Seizure Suppression by High Frequency Optogenetic Stimulation Using In Vitro and In Vivo Animal Models of Epilepsy

BackgroundElectrical high frequency stimulation (HFS) has been shown to suppress seizures. However, the mechanisms of seizure suppression remain unclear and techniques for blocking specific neuronal populations are required.ObjectiveThe goal is to study the optical HFS protocol on seizures as well as the underlying mechanisms relevant to the HFS-mediated seizure suppression by using optogenetic methodology.MethodsThy1-ChR2 transgenic mice were used in both vivo and in vitro experiments. Optical stimulation with pulse trains at 20 and 50 Hz was applied on the focus to determine its effects on in vivo seizure activity induced by 4-AP and recorded in the bilateral and ipsilateral-temporal hippocampal CA3 regions. In vitro methodology was then used to study the mechanisms of the in vivo suppression.ResultsOptical HFS was able to generate 82.4% seizure suppression at 50 Hz with light power of 6.1 mW and 80.2% seizure suppression at 20 Hz with light power of 2.0 mW. The suppression percentage increased by increasing the light power and saturated when the power reached above-mentioned values. In vitro experimental results indicate that seizure suppression was mediated by activation of GABA receptors. Seizure suppression effect decreased with continued application but the suppression effect could be restored by intermittent stimulation.ConclusionsThis study shows that optical stimulation at high frequency targeting an excitatory opsin has potential therapeutic application for fast control of an epileptic focus. Furthermore, electrophysiological observations of extracellular and intracellular signals reveled that GABAergic neurotransmission activated by optical stimulation was responsible for the suppression.     

Participation of bone marrow-derived cells in hippocampal vascularization after status epilepticus

PurposeDiseases such as temporal lobe epilepsy, brain trauma and stroke can induce endothelial cell proliferation and angiogenesis in specific brain areas. During status epilepticus (SE), bone marrow-derived cells are able to infiltrate and proliferate, dramatically increasing at the site of injury. However, it is still unclear whether these cells directly participate in vascular changes induced by SE.MethodTo investigate the possible role of bone marrow-derived cells in angiogenesis after seizures, we induced SE by pilocarpine injection in previously prepared chimeric mice. Mice were euthanized at 8 h, 7 d or 15 d after SE onset.ResultsOur results indicated that SE modified hippocampal vascularization and induced angiogenesis. Further, bone marrow-derived GFP⁺ cells penetrated through the parenchyma and participated in the formation of new vessels after SE. We detected bone marrow-derived cells closely associated with vessels in the hippocampus, increasing the density of blood vessels that had decreased immediately after pilocarpine-induced SE.ConclusionWe conclude that epileptic seizures directly affect vascularization in the hippocampus mediated by bone marrow-derived cells in a time-dependent manner.     

Loss of CB1 receptors leads to decreased cathepsin D levels and accelerated lipofuscin accumulation in the hippocampus

Early onset of age-related changes in the brain of cannabinoid 1 receptor knockout (Cnr1^−/−) mice suggests that cannabinoid 1 (CB1) receptor activity significantly influences the progression of brain aging. In the present study we show that lack of CB1 receptors leads to a significant increase in lipofuscin accumulation and a reduced expression and activity of cathepsin D, lysosomal protease implicated in the degradation of damaged macromolecules, in the hippocampus of 12-month-old mice. The impaired clearance of damaged macromolecules due to the low cathepsin D levels and not enhanced oxidative stress may be responsible for the lipofuscin accumulation because macromolecule oxidation levels were comparable between the genotypes within the same age group. The altered levels of autophagy markers p62 and LC3-II suggest that autophagy is upregulated in CB1 knockout mice. Increased autophagic flux in the absence of CB1 receptors is probably a compensatory mechanism to partially counteract decreased lysosomal degradation capacity. Together, these results suggest that CB1 receptor activity affects lysosomal activity, degradation of damaged macromolecules and thus it may influence the course and onset of brain aging.     

Voxel-based morphometric gray matter correlates of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is associated with functional abnormalities within a neurocircuitry that includes the hippocampus, amygdala, and medial prefrontal cortex. Evidence of structural abnormalities within these regions, and their association with PTSD severity and symptom burden is, however, sparse. The present study evaluated the relation between indices of gray matter volume and PTSD symptom severity using voxel-based morphometry. Fifteen individuals meeting DSM-IV criteria for PTSD completed the Clinician Administered PTSD Scale and underwent structural magnetic resonance imaging. Greater PTSD severity and avoidance/numbing were correlated with increased gray matter volume of the right amygdala–hippocampal complex. Greater hyper-arousal was associated with reduced gray matter volume in the left superior medial frontal gyrus. Findings are consistent with current neurocircuitry models of PTSD, which posit that the disorder is associated with structural and functional variance within this distributed network.     

Unique Hippocampal Changes and Allodynia in a Model of Chronic Stress

Sustained stress can have numerous pathologic effects. There have been several animal models for chronic stress. We tried to identify the changes of pain threshold and hippocampus in a model of chronic stress. Male Sprague-Dawley rats were kept in a cage filled with 23℃ water to a height of 2.2 cm for 7 days. Nociceptive thresholds, expressed in grams, were measured with a Dynamic Plantar Aesthesiometer. Golgi staining was used to identify hippocampal changes. To demonstrate how long allodynia was lasting, behavioral test was repeated daily on another experiment. Compared to control group, chronic stress group showed bilateral mechanical hyper-responsiveness on days 5 (P = 0.047) and 7 (P = 0.032). In general, dendrite atrophic changes within hippocampus of chronic stress model were much more prominent in comparison with control. Compared to control, decreased spine number (P < 0.001) and spine length (P < 0.001) on Golgi staining were seen in the hippocampus of animals with chronic stress. Bilateral mechanical hyperresponsiveness was recovered on day 19 in animals with chronic stress. Chronic stress may bring about central sensitization and hippocampal changes in rats.     

Epigenetic mechanisms regulating learning and long-term memory

A balance between rapid, short lived, neuronal responses and prolonged ones fulfill the biochemical and cellular requirements for creating a molecular memory. I provide an overview of epigenetic mechanisms in the brain and discuss their impact on synaptic plasticity, cognitive functions, and discuss a recent example of how they can contribute to neurodegeneration and the cognitive decline associated with Alzheimer's disease.     

Activation of microglia and induction of pro-inflammatory cytokines in the hippocampus of type 2 diabetic rats

Abstract

Objectives:

The majority of immune cells in the brain are comprised of microglia, which undergo morphological changes when activated to remove damaged neurons and infectious agents from the brain tissue. In this study, we investigated the effects of type 2 diabetes on microglial activation and the subsequent secretion of pro-inflammatory cytokines, such as interferon-gamma (IFN-gamma) and interleukin-1beta (IL-1beta), in the hippocampus using Zucker diabetic fatty (ZDF) rats and Zucker lean control (ZLC) rats at various diabetic stages.

Methods:

Zucker lean control and Zucker diabetic fatty rats were sacrificed at 12 (early diabetic stage), 20, or 30 weeks of age (chronic diabetic stage), and the hippocampus was obtained via transcardiac perfusion or dissection for immunohistochemistry and western blot analysis, respectively.

Results:

Zucker diabetic fatty rats demonstrated significantly higher glucose levels at 12 and 30 weeks of age compared to ZLC rats. Microglia immunoreactive to ionized calcium-binding adapter molecule 1 (Iba-1) had hypertrophied cytoplasm with retracted processes at 30 weeks of age. In contrast, Iba-1-immunoreactive microglia displayed similar morphology in ZDF and ZLC rats at 12 and 20 weeks of age. Similarly, IFN-gamma and IL-1beta protein levels were significantly increased in ZDF rats compared to ZLC rats at 30 weeks of age, but not at 12 and 20 weeks of age. Interleukin-1beta immunoreactivity in the ZDF rats predominantly increased in the dentate gyrus and CA1 region of the hippocampus compared to that of ZLC rats at 30 weeks of age. In addition, IL-1beta immunoreactive structures in ZDF rats at 30 weeks of age were detected near the astrocytes and microglia.

Conclusion:

These results suggest that chronic diabetes activates microglia and significantly increases pro-inflammatory cytokine levels in the hippocampus.     

Prenatal stress increased Snk Polo-like kinase 2, SCF β-TrCP ubiquitin ligase and ubiquitination of SPAR in the hippocampus of the offspring at adulthood

Exposure to excessive glucocorticoids during fetal development period contributes to later life psychopathology. Prenatal stress decreases dendritic spine density and impair LTP in the hippocampus of rat pups, however, the mechanisms regulating these changes are still unclear.     

Post-ischemic treatment with a lazaroid (U74389G) prevents transient global ischemic damage in rat hippocampus

Abstract

The ability of an experimental lazaroid, U74389G, to prevent damage to hippocampal CA 1 cytoarchitecture due to transient global ischemia was studied by light and electron microscopy. Post-ischemic rats were given a single i.p. dose of lazaroid (6 or 18 mg kg-¹) at 5 min after revival by cardiopulmonary resuscitation (CPR). Without lazaroid treatment the number of normal-appearing neurons in the CA1 region declined from a normal value of 75.49± 2.21 to 8.40± 10.08 per 100 μ,m² on day 7 after the ischemic episode, and there was extensive damage visible in the cytoarchitecture of this region. In lazaroid treated rats, the normal cytoarchitecture was retained and the number of normal-appearing cells was maintained at 15.1O± 2.22 per 100 ¼,m²? Ultrastructure studies indicated that pyknotic pyramidal cells laden with Pysosomal aggregates were common in untreated post-ischemic rats but rare in lazaroid-treated rats. These results indicate that U74389G maintained the structural integrity of this region of the brain after transient global ischemia and suggest that this lazaroid may be an effective neuroprotectant. [Neural Res 1997; 19: 431-434]