Biomedical subjects

Asla Pitkänen

Publications and source records attributed to Asla Pitkänen.

At least 19 recordsLinked to original sources

PubMed2006

Gene therapy in epilepsy: the focus on NPY.

Gene therapy represents an innovative and promising alternative for the treatment of epileptic patients who are resistant to conventional antiepileptic drugs. Among the various approaches for the application of gene therapy in the treatment of CNS disorders, recombinant viral vectors have been most widely used so far. Several gene targets could be used to correct the compromized balance between inhibitory and excitatory transmission in epilepsy. Transduction of neuropeptide genes such as galanin and neuropeptide Y (NPY) in specific brain areas in experimental models of seizures resulted in significant anticonvulsant effects. In particular, the long-lasting NPY over-expression obtained in the rat hippocampus using intracerebral application of recombinant adeno-associated viral (AAV) vectors reduced the generalization of seizures from their site of onset, delayed acquisition of fully kindled seizures and afforded neuroprotection. These results establish a proof-of-principle for the applicability of AAV-NPY vectors for the inhibition of seizures in epilepsy. Additional investigations are required to demonstrate a therapeutic role of gene therapy in chronic models of seizures and to address in more detail safety concerns and possible side-effects.

Epilepsy↗

PubMed2006

Effect of antiepileptic drugs on spontaneous seizures in epileptic rats.

The present study investigated whether spontaneously seizing animals are a valid model for evaluating antiepileptic compounds in the treatment of human epilepsy. We examined whether clinically effective antiepileptic drugs (AEDs), including carbamazepine (CBZ), valproic acid (VPA), ethosuximide (ESM), lamotrigine (LTG), or vigabatrin (VGB) suppress spontaneous seizures in a rat model of human temporal lobe epilepsy, in which epilepsy is triggered by status epilepticus induced by electrical stimulation of the amygdala. Eight adult male rats with newly diagnosed epilepsy and focal onset seizures were included in the study. Baseline seizure frequency was determined by continuous video-electroencephalography (EEG) monitoring during a 7 days baseline period. This was followed by a 2-3 days titration period, a 5-7 days treatment period, and a 2-3 days wash-out period. During the 5-7 days treatment period, animals were treated successively with CBZ (120 mg/kg/day), VPA (600 mg/kg/day), ESM (400 mg/kg/day), LTG (20 mg/kg/day), and VGB (250 mg/kg/day). VPA, LTG, and VGB were the most efficient of the compounds investigated, decreasing the mean seizure frequency by 83, 84, and 60%, respectively. In the VPA group, the percentage of rats with a greater than 50% decrease in seizure frequency was 100%, in the LTG group 88%, in the VGB group 83%, in the CBZ group 29%, and in the ESM group 38%. During the 7 day treatment period, 20% of the VPA-treated animals and 14% of the CBZ-treated animals became seizure-free. These findings indicate that rats with focal onset spontaneous seizures respond to the same AEDs as patients with focal onset seizures. Like in humans, the response to AEDs can vary substantially between animals. These observations support the idea that spontaneously seizing animals are a useful tool for testing novel compounds for the treatment of human epilepsy.

Amygdala↗

PubMed2006

Diazepam binding inhibitor overexpression in mice causes hydrocephalus, decreases plasticity in excitatory synapses and impairs hippocampus-dependent learning.

Diazepam binding inhibitor (DBI) and its processing products are endogenous modulators of GABAA and linked to various brain disorders ranging from anxiety and drug dependence to epilepsy. To investigate the physiological role of endogenously expressed DBI in the brain we created a transgenic mouse line overexpressing DBI gene. Transgenic mice had a 37x increased protein expression and immunohistochemistry showed excessive glial expression in the infragranular region of the dentate gyrus. Transgenic animals had significantly larger lateral ventricles and decreased plasticity of excitatory synapses without affecting either inhibitory or excitatory synaptic transmission. In behavioral tests transgenic animals had no differences in motor and exploratory activity, yet impaired hippocampus-dependent learning and memory. Overexpression did not cause anxiety or proconflict behavior, nor influenced kainic acid or pentylenetetrazole induced seizure activity. Our transgenic mouse line demonstrates that endogenously overexpressed DBI impairs hippocampus-dependent learning without anxiety or proconflict behavior.

Animals↗

PubMed2006

Increased expression and activity of urokinase-type plasminogen activator during epileptogenesis.

Our recent large-scale molecular profiling study revealed a sevenfold upregulation in the expression of urokinase-type plasminogen activator (uPA) during epileptogenesis. uPA is a member of the plasminogen activation system, which is a major contributor to the reorganization of neuronal circuits after trauma. Here, we investigated the expression and activity of uPA in normal and epileptogenic rat hippocampus to test a hypothesis that the expression of uPA is altered in brain areas that undergo epilepsy-related circuitry reorganization. Epileptogenesis was triggered by inducing status epilepticus (SE) with electrical stimulation of the amygdala in rats. Continuous video-electroencephalogram recordings were used to monitor the development of SE and the occurrence of spontaneous seizures. Animals were killed at 1, 4 or 14 days after SE, and brains were processed for immunohistochemistry or protein extraction. Confocal microscopy analysis of double-immunolabelled preparations indicated that SE triggered an increased expression of uPA in hippocampal astrocytes, neurons, white matter and blood vessels. Zymography revealed that the expression of uPA protein is associated with increased levels of enzymatically active uPA during epileptogenesis. uPA expression and enzymatic activity peaked within 1-4 days after SE, that is, before the occurrence of spontaneous seizures, and remained elevated for at least 2 weeks. These data suggest that uPA is involved in the reorganization of neuronal tissue during the epileptogenic process.

Amygdala↗

PubMed2006

A long-term video-EEG and behavioral follow-up after endothelin-1 induced middle cerebral artery occlusion in rats.

The aim was to test the hypothesis that occlusion of the middle cerebral artery (MCA) results in the development of epilepsy in rats. Further, we investigated whether lesion volume, hippocampal pathology, early seizures, or severity of behavioral impairment is associated with the development and severity of epilepsy or interictal spiking. MCA occlusion was induced by intracerebral injection of endothelin-1 (ET; 120 pmol). One group of ET-injected rats were followed-up for 6 months (n = 15) and another for 12 months (n = 20). Sham-operated animals were injected with saline (n = 12). Occurrence of early and late seizures was monitored by intermittent video-electroencephalography. Sensorimotor function was tested with the running wheel and tapered beam-walking tests. Emotional learning and memory were assessed with the fear conditioning test and spatial learning and memory with the Morris water maze. Finally, brains were processed for histology. Only one rat developed late spontaneous seizures (i.e., epilepsy). Epileptiform interictal spiking was detected in 9 of 26 animals. Early seizures did not predict the development of epilepsy, spiking activity, or severity of behavioral impairment. Production of MCA stroke by intracerebral injection of ET was not a strong trigger of epileptogenesis in adult rats. Further studies are needed to investigate the effect of age, genetic background, and location of ET-injection on the development of hyperexcitability and the risk of post-stroke epileptogenesis.

Animals↗

PubMed2006

Epileptogenesis-related genes revisited.

The main goal of this study was to identify common features in the molecular response to epileptogenic stimuli across different animal models of epileptogenesis. Therefore, we compared the currently available literature on the global analysis of gene expression following epileptogenic insult to search for (i) highly represented functional gene classes (GO terms) within data sets, and (ii) individual genes that appear in several data sets, and therefore, might be of particular importance for the development of epilepsy due to different etiologies. We focused on two well-described models of brain insult that induce the development of spontaneous seizures in experimental animals: status epilepticus and traumatic brain injury. Additionally, a few papers describing gene expression in rat and human epileptic tissue were included for comparison. Our analysis revealed that epileptogenic insults induce significant changes in gene expression within a subset of pre-defined GO terms, that is, in groups of functionally linked genes. We also found individual genes for which expression changed across different models of epileptogenesis. Alterations in gene expression appear time-specific and underlie a number of processes that are linked with epileptogenesis, such as cell death and survival, neuronal plasticity, or immune response. Particularly, our analysis highlighted alterations in gene expression in glial cells as well as in genes involved in the immune response, which suggests the importance of gliosis and immune reaction in epileptogenesis.

Animals↗

PubMed2006

Animal models of post-traumatic epilepsy.

Epilepsy is a major unfavorable long-term consequence of traumatic brain injury (TBI). Moreover, TBI is one of the most important predisposing factors for the development of epilepsy, particularly in young adults. Understanding the molecular and cellular cascades that lead to the development of post-traumatic epilepsy (PTE) is key for preventing its development or modifying the disease process in such a way that epilepsy, if it develops, is milder and easier-to-treat. Tissue from TBI patients undergoing epileptogenesis is not available for such studies, which underscores the importance of developing clinically relevant animal models of PTE. The goal of this review is to (1) provide a description of PTE in humans, which is critical for the development of clinically relevant models of PTE, (2) review the characteristics of currently available PTE models, and (3) provide suggestions for the development of future models of PTE based on our current understanding of the mechanisms of TBI and epilepsy. The development of clinically relevant models of PTE is critical to advance our understanding of the mechanisms of post-traumatic epileptogenesis and epilepsy, as well as for producing breakthroughs in the development and testing of novel antiepileptogenic treatments.

Animals↗

PubMed2006

Status epilepticus in 12-day-old rats leads to temporal lobe neurodegeneration and volume reduction: a histologic and MRI study.

PURPOSE: Whether status epilepticus (SE) in early infancy, rather than the underlying illness, leads to temporal lobe neurodegeneration and volume reduction remains controversial. METHODS: SE was induced with LiCl-pilocarpine in P12 rats. To assess acute neuronal damage, brains (five controls, five with SE) were investigated at 8 h after SE by using silver and Fluoro-Jade B staining. Some brains from the early phase were processed for electron microscopy. To assess chronic changes, brains from nine controls and 13 rats with SE at P12 were analyzed after 3 months by using histology and magnetic resonance imaging (MRI). RESULTS: MRI analysis of the temporal lobe of adult animals with SE at P12 indicated that 23% of the rats had hippocampal, 15% had amygdaloid, and 31% had perirhinal volume reduction. Histologic analysis of sections from the MR-imaged brains correlated with the MRI data. Analysis of neurodegeneration 8 h after SE by using both silver and Fluoro-Jade B staining revealed degenerating neurons located in the same temporal lobe regions as the volume reduction in chronic samples. Electron microscopic analysis revealed irreversible ultrastructural alterations. As with the chronic histologic and MRI findings, interanimal variability was seen in the distribution and severity of acute damage. CONCLUSIONS: Our data indicate that SE at P12 can cause acute neurodegeneration in the hippocampus as well as in the adjacent temporal lobe. It is likely that acute neuronal death contributes to volume reduction in temporal lobe regions that is detected with MRI in a subpopulation of animals in adulthood.

Amygdala↗

PubMed2006

Fear conditioning is impaired in systemic kainic acid and amygdala-stimulation models of epilepsy.

PURPOSE: The lateral nucleus of the amygdala is critical for fear conditioning, a paradigm of emotional learning, which requires recognition of an unconditioned stimulus as aversive and association of conditioned stimuli with an unconditioned stimulus. Some patients with temporal lobe epilepsy have amygdaloid damage associated with impaired emotional learning. Fear conditioning also is impaired at least in some animal models of epilepsy. We studied whether contextual or tone-cued fear conditioning is impaired in two status epilepticus models of epilepsy and whether impairment correlates with the extent of damage in the lateral nucleus of the amygdala. METHODS: We induced epilepsy in rats by either systemic kainic acid administration or electrical amygdala stimulation. Behavioral reactions in all phases of fear conditioning were analyzed from videotapes. Damage to the lateral nucleus of the amygdala was analyzed from thionin-stained sections both histologically and by volumetry. RESULTS: Immediate reflexive responses to unconditioned and conditioned stimuli were preserved, whereas the freezing response to an unconditioned stimulus was reduced. Contextual conditioning was severely impaired, whereas tone-cued conditioning was better preserved. The lateral nucleus pathology did not correlate with impaired fear conditioning. CONCLUSIONS: These data suggest that processing of complex contextual stimuli is severely affected in experimental epilepsy, whereas conditioning to simple cues is better preserved.

Acoustic Stimulation↗

PubMed2005

Cystatin C expression is increased in the hippocampus following photothrombotic stroke in rat.

Stroke is a major cause of epilepsy, but the molecular mechanisms underlying post-stroke epileptogenesis are unknown. The expression of cystatin C, a cysteine protease inhibitor, is increased in the hippocampus during status epilepticus (SE)-induced epileptogenesis, and regulates both cell death and birth. To test the hypothesis that increased cystatin C expression represents a common molecular alteration induced by epileptogenic brain insults, we investigated the time course, cellular localization, and association of cystatin C expression with neuronal damage during post-stroke epileptogenesis. Stroke was induced with photothrombosis, which leads to epilepsy in approximately 20-30% of rats. Cystatin C expression was increased in the CA1 area of the hippocampus 4 days after photothrombosis, when the diameter of the lesion was the largest. Double-labeling and confocal analysis indicated that cystatin C was expressed in astrocytes and microglia. Unlike after SE, cystatin C expression did not change in the dentate gyrus. Also, increased cystatin C expression was not associated with neurodegeneration, which was demonstrated as an absence of Fluoro Jade B-positive cells in adjacent sections. The present study provides evidence that cystatin C may be involved in cellular alterations that occur after an epileptogenic insult, not only after SE but also after photothrombotic stroke.

Animals↗

PubMed2005

Manganese-enhanced magnetic resonance imaging of mossy fiber plasticity in vivo.

Mn(2+)-enhanced magnetic resonance imaging (MEMRI) was used to characterize activity-dependent plasticity in the mossy fiber pathway after intraperitoneal kainic acid (KA) injection. Enhancement of the MEMRI signal in the dentate gyrus and the CA3 subregion of the hippocampus was evident 3 to 5 days after injection of MnCl(2) into the entorhinal cortex both in control and KA-injected rats. In volume-rendered three-dimensional reconstructions, Mn(2+)-induced signal enhancement revealed the extent of the mossy fiber pathway throughout the septotemporal axis of the dentate gyrus. An increase in the number of Mn(2+)-enhanced pixels in the dentate gyrus and CA3 subfield of rats with KA injection correlated (P < 0.05) with histologically verified mossy fiber sprouting. These data demonstrate that MEMRI can be used to detect specific changes at the cellular level during activity-dependent plasticity in vivo. The present findings also suggest that MEMRI signal changes can serve as an imaging marker of epileptogenesis.

Animals↗

PubMed2005

Cystatin C expression is associated with granule cell dispersion in epilepsy.

Human temporal lobe epilepsy (TLE) is associated with cellular alterations (eg, hilar cell death, neurogenesis, and granule cell dispersion) in the dentate gyrus but their underlying molecular mechanism are not known. We previously demonstrated increased expression of cystatin C, a protease inhibitor linked to both neurodegeneration and neurogenesis, during epileptogenesis in the rat hippocampus. Here, we investigated cystatin C expression in the dentate gyrus in chronic epilepsy and its association with neuronal loss and neurogenesis. In both rats with epilepsy and human patients with TLE, cystatin C expression was increased in glial cells in the molecular layer of the dentate gyrus, being most prominent in cases with granule cell dispersion. In patients with TLE, high cystatin C expression associated with greater numbers of polysialylated neural cell adhesion molecule-positive newborn cells in the molecular layer, although the overall number was decreased, indicating that the newborn cells migrate to abnormal locations in the epileptic dentate gyrus. These data thus demonstrate that cystatin C expression is altered during the chronic phase of epilepsy and suggest that cystatin C plays a role in network reorganization in the epileptic dentate gyrus, especially in granule cell dispersion and guidance of migrating newborn granule cells.

Adolescent↗

PubMed2005

Epileptogenesis after experimental focal cerebral ischemia.

Cerebrovascular diseases are one of the most common causes of epilepsy in adults, and the incidence of stroke-induced epileptogenesis is increasing as the population ages. The mechanisms that lead to stroke-induced epileptogenesis in a subpopulation of patients, however, are still poorly understood. Recent advances in inducing epileptogenesis in rodent focal ischemia models have provided tools that can be used to identify the risk factors and neurobiologic changes leading to development of epilepsy after stroke. Here we summarize data from models in which epileptogenesis has been studied after focal ischemia; photothrombosis, middle cerebral artery (MCA) occlusion with filament, and endothelin-1-induced MCA occlusion. Analysis of the data indicates that neurobiologic changes occurring during stroke-induced epileptogenesis share some similarities to those induced by status epilepticus or traumatic brain injury.

Animals↗

PubMed2005

Epileptic seizure detection: a nonlinear viewpoint.

This study concerns the detection of epileptic seizures from electroencephalogram (EEG) data using computational methods. Using short sliding time windows, a set of features is computed from the data. The feature set includes time domain, frequency domain and nonlinear features. Discriminant analysis is used to determine the best seizure-detecting features among them. The findings suggest that the best results can be achieved by using a combination of features from the linear and nonlinear realms alike.

Algorithms↗

PubMed2005

Cystatin C modulates neurodegeneration and neurogenesis following status epilepticus in mouse.

Brain damaging insults cause alterations in neuronal networks that trigger epileptogenesis, and eventually lead to the appearance of spontaneous seizures. The present experiments were designed to study the cellular expression and functions of a cysteine proteinase inhibitor, cystatin C, whose gene expression is previously shown to be upregulated in the rat hippocampus during status epilepticus (SE)-induced epileptogenesis. The present data showed that the expression of cystatin C protein increased in the mouse hippocampus 7 days following SE and localized mainly to astrocytes and microglia. Acute neuronal death in the hippocampus at 24 h after SE was reduced in cystatin C-/- mice. Also, the basal level of neurogenesis in the subgranular layer of dentate gyrus was decreased in cystatin C-/- mice compared to wildtype littermates. Interestingly, migration of newly born neurons within the granule cell layer was attenuated in cystatin C-/- mice. These data demonstrate that cystatin C has a role in neuronal death and neurogenesis during SE-induced network reorganization.

Animals↗

PubMed2005

MR volumetric analysis of the piriform cortex and cortical amygdala in drug-refractory temporal lobe epilepsy.

BACKGROUND AND PURPOSE: The assessment of patients with temporal lobe epilepsy (TLE) traditionally focuses on the hippocampal formation. These patients, however, may present structural abnormalities in other brain areas. Our purpose was to develop a method to measure the combined volume of the human piriform cortex and cortical amygdala (PCA) by using MR imaging and to investigate PCA atrophy. METHODS: The definition of anatomic landmarks on MR images was based on histologic analysis of 23 autopsy control subjects. Thirty-nine adults with chronic TLE and 23 age-matched control subjects were studied. All underwent high-spatial-resolution MR imaging at 1.5T, including a tilted T1-weighted 3D dataset. The PCA volumes were compared with the control values and further correlated with hippocampal, amygdala, and entorhinal cortex volumes. RESULTS: The normal volume was 530 +/- 59 mm(3) (422-644) [mean +/- 1 SD (range)] on the right and 512 +/- 60 mm(3) (406-610) on the left PCA (no asymmetry, and no age or sex effect). The intraobserver and interobserver variability were 6% and 8%, respectively. In right TLE patients, the mean right PCA volume was 18% smaller than in control subjects (P < .001) and 15% smaller than in left TLE (P < .001). In left TLE, the mean left PCA volume was 16% smaller than in control subjects (P < .001) and 19% smaller than in right TLE (P < .001). Overall, 46% (18/39) of the patients had a greater than 20% volume reduction in the ipsilateral PCA. There was bilateral atrophy in 18% (7/39). Patients with hippocampal volumes of at least 2 SDs below the control mean had an 18% reduction in the mean PCA volume compared with patients without hippocampal atrophy (P < .001). Ipsilaterally, hippocampal (r = 0.756, P < .01), amygdaloid (r = 0.548, P < .01), and entorhinal (r = 0.500, P < .01) volumes correlated with the PCA volumes. CONCLUSION: The quantification of PCA volume with MR imaging showed that the PCA is extensively damaged in chronic TLE patients, particularly in those with hippocampal atrophy.

Adolescent↗

PubMed2004

Administration of diazepam during status epilepticus reduces development and severity of epilepsy in rat.

Prevention of epileptogenesis after brain insults, such as status epilepticus (SE), head trauma, or stroke, remains a challenge. Even if epilepsy cannot be prevented, it would be beneficial if the pathologic process could be modified to result in a less severe disease. We examined whether early discontinuation of SE reduces the risk of epilepsy or results in milder disease. Epileptogenesis was triggered with SE induced by electrical stimulation of the amygdala. Animals (n = 72) were treated with vehicle or diazepam (DZP, 20 mg/kg) 2 h or 3 h after the beginning of SE. Electrode-implanted non-stimulated rats served as controls for histology. All animals underwent continuous long-term video-electroencephalography monitoring 7-9 weeks and 11-15 weeks later to detect the occurrence and severity of spontaneous seizures. As another outcome measure, the severity of hippocampal damage was assessed in histologic sections. In the vehicle group, 94% of animals developed epilepsy. DZP treatment reduced the percentage of epileptic animals to 42% in the 2-h DZP group and to 71% in the 3-h DZP group (p < 0.001 and p < 0.05 compared to the vehicle group, respectively). If epilepsy developed, the seizures were less frequent in DZP-treated animals compared to the vehicle group (median 16.4 seizures/day), particularly in the 2-h DZP group (median 0.4 seizures/day). Finally, if DZP treatment was started 2 h, but not 3 h after SE, the severity of hippocampal cell loss was milder and the density of mossy-fiber sprouting was lower than in the vehicle group. These data indicate that treatment of SE with DZP within 2 h reduces the risk of epilepsy later in life, and if epilepsy develops, it is milder.

Action Potentials↗

PubMed2004

Projections from the amygdaloid complex to the piriform cortex: A PHA-L study in the rat.

Projections from the amygdala to the piriform cortex are proposed to provide a pathway via which the emotional system can modulate the processing of olfactory information as well as mediate the spread of seizure activity in epilepsy. To understand the details of the distribution and topography of these projections, we injected the anterograde tracer Phaseolus vulgaris-leucoagglutinin into different nuclear divisions of the amygdaloid complex in 101 rats and analyzed the distribution and density of projections in immunohistochemically processed preparations. The heaviest projections from the amygdala to the piriform cortex originated in the medial division of the lateral nucleus, the periamygdaloid and sulcal subfields of the periamygdaloid cortex, and the posterior cortical nucleus. The heaviest terminal labeling was observed in layers Ib and III of the medial aspect of the posterior piriform cortex. Lighter projections to the posterior piriform cortex originated in the dorsolateral division of the lateral nucleus, the magnocellular and parvicellular divisions of the basal and accessory basal nuclei, and the anterior cortical nucleus. The projections to the anterior piriform cortex were light and originated in the dorsolateral and medial divisions of the lateral nucleus, the magnocellular division of the basal and accessory basal nuclei, the anterior and posterior cortical nuclei, and the periamygdaloid subfield of the periamygdaloid cortex. The results indicate that only selective amygdaloid nuclei or their subdivisions project to the piriform cortex. In addition, substantial projections from several amygdaloid nuclei converge in the medial aspect of the posterior piriform cortex. Via these projections, the amygdaloid complex can modulate the processing of olfactory information in the piriform cortex. In pathologic conditions such as epilepsy, these connections might provide pathways for the spread of seizure activity from the amygdala to extra-amygdaloid regions.

Amygdala↗