Effects of a benzodiazepine, bretazenil (Ro 16-6028), on rhythmic metrazol EEG activity: comparison with standard anticonvulsants

Synthesis, anticonvulsant, sedative and anxiolytic activities of novel annulated pyrrolo[1,4]benzodiazepines

Four new pentacyclic benzodiazepine derivatives (PBDTs 13–16) were synthesized by conventional thermal heating and microwave-assisted intramolecular cyclocondensation. Their anticonvulsant, sedative and anxiolytic activities were evaluated by drug-induced convulsion models, a pentobarbital-induced hypnotic model and an elevated plus maze in mice. PBDT 13, a triazolopyrrolo[2,1-c][1,4]benzodiazepin-8-one fused with a thiadiazolone ring, exhibited the best anticonvulsant, sedative and anxiolytic effects in our tests. There was no significant difference in potency between PBDT 13 and diazepam, and we proposed that the action mechanism of PBDT 13 could be similar to that of diazepam via benzodiazepine receptors.

Synthesis and cytotoxicity testing of new amido-substituted triazolopyrrolo[2,1-c][1,4]benzodiazepine (PBDT) derivatives

A series of amido-substituted triazolopyrrolo[2,1-c][1,4]benzodiazepine (PBDT) derivatives was synthesized from isatoic anhydride, and their cytotoxicity against the MRC-5 and Mahlavu cell lines was evaluated. The results suggest that compound PBDT-7i with the meta-trifluoromethylbenzoyl substituent can selectively inhibit the growth of Mahlavu cells and has low toxicity towards MRC-5 cells.

Animal models

Epilepsy accounts for a significant portion of the dis-ease burden worldwide. Research in this field is fundamental and mandatory. Animal models have played, and still play, a substantial role in understanding the patho-physiology and treatment of human epilepsies. A large number and variety of approaches are available, and they have been applied to many animals. In this chapter the in vitro and in vivo animal models are discussed,with major emphasis on the in vivo studies. Models have used phylogenetically different animals - from worms to monkeys. Our attention has been dedicated mainly to rodents.In clinical practice, developmental aspects of epilepsy often differ from those in adults. Animal models have often helped to clarify these differences. In this chapter, developmental aspects have been emphasized.Electrical stimulation and chemical-induced models of seizures have been described first, as they represent the oldest and most common models. Among these models, kindling raised great interest, especially for the study of the epileptogenesis. Acquired focal models mimic seizures and occasionally epilepsies secondary to abnormal cortical development, hypoxia, trauma, and hemorrhage.Better knowledge of epileptic syndromes will help to create new animal models. To date, absence epilepsy is one of the most common and (often) benign forms of epilepsy. There are several models, including acute pharmacological models (PTZ, penicillin, THIP, GBL) and chronic models (GAERS, WAG/Rij). Although atypical absence seizures are less benign, thus needing more investigation, only two models are so far available (AY-9944,MAM-AY). Infantile spasms are an early childhood encephalopathy that is usually associated with a poor out-come. The investigation of this syndrome in animal models is recent and fascinating. Different approaches have been used including genetic (Down syndrome,ARX mutation) and acquired (multiple hit, TTX, CRH,betamethasone-NMDA) models.An entire section has been dedicated to genetic models, from the older models obtained with spontaneous mutations (GEPRs) to the new engineered knockout, knocking, and transgenic models. Some of these models have been created based on recently recognized patho-genesis such as benign familial neonatal epilepsy, early infantile encephalopathy with suppression bursts, severe myoclonic epilepsy of infancy, the tuberous sclerosis model, and the progressive myoclonic epilepsy. The contribution of animal models to epilepsy re-search is unquestionable. The development of further strategies is necessary to find novel strategies to cure epileptic patients, and optimistically to allow scientists first and clinicians subsequently to prevent epilepsy and its consequences.

In vivo characterization of sedative activities of Fossilia Mastodi OSSIS

Fossilia Mastodi OSSIS, which is a skeletal fossil of a Mastodon, an ancient mammal, has been found to have anxiolytic, sedative and anticonvulsant activities in Oriental medicine. In this study, in vivo characterization of the sedative activities of Fossilia Mastodi OSSIS was performed in order to obtain basic information for the development of a putative natural sedative. The 80% methanol extract of Fossilia Mastodi OSSIS given per os at a dose of 3 g/kg in mice showed anxiolysis, potentiation of pentobarbital sleeping time, reduced locomotor activity, and anticonvulsive activity. Fossilia elicited GABA(A) receptor-mediated anxiolysis. The data obtained suggest that the 80% methanol extract of Fossilia Mastodi OSSIS contains some biologically active principles with sedative activity.

Anticonvulsant action of an antagonist of metabotropic glutamate receptors mGluR5 MPEP in immature rats

Antagonists of type I of metabotropic glutamate receptors exhibit anticonvulsant action in adult as well as immature rodents. To know the anticonvulsant profile of a specific mGluR5 antagonist MPEP in developing rats, two models of epileptic seizures were used. MPEP (10, 20 or 40 mg/kg i.p.) suppressed in a dose-dependent manner epileptic afterdischarges induced by electrical stimulation of sensorimotor cortical area in three age groups (12, 18 and 25 days old). The anticonvulsant action was more expressed in the youngest group than in older animals so that in 25-day-old rats an additional dose of 80 mg/kg was used. In contrast to this marked anticonvulsant action, MPEP at a dose of 40 mg/kg i.p. in 18-day-old rat pups and at doses of 40 and 80 mg/kg in 25-day-old rat pups did not affect episodes of spike-and-wave rhythm elicited by low doses of pentetrazol. Our results delineate the profile of the anticonvulsant action of MPEP and confirm the higher efficacy of this antagonist at early developmental stages in comparison with prepubertal animals.

Bicuculline-induced rhythmic EEG episodes: gender differences and the effects of ethosuximide and baclofen treatment

PURPOSE

There are gender differences in the expression of seizures. We tested rhythmic EEG episodes induced by low doses of bicuculline in rats for gender differences. To verify the validity of these discharges as a model of absence seizures in both male and female rats, we tested the antiabsence drug ethosuximide (ESM) and a gamma-aminobutyric acid (GABA(B))-receptor agonist, baclofen, which may exacerbate absence seizures.

METHODS

Adult rats of both sexes were used. Under general anesthesia, EEG electrodes were implanted over frontal and occipital cortex, and some females were ovariectomized. After recovery, male, intact female rats, and female rats ovariectomized and ovariectomized rats with estradiol replacement were compared for occurrence of rhythmic EEG episodes (approximately 6 cycles/ s) induced by 2.5 mg/kg of bicuculline, s.c. Because of gender differences in sensitivity to bicuculline, further pharmacologic effects of ESM (125 and 250 mg/kg, i.p.) and baclofen (2 mg/kg, i.p.) were tested separately in male (3.0 mg/kg of bicuculline), and female (2.5 mg/kg of bicuculline) rats.

RESULTS

After the identical dose of bicuculline, s.c., male and female rats differed in the incidence of rhythmic episodes and in the latency to onset of the first as well as the generalized episode. Female rats with natural or exogenous estrogens (but not ovariectomized rats) developed EEG episodes more often than did males, and this effect could be attributed to the presence of estrogens. ESM pretreatment suppressed the episodes, whereas baclofen enhanced their occurrence, as well as the total duration of episodes without gender-specific differences.

CONCLUSIONS

The study demonstrates gender differences (related probably to the presence of circulating estrogens) in the susceptibility of rats to develop rhythmic EEG episodes induced by threshold doses of bicuculline. This activity has some features of an acute absence seizure model.

Ontogeny of ethosuximide action against two seizure models in rats is different

Action of ethosuximide (ESI) against two types of experimental seizures elicited by systemic administration of pentylenetetrazol (PTZ) and characterized by spike-and-wave activity in the EEG was studied in immature rats 18 and 25 days old, i.e. in such age groups where these age-dependent seizures could be reliably induced. Pretreatment with ESI in doses of 62.5 and 125 mg/kg i.p. suppressed episodes of spike-and-wave rhythm (rhythmic metrazol activity) elicited by a 40-mg/kg dose of PTZ in both age groups in a dose-dependent manner. Minimal metrazol seizures induced by higher dose of PTZ (70 mg/kg i.p.) were similarly suppressed by ESI in 25-day-old rats only. In 18-day-old animals ESI did not exhibit an anticonvulsant effect. These results speak against the adequacy of minimal metrazol seizures as a model of human absences. In addition, different development of ESI action against two types of experimental seizures suggests a possibility that there is more than one mechanism of action of ESI.

The effects of malignant glioma on the EEG and seizure thresholds: an experimental study

Generalised or partial seizures are a common problem with many supratentorial gliomas. Their underlying pathophysiological mechanisms are poorly understood. To investigate this problem clinical and EEG seizure thresholds were investigated in experimental rodent gliomas using the epileptogenic drug pentylenetetrazole (PTZ). Mixed C6/A15A5 malignant gliomas were grown in adult Wistar rats after unilateral stereotactic implantation of a 50:50 cell mix into the caudoputaminal region. Eleven to 14 days later EEG (raw and spectrally analysed) was recorded bilaterally from the frontal and parietal regions under mixed alpha-chloralose and urethane anaesthesia. Baseline EEG (15 minutes), EEG during and after (30 minutes) PTZ infusion (100 microliters/min) and the time to appearance of seizure manifestations after starting PTZ were recorded. Fourteen animals were studied (5 normal, 5 with tumours, 4 sham implants) and mean BP, PaCO2, PaO2 and temperature were similar in the three groups. Baseline raw EEG showed predominate slow wave activity with lower amplitude and less spontaneous activity overlying tumours. Following PTZ infusion a sequence of vibrissal twitching (following a mean of 14.5 mg/kg PTZ in control and sham animals); jaw/nasal twitches (17.5 mg/kg); fore and hind limb jerking (46 mg/kg); myoclonic jerking (47 mg/kg); and status (77.5 mg/kg) was observed. The seizure thresholds for all PTZ induced seizure phenomena were, except for status epilepticus, highest in the tumour bearing animals. The time to 70% seizure activity on the EEG was also significantly longer in the tumour bearing animals. Spectral analysis of the EEG, although showing increased alpha and theta activity after PTZ infusion, did not discriminate between the three experimental groups either before or after PTZ activation. These studies have confirmed that experimental gliomas alter baseline EEG and both the EEG and behavioural response to PTZ. The reasons for the raised seizure threshold in the glioma bearing animals and the relevance of this experimental paradigm to human tumour associated epilepsy are discussed.

Pharmacology of cortical epileptic afterdischarges in rats

Afterdischarges (ADs) elicited by electrical stimulation of the sensorimotor cortical area are characterized by rhythmic spikes and spike-wave complexes in the EEG and by clonic face and forelimb seizures. We studied the sensitivity of such ADs to phenytoin (PHT), carbamazepine (CBZ), phenobarbital (PB), primidone (PRM), and valproate (VPA) in 78 adult male Wistar rats with implanted electrodes. Neither PHT (30 and 60 mg/kg intraperitoneally, i.p.) nor CBZ (25 and 50 mg/kg i.p.) suppressed cortical ADs. Indeed, ADs were prolonged by higher doses of both drugs. PRM had a similar effect: A dose of 40 mg/kg transiently shortened ADs, but a dose of 80 mg/kg prolonged ADs. PB (20 and 40 mg/kg) and VPA (200 and 400 mg/kg) were effective in suppressing ADs. Higher doses of VPA and PB reduced the intensity of motor phenomena related to the stimuli but had no effect on the motor correlates of ADs. These findings suggest that cortically induced ADs are not a good model of secondarily generalized seizures. The response to VPA and PB suggests that cortical ADs may represent a model of myoclonic seizures.