Vasopressinergic hypothalamic neurons are recruited during the audiogenic seizure of WARs.

The Wistar Audiogenic Rat (WAR) is a genetic model of reflex epilepsy with seizures induced by high-intensity sound stimulation (120 dB SPL). In spite of the known neural substrates involved in WAR seizure phenotype, neuroendocrine hypothalamic neurons were never investigated. In this work, AVP immunohistochemistry in the hypothalamus and radioimmunoassay (RIA) in plasma and in hypothalamic and hypophysial tissues were performed on both controls and WARs in order to evaluate the dynamics of AVP release due to seizure induction. Susceptible animals (WARs) displayed at least tonic-clonic convulsions followed by clonic spasms, while resistant Wistar rats (R) had no convulsive behavior. Animals were sacrificed at 3 instances: basal condition (without stimulus) and at 3 and 10 min after sound stimulation. For the immunohistochemistry AVP study, brains were harvested and processed by the avidin-biotin-peroxidase detection method. Optic densitometry was used for quantifying AVP labeling in supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei. SON presented higher densitometry levels (%D--relative to background) for both WARs and R when compared to PVN. Nevertheless, both nuclei presented a marked decrease, referenced to basal levels, in %D for WARs at 3 min (approximately 35%) against a discrete change for R (approximately 90%). RIA results were significantly higher in the hypophysis of WARs when compared to R rats, at 3 min. Also, at 3 min, plasma AVP in WARs (89.32 +/- 24.81 pg/mL) were higher than in R (12.01 +/- 2.39 pg/mL). We conclude, based on the AVP releasing profiles, that vasopressinergic hypothalamic neurons are recruited during the audiogenic seizure of WARs.

Dipyrone, a novel anticonvulsant agent? Insights from three experimental epilepsy models.

Dipyrone, a non-steroidal anti-inflammatory agent, was anticonvulsant in three experimental epilepsy models. At a dose of 300 mg/kg i.p., dipyrone blocked the maximal hind limb extension in the electroshock model in Wistar rats, the tonic-clonic component of acute sound-induced seizures and the limbic component of audiogenic kindling in genetically susceptible Wistar-derived rats, all in 100% of the animals. In the electroshock model higher doses (400 and 500 mg/kg) were also effective but lower doses (100 and 200 mg/kg) were not. In this model dipyrone had no effect on the recovery of the righting reflex and intensified the postictal antinociception in a dose-dependent manner. Other non-steroidal anti-inflammatory agents such as indomethacin, diclofenac and aspirin had no anticonvulsant effect in the electroshock-induced seizures.

Midbrain substrates of audiogenic seizures in rats.

Audiogenic seizures (AS) are a rodent model of generalized tonic-clonic seizures, induced in susceptible (S) animals by high intensity (110 dB) acoustic stimulation. Resistant (R) animals do not respond to the sound with any seizure-related behavior, but they display facial automatisms and grooming clusters. Genetic selection and neuroethology are the basic tools used in our laboratory to perform behavioral analysis of AS S and R animals. Based upon selective lesion and microinjection (GABA, clobazam, NMDA) studies of substantia nigra (SN), inferior colliculus (IC), superior colliculus (SC), and on specific knife cuts at midcollicular levels, we have suggested differential roles for these substrates in the origin and spreading of AS. The IC central nucleus is suggested to be the most critical area involved in the afferent pathway whose activation is necessary for AS origin. IC cortical nuclei seem to be the most important structures involved in the transduction of sensory to motor activity. SC, SN and other reticular subnuclei are suggested to be modulators or components of the efferent pathway. Although the midbrain is considered to be the only network necessary for acute AS origin, both emotion-linked acoustic memories and plastic changes linked to audiogenic kindling involve midbrain-forebrain connections. This paper reviews the behavioral manifestations of acute and chronic AS, our contribution to the knowledge of some AS neurobiological midbrain substrates and the suggested implications of midbrain-forebrain interactions typical of AS kindling.

New insights into behavioral evaluation of audiogenic seizures. A comparison of two ethological methods.

Wistar male rats were tested for susceptibility to audiogenic seizures (AS) and classified into sensitive (S) and resistant (R) groups by means of a severity index (SI). Susceptible animals were those which displayed wild running behavior (gyri, jumping and atonic falling) followed by generalized tonic-clonic seizures and consequently had an SI = 0.85 (maximum; n = 10). Resistant animals were considered those with no convulsive response to the acoustic stimulation having an SI = 0 (n = 10). Behavioral sequences of susceptible and resistant animals were recorded and analyzed using two ethological methods which basically considered behavior item frequency and statistical interactions of sequential patterns. Both methods include the concept of cluster analysis but do not include a simultaneous analysis of behavior frequency and time spent in each behavior. Thus, a third method is proposed to graphically display both frequency and temporal patterns in a more complex cluster analysis. The methods discussed here allow comparisons of behavioral sequences in a given experimental situation such as susceptible against resistant animals, acute and chronic seizures, comparison of pre- and postdrug effects, etc. Consequently, they may be the micro-behavioral substrate for correlation with contemporary molecular analysis of epileptic seizures.

Zinc, magnesium and copper profiles in three experimental models of epilepsy.

Trace metals are involved in the mechanisms of CNS excitability, including epilepsy. In this study, atomic absorption spectrophotometry was used to determine concentrations of Mg(2+), Cu(2+) and Zn(2+) in plasma (microg/ml) and hair (microg/g) samples. Differential profiles of trace metals were detected in rats displaying three different kinds of seizures, i.e. acute audiogenic seizures (generalized tonic-clonic type GTC) and audiogenic kindling (limbic type; LS) in Wistar Audiogenic Rats (WARs) and electroshock-induced seizures (ES) in Wistar non-epileptic rats (resistant). Significantly lower Zn(2+) concentrations were observed in the plasma of WARs (0.80+/-0.02) compared with resistants (0.89+/-0.03) in the basal (non-seizing) condition. After GTC, WARs showed lower Zn(2+) levels (0.64+/-0.12) while both Mg(2+) (12.56+/-1.51) and Cu(2+) (0.81+/-0.14) were higher than in non-seizing WARs. After ES-induced seizures only Mg(2+) changed, being higher than in the basal condition (11.78+/-2.25 and 8.90+/-0.95). In hair, basal levels of Mg(2+) and Cu(2+) (192.49+/-36.73 and 13.33+/-1.76) were higher whereas Zn(2+) (136.53+/-15.67) was lower in WARs than in resistants. WARs submitted to 0, 3 and 25 stimuli presented higher Mg(2+) concentrations as the number of stimuli increased. In animals receiving the same number of stimuli, Zn(2+) levels were higher for animals displaying GTC (151.09+/-5.53) than those displaying LS (128.07+/-8.51). In conclusion, seizure type (limbic or generalized tonic-clonic) and number of stimuli seem to be the determinant factors for changes in Zn(2+) and Mg(2+) levels, respectively.

Assessment of the seizure susceptibility of Wistar Audiogenic rat to electroshock, pentyleneterazole and pilocarpine.

This work evaluates the seizure susceptibility of nai;ve female Wistar Audiogenic rats (WARs), a genetic model of reflex epilepsy in which seizures are induced by high-intensity sound stimulation (120 dB SPL), to other pro-convulsive stimuli: transauricular electroshock (ES), pentylenetetrazole (PTZ) and pilocarpine (PILO). Normal Wistar rats from the main breeding stock of the Institute of Biological Sciences, UFMG were taken as controls. Electroshock seizures were induced through a pair of ear-clip electrodes (10 mA, at a frequency of 60 Hz, applied for 1 s). In order to test WAR susceptibility to chemically induced seizures, animals were treated either with PTZ (37.5 mg/kg i.p.) or PILO (200, 270 and 300 mg/kg i.p.). Seizure severity was evaluated by appropriate behavioral severity index scales (SI) specific to each epilepsy model and tested for statistical significance using the non-parametric Mann-Whitney Rank Sum test. Results show a significantly greater susceptibility of WARs for ES (SI(WAR)=3+/-3/3, SI(Wistar)=1+/-1/1; median+/-interquartile range 25%/75%, P<0.01) and PTZ (SI(WAR)=4+/-4/4, SI(Wistar)=1+/-1/4; median+/-interquartile range 25%/75%, P<0.02), as indicated by significantly higher SI scores and shorter latencies for seizure onset (T(WAR)=71+/-7 s, T(Wistar)=94+/-8 s; P<0.05 Student t-test, mean+/-S.E.M.). Although PILO also caused higher SI scores in WARs (WAR(200 mg)=1+/-1/1, Wistar(200 mg)=1+/-1/1; WAR(270 mg)=1.5+/-1/2, Wistar(270 mg)=1+/-1/1.25; WAR(300 mg)=9+/-1/9, Wistar(300 mg)=4+/-1.5/7.5; median+/-interquartile range 25%/75%), statistically significant differences were not observed. In conclusion, our results show that WARs have an inherited broader predisposition for seizures.

Involvement of prolactin, vasopressin and opioids in post-ictal antinociception induced by electroshock in rats.

The neurochemical mechanisms involved in post-ictal antinociception remain to be elucidated. Application of electroconvulsive shock (ECS) to rats results in post-ictal antinociception. The objective of this study was to identify endogenous substances that could participate in antinociception during post-ictal depression induced by ECS (70 mA, 60 Hz, 1 s). Antinociception was measured by the rat paw-pressure test, in which increased sensitivity is induced by intraplantar injection of carrageenan. This test proved to be efficient in detecting the electroshock-induced antinociception. Intense post-ictal antinociception was observed over a period of 30 min after the end of the seizure. It was used nonspecific opioid and specific vasopressin antagonists and the prolactin (PRL) release inhibitor to test the reversal of antinociception. Administration of naloxone (5, 7.5 and 10 mg/kg) blocked the post-ictal antinociception. The V(1) (125 microg/kg) and V(2) (250 microg/kg) vasopressin receptor antagonists ([beta-mercapto-beta,beta-cyclopentamethylenepropionyl(1),O-Et-Tyr(2),Val(4),Arg(8)]-vasopressin and [adamantaneacetyl(1),O-Et-d-Tyr(2),Val(4),Abu(6),Arg(8,9)]-vasopressin) also inhibited the nociceptive response. The antinociception blockade was more intense after administration of the V(1) receptor antagonist. Bromocriptine (4, 8 and 12 mg/kg) was able to reverse antinociception behavior during the post-ictal period. Morphine (1, 2 and 4 mg/kg), vasopressin (12.5, 100 and 400 microg/kg) and prolactin (100, 200 and 400 microg/kg) administration promoted a higher nociceptive threshold. It was administered the three substances with their respective antagonists to verify the opioidergic pathway and vasopressin and prolactin release interactions, and as a positive control. We observed that the tested mediators were released in an independent manner, indicating no interference in which other.

Effect of lactation on the expression of audiogenic seizures: association with plasma prolactin profiles.

Female Wistar rats and Wistar audiogenic rats (WARs) were used to investigate the potential roles of prolactin (PRL) and progesterone in the modulation of seizure expression. Animals were screened for seizure severity in both groups. All WARs at least displayed tonic-clonic convulsions followed by clonic spasms (TC) whereas none of the Wistar rats displayed seizures (Resistant). After seizures the plasma level of PRL in nulliparous female WARs increased about 8-fold compared to their basal levels and to the levels of Resistant animals. This value was still significantly higher than basal levels 15 min later. Lactation produced a decrease in the TC proportion in seizures in WARs both with and without pups. Two sub-populations of animals could be characterized: one that had TC suppressed (low seizure severity; LSS) and one that did not (high seizure severity; HSS). In animals of the LSS subgroup, either with or without pups, seizure severity decreased gradually and lowest values were seen on the 30th day after delivery. The temporal profile of plasma PRL during a 90-min period of suckling without sound stimulation showed significantly higher levels for LSS, the HSS levels being similar to those of the Resistant group. A progressive decrease in the group means for progesterone plasma concentration between the 9th and 29th days of lactation was detected in Resistant rats (P<0.05) but not in WARs. No significant differences between groups were revealed by comparison of the overall means. Taken together these data confirm the presence of a clear-cut post-ictal PRL peak after TC with a decrease in seizure severity in female WARs with and without pups. An eventual long-term role of PRL in modulating seizure activity might be related to the multifactorial physiological conditions of both pregnancy and lactation.

A microdialysis study of amino acid concentrations in the extracellular fluid of the substantia nigra of freely behaving GEPR-9s: relationship to seizure predisposition.

Substantia nigra (SN) is known to play an important role in seizure generalization. Both excitatory and inhibitory neurotransmitters can modulate this role of SN. Previous studies have shown that GABA as well as aspartate and glutamate participate in seizure regulation through this site. Evidence for such a role comes from studies on the genetically epilepsy-prone rat (GEPR) and other seizure models. In the GEPR, bilateral microinjections of NMDA receptor antagonists in SN block or reduce seizure severity. In order to further evaluate which neurotransmitters are specifically involved at the SN level of seizure regulation in the GEPR, we undertook a microdialysis study of K+ stimulated release of amino acids in the SN of GEPR-9s- and non-epileptic controls. A 1 mm loop-type microdialysis probe was inserted through pre-implanted guides into the SN of awake and freely moving rats (seven GEPR-9s and four non-epileptic controls), and used to perfuse a 100 mM K+ (high K+) solution for 2 h. Four 30 microliters samples were collected prior to high K+ stimulation (basal release), during high K+ perfusion, and after high K+ infusion. After precolumn derivatization with phenylisothiocyanate, levels of aspartic (ASP) and glutamic (GLU) acids, glycine (GLY), taurine (TAU) and GABA were measured by reversed phase high performance liquid chromatography. Two hours after the initiation of high K+ infusion, the increases relative to basal were, for non-epileptic controls, 35%, 74%, 68%, 847% and 283% respectively for ASP, GLU, GLY, TAU and GABA. Corresponding increases for GEPR-9s were 14%, 10%, 41%, 505% and 123% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential audiogenic seizure sensitization by selective unilateral substantia nigra lesions in resistant Wistar rats.

Evaluation of the participation of different substantia nigra sites in the sensitization of resistant (R) animals to audiogenic seizures (AS), was performed after series of small (5 mC; n = 28), medium (10 mC; n = 57) and large (15 mC; 3 points of 5 mC each, n = 19) unilateral electrolytic lesions of the substantia nigra (SN) in R rats. Animals were evaluated at 5, 10, 15, and 30 days post surgery and behavior was measured by a neuroethological method. Small unilateral lesions induced AS susceptibility in 14% R animals with 3% of them displaying tonic-clonic AS. Medium sized lesions induced AS susceptibility in 50% of the animals with 18% of these exhibiting tonic-clonic seizures similar to those displayed by naturally susceptible (S) animals, but with predominance of wild running (gyri, jumping and atonic falling) contralateral to the lesioned SN. AS severity was significantly higher at day 5 postsurgery, decreasing at days 10, 15 and 30. Large unilateral lesions destroying the entire SN failed to cause tonic-clonic seizures although wild running occurred in 10% of the animals. Bilateral large SN lesions (15 mC; n = 24) did not modify AS severity in S animals, but only induced a statistically significant increase in the AS latency. The present data suggest: (i) AS severity after SN lesions is not a linear function of the lesion size; (ii) functionally different and antagonistic AS related substrates may exist in the SN; (iii) neurochemical and hodological characterization of these areas should be important for a better understanding of their role in AS.

Reduction of streptomycin-induced acute and chronic toxicities.

The acute and chronic toxicities of streptomycin sulfate (SS) and of the streptomycin hydrochloride-calcium chloride complex (SCC) were compared. The LD50 determined in mice was significantly higher for SCC than for SS. Chronic toxicity was evaluated by recording the nystagmus induced by damped torsion pendulum in rabbits. SS and SCC treatments (200 mg/kg intramuscularly of absolute streptomycin base) decreased the duration, the maximal frequency, and the total number of beats of nystagmus. However, SCC-induced changes were significantly lower than SS-induced ones. The extent of the lesion in the crista ampullaris was evaluated by light and electron microscopy and was correlated with the electrophysiological findings. Because the authors also demonstrated that there are no differences in the antibacterial effects of these salts, SCC may have a place in long-term streptomycin treatment.

Audiogenic and audiogenic-like seizures: locus of induction and seizure severity determine postictal prolactin patterns.

Audiogenic seizures (AS) are a model of generalized tonic-clonic seizures, evoked by high-intensity (110 dB) acoustic stimulation evaluated by means of behavioral severity indexes (SI). Postictal prolactin (PRL) is a marker of generalized seizures, both in animals and humans. Thus, in the present work we assayed postictal PRL in a) male Wistar AS susceptible (S, n = 5) and AS resistant (R, n = 13) rats made susceptible by specific midbrain lesions. b) In rats electrically stimulated in the central nucleus (CN) of the inferior colliculus (IC) (n = 20), or the cortical IC (CxIC, n = 18). In c) S rats pretreated with either bromocriptine (BRO; 4 mg/kg; SC), a PRL release inhibitor, or vehicle (V), 30 min before the electrical stimulation. Basal PRL was 2-10 ng/ml at time 0. In the S group, only animals with generalized seizures presented a postictal PRL elevation between 5 and 15 min (60-90 ng/ml; p < 0.05). R rats displayed a discrete PRL response lower than that of S animals. CxIC stimulation produced more severe seizures and greater postictal PRL enhancement than CNIC stimulation, always raising at 5-15 min (p < 0.01). BRO blocked the PRL increase even in the presence of higher seizure scores (p < 0.02). The positive correlation between seizure intensity (SI values), site of initiation (central or cortical IC nuclei), and postictal PRL patterns makes this a reliable model for studying the neurochemistry of the postictal phase and the interaction between hormones and epilepsy.

Do endogenous opioids and nitric oxide participate in the anticonvulsant action of dipyrone?

It was previously reported that systemic administration of dipyrone inhibited the tonic component of generalized tonic-clonic seizures in both the electroshock and the audiogenic seizure models. The aim of the present study was to investigate the mechanisms involved in the anticonvulsant action of dipyrone by assessing the role of nitric oxide and opioids in the electroshock (female 60- to 90-day-old Wistar rats, N = 5-11) and audiogenic seizure (female 60- to 90-day-old Wistar audiogenic rats, N = 5-11) models of epilepsy. Naloxone (5 mg/kg, sc) significantly reversed the anticonvulsant effect of dipyrone in rats submitted to the induction of audiogenic seizures (ANOVA/Bonferroni's test), suggesting the involvement of opioid peptides in this action. In the electroshock model no reversal of the anticonvulsant effect of dipyrone by naloxone (5 mg/kg, sc) was demonstrable. The acute (120 mg/kg, ip) and chronic (25 mg/kg, ip, twice a day/4 days) administration of L-NOARG did not reverse the anticonvulsant action of dipyrone in the audiogenic seizure model, suggesting that the nitric oxide pathway does not participate in such effect. Indomethacin (10, 20 and 30 mg/kg, ip) used for comparison had no anticonvulsant effect in the audiogenic seizure model. In conclusion, opioid peptides but not nitric oxide seem to be involved in the anticonvulsant action of dipyrone in audiogenic seizures.

Anticonvulsant and antiarrhythmic effects of nifedipine in rats prone to audiogenic seizures.

Calcium ion participates in the regulation of neural transmission and the presynaptic release of neurotransmitters. It is also involved in epileptic events, cardiac arrhythmias and abnormal conduction of stimuli. The purpose of the present study was to evaluate the effects of nifedipine, a calcium channel blocker, on epileptic seizures and on reperfusion arrhythmias in rats prone to audiogenic epileptic seizures (Wistar audiogenic rats, WAR) and in normal Wistar rats (N = 6/group). The seizure severity index was applied after an intraperitoneal injection of 20 or 40 mg/kg nifedipine (N20 and N40 groups, respectively). The Langendorff technique was used to analyze cardiac function, as well as the incidence and severity of the reperfusion arrhythmias after ligature and release of the left coronary artery in rats treated or not with nifedipine. We found that nifedipine treatment decreased seizure severity (0.94 ± 0.02 for WAR; 0.70 ± 0.10 for WAR + N20; 0.47 ± 0.08 for WAR + N40) and increased the latent period (13 ± 2 s for WAR; 35 ± 10 s for WAR + N20; 48 ± 7 s for WAR + N40) for the development of seizures in WAR. Furthermore, the incidence and severity of the reperfusion arrhythmias were lower in WAR and normal Wistar rats injected with nifedipine. In WAR, these effects were mediated, at least in part, by a decrease in heart rate. Thus, our results indicate that nifedipine may be considered to be a potential adjuvant drug for epilepsy treatment, especially in those cases associated with cardiac rhythm abnormalities.

Reduced hippocampal GABAergic function in Wistar audiogenic rats.

Epilepsy is a neurological disorder associated with excitatory and inhibitory imbalance within the underlying neural network. This study evaluated inhibitory γ-amino-butyric acid (GABA)ergic modulation in the CA1 region of the hippocampus of male Wistar rats and Wistar audiogenic rats (aged 90 ± 3 days), a strain of inbred animals susceptible to audiogenic seizures. Field excitatory postsynaptic potentials and population spike complexes in response to Schaffer collateral fiber stimulation were recorded in hippocampal slices before and during application of picrotoxin (50 µM, 60 min), a GABA A antagonist, and the size of the population spike was quantified by measuring its amplitude and slope. In control audiogenic-resistant Wistar rats (N = 9), picrotoxin significantly increased both the amplitude of the population spike by 51 ± 19% and its maximum slope by 73 ± 21%. In contrast, in slices from Wistar audiogenic rats (N = 6), picrotoxin caused no statistically significant change in population spike amplitude (33 ± 46%) or slope (11 ± 29%). Data are reported as means ± SEM. This result indicates a functional reduction of GABAergic neurotransmission in hippocampal slices from Wistar audiogenic rats.

Anticonvulsant and antiarrhythmic effects of nifedipine in rats prone to audiogenic seizures

Calcium ion participates in the regulation of neural transmission and the presynaptic release of neurotransmitters. It is also involved in epileptic events, cardiac arrhythmias and abnormal conduction of stimuli. The purpose of the present study was to evaluate the effects of nifedipine, a calcium channel blocker, on epileptic seizures and on reperfusion arrhythmias in rats prone to audiogenic epileptic seizures (Wistar audiogenic rats, WAR) and in normal Wistar rats (N = 6/group). The seizure severity index was applied after an intraperitoneal injection of 20 or 40 mg/kg nifedipine (N20 and N40 groups, respectively). The Langendorff technique was used to analyze cardiac function, as well as the incidence and severity of the reperfusion arrhythmias after ligature and release of the left coronary artery in rats treated or not with nifedipine. We found that nifedipine treatment decreased seizure severity (0.94 ± 0.02 for WAR; 0.70 ± 0.10 for WAR + N20; 0.47 ± 0.08 for WAR + N40) and increased the latent period (13 ± 2 s for WAR; 35 ± 10 s for WAR + N20; 48 ± 7 s for WAR + N40) for the development of seizures in WAR. Furthermore, the incidence and severity of the reperfusion arrhythmias were lower in WAR and normal Wistar rats injected with nifedipine. In WAR, these effects were mediated, at least in part, by a decrease in heart rate. Thus, our results indicate that nifedipine may be considered to be a potential adjuvant drug for epilepsy treatment, especially in those cases associated with cardiac rhythm abnormalities.

Reduced hippocampal GABAergic function in Wistar audiogenic rats

Epilepsy is a neurological disorder associated with excitatory and inhibitory imbalance within the underlying neural network. This study evaluated inhibitory γ-amino-butyric acid (GABA)ergic modulation in the CA1 region of the hippocampus of male Wistar rats and Wistar audiogenic rats (aged 90 ± 3 days), a strain of inbred animals susceptible to audiogenic seizures. Field excitatory postsynaptic potentials and population spike complexes in response to Schaffer collateral fiber stimulation were recorded in hippocampal slices before and during application of picrotoxin (50 µM, 60 min), a GABA A antagonist, and the size of the population spike was quantified by measuring its amplitude and slope. In control audiogenic-resistant Wistar rats (N = 9), picrotoxin significantly increased both the amplitude of the population spike by 51 ± 19 percent and its maximum slope by 73 ± 21 percent. In contrast, in slices from Wistar audiogenic rats (N = 6), picrotoxin caused no statistically significant change in population spike amplitude (33 ± 46 percent) or slope (11 ± 29 percent). Data are reported as means ± SEM. This result indicates a functional reduction of GABAergic neurotransmission in hippocampal slices from Wistar audiogenic rats.

Quantitative study of the response to genetic selection of the Wistar audiogenic rat strain (WAR).

To study the relationship between genetics and epilepsy, Wistar rats susceptible to audiogenic seizure were selected from the main breeding stock of the Ribeirão Preto School of Medicine at the University of São Paulo, Brazil, and inbred. The criteria for selection were the highest seizure severity index (SI) and shortest latencies of the first running fit (LI). Because behavioral response to sound stimulation (120 dB) at 70 to 78 days of age was very stable, SI and LI were evaluated within this age range. Analysis of 9450 observations in 1575 animals from the 3rd to 17th generations demonstrated significant effects of generation, parity, and litter on SI and of generation and litter on LI. The SI and LI averages were, respectively, 37.13 and 22.82 s in the 3rd generation and 83.06 and 7.84 in the 17th generation. Heritabilities of both characters were estimated, by maximum likelihood, as 0.37 +/- 0.066 and 0.44 +/- 0.059, respectively. Because a significant regression related individual breeding values for both SI and LI to generation number, we concluded that genetic selection has a positive impact on the traits analyzed. Therefore, the Wistar audiogenic rat (WAR) strain appears, as per the 17th to 20th generations of genetic selection to be an audiogenic rat strain suitable for epilepsy studies.

Do endogenous opioids and nitric oxide participate in the anticonvulsant action of dipyrone?

It was previously reported that systemic administration of dipyrone inhibited the tonic component of generalized tonic-clonic seizures in both the electroshock and the audiogenic seizure models. The aim of the present study was to investigate the mechanisms involved in the anticonvulsant action of dipyrone by assessing the role of nitric oxide and opioids in the electroshock (female 60- to 90-day-old Wistar rats, N = 5-11) and audiogenic seizure (female 60- to 90-day-old Wistar audiogenic rats, N = 5-11) models of epilepsy. Naloxone (5 mg/kg, sc) significantly reversed the anticonvulsant effect of dipyrone in rats submitted to the induction of audiogenic seizures (ANOVA/Bonferroni's test), suggesting the involvement of opioid peptides in this action. In the electroshock model no reversal of the anticonvulsant effect of dipyrone by naloxone (5 mg/kg, sc) was demonstrable. The acute (120 mg/kg, ip) and chronic (25 mg/kg, ip, twice a day/4 days) administration of L-NOARG did not reverse the anticonvulsant action of dipyrone in the audiogenic seizure model, suggesting that the nitric oxide pathway does not participate in such effect. Indomethacin (10, 20 and 30 mg/kg, ip) used for comparison had no anticonvulsant effect in the audiogenic seizure model. In conclusion, opioid peptides but not nitric oxide seem to be involved in the anticonvulsant action of dipyrone in audiogenic seizures

Epilepsia experimental: da análise comportamental à biologia molecular / Experimental epilepsy: behavioral analysis to molecular biology

A epilepsia é uma patologia neurológica que afeta milhöes de pessoas em todo o mundo, sendo que 25 por cento destes, continuam apresetnado convulsöes, apesar do tratamento medicamentoso. Nas últimas décadas tem ocorrido um desenvolvimento importante nas pesquisas na área da fisiopatologia das epilepsias, mas seus mecanismos moleculares ainda säo desconhecidos. Ainda é difícil correlacionar aspectos clínicos das epilepsias com mecanismos neurais, porque o progresso nas técnicas de biologia molecular näo foram seguidos por uma evoluçäo concomitante da análise comportamental. Este trabalho tem como objetivo revisar a avaliaçäo comportamental nas pesquisas sobre epilepsia e sua correlaçäo com a biologia molecular