Temporal Lobe Epileptogenesis and Epilepsy in the Developing Brain: Bridging the Gap Between the Laboratory and the Clinic. Progression, But in What Direction?

Summary:  The origins of human mesial temporal lobe epilepsy and hippocampal sclerosis are still not well understood. Hippocampal sclerosis and temporal lobe epileptogenesis involve a series of pathologies including hippocampal neuronal loss and gliosis, axonal reorganization, and maybe hippocampal neoneurogenesis. However, the causality of these events is unclear as well as their relation to the factors that may precipitate epileptogenesis. Significant differences between temporal lobe epileptogenesis in the adult and immature brain may require differential approaches. Hereditary factors also may participate in some cases of hippocampal sclerosis. The key point is to identify the significance of these age-dependent changes and to design preventive treatments. Novel strategies for the prevention and treatment of mesial temporal lobe epilepsy and hippocampal sclerosis may include rational use of neuroprotective agents, hormonotherapy, immunizations, and immunotherapy.     

Effect of nilvadipine on the voltage-dependent Ca channels in rat hippocampal CA1 pyramidal neurons

Effects of nilvadipine on the low- and high-voltage activated Ca²⁺ currents (LVA and HVA I_Ca, respectively) were compared with other organic Ca²⁺ antagonists in acutely dissociated rat hippocampal CA1 pyramidal neurons. The inhibitory effects of nilvadipine, amlodipine and flunarizine on LVA I_Ca were concentration- and use-dependent. The apparent half-maximum inhibitory concentrations (IC₅₀s) at every 1- and 30-s stimulation were 6.3×10⁻⁷ M and 1.8×10⁻⁶ M for flunarizine, 1.9×10⁻⁶ M and 7.6×10⁻⁶ M for nilvadipine, and 4.0×10⁻⁶ M and 8.0×10⁻⁶ M for amlodipine, respectively. Thus, the strength of the use-dependence was in the sequence of nilvadipine>flunarizine>amlodipine. Nilvadipine also inhibited the HVA I_Ca in a concentration-dependent manner with an IC₅₀ of 1.5×10⁻⁷ M. The hippocampal CA1 neurons were observed to have five pharmacologically distinct HVA Ca²⁺ channel subtypes consisting of L-, N-, P-, Q- and R-types. Nilvadipine selectively inhibited the L-type Ca²⁺ channel current which comprised 34% of the total HVA I_Ca. On the other hand, amlodipine non-selectively inhibited the HVA Ca²⁺ channel subtypes. These results suggest that the inhibitory effect of nilvadipine on the neuronal Ca²⁺ influx through both LVA and HVA L-type Ca²⁺ channels, in combination with the cerebral vasodilatory action, may prevent neuronal damage during ischemia.     

Effects of cromakalim (BRL 34915) on potassium conductances in CA3 neurons of the guinea-pig hippocampus in vitro

Summary The action of the potassium channel activator, cromakalim (BRL 34915), on membrane potential, input resistance and current-voltage-relationship of CA3 neurons in a slice preparation of the guinea-pig hippocampus was investigated by means of intracellular recordings. In the presence of tetrodotoxin, cromakalim (30–100 mol/l) produced a hyperpolarization up to 4 mV associated with a decrease in input resistance up to 10 MOhms. Determination of the equilibrium potential of the cromakalim action revealed that the hyperpolarization is due to the activation of a potassium conductance. This cromakalim-activated potassium conductance was voltage-dependent, i.e. it increased with hyperpolarization. Among a number of potassium channel blockers tested, only Cs⁺ (2 mmol/l) and Ba²⁺ (0.5 mmol/1) were able to inhibit the cromakalim-induced effects. Simultaneously, both cations suppressed the hyperpolarizing inward rectification (anomalous rectification) in these neurons, indicating that cromakalim activated or potentiated an inwardly rectifying potassium conductance. In addition, cromakalim slightly enhanced both amplitude and duration of afterhyperpolarizations following single calcium-dependent action potentials, suggesting that cromakalim might have a weak facilitatory effect on calcium-dependent potassium conductances.Send offprint requests to C. Alzheimer at the above address     

Subthreshold oscillations generated by TTX-sensitive sodium currents in dorsal cochlear nucleus pyramidal cells

During intracellular recordings in rodent brainstem slice preparations, dorsal cochlear nucleus (DCN) pyramidal cells (PCs) exhibit characteristic discharge patterns to depolarizing current injection that depend on the membrane potential from which the responses are evoked. When depolarized from hyperpolarized potentials, PCs can respond with a short-latency action potential followed by a long silent interval (pauser) or a train of action potentials with a long latency (buildup). During the silent intervals in a pauser or a buildup response, the membrane potential slowly depolarizes towards spike threshold, often exhibiting distinct voltage oscillations of 1–2 mV before the first spike. The subthreshold voltage oscillations were investigated using whole cell recordings from DCN PCs in rat pup (P10–14) brainstem slices. The oscillations were unaffected by excitatory and inhibitory neurotransmitter antagonists, and were not temporally locked to the onset of the depolarization. The oscillations typically became larger as spike threshold was approached, and had a characteristic frequency between 40 and 100 Hz. In the presence of tetrodotoxin (TTX, 500 nM), the oscillations were significantly suppressed, and could not be evoked at any voltage below or above spike threshold. The oscillations were not blocked by phenytoin or Cd²⁺, but they were affected by prior activity in the neuron for approximately 1 s. We conclude that voltage-gated Na⁺ channels are required to generate membrane oscillations during the buildup phase. We suggest that the subthreshold oscillations play a role in controlling spike timing in PCs when the membrane potential slowly approaches, or hovers near, spike threshold.     

实验性抑郁症大鼠缰核和海马BDNF基因表达

目的：研究抑郁症大鼠缰核和海马BDNF基因的表达情况。方法：采用长期未预知应激刺激致大鼠抑郁症模型，运用open-field和forced swinmming test法观察大鼠行为学变化。运用免疫组化法检测缰核和海马BDNT基因的表达。结果：与正常对照组相比，抑郁症模型组大鼠海马和缰核均表现为BDNF阳性细胞数量明显减少。结论：实验性抑郁症大鼠缰核、海马BDNF基因表达水平降低。     

Levetiracetam Inhibits both ryanodine and IP3 receptor activated calcium induced calcium release in hippocampal neurons in culture

Epilepsy affects approximately 1% of the population worldwide, and there is a pressing need to develop new anti-epileptic drugs (AEDs) and understand their mechanisms of action. Levetiracetam (LEV) is a novel AED and despite its increasingly widespread clinical use, its mechanism of action is as yet undetermined. Intracellular calcium ([Ca²⁺]_i) regulation by both inositol 1,4,5-triphosphate receptors (IP3R) and ryanodine receptors (RyR) has been implicated in epileptogenesis and the maintenance of epilepsy. To this end, we investigated the effect of LEV on RyR and IP3R activated calcium-induced calcium release (CICR) in hippocampal neuronal cultures. RyR-mediated CICR was stimulated using the well-characterized RyR activator, caffeine. Caffeine (10 mM) caused a significant increase in [Ca²⁺]_i in hippocampal neurons. Treatment with LEV (33 μM) prior to stimulation of RyR-mediated CICR by caffeine led to a 61% decrease in the caffeine induced peak height of [Ca²⁺]_i when compared to the control. Bradykinin stimulates IP3R-activated CICR—to test the effect of LEV on IP3R-mediated CICR, bradykinin (1 μM) was used to stimulate cells pre-treated with LEV (100 μM). The data showed that LEV caused a 74% decrease in IP3R-mediated CICR compared to the control. In previous studies we have shown that altered Ca²⁺ homeostatic mechanisms play a role in seizure activity and the development of spontaneous recurrent epileptiform discharges (SREDs). Elevations in [Ca²⁺]_i mediated by CICR systems have been associated with neurotoxicity, changes in neuronal plasticity, and the development of AE. Thus, the ability of LEV to modulate the two major CICR systems demonstrates an important molecular effect of this agent on a major second messenger system in neurons.     

Potent depressant effects of adenosine analogs on hippocampal slow-wave activity in the unanesthetized rat

Summary Adenosine and its analogs have previously been shown to exert a depressant effect on several measures of hippocampal excitability in the hippocampal slice and intact anesthetized preparation. In the present report, we examined the effects of intraventricular injections of adenosine analogs on hippocampal slow-wave activity in the freely moving rat. Each of three adenosine analogs— 5-N-ethylcarboxamidoadenosine (NECA) and N⁶-(phenylisopropyl) adenosine (L- and D-PIA) — were found to strongly suppress hippocampal electroencephalographic (EEG) activity. For instance, low doses of NECA (0.5 g) produced an 80–90% decrease in the amplitude of the hippocampal EEG. NECA was approximately 20-fold more potent than L-PIA, and L-PIA was twice the potency of D-PIA. In separate experiments in the anesthetized rat, NECA and L-PIA were found to block completely the activation of the hippocampal theta rhythm elicited with brainstem stimulation. The effects of adenosine analogs on both the hippocampal EEG and theta rhythm were very effectively reversed with methylxanthine, 8-para-sulphophenyl-theophylline (8-PSPT). The present findings demonstrate that adenosine analogs exert a powerful depressant effect on the hippocampal EEG in the natural unanesthetized state, and suggest that changes in the levels of endogenous adenosine may play a significant role in modulating the normal activity and function of the hippocampus.This work was supported in part by National Science Foundation grant BNS-8403544 to RPV     

老年大鼠的海马神经元对微量注射Ach的敏感性

本工作观察了老年大鼠海马神经元对微量注射Ach(10μg/0.5μl)的敏感性。 实验在6只老年大鼠(大于30月龄)和5只年青大鼠(4～5月龄)上进行。结果表明:年青大鼠和老年大鼠的海马神经元对Ach的主要反应模式有所不同,前者多出现神经元放电明显增加的兴奋反应。后者多出现抑制反应,神经元的放电明显减少。此外,老年大鼠的海马神经元对Ach反应的持续时间(包括兴奋和抑制反应)也明显长于年青大鼠。本文对海马神经元敏感性和适应能力的改变可能是影响老年记忆的重要因素进行了讨论。     

Adenosine receptor density and the depression of evoked neuronal activity in the rat hippocampus in vitro

The relationship between the heterogeneous distribution of A-1 adenosine receptors and the capacity of adenosine to depress neuronal activity was examined in the rat hippocampus. Utilizing autoradiographic techniques, the distribution of A-1 adenosine receptors was assessed by the binding of [3H]cyclohexyladenosine ([3H]CHA) to cryostat sections of rat brain. The apical dendritic region of CA1 showed a differential distribution of adenosine receptors between the stratum radiatum and stratum lacunosum/moleculare. The physiological relevance of this binding difference was studied in the hippocampal slice by examining the capacity of adenosine to depress evoked potentials in these two strata. It was observed that the receptor differences correlated with differential sensitivities to adenosine modulation of the evoked potentials. These data suggest that receptor density, as shown by binding techniques, may provide not only a qualitative but also a quantitative map of the sites of adenosine action.     

OGD增加小鼠离体海马组织内cPKCβII和nPKCε的膜转位

目的:通过观察无糖低氧(OGD)刺激对小鼠海马脑片内蛋白激酶C(PKC)特定亚型膜转位水平(激活程度)的影响,进一步证实我们在整体低氧预适应小鼠模型上所获实验结果,并为离体海马脑片缺血/低氧预适应(I/HPC)模型建立及后续药物干预实验打下基础。方法:急性分离小鼠海马组织、制备400!μm厚度的脑片,并用无糖低氧(OGD)人工脑脊液(ACSF)模拟缺血/低氧刺激;应用SDS-PAGE和Westernbolt等生化技术,并结合GelDoc凝胶成像系统,半定量检测OGD刺激2、5、10、15和30min后海马脑片内cPKCβII和nPKCε的膜转位水平。结果:OGD刺激可增高海马脑片内cPKCβII和nPKCε的膜转位水平,且这种增高从刺激5min开始持续至30min均有显著差异(P<0.001,n=6)。结论:实验结果进一步证实cPKCβII和nPKCε可能参与脑缺血/低氧性预适应的形成过程,并提示OGD10min作为制备离体海马脑片I/HPC模型的预处理刺激较为合理。