Ontogenetic development of convulsant action of Ro 5-3663 in the rat

Motor seizures were induced by Ro 5-3663 in 156 male albino rats aged 7,12,18,25, and 90 days. Both minimal and maximal seizures could be elicited in 18-day-old and older animals, whereas only maximal seizures were induced in the two youngest groups. ECoG changes were studied in other 21 young rats. First changes induced by Ro 5-3663 were formed by isolated sharp waves in 7- and 12-day-old rats and by episodes of rhythmic activity in older animals. An imperfect form of this rhythmic activity could be seen even in 12-day-old rats. Ictal ECoG activity exhibited an increase in frequency of individual graphoelements, in generalization and in synchronization of activity among different cortical regions with maturation. Correlation between motor and ECoG phenomena was poor in 7-day-old rats and ameliorated with age but it never reached perfection. The actions of Ro 5-3663 are identical with those induced by metrazol but they differ from those elicited by bicuculline or 3-mercaptopropionic acid.     

Influence of ethosuximide on metrazol-induced seizures during ontogenesis in rats

Effects of metrazol (pentylenetetrazole and ethosuximide were studied in male albino rats aged 7, 12, 18 and 90 days. The 18-day-old rats exhibited the highest sensitivity to metrazol. CD50s in the remaining three age groups were nearly the same. Ethosuximide was reliably effective against metrazol only in adult rats; in young animals it did not significantly change CD50s. Metrazol induced in ethosuximide-pretreated young rats either modified (long-lasting minimal seizures in 18-day-old animals) or new seizure patterns (minimal seizures in 7- and 12-day-old rats).     

Action of two neuroactive steroids against motor seizures induced by pentetrazol in rats during ontogeny

The anticonvulsant action of two neuroactive steroids, 3alpha-hydroxy-5beta-pregnan-20-one (pregnanolone) and triethylammonium 3 alpha-hydroxy-20-oxo-5 alpha-pregnan-21-yl hydrogensuccinate (THDOC-conjugate), was tested against motor seizures induced by pentetrazol in immature rats. Five age groups (7, 12, 18 and 25 days old and adult rats) were pretreated with the steroids in doses from 2.5 to 40 mg/kg i.p. Twenty minutes later pentetrazol (100 mg/kg s.c.) was administered. Minimal seizures (clonic seizures of head and forelimb muscles with preserved righting ability) could be induced in the three older age groups. They were suppressed by pregnanolone in all these tested groups (this effect was best expressed in 18-day-old rats and decreased with age), whereas significant changes in THDOC-conjugate-pretreated animals appeared only in 18-day-old rats. Generalized tonic-clonic seizures were suppressed by both neuroactive steroids in all age groups, this effect being more marked with pregnanolone and again decreased with age. The 7- and 12-day-old rats exhibited higher sensitivity of the tonic phase so that generalized clonic seizures were observed. Duration of the effect was studied in 12- and 25-day-old animals; it was substantially shorter in the older rats than in 12-day-old animals. Both drugs exhibited an anticonvulsant action in developing rats but, unfortunately, their effect was only shortlasting.     

Antipentylenetetrazol action of clobazam in developing rats

Clobazam (0.5 to 7.5 mg/kg i.p.) was tested against motor seizures elicited by pentylenetetrazol in rats 7, 12, 18, 25 and 90 days old. Minimal, predominantly clonic seizures with preserved righting ability were reliably induced by pentylenetetrazol and suppressed by clobazam in rats aged 18 days or more. The incidence of minimal seizures after clobazam pretreatment was not increased in 7- and 12-day-old rat pups. Generalized tonic-clonic seizures were markedly suppressed by clobazam in all age groups. In 18-day-old and older animals clobazam doses suppressing generalized seizures were always lower than those necessary for exerting an effect on minimal seizures. The differences in clobazam action appearing at various levels of maturation are only quantitative.     

Cortical Na+,K+-ATPase of immature rats following bicuculline-induced seizures

The Na+,K+-ATPase activity was investigated in cerebral cortex homogenates of 7-, 12- and 18-day-old rats in which seizures were induced by systemic (i.p.) administration of bicuculline. Na+,K+-ATPase activities in control animals increased during postnatal development, but they were not significantly influenced by seizure activity when determined under optimal conditions in vitro. Although the ratio of neuronal vs. non-neuronal cells in cortical samples of 7-, 12- and 18-day-old rats was different, there was a remarkable similarity in the activation curves for K+, obtained for Na+,K+-ATPase of all age groups under normal conditions; 50% of enzyme activities were attained at 1 mmol.l-1 K+ and the maximal activities were found around 10 mmol.l-1 K+. The activation curves for K+ in rats with bicuculline-induced seizures were not significantly different from those of the controls.     

Convulsant action of diphenylhydantoin overdose in young rats

Acute toxicity of diphenylhydantoin (DPH) was studied in 241 male albino rats aged 7, 12, 18, 25 and 90 days. Single intraperitoneal dose of DPH (from 200 to 1000 mg/kg) induced only ataxia and loss of righting reflex in 25-day-old and adult rats. In rats aged 18 days or less ataxia of hindlimbs was also marked. In all these age groups generalized convulsions appeared; they were formed by wild running followed by a clonic phase. The dose of DPH necessary for elicitation of seizures was lowest in 7-day-old rats (75 mg/kg) and increased with age up to 200 mg/kg in 18-day-old rats. The 1000 mg/kg dose was lethal for 25- and 12-day-old rats, but not for 7-day-old ones. The uneven development of excitatory and inhibitory action of DPH is suggested.     

Antimetrazol action of two potential anticonvulsants, CM 40907 and SR 41378, in immature rats.

The action of two potential anticonvulsants, CM 40907 (10-50 mg/kg i.p.) and SR 41378 (1.25-20 mg/kg i.p.) against metrazol-induced seizures was studied in rats 7, 12, 18 and 25 days old. Two types of motor seizures--minimal, clonic and major, generalized tonic-clonic--were elicited by a 100-mg/kg dose of metrazol (s.c.) and their incidence and latency were evaluated. The severity of seizures was expressed as a score on a 5-point scale. Dimethylsulfoxide, an organic solvent, exhibited anticonvulsant action only in doses far exceeding those used for dissolving the two anticonvulsants. Both drugs suppressed minimal as well as major seizures in all age groups studied in a dose-dependent manner, SR 41378 being approximately four times more potent than CM 40907. The latencies could be measured only in animals given low doses of anticonvulsants. CM 40907 did not change the latencies whereas SR 41378 prolonged them. The severity of seizures was decreased again in a dose-dependent manner. There were only minor changes in the efficacy of CM 40907 among the four age groups. On the contrary, SR 41378 exhibited an extreme efficacy in 7-day-old rat pups, where even the 1.25 mg/kg dose significantly decreased the incidence and severity of seizures. The efficacy in the remaining three age groups was approximately at the same level as in adult rats.     

The GABA(B) antagonist CGP 52432 attenuates the stimulatory effect of the GABA(B) agonist SKF 97541 on luteinizing hormone secretion in the male sheep

The objectives of this study were to determine if the gamma-aminobutyric acid (GABA)(B) agonist, 3-aminopropyl (methyl) phosphinic acid (SKF97541), would increase luteinizing hormone (LH) secretion when infused by microdialysis into the medial basal hypothalamus (MBH) of the castrated ram, and to determine if the action of SKF97541 would be attenuated by co-infusion of the GABA(B) antagonist CGP52432. Initial experiments established that infusion of SKF alone, at concentrations as low as 5 microM, increased mean LH, LH pulse amplitude, and in some cases, pulse interval. In the last experiment, animals were treated with artificial cerebrospinal fluid (CSF) alone, SKF alone (30 microM), 3-[[(3, 4-dichlorophenol) methyl] amino] propyl] diethoxymethyl) phosphinic acid (CGP) alone (500 microM), or SKF plus CGP. SKF increased both mean LH and LH pulse amplitude as compared with CSF. CGP alone had no significant effect on LH, but it attenuated the effect of SKF on mean LH. These observations indicate that the stimulatory effects of GABA(B) agonists on LH pulse patterns are mediated through GABA(B) receptors and provide further evidence that GABA(B) receptors located in the MBH can regulate pulsatile GnRH-LH release.     

Developmental changes in audiogenic epilepsy and myoclonus in KM rats

The reaction to a single sound stimulation (a bell) applied daily and the time of the first appearance of myoclonus were recorded in Krushinsky-Molodkina (KM) rats of different ages (30, 60, and 150-200 days). The audiogenic seizures in adult animals were of short latency and always resulted in tonic convulsions, which were stable in their patten. In contrast, in young animals (in particular, in 30-day-old rats), the seizures were less pronounced and unstable. The daily sound stimulation produced a gradual development of myoclonic seizures in young and adult rats. In old rats, the stable myoclonus appeared on the 17th day of stimulation, and in 30-day-old animals the myoclonus was recorded on the 26th day. In 60-day-old rats the myoclonus appeared for the first time on the 20th day of stimulation. It is suggested that these age differences can be explained by the btain immaturity (in particular, of neurotransmitter system) in young animals.     

The temporal dimensions of anticonvulsant action of some newer benzodiazepines against metrazol induced seizures in mice and rats

In a time-distribution study, the anticonvulsant effects of four benzodiazepine compounds were compared with those of three standard antiepileptics against metrazol-induced seizures in mice and rats. Ethosuximide and trimethadione had the shortest duration of action in mice, but protected the rats up to 6 hr. Phenobarbitone, diazepam, flurazepam and nitrazepam protected the mice up to 12 hr, but the rats were effectively protected only up to 3-4 hr. Clonazepam, the most potent and effective agent, protected the mice from clonic-tonic seizures up to 18-20 hr and the rats up to 6-7 hr. Comparison of the PD50 from clonic seizure at the peak-effect hours revealed that the benzodiazepines were 16 to 96 times more potent than phenobarbitone on a molar basis, while phenobarbitone itself was 12 to 26 times more potent than ethosuximide and trimethadione. Tonic seizures and mortality were largely suppressed by all drugs until 18-20 hr in mice and 6-7 hr in rats. Seizure latency and mortality patterns varied from drug to drug but not in a dose-dependent manner.     

Specific [3H] Glutamate Binding in the Cerebral Cortex and Hippocampus of Rats During Development: Effect of Homocysteine-Induced Seizures

Specific [³H]glutamate binding to synaptic membranes from the cerebral cortex and hippocampus of 7-, 12- and 18-day-old rats was examined, both in control animals and during seizures induced by homocysteine. In the cerebral cortex a transient peak of glutamate binding was observed in 7-day-old group, whereas in the hippocampus it occurred in 12-day-old animals. Total specific [³H]glutamate binding was not influenced by preceding seizure activity in either of the age groups and both the studied regions. NMDA- and QA-sensitive glutamate bindings represent the highest portion of the total binding. Moreover, NMDA-sensitive binding in the cerebral cortex of 7-day-old rats is significantly higher as compared to the two more mature groups. The proportion of individual receptor subtypes on total binding in each age group was not influenced by preceding seizure activity. However, NMDA-sensitive binding in the hippocampus of 12-day-old rats, sacrificed during homocysteine-induced seizures, was significantly increased as compared to corresponding controls. In contrast to the effect of NMDA, AMPA, kainate and quisqualate which displaced to a different extent [³H]glutamate binding, homocysteine had no effect when added to membrane preparations. Similarly, [³H]CPP and [³H]AMPA bindings were not affected in the presence of homocysteine. It thus seems unlikely that homocysteine is an effective agonist for conventional ionotropic glutamate receptors. Its potential activity at some of the modulatory sites at the NMDA receptor channel complex or at metabotropic receptors has to be clarified in further experiments.     

Influence of phenobarbital on ECoG phenomena induced by metrazol in rats during ontogenesis.

Effect of phenobarbital (PhB, 20 and/or 40 mg/kg) on epileptic ECoG phenomena induced by metrazol was studied in acute experiments in rats aged 7, 12, 18, 25 and 90 days. Fractionated administration of metrazol (20 mg/kg i.p. each 300 s) was used to quantify the effects of PhB. First signs of metrazol action (sharp elements and/or rhythmic metrazol activity) were not reliably influenced by PhB. On the contrary, the latency of the first EEG seizures as well as of the first generalized EEG seizures was prolonged and thus a dose necessary for their elicitation was increased in all age groups. These differences reached statistical significance in 12-, 18- and 25-day-old rats. A lack of effect of PhB against the rhythmic metrazol activity supports the adequacy of this activity as a model of human absences. Differences between the development of antiepileptic and hypnotic effects of PhB (described earlier) suggest two different mechanisms of action.     

Influence of ethosuximide and dipropylacetate on metrazol-induced electrocorticographic changes during ontogenesis in rats

Influence of ethosuximide (ESI, 125 mg/kg i.p.) and dipropylacetate (DPA, 300 mg/kg i.p.) pretreatment on electrocorticographic changes induced by pentamethylenetetrazole (PTZ, 20 mg/kg dose every 5 min) was studied in rats aged 7, 12, 18 and 90 days. PTZ alone induced isolated spikes and/or sharp waves as the first sign of its action in all age groups except in adult animals where rhythmic theta activity was elicited. The antiepileptic effect of DPA was observed in 12- and 18-day-old rats, ESI specifically inhibited rhythmic activity in adult rats. ECoG seizures induced by high doses of PTZ were inhibited by DPA in all age groups, ESI tended to be effective in adult rats only. DPA did not change the pattern of ECoG seizures, whereas ESI led to replacement of the spike-and-wave rhythm by serrated waves in adult animals. The low ability of immature brain to generalize ictal activity was further diminished by ESI.     

Does vigabatrin possess an anticonvulsant action against pentylenetetrazol-induced seizures in developing rats?

Anticonvulsant action of vigabatrin (300, 600, 900 and/or 1200 mg/kg i.p.), an inhibitor of GABA-transaminase, was studied in a model of motor sezures elicited by pentylenetetrazol. Five age groups of rats (7, 12, 18, 25 and 90 days old) received a s.c. injection of pentylenetetrazol 4, 6 and/or 24 hours after vigabatrin administration. The incidence of minimal, predominantly clonic seizures was not changed in any age group, but their latencies were prolonged in 18- and 25-day-old rats. Generalized tonic-clonic seizures were influenced in a more complex manner. Incidence of these seizures was decreased in 7-day-old rat pups 24 hours after vigabatrin administration. Higher doses of vigabatrin exhibited a similar effect in adult rats at all intervals studied. Specific suppression or at least restriction of the tonic phase was observed in all groups of immature rats, the effect was more marked 24 hours after vigabatrin than at shorter intervals. The anticonvulsant action of vigabatrin, which could be demonstrated mainly against generalized tonic-clonic seizures, varies markedly during development.     

Epileptic phenomena produced by kainic acid in laboratory rats during ontogenesis

Because of its preferential neuroexcitatory effects on the hippocampal neurones kainic acid (KA) is used for inducing partial seizures with a complex symptomatology. In this study the authors investigated the effect of intraperitoneal administration of KA, in doses of 2-16 mg/kg, on the laboratory rat during ontogenesis. The experimental animals were males aged 7, 12, 18, 25 and 90 days. The first signs of an effect in adult rats were automatisms; in young animals, jerks also appeared. The most important automatisms were wet dog shakes, which preponderated in 25-day-old and older animals, whereas in the young rats they consisted chiefly of intensive scratching. Minimal seizures with a motor pattern identical to minimal metrazol seizures were observed in all the age groups and so were generalized tonic-clonic convulsions, which appeared after large doses of KA. The systemic administration of KA is a convenient model of temporal seizures and their progressive generalization and could act as a model for testing broad spectrum antiepileptics.     

Effect of cortisone on the developmental pattern of the neutral and the acid β-galactosidases of the small intestine of the rat

1. The developmental pattern and effect of cortisone on acid beta-galactosidase and neutral beta-galactosidase were studied in postnatal rats by a recently proposed method for their independent determination. 2. After birth the acid beta-galactosidase activity increases in the ileum, whereas it decreases slightly in the jejunum. On day 16 after birth the activity in the ileum decreases and in 20-day-old rats activity in both parts of the intestine decreases to adult values. In suckling animals the activity in the ileum exceeds the jejunal activity severalfold and in adult animals the activity in the jejunum is slightly higher than that in the ileum. 3. Neutral beta-galactosidase activity is high after birth and decreases in both jejunum and ileum after day 20 after birth. In 12-20-day-old rats activity in both parts is essentially the same, but in adult animals jejunal activity exceeds ileal activity four-to five-fold. 4. Cortisone (0.5, 2.0 or 5.0mg/100g body wt. daily for 4 days) does not influence the activity of either enzyme in 60-day-old rats. Acid beta-galactosidase activity is decreased after cortisone treatment in 8-, 12-, 16-and 18-day-old rats, with sensitivity to cortisone increasing with the approach of weaning. No effect of cortisone on acid beta-galactosidase is seen in 8-day-old rats. Neutral beta-galactosidase activity is increased in the ileum of 8-, 12-, 16- and 18-day old rats, but only in the jejunum of 8-and 12-day-old rats.     

Cerebral blood flow modulates hyperbaric oxygen induced neurotoxicity by neuronal and endothelial nitric oxide

The goal of work was to reveal changes in microcirculation of the rat brain and the role of nitric oxide (NO) in development of seizures at hyperbaric oxygen exposure. The Wistar rats with implanted paired platinum electrodes in left and right striatum were used for experiments. The latency of seizures was defined by the EEG, the cerebral blood flow (CBF) was measured by hydrogen clearance. One group of animals was exposed to a 5-ata oxygen, while the others before oxygen treatment were injected with: Nw-nitro-L-arginine methyl ester (L-NAME), blockator of constitutive NO synthase; 7-nitroindozol (7NI), specific inhibitor of neural NO synthase. The latency of seizures was 41 +/- 1.9 min at 5 ata oxygen exposure. CBF was decreased to 10-14% but before seizures it increased to 23 +/- 9%. L-NAME and 7NI prevented development of hyperoxygen hyperemia and onset of seizures. The results indicate occurrence of hyperbaric oxygen changes of the CBF that modulate neurotoxic effects of NO in neurons as well as in cerebral vessels.     

The anticonvulsive effect of BCH 325 is age dependent

The two different experimental approaches which were applied to study the anticonvulsive effectiveness of BCH 325, a des-tyrosine derivative of bovine beta-casomorphin-(5), in immature (22-day-old) and mature (7-week-old) female rats revealed that the peptide was able to protect mature females from electrically induced seizures and that it had no effect on pentylenetetrazol-induced convulsions. As opposed to this, immature animals were protected against chemically induced seizures but no effect was found using electrically induced seizures.     

Inhibition of forskolin-stimulated cAMP formation in vitro by paraoxon and chlorpyrifos oxon in cortical slices from neonatal, juvenile, and adult rats

Parathion (PS) and chlorpyrifos (CPF) are organophosphorus insecticides, which elicit toxicity following biotransformation to the potent acetylcholinesterase inhibitors, paraoxon (PO) and chlorpyrifos oxon (CPO). Both oxons have also been shown to interact directly with muscarinic receptors coupled to inhibition of adenylyl cyclase. Immature animals are more sensitive than adults to the acute toxicity of PS and CPF but little is known regarding possible age-related differences in interactions between these toxicants and muscarinic receptors. We compared the inhibition of forskolin-stimulated cAMP formation by PO and CPO (1 nM-1 mM) in vitro in brain slices from 7-, 21-, and 90-day-old rats to the effects of well-known muscarinic agonists, carbachol and oxotremorine (100 microM). Both agonists inhibited cAMP formation in tissues from all age groups and both were more effective in adult and juvenile (20-26% inhibition) than in neonatal (12-13% inhibition) tissues. Atropine (10 microM) completely blocked agonist-induced inhibition in all cases. PO maximally inhibited (37-46%) cAMP formation similarly in tissues from all age groups, but atropine blocked those effects only partially and only in tissues from 7-day-old rats. CPO similarly inhibited cAMP formation across age groups (27-38%), but ATR was partially effective in tissues from all three age groups. Both oxons were markedly more potent in tissues from younger animals. We conclude that PO and CPO can directly inhibit cAMP formation through muscarinic receptor-dependent and independent mechanisms and that the developing nervous system may be more sensitive to these noncholinesterase actions.     

Development of the interhemispheric response in rats.

In acute experiments on curarized rats, an interhemispheric response was observed for the first time at the age of 5 days. A stimulus of threshold intensity evoked both components of the response in the youngest animals, but only the negative phase of the evoked potential from the 9th day of age, with the initial positive phase appearing only after stimuli of high intensity. Upon using stimuli of double the value of threshold intensity, the responses had the same shape, i.e. positive-negative throughout the whole development. Marked changes in the latency of both components of the response were found during development. Up to 14 days latencies decreased rapidly; this was followed by a phase of relative stability and then, after the 19th day, by further, less pronounced decrease. An after-discharge, a late component of the response in adult animals, appeared for the first time in a mature form at 18 days. An after-discharge of a different shape was seen in young rats aged 7-14 days and none at all was observed in 5-day-old animals.