanzapine 10 mg/d, Clonazepam 3 mg/qn and Valproate acid (VPA) 500 mg/bid for nearly a month, his mental status and psychotic symptoms fluctuated. A search of Pub Med showed little report of hydrocephalus and DWS comorbidity with seizure and psychosis. Here we presented the whole process of a rare disease from the very beginning with all his symptoms, examinations and treatments.

CONCLUSION

VPS placement surgery at an earlier stage may be an effective way to avoid inevitable brain damage so as to improve the clinical outcomes for patients with DWS. Continued treatment with regard to DWS condition may include shunt placement, but it mainly focus on developmental concerns, with occupational and physical therapy along with ongoing supportive psychotherapy to improve the coping skills and quality of life.

Neural Regulation of Cancer: Cancer-Induced Remodeling of the Central Nervous System

In recent years, there have been significant advances in understanding the neuronal influence on the biology of solid tumors such as prostate, pancreatic, gastric, and brain cancers. An increasing amount of experimental evidence across multiple tumor types strongly suggests the existence of bidirectional crosstalk between cancer cells and the neural microenvironment. However, unlike cancers affecting many solid organs, brain tumors, namely gliomas, can synaptically integrate into neural circuits and thus can exert a greater potential to induce dynamic remodeling of functional circuits resulting in long-lasting behavioral changes. The first part of the review describes dynamic changes in language, sensory, and motor networks following glioma development and presents evidence focused on how different patterns of glioma-induced cortical reorganization may predict the degree and time course of functional recovery in brain tumor patients. The second part focuses on the network and cellular-level mechanisms underlying glioma-induced cerebral reorganization. Finally, oncological and clinical factors influencing glioma-induced network remodeling in glioma patients are reviewed.

Chronic α1-Na/K-ATPase inhibition reverses the elongation of the axon initial segment of the hippocampal CA1 pyramidal neurons in Angelman syndrome model mice

Angelman syndrome (AS) is a neurodevelopmental disorder caused by the loss of function of the maternal UBE3A gene. The hippocampus is one of the most prominently affected brain regions in AS model mice, manifesting in severe hippocampal-dependent memory and plasticity deficits. Previous studies in AS mice reported an elongated axon initial segment (AIS) in pyramidal neurons (PNs) of the hippocampal CA1 region. These were the first reports in mammals to show AIS elongation in vivo. Correspondingly, this AIS elongation was linked to enhanced expression of the α1 subunit of Na⁺/K⁺-ATPase (α1-NaKA). Recently, it was shown that selective pharmacological inhibition of α1-NaKA by marinobufagenin (MBG) in adult AS mice rescued the hippocampal-dependent deficits via normalizing their compromised activity-dependent calcium (Ca⁺²) dynamics. In the herein study, we showed that a chronic selective α1-NaKA inhibition reversed the AIS elongation in hippocampal CA1 PNs of adult AS mice, and differentially altered their excitability and intrinsic properties. Taken together, our study is the first to demonstrate in vivo structural plasticity of the AIS in a mammalian model, and further elaborates on the modulatory effects of elevated α1-NaKA levels in the hippocampus of AS mice.

Epileptic seizures in a heterogeneous excitatory network with short-term plasticity

Epilepsy involves a diverse group of abnormalities, including molecular and cellular disorders. These abnormalities prove to be associated with the changes in local excitability and synaptic dynamics. Correspondingly, the epileptic processes including onset, propagation and generalized seizure may be related with the alterations of excitability and synapse. In this paper, three regions, epileptogenic zone (EZ), propagation area and normal region, were defined and represented by neuronal population model with heterogeneous excitability, respectively. In order to describe the synaptic behavior that the strength was enhanced and maintained at a high level for a short term under a high frequency spike train, a novel activity-dependent short-term plasticity model was proposed. Bifurcation analysis showed that the presence of hyperexcitability could increase the seizure susceptibility of local area, leading to epileptic discharges first seen in the EZ. Meanwhile, recurrent epileptic activities might result in the transition of synaptic strength from weak state to high level, augmenting synaptic depolarizations in non-epileptic neurons as the experimental findings. Numerical simulation based on a full-connected weighted network could qualitatively demonstrate the epileptic process that the propagation area and normal region were successively recruited by the EZ. Furthermore, cross recurrence plot was used to explore the synchronization between neuronal populations, and the global synchronization index was introduced to measure the global synchronization. Results suggested that the synchronization between the EZ and other region was significantly enhanced with the occurrence of seizure. Interestingly, the desynchronization phenomenon was also observed during seizure initiation and propagation as reported before. Therefore, heterogeneous excitability and short-term plasticity are believed to play an important role in the epileptic process. This study may provide novel insights into the mechanism of epileptogenesis.