Hana Kubová

Seizures Induced by Homocysteine in Rats During Ontogenesis

Summary: We studied the convulsant action of homocysteine in 211 immature and adult Wistar albino rats. Homocysteine elicited minimal, predominantly clonic, and major generalized tonic‐clonic seizures at six different developmental stages, from 7 days to adulthood. Nevertheless, some age‐dependent differences in the seizure pattern were apparent. Minimal seizures in immature rats lasted ≤20 min, thus representing an epileptic status, whereas in adult animals these seizures were much shorter, lasting only ≥40 s. In addition, flexion seizures were observed in 7‐and 12‐day‐old rats, only rarely in 15‐and 18‐day‐old animals, and never in the 25‐day‐old and adult rats. ECoG recordings demonstrated a nearly iso‐electric pattern during homocysteine‐induced seizures in 7‐and 12‐day‐old rat pups. In older rats, spikes or sharp waves were recorded, but precise electroclinical correlations were poor. The greater sensitivity of younger animals to kainic acid (KA) and N‐methyl‐D‐aspartate (NMDA), as reported previously, was not evident in the case of homocysteine‐induced seizures. This observation, together with a different behavioral pattern, suggests that homocysteine cannot be considered a simple agonist of the kainate or NMDA type of excitatory amino acid receptors. The exact mechanism of the convulsant action of homocysteine, both during development and in adulthood, remains to be clarified.

Anticonvulsant Action of Oxcarbazepine, Hydroxycarbamazepine, and Carbamazepine Against Metrazol‐Induced Motor Seizures in Developing Rats

Summary: Antimetrazol effects of carbamazepine (CBZ, 5, 12.5, 25, or 50 mg/kg), oxcarbazepine (OCBZ, 5, 10, 30, or 60 mg/kg), and hydroxycarbamazepine (HCBZ, the main human metabolite of OCBZ, 10, 30, or 60 mg/kg) were studied in 7–, 12–, 18–, 25–, and/or 90‐day‐old laboratory rats. No drug tested affected the incidence of minimal (clonic) metrazol seizures (mMs) in animals aged ≥18 days; in rats aged 7 or 12 days in which mMs are rare under control conditions, the incidence of mMs was increased by lower doses of CBZ and HCBZ. All drugs tested specifically abolished the tonic phase of major generalized tonic‐clonic seizures (MMs) in a dose‐dependent manner. In addition, CBZ and OCBZ were able to suppress all phases of MMs in the two youngest groups (7‐and 12‐day‐old). There were no marked differences among the three drugs tested (CBZ, OCBZ, and HCBZ) on their action against metrazol‐induced seizures during ontogenesis of rats; i.e., all these drugs appeared to possess an identical profile of anticonvulsant action.

Motor and electrocorticographic epileptic activity induced by 3-mercaptopropionic acid in immature rats

The convulsant action of 3-mercaptopropionic acid (3-MPA), a known inhibitor of glutamate decarboxylase activity, was studied in 7-, 12-, 18- and 25-day-old rats and in adult animals. 3-MPA elicited predominantly clonic, minimal seizures as well as generalized tonic-clonic (major) seizures at all developmental stages studied. The CD50 for major seizures did not change during development; CD50 for minimal seizures was significantly lower in 18-day-old rats than in older animals. Latency to the onset of seizures was shortest in 18-day-old rats and extremely long in 12- and, especially, in 7-day-old rats. This long latency might signify either changing molecular properties of glutamate decarboxylase during development or slow turnover of GABA at early postnatal stages. Electrocorticographic recordings demonstrated sharp EEG components in the frontal region as a first sign of 3-MPA action, and seizure patterns exhibited similar developmental changes as found with other seizure models (a decrease in duration of individual graphoelements and an increase in synchronization among various cortical regions). This indicates the primary importance of brain maturation in the expression of epileptic EEG phenomena. The correlation between EEG and motor phenomena was poor in the youngest animals and it ameliorated with age, but it never became perfectly coincidental.

Action of antiepileptic drugs against kainic acid-induced seizures and automatisms during ontogenesis in rats

Summary: Kainic acid (KA 4–14 mg/kg) administered intraperitoneally (i.p.) produces automatisms (scratching until third postnatal week, “wet dog” shakes thereafter), and clonic and tonic‐clonic seizures in rats aged 7, 12, 18, 25, and 90 days. Administration of carbamazepine (CBZ) i.p. (25 or 50 mg/kg), phenobarbital (PB 20–80 mg/kg), clonazepam (CZP 0.2 or 1 mg/kg), or valproate (VPA 200 mg/kg) influenced neither incidence nor latency of automatisms. Clonic seizures that are regularly observed after the third postnatal week in controls were either abolished or substantially suppressed by any of the aforementioned antiepileptic drugs (AEDs). Tonic‐clonic seizures observed in the first 3 postnatal weeks were suppressed only by solvent [including propyleneglycol (PEG), ethanol, and water]; the effect of AEDs on tonic‐clonic seizures was proconvulsant instead. The automatisms were most resistant to AED therapy. These results induce some doubts about the adequacy of the KA model for identifying AEDs effective against complex partial seizures, but forthcoming AEDs that suppress automatisms in the KA rat model might also be active against human complex partial seizures.

Kainate/AMPA receptor antagonists are anticonvulsant against the tonic hindlimb component of pentylenetetrazol-induced seizures in developing rats.

Non-NMDA receptor antagonists CNQX, DNQX, and NBQX (10-40 mg/kg IP) were tested against pentylenetetrazol-induced (100 mg/kg SC) seizures in 7 to 90-day-old rats. All three drugs significantly decreased the incidence of tonic hindlimb component of tonic-clonic pentylenetetrazol seizures, often in favor of increased incidence of forelimb tonus throughout development. In addition, in 7 to 25-day-old rats, DNQX and NBQX decreased the severity of seizures due to a decrease in total incidence of the tonic component of tonic-clonic seizures compared to age-matched controls. However, neither drug was able to consistently suppress the incidence or increase latency to onset of clonic and tonic-clonic pentylenetetrazol seizures. The data suggest that, during development, non-NMDA receptor transmission may play a role in the generation of the tonic component, but not in the generation of other components of pentylenetetrazol-induced seizures.

New model of cortical epileptic foci in freely moving developing rats

Electrocorticographic and motor phenomena produced by epileptogenic foci were studied in freely moving rats with implanted electrodes in five age groups (7, 12, 18, 25 days and adults). Foci were induced by local application of a 1 or 2 mM solution of bicuculline methiodide to the sensorimotor cortical area by means of an implanted cannula in 106 rats. Interictal focal discharges formed by mono- to triphasic spikes (in rats aged 18 days and more) or sharp waves (in 7-day-old rats) were recorded in all animals. Spontaneous transition into an ictal phase was common in all age groups, there was no clear dependence on the age. Ictal EEG was formed by spike-and-wave rhythm in rats 18 days old and older, by huge delta waves in the youngest rats. Electroclinical correlation was poor in the youngest rats and ameliorated with age. The most frequent motor counterpart of focal discharges was represented by a jerk of the contralateral limbs or of the whole body. EEG seizures were mostly accompanied by clonus of facial and forelimb muscles, but EEG ictal phases without any motor correlate were also common.

Aminophylline exhibits convulsant action in rats during ontogenesis

Aminophylline-induced seizures were studied in 166 male albino rats in five age groups--7, 12, 18, 25 and 90 days old. Aminophylline injected in doses from 150-350 mg/kg i.p. elicited both minimal, clonic and major, i.e. generalized tonic-clonic seizures during the 60-min observation period. The pattern of minimal seizures did not change during development; major seizures exhibited changes in proportion to their three phases--running, tonic and clonic phases. Dependence on the dose of aminophylline was observed in the incidence of major seizures as well as in shortening of latencies of both types of seizures. More marked convulsant effects of aminophylline in 7-, 12- and 18-day-old rat pups than in older animals might be due to pharmacokinetic as well as pharmacodynamic factors.

Effects of a Benzodiazepine, Bretazenil (Ro 16‐6028), on Rhythmic Metrazol EEG Activity: Comparison with Standard Anticonvulsants

A novel anticonvulsant benzodiazepine breta‐zenil (Ro 16–6028) was studied electrophysiologically in a model of human absence seizures: rhythmic metrazol activity (RMA) in rats. The effects of Ro 16–6028 pretreatment (0.01, 0.05, or 0.1 mg/kg intraperitoneally, i.p.) were compared with those of clonazepam (CZP, 0.02 or 0.1 mg/kg i.p.), valproate (VPA, 200, 300, or 400 mg/kg) and ethosuximide (ESM, 31.25, 62.5, or 125 mg/kg i.p.) in 45 rats with implanted electrocorticographic electrodes. RMA was elicited by an injection of pentylenetetrazol (metrazol, PTZ) in a dose of 40 or 35 mg/kg i.p. The effects of Ro 16–6028 were similar to those of CZP and VPA, i.e., suppression of RMA episodes, an increase in latency and a decrease in number, and total as well as mean duration. On the other hand, ESM differed from these antiepileptic drugs (AEDs) in inability to shorten the duration of RMA episodes. Based on these results, Ro 16–6028 might be predicted to be efficient against human absence seizures.

Ketamine blocks cortical epileptic afterdischarges but not paired-pulse and frequency potentiation

Cortical epileptiform afterdischarges (spike-and-wave rhythm) induced by low-frequency stimulation of the sensorimotor cortex were dose-dependently shortened by ketamine (10, 20 and 40 mg/kg, i.p.). Myoclonic jerking during stimulation was unaffected by ketamine whereas the same motor pattern accompanying afterdischarges was markedly suppressed by this drug. Paired-pulse as well as frequency potentiation of the cortical interhemispheric (transcallosal) responses were not significantly altered by the 40 mg/kg dose of ketamine. The two simple potentiation phenomena studied probably did not play a role in initiation of cortical epileptic afterdischarges.

Anticonvulsant activity of flumazenil in rats during ontogenetic development.

The influence of flumazenil on seizures induced by pentylenetetrazol (PTZ) was studied in rats aged 7, 12, 18, 25, and 90 days. Flumazenil in doses of 25, 37.5, and 50 mg/kg IP injected 10 min before PTZ exhibited a dose-dependent anticonvulsant action in all age groups studied. It was more effective against generalized tonic-clonic than against minimal clonic seizures at all developmental stages studied. In the two youngest groups, minimal seizures were elicited only rarely under control conditions. Pretreatment with the two lower doses of flumazenil resulted in an increased incidence of this type of seizure for these two groups. The anticonvulsant activity found in all age groups is in agreement with data from other benzodiazepines and speaks against a pure benzodiazepine-antagonistic action of flumazenil.