A microdialysis study of glutamate concentration in the hippocampus of rats after TsTX toxin injection and blockade of toxin effects by glutamate receptor antagonists

Dopaminergic metabolism is affected by intracerebral injection of Tb II-I isolated from Tityus bahiensis scorpion venom

Tb II-I isolated from Tityus bahiensis venom causes epileptic-discharges when injected into the hippocampus of rats. The involvement of neurotransmitters in this activity was investigated. Our results demonstrated that Tb II-I increases the concentrations of dopamine metabolite but does not alter other neurotransmitters. Thus, dopaminergic system seems to be partially responsible for the convulsive process. Specific action on particular neurotransmitter can make this toxin a useful tool to better understand the functioning of the system.

•

The dopaminergic system is affected by intracerebral injection of Tb II-I

•

The dopaminergic system seems to be partially responsible for the convulsive process.

•

The hippocampal level of glutamate and GABA is not affected by Tb II-I

Cellular-Scale Microelectrode Arrays to Monitor Movement-Related Neuron Activities in the Epileptic Hippocampus of Awake Mice

OBJECTIVE

Epilepsy affects 50 million people worldwide and its pathogenesis is still unknown. In particular, the movement-related neural activities involving glutamate (Glu) and electrophysiological signals at cellular level remains unclear.

METHODS

A cellular-scale implantable microelectrode array (MEA) was fabricated to detect the movement-related neural activities involving Glu concentration and electrophysiological signals. Platinum and reduced graphene oxide nanocomposites were deposited to enhance the surface area. Glu oxidase (Gluox) were coated to effectively recognize Glu molecule.

RESULTS

Neural activities in the hippocampus of normal and epileptic mice is different, and the changes are closely connected with movement. Glu concentration and spike firing rate in the epileptic mice were much higher than those in the normal ones. And the neural activities with significant synchronization were detected in the epileptic mice even without seizure occurrence. Meanwhile, the spikes fire more intensively and Glu level became much higher during the movement of the mice compared to the stationary state.

CONCLUSION

The existing abnormality of neural activities in the epileptic mice are potential factors to induce a seizure. Movement may impact the neural activities and the duration of seizure.

SIGNIFICANCE

The MEA can monitor changes of movement, Glu and neuron discharges synchronously and provides us an effective technology to understand the neuronal disease.

Tb1, a Neurotoxin from Tityus bahiensis Scorpion Venom, Induces Epileptic Seizures by Increasing Glutamate Release

Here, we report the neurotoxic effects aroused by the intracerebral injection (in rats) of Tb1, which is a neurotoxin isolated from Tityus bahiensis scorpion venom. Biochemical analyses have demonstrated that this toxin is similar to the gamma toxin from T. serrulatus, which is a β-scorpion toxin that acts on sodium channels, causing the activation process to occur at more hyperpolarized membrane voltages. Male Wistar rats were stereotaxically implanted with intrahippocampal electrodes and cannulas for electroencephalographic recording and the evaluation of amino acid neurotransmitters levels. Treated animals displayed behavioral and electroencephalographic alterations similar to epileptiform activities, such as myoclonus, wet dog shakes, convulsion, strong discharges, neuronal loss, and increased intracerebral levels of glutamate. Scorpion toxins are important pharmacological tools that are widely employed in ion channel dysregulation studies. The current work contributes to the understanding of channelopathies, particularly epilepsy, which may originate, among other events, from dysfunctional sodium channels, which are the main target of the Tb1 toxin.

Tb II-I, a Fraction Isolated from Tityus bahiensis Scorpion Venom, Alters Cytokines': Level and Induces Seizures When Intrahippocampally Injected in Rats

Scorpion venoms are composed of several substances with different pharmacological activities. Neurotoxins exert their effects by targeting ion channels resulting in toxic effects to mammals, insects and crustaceans. Tb II-I, a fraction isolated from Tityus bahiensis scorpion venom, was investigated for its ability to induce neurological and immune-inflammatory effects. Two putative β-sodium channel toxins were identified in this fraction, Tb2 II and Tb 4, the latter having been completely sequenced by mass spectrometry. Male Wistar rats, stereotaxically implanted with intrahippocampal cannulas and electrodes, were injected with Tb II-I (2 µg/2 µL) via the intrahippocampal route. The behavior, electrographic activity and cellular integrity of the animals were analyzed and the intracerebral level of cytokines determined. Tb II-I injection induced seizures and damage in the hippocampus. These alterations were correlated with the changes in the level of the cytokines tumoral necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Therefore, the binding of Tb II-I to its target in the central nervous system may induce inflammation resulting in neuropathological and behavioral alterations.

Anti-scorpion venom activity of Thapsia garganica methanolic extract: Histopathological and biochemical evidences

ETHNOPHARMACOLOGICAL RELEVANCE

Thapsia garganica, is a herbal medicine traditionally used as diuretic, emetic and purgative. It is also used as anti-scorpion venom in Morocco; however, its protective effects against scorpion venom remain elusive.

AIM OF THE STUDY

The present study was undertaken to evaluate anti-venom activity of T. garganica in vivo through histological and biochemical studies.

MATERIALS AND METHODS

Methanolic leaves extract of T. garganica was evaluated for anti-venom activity against buthus. occitanus under in vivo conditions. Histopathological and biochemical changes in envenomed and treated mice were also examined. Phytochemical screening was conducted to estimate the major constituents whereas DPPH, β -Carotene-linoleic acid and reducing power assays were performed to evaluate the anti-oxidant activity of T. garganica extract.

RESULTS

Methanolic leaves extract of T. garganica (2g/kg) increased the survival time (> 18h) of mice injected with lethal doses of B. occitanus venom, with remarkable recovery of histology damage. Furthermore T. garganica induced a significant decreased of biochemical markers of kidney, liver and heart function. Phytochemistry screening revealed the presence of phenolic compounds, flavonoids, tannins and steroids/terpenoids, which might explain the bioactivity of the extract. It was also shown that the extract has an exceptionally high antioxidant activity compared to well-known antioxidants used as standards.

CONCLUSION

The present study provides strong evidence that support the use of T. garganica as anti-scorpion venom in traditional medicine in Morocco. However, additional studies are required to isolate and identify the metabolites responsible for the activity.

Effects of Brazilian scorpion venoms on the central nervous system

In Brazil, the scorpion species responsible for most severe incidents belong to the Tityus genus and, among this group, T. serrulatus, T. bahiensis, T. stigmurus and T. obscurus are the most dangerous ones. Other species such as T. metuendus, T. silvestres, T. brazilae, T. confluens, T. costatus, T. fasciolatus and T. neglectus are also found in the country, but the incidence and severity of accidents caused by them are lower. The main effects caused by scorpion venoms - such as myocardial damage, cardiac arrhythmias, pulmonary edema and shock - are mainly due to the release of mediators from the autonomic nervous system. On the other hand, some evidence show the participation of the central nervous system and inflammatory response in the process. The participation of the central nervous system in envenoming has always been questioned. Some authors claim that the central effects would be a consequence of peripheral stimulation and would be the result, not the cause, of the envenoming process. Because, they say, at least in adult individuals, the venom would be unable to cross the blood-brain barrier. In contrast, there is some evidence showing the direct participation of the central nervous system in the envenoming process. This review summarizes the major findings on the effects of Brazilian scorpion venoms on the central nervous system, both clinically and experimentally. Most of the studies have been performed with T. serrulatus and T. bahiensis. Little information is available regarding the other Brazilian Tityus species.

Some pharmacological effects of Tityus obscurus venom in rats and mice

There are a great number of studies about Brazilian scorpions. However, little is known about the venom of scorpions of northern Brazil, mainly about Tityus obscurus, which is responsible for the most number of accidents in the Amazon. Thus, this study aimed to evaluate some pharmacological effects of T. obscurus venom in rats and mice. In rats, the venom (10 mg/kg i.p.) caused hemorrhagic patches in the lung parenchyma but did not lead to pulmonary edema. There was a decrease in general activity, observed in the activity box after venom injection. The venom did not induce changes in the occurrence and intensity of experimentally induced convulsions, nor did it cause hippocampal neuronal loss. In mice, the LD₅₀ obtained was 3.13 mg/kg (i.p.). Different doses of the venom (0.2; 1; 5; 10; 15 μg/30 μL per hind paw) induced edematogenic and moderate nociceptive activity in mice. The Tiyus serrulatus venom used as comparison caused more intense symptomatology in mice. Comparing to the venom of other Tityus scorpions of medical importance, that have convulsant and intense nociceptive effects and cause lung edema, as described in the literature, we can conclude that the venom of T. obscurus probably has different characteristics.

Neuroactive compounds obtained from arthropod venoms as new therapeutic platforms for the treatment of neurological disorders

The impact of neurological disorders in society is growing with alarming estimations for an incidence increase in the next decades. These disorders are generally chronic and can affect individuals early during productive life, imposing real limitations on the performance of their social roles. Patients can have their independence, autonomy, freedom, self-image, and self-confidence affected. In spite of their availability, drugs for the treatment of these disorders are commonly associated with side effects, which can vary in frequency and severity. Currently, no effective cure is known. Nowadays, the biopharmaceutical research community widely recognizes arthropod venoms as a rich source of bioactive compounds, providing a plethora of possibilities for the discovery of new neuroactive compounds, opening up novel and attractive opportunities in this field. Several identified molecules with a neuropharmacological profile can act in the central nervous system on different neuronal targets, rendering them useful tools for the study of neurological disorders. In this context, this review aims to describe the current main compounds extracted from arthropod venoms for the treatment of five major existing neurological disorders: stroke, Alzheimer’s disease, epilepsy, Parkinson’s disease, and pathological anxiety.

Intrahippocampal injection of TsTX-I increases the levels of INF-γ in the cerebral tissue but not the levels of glutamate

TsTX-I, isolated from Tityus serrulatus scorpion venom, causes epileptic-like discharges when injected into the central nervous system. The involvement of excitatory amino acids and cytokines in this activity was investigated. Our results have demonstrated that TsTX-I increases the release of IFN-γ but does not alter the intracerebral concentration of the excitatory amino acids in rats. Thus, this cytokine seems to be more important in the convulsive process than glutamate.

Convulsive and Neurodegenerative Effects in Rats of Some Isolated Toxins from the Tityus bahiensis Scorpion Venom

Despite Tityus bahiensis being one of the most dangerous scorpions in Brazil, there are few studies about the effects of its venom, which acts mainly on the central nervous system. Previous studies demonstrated the convulsive ability of this venom. The present work aimed to study the hippocampal effects in rats of some toxins isolated from pool V, which induces a pronounced epileptogenic effect. The pool was separated by reverse-phase HPLC, and the peaks with higher yield (Tb V-1, V-5, V-24, V-27, and V-28) were used in the experiments. Cannulae and electrodes were implanted in the hippocampus of male Wistar rats (240–250 g). The animals were divided into six groups that received intracerebral injection of toxin solution (1 or 2 μg/μL) or Ringer solution (control group), and they were submitted to behavioral, electrographic, and histological analysis. All toxins studied evoked electrographic and behavioral epileptic-like activity to different degrees. Moreover, the toxins V-1, V-24, and V-28 caused significant neuronal loss in CA4 ipsi- and contralateral hippocampal areas. These results suggest that toxins from T. bahiensis scorpion, when injected into the hippocampus, are able to act directly on the central nervous system inducing convulsive and neurodegenerative effects.

Effects of a toxin isolated from Tityus bahiensis scorpion venom on the hippocampus of rats

AIMS

The objective of the present study was to determine the effects of a toxin from T. bahiensis scorpion venom on the hippocampus of rats. This toxin, called Tb V-4, was chosen since it shows remarkable convulsive activity.

MAIN METHODS

Male Wistar rats weighing 250g were used. The toxin (1.0μg/μl) was injected into the hippocampus. The animals were then submitted to electroencephalographic and behavioral examinations or to microdialysis to determine the levels of neurotransmitters. The location of the implanted guide cannulae and electrodes was checked histologically. The number of cells in the CA1, CA3 and CA4 areas of the hippocampus was determined by light microscopy. Changes in the concentration of cytosolic free calcium were evaluated by confocal microscopy.

KEY FINDINGS

The toxin evoked behavioral alterations such as wet dog shakes, myoclonus, yawning and orofacial automatisms. Electroencephalographic recordings exhibited alterations such as isolated or grouped spikes and epileptic-like discharges. Injection of the toxin augmented glutamate concentration in the extracellular fluid in some animals. There was also a decrease in the number of pyramidal cells, mainly in the CA1 and CA4 areas for some rats. In some slices of the hippocampus, an increase in intracellular calcium mobilization was seen.

SIGNIFICANCE

The present results suggest that the Tb V-4 toxin may be responsible for the epileptic and behavioral effects observed with the crude venom. We suggest that the convulsive and degenerative effects induced by the toxin could be due to the enhanced release of excitatory amino acids involved in the most important pathways of the hippocampus.

Intrahippocampal injection of TsTX-I, a beta-scorpion toxin, causes alterations in electroencephalographic recording and behavior in rats

AIMS

TsTX-I scorpion toxin, also known as γ-toxin, is a β-toxin which binds to site 4 of the sodium channel, shifting its activation potential. There are few studies about its pharmacological action in the central nervous system. The objective of this work was to determine the electroencephalographic, behavioral and histopathological effects of intrahippocampal injection of TsTX-I.

MAIN METHODS

Rats were anesthetized and fitted with cannulae for injection into the hippocampus and with electrodes for cerebral recording. The animals were treated with Ringer solution, some doses of TsTX-I, DMSO 0.1% or veratridine. Behavioral and electrographic recordings were observed for 4 hours after the injection. After 7 days, the rats were perfused, and their brains removed for histological analysis.

KEY FINDINGS

Increasing doses of the toxin evoked epileptic-like discharges, wet dog shakes, and in some cases hind limb paralysis and intense respiratory difficulty followed by death. The histopathological analysis demonstrated no cell loss. Animals injected with veratridine developed epileptiform activity in the electrographic recording and neuronal loss.

SIGNIFICANCE

The results suggest that TsTX-I toxin may be responsible, at least in part, for the epileptic and behavioral effects observed with the crude venom, and although veratridine and TsTX-I act on Na-channel, the differences between them are remarkable, demonstrating that toxins can have different functional effects depending on the site of action in the channel. Thus, animal neurotoxins are often highly selective and may be useful for the identification of the sequence of events underlying neurotransmission.

Diazepam and pentobarbital protect against scorpion venom toxin-induced epilepsy

We have characterized earlier the long-term behavioural, electroencephalographic and histopatologic features after a single TsTx microinjection, consisting of a neuropeptide isolated from the Tityus serrulatus scorpion venom, into the hippocampus of rats. TsTx was able to induce status epilepticus (SE) and developed later epilepsy. The present study was designed to investigate the outcomes of diazepam plus pentobarbital administered at 30 min, 1, 2 or 6h after the beginning of TsTx-induced SE, on the development of spontaneous recurrent motor seizures (SRMSs), mossy fibre sprouting and hippocampal neurodegeneration in rats. The administration of diazepam (DZ)+pentobarbital (PB) 30 min after the beginning of the TsTx-induced SE was able to markedly reduce the frequency of the SRMSs and prevent the development of mossy fibres sprouting and hippocampal lesion. In the other groups the augment of the extent of hipocampal neurodegeneration, the frequency of SRMSs and degree of aberrant mossy fibre sprouting was directly proportional to the time that the animals were subjected to TsTx-induced SE. In conclusion, our results point out that the early blockade of the TsTx-induced SE with diazepam plus pentobarbital, was effective treatment against later epilepsy development. The effectiveness of this treatment depends on the time that the animals were subjected to the SE. Furthermore, the TsTx model could be a useful tool to study antiepileptogenic drugs in chronic epileptic animals, neuronal degeneration, as well as for the mechanisms underlying epilepsy.

Characterization of the neurotoxicity induced by the extract of Magnistipula butayei (Chrysobalanaceae) in rat: Effects of a new natural convulsive agent

This study was designed to document convulsant and neurotoxic properties of extracts of a tropical tree, Magnistipula butayei subsp. Montana, and to investigate the involvement of the glutamatergic system in these effects. Continuous behavioral observations and electroencephalographic (EEG) records were obtained after per os administration of an aqueous extract of Magnistipula (MBMAE) in rats. MBMAE (800 mg/kg) induced behavioral changes resembling motor limbic seizures: staring and head tremor, automatisms, forelimb clonic movements and violent tonic-clonic seizures leading to death in all animals. Concomitantly, important seizure activity that gradually evolved to epileptiform activity was recorded on the EEG. Moreover, c-Fos immunohistochemistry has revealed an increased c-Fos expression in the dentate gyrus and in piriform, peri- and entorhinal cortices 2 and 4h after treatment. This expression pattern suggested that the mechanism of action for the MBMAE is similar to that observed in glutamate-induced models of epilepsy. The MBMAE increased cell death also in hippocampal cell cultures. Furthermore, the build-up of convulsive activity and epileptic discharges induced by MBMAE in rat were abolished by MK-801, an NMDA receptor antagonist. Our study suggests that MBMAE contains a potent toxin, with a powerful neurotoxic activity in rat, and corresponding to a new natural component(s) that act as an NMDA-mediated convulsant molecule.

Neurotoxins from invertebrates as anticonvulsants: From basic research to therapeutic application

Invertebrate venoms have attracted considerable interest as a potential source of bioactive substances, especially neurotoxins. These molecules have proved to be extremely useful tools for the understanding of synaptic transmission events, and they have contributed to the design of novel drugs for the treatment of neurological disorders and pain. In this context, as epilepsy involves neuronal substrates, which are sites of action of many neurotoxins; venoms may be particularly useful for antiepileptic drug (AED) research. Epilepsy is a chronic disease whose treatment consists of controlling seizures with antiepileptics that very often induce strong undesirable side effects that may limit treatment. Here, we review the vast, but yet unexplored, world of neurotoxins from invertebrates used as probes in pharmacological screening for novel and less toxic antiepileptics. We briefly review (1) the molecular basis of epilepsy, as well as the sites of action of commonly used anticonvulsants (we bring a comprehensive review of the elements from invertebrate venoms which are mostly studied in neuroscience research and may be useful for drug development); (2) peptides from conus snails; (3) peptides and polyamine toxins from spiders and wasps; and (4) peptides from scorpions.

Effects of Tityus serrulatus scorpion venom and its toxin TsTX-V on neurotransmitter uptake in vitro

Scorpion neurotoxins targeting the Na(v) channel can be classified into two classes: alpha- and beta-neurotoxins and are reported as highly active in mammalian brain. In this work, we evaluate the effects of Tityus serrulatus venom (Ts venom) and its alpha-neurotoxin TsTX-V on gamma-aminobutyric acid (GABA), dopamine (DA) and glutamate (Glu) uptake in isolated rat brain synaptosomes. TsTX-V was isolated from Ts venom by ion exchange chromatography followed by reverse-phase (C18) high-performance liquid chromatography. Neither Ts venom nor TsTX-V was able to affect (3)H-Glu uptake. On the other hand, Ts venom (0.13 microg/mg) significantly inhibited both (3)H-GABA and (3)H-DA uptake ( approximately 50%). TsTX-V showed IC(50) values of 9.37 microM and 22.2 microM for the inhibition of (3)H-GABA and (3)H-DA uptake, respectively. These effects were abolished by pre-treatment with tetrodotoxin (TTX, 1 microM), indicating the involvement of voltage-gated Na(+) channels in this process. In the absence of Ca(2+), and at low Ts venom concentrations, the reduction of (3)H-GABA uptake was not as marked as in the presence of Ca(2+). TsTX-V did not reduce (3)H-GABA uptake in COS-7 cells expressing the GABA transporters GAT-1 and GAT-3, suggesting that this toxin indirectly reduces the transport. The reduced (3)H-GABA uptake by synaptosomes might be due to rapid cell depolarization as revealed by confocal microscopy of C6 glioma cells. Thus, TsTX-V causes a reduction of (3)H-GABA and (3)H-DA uptake in a Ca(2+)-dependent manner, not directly affecting GABA transporters, but, in consequence of depolarization, involving voltage-gated Na(+) channels.

Non-NMDA glutamatergic receptors modulate acetylcholine release in the rat subfornical organ area

The present study was designed to examine whether glutamatergic receptor mechanisms modulate the release of acetylcholine (ACh) in the region of the subfornical organ (SFO) using intracerebral microdialysis methods in freely moving rats. Perfusion of either non-N-methyl-d-aspartate (NMDA) agonist quisqualic acid (QA, 50 microM) or kainic acid (KA, 50 microM) through the microdialysis probe significantly enhanced the ACh release in the SFO area. Local perfusion of the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 and 50 microM) did not change the basal release of ACh. CNQX (10 microM) administered together with either QA (50 microM) or KA (50 microM) in the SFO area antagonized the stimulant effect of the agonists on the ACh release. In urethane-anesthetized rats, repetitive electrical stimulation (500 microA, 10 Hz) of the medial septum (MS) significantly increased dialysate ACh concentrations in the region of the SFO. The increase in the ACh release elicited by the MS stimulation was significantly potentiated by perfusion of QA (50 microM), and the QA-induced potentiation was prevented by CNQX (10 microM) treated together with QA. These results show that the glutamatergic synaptic inputs enhance the ACh release in the SFO area through non-NMDA receptors. The data further suggest that the septal cholinergic inputs to the SFO area are potentiated by non-NMDA receptor mechanisms.

Dantrolene protects hippocampal cells from damage induced by TsTX, an alpha-scorpion toxin from Tityus serrulatus

We examined the effects of dantrolene, an inhibitor of intracellular calcium release, on alterations associated with the intrahippocampal injection of the TsTX scorpion toxin. Male Wistar rats (230-250 g) were injected with Ringer solution (1 microl; n = 6); TsTX toxin (1 microg/microl; n = 8); and dantrolene (10.0 mg/kg) plus TsTX toxin (1 microg/microl; n = 6). After injection, electroencephalographic (EEG) recordings and observation of animals behaviour were performed continuously for 4 h. One week later, animals were submitted to histopathological analysis. TsTX caused electrographic seizure expressed by moderate or intense discharges and neuronal loss in hippocampal areas in all injected animals (n = 8). Dantrolene reduced the effect of TsTX. Thus, 67% of rats (four out of six) treated with toxin and dantrolene had electrographic convulsions, but only for 30 min after injection and none of them presented neuronal damage. Dantrolene or Ringer had no effects on the EEG.

TSII toxin isolated from Tityus serrulatus scorpion venom: behavioral, electroencephalographic, and histopathologic studies

We have reported earlier that intrahippocampal administration of the C-pool from Tityus serrulatus scorpion venom induces convulsions in rats. Here we report the effects of seven toxins isolated from the C-pool. The strongest effects were seen after toxin 5C, which was sequenced and identified as TSII, a beta-type toxin that affects Na+ channel activation. Unilateral injection of TSII in the rat hippocampus (1.7 microg/microl) induced clusters of spikes and epileptic discharges of mainly moderate intensity, convulsion-related behavioral changes (wet dog shakes, staring, masticatory jaw movements, facial automatisms, orofacial movements, intense sniffing, blinking, and forelimb clonus with rearing and falling) and a massive neuronal loss of pyramidal cells in the ipsilateral CA1, CA3, and CA4 subfields and of granulate cells of the ipsilateral dentate gyrus. Toxins C3, C4, and C6 induced weaker changes in the EEG and behavioral changes and failed to induce cell death, and toxins C1, C2, and C7 had no effects. The similarities in the effects of TsTx, a alpha-type toxin that affects Na+ channel, suggest that the loss of modulation of activation of the sodium channel caused by TSII increases glutamate release, leading to long-lasting increases in intracellular Ca2+ and cell death.

TsTx toxin isolated from Tityus serrulatus scorpion venom induces spontaneous recurrent seizures and mossy fiber sprouting

PURPOSE

To characterize the long-term behavioral, electroencephalographic (EEG) and histopathologic features after a single TsTx microinjection into the hippocampus of rats.

METHODS

TsTx, 2 microg, or 1 microl of 0.1 M phosphate buffer was injected into the right dorsal hippocampus of the rat. EEG records and behavioral observations were made over a period of 10 h after injection. For a period of 4 months, the animals were observed for the occurrence of convulsive seizures. At the end of the experiment, the brains were processed by the neo-Timm and Nissl methods.

RESULTS

After intrahippocampal TsTx injection, three distinct phases were observed: (a) an immediate period that lasted 1 day, during which the motor and electrographic seizures characteristic of status epilepticus (SE) were seen; (b) a silent period (31-49 days), characterized by normal EEG and behavior; and (c) a period of spontaneous recurrent seizures (SRSs). The seizure frequency was one to two per week. Four months after TsTx injection, hippocampal neuronal loss and mossy fiber sprouting in the supragranular layer of the dentate gyrus were observed.

CONCLUSIONS

The SRSs observed in this study may be associated with the TsTx-induced SE and brain damage. All animals injected with the toxin showed massive pyramidal neuronal loss in the dorsal hippocampus as well as intense gliosis and atrophy. Mossy fiber sprouting in the supragranular layer of the dentate gyrus was observed in those animals that had SRSs. The effects observed may be due, at least in part, to TsTx-enhanced release of glutamate in hippocampal pathways.