Accumulation of abnormal adult-generated hippocampal granule cells predicts seizure frequency and severity

Electroacupuncture at ST36-ST37 and at ear ameliorates hippocampal mossy fiber sprouting in kainic acid-induced epileptic seizure rats

Our previous study showed that mossy fiber sprouting can occur in the hippocampus region in rats 6 wk after kainic acid-induced epileptic seizure, and this mossy fiber sprouting can facilitate epileptogenesis. Transcutaneous auricular vagal nerve stimulation (VNS), which is similar to cervical VNS, can reduce the occurrence of epileptic seizure in intractable epilepsy patients. Greater parasympathetic nerve activity can be caused by 2 Hz electroacupuncture (EA). Therefore, we investigated the effect of 2 Hz EA at ST-36-ST37 and at the ear on mossy fiber sprouting in kainic-treated Sprague-Dawley rats. The results indicated that applying 2 Hz EA at ST36-ST37 and at the ear for 3 d per week over 6 consecutive weeks can ameliorate mossy fiber sprouting in the hippocampus region of rats. These results indicated that applying 2 Hz EA at ST36-ST37 and at the ear might be beneficial for the treatment and prevention of epilepsy in humans.

Why looking at the whole hippocampus is not enough-a critical role for anteroposterior axis, subfield and activation analyses to enhance predictive value of hippocampal changes for Alzheimer's disease diagnosis

The hippocampus is one of the earliest affected brain regions in Alzheimer's disease (AD) and its dysfunction is believed to underlie the core feature of the disease-memory impairment. Given that hippocampal volume is one of the best AD biomarkers, our review focuses on distinct subfields within the hippocampus, pinpointing regions that might enhance the predictive value of current diagnostic methods. Our review presents how changes in hippocampal volume, shape, symmetry and activation are reflected by cognitive impairment and how they are linked with neurogenesis alterations. Moreover, we revisit the functional differentiation along the anteroposterior longitudinal axis of the hippocampus and discuss its relevance for AD diagnosis. Finally, we indicate that apart from hippocampal subfield volumetry, the characteristic pattern of hippocampal hyperactivation associated with seizures and neurogenesis changes is another promising candidate for an early AD biomarker that could become also a target for early interventions.

Mechanisms regulating neuronal excitability and seizure development following mTOR pathway hyperactivation

The phosphatidylinositol-3-kinase/phosphatase and tensin homolog (PTEN)-mammalian target of rapamycin (mTOR) pathway regulates a variety of neuronal functions, including cell proliferation, survival, growth, and plasticity. Dysregulation of the pathway is implicated in the development of both genetic and acquired epilepsies. Indeed, several causal mutations have been identified in patients with epilepsy, the most prominent of these being mutations in PTEN and tuberous sclerosis complexes 1 and 2 (TSC1, TSC2). These genes act as negative regulators of mTOR signaling, and mutations lead to hyperactivation of the pathway. Animal models deleting PTEN, TSC1, and TSC2 consistently produce epilepsy phenotypes, demonstrating that increased mTOR signaling can provoke neuronal hyperexcitability. Given the broad range of changes induced by altered mTOR signaling, however, the mechanisms underlying seizure development in these animals remain uncertain. In transgenic mice, cell populations with hyperactive mTOR have many structural abnormalities that support recurrent circuit formation, including somatic and dendritic hypertrophy, aberrant basal dendrites, and enlargement of axon tracts. At the functional level, mTOR hyperactivation is commonly, but not always, associated with enhanced synaptic transmission and plasticity. Moreover, these populations of abnormal neurons can affect the larger network, inducing secondary changes that may explain paradoxical findings reported between cell and network functioning in different models or at different developmental time points. Here, we review the animal literature examining the link between mTOR hyperactivation and epileptogenesis, emphasizing the impact of enhanced mTOR signaling on neuronal form and function.

Synchronous alteration pattern between serine-threonine kinase receptor-associated protein and Smad7 in pilocarpine-induced rats of epilepsy

PURPOSE

Recent studies have shown that transforming growth factor β (TGFβ) signaling participates in the epileptogenesis. Serine-threonine kinase receptor-associated protein (STRAP) and Smad7 synergize in the inhibition of the TGFβ signaling. The aim of the present study was to determine the expression pattern of STRAP and Smad7 in the hippocampus and temporal lobe cortex of pilocarpine-induced rats models of epilepsy.

METHODS

Lithium chloride-pilocarpine-induced rats with status epilepticus (SE) were established. Total of 60 male Sprague-Dawley rats was used as control (n = 10), 24 h (n = 10), 72 h (n = 10), 1 week (n = 10), 1 month (n = 10), and 2 months (n = 10) after pilocarpine-induced SE, respectively. We detected the expression levels of STRAP and Smad7 in the hippocampus and temporal lobe cortex of rats at the aforementioned time points using western blotting and immunohistochemistry.

RESULTS

STRAP level was significantly decreased in 24 h, 72 h (acute stage), 1 week (latent stage), 1 month, 2 months (chronic stage), respectively, in the rat models compared with the control rats by using both western blotting and immunohistochemistry. Smad7 had similar reduced pattern as STRAP.

CONCLUSIONS

Our results indicate that STRAP and Smad7 proteins might be involved in the development of temporal lobe epilepsy.

Morphological changes among hippocampal dentate granule cells exposed to early kindling-epileptogenesis

Temporal lobe epilepsy is associated with changes in the morphology of hippocampal dentate granule cells. These changes are evident in numerous models that are associated with substantial neuron loss and spontaneous recurrent seizures. By contrast, previous studies have shown that in the kindling model, it is possible to administer a limited number of stimulations sufficient to produce a lifelong enhanced sensitivity to stimulus evoked seizures without associated spontaneous seizures and minimal neuronal loss. Here we examined whether stimulation of the amygdala sufficient to evoke five convulsive seizures (class IV or greater on Racine's scale) produce morphological changes similar to those observed in models of epilepsy associated with substantial cell loss. The morphology of GFP-expressing granule cells from Thy-1 GFP mice was examined either 1 day or 1 month after the last evoked seizure. Interestingly, significant reductions in dendritic spine density were evident 1 day after the last seizure, the magnitude of which had diminished by 1 month. Further, there was an increase in the thickness of the granule cell layer 1 day after the last evoked seizure, which was absent a month later. We also observed an increase in the area of the proximal axon, which again returned to control levels a month later. No differences in the number of basal dendrites were detected at either time point. These findings demonstrate that the early stages of kindling epileptogenesis produce transient changes in the granule cell body layer thickness, molecular layer spine density, and axon proximal area, but do not produce striking rearrangements of granule cell structure.