Low potency and limited efficacy of antiepileptic drugs in the mouse 6 Hz corneal kindling model.

Corneal kindling is a useful alternative to electrically induced amygdala or hippocampal kindling, which requires advanced surgical and EEG techniques that may not be easily available in many laboratories. Therefore the first aim of this study was to evaluate whether repeated 6 Hz corneal stimulation in mice would lead to an increased and persistent seizure response as described for higher frequency (50/60 Hz) corneal kindling. Male NMRI mice stimulated twice daily (except weekends) for 3 s with 6 Hz electrical current at 44 mA displayed robust kindling development, i.e., a progressive increase in seizure severity. The majority of the animals (about 90%) developed a fully kindled state, defined as at least 10 consecutive stage 3-5 seizures within 5 weeks of corneal stimulation. Afterwards, the fully kindled state was maintained for at least 8 weeks with only two days of stimulations per week. Next, the protective efficacy of four mechanistically different antiepileptic drugs (AEDs; clonazepam, valproate, carbamazepine and levetiracetam) was assessed and compared between 6 Hz and 50 Hz fully kindled mice. All tested AEDs showed a relatively lower potency in the 6 Hz kindling model and a limited efficacy against partial seizures was observed with carbamazepine and levetiracetam. We can conclude that 6 Hz kindling may be more advantageous than the previously described 50/60 Hz corneal kindling models due to its robustness and persistence of the fully kindled state. Furthermore, the observed low potency and limited efficacy of AEDs in 6 Hz fully kindled mice suggest that this model could be a useful tool in the discovery of novel AEDs targeting treatment resistant epilepsy.

Expression pattern of synaptic vesicle protein 2 (SV2) isoforms in patients with temporal lobe epilepsy and hippocampal sclerosis.

AIMS: Synaptic vesicle proteins 2 (SV2) are neuronal vesicles membrane glycoproteins that appear as important targets in the treatment of partial and generalized epilepsies. Therefore, we analysed the expression of SV2 isoforms in the hippocampus of patients with temporal lobe epilepsy (TLE). METHODS: SV2A, SV2B and SV2C immunostaining and QuantiGene branched DNA assay were performed on biopsies from 31 consecutive TLE patients with mesial temporal sclerosis (MTS) and compared with 10 autopsy controls. SV2 expression was further compared with Timm's staining, and synaptophysin, Zinc transporter 3 (ZnT3), dynorphin, vesicular glutamate transporter 1 (VGLUT1) and vesicular GABA transporter (VGAT) expression. RESULTS: In TLE patients, SV2A and SV2B expression was decreased in areas of synaptic loss. SV2C, which is weakly expressed or absent in the hippocampus of controls, was overexpressed in 10/11 cases with classical MTS1A and mossy fibre sprouting but not in cases with other types of MTS. SV2C staining was located in the inner molecular layer of the dentate gyrus and colocalized with dynorphin, ZnT3 and VGLUT1, suggesting selective expression in presynaptic glutamatergic Zn(2+) -rich terminals of abnormal sprouting fibres. SV2 expression patterns correlated with histological subtypes of MTS, but not with clinical features or therapeutic regimens in this patient cohort. CONCLUSION: In classical MTS1A, the expression of SV2 isoforms is altered with a marked decrease of SV2A and SV2B paralleling synaptic loss and a selective increase of SV2C in sprouting mossy fibres. These findings suggest a different physiology of sprouting synapses and the possibility to target them with SV2C-specific strategies.

Modulation of the conformational state of the SV2A protein by an allosteric mechanism as evidenced by ligand binding assays.

BACKGROUND AND PURPOSE: Synaptic vesicle protein 2A (SV2A) is the specific binding site of the anti-epileptic drug levetiracetam (LEV) and its higher affinity analogue UCB30889. Moreover, the protein has been well validated as a target for anticonvulsant therapy. Here, we report the identification of UCB1244283 acting as a SV2A positive allosteric modulator of UCB30889. EXPERIMENTAL APPROACH: UCB1244283 was characterized in vitro using radioligand binding assays with [(3)H]UCB30889 on recombinant SV2A expressed in HEK cells and on rat cortex. In vivo, the compound was tested in sound-sensitive mice. KEY RESULTS: Saturation binding experiments in the presence of UCB1244283 demonstrated a fivefold increase in the affinity of [(3)H]UCB30889 for human recombinant SV2A, combined with a twofold increase of the total number of binding sites. Similar results were obtained on rat cortex. In competition binding experiments, UCB1244283 potentiated the affinity of UCB30889 while the affinity of LEV remained unchanged. UCB1244283 significantly slowed down both the association and dissociation kinetics of [(3)H]UCB30889. Following i.c.v. administration in sound-sensitive mice, UCB1244283 showed a clear protective effect against both tonic and clonic convulsions. CONCLUSIONS AND IMPLICATIONS: These results indicate that UCB1244283 can modulate the conformation of SV2A, thereby inducing a higher affinity state for UCB30889. Our results also suggest that the conformation of SV2A per se might be an important determinant of its functioning, especially during epileptic seizures. Therefore, agents that act on the conformation of SV2A might hold great potential in the search for new SV2A-based anticonvulsant therapies.

Brivaracetam does not alter spatial learning and memory in both normal and amygdala-kindled rats.

Several antiepileptic drugs (AEDs) may induce memory deficits when tested in preclinical models at doses that exert significant protection against seizures. Brivaracetam (BRV) is a novel high-affinity SV2A ligand also displaying inhibitory activity at neuronal voltage-gated sodium channels. In the present study we have investigated the effects of BRV, at doses that exerted marked anticonvulsant effects in kindled rats, upon cognitive functioning and memory in both normal and amygdala-kindled rats using place learning version of Morris water maze. In addition the effect of BRV on long-term potentiation (LTP) in rat hippocampal slices has been investigated. BRV (2.1, 6.8 or 21.0mg/kg i.p.) was injected daily, 60min before each session. Results indicated that in both normal and amygdala-kindled rats BRV did not alter the latency to find the hidden platform or swimming speed during the four consecutive days of learning. Similarly, the time spent in the target quadrant, used as a further independent index of spatial memory, was not modified by BRV treatment. Likewise, BRV did not affect the LTP induction in CA1 hippocampal region when tested at 3-30microM concentration range, which had been demonstrated to significantly reduce epileptiform activity in slice models. Based on the results of the present study it can be expected that BRV will not have detrimental effects on hippocampal-dependent cognitive functions in patients with epilepsy.

L-histidine is a beneficial adjuvant for antiepileptic drugs against maximal electroshock-induced seizures in mice.

Endogenous histamine has been reported to be involved in regulation of seizure susceptibility. Enhancement of histamine neurotransmission engendered by L-histidine treatment produces anticonvulsant effects in experimental animals. The present study investigated the influence of L-histidine on the protective effects of carbamazepine and phenytoin against maximal electroshock-induced seizures in mice.L-Histidine, administered at the doses that did not influence the threshold for electroconvulsions (250-500 mg/kg), enhanced by nearly 30% the protective effects of carbamazepine against maximal electroshock-induced seizures. D-Histidine (1000 mg/kg), an inactive isomer of histidine, was without any effect in this regard. L-Histidine (500 mg/kg) also augmented the protective effects of phenytoin. Importantly, the enhancement of the anticonvulsant effects of these antiepileptic drugs produced by L-histidine co-administration was not associated with augmentation of their unwanted effects on memory and motor performance. A pharmacokinetic interaction was also excluded since the free plasma levels of these antiepileptics remained unchanged in the presence of L-histidine. It may be suggested that L-histidine could serve as a beneficial adjuvant for selected antiepileptic drugs.

AMPA and GABA(B) receptor antagonists and their interaction in rats with a genetic form of absence epilepsy.

The effects of combined and single administration of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, 7,8-methylenedioxy-1-(4-aminophenyl)-4-methyl-3-acetyl-4,5-dihydro-2,3-benzodiazepine (LY 300164), and of the GABA(B) receptor antagonist gamma-aminopropyl-n-butyl-phosphinic acid (CGP 36742), on spontaneously occurring spike-wave discharges were investigated in WAG/Rij rats. LY 300164 had minor effects; only the highest dose (16 mg/kg) reduced the number of spike-wave discharges in a short time window. CGP 36742 was more effective as it significantly reduced the number of spike-wave discharges and shortened their duration at the doses of 25 and 100 mg/kg. The ED(50) values for the inhibition of spike-wave discharges by LY 300164 and CGP 36742 in a time window 30-60 min after injection were 15.5 and 16.6 mg/kg, respectively. The ED(50) of CGP 36742 was reduced to 8.0 mg/kg when this antagonist was administered in combination with LY 300164 (6 mg/kg). The interaction between the two antagonists appeared to be additive according to isobolographic analysis. Importantly, CGP 36742 and LY 300164 administered either alone or in combination had no apparent effects on behavior. These results may provide information for a rational approach to polytherapy for the treatment of generalized absence epilepsy.

Amlodipine enhances the activity of antiepileptic drugs against pentylenetetrazole-induced seizures.

Amlodipine (AML), which belongs to the 1,4-dihydropyridine calcium channel antagonists, possesses pharmacological and pharmacokinetic profile that distinguishes it from other agents of this class. Pentylenetetrazole (PTZ)-induced clonic and tonic convulsions in mice were significantly reduced by administration of AML at 10 mg/kg. At this dose AML remained without influence upon the plasma level of PTZ. The ED50 value of AML against clonic seizures induced by PTZ was 5.4 mg/kg. This calcium channel antagonist (at 2.5 mg/kg) combined with ethosuximide (ETX), valproate magnesium (VPA) or phenobarbital (PB) significantly reduced their ED50 values against clonic phase of PTZ-induced seizures. AML administered alone or in combination with antiepileptic drugs (AEDs) worsened the motor performance of mice in the chimney test. However, these treatments remained without significant influence on the retention time in the passive avoidance test. Plasma levels of antiepileptics remained unchanged in the presence of AML. The results indicate that AML does not seem a good candidate for a combination therapy in epileptic patients because of its adverse potential.

Acute hemorrhagic conjunctivitis caused by enterovirus type 70: an epidemic in American Samoa.

From December 1981 to February 1982, an estimated 22,000 cases of acute hemorrhagic conjunctivitis (AHC) caused by enterovirus type 70 (EV 70) occurred among Samoan and non-Samoan residents of American Samoa. The overall attack rate was estimated to be 68%. Samoans of all ages resident in traditional housing and of large family size were at greatest risk of acquiring AHC, while non-Samoan adults resident in western style housing were at lowest risk. Epidemiologic aspects of AHC acquisition were also different for the Samoan and non-Samoan communities; index cases in Samoan households were frequently young adults, whereas index cases in non-Samoan households were commonly school age children, suggesting a role for school transmission in non-Samoans only. In this outbreak, subclinical AHC was rare; of 50 asymptomatic members of affected households, only 3 had neutralizing antibody to EV 70 (all with titers of 1:10). Investigation documented the highly contagious nature of AHC caused by EV 70, and the ease with which epidemic transmission may develop under conditions of crowding and frequent interpersonal contact.

National case-control study of Kaposi's sarcoma and Pneumocystis carinii pneumonia in homosexual men: Part 2. Laboratory results.

The Centers for Disease Control conducted a case-control study to investigate an outbreak of Kaposi's sarcoma and Pneumocystis carinii pneumonia in homosexual men. The occurrence of these diseases was found to be associated with certain aspects of lifestyle, including a greater number of male sex partners per year, exposure to feces during sex, history of syphilis and non-B hepatitis, treatment for enteric parasites, and use of various illicit substances. Laboratory studies reflected both this lifestyle and the probable underlying cause of the Kaposi's sarcoma and P. carinii pneumonia--cellular immune deficiency. Patients were found to have lymphopenia, specifically a deficiency of the T-helper subpopulation, resulting in a reversal of the T-helper to T-suppressor ratio. Levels of IgG and IgA were increased. When compared with controls, patients were also found to have significantly higher titers of antibody to Epstein-Barr virus and cytomegalovirus, a higher prevalence of antibody to hepatitis A virus and Treponema pallidum, a lower prevalence of antibody to varicella zoster virus, and a higher frequency of isolation of cytomegalovirus.

Acute hemorrhagic conjunctivitis Investigation of a large-scale community outbreak in Dade County, Florida.

An outbreak of acute hemorrhagic conjunctivitis (AHC) due to enterovirus type 70 occurred in Dade County, Florida, from September to December 1981. Younger age groups, members of larger households, and the poor were at significantly greater risk of acquiring AHC than others in the community. Schoolchildren were most likely to introduce AHC into the household. After exclusion of all affected children from school, there was a dramatic reduction in reported cases, with attack ratesups, members of larger households, and the poor were at significantly greater risk of acquiring AHC than others in the community. Schoolchildren were most likely to introduce AHC into the household. After exclusion of all affected children from school, there was a dramatic reduction in reported cases, with attack ratesups, members of larger households, and the poor were at significantly greater risk of acquiring AHC than others in the community. Schoolchildren were most likely to introduce AHC into the household. After exclusion of all affected children from school, there was a dramatic reduction in reported cases, with attack rates declining more rapidly for school-aged children than for other age groups. Although AHC spread readily among family members, a retrospective study of 124 affected households showed an association between lower attack rates and simple hygienic measures. Should outbreaks of AHC recur, measures to reduce transmission should include exclusion of affected schoolchildren and educating the public about hygienic precautions.

Antibody to Ebola virus in guinea pigs: Tandala, Zaire.

A case-control study was conducted to investigate the findings of antibody to Ebola virus in the serum of a guinea pig from Tandala, Zaire. Case households, defined by the possession of one or more guinea pigs, were compared to neighboring households without guinea pigs. Seven (5.1%) of 138 samples of human sera and 36 (26%) of 138 samples of guinea pig sera had antibody to Ebola virus. There was no clustering of seropositivity among humans or guinea pigs within households, nor was there any association between the ownership of guinea pigs and seropositivity among household members. These data suggest sporadic subclinical infection of guinea pigs and humans without a dominant role for person-to-person or guinea pig-to-guinea pig transmission.

Kawasaki syndrome: association with the application of rug shampoo.

An outbreak of Kawasaki syndrome occurred in eastern Colorado during April and May, 1982. 48% of 23 cases had been exposed to the application of rug shampoo in the home in the 30 days before onset of disease, compared with 10% of 30 matched neighbourhood controls and 11% of 56 randomly chosen, matched community controls (p less than 0.01). The interval between rug shampooing and onset of disease was 16-25 days in 9 of 11 cases; 4 of the 9 had intervals of exactly 20 days. Although many brands of shampoo and three different methods of application were used, all but 1 of the cases had walked or crawled on the shampooed rugs within 2 h, the interval being significantly longer for those controls who had been exposed to the shampoo. 3 of 5 sporadic cases in Colorado who fell ill after November, 1981, had similar histories of exposure, as did 9 of 15 sporadic cases in eight other states who were contacted after the Colorado investigation. These findings suggest that exposure to the application of rug shampoo may be a risk factor for some cases of Kawasaki syndrome, although the mechanism remains to be determined.