Changes in glucose metabolism and metabolites during the epileptogenic process in the lithium-pilocarpine model of epilepsy

Purpose: The metabolic and biochemical changes that occur during epileptogenesis remain to be determined. ¹⁸F‐Fluorodeoxyglucose positron emission tomography (FDG‐PET) and proton magnetic resonance spectroscopy (¹H MRS) are noninvasive techniques that provide indirect information on ongoing pathologic changes. We, therefore, utilized these methods to assess changes in glucose metabolism and metabolites in the rat lithium‐pilocarpine model of epilepsy as markers of epileptogenesis from baseline to chronic spontaneous recurrent seizures (SRS). Methods: PET and MRS were performed at baseline, and during the acute, subacute, silent, and chronic periods after lithium‐pilocarpine induced status epilepticus (SE). Sequential changes in glucose metabolism on ¹⁸F‐FDG PET using SPM2 and the ratios of percent injected dose per gram (%ID)/g of regions of interest (ROIs) in the bilateral amygdala, hippocampus, basal ganglia with the thalamus, cortex, and hypothalamus normalized to the pons were determined. Voxels of interest (VOIs) on ¹H MRS were obtained at the right hippocampus and the basal ganglia. NAA/Cr levels and Cho/Cr at various time points were compared to baseline values. Key Findings: Of 81 male Sprague‐Dawley rats, 30 progressed to SRS. ¹⁸F‐FDG PET showed widespread global hypometabolism during the acute period, returning to baseline level during the subacute period. Glucose metabolism, however, declined in part of the hippocampus during the silent period, with the hypometabolic area progressively expanding to the entire limbic area during the chronic period. ¹H MRS showed that the NAA/Cr levels in the hippocampus and basal ganglia were reduced during the acute period and were not restored subsequently from the subacute to the chronic period without any significant change in the Cho/Cr ratio throughout the entire experiment. Significance: Serial metabolic and biochemical changes in the lithium‐pilocarpine model of epilepsy indirectly represent the process of human epileptogenesis. Following initial irreversible neural damage by SE, global glucose metabolism transiently recovered during the subacute period without neuronal recovery. Progressive glucose hypometabolism in the limbic area during the silent and chronic periods may reflect the important role of the hippocampus in the formation of ongoing epileptic network during epileptogenesis.     

匹鲁卡品对Wistar大鼠心律失常的影响

目的观察匹罗卡品对Wistar大鼠心律失常的作用。方法分别以乌头碱、氯化钡制作Wistar大鼠心律失常模型,观察0.2 mg.kg-1匹罗卡品舌下静脉注射对心律失常的作用。结果匹罗卡品可明显延迟乌头碱引起Wistar大鼠室性心律失常的出现(P<0.05)、延长其出现心律失常后的存活时间(P<0.05);匹罗卡品能明显延迟氯化钡引起Wistar大鼠双相室性心律失常的出现(P<0.01)、缩短其心律失常的持续时间(P<0.01);但上述作用可被M3受体阻滞剂4-DAMP完全逆转。结论匹罗卡品通过激动Wistar大鼠心肌M3受体而产生对抗乌头碱和氯化钡诱发Wistar大鼠心律失常的作用。     

HPLC法测定硝酸毛果芸香碱注射液的含量与有关物质

目的:建立高效液相色谱法测定硝酸毛果芸香碱注射液的含量及有关物质。方法:采用C18柱,流动相为甲醇-含0.002mol.L-1磷酸二氢铵和0.0018 mol.L-1四丁基氢氧化铵的水溶液(30∶70),检测波长220 nm。用外标法测定含量,不加校正因子的自身对照法测定有关物质。结果:有关物质浓度在0.510～153.1μg.mL-1,含量测定浓度在51.58～515.8μg.mL-1范围内与峰面积呈良好的线性关系。硝酸毛果芸香碱主成分峰与有关物质峰的分离度均符合要求,硝酸毛果芸香碱的检出限为4 ng。结论:本方法简便、准确,灵敏度高,适用于该制剂的含量及有关物质测定。     

褪黑素对匹罗卡品致痫模型鼠行为改变的影响

目的　探讨褪黑素在匹罗卡品致痫大鼠模型中的抗癫痫作用及其机制。方法　采用匹罗卡品癫痫模型,观 察长期给予褪黑素对匹罗卡品致痫大鼠原发性癫痫反复发作、海马神经元丢失,苔癣纤维轴突发芽的影响。结果　给予 褪黑素后匹罗卡品致痫大鼠原发性癫痫反复发作出现的潜伏期延长,发作程度和频率均降低(P<0.01);给予褪黑素治疗 的大鼠海马CA1区Nissl染色和Timms染色评分均明显低于未用褪黑素处理的致痫大鼠(P<0.01)。结论　褪黑素能明显 降低匹罗卡品致痫大鼠原发性癫痫反复发作的频率和程度,该作用可能与褪黑素对海马神经元损伤的保护及对苔癣纤维 轴突发芽的抑制作用有关。     

Cortical network dynamics are coupled with cognitive aging in rats

Changes in neuronal network activity and increased interindividual variability in memory are among the most consistent features of growing older. Here, we examined the relationship between these hallmarks of aging. Young and aged rats were trained on a water maze task where aged individuals reliably display an increased range of spatial memory capacities relative to young. Two weeks later, neuronal activity was induced pharmacologically with a low dose of pilocarpine and control animals received vehicle. Activity levels were proxied by quantifying the immediate early gene products Arc and c‐Fos. While no relationship was observed between basal, resting activity, and individual differences in spatial memory in any brain region, pilocarpine‐induced marker expression was tightly coupled with memory in all areas of the prefrontal cortex (PFC) and hippocampus examined. The nature of this association, however, differed across regions and in relation to age‐related cognitive outcome. Specifically, in the medial PFC, induced activity was greatest in aged rats with cognitive impairment and correlated with water maze performance across all subjects. In the hippocampus, the range of induced marker expression was comparable between groups and similarly coupled with memory in both impaired and unimpaired aged rats. Together the findings highlight that the dynamic range of neural network activity across multiple brain regions is a critical component of neurocognitive aging.     

Dynamic seizure-related changes in extracellular signal-regulated kinase activation in a mouse model of temporal lobe epilepsy

Extracellular signal-regulated kinase (ERK) is highly sensitive to regulation by neuronal activity and is critically involved in several forms of synaptic plasticity. These features suggested that alterations in ERK signaling might occur in epilepsy. Previous studies have described increased ERK phosphorylation immediately after the induction of severe seizures, but patterns of ERK activation in epileptic animals during the chronic period have not been determined. Thus, the localization and abundance of phosphorylated extracellular signal-regulated kinase (pERK) were examined in a pilocarpine model of recurrent seizures in C57BL/6 mice during the seizure-free period and at short intervals after spontaneous seizures. Immunolabeling of pERK in control animals revealed an abundance of distinctly-labeled neurons within the hippocampal formation. However, in pilocarpine-treated mice during the seizure-free period, the numbers of pERK-labeled neurons were substantially decreased throughout much of the hippocampal formation. Double labeling with a general neuronal marker suggested that the decrease in pERK-labeled neurons was not due primarily to cell loss. The decreased ERK phosphorylation in seizure-prone animals was interpreted as a compensatory response to increased neuronal excitability within the network. Nevertheless, striking increases in pERK labeling occurred at the time of spontaneous seizures and were evident in large populations of neurons at very short intervals (as early as 2 min) after detection of a behavioral seizure. These findings suggest that increased pERK labeling could be one of the earliest immunohistochemical indicators of neurons that are activated at the time of a spontaneous seizure.     

A physiologically based pharmacokinetic model for the intraocular distribution of pilocarpine in rabbits

This report presents a mathematical model which has been developed to describe the intraocular disposition of pilocarpine following topical dosing in rabbits. The model uses experimentally determined parameters such as rates of tissue uptake of drug and equilibrium distribution coefficients. Differential mass balance equations for pilocarpine in the cornea, aqueous humor, irisciliary body, and lens were written and solved numerically. Measured tear concentrations, following topical dosing with pilocarpine, were fit by a monoexponential curve and used as the forcing function for the model. By using a combination of known physiological and experimentally determined parameters, predictions of intraocular tissue levels of pilocarpine were made. These predictions were then compared to experimentally determined concentration-time profiles.     

Effect of parasympathetic and vasoactive drugs on ciliary epithelium permeability

The effects of bradykinin, histamine and acetylcholine, at concentrations known to induce changes in the living rabbit eye, have been examined on both secretion and passive permeability of the isolated rabbit ciliary epithelium. All compounds, including in addition pilocarpine and atropine, increased the fluid permeability of the ciliary epithelium, although different concentrations were required to induce changes. With pilocarpine for example, the passive fluid permcability increased linearly up to 10^?2m but atropine had no effect until 10^?4m was reached. Acetylcholine increased both fluid secretion and passive permeability, an effect which was reduced by atropine. Bradykinin also increased fluid secretion at concentrations greater than 10^?10m. The in vitro data correlate with previous observations on the living eye and indicate that these vasoactive drugs not only increase vascular permeability but in addition also have direct and independent effects on the permeability of the ciliary epithelium.