Phospholipases A2 isolated from Micrurus lemniscatus coral snake venom: behavioral, electroencephalographic, and neuropathological aspects.

The present study evaluated four phospholipase A2 (PLA2) (Mlx-8, Mlx-9, Mlx-11 and Mlx-12) isolated from Micrurus lemniscatus snake venom (Elapidae). The effects of intrahippocampal administration of these toxins have been determined on behavior, electroencephalography, and neuronal degeneration in rats. These four PLA2 toxins induced motor and EEG alterations in a dose-dependent manner. Behavioral convulsions were characterized by clonic movements and were often accompanied by EEG alterations. Mlx toxins were convulsive but weakly epileptogenic, since low rates of seizure discharges were observed in EEG records. Neuronal injury seemed to depend on the dose of the toxin used. The highest doses of toxins caused severe intoxication and death of some animals. The injury of hippocampal cells was characterized by massive neuronal loss and hippocampal gliosis. A high occurrence of compulsive scratching was observed. Moreover, the onset of seizures induced by Mlx toxins was markedly delayed. The similarities between the effects of Mlx PLA2s and those isolated from other Elapidae snakes venoms suggest that their toxicity are probably due to their specific binding to neuronal membranes and to the catalysis of phospholipid hydrolysis, producing lysophospholipids and fatty acids. These compounds likely disturb the membrane conformation, causing a marked increase in the release of neurotransmitters and concurrent inhibition of vesicle fission and recycling. These toxins can be a useful tool to investigate properties of endogenous secretory PLA2s and therefore may be important both to study mechanisms involved in neurotransmitter release at nerve terminals and to explain the convulsive properties of PLA2s toxins.

TsTx toxin isolated from Tityus serrulatus scorpion venom-induced spontaneous recurrent seizures and mossy fiber sprouting.

PURPOSE: TsTx is a scorpion alpha-type toxin that binds to site 3 of the Na+ channels in a voltage-dependent mode, slowing or blocking the inactivation mechanism of these channels (Possani et al., Eur J Biochem 1999). This binding increases depolarization time of the channel and consequently induces excessive neurotransmitter release. Previously we reported that hippocampal injection of TsTx induces clonic convulsions, electrographic seizures, and hippocampal damage. This investigation was designed to characterize the long-term behavioral, electroencephalographic (EEG), and histopathologic features after a single TsTx injection into the rat hippocampus. METHODS: Cannulas and electrodes were stereotaxically implanted in the CA1 dorsal hippocampus of rats. Three days after surgery, the animals were injected into the hippocampus with 1 microl of TsTx, 2 microg (n = 9) or 0.1 M phosphate buffer (n = 5). After injection, EEG records and behavioral observations were made during 10 h. For a period of 4 months, the animals were observed through direct visual observation for 8 h/day, 5 days/week for occurrence of convulsive seizures. At the end of the experiment, the animals were processed for histologic analyses. Sections 40- and 20-microm thick were stained according to neo-Timm or Nissl methods, respectively. Cell counts in the cresyl violet-stained sections were performed within the hippocampal pyramidal cell layers (CA1, CA3, and CA4) and granule cell of the dentate gyrus. RESULTS: Fifteen minutes after TsTx injection, facial automatisms, rearing, masticatory jaw movements, sniffing, and wet-dog shakes were observed. In approximately 1 h, limbic convulsions characterized by forelimb clonus, rearing, and falling after generalized clonic convulsion with jumping, wild running, and falling were observed. EEG showed isolated spikes and clusters of spikes that started in the hippocampus and evolved to the cortex, isolated seizures, and epileptic discharges delayed 1-2 min. These recurred repeatedly characterizing the status epilepticus (SE). SE was characterized in 77.5% of animals. Seizures were no longer observed 24 h after the injection. Spontaneous recurrent seizures (SRSs) occurred 31-49 days after TsTx injection. All animals that showed SE in the acute period developed SRSs. Facial myoclonus, generalized clonus, forelimb clonus, rearing, and falling characterized the seizures. The seizure frequency was 1-2 per animal per week. All rats injected with TsTx had significantly fewer cells in CA1, CA3, and CA4 subfield of the hippocampal formation compared with the animals of the control group (p < 0.05, analysis of variance, followed by Tukey test). Neo-Timm-positive granules, normally absent in the supragranular layer, were present in dentate gyrus of rats with TsTx-induced SRSs. CONCLUSIONS: Our results suggest that SRSs observed in this study may be a consequence of the TsTx-induced SE. All animals injected with the toxin showed massive neuronal loss in the hippocampal subfields CA1, CA3, and CA4, but only those that had SRSs showed mossy fiber sprouting in the supragranular layer of the dentate gyrus. This shows synaptic reorganization that also is observed in human epileptogenic tissue. These results indicate that TsTx toxin may be a useful tool for studies on neuronal lesions and/or experimental epilepsy. Studies on the mechanisms involved are under investigation.

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

TsTx is a scorpion á-type toxin that binds to site 3 of the Na+ channels in a voltage-dependent mode, slowing or blocking the inactivation mechanism of these channels (Possani et al., Eur J Biochem 1999). This binding increases depolarization time of the channel and consequently induces excessive neurotransmitter release. Previously we reported that hippocampal injection of TsTx induces clonic convulsions, electrographic seizures, and hippocampal damage. This investigation was designed to characterize the long-term behavioral, electroencephalographic (EEG), and histopathologic features after a single TsTx injection into the rat hippocampus.

Convulsive effects of some isolated venom fractions of the Tityus serrulatus scorpion: behavioral, electroencephalographic, and neuropathological aspects

It has been previously shown that the crude venom of Tityus serrulatus can cause convulsions. This study was designed to investigate the neurotoxic effects of B, C, G, and K fractions isolated from this venom. Intravenous injection of these fractions in mice (0.6 - 6.0 mg/kg body weight) showed that the C fraction is a potent convulsant and G fraction decreased the threshold for tonic hand limb extension elicited by transauricular electroshock. Unilateral injection of B, C, and K fractions, but not G fraction, into the spikes and epileptic discharges that began in the hippocampus and evolved to the cortex. The following motor signs were observed: movements of facial muscles, wet dog shake, immobility, myoclonus, wild-running with clonus, and in some cases, loss of postural control. Intrahippocampal injection of B, C, and K fraction, but not G fraction, caused neuronal loss at the injection site as well as in other hippocampal areas. The effect of these fractions on epileptiform activity and on neuronal loss was dose-dependent. The severity of the epileptiform activity in the ipsilateral hippocampus correlated with the severity of the neuronal loss. The electrographic, behavioral, and histological changes induced by b, C, and K fractions were similar to those obtained with other drugs that are commonly used to induce convulsion. The convulsant effects of the crude venom may be caused by the fractions studied in this work.

Effect of manipulation of the GABA system on dopamine-related behaviors

The interaction between GABAergic and dopaminergic system within the central nervous system was investigated in rats using the open-field apparatus and apomorphine-induced stereotypy, and in mice using haloperidol-induced catalepsy. The single intraperitoneal adminsitration of baclofen 3.0 mg/kg, 4,5,6,7-tetrahydroisoxasolo-(5,4-c) piridin-3-ol (THIP) 10.0 mg/kg and picrotoxin 2.0 mg/kg decreased both ambulation and rearing frequencies of the rats in the open-field; only the GABA agonists increased the duration of animal immobility. THIP (10.0 mg/kg) increased the duration of haloperidol-induced catalepsy. For apomorphine-induced stereotypy, baclofen 3.0 mg/kg and picrotoxin 1.0 mg/kg induced a significant leftward displacement of the control dose-response curve constructed for apomorphine (0.1-10 mg/kg) in relation to the control. In addition, baclofen, THIP, picrotoxin and 3-mercaptopropionic acid (3-MPA) 10.0 mg/kg decreased both rearing and sniffing behaviors elicited by apomorphine and increased licking and/ or gnawing. Different mechanisms seem to be involved in the similar effects induced by GABA agonists and antagonists. Picrotoxin induced stereotyped movements per se with a dose-dependent effect, but baclofen and THIP did not. The present data suggest that GABA manipulation facilitates the progressive activation of the different dopaminergic pathways involved in stereotyped behaviors, thus increasing those stereotyped components (gnawing and licking) that appear after a high level of activation of dopaminergic pathways

Effects of Tityus serrulatus crude venom on the gabaergic and dopaminergic systems of the rat brain

This study was designed to investigate the effect of T. serrulatus scorpion venom on dopamine (DA) and gamma amino butyric acid (GABA) concentrations in different regions of the brain. The ratio of homovanillic acid (HVA) to DA, and the glutamic acid decarboxylase (GAD) activity were determined following intravenous or intracerebral venom injections. The increase in the HYA/DA ratio in the striatum after i.v. or intrastriatal injection could indicate an increase in DA turnover. One hour after i.v. injection of the venom GAD activity was shown to be decreased in the striatum and hypothalamus. After 24 hr GAD activity increased in the striatum and decreased in the hypothalamus and brain stem. These results could indicate different effects of the venom on the GABA system in different areas of the brain. After intrastriatal injection of the scorpion venom, the animals showed stereotyped behavior and rotation activity. Following intrahippocampal injection, myoclonus and orofacial automatisms, which constitute pro-convulsive signals, were observed. These behavioral alterations could be, at least in part, related to the GABA and dopamine alterations caused by the venom, since stereotypy, circling behavior and convulsions are dependent on dopamine and/or GABA.

Behavioural and electroencephalographic effects of Tityus serrulatus scorpion venom in rats

This study was designed to investigate the convulsant effects of T. serrulatus scorpion venom in rats. Pretreatment of rats with venom increased the minimum convulsant dose of picrotoxin, impaired convulsion generalization and displaced to the left the dose-response curve for picrotoxin. It also decreased the intensity but prolonged the duration of seizures caused by pentylenetetrazol injection. Microinjection of the venom into the dorsal hippocampus induced behavioural alterations and epileptiform waves int he EEG. Venom also altered the threshold for, and intensity of, convulsions induced in different experimental models of epilepsy. Different fractions of the venom may be responsible for these different effects. Therefore, purification of venom toxins is necessary for the complete understanding of the present results.

Behavioral aspects of GABAergic-dopaminergic interactions in the central nervous system

GABAergic-dopaminergic relationships in rats were analysed quantitatively by means of behavioral studies. Acute and long-term haloperidol administration induced significant leftward displacement of the control dose-response curves for picrotoxin but not those for strychnine or 3-mercaptopropionic acid (3-MPA). Apomorphine given acutely increased the sensitivity of the animal to strychnine but not to picrotoxin or 3-MPA. In animals that presented convulsion a stereotyped gnawing and/or licking behavior was observed immediately after the ictus activity as a consequence of the combined acute administration of haloperidol and picrotoxin. Long-term haloperidol treatment increased the gnawing and/or licking behavior immediately before and/or after the ictus activity induced by picrotoxin (1 and 72 h after haloperidol withdrawal) or 3-MPA (72 h after withdrawal). A possible effect of the drugs employed on the DA-nigroamygdaloid and/or the GABA-striatonigral fiber systems is discussed.

Gabaergic influences on barbital withdrawal induced convulsions

Animals which had been long-term treated with increasing concentrations of sodium barbitalin the drinking water were killed 30 min or 72 hr after the last day of treatment, to determine striatalGABA levels and turnover rate. The effects of pentobarbital administration on GABA metabolism of rats withdrawn or notwithdrawn from barbital were also studied. Barbital withdrawal induced a significant decrease in striatal GABA levels and also in the turnoverrate after pentobarbital treatment.The latter effect was greater in rats killed 72 hr after drug removal. In control animals, pentobarbital treatment increased striatal GABA levels but did not affect theturnover rate. Barbital removal also made the rats less responsive to the effects of pentobarbital on striatal GABAlevels. These results suggest the participation of a central GABAergic system inbarbital withdrawal convulsions.