Polysialylation of NCAM is upregulated by hyperthermia and participates in heat shock preconditioning-induced neuroprotection

"Brain tolerance"--a phenomenon in which a subtoxic challenge confers resistance to subsequent brain injuries--provides an ideal opportunity for investigating endogenous neuroprotective mechanisms. We investigated the potential role of the polysialylated (PSA) form of neural cell adhesion molecule (NCAM), which is thought to play a key role in plasticity. In a model where prior exposure to heat shock protects against kainate-induced cell damage in the hippocampus, we show that hyperthermia upregulates PSA-NCAM expression for at least 1 week, without affecting neurogenesis. Pharmacological manipulation of heat shock protein (HSP) expression demonstrates a tight positive link between HSP70 and PSA-NCAM. Finally, the presence of PSA was functionally linked to brain tolerance, as protection against kainate-induced cell death by heat shock pre-exposure was abolished in the absence of NCAM polysialylation. The upregulation of PSA-NCAM by hyperthermia may have a significant impact on hippocampal plasticity, permitting induction of the complex molecular cascade responsible for neuroprotection.

Patterns of dentate granule cell responses to perforant path stimulation in epileptic mice with granule cell dispersion

In adult mice, intrahippocampal administration of kainic acid induces a structural modification of the granule cell layer reminiscent of granule cell dispersion (GCD) seen in humans with temporal lobe epilepsy. We tested that GCD might be involved in the patterns of granule cell responses to perforant path stimulation by recording field potentials in vivo after kainic acid-induced status epilepticus until the phase of chronic seizure activity in presence of GCD or after its alteration by K252a co-treatment, an inhibitor of tyrosine kinase activities. Stimulation triggered bursts of multiple population spikes, the number of which progressively increased with time whereas their amplitude decreased in parallel with the progressive decrease in granule cell density. The population spike threshold was reached for a lower excitatory synaptic drive than in controls, as assessed by the initial slope of the field excitatory post-synaptic potential. This indicates that, for identical synaptic responses, granule cells were closer to the firing threshold. Fast inhibition, assessed by paired pulse stimulation, was compromised immediately after the initial status epilepticus, consistent with the rapid loss of most hilar cells. Neither the epileptic course nor the epileptiform responses of the granule cells were modified and manipulation by alteration following GCD manipulation while granule cell neuropeptide-Y immunostaining was substantially decreased. In this mouse model of TLE, granule cells display a progressive increase in epileptiform responses to afferent input until the occurrence of spontaneous seizures. The population spike amplitude decreases in parallel with GCD while the granule cell excitability is enhanced. Consequently, data from field potentials in epilepsy experiments should be interpreted with care, taking into account the possible variations in the neuronal density in the recorded area.

[Temporal lobe epilepsy and complete bilamination of the granule cell layer of the dentate gyrus]

A bilamination involving the whole dentate stratum granulosum associated with a hippocampal sclerosis is reported. This morphological abnormality could be an unusual aspect of granule cell dispersion, plastic change induced by an early post-natal injury, or the the result from a neuronal migration disorder during the embryonic period. Whatever its origin, this bilamination is an abnormality of the hippocampal development which continues during the first years of life.

Decreased epileptic susceptibility correlates with neuropeptide Y overexpression in a model of tolerance to excitotoxicity

Prior epileptic episodes have been shown to decrease markedly the neuronal damage induced by a second epileptic episode, similar to the tolerance following an episode of mild ischemia. Endogenous neuroprotective effects mediated by various mechanisms have been put forward. This study investigated whether neuroprotection against the excitotoxic damage induced by re-exposure to an epileptic challenge can reflect a change in epileptic susceptibility. Tolerance was elicited in rats by a preconditioning session using intrahippocampal kainic acid (KA) administration followed at 1, 7 and 15-day intervals by a subsequent intraventricular KA injection. The degree of pyramidal cell loss in the vulnerable CA3 subfield contralateral to the KA-injected hippocampus was extensively reduced in animals experiencing KA ventricular administration. This neuroprotection was highly significant 1 and 7 days after injection, but not 15 days after injection. In preconditioned animals, the after-discharge threshold was assessed as an index of epileptic susceptibility. It increased significantly from 1 to 15 days after intrahippocampal KA administration. Finally, an enhancement of neuropeptide Y expression in both non-principal cells and mossy fibers was detected, occurring at the same time as the decrease in epileptic susceptibility. These results provide further evidence of an 'epileptic tolerance' as shown by the substantial neuroprotective effect of a prior episode of epileptic activity upon subsequent epileptic insult and suggest that the prevention of excitotoxic damage after preconditioning results from an endogenous neuroprotective mechanism against hyperexcitability and seizures.

Correlations between granule cell dispersion, mossy fiber sprouting, and hippocampal cell loss in temporal lobe epilepsy

PURPOSE

Correlations between granule cell dispersion (GCD), collateral mossy fiber (MF) sprouting, and hippocampal cell loss were studied to assess the relation between GCD and synaptic reorganization in the dentate gyrus of patients with epilepsy.

METHODS

Twenty specimens from patients with medically intractable temporal lobe epilepsy (TLE) were studied along with two control specimens. GCD was considered to be present when the stratum granulosum was wider than 120 microm, the close apposition between the granule cell (GC) soma was lost, and GCs were scattered in the molecular layer (ML). Patterns of MF sprouting were differentiated as wide or narrow according to the area of neo-Timm's staining in the ML. GC loss and volumetric cell-density decreases in the different subfields were assessed.

RESULTS

MF sprouting was observed in 16 (80%) and GCD in nine (45%) cases. A significant correlation was found between MF sprouting and cell loss in all the subfields except the cornu Ammonis field 2 (CA2). A wide band of MF sprouting was associated with severe cell loss. Cases with GCD had a wide band of MF sprouting and also a higher degree of cell loss than cases without GCD.

CONCLUSION

GCD is associated with a specific pattern of MF sprouting, but cell loss was found to be a major determinant for MF reorganization.

Recurrent seizures and hippocampal sclerosis following intrahippocampal kainate injection in adult mice: electroencephalography, histopathology and synaptic reorganization similar to mesial temporal lobe epilepsy

Human mesial temporal lobe epilepsy is characterized by hippocampal seizures associated with pyramidal cell loss in the hippocampus and dispersion of dentate gyrus granule cells. A similar histological pattern was recently described in a model of extensive neuroplasticity in adult mice after injection of kainate into the dorsal hippocampus [Suzuki et al. (1995) Neuroscience 64, 665-674]. The aim of the present study was to determine whether (i) recurrent seizures develop in mice after intrahippocampal injection of kainate, and (ii) the electroencephalographic, histopathological and behavioural changes in such mice are similar to those in human mesial temporal lobe epilepsy. Adult mice receiving a unilateral injection of kainate (0.2 microg; 50 nl) or saline into the dorsal hippocampus displayed recurrent paroxysmal discharges on the electroencephalographic recordings associated with immobility, staring and, occasionally, clonic components. These seizures started immediately after kainate injection and recurrid for up to eight months. Epileptiform activities occurred most often during sleep but occasionally while awake. The pattern of seizures did not change over time nor did they secondarily generalize. Glucose metabolic changes assessed by [14C]2-deoxyglucose autoradiography were restricted to the ipsilateral hippocampus for 30 days, but had spread to the thalamus by 120 days after kainate. Ipsilateral cell loss was prominent in hippocampal pyramidal cells and hilar neurons. An unusual pattern of progressive enlargement of the dentate gyrus was observed with a marked radial dispersion of the granule cells associated with reactive astrocytes. Mossy fibre sprouting occurred both in the supragranular molecular layer and infrapyramidal stratum oriens layer of CA3. The expression of the embryonic form of the neural cell adhesion molecule coincided over time with granule cell dispersion. Our data describe the first histological, electrophysiological and behavioural evidence suggesting that discrete excitotoxic lesions of the hippocampus in mice can be used as an isomorphic model of mesial temporal lobe epilepsy.

Adenovirus-mediated transfer of a functional GAD gene into nerve cells: potential for the treatment of neurological diseases

The recent development of efficient virus-mediated gene transfer into nerve cells allows the prospect of new strategies for the treatment of drug-resistant neurological diseases. Some forms of epilepsy may be amenable to gene therapy. Although there is no obvious candidate gene, the consensual GABA hypothesis of epilepsy suggests that the GAD gene may be beneficial. GAD gene expression may be useful in supplying the inhibitory neurotransmitter GABA to particular critical brain territories. We show herein that a nonreplicative recombinant adenovirus carrying the GAD67 gene under the control of Rous sarcoma virus long terminal repeat promoter is able to express the transgene in primary cultures of neurons and glial cells. Expression of the GAD67 gene was assessed by immunoblotting and immunohistochemical analysis. We demonstrated the functionality of the transgene, the expression of which resulted in production of large amounts of GABA in neuronal and glial cell cultures. Substantial production of the enzyme was also detected for several weeks in infected organotypic slices cultured from new-born rat hippocampal tissues. The virally encoded GAD67 was also expressed in vivo in various brain areas involved in various neurological disorders and thus may be of value for the development of gene therapies.

Prevention of kainic acid-induced limbic seizures and Fos expression by the GABA-A receptor agonist muscimol

Fos oncoprotein expression has been shown to be a sensitive marker for sequential neuronal activation in response to a specific stimulus. The present study investigated the effect of the gamma-aminobutyric acid (GABA)-A receptor agonist muscimol on kainic acid (KA)-induced limbic seizures and Fos expression in the rat forebrain. One hour after KA injection, a substantial Fos expression was observed in the hippocampal dentate gyrus, whereas only a low level of Fos induction was seen in CA1-3 fields. Six hours post-injection a prominent increase of Fos expression occurred in most forebrain structures, including the whole hippocampus. Following 0.5 mg/kg muscimol treatment a remarkable decrease of Fos expression occurred but only in the caudate putamen and core of the accumbens nucleus. Treatment with 1 mg/kg muscimol led to further significant decreases of Fos expression in CA1-3 pyramidal neurons and the disappearance of Fos induction in the cerebral cortex above the rhinal fissure, reticular thalamic nucleus, claustrum, fundus striati, ventral pallidum, septal nucleus, lateral habenular nucleus, and lateral amygdaloid nucleus. When 2 mg/kg muscimol was injected, animals exhibited "absence seizures' instead of limbic seizures, and Fos expression in the hippocampus was effectively blocked. These results suggest that a reduction of GABAergic inhibition plays a crucial role not only in limbic seizure genesis in the dentate gyrus, but also in the seizure spread mechanism in many brain structures, among which the hippocampal CA1-3 fields are most markedly involved, less marked in the cerebral cortex and some other structures, and least marked in the caudate putamen and core of the accumbens nucleus.

Fos oncoprotein expression in the rat forebrain following muscimol-induced absence seizures

Fos oncoprotein expression is a marker of neuronal activation following seizures. Here, using this method we examined the anatomical locations of muscimol-induced absence seizures in the rat forebrain. Six hours after a systemic injection of muscimol a massive Fos immunoreactivity appeared in the olfactory system, retrosplenial cortex and paraventricular thalamic nucleus, whereas other cortical areas contained low level of Fos expression. These results provide the first functional morphological evidence suggesting that these forebrain structures with Fos expression may play an important role in the pathophysiology of muscimol-induced absence seizures.

Adenovirus mediated gene transfer in organotypic brain slices

A replication-defective adenovirus vector carrying the reporter gene encoding beta-galactosidase was used to transfect organotypic slices maintained in culture for up to 1 month. Three different delivery systems were used to inoculate the viral solution, either into the culture medium, or directly onto the surface of the slices or by microinjection into the tissue. Using the two first paradigms beta-galactosidase expressing cells were mostly of glial phenotype and distributed throughout the slices without any specific regional pattern. In contrast, microinjection of the adenovirus resulted in a large number of both infected neurones and glia, concentrated at the site of injection. This method thus appears to be able to circumvent some of the constraints and limitations associated with in vivo gene transfer.

Reflex epilepsy of the fowl and its transfer to normal chickens by brain embryonic grafts

The genetic photosensitive epilepsy of the Fayoumi chicken was transferred to normal chickens by in situ grafts at 2 days of incubation, of both the prosencephalic and mesencephalic brain vesicles taken from epileptic embryos. However, mesencephalic graft is sufficient to allow convulsions under sound stimulation. Typical EEG patterns are recorded in chimeras having the prosencephalon plus or not the mesencephalon. We conclude that, in this mutant, the whole neural tissue is affected, but the seizure generator is localized inside the mesencephalon, and specific sensory pathways are necessary for seizures to occur.

Adenoviral vectors as functional retrograde neuronal tracers

Adenoviruses have been recently recognized as a highly efficient system for gene delivery to various tissues. The ability of replication-defective recombinant adenovirus to transfer the lacZ reporter gene encoding beta-galactosidase to nerve cells in various brain structures has been demonstrated. Here, on the continuation of these studies, we present evidence that the adenovirus can be transported in a retrograde manner to nerve cell bodies from axonal terminals. This method may be of great value for infecting selected subsets of specific neurons for either anatomo-functional studies or even therapeutic purposes.

The use of adenovirus vectors for intracerebral grafting of transfected nervous cells

Grafting genetically-modified cells into the brain is a promising approach to address fundamental and clinical issues in neurobiology. Despite recent substantial progress, most of the methods used for introducing DNA sequences into donor cells result in weak efficacy or transient gene expression after transplantation. We tested whether the use of adenovirus as the vector for foreign genes avoided these problems. A replication-defective adenovirus vector carrying a reporter gene encoding for beta-galactosidase was used to transfect primary astrocytes. After grafting into various brain structures, transfected cells exhibited robust survival and expressed the transgene for at least five months. These results demonstrate the advantage of adenovirus-mediated gene transfer for prolonged transgene expression in grafted primary cells.

Ex vivo culture of adult microglial cells from previously lesioned rat brains

In an attempt to study more precisely the glial cells involved in reactions following specific brain injuries, we tried to culture cells derived from surgically-lesioned rat brains or adult rat hippocampus previously treated with kainic acid, a convulsant which induces status epilepticus associated with structural modifications. We find that, contrary to cultures derived from normal adult rat brain, cultures from lesioned rat brains can survive and proliferate in vitro. Characterization of the cell types using double labeling with isolectin B4 for microglia and GFAP antisera for astrocytes shows that cultures from KA-treated adult rats consist of nearly 100% macrophagic-microglial cells, whereas those obtained from surgically-lesioned brains are composed of a mixed population of microglial cells and astrocytes. These models are proposed as suitable for the further study of microglial-neuronal interactions involved in brain damage and repair.

Transfer of a genetic form of epilepsy in the chicken by embryonic brain grafts

The genetic photosensitive epilepsy of the Fayoumi chickens was transferred to normal chickens by grafting, in situ, on the 2nd day of incubation, the prosencephalic and mesencephalic vesicles from epileptic embryos. Such chimeras displayed typical interictal EEG and developed intermittent light stimulation-induced seizures phenotypically and electrically similar to the epileptic strain seizures.

Epilepsy induced collateral sprouting of hippocampal mossy fibers: does it induce the development of ectopic synapses with granule cell dendrites?

In the present study, using Golgi and electron microscopy techniques, experimentally induced epilepsy (kindling and kainate treatment) elicited collateral sprouting of mossy fibers in rat hippocampus. Collateral branches invade the hilus, cross the granule cell layer, and distribute throughout the inner third of the molecular layer. These newly developed collaterals may acquire the typical features of mossy fibers including giant fiber varicosities (mousses), although the mean surface of these mousses was thinner in these collaterals than in terminal branches. Granule cell dendrites may develop giant thorny excrescences, suggesting that the targets of these collaterals are granule cells. Giant synaptic boutons appear in the inner third of molecular layer of epileptic rats. These boutons acquire the morphological features of mossy fiber boutons and made multiple synaptic contacts with dendritic spines. The analysis of the profile types suggests that some of the newly developed collateral mossy fibers made hypotrophic synaptic contacts.

An adenovirus vector for gene transfer into neurons and glia in the brain

The efficient introduction of genetic material into quiescent nerve cells is important in the study of brain function and for gene therapy of neurological disorders. A replication-deficient adenoviral vector that contained a reporter gene encoding beta-galactosidase infected rat nerve cells in vitro and in vivo. beta-Galactosidase was expressed in almost all sympathetic neurons and astrocytes in culture. After stereotactic inoculations into the rat hippocampus and the substantia nigra, beta-galactosidase activity was detected for 2 months. Infected cells were identified as microglial cells, astrocytes, or neurons with anatomical, morphological, and immunohistochemical criteria. No obvious cytopathic effect was observed.

The embryonic form of neural cell surface molecule (E-NCAM) in the rat hippocampus and its reexpression on glial cells following kainic acid-induced status epilepticus

The neural cell adhesion molecule (NCAM) changes at the cell surface during development, from highly sialylated forms (embryonic or E-NCAM) to three size classes of less sialylated proteins with apparent molecular mass of 180, 140, and 120 kDa (adult NCAM). In the nervous system, E-NCAM has been localized in developing tissues, where it is thought to play a role in the structuring of neuronal groups and tissue pattern formation. In the present study a monoclonal antibody that specifically detects E-NCAM was used in immunoblot and immunohistochemical procedures. In developing rat hippocampus, E-NCAM cell expression was found to change according to a precise pattern and persisted until 1 month after birth. It was closely associated with the mossy fiber system, an area known for its sprouting propensity. In adult rats, although immunoreactivity considerably decreases and becomes undetectable by immunoblot analysis, E-NCAM was still found to be associated with a few pyramidal-shaped cells in the innermost part of the dentate gyrus. In order to acquire some insight into potential histogenetically plastic functions of E-NCAM, in another series of experiments adult rats were treated with kainic acid, a powerful excitotoxic and convulsant glutamate analog eliciting status epilepticus. When these animals were examined for E-NCAM expression, an intense labeling was found associated with glial-like cells, particularly in the hippocampal formation, and corresponding approximately to the reactive gliosis, as confirmed by staining with anti-glial fibrillary acidic protein antibodies. This expression was detectable from about 3 d following kainic acid administration and persisted for at least 12 weeks; it developed according to an observable spatiotemporal distribution pattern. In animals submitted to amygdala kindling, a nonlesional model of secondarily generalized epilepsy, no such reexpression of E-NCAM was observed. Our observations imply that polysialylation may be a means of identifying neuronal structures capable of plasticity in the CNS. Moreover, intense reexpression of E-NCAM could be a marker of reactive gliosis following brain damage.

Transfer of genetic epilepsy by embryonic brain grafts in the chicken

In the Fayoumi chicken, a spontaneous recessive autosomal mutation (F.Epi) is responsible for high susceptibility to seizures that are especially inducible by intermittent light stimulation. Substitution of defined areas of the encephalic neuroepithelium in normal chicken embryos at 2 days of incubation by their counterparts from homozygous F.Epi embryos generates the epileptic phenotype in the chimeras. It was found that grafting primordia of both prosencephalon and mesencephalon of homozygous F.Epi birds is necessary and sufficient for transfer of the full disease. When grafted alone, the homozygous F.Epi prosencephalon, although showing the typical epileptic interictal electroencephalogram, does not allow the complete epileptic seizures to occur in the hosts. Grafts of mesencephalon and/or rhombencephalon modify neither the behavior nor the electroencephalographic pattern of the recipient chickens. Cooperation of forebrain and midbrain activities is therefore required to yield epileptic seizures in this model.

Fos expression in GHB-induced generalized absence epilepsy in the thalamus of the rat

Using the model of gamma-hydroxybutyrate (GHB)-induced generalized absence epilepsy, the present work investigated the distribution of fos oncoprotein expression in the rat thalamus with fos antibody immunohistochemistry. Thirty minutes after absence-like seizures, some fos-immunoreactive cell nuclei were found in bilateral thalamic paraventricular nuclei (PV). After a further 30 min, a massive bilateral induction of fos was observed in the lateral habenular nucleus (LHb), the PV, the rhomboid thalamic nucleus, and the intralaminar nuclei of the thalamus. These results suggest that the LHb and the midline and intralaminar thalamic nuclei may very likely be involved in the pathophysiology of absence seizures.

Immunological identification of a new 14X10(3) Mr membrane-bound protein in Torpedo electric organ

A series of monoclonal antibodies binding to different epitopes shared by a 14 × 10(3)Mr membrane-bound polypeptide has been obtained. By indirect immuno-fluorescence, it was shown that the 14 × 10(3)Mr antigen is present in various cell types in Torpedo electric organ and muscle, especially fibroblasts, capillary endothelial cells, axonal cuff cells and, to a lesser extent, Schwann cells. At the electron-microscope level, after immunogold labelling, the antigen was found associated with the external surface of the plasma membrane of these cells, with the exception of the axonal cuff cells where part of the labelling was intracellular. The possible biological role of this 14 × 10(3)Mr protein is unknown but preliminary experiments suggest that this antigen has affinity for other Torpedo electric organ membrane proteins.

Audiogenic seizures evoked in DBA/2 mice induce c-fos oncogene expression into subcortical auditory nuclei

Recently the nuclear proto-oncogene c-fos has been shown to be rapidly and transiently expressed following seizures in many types of epilepsies. Until now, immunohistochemical as well as in situ hybridization studies have reported that the dentate gyrus of the hippocampus and most of the cortical areas were invariably heavily labeled. In order to see whether this distribution was reproduced or not in a model of epilepsy which has been proved to not involve these structures, a study was performed on genetically epilepsy-prone DBA/2 mice. Here we show that following audiogenic seizures, c-fos oncoprotein is not expressed in cortical and limbic structures but rather mapped the subcortical auditory nuclei.

Local asymptomatic status epilepticus induced by withdrawal of GABA infusion into limbic structures

Most of the experimental models of status epilepticus result either from administration of a variety of excitatory neurotoxins or repeated electrical stimulation. Here we propose a new model based on the withdrawal of chronic gamma-aminobutyric acid (GABA) infusion into limbic structures via osmotic minipumps. Appearing with a latency of about 50 min, continuous pseudo-rhythmic EEG epileptic spiking was elicited for about 12-24 h after removal of GABA infusion in hippocampus or amygdala. No apparent distant brain damage was observed. This model differs from many others by several features and could result from different mechanisms.

Long-lasting and sequential increase of c-fos oncoprotein expression in kainic acid-induced status epilepticus

Increased but transient expression of the proto-oncogene c-fos has been recently reported in metrazol and kindling-induced seizures. Here we tested whether kainic acid-induced status epilepticus may result in a long-term increase of this oncogene. A specific pattern of immunoreactive c-fos material was observed with the development of the seizures. Intense labeling first appeared in the dentate gyrus of the hippocampus and the entorhinal cortex. Pyramidal cell layer CA3, CA4 and CA1 as well as other limbic structures were then positively stained during status epilepticus. In addition, the duration of c-fos expression was different according to the anatomical sites. In the dentate gyrus labeling did not exceed 4-5 h whereas the pyramidal cell layer CA1 exhibited increased c-fos expression for as long as 24 h. Here we propose that c-fos which has been related to growth and differentiation in previous studies, could be involved in processes inducing long-term plastic alterations in the limbic system.

[Role of the hippocampus, amygdala and the substantia nigra in the evolution of status epilepticus induced by systemic injection of kainic acid in the rat]

The effects of bilateral microinjection of gamma-vinyl GABA (GVG, an irreversible inhibitor of GABA-T) were tested during the development of seizures induced by i.p. administration of 10 mg/kg of kainic acid. Intrahippocampal injection of GVG prevents the development of the seizures at an early stage in about half of the cases. In the remaining animals status epilepticus comparable to that of controls develops. Intra-amygdaloid injection reduces the severity of the seizures from the first motor limbic signs. Finally, intranigral injection prevents the appearance of convulsive status epilepticus or, when it develops, reduces its duration. The role that these three structures could play in the electro-clinical development of kainic acid-induced seizures is discussed.

Electroencephalographic, behavioral, and histopathologic features of seizures induced by intra-amygdala application of folic acid in cats

The effects of intracerebral injection of folic acid are still controversial. We studied the electroencephalographic, behavioral, and histopathologic consequences of the seizures induced by intra-amygdala administration of various doses of FA in freely moving cats. The severity of the seizures was dose-dependant. For doses of 25 and 50 nmol, single low-amplitude spikes appeared in the amygdala 15 to 20 min after injection and a typical amygdala symptomatology was observed. From doses of 100 nmol recurrent limbic seizures occurred 40 to 80 min after injection. Finally, from doses of 150 nmol secondarily generalized seizures were induced, which could be followed by death 4 to 6 h after injection. The severity of the cerebral lesions was related to both the dose and the paroxysmal manifestations. In cases with short survival time (6 h) and few seizures the pathology was restricted to a lymphocytic and glial reaction with some ischemic cells at the injected site. In cases with status epilepticus, edema and neuronal degeneration was observed in the hippocampus, amygdala, thalamic nuclei of the midline, entorhinal cortex, and cerebellum. No neuronal alteration at the injected site was observed. For longer survival times (8 days) edema was less severe, but hyperchromatic cells were still numerous. These results, compared with those of intra-amygdala administration of kainic acid, suggest that pathologic lesions induced in cats by folic acid more closely resemble those described in man after some status epilepticus.

Role of the amygdala in development of hippocampal kindling in the rat

The influence that the amygdala may exert on the development of hippocampal kindling was investigated using three different approaches: (i) after uni- or bilateral amygdalectomy by thermocoagulation, (ii) after prestimulation of the amygdala until the appearance of masticatory movements, and (iii) after increasing the GABA concentration in the amygdala with gamma-vinyl GABA. Hippocampal kindling was not significantly modified in amygdalectomized animals. On the contrary, prestimulation of the ipsilateral amygdala facilitated the subsequent hippocampal kindling. Finally, microinjection of gamma-vinyl GABA in both amygdalae either reduced the seizures to a prekindled level or strongly delayed the appearance of the motor signs of kindling. It is suggested that hippocampal kindling may develop preferentially through the amygdala.

Studies of wet-dog shake behavior induced by septohippocampal stimulation in the rat

Stimulation of the septum and the hippocampus were found to elicit a great number of "wet-dog" shakes (WDS). Their occurrence is strongly related to the evocation and to the time course of the afterdischarges elicited by the stimulation. Morphine, apomorphine, diazepam, and antiserotoninergic drugs greatly reduce the incidence of these WDS but do not alter the afterdischarge duration. Based on electroencephalographic and pharmacological data we propose that WDS induced by stimulation of the septohippocampal system may share some common mechanisms with many other models inducing WDS and offer a useful method to study further the neuroanatomical substrate of this behavior.

The partial benzodiazepine agonist properties of Ro 15-1788 in pentylenetetrazol-induced seizures in cats

The effects of Ro 15-1788, a specific benzodiazepine antagonist, were studied on pentylenetetrazol-induced seizures in cats. Ro 15-1788 decreased the number of myoclonic jerks induced by a subconvulsive dose of pentylenetetrazol (12.5 mg/kg, i.m.). Ro 15-1788 suppressed generalized convulsive seizures induced by a minimal convulsive dose of pentylenetetrazol (25-35 mg/kg), but did not block the effects of higher doses (35-45 mg/kg). These results indicate that Ro 15-1788 is not a pure benzodiazepine antagonist, but has partial agonistic properties.

Abortive amygdaloid kindled seizures following microinjection of gamma-vinyl-GABA in the vicinity of substantia nigra in rats

The effects of microinjection of a GABA-elevating substance (gamma-vinyl-GABA) in the substantia nigra were assessed on kindled convulsive seizures induced by daily appropriate amygdaloid stimulation in the rat. Bilateral administration of 20 micrograms of gamma-vinyl-GABA strongly reduced the afterdischarge duration of the seizures without significantly modifying the motor convulsions. This effect was noted 24 h after injection and lasted for up to 48 h. Administration of gamma-vinyl-GABA in structures 1.5 mm distant from the substantia nigra had no effect on kindled seizures. It is suggested that the substantia nigra may intervene in a negative feedback system that tends to suppress the paroxysmal activity initiated from the amygdala.

Reversal of the anticonvulsant effects of diazepam on amygdaloid-kindled seizures by a specific benzodiazepine antagonist: RO 15-1788

The benzodiazepine antagonist RO 15-1788 was tested in an animal model of experimental epilepsy, the kindling effect. In animals fully kindled from repeated electrical amygdaloid stimulation, RO 15-1788 reversed the anticonvulsant effects of diazepam (2 mg/kg) from doses of 0.4-0.5 mg/kg. Doses up to 20 mg/kg also antagonized the preventive action of diazepam. RO 15-1788 alone had neither proconvulsant effects on the amygdaloid afterdischarges nor benzodiazepine-like activity on the kindled seizures.

Long-term effects of intrahippocampal kainic acid injection in rats: a method for inducing spontaneous recurrent seizures

Kainic acid (KA) is known as a powerful convulsant and neurotoxic agent. When intracerebrally administered it causes repetitive seizures for about 1 or 2 days and brain damage both locally and in several remote brain regions. In the present paper the long-term effects of intrahippocampal KA administration are reported. Doses from 0.1 to 3.0 micrograms of KA were injected in the right hippocampus of Wistar rats and both the behaviour and EEG were observed during a period of about 3 months. Following KA doses of 0.8-2.0 micrograms, 4 distinct phases were observed: (1) acute phase which lasted 1-2 days and corresponded to the pattern of repetitive seizures as already described; (2) silent phase (5-21 days) which was characterized by a progressive return to apparently normal EEG and behaviour except for some aggressive behaviour in those animals receiving the highest doses; (3) phase of spontaneous recurrent seizures (these seizures started 6-22 days after KA injections and were mostly triggered upon handling and recurred approximately 2 times by day for about 30 days; usually they resembled the amygdaloid kindled seizures); and (4) post-seizure phase where no more seizures were observed but significant spiking activity in the amygdala recordings could be seen. Animals receiving KA doses of 0.1-0.4 microgram did not evolve beyond the acute phase whereas those receiving 3.0 micrograms died during this first phase. Neuropathological examination revealed dose-dependent alterations. These serial events offer a new method to induce spontaneous recurrent seizures with brain damage.

Inhibition of kindling-induced generalized seizures by aminooxyacetic acid

The anticonvulsant effect of aminooxyacetic acid (AOAA) was examined on a model of experimental epilepsy (kindling) induced by daily appropriate amygdaloid stimulation in the rat. Doses from 5 to 30 mg/kg were intraperitoneally administered in fully kindled animals 3--4 h before triggering a seizure. At low doses (less than 15 mg/kg) AOAA had no effect whereas at higher doses (greater than 15 mg/kg) it reduced the severity of the generalized kindled seizures in over half the cases, and even sometimes completely blocked them. The inhibition of epileptic activity by AOAA is in accordance with the hypothesis that an increase in GABA level is associated with a reduction of epileptic sensitivity. An unexpected lengthening of the afterdischarge duration was also observed in about 20% of the cases, independently of the amount administered. This fact is discussed in regard to the complex action of AOAA on gamma-aminobutyric acid related enzymes. Finally, since the afterdischarge threshold was shown to be unaffected by the drug, it is suggested that it may act on the afterdischarge propagation rather than at the focal amygdaloid level.

Choline acetyltransferase and acetylcholinesterase containing projections from the basal forebrain to the amygdaloid complex of the rat

The origin of the cholinergic innervation to the amygdaloid complex was investigated with the use of acetylcholinesterase (AChE) histochemistry and choline acetyltransferase (ChAT) assay of microdissected nuclei. Visualization of AChE-positive neurones in the ventral forebrain was facilitated by pretreatment of rats with 1.5 mg/kg di-isopropyl phosphofluoridate (DFP). The AChE-positive neurones in the ventral forebrain are distributed in a continuous system from the septum through the lateral preoptic area to the entopeduncular nucleus caudally. Knife cuts or kainic acid injections (1.5 microgram/l microliter) placed in the lateral preoptic area resulted in substantial depletion of the AChE and ChAT content of the amygdala nuclei. Kainic acid injections (1.5 microgram/l microliter) in the diagonal band area or cuts through the stria terminalis dorsally did not significantly modify the AChE staining or ChAT content of the amygdala (although diagonal band injections partially depleted the hippocampus of ChAT). Knife cuts severing both the so-called ventral pathway and the stria terminalis did not produce significantly greater ChAT depletion in the amygdala than those produced by the knife cuts or kainic acid injections in the lateral preoptic area. Parasagittal knife cuts undercutting the lateral pyriform cortex also failed to modify the AChE or ChAT content of the amygdala, but they depleted the undercut cortex of both ChAT and AChE; AChE-positive material accumulated ventrally and medially to the knife cut. It is suggested that the major source of the cholinergic innervation of the amygdala is the magnocellular AChE-positive neurones in the lateral preoptic area and adjacent regions of the ventral forebrain.

Histamine synthesizing afferents within the amygdaloid complex and bed nucleus of the stria terminalis of the rat

The regional distribution of histidine decarboxylase (HD) activity has been studied in the amygdaloid complex and the bed nucleus of the stria terminalis (BST) of the rat. The central and medial nuclei of the amygdala had 2-fold higher HD activity levels than the remaining nuclei of the complex. HD activity was exceptionally high in the BST, particularly in its ventral part. A lesion of the stria terminalis had no effect on this distribution whereas a combined lesion of the stria terminalis and the so-called ventral pathway induced a decrease of approximately 60% in all the amygdaloid nuclei, but not in the BST. On the other hand, a lesion of the medial forebrain bundle (MFB) induced a similar decrease in both the amygdaloid nuclei and the BST. These results confirm that HD-containing fibres are present in the MFB. On the one hand these project massively to the BST and on the other penetrate in the amygdala ventromedially along the ansa peduncularis and preferentially innervate the more medially located nuclei.