Regional brain [3H]muscimol binding in kindled rat brain: a quantitative autoradiographic examination

doi:10.1016/0920-1211(90)90084-9

Epilepsy Research

Volume 6, Issue 2, July 1990, Pages 102-109

https://doi.org/10.1016/0920-1211(90)90084-9 Get rights and content

Abstract

Quantitative [³H]muscimol autoradiography was used to perform a comprehensive examination of the GABA_A receptor site in entorhinal cortex kindled and handled control rats. Ninety-eight brain areas were analyzed 24 h or 28 days after the last kindled seizure. A significant post-kindling change was observed in only one area, the fascia dentata of the hippocampus, which showed an increase of 55% at 24 h, but not at 28 days. This acute change appeared in both the dorsal and ventral divisions of the hippocampus and in both the infrapyramidal and suprapyramidal blades of the fascia dentata. These data closely parallel the pattern previously obtained with [³H]flunitrazepam in the same animals. The comprehensive nature of this examination further suggests that the fascia dentata is the only site in the brain which shows altered GABA_A binding after kindling. Although our data indicate that elevated [³H]muscimol binding is not a permanent feature of the kindled state, the possibility exists that the fascia dentata change observed at 24 h reflects a permanent alteration in the acute reactivity of hippocampal GABA_A receptors to electrical stimulation.

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Receptor binding in the kindling model of epilpsy

Cited by (29)

The piriform cortex in epilepsy: What we learn from the kindling model
2020, Experimental Neurology
Epilepsy is a circuit-level brain disorder characterized by excessive or hypersynchronous epileptic seizures involving a complex epileptogenic network. Cumulative evidence suggests that the piriform cortex (PC) is a crucial site in seizure initiation, propagation, and generalization in epilepsy. The kindling model is a classic animal model of complex partial seizures with secondarily generalized tonic seizures, which is usually used for the study of epilepsy pathogenesis and preclinical anti-epilepsy drug evaluation. Various essential functions of the PC in epilepsy were discovered in the kindling model, therefore, this review focuses on discussing the role of the PC in the kindling model. We review what pathological changes happen in the PC in the kindling model, how the PC is involved in the kindling model through different interventions, and finally we also provide perspectives on some possible research directions for future studies.
Pentylenetetrazole-induced seizures affect binding site densities for GABA, glutamate and adenosine receptors in the rat brain
2009, Neuroscience
Pentylenetetrazole (PTZ) is a convulsant used to model epileptic seizures in rats. In the PTZ-model, altered heat shock protein 27 (HSP-27) expression highlights seizure-affected astrocytes, which play an important role in glutamate and GABA metabolism. This raises the question whether impaired neurotransmitter metabolism leads to an imbalance in neurotransmitter receptor expression. Consequently, we investigated the effects of seizures on the densities of seven different neurotransmitter receptors in rats which were repeatedly treated with PTZ (40 mg/kg) over a period of 14 days. Quantitative in vitro receptor autoradiography was used to measure the regional binding site densities of the glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate and N-methyl-d-aspartate (NMDA) receptors, the adenosine receptor type 1 (A₁), which is part of the system controlling glutamate release, and the γ-aminobutyric acid (GABA) receptors GABA_A and GABA_B as well as the GABA_A-associated benzodiazepine (BZ) binding sites in each rat. Our results demonstrate altered receptor densities in brain regions of PTZ-treated animals, including the HSP-27 expressing foci (i.e. amygdala, piriform and entorhinal cortex, dentate gyrus). A general decrease of kainate receptor densities was observed together with an increase of NMDA binding sites in the hippocampus, the somatosensory, piriform and the entorhinal cortices. Furthermore, A₁ binding sites were decreased in the amygdala and hippocampal CA1 region (CA1), while BZ binding sites were increased in the dentate gyrus and CA1. Our data demonstrate the impact of PTZ induced seizures on the densities of kainate, NMDA, A₁ and BZ binding sites in epileptic brain. These changes are not restricted to regions showing glial impairment. Thus, an altered balance between different excitatory (NMDA) and modulatory receptors (A₁, BZ binding sites, kainate) shows a much wider regional distribution than that of glial HSP-27 expression, indicating that receptor changes are not following the glial stress responses, but may precede the HSP-27 expression.
Altered expression of GABA<inf>A</inf> and GABA<inf>B</inf> receptor subunit mRNAs in the hippocampus after kindling and electrically induced status epilepticus
2005, Neuroscience
Citation Excerpt :
Thus, overall limited expression of α-subunits could limit formation of additional functioning GABAA receptors in epilepsy. Binding studies, however, revealed increases in muscimol, benzodiazepine and t-butylclophosphorothionate binding in the dentate gyrus, labeling the GABA, the benzodiazepine and chloride channel sites of the GABAA receptor complex, respectively (Burnham et al., 1983; Shin et al., 1985; Nobrega et al., 1989, 1990; Titulaer et al., 1994, 1995b,c). Also functional studies indicate augmented GABA-ergic transmission in the dentate gyrus of kindled rats (Otis et al., 1994; Titulaer et al., 1995a; Buhl et al., 1996; Gibbs et al., 1997; Nusser et al., 1998).
Epilepsy may result from altered transmission of the principal inhibitory transmitter GABA in the brain. Using in situ hybridization in two animal models of epileptogenesis, we investigated changes in the expression of nine major GABA_A receptor subunits (α1, α2, α4, α5, β1-β3, γ2 and δ) and of the GABA_B receptor species GABA_BR1a, GABA_BR1b and GABA_BR2 in 1) hippocampal kindling and 2) epilepsy following electrically-induced status epilepticus (SE). Hippocampal kindling triggers a decrease in seizure threshold without producing spontaneous seizures and hippocampal damage, whereas the SE model is characterized by spontaneous seizures and hippocampal damage. Changes in the expression of GABA_A and GABA_B receptor mRNAs were observed in both models, and compared with those seen in other models and in human temporal lobe epilepsy.
The most prominent changes were a relatively fast (24 h after kindling and electrically-induced SE) and lasting (7 and 30 days after termination of kindling and SE, respectively) reduction of GABA_A receptor subunit δ mRNA levels (by 43–78%) in dentate granule cells, accompanied by increases in mRNA levels of all three β-subunits (by 8–79%) and subunit γ2 (by 11–43%). Levels of the minor subunit α4 were increased by up to 60% in dentate granule cells in both animal models, whereas those of subunit α5 were decreased 24 h and 30 days after SE, but not after kindling. In cornu ammonis 3 pyramidal cells, downregulation of subunits α2, α4, α5, and β1–3 was observed in the ventral hippocampus and of α2, α5, β3 and γ2 in its dorsal extension 24 h after SE. Similar but less pronounced changes were seen in sector cornu ammonis 1. Persistent decreases in subunit α2, α4 and β2 transcript levels were presumably related to SE-induced cell loss. GABA_B receptor expression was characterized by increases in GABA_BR2 mRNA levels at all intervals after kindling and SE.
The observed changes suggest substantial and cell specific rearrangement of GABA receptors. Lasting downregulation of subunits δ and α5 in granule cells and transient decreases in subunit α2 and β1–3 mRNA levels in cornu ammonis 3 pyramidal cells are suggestive of impaired GABA_A receptor-mediated inhibition. Persistent upregulation of subunits β1–3 and γ2 of the GABA_A receptor and of GABA_BR2 mRNA in granule cells, however, may result in activation of compensatory anticonvulsant mechanisms.
Kindling and status epilepticus models of epilepsy: Rewiring the brain
2004, Progress in Neurobiology
This review focuses on the remodeling of brain circuitry associated with epilepsy, particularly in excitatory glutamate and inhibitory GABA systems, including alterations in synaptic efficacy, growth of new connections, and loss of existing connections. From recent studies on the kindling and status epilepticus models, which have been used most extensively to investigate temporal lobe epilepsy, it is now clear that the brain reorganizes itself in response to excess neural activation, such as seizure activity. The contributing factors to this reorganization include activation of glutamate receptors, second messengers, immediate early genes, transcription factors, neurotrophic factors, axon guidance molecules, protein synthesis, neurogenesis, and synaptogenesis. Some of the resulting changes may, in turn, contribute to the permanent alterations in seizure susceptibility. There is increasing evidence that neurogenesis and synaptogenesis can appear not only in the mossy fiber pathway in the hippocampus but also in other limbic structures. Neuronal loss, induced by prolonged seizure activity, may also contribute to circuit restructuring, particularly in the status epilepticus model. However, it is unlikely that any one structure, plastic system, neurotrophin, or downstream effector pathway is uniquely critical for epileptogenesis. The sensitivity of neural systems to the modulation of inhibition makes a disinhibition hypothesis compelling for both the triggering stage of the epileptic response and the long-term changes that promote the epileptic state. Loss of selective types of interneurons, alteration of GABA receptor configuration, and/or decrease in dendritic inhibition could contribute to the development of spontaneous seizures.
Ionotropic glutamate and GABA receptors in human epileptic neocortical tissue: quantitative in vitro receptor autoradiography
1999, Neuroscience
Since a disturbed balance between excitatory and inhibitory amino acid receptors is suggested to be an important condition for epileptogenic cortical activity, the present study has focused on the analysis of the densities of (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl-d-aspartate, kainate and GABA subtype A receptors in neocortical tissue surgically removed from patients with focal epilepsy. The mean densities (collapsed over cortical layers I–VI) and the laminar distribution patterns of [³H]AMPA, [³H]MK-801, [³H]kainate and [³H]muscimol binding to AMPA, N-methyl-d-aspartate, kainate and GABA_A receptors were determined with quantitative receptor autoradiography in the neocortex of patients with focal epilepsy and controls. The tissue probes used in the present study were functionally characterized by parallel electrophysiological investigations. From that, the different probes could be subdivided into a spontaneously spiking and a non-spontaneously spiking group. The mean density of [³H]AMPA binding sites was significantly increased (+37%) in the group of epileptic brains (n=10) compared with controls (n=10), but the mean densities of [³H]MK-801, [³H]kainate and [³H]muscimol binding sites were not significantly altered (−8%, ±0% and −7%, respectively). The relation between the densities of all four binding sites were simultaneously displayed as polar plots in each single brain (“receptor fingerprints”). The consistent up-regulation of [³H]AMPA binding sites in all epileptic brains was found to be associated with a down-regulation of the N-methyl-d-aspartate receptor in four of the five non-spontaneously spiking cases, and an associated up-regulation of the N-methyl-d-aspartate receptor was seen in all spontaneously spiking cases. Finally, the laminar distribution of binding site densities was analysed, since the mean densities collapsed over all neocortical layers may obscure layer-specific alterations. Layer- and receptor- specific up- or down-regulations were found in epileptic tissue compared with controls. Moreover, the laminar distribution pattern of current sinks associated with epileptiform potentials in a spontaneously spiking cortical slice was found to be co-localized with local maxima of AMPA receptor densities.
The present analysis of four ionotropic glutamate and GABA receptor subtypes demonstrates a consistent and significant up-regulation of [³H]AMPA binding sites in all cases of human focal epilepsy, which co-localizes with the occurrence of sinks in current–source–density analysis. The receptor fingerprint analysis suggests a subdivision of focal epilepsy into two subtypes on the basis of neurochemical/functional correlations: (i) a spontaneously spiking subtype with increased N-methyl-d-aspartate receptor density, and (ii) a non-spontaneously spiking subtype with decreased N-methyl-d-aspartate receptor density.
Sensitivity of the rat hippocampal GABA(A) receptor α4 subunit to electroshock seizures
1998, Neuroscience Letters
The effects of one and five electroshock seizures on [³H]flunitrazepam binding, diazepam-insensitive (DIS) [³H]Ro 15–4513 binding, and levels of mRNA for GABA_A receptor α1, α4, β3 and γ2 subunits were examined in rats. No changes in any parameter were observed in the CA1 region of hippocampus or in parietal cortex. However, a single seizure produced a rapid and transient increase of α4 mRNA in the dentate gyrus, without altering the expression of the other subunits. The putative α4 protein, as measured by DIS [³H]Ro 15–4513 binding, was also elevated in the dentate gyrus by a single shock. Repeated electroshock (48-h intervals) resulted in an enhanced response of the α4 subunit to the seizure. Neither one nor five seizures altered [³H]flunitrazepam binding.

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Research reportRegional brain [3H]muscimol binding in kindled rat brain: a quantitative autoradiographic examination

Abstract

Exp. Neurol.

Exp. Neurol.

Brain Res.

Prog. Neurobiol.

Brain Res.

Prog. Neurobiol.

Electroenceph. Clin. Neurophysiol.

Rev. E.E.G. Neurophysiol. Clin.

Life Sci.

Brain Res.

Brain Res.

Receptor binding in the kindling model of epilpsy

Research report
Regional brain [³H]muscimol binding in kindled rat brain: a quantitative autoradiographic examination