Suppression of kindling epileptogenesis in rats by intrahippocampal cholinergic grafts

Selective immunolesioning of the basal forebrain cholinergic system by 192 IgG-saporin, which leads to a dramatic loss of the cholinergic innervation in cortical and hippocampal regions, facilitates the development of hippocampal kindling in rats. The aim of the present study was to explore whether grafted cholinergic neurones are able to reverse the lesion-induced increase of seizure susceptibility. Intraventricular 192 IgG-saporin was administered to rats which 3 weeks later were implanted with rat embryonic, acetylcholine-rich septal-diagonal band tissue (‘cholinergic grafts’) or cortical tissue/vehicle (‘sham grafts’) bilaterally into the hippocampal formation. After 3 months, the grafted animals as well as non-lesioned control rats were subjected to daily hippocampal kindling stimulations. In the animals with cholinergic grafts, which had reinnervated the hippocampus and dentate gyrus bilaterally, there was a marked suppression of the development of seizures as compared with the hyperexcitable, sham-grafted rats. This effect was significantly correlated to the density of the graft-derived cholinergic innervation of the host hippocampal formation. The kindling rate in the rats with cholinergic grafts was similar to that in non-lesioned controls. These results provide further evidence that the intrinsic basal forebrain cholinergic system dampens kindling epileptogenesis and demonstrate that this function can be exerted also by grafted cholinergic neurones.     

Septal innervation regulates the function of alpha7 nicotinic receptors in CA1 hippocampal interneurons

The hippocampus receives substantial input from the medial septum/diagonal band of broca (MS/DB) via the fibria-fornix (FF). Projections from the MS/DB innervate hippocampal interneurons that express alpha7 nicotinic receptors and regulate excitation in principal cell populations. In the present report we used stereotaxic surgery, whole-cell patch clamping, and immunohistochemical techniques to evaluate the effects of FF and MS/DB lesions on alpha7 nicotinic receptors in stratum radiatum interneurons. Focal somatic application of ACh (1 mM) evoked methyllycaconitine (MLA)-sensitive currents that were markedly reduced following aspirative lesions of the FF. Reductions in current amplitudes were prevented or restored to levels not significantly different from controls following in vivo treatment with the alpha7-selective agonist GTS-21, and GTS-21 treatment did not change current amplitudes measured in tissue from unlesioned animals. MS/DB injections of the selective cholinergic neurotoxin 192 IgG-saporin did not affect alpha7 receptor currents, although MS/DB ChAT and hippocampal AChE immunolabeling were significantly reduced. In contrast, kainic acid lesions of the MS/DB, potentially more selective for GABAergic projection neurons, produced significant reductions in current amplitudes. These findings are the first to show functional changes in alpha7 receptors following hippocampal denervation and suggest that MS/DB hippocampal innervation regulates functional aspects of hippocampal alpha7 receptors. The results confirm hippocampal alpha7 nicotinic receptors as viable therapeutic targets in diseases that involve degradation of the septohippocampal pathway and may indicate that GABAergic MS/DB hippocampal input plays a more substantial role in the regulation of alpha7 nicotinic receptor function than MS/DB hippocampal cholinergic input.     

Emergence of spatial impairment in rats following specific cholinergic depletion of the medial septum combined with chronic stress

A consistent finding in patients suffering from Alzheimer's disease is a loss of the cholinergic neurons of the basal forebrain that project to the hippocampus. However, the role this depletion plays in the development of Alzheimer's disease remains unclear. The loss of this ascending neurotransmitter system could potentially render hippocampal neurons more susceptible to further insult, such as chronic stress, ultimately resulting in neuronal death and memory loss. We explored this possibility by using the highly specific toxin 192 IgG-Saporin to destroy the majority of cholinergic activity in the septo-hippocampal pathway in rats. Following depletion, rats were subjected to 2 weeks of restraint stress. Rats were divided into two groups and were tested either on a hippocampal-dependent (water maze) task or a hippocampal-independent task (fear conditioning to tone and context). We showed that cholinergic depletion or stress alone had no effect on the successful performance of either of the tasks. However, rats with a combination of cholinergic depletion and stress were significantly impaired on the water-maze task. No deficits were apparent in the combined group that was tested on fear conditioning to tone or context, suggesting that this impairment is specific to spatial working memory. These rats had no obvious hippocampal neuronal loss or damage; however, there were likely subtle changes in hippocampal processing that led to the observed deficit on the hippocampal-dependent task. These findings support our theory that cholinergic depletion of the medial septum increases hippocampal vulnerability to further insults such as stress.     

Reduced cholinergic status in hippocampus produces spatial memory deficits when combined with kainic acid induced seizures

Alzheimer's disease is the most common form of dementia in North America today. Though many risk factors have been suggested to increase the likelihood of developing this disease, an accurate etiology has yet to be described. One of these risk factors commonly associated with Alzheimer's disease is the loss of cholinergic neurons of the medial septum that project to the hippocampus, leading to depletion in cholinergic activity. A second risk factor is the presence of seizures, which can increase the risk of excitotoxic cell death. To examine the interaction between these two common risk factors, we gave rats a focal cholinergic lesion of the medial septum using the specific immunotoxin 192-IgG Saporin, followed 2 weeks later by a non-convulsive dose of kainic acid. We then assessed the rats for seizure severity, hippocampal damage and performance on a spatial memory task. The combination of the two factors resulted in a trend towards increased seizure severity in the cholinergic depleted rats, but more importantly, the lesioned rats that had non-convulsive seizures were significantly impaired on a spatial version of the Morris water maze when compared with either the rats with a cholinergic depletion or non-convulsive seizure alone. This result could not be explained by seizure severity or the extent of hippocampal damage, suggesting a more subtle interaction between these two risk factors in the development of a hippocampal based memory impairment.     

"自杀性传输"及相关毒素在疼痛治疗中的应用

某些毒素具有逆向轴浆运输作用,可造成神经系统的选择性损伤,即“自杀性传输”,并被命名为“分子神经外科”。近年来此技术应用于伤害性感受研究领域,证明为分析伤害性感受系统的一种有用工具,并有希望界定特殊类型神经元在疼痛感受和发现疼痛治疗新方法中的作用。     

Severe learning impairment caused by combined immunotoxic lesion of the cholinergic projections to the cortex and hippocampus in monkeys

Monkeys with immunotoxic lesions of both the basal nucleus of Meynert and the vertical limb of the diagonal band of Broca (NBM+VDB) lost cholinergic innervation throughout the cortex and hippocampus. They were impaired at learning discriminations between objects differing in either few, or many, attributes and at learning visuospatial conditional discriminations. Monkeys with immunotoxic lesions of the NBM lost cholinergic innervation of the neocortex only. Initially, they were unable to learn a simple visual discrimination where the stimuli differed in a limited number of attributes but they were unimpaired at learning discriminations between objects that differed in more attributes. They were mildly impaired at learning a visuospatial conditional task. The impairment exhibited by monkeys with lesions of the NBM alone ameliorated with time but that following NBM+VDB lesions did not. Previous experiments have shown that monkeys with immunotoxic lesions of the VDB alone are impaired at learning visuospatial conditional discriminations but are unimpaired at learning simple visual discriminations. When monkeys with NBM lesions were given excitotoxic lesions of the CA1 field of the hippocampus the learning impairment on discriminations between objects which differed in few attributes was reinstated. Pretreatment with a cholinergic agonist improved learning ability on visual discrimination learning in all monkeys but this improvement was significantly greater in monkeys with lesions of the NBM. On conditional discrimination learning, which is particularly sensitive to hippocampal damage, pilocarpine produced a significant improvement in monkeys with NBM+VDB lesions (where the hippocampal dysfunction was cholinergic) but not in monkeys with NBM+CA1 lesions (where the hippocampal damage was structural).     

192-Saporin对SD大鼠股骨发育的作用研究

目的研究胆碱能神经系统对骨发育的影响。方法用192-Saporin抑制SD乳鼠胆碱能神经系统的发育和功能,每2d腹腔注射1次,持续2周,股骨进行大体测量和生物力学检测,坐骨神经行Loyez髓鞘染色。结果药物处理对乳鼠生理状态和运动能力无明显影响,处理前后处理组与对照组体重比较无显著性差异(P>0.05);处理组股骨中段冠状面皮质直径小于对照组(P<0.01),直径/全长比值无显著性差异(P>0.05);处理组股骨最大抗折应力小于对照组(P<0.05),刚性比较则无显著性差异(P>0.05);处理组坐骨神经轴突排列较紊乱,密度较对照组低(P<0.01)。结论处理组股骨发育较慢但发育比例正常,以及矿化程度未受影响,提示胆碱能神经系统可能在成骨细胞的增殖过程中起重要作用。     

导向药物转化生长因子α-Sporin对增殖平滑肌细胞生长的抑制作用

为证实生物导向药物对平滑肌细胞增殖的作用,用SPDP化学联结法合成了转化生长因子α-Saporin,通过MTS比色法观察了转化生长因子α-Saporin对培养中的增殖平滑肌细胞的细胞毒性作用,并用氟标胸腺脱氧嘧啶核苷掺入法进一步探讨了转化生长因子α－Saporin对平滑肌细胞的DNA合成的影响以及过量转化生长因子α-对转化生长因子α-Saporin的受体竞争抑制作用。结果发现,联结后的转化生长因子α－Saporin可明显抑制平滑肌细胞的增殖,而Saporin的抑制作用却很弱,转化生长因子α－Saporin对培养的平滑肌细胞氘标胸腺脱氧嘧啶核苷掺入量有明显抑制作用。与对照组比较氘标胸腺脱氧嘧啶苷掺入量降低了39．1％（P＝0．0017）,而在加入表皮生长因子受体的配体转化生长因子α后可明显竞争抑制转化生长因子α－Saporin对平滑肌细胞增殖的细胞毒性作用。实验结果提示：转化生长因子α－Saporin通过表皮生长因子受体介导已具有较Saporin明显增强的细胞毒性作用。本实验为转化生长因子α－saporin在经皮腔内冠状动脉成形术术后再狭窄的临床防治中的应用的研究提供初步的实验依据。αα     

Hepatotoxicity of ricin, saporin or a saporin immunotoxin: xanthine oxidase activity in rat liver and blood serum

Male Wistar rats each received an i.p. injection of the ribosome-inactivating proteins ricin or saporin, or a Ber-H2 (anti-CD30)-saporin immunotoxin at a dose corresponding to three times the LD₅₀ calculated for mice. Animals were killed 24, 48 or 72 h after treatment. Histological examination showed hepatic necrosis in all treated animals, although the sinusoidal lining was affected only in ricin-poisoned rats. The activities of xanthine dehydrogenase (D-form) and oxidase (O form) were determined spectrophotometrically in liver and serum samples. In ricin-treated animals the liver enzyme was progressively converted from the D- to the O-form, which accounted for more than 60% of total activity after 48 h of poisoning, whilst no change in the xanthine oxidase activity was found in the serum. In the liver of rats treated with free or Ber-H2-conjugated saporin, the D-form was more than 75%, as in normal animals. In the same animals the serum xanthine oxidase activity was up to three-fold control values. The determination of serum xanthine oxidase may prove helpful in the evaluation of liver damage in patients treated with immunotoxins. It may become a diagnostic tool for the differential diagnosis of liver diseases.     

Visual agnosia and Klüver–Bucy syndrome in marmosets (Callithrix jacchus) following ablation of inferotemporal cortex, with additional mnemonic effects of immunotoxic lesions of cholinergic projections to medial temporal areas

Inferotemporal ablations in the New World monkey, the common marmoset (Callithrix jacchus), produced a persistent impairment on visual discrimination learning and a florid, but transient, Klüver–Bucy syndrome. Monkeys with these ablations were impaired on acquisition of object discriminations to a high criterion and on concurrent discrimination learning, to a single high criterion across all trials. Neither the control monkeys nor the monkeys with inferotemporal ablations found acquisition more difficult when the component discriminations of a set were presented concurrently compared to consecutively, although the monkeys with inferotemporal ablations found acquisition under both these conditions somewhat more difficult than did control monkeys. This suggests that the severe impairment caused by inferotemporal ablations on concurrent learning measured across all trials is due to the need for sustained performance across a concurrent set rather than to the extra mnemonic demands of concurrent presentation. When immunotoxic lesions of the cholinergic projection to the hippocampal formation were added to the inferotemporal ablations, a further impairment on retention, and a differential impairment on concurrent, compared to consecutive, learning was observed. Previous studies have shown that lesions of the cholinergic projection to the hippocampus alone, or excitotoxic hippocampal lesions, do not affect simple visual discrimination learning. It is suggested that large inferotemporal ablations in monkeys produce a visual agnosia which causes severe ‘psychic blindness’ in the first instance, and a persistent impairment on visual discrimination learning. The hippocampus makes a contribution, which may be mnemonic, to discrimination performance after inferotemporal ablations.