Distemper virus encephalitis exerts detrimental effects on hippocampal neurogenesis

E.‐L. von Rüden, J. Avemary, C. Zellinger, D. Algermissen, P. Bock, A. Beineke, W. Baumgärtner, V. M. Stein, A. Tipold and H. Potschka (2012) Neuropathology and Applied Neurobiology 38, 426–442 Distemper virus encephalitis exerts detrimental effects on hippocampal neurogenesis Aims: Despite knowledge about the impact of brain inflammation on hippocampal neurogenesis, data on the influence of virus encephalitis on dentate granule cell neurogenesis are so far limited. Canine distemper is considered an interesting model of virus encephalitis, which can be associated with a chronic progressing disease course and can cause symptomatic seizures. Methods: To determine the impact of canine distemper virus (CDV) infection on hippocampal neurogenesis, we compared post‐mortem tissue from dogs with infection with and without seizures, from epileptic dogs with non‐viral aetiology and from dogs without central nervous system diseases. Results: The majority of animals with infection and with epilepsy of non‐viral aetiology exhibited neuronal progenitor numbers below the age average in controls. Virus infection with and without seizures significantly decreased the mean number of neuronal progenitor cells by 43% and 76% as compared to age‐matched controls. Ki‐67 labelling demonstrated that hippocampal cell proliferation was neither affected by infection nor by epilepsy of non‐viral aetiology. Analysis of CDV infection in cells expressing caspase‐3, doublecortin or Ki‐67 indicated that infection of neuronal progenitor cells is extremely rare and suggests that infection might damage non‐differentiated progenitor cells, hamper neuronal differentiation and promote glial differentiation. A high inter‐individual variance in the number of lectin‐reactive microglial cells was evident in dogs with distemper infection. Statistical analyses did not reveal a correlation between the number of lectin‐reactive microglia cells and neuronal progenitor cells. Conclusions: Our data demonstrate that virus encephalitis with and without seizures can exert detrimental effects on hippocampal neurogenesis, which might contribute to long‐term consequences of the disease. The lack of a significant impact of distemper virus on Ki‐67‐labelled cells indicates that the infection affected neuronal differentiation and survival of newborn cells rather than hippocampal cell proliferation.     

Kindling with rapidly recurring hippocampal seizures

Bipolar electrodes, stereotactically implanted in the hippocampus of adult rats, were used to deliver 10 s trains of suprathreshold tetanic electrical stimuli every few minutes. As indices of seizure intensity, durations of the afterdischarges triggered by these stimuli were measured, and the accompanying behaviors were scored on a 5-point scale. After 2–3 h, prolonged afterdischarges appeared in conjunction with severe limbic seizures, separated by periods of approximately 60 min. After 3–9 h, the stimulation was withheld until the following day. Upon reinstitution of the stimuli, intense seizures were seen at the onset, and the cycle time between them was shortened. Enhanced responsiveness to a fixed stimulus persisted for several months, the longest period tested. In addition, the enhanced epileptogenicity showed transference and was not stimulus-specific. These studies, using stimuli with low intertrain frequency and short interstimulus intervals, establish a robust and rapidly-developing model of epileptogenesis in the hippocampus that is comparable to traditional kindling.     

Unidirectional interaction between flurothyl seizures and amygdala kindling

In this report, the interaction between flurothyl convulsions and electrical kindling of the amygdala was investigated. Three flurothyl convulsions decreased the afterdischarge threshold of the amygdala and enhanced the rate of development of electrical kindling without affecting the intensity of postictal refractoriness. On the other hand, 3 generalized kindled convulsions did not alter the flurothyl convulsive threshold. The data suggest that the influence of generalized convulsions on future seizure susceptibility may depend on the agents used to induce the convulsions.     

Angular bundle kindling is accelerated in rats with a genetic predisposition to acoustic stimulus-induced seizures

Limbic kindling was examined in genetically epilepsy-prone (GEPR) and non-epileptic control rats. The early stage of kindling development was accelerated in both groups of GEPR rats compared to controls. Later stages of kindling were accelerated in GEPR-9 but not GEPR-3 rats. These results indicate that GEPR rats have an enhanced susceptibility to limbic kindling and suggest that limbic brain alterations may contribute to acceleration of the early stage kindling development in GEPR rats.     

Reduced kainic acid binding in rat hippocampal formation after limbic kindling

The specific binding of [3H]kainic acid to hippocampal membranes was examined autoradiographically in rats kindled by tetanic stimulation of the amygdala or angular bundle. One day after the last of 3 class 4-5 kindled seizures, the specific binding of [3H]kainic acid in stratum lucidum of area CA3 was 47-61% less than in electrode-implanted unstimulated controls. Specific binding in the inner third of the dentate molecular layer was reduced to a lesser degree. These observations demonstrate that kainic acid receptors are down-regulated by kindling stimulation.     

Modulation of adult hippocampal neurogenesis during myelin-directed autoimmune neuroinflammation

In chronic autoimmune diseases of the central nervous system (CNS) such as multiple sclerosis (MS) clinical signs of cognitive dysfunction have been associated with structural changes in the hippocampus. Moreover, experimental studies indicate that inflammatory responses within the CNS modulate the homeostasis of newborn cells in the adult dentate gyrus (DG). However, it remained open whether such changes happen regardless of the primary immunological target or whether a CNS antigen-directed T lymphocyte-mediated autoimmune response may exert a specific impact. We therefore induced experimental autoimmune encephalomyelitis (EAE), a common model of MS serving as a paradigm for a CNS-specific immune response, by immunizing C57BL/6 mice with encephalitogenic myelin oligodendrocyte glycoprotein (MOG) p35-55. In EAE animals, we found enhanced de novo generation and survival of doublecortin (DCX)-positive immature neurons when compared with controls immunized with CNS-irrelevant antigen (ovalbumine). However, despite activation of neurogenesis, we observed a reduced capacity of these cells to generate mature neurons. Moreover, the high number of newly born cells retained the expression of the glial marker GFAP. These effects were associated with downregulation of pro-neurogenic factors Neurogenin1 and Neurogenin2 and dysregulation of Notch, β-catenin, Sonic Hedgehog (Shh) signaling as suggested by altered gene expression of effector molecules. Thus, a CNS antigen-specific immune response leads to an aberrant differentiation of neural precursors associated with dysbalance of signaling pathways relevant for adult hippocampal neurogenesis. These results may further extend our understanding of disturbed regeneration in the course of chronic inflammatory CNS diseases such as MS.     

Unilateral peri-substantia nigra catecholaminergic lesion and amygdala kindling

Recent evidence suggests that the substantia nigra (SN) may be involved in the modulation of kindled seizures in adult rats. In this report we investigated the role of the dopaminergic nigrostriatal pathway in mediating the SN effect on seizures by lesioning this pathway with unilateral infusions of 6-hydroxydopamine (6-OHDA) in the vicinity of the right SN with or without desmethylimipramine pretreatment. Our data suggest that the facilitation of amygdala kindling observed following 6-OHDA lesion in the vicinity of the ipsilateral SN is due to norepinephrine depletion of the ipsilateral forebrain. Selective destruction of the nigrostriatal dopaminergic neurons neither facilitates nor inhibits the development of amygdala-kindled convulsions in adult rats.     

Basal forebrain neurons suppress amygdala kindling via cortical but not hippocampal cholinergic projections in rats

Intraventricular administration of the immunotoxin 192 IgG-saporin in rats has been shown to cause a selective loss of cholinergic afferents to the hippocampus and cortical areas, and to facilitate seizure development in hippocampal kindling. Here we demonstrate that this lesion also accelerates seizure progression when kindling is induced by electrical stimulations in the amygdala. However, whereas intraventricular 192 IgG-saporin facilitated the development of the initial stages of hippocampal kindling, the same lesion promoted the late stages of amygdala kindling. To explore the role of various parts of the basal forebrain cholinergic system in amygdala kindling, selective lesions of the cholinergic projections to either hippocampus or cortex were produced by intraparenchymal injections of 192 IgG-saporin into medial septum/vertical limb of the diagonal band or nucleus basalis, respectively. Cholinergic denervation of the cortical regions caused acceleration of amygdala kindling closely resembling that observed after the more widespread lesion induced by intraventricular 192 IgG-saporin. In contrast, removal of the cholinergic input to the hippocampus had no effect on the development of amygdala kindling. These data indicate that basal forebrain cholinergic neurons suppress kindling elicited from amygdala, and that this dampening effect is mediated via cortical but not hippocampal projections.     

Hormonal influences on seizure kindling: The effects of post-stimulation ACTH or cortisone injections

Repeated application of brain stimulation can lead to a progressively augmenting electrical and behavioral response — a phenomenon termed seizure kindling. In this experiment, stimulation was delivered once per day, and was followed by peripheral (intraperitoneal) administration of ACTH or cortisone. An intermediate or a high dose of either hormone (0.3 IU or 3.0 IU of ACTH/animal, 10 mg or 25 mg cortisone/animal) delayed the completion of kindling if administered shortly after each kindling stimulation. Lower doses (0.03 IU of ACTH or 2 mg of cortisone) had no significant effects. The high dose of ACTH or cortisone was no longer effective if administration was delayed more than 4 h after stimulation. Peripherally administered ACTH and cortisone can influence processes initiated by the brain stimulation which presumably underlie the augmentation of response to successive stimulations. This time-limited action is analogous to the effects of these hormones on memory consolidation.     

Neuropathological profile of the pentylenetetrazol (PTZ) kindling model

ABSTRACT

Introduction: There are three phases of seizure developing in pentylenetetrazol (PTZ)-induced kindling animal model: (i) pre-kindling phase; (ii) kindling phase or after animals are fully kindled; (iii) post-kindling phase with non-provoked spontaneous recurrent seizures. The aims of this review were to summarize the progress over time of the electroencephalographic features and neuropathological alterations in kindled PTZ treated animals.

Materials and methods: Keywords relevant to PTZ kindling were used to a guide a literature search on Pubmed, Medline and Cochrane Library.

Results: Clonic seizures induced PTZ at kindling phase led to a strong c-Fos expression in the hippocampus. Although, decline hippocampal neuron and metabolism disturbances were detected at pre-kindlig phase. Repeated PTZ induced seizures alter the GABA-mediated inhibition and glutamate-mediated excitation, which may contribute to increased seizure susceptibility. Similar to chemical animal models such as the pilocarpine and the kainic acid models, mossy fiber sprouting, hippocampal damage, and glucose hypometabolism had been seen after PTZ induced seizures.

Conclusion: PTZ kindling model may improve understanding of the seizures development provided that the differences existing between the phases of kindling model are taken into account.     

Selective and reversible increase in the number of quisqualate-sensitive glutamate binding sites on hippocampal synaptic membranes after angular bundle kindling

The specific binding of L-[3H]glutamate to hippocampal synaptic membranes was examined in rats kindled by tetanic stimulation of the angular bundle. One day after the last of a minimum of 3 class 4 kindled seizures, the binding of L-[3H]glutamate to a quisqualate-sensitive site (GLU A) was about 40% greater than in electrode-implanted unstimulated controls. Saturation binding data indicated an increase in the maximum density of GLU A binding sites with no change in their affinity for L-glutamate. No such increase was detected 28 days after the last kindled seizure, although the animals were still kindled. Radioligand binding to a site that is much less sensitive to quisqualate (GLU B) was unaffected by kindling stimulation. These observations suggest that an increase in GLU A binding sites could be involved in the induction, but not in the maintenance, of the kindled state.     

Different effects of mild and severe seizures on hippocampal neurogenesis in adult rats

Recent evidence shows that functional neurogenesis exists in the adult hippocampus and that epileptic seizures can increase neurogenesis in the dentate gyrus (DG). However, it is unknown whether different seizure severity has different effects on neurogenesis in the DG of adult rats. In this study, we examined hippocampal neurogenesis in the rat mild and severe seizure preparations characterized with frequent wet dog shakes and severe status epilepticus, respectively. Both mild and severe seizures promoted the mitotic activity in the DG, but severe seizures caused a stronger cell proliferative response than mild seizures. Less than 20% of newborn cells in the DG differentiated into neurons in rats suffering severe seizures, whereas more than 60% of newborn dentate cells differentiated into neurons in control and mild seizure groups. Most newborn neurons migrated into the granular cell layer in control and mild seizure groups, but severe seizures were associated with an aberrant migration of newborn neurons into the dentate hilus. Severe seizures induced astrocyte activation and the expression of nestin and the migration directional molecules netrin 1 and Sema-3A in the hilus, which were not present in the hilus of control and mild seizure-attacked rats, suggesting that these molecules are involved in the aberrant migration of newborn neurons.     

Facilitation of neocortical kindling by depletion of forebrain noradrenaline

The role of forebrain noradrenaline in seizures induced by electrical stimulation of the anterior neocortex (kindling) was investigated in control rats and rats pretreated with bilateral injections of 6-hydroxydopamine (6-OHDA) into the mesencephalic trajectory of the dorsal tegmental noradrenergic bundle. Extensive depletion of forebrain noradrenaline significantly facilitated the rate of development of cortico-generalized seizures.     

Enhanced rate of kindling after prolonged electrode implantation into the amygdala of rats

A comparison was made between the rate of amygdaloid kindling in rats which had been implanted with electrodes either 6–8 days or 28–33 days before the start of a series of kindling stimulations. Using both stainless-steel and platinum/iridium electrodes the rate of kindling was significantly reduced after the longer implantation time. Possible mechanisms by which the presence of an electrode in the amygdala may influence the rate of subsequent kindling, and the implications for studies on kindling, are discussed.     

尼卡地平对戊四唑化学性点燃的拮抗作用

目的:研究二氢吡啶类钙通道阻滞剂尼卡地平对大鼠戊四唑(PTZ)化学性点燃(kindling)的拮抗作用。方法:建立大鼠PTZ化学性点燃模型,观察尼卡地平对PTZ点燃发展进程和点燃发作的影响。结果:尼卡地平2mg·kg~(-1)ip明显抑制PTZ点燃的发展进程(P<0.001);2～20mg·kg~(-1)ip显著抑制PTZ点燃发作(P<0.01)。并呈量效关系;尼卡地平20mg·kg~(-1)ip对小鼠PTZ惊厥有保护作用(P<0.01)。结论:尼卡地平对PTZ化学性点燃的发展和发作有拮抗作用。     

Kindling phenomenon of hyperthermic seizures in the epilepsy-prone versus the epilepsy-resistant rat

A kindling-like effect was produced by exposing 30-day-old rats to repeated hyperthermia-induced seizures. Naive audiogenic seizure (AGS)-susceptible rats (P77PMC) were easier to be kindled than AGS-resistant rats (Wistar). This hyperthermic kindling model may be used to study the outcome and mechanisms of human febrile seizures. The mechanisms underlying hyperthermic kindling remain to be investigated.     

Electroconvulsive shock (ECS) does not facilitate the development of kindling

Kragh Jørn, Torben Bruhn, David P.D. Woldbye and Tom G. Bolwig: Electroconvulsive shock (ECS) does not facilitate the. development of kindling. Prog. Neuro. Psychopharmacol. & Biol. Psychiat. 1993, 17(6): 985–989.

1. 1. For many years it has been discussed whether repeated electroconvulsive shock (ECS) may induce a lasting epileptogenic effect on the brain (i.e. a kindling effect). In the present study the authors investigated whether weekly ECS do exert such an effect.

2. 2. Bipolar electrodes were implanted in amygdala of 32 rats. Following a two to three week recovery period the rats were randomly allocated to two groups. One group received 12 weekly ECS, the other 12 weekly sham-ECS.

3. 3. Three months after the last ECS/sham-ECS, kindling was initiated. Daily stimulation, eliciting an EEG-afterdischarge was given to all the rats. The animals received a total of 15 stimulations.

4. 4. ECS-pretreated animals did not kindle faster than the sham-group. The two groups reached stage 4 (clonic rearing) after 5.8 (ECS-group) and 5.7 (sham-group) stimulations, respectively.

5. 5. The authors did not find a facilitated development of kindling following ECS, instead they observed a slight, yet statistically significant inhibition of the development of the maximally generalized kindling-seizure — the stage 5 seizure — in the ECS-group.

6. 6. In conclusion: The present study did not show a kindling effect of weekly ECS suggesting that kindling requires more than repeated elicitation of after-discharge.

大鼠海马快速点燃模型的建立及机制研究

目的：建立大鼠海马快速点燃模型并对其机制进行初步探讨。方法：制备大鼠海马快速点燃模型;观察经典抗杏仁核点燃药物对该模型的影响;观察大鼠海马快速点燃模型和大鼠杏仁核点燃模型海马CA_3区和皮层区c-fos蛋白的表达情况及蛋白抑制剂对其表达的影响。结果：大鼠海马快速点燃模型点燃成功率与刺激参数有关;苯巴比妥20,50mg·kg~1 及地西泮2,5mg·kg~(-1)对大鼠海马快速点燃ADD和Racine＇s分级有抑制作用(P＜0．05);与正常组比较,海马快速点燃大鼠和杏仁核点燃大鼠海马CA_3区、大脑皮层c-fos免疫阳性细胞增多(P＜0．05),在蛋白抑制剂作用下,海马c-fos免疫阳性细胞减少,但仍比正常组高(P＜0．05)。结论：大鼠海马快速点燃成功率与刺激参数具有相关性;传统抗点燃药物具有抗海马快速点燃作用;大鼠海马快速点燃模型c-fos蛋白在不同脑区和核团的免疫阳性表达细胞增加。