The alteration of gamma-aminobutyric acid-transaminase expression in the gerbil hippocampus induced by seizure

New Animal Models for Understanding FMRP Functions and FXS Pathology

Fragile X encompasses a range of genetic conditions, all of which result as a function of changes within the FMR1 gene and abnormal production and/or expression of the FMR1 gene products. Individuals with Fragile X syndrome (FXS), the most common heritable form of intellectual disability, have a full-mutation sequence (>200 CGG repeats) which brings about transcriptional silencing of FMR1 and loss of FMR protein (FMRP). Despite considerable progress in our understanding of FXS, safe, effective, and reliable treatments that either prevent or reduce the severity of the FXS phenotype have not been approved. While current FXS animal models contribute their own unique understanding to the molecular, cellular, physiological, and behavioral deficits associated with FXS, no single animal model is able to fully recreate the FXS phenotype. This review will describe the status and rationale in the development, validation, and utility of three emerging animal model systems for FXS, namely the nonhuman primate (NHP), Mongolian gerbil, and chicken. These developing animal models will provide a sophisticated resource in which the deficits in complex functions of perception, action, and cognition in the human disorder are accurately reflected and aid in the successful translation of novel therapeutics and interventions to the clinic setting.

De novo sequencing and initial annotation of the Mongolian gerbil (Meriones unguiculatus) genome

The Mongolian gerbil (Meriones unguiculatus) is a member of the rodent family that displays several features not found in mice or rats, including sensory specializations and social patterns more similar to those in humans. These features have made gerbils a valuable animal for research studies of auditory and visual processing, brain development, learning and memory, and neurological disorders. Here, we report the whole gerbil annotated genome sequence, and identify important similarities and differences to the human and mouse genomes. We further analyze the chromosomal structure of eight genes with high relevance for controlling neural signaling and demonstrate a high degree of homology between these genes in mouse and gerbil. This homology increases the likelihood that individual genes can be rapidly identified in gerbil and used for genetic manipulations. The availability of the gerbil genome provides a foundation for advancing our knowledge towards understanding evolution, behavior and neural function in mammals. ACCESSION NUMBER: The Whole Genome Shotgun sequence data from this project has been deposited at DDBJ/ENA/GenBank under the accession NHTI00000000. The version described in this paper is version NHTI01000000. The fragment reads, and mate pair reads have been deposited in the Sequence Read Archive under BioSample accession SAMN06897401.

Gerbils

The gerbil is usually nonaggressive and is one of the easiest rodents to maintain and handle. Its disposition, curious nature, relative freedom from naturally occurring infectious diseases, and adaptability to its environment have contributed to its popularity as a laboratory animal. Gerbils are found in deserts and semiarid geographical regions of the world. The Mongolian gerbils that are available today originated from 20 pairs of captured animals that were maintained in 1935 in a closed, random-bred colony at the Kitasato Institute in Japan. Gerbils have several unique anatomical and physiological features. Mature gerbils are smaller than rats, but larger than mice. Mongolian gerbils are attracted to saliva and use salivary cues to discriminate between siblings and nonsiblings, and females use oral cues in the selection of sociosexual partners. Gerbils have been used as experimental models in a number of areas of biomedical research. Gerbils are excellent subjects for laboratory animal research as they are susceptible to bacterial, viral, and parasitic pathogens that affect humans and other species. Gerbils may have spontaneous seizures secondary to stress such as handling, cage change, abrupt noises, or changes in the environment. Cystic ovaries are seen commonly in female gerbils over 1 year of age. Gerbils have unique characteristics, which make them appropriate for a number of animal models. Classically, gerbils have been used in research involving stroke, parasitology, infectious diseases, epilepsy, brain development and behavior, and hearing.

Voltage-gated Na+ channel II immunoreactivity is selectively up-regulated in hippocampal interneurons of seizure sensitive gerbils

In the present study, we investigated the distribution of voltage-gated Na(+) channels (VGSCs) in the normal and epileptic hippocampus of gerbils (a genetic epilepsy model) in order to confirm the relationship between VGSC and seizure activity in these animals. There was no difference of VGSC I immunoreactivity in the hippocampus between seizure-resistant (SR) and seizure sensitive (SS) gerbils. VGSC II immunoreactivity was rarely detected in the perikarya of principal neurons and interneurons in the SR gerbil hippocampus. However, in the SS gerbil hippocampus, VGSC II immunoreactivity was densely observed in the somata of interneurons located in the stratum radiatum and stratum lacunosum-moleculare. Double immunofluorescent study showed immunoreactivity for calretinin (approximately 80% in VGSC II-positive neurons) or calbindin D-28k (approximately 20% in VGSC II-positive neurons) in VGSC II-immunoreactive neurons. VGSC II-immunoreactive neurons did not show parvalbumin immunoreactivity. These findings suggest that seizure activity in SS gerbils may be related to the selective hyperactivation of interneurons in stratum lacunosum-moleculare via the up-regulation of VGSC II expression, which leads to the disinhibition of CA1 pyramidal cells.

Up-regulated astroglial TWIK-related acid-sensitive K+ channel-1 (TASK-1) in the hippocampus of seizure-sensitive gerbils: a target of anti-epileptic drugs

In order to identify the modulation of TASK (TWIK-related Acid-Sensitive K(+)) channel expressions in epilepsy, we conducted a comparative analysis of TASK channel immunoreactivities in the hippocampus of seizure-resistant (SR) and seizure-sensitive (SS) gerbils. There was no difference of the TASK-1 and TASK-2 channel expressions in the hippocampi of young SR and SS gerbils (1-2 months old). In adult SS gerbil hippocampus, TASK-1 immunoreactivity in astrocytes was higher than that in adult SR gerbil hippocampus. After seizures, TASK-1 immunoreactivity was significantly down-regulated in astrocytes of the SS gerbil hippocampus. In addition, various anti-epileptic drugs selectively affect TASK-1 immunoreactivity in astrocytes of the SS gerbil hippocampus. Gabapentin, lamotrigine, topiramate and valproic acid reduced the number of TASK-1(+) astrocytes in the hippocampus to 10-25% of that in saline-treated SS adult gerbils, whereas carbamazepine and vigabatrin decreased to approximately 50%. Therefore, the present study demonstrates that up-regulated TASK-1 immunoreactivity in astrocytes may be involved in the seizure activity of SS adult gerbils and suggests that the astroglial TASK-1 channel may be a target for epilepsy therapeutics.

Seizure activity selectively reduces 5-HT1A receptor immunoreactivity in CA1 interneurons in the hippocampus of seizure-prone gerbils

Since the correlation between the serotonin (5-hydroxytryptamine, 5-HT) system and seizure activity remains to be clarified, we investigated the 5-HT system in the hippocampus of seizure-resistant (SR) and seizure-sensitive (SS) gerbils. There was no difference of the 5-HT system in the hippocampi of young animals (predisposed and juvenile gerbils) in both SR and SS gerbils. 5-HT immunoreactivity in the dorsal raphe nucleus and the median raphe nucleus was also similarly detected in both animal groups. As compared to SR adult gerbils, only 5-HT1A receptor immunoreactivity was selectively reduced in CA1 interneurons within SS adult gerbils. (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (a 5-HT1A receptor agonist, 1 and 2 mg/kg) markedly reduced paired-pulse inhibition in the CA1 region of SS adult gerbils only. These findings suggest that the selective reduction in 5-HT1A receptor expression on CA1 interneurons of SS adult gerbil may not be developmental defects, but be an acquired compensatory change induced by repeated seizure activity.

Up-regulation of P/Q-type voltage-gated Ca2+ channel immunoreactivity within parvalbumin positive neurons in the rat hippocampus following status epilepticus

To identify the roles of VGCC subtypes in damages/impairs of inhibitory transmission during epileptogenesis, we investigated temporal- and spatial-specific alterations in voltage-gated Ca(2+) channel (VGCC) immunoreactivities within parvalbumin (PV, a Ca(2+) binding protein) positive neurons in the rat hippocampus following status epilepticus (SE). Compared to controls, only P/Q-type (alpha1A) VGCC immunoreactivity was enhanced in PV positive neurons at the early point following SE. The alteration in P/Q-type (alpha1A) VGCC immunoreactivity showed an inverse proportionality to that in PV immunoreactivity in the dentate gyrus and the CA1 region. These findings suggest that SE may induce prolonged up-regulation in P/Q-type VGCC expression within PV positive neurons.

The selective effects of somatostatin- and GABA-mediated transmissions on voltage gated Ca2+ channel immunoreactivity in the gerbil hippocampus

To identify whether altered expressions of voltage gated Ca(2+) channel (VGCC) are linked to inhibitory transmission abnormalities in the gerbil hippocampus, we investigated the effects of GABA receptor or somatostatin receptor (SST) antagonists/agonists on VGCC immunoreactivity in vivo. VGCC immunoreactivities in the hippocampus were significantly higher in seizure sensitive (SS) gerbils than in seizure resistant (SR) gerbils. P/Q-type VGCC immunoreactivity in the gerbil hippocampus was reduced by enhancement in GABA(A) and GABA(B) receptor-mediated transmission, but not by SST-mediated transmission. N-type VGCC immunoreactivity was reduced only by a SST agonist, whereas L-type (alpha1C) VGCC immunoreactivity was reduced only by a GABA(A) receptor agonist, and L-type (alpha1D) VGCC immunoreactivity was modulated by the GABA(B) receptor acting drugs. These findings provide a comprehensive description of the differential responses of VGCC subunits to alteration in GABAergic or somatostatinergic transmission. These findings also suggest that up-regulated VGCC immunoreactivity may be consequence of the neuronal excitability caused by a reduction in inhibitory neurotransmission in the gerbil hippocampus.

Altered expression of K+ -Cl- cotransporters affects fast paired-pulse inhibition during GABA receptor activation in the gerbil hippocampus

K+ -Cl- cotransporter (KCC) plays an important role in maintaining neuronal activity. However, the effect of seizure activity or pharmacological manipulation of GABAergic transmission on KCC expression remains to be clarified. Therefore, the present study was performed to investigate whether seizure activity or GABA receptor agonist treatment changes KCC expression in the gerbil hippocampus. Furthermore, the effect of blockade of KCC on inhibitory transmission in the dentate gyrus was identified following applications of GABA receptor agonists. The distribution of KCC immunoreactivity in the hippocampus was similarly detected between seizure-resistant (SR) and seizure-sensitive (SS) gerbils. Baclofen (a GABAB receptor agonist) treatment markedly increased KCC expression in the gerbil hippocampus. Baclofen treatment significantly reduced paired-pulse inhibition in the dentate gyrus. Furosemide (a KCC inhibitor) treatment amplified the effect of baclofen on paired-pulse responses. In contrast, muscimol (a GABAA receptor agonist) treatment reduced KCC expression. Enhanced paired-pulse inhibition by muscimol treatment was not affected by furosemide treatment. These findings suggest that seizure activity in the gerbil may not affect KCC expression in the hippocampus. In addition, altered KCC immunoreactivity induced by baclofen or muscimol may play an important role in maintaining or regulating inhibitory transmission during GABA receptor activation.

The effect of topiramate on GABAB receptor, vesicular GABA transporter and paired-pulse inhibition in the gerbil hippocampus

To extend our understanding of the properties of topiramate (TPM), we investigated the effect of TPM on GABAergic transmission in the dentate gyrus of gerbil. TPM treatment (> or = 40 mg/kg) dramatically decreased GABA(B)R2, not GABA(B)R1, immunoreactivity in hilar interneurons. In contrast, TPM treatment increased vesicular GABA transporter immunoreactivity and the paired-pulse inhibition in the dentate gyrus of seizure prone gerbils. Furthermore, TPM effectively prevented the reduction of paired-pulse inhibition induced by baclofen treatment. These findings suggest that TPM may enhance GABA release in the dentate gyrus of gerbils by down-regulation of GABA(B) autoreceptor expression. Therefore, these properties of TPM may be another possible antiepileptic effect, which plays an important role in preventing the spread of seizure activity without proconvulsive effects.

Age-dependent changes of pyridoxal phosphate synthesizing enzymes immunoreactivities and activities in the gerbil hippocampal CA1 region

In the present study, age-related changes of pyridoxal 5'-phosphate (PLP) synthesizing enzymes, pyridoxal kinase (PLK) and pyridoxine 5'-phosphate oxidase (PNPO), their protein contents and activities were examined in the gerbil hippocampus proper. Significant age-dependent changes in PLK and PNPO immunoreactivities were found in the CA1 region, but not in the CA2/3 region. In the postnatal month 1 (PM 1) group, PLK and PNPO immunoreactivities were detected mainly in the stratum pyramidale of the CA1 region. PLK and PNPO immunoreactivities and their protein contents were highest in the PM 6 group, showing that many CA1 pyramidal cells had strong PLK and PNPO immunoreactivities. Thereafter, PLK and PNPO immunoreactivities started to decrease and were very low at PM 24. Alterations in the change patterns in protein contents and total activities of PLK and PNPO corresponded to the immunohistochemical data, but their specific activities were not altered in any experimental group. Based on double immunofluorescence study, PLK and PNPO immunoreactive cells in the strata oriens and radiatum were identified as GABAergic cells. Therefore, decreases of PLK and PNPO in the hippocampal CA1 region of aged brains may be involved in aging processes related with gamma-aminobutyric acid (GABA) function.

Bilateral enhancement of excitation via up-regulation of vesicular glutamate transporter subtype 1, not subtype 2, immunoreactivity in the unilateral hypoxic epilepsy model

In the present study, the change of vesicular glutamate transporter (VGLUT) immunoreactivity on long-term impaired excitability in the hippocampus after recovery from unilateral hypoxic-ischemic insult was investigated in order to extend our understanding of the mechanism of epileptogenesis using unilateral hypoxic epilepsy models. Both the lesioned (submitted to ischemia) and the unlesioned hippocampi exhibited the frequent occurrence of interictal spikes and occasionally the sustained ictal discharges. However, paired-pulse inhibition was significantly reduced in the unlesioned dentate gyrus, not in the lesioned dentate gyrus. VGLUT1 immunoreactivity was significantly elevated in both hippocampi following hypoxic ischemia, although VGLUT2 immunodensity was unaltered. These findings suggest that the enhancement of VGLUT1 immunoreactivity in both hippocampi after unilateral hypoxic ischemia may contribute to the hyperexcitability, which may play an important role in the epileptogenesis (presumably accompanied by altered inhibitory transmission) after neurodegeneration.

Elevated substance P (NK-1) receptor immunoreactivity in the cerebellum of seizure prone gerbil

In the present study, we performed a comparative analysis of the distribution of substance P (SP) receptor (NK-1) immunoreactivity in order to determine the characteristics of the SP system in the cerebelli of rat and gerbils. In the rat cerebellar cortex, only a few Purkinje cells exhibited weak NK-1 receptor immunoreactivity. Similar to the case of rat, NK-1 receptor immunoreactivity in the cerebellar cortex of seizure resistant (SR) gerbils was rarely detected. In contrast, in the cerebellar cortex of seizure sensitive (SS) gerbils, dendrites and cell bodies of Purkinje cell showed strong NK-1 receptor immunoreactivity. Similar to the cerebellar cortex, little NK-1 receptor immunoreactivity in deep cerebellar nuclei was observed in the rat. In SR gerbils, however, deep cerebellar nuclei showed weak NK-1 receptor immunoreactivity. NK-1 receptor immunoreactivity in the deep cerebellar nuclei of SS gerbils was markedly increased, as compared with SR gerbils. Based on the present data, we suggest that the SP system of cerebellar circuit in gerbil are different from rat, and over-expression of NK-1 receptor immunoreactivity in Purkinje cells of SS gerbils may be relevant to Purkinje cell loss induced by seizure activity.

Elevated voltage-gated Ca2+ channel immunoreactivities in the hippocampus of seizure-prone gerbil

In present study, we investigated voltage-gated Ca2+ channel (VGCC) expressions in the hippocampus of the Mongolian gerbil and its association with different sequelae of spontaneous seizures, in an effort to identify the epileptogenesis in this animal. In the hippocampus of pre-seizure seizure sensitive (SS) gerbils, VGCC subunit expressions were significantly elevated, as compared with seizure-resistant (SR) gerbils. In 3 h postictal group, the alteration of VGCC expressions showed regional- and neuronal-specific manners; VGCC immunoreactivities in principal neurons were markedly decreased; however, their immunoreactivities in interneurons were significantly elevated. These results are the first comprehensive description of the distribution of VGCC immunoreactivities in the normal and epileptic hippocampus of gerbils, and suggest that these alterations in the hippocampus of the SS gerbil may be related with tissue excitability and have a role in modulating recurrent excitation following seizures.

Elevated voltage gated Cl− channel expression enhances fast paired-pulse inhibition in the dentate gyrus of seizure sensitive gerbil

The present study was performed to determine whether the voltage gated Cl- channel (CLC) expression is altered in the hippocampus of seizure sensitive (SS) gerbils, and to identify the strong fast paired-pulse inhibition in the dentate gyrus of SS gerbils is associated with altered CLC expression. In the hippocampal proper and the granule cell layer of the dentate gyrus of the SS gerbils, strong CLC-2 immunoreactivity was detected, as compared with seizure resistant (SR) gerbils. In addition, CLC-3 immunoreactivity was observed in the CA1-3 pyramidal cells, and the granule cell and the molecular layer of the dentate gyrus in the SS gerbils, whereas its immunoreactivity was rarely detected in the SR gerbils. However, CLC-3 immunoreactivity in the mossy fiber was reduced, as compared with SR gerbils. Moreover, infusion of the potential CLC inhibitor (4,4'-diisothiocyanostibene-2,2'-disulfanic acid, DIDS) reduced fast paired-pulse inhibition in the dentate gyrus of SS gerbils, although evoked responses in the dentate gyrus between SR and SS gerbils were similarly detected. These findings suggest that enhancement of CLC expression in the dentate gyrus of SS gerbils may be one of the compensatory responses for reduced GABA(A) receptor-mediated fast postsynaptic inhibitory potentials.

Effects of GABAergic transmissions on the immunoreactivities of calcium binding proteins in the gerbil hippocampus

Although reduced calcium binding protein (CBP) immunoreactivities in the epileptic hippocampus have been well established, it has been controversial that these changes may directly indicate neuronal degeneration. In the present study, therefore, we investigated CBP expressions in the gerbil hippocampus following treatment with gamma-aminobutyric acid (GABA) receptor antagonists in order to assess whether altered CBP expressions are the result of either abnormal excitation or indicative of neuronal damage/degeneration. Seizure-sensitive (SS) gerbils showed a loss/decline of CBP immunoreactivities in some hippocampal neurons as compared with seizure-resistant (SR) gerbils. In muscimol (GABA(A) receptor agonist) treated SS gerbils, expression levels of CBP were enhanced as compared with saline-treated SS gerbils. Bicuculline (a GABA(A) receptor antagonist) treatment markedly reduced CBP immunoreactivities in hippocampal neurons of the SR gerbil. Baclofen (a GABA(B) receptor agonist) treatment increased CBP immunoreactivities in the hippocampus of SS gerbils, although its effect was lower than that of muscimol treatment. Moreover, phaclofen (GABA(B) receptor antagonist) treated SR gerbil showed reduction in calbindin D-28K immunoreactivity, not parvalbumin immunoreactivity, in the hippocampus. These findings therefore suggest that reduced CBP immunoreactivities may be the consequence of abnormal discharge caused by loss of GABAergic inhibition rather than an indication of the neuronal damage/degeneration.

Altered GABAB receptor immunoreactivity in the gerbil hippocampus induced by baclofen and phaclofen, not seizure activity

The present study was performed to determine whether the effects induced by GABA(B) receptor-acting drugs would be related with the alteration in GABA(B) receptor expression in the hippocampus using Mongolian gerbil, a genetic epilepsy model. The distribution patterns of both GABA(B) receptor 1A/B and GABA(B)receptor 2 immunoreactivities were similarly detected in the hippocampi of normal and seizure-prone gerbils. Following baclofen (GABA(B) receptor agonist) or phaclofen (GABA(B) receptor antagonist) treatment, GABA(B) receptor immunoreactivities were decreased or increased by dose-dependent manners, respectively. Vigabatrin (GABA transaminase inhibitor) or 3-mercaptopropionic acid (GAD inhibitor) treatment did not affect GABA(B) receptor expressions. These findings suggest that GABA(B) receptor expression in the gerbil hippocampus may be altered by baclofen or phaclofen treatment.

Age-related changes of γ-aminobutyric acid transaminase immunoreactivity in the hippocampus and dentate gyrus of the Mongolian gerbil

We investigated the age-related changes of gamma-aminobutyric acid transaminase (GABA-T, a GABA degradation enzyme) in the hippocampus and dentate gyrus of the gerbil at postnatal month 1 (PM 1), PM 3, PM 6, PM 12, and PM 24. Age-related changes of GABA-T immunoreactivity were distinct in the hippocampal CA1 region and in the dentate gyrus. GABA-T immunoreactivity was weak at PM 1, but at PM 3, it had increased significantly, and then increased further. Between PM 6 and PM 12, strong GABA-T immunoreactivity was found in nonpyramidal cells (GABAergic) in the stratum pyramidale of the CA1 region, and at PM 6, strong GABA-T immunoreactivity was found in neurons of the dentate gyrus subgranular zone. At PM 24, CA1 pyramidal cells showed strong GABA-T immunoreactivity. Western blot analysis showed a pattern of GABA-T expression similar to that shown by immunohistochemistry at various ages. In conclusion, our results suggest that the age-related changes of GABA-T provide important information about the aged brain with GABA dysfunction.

GABAA, not GABAB, receptor shows subunit- and spatial-specific alterations in the hippocampus of seizure prone gerbils

In the present study, we investigated site-specific expressions of GABA(A) and GABA(B) receptor subunits in the seizure-sensitive (SS) and seizure-resistant (SR) gerbil hippocampus to elucidate the function of the gamma-aminobutyric acid (GABA) receptor in seizure activity in this animal. There were no differences of the immunoreactivities of GABA(B) receptor and some GABA(A) receptor subunits (alpha3, alpha4, pan beta and delta) in the hippocampus between SR and SS gerbils. The alpha1 subunit expression was mainly detected in interneurons of stratum radiatum and hilar region of dentate gyrus in the SR gerbil. However, in SS gerbil, interneurons were nearly devoid of alpha1 subunit immunoreactivity and mainly detected in the molecular layer of dentate gyrus. In SR gerbil, alpha2 subunit immunoreactivity was detected in Ammon's horn, particularly in the CA2 region. In SS gerbil, granule cell layer of the dentate gyrus in SS gerbil showed strong alpha2 subunit immunoreactivity. The distribution of alpha5 and gamma2 subunit immunoreactivity in the hippocampus was similarly detected in SR and SS gerbil. However, alpha5 immunodensity of SR gerbil was slightly lower than that of SS gerbil in CA1 region and was slightly strong than that of SS gerbil in subiculum. These differences in distribution of GABA(A) receptor, not GABA(B) receptor, in the SR and SS gerbil hippocampus may indicate that abnormal hyperactive neuronal discharges are occurred in SS gerbil, which presumably result in spontaneous and repetitive seizure activity in this animal.

GABA and its receptors in epilepsy

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the mammalian brain. It acts through 2 classes of receptors, GABAA receptors that are ligand-operated ion channels and the G-protein-coupled metabotropic GABAB receptors. Impairment of GABAergic transmission by genetic mutations or application of GABA receptor antagonists induces epileptic seizures, whereas drugs augmenting GABAergic transmission are used for antiepileptic therapy. In animal epilepsy models and in tissue from patients with temporal lobe epilepsy, loss in subsets of hippocampal GABA neurons is observed. On the other hand, electrophysiological and neurochemical studies indicate a compensatory increase in GABAergic transmission at certain synapses. Also, at the level of the GABAA receptor, neurodegeneration-induced loss in receptors is accompanied by markedly altered expression of receptor subunits in the dentate gyrus and other parts of the hippocampal formation, indicating altered physiology and pharmacology of GABAA receptors. Such mechanisms may be highly relevant for seizure induction, augmentation of endogenous protective mechanisms, and resistance to antiepileptic drug therapy. Other studies suggest a role of GABAB receptors in absence seizures. Presynaptic GABAB receptors suppress neurotransmitter release. Depending on whether this action is exerted in GABAergic or glutamatergic neurons, there may be anticonvulsant or proconvulsant actions.

P2X2 and P2X4 receptor expression is regulated by a GABA(A) receptor-mediated mechanism in the gerbil hippocampus

Fast responses to extracellular ATP are mediated by the activation of P2X receptors. Native and cloned P2X receptors are permeable to monovalent cations such as Na+ and K+ as well as divalent cations such as Ca2+. However, altered P2X receptor expression has not been definitively determined under pathological conditions, particularly in epilepsy. Here we show that, in the seizure-sensitive (SS) gerbil hippocampus, a recognized genetic epilepsy model, the expressions of both P2X2 and P2X4 receptors are markedly decreased as compared with that in the seizure-resistant (SR) gerbil. These alterations are closely related to changes in gamma-aminobutyric acid (GABA) concentrations induced by vigabatrin (VGB) or 3-mercaptopropionic acid (3-MPA) treatment. Furthermore, the regulation of both P2X receptor expression in the gerbil hippocampus was mediated by the GABA(A) receptor, not GABA(B). These results suggest that the GABA(A) receptor-mediated modulation of P2X receptor expression may play an important role in the regulation of neuronal excitability.

Altered corticotropin-releasing factor (CRF) receptor immunoreactivity in the gerbil hippocampal complex following spontaneous seizure

Considerable attention has been focused on the role of corticotropin-releasing factor (CRF) in neuropsychiatric disorders and neurodegenerative diseases including epilepsy. Therefore, in the present study, we investigated the temporal and spatial alteration of CRF receptor in the gerbil hippocampal complex in order to characterize the possible changes and associations with different sequelae of spontaneous seizure in these animals. Thirty minutes postictal, a decline in CRF receptor immunoreactivity was observed in the granule cells and hilar neurons. In the subiculum, CRF receptor immunoreactivity was also significantly decreased at this time point. Twenty-four hours after seizure onset, the immunoreactivity in these regions recovered to the pre-seizure level. Moreover, 30 min after seizure in the entorhinal cortex, the density of CRF receptor immunoreactivity began to decrease, particularly in the layers II and III, compared to pre-seizure group. Nevertheless, 24h after seizure onset, CRF receptor immunodensity had recovered to its seizure-sensitive (SS) level. These results suggest that altered CRF receptor expression in the hippocampal complex may affect tissue excitability and seizure activity in SS gerbils.

Gastrodin decreases immunoreactivities of gamma-aminobutyric acid shunt enzymes in the hippocampus of seizure-sensitive gerbils

Gastrodin is one of the natural compound isolated from Gastrodia elata and has known anticonvulsant effects, although the exact pharmacological principles of this natural compound and its effects on other aspects of gamma-aminobutyric acid (GABA) metabolism in vivo have not been explored. Therefore, in the present study, the effects of gastrodin on GABA metabolism in the gerbil hippocampus were examined, in an effort to identify the antiepileptic characteristics of this substance. Gastrodin reduced the seizure score in the treated group, although the immunoreactivities of GABA synthetic enzymes and GABA transporters were unaltered in gastrodin-treated animals. Interestingly, in the gastrodin-treated group, GABA transaminase (GABA-T) immunoreactivity in the hippocampus, particularly in neurons, was significantly decreased. In the gastrodin-treated group, both succinic semialdehyde dehydrogenase (SSADH) and succinic semialdehyde reductase (SSAR) immunoreactivities in the hippocampus was also decreased significantly, which stood in contrast to the nontreated group, in which strong SSADH and SSAR immunoreactivities were detected. From the neuroanatomical viewpoint, these findings suggest that gastrodin may cause the elevation of GABA concentration by inhibiting the GABA shunt.

The altered expression of GABA shunt enzymes in the gerbil hippocampus before and after seizure generation

In the present study, the distribution of succinic semialdehyde dehydrogenase (SSADH) and succinic semialdehyde reductase (SSAR) in the hippocampus of the Mongolian gerbil and its association with various sequelae of spontaneous seizure were investigated in order to identify the roles of GABA shunt in the epileptogenesis and the recovery mechanisms in these animals. Both SSADH and SSAR immunoreactivities in the GABAergic neurons were significantly higher in the pre-seizure groups of seizure sensitive (SS) gerbil as compared to those seen in the seizure resistant (SR) gerbils. The distributions of both SSADH and SSAR immunoreactivities in the hippocampus showed significant differences after the on-set of seizure. At 3 h postictal, when compared to the pre-seizure group of SS gerbils, a decline in the immunoreactivities in the perikarya was observed. At 12 h after seizure on-set, the densities of both SSADH and SSAR immunoreactivities were begun to recover to the pre-seizure level of SS gerbils. These results suggest that the GABAergic neurons in the hippocampal complex of the SS gerbil may be highly activated. In addition, the imbalance of GABA shunt expressions in the GABAergic neurons may imply a malfunction of the metabolism of GABAergic neurons in the SS gerbils, and this defect may trigger seizure on-set. Therefore, the initiation of seizure, at least in gerbils, may be the result of a malfunction in GABA shunt in the GABAergic neurons.

Changed vesicular GABA transporter immunoreactivity in the gerbil hippocampus following spontaneous seizure and vigabatrin administration

To identify the roles of vesicular gamma-aminobutyric acid (GABA) transporter (VGAT) in epileptogenesis and the recovery mechanisms in spontaneous seizure, we conducted a chronological and comparative analysis of VGAT expression. VGAT immunoreactivity was stronger in the seizure resistant group than that in the pre-seizure group of seizure sensitive (SS) gerbils. In 3 h postictal group, the density of VGAT immunoreactivity was significantly increased in the hippocampus, as compared to pre-seizure group. In 24 h postictal group, VGAT immunodensity had recovered to its pre-seizure level. In addition, VGAT immunoreactivity in the hippocampus was also increased by vigabatrin (GVG) administration. These results suggest that decreased VGAT expression in the SS gerbil hippocampus may affect epileptogenesis in this animal, and that the subsequent alteration in its expression induced by seizure and the administration of GVG may reflect a modulation of GABA release to alleviate seizure activity.

The differential expression of corticotropin releasing factor and its binding protein in the gerbil hippocampal complex following seizure

Considerable attention has been focused on the role of corticotropin releasing factor (CRF) as well as CRF-binding protein (CRF-BP) in neuropsychiatric disorders and neurodegenerative diseases including epilepsy. Therefore, in the present study, we investigated the temporal and spatial alteration of CRF and CRF-BP in the gerbil hippocampal complex in order to characterize the possible changes and associations with different sequelae of spontaneous seizure in these animals. CRF immunoreactivity was shown in the interneurons of the hippocampal complex at 30 min following seizure. Additionally, alteration of CRF-BP immunoreactivity was restricted to the entorhinal cortex after seizure. These results indicate some factors for consideration. First, in the gerbil hippocampal complex, the delayed increase of CRF immunoreactivity, in spite of its excitatory function, may attenuate seizure activity, but may not do so in epileptogenesis. Second, in contrast to the hippocampal complex, the increase in CRF-BP immunoreactivity in the entorhinal cortex following seizure may participate in feedback inhibitory modulation.

Alterations in Na+/H+ exchanger and Na+/HCO3- cotransporter immunoreactivities within the gerbil hippocampus following seizure

In this study, a chronological and comparative analysis of the immunoreactivities of Na(+)/H(+) exchanger 1 (NHE1), Na(+)/HCO(3)(-) cotransporter (NBC) and Na(+)/Ca(2+) exchanger (NCE) was conducted in order to identify the effects of spontaneous seizure on their protein expression levels using the gerbil model. The distribution of NHE1 and NBC immunoreactivity in the hippocampus of seizure-resistant (SR) gerbils was similar to that observed in the pre-seizure group of seizure-sensitive (SS) gerbils. From 30 min to 3 h after the onset of the seizure, both NHE1 and NBC immunoreactivities were elevated in the hippocampus, as compared to the pre-seizure group of SS gerbils. At 6 h postictal, these immunoreactivities in the hippocampus had reduced to the pre-seizure level. However, NCE immunoreactivity within the hippocampus was unaltered. These findings suggest that the changes in both NHE1 and NBC immunoreactivity within the hippocampus following seizure may affect tissue excitability and play a role in the reduction of the seizure activity in the gerbil.

Changes in pyridoxal kinase immunoreactivity in the gerbil hippocampus following spontaneous seizure

To identify the roles of pyridoxal kinase (PLK) in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of PLK expression in the gerbil hippocampus was conducted. PLK immunoreactivity in a pre-seizure group of seizure sensitive (SS) gerbils was more strongly detected than that in a seizure resistant (SR) group. The density of PLK immunoreactivity in a 30-min postictal group was significantly lower than that of a pre-seizure group. In a 12 h postictal group, PLK immunodensity recovered to pre-seizure level. The over-expression of PLK in the hippocampus of pre-seizure SS gerbils suggests that PLP play an important role in the modulation of GAD activity and GABA reuptake as mediated by membrane transporter via neurons.

Changes in Na(+)-K(+)-Cl(-) cotransporter immunoreactivity in the gerbil hippocampus following spontaneous seizure

The immunoreactivity of Na(+)-K(+)-Cl(-) cotransporter (NKCC) in the gerbil hippocampus associated with various sequelae of spontaneous seizures were investigated in order to identify the roles of NKCC in the epileptogenesis and the recovery mechanisms in these animals. The NKCC immunoreactivities in the CA2-3 regions, the subiculum and the entorhinal cortex, were significantly more intensified in the pre-seizure group of seizure sensitive (SS) gerbils than in the seizure resistant (SR) gerbils. Following the on-set of seizure, the immunoreactivity of NKCC was significantly changed. In the hippocampal complex except the CA1 region, NKCC immunoreactivity in GABAergic neurons was significantly decreased 30 min after seizure on-set, versus the pre-seizure group. On the other hand, NKCC immunoreactivity was dramatically elevated in the CA1 regions, and 3 h postictal NKCC immunoreactivity increased significantly in the dentate gyrus and the dendrites of the pyramidal cells in the CA2-3 regions. These findings suggest that altered NKCC expression may be associated with seizure activity, and have an important role in the postictal recovery by regulating GABA-mediated inhibitory circuit in the hippocampal complex of the gerbil.

Chronological changes in pyridoxine-5'-phosphate oxidase immunoreactivity in the seizure-sensitive gerbil hippocampus

To identify the roles of pyridoxine-5'-phosphate (PNP) oxidase in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of PNP oxidase expression was conducted. PNP oxidase immunoreactivity in a preseizure group of seizure-sensitive (SS) gerbils was detected more strongly than that in a seizure-resistant (SR) group. The density of PNP oxidase immunoreactivity in a 30 min postictal group was significantly lower than that in a preseizure group. In a 12 hr postictal group, PNP oxidase immunodensity had recovered to a preseizure level. The overexpression of PNP oxidase in the hippocampus of preseizure SS gerbils suggests that PNP or pyridoxal 5'-phosphate plays an important role in the modulation of glutamic acid decarboxylase activity and gamma-aminobutyric acid reuptake as mediated by membrane transporter via neurons. In addition, this change in the PNP oxidase immunoreactivity following seizure may be a compensatory response designed to reduce epileptic activity in this animal.

The decreases in calcium binding proteins and neurofilament immunoreactivities in the Purkinje cell of the seizure sensitive gerbils

In previous studies, it has been reported that Purkinje cell degeneration during seizure is evoked by excitotoxicity due to an increase in the intracellular Ca(2+) level, though calbindin D-28k (CB) and parvalbumin (PV), intracellular free calcium buffers, are abundantly colocalized in these cells. In the present study, we investigated the expressions of CB, PV, neurofilament (NF) 68, 150, 200, and polyphosphorylated epitope in NF (RT 97), in the cerebellum of gerbils to identify the mechanism of Purkinje cell damages induced by seizure. In seizure resistant gerbils, nearly all the Purkinje cells showed CB, PA, NF 150, NF 200 and RT 97 immunoreactivity. In SS gerbils, however, a clear decrease in the number of CB(+) and PV(+) Purkinje cells was observed. The NF and RT 97 immunoreactivities, in the Purkinje cells was also lower (except NF 68), but not absent. These results suggest several points. First, the decrease in the concentrations of CB and PV may render the Purkinje cells more susceptible to intermittent Ca(2+) fluctuations and more prone to accumulating intolerable quantities of Ca(2+). Second, during the Ca(2+)-PV interaction PV plays an important role in facilitating donations of Mg(2+), which is a potent enzyme activator in phosphorylation. Thus the decline in PV concentration also implicated the defects of phosphorylation in the NF. Third, increases in both the intracellular Ca(2+) level and dephosphorylation trigger the degradation of the NF, particularly NF 200. Finally, these degradations in the NF induce the functional defects in Purkinje cell, which then cause Purkinje cell degeneration.

The temporal alteration of GAD67/GAD65 ratio in the gerbil hippocampal complex following seizure

In the present study, the distribution of glutamic acid decarboxylase (GAD) isoforms in the hippocampus of the Mongolian gerbil and its association with different sequelae of spontaneous seizure were investigated to identify the roles of balance of GAD isoforms in the epileptogenesis and the recovery mechanisms in these animals. The GAD67/GAD65 ratio in the hippocampus of pre-seizure seizure sensitive (SS) gerbil was approximately 3.5-fold higher as compared to seizure resistant (SR) gerbil. Following seizure, this ratio shifted to the level of SR gerbils up to 12 h postical. Therefore, the mismatched GAD67/GAD65 ratio (imbalance of GAD isoform expressions) in the hippocampus of SS gerbil implies that GABAergic neurons may be highly activated in order to regulate the increased neuronal excitability. In addition, the alteration in this ratio after seizure may be the compensatory response for reduction of epileptic activity in this animal.

The changes in the expressions of gamma-aminobutyric acid transporters in the gerbil hippocampal complex following spontaneous seizure

To identify the roles of gamma-aminobutyric acid (GABA) transporter in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of GABA transporters (GAT) expression was conducted. GAT-1 immunoreactivity was more strongly detected in the pre-seizure group of seizure sensitive (SS) gerbils than that seen in the seizure resistant group. 30 min postictal, the density of GAT-1 immunoreactivity was significantly decreased in the hippocampal complex, as compared to pre-seizure group. 12 h after seizure on-set, the GAT immunodensity recovered to the pre-seizure level. Following the onset of seizure, GAT-3 immunoreactivity remained unchanged. These results suggest that the increase of GAT-1 expression in the SS gerbil hippocampus may affect epileptogenesis in this animal, and the alteration of immunoreactivity following seizure may be compensatory responses to modulate seizure activity.