The influence of strain and housing on two types of spike-wave discharges in rats

WAG/Rij rats, a genetic model of absence epilepsy, show two types of spike-wave discharges (Type 1 and Type 2) in their EEG activity. The large interindividual variation in the expression of the phenotypes (number and mean duration of spike-wave discharges) suggests that as well as genetic, environmental factors also play a role. The aim of our study was to establish effects of strain and housing on the incidence and expression of both types of paroxysms. Therefore, WAG/Rij and ACI rats were housed from weaning in either an enriched or impoverished environment for 60 days. At three months of age the EEG of the rats was recorded for four hours to examine the effects of strain and housing on the incidence and expression of the two types of paroxysms. Generally, enriched housing led to worsening of Type 1 and Type 2 spike-wave discharges (SWD). However, the number of affected rats and the expression (number and mean duration) of Type 1 and Type 2 spike-wave discharges were differently influenced by strain and housing. This suggests that Type 1 and Type 2 spike-wave discharges are independent phenomena and that number and mean duration of these paroxysms are controlled by different mechanisms. Finally, the worsening of absence seizures after enrichment is different from what has been found for convulsive seizures.     

Influence of transcranial magnetic stimulation on spike-wave discharges in a genetic model of absence epilepsy

Transcranial magnetic stimulation (TMS) impulses, (0.5 Hz, 3 impulses) were presented at threshold intensity to male WAG/Rij rats. One group received stimuli, which involved motor responses of hindlimbs, rats of the second group received sham stimulation. Electrocorticograms (ECoG) were recorded before and up to 2 hr from the moment of transcranial magnetic stimulation. It was established that such stimulation engendered a reduction of spike-wave discharge (SWD) bursts duration. This effect was most pronounced in 30 min from the moment of cessation of stimulation, when a decrease of 31.4% was noted in comparison with sham-stimulated control group. The number of bursts of spike-wave discharges was reduced, but did not reach significant difference when compared both with pre-stimulative base-line level and with sham-stimulated control rats. Bursts of spike-wave discharges restored up to pre-stimulative level in 90-150 minutes from the moment of cessation of transcranial stimulation. It can be concluded that transcranical magnetic stimulation possessed an ability to engender short-time suppression of bursts of spike-wave discharges in WAG/Rij rats.     

Anxiety and behavior in WAG/Rij strain rats with genetically induced absence attacks

Behavior of nonlinear rats and animals from Wistar and WAG/Rij (with inborn generalized absence epilepsy) strains was examined in the elevated plus-maze and the hole board. WAG/Rij rats demonstrated low exploratory behavior in both tests. In the elevated plus-maze, WAG/Rij rats were more balanced and more anxious than Wistar and nonlinear rats. Administration of ethosuximide completely eliminated spike-wave discharges but did not change behavioral interstrain differences. Since the spike-wave patterns develop in WAG/Rij at the age of 3 months, the behavior of young (2-moth-old) pups from different strains was compared and significant differences were revealed. Correlation between the genetically defined features (spike-wave discharges) and behavioral peculiarities in WAG/Rij rats is supposed.     

Audiogenic kindling in WAG/Rij rats: change in behavioral and electrophysiological responses to repetitive short acoustic stimulation

Running and tonic convulsions induced by sound stimulation (audiogenic seizures, AS) are known to be brainstem-dependent, but their repeated induction leads to the recruiting forebrain structures into AS expression manifested by the development of clonic convulsions and cortical epileptic activity (audiogenic kindling). Behavioral and electrophysiological manifestations of audiogenic kindling were studied in AS-prone WAG/Rij rats exhibiting two types of genetically determined generalized seizures: convulsive audiogenic and nonconvulsive absence (spontaneous spike-wave discharges generated by thalamocortical circuits). Twenty three repeated (with 2 days intervals) sound stimulations inducing a short running episode led to a progressive increase in AS duration from 6.2 +/- 0.4 s to 24.7 +/- 2.9 s mainly due to the appearance of additional postrunning facial-forelimb clonic convulsions of increasing duration and severity. Fully kindled (Racine's stage 5) seizures were accompanied by a bilateral slow-potential wave of cortical spreading depression (SD) nonsynaptically propagating to both striata and by a long-term postictal suppression of spontaneous absence seizures. Neither corticostriatal SD, nor the spike-wave discharges suppression were observed after running induced by sound in non-kindled rats or by attenuated (subthreshold for clonus) sound in kindled rats. Subthreshold stimulation of kindled rats provoked postictal high-amplitude spiking in the cortex. It is concluded that the recruitment of the cortex into a kindled AS network triggers a corticostriatal SD which may underlie the postictal inhibition of non-convulsive seizures, which follow the kindled AS.     

Does antiabsence drug ethosuximide exert antidepressant effect?

Antiabsence drug ethosuximide (300 mg/kg/day in drinking water for 17 days) produced an antidepressant effect (a decrease in immobility time in forced swimming test) only in WAG/Rij rats genetically predisposed to absence epilepsy only at age of 5 months when spike-wave discharges well pronounced. On rats without spike-wave discharges (21-day-old WAG/Rij and Wistar rats at the age of both at 21 day and 5 months), ethosuximide didn't produce the antidepressant effect but tended to increases the immobility time and significantly decreases the number of divings (active behavior oriented to escape from stressful situation). Ethosuximide didn't substantially change the anxiety level in WAG/Rij rats but significantly enhanced anxiety in 21-day-old Wistar rats. The results suggest that ethosuximide is not possessed of antidepressant potential unrelated to its suppressive effect on spike-wave discharges.     

Differential expression of high voltage-activated Ca2+ channel types in the rostral reticular thalamic nucleus of the absence epileptic WAG/Rij rat

In the WAG/Rij rat, a model for human absence epilepsy, spike-wave discharges (SWD) and absence epileptic behavior develop after the age of 3 months. The rostral part of the reticular thalamic nucleus (rRTN) is involved in SWD. Ca(2+) channels play a central role in the initiation and maintenance of burst firing activity of thalamic cells. We hypothesize that a changed expression of alpha(1)-subunits of one or more high voltage-activated Ca(2+) channel types in the rRTN underlies the development of SWD. To test this hypothesis we compared 3- and 6-month-old WAG/Rij rats with nonepileptic, age-matched control rats. By immunocytochemistry, the expressions of alpha(1)1.3-, alpha(1)2.1-, alpha(1)2.2-, and alpha(1)2.3-subunits were shown in both strains, demonstrating the presence of Ca(v)1.3, Ca(v)2.1, Ca(v)2.2, and Ca(v)2.3 channels, respectively. Quantification of channel expression indicates that the development of SWD in WAG/Rij rats is concomitant with an increased expression of Ca(v)2.1 channels in the rRTN. These channels are mainly presynaptic, as revealed by double immunofluorescence involving the presynapse marker syntaxin. The mechanism by which this increase could be related to the occurrence of SWD has been discussed.     

Changes in the sensitivity of brain dopamine and serotonin receptors during the prolonged administration of carbidine

Male Wistar rats were treated chronically with either carbidine (10 mg/kg/day) or haloperidol (1 mg/kg/day) for 23 consecutive days. On days 4-5 after the treatment discontinuation the animals were challenged with apomorphine HCl (0.5 mg/kg) or 5-OTP (150 mg/kg i. p) in combination with pargiline (40 mg/kg i. p) and stereotype responses were scored. In carbidine-treated rats the intensity of stereotype sniffings was increased after apomorphine treatment. In contrast, animals treated with haloperidol exhibited more intensive gnawing after apomorphine in comparison to vehicle-treated rats. 5-OTP-induced head twitches were increased only in carbidine-treated rats. Prolonged carbidine treatment in contrast to haloperidol induced a decrease in 5H-spiperone and 3H-LSD binding in the frontal cortex, with the density of D-2 receptors in the striatum practically unchanged. It is concluded that neuroleptic carbidine in contrast to classical neuroleptics has a more selective effect in serotonin (S-2) receptors and antidepressive properties of this compound may be due to the down-regulation of S-2 receptors in the brain.     

Antagonism between L-DOPA and apomorphine in their effects on rat behavior

The effect of simultaneous injections of apomorphine and l-DOPA on stereotypy, aggressiveness, on the exploratory motor activity, the threshold of emotional reactivity and aggressiveness elicited by painful electrical stimulation was studied in experiments on male albino rats. When injected separately, in control experiments, both compounds had similar effects on the exploratory-motor activity and the emotional behaviour, but when injected simultaneously in various doses a distinct antagonism between l-DOPA and apomorphine, according to all the behaviour tests, was noted (a decrease of sterotypy, aggressiveness and emotional reactivity). Against the background of l-DOPA apomorphine (5 mg/kg) increased the dopamine content in the forebrain and in the diencephalon even more. It is suggested that the increased level of the functionally active mediator suppressed the activity of postsynaptic receptors sensitive to it.     

The Modulatory Effect of Metabotropic Glutamate Receptor Type-1α on Spike-Wave Discharges in WAG/Rij Rats

Modulatory function of metabotropic glutamate type 1 (mGlu1) receptors plays a crucial role in the pathophysiology of some neurological disorders, including schizophrenia and epilepsy. In this study, the expression of mGlu1α receptors in the thalamic nuclei was assessed during development of absence seizures in the WAG/Rij rats, a valid genetic animal model of absence epilepsy. In addition, the effect of pharmacological modulation of mGlu1α receptors in the laterodorsal (LD) nucleus of the thalamus on the characteristic features of bioelectrical brain activities in the WAG/Rij rats was assessed. The expression of mGlu1α receptors in the LD was assessed in four experimental groups of both WAG/Rij and Wistar rats with 2 and 6 months of age. Agonist and antagonist of mGlu1α receptors were infused in LD in the six months old WAG/Rij (epileptic) rats. The protein level of mGlu1α receptors in the thalamus of the 6-month-old WAG/Rij rats was lower than non-epileptic animals. In addition, the distribution of mGlu1α receptors in different thalamic nuclei was lower in the 6-month-old WAG/Rij compared to age-matched Wistar rats. The gene expression of mGlu1α receptor was also significantly lower in 6-month-old WAG/Rij rats in the LD compared to other animal groups. The microinjection of mGlu1α receptors agonist and antagonist in the LD reduced the duration of spike-wave discharges (SWDs) and increased the amplitude and duration of SWDs, respectively, in 6-month-old WAG/Rij rats. The alterations of mGlu1α receptors expression in the thalamus of epileptic WAG/Rij rats as well as its modulatory effects in the generation of SWDs suggest the potential of mGlu1 receptors as a therapeutic target in absence epilepsy.     

Use of siRNA in knocking down of dopamine receptors, a possible therapeutic option in neuropsychiatric disorders

Heightened dopaminergic activity has been shown to be implicated in some major neuropsychiatric disorders such as schizophrenia. Use of dopaminergic antagonists was limited by some serious side effects related to unspecific blocking of dopamine receptors. Thus a target specific dopamine receptor gene silencing method such as using small interfering RNA (siRNA) might be useful. In this study recombinant plasmids expressing siRNA against dopamine receptors (D1-D5DRs) were produced, and their efficiency in knocking down of receptors in were assessed in rat neuroblastoma cell line (B65), using Real-time PCR method. Furthermore, D2DR siRNA expressing plasmid was injected into the rat nucleus accumbens bilaterally to investigate whether it can prevent the hyperactivity induced by apomorphine. Locomotion was measured in 10 min intervals, 50 min before and 60 min after apomorphine injection (0.5 mg/kg, S.C). Our results indicated that the mRNA level of dopamine receptors were reduced between 25 and 75% in B65 cells treated with the plasmids in vitro. In behavioral tests, locomotion was lower at least in the second 10 min after apomorphine injection in rats treated with plasmid expressing D2DR siRNA compare to control group [F (4,24) = 2.77, (P < 0.05)]. The spontaneous activity of treated rats was normal. In conclusion, dopamine receptors can be downregulated by use of siRNA expressing plasmids in nucleus accumbens. Although our work may have some possible clinical applications; the potentially therapeutic application of siRNA in knocking down of dopamine receptors needs further studies.     

The hippocampus as the determinant structure generating epileptic activity during korazol kindling

It has been shown in chronic experiments on rats that two periods of EEG and behavioral alterations may be distinguished during korazol kindling. The bursts of slow waves and spike-wave activity appear on the EEG during the first period as response to subthreshold doses of korazol, which is accompanied behaviorally by standing and myoclonuses. The second period is characterized by the appearance of high-frequency polymorphous generalized seizure discharges on the EEG accompanied by clonicotonic seizures. Interictal and ictal epileptic discharges appear primarily in the hippocamp and then in other brain structures during the development of korazol kindling. The conclusion is made that the hippocamp plays the role of a pathological determinant structure in the development of chronic brain epileptization during korazol kindling.     

gamma-Endorphin and N alpha-acetyl-gamma-endorphin interfere with distinct dopaminergic systems in the nucleus accumbens via opioid and non-opioid mechanisms

Low doses (10 ng) of the dopamine agonist apomorphine induced hypolocomotion when injected into the nucleus accumbens of rats. This behavioral response was antagonized by local treatment with either the opioid peptide gamma-endorphin (gamma E) or the non-opioid peptide N alpha-acetyl-gamma-endorphin (Ac gamma E) in a dose of 100 pg. High doses of apomorphine (10 micrograms) r amphetamine (2 micrograms) injected into the nucleus accumbens resulted in hyperlocomotion. This response was blocked by pretreatment with gamma E but not with Ac gamma E. This effect of gamma E could be prevented by local treatment with naloxone. Neither peptides interfered with the apomorphine-induced stereotyped sniffing when the substances were injected into the nucleus caudatus. It is concluded that gamma E and Ac gamma E differentially interact with distinct dopaminergic systems in the nucleus accumbens of the rat brain via an opioid and a non-opioid mechanism, suggesting that the peptide fragments originating from pro-opiomelanocortin may be specifically implicated in the control of dopaminergic activity in this brain area.     

Antiepileptic effects of amphetamine may require GABA (benzodiazepine) activity

Secondary components of visual evoked potentials (slow negative wave-SNW, and photically-evoked sensory afterdischarge-SAD) are known to be precursors of experimentally activated wave-spike discharges, similar to wave-spikes of petit mal epilepsy. Both SNW and SAD may be potently suppressed wither by amphetamine or GABAergic compounds such as diazepam and sodium valproate. A hypothesis was tested in the present study, that amphetamine-induced suppression of wave-spike discharges may require GABA-benzodiazepine activity for its expression.Electrocortical activity was recorded and averaged in unrestrained albino rats with chronically implanted epicortical electrodes. SNW and SAD obtained in habituated rats in the predrug state were potently suppressed by amphetamine (1 mg/kg, i.p.). Fifteen minutes after amphetamine injection, a challenging drug (metrazol, picrotoxin, convulsant benzodiazepine, Ro 5-3663, or imidazodiazepine, Ro 15-1788) was administered intraperitoneally. Subconvulsive doses of metrazol (10 mg/kg) reversed amphetamine suppression; imidazodiazepine (20 mg/kg) and picrotoxin (1.5 mg/kg) reliably opposed the SNW suppression; convulsant benzodiazepine, Ro 5-3663 (2 mg/kg), showed modest and nonsignificant effect in the same direction. It is proposed that the antiepileptic potency of amphetamine may be associated with its ability, apparently via modulatory effect of norepinephrine, to facilitate the activation of benzodiazepine-GABA receptors.     

Responsiveness of nigral neurons to the stimulation of striatal dopaminergic receptors in the rat

The microinfusion of low doses of apomorphine into the striatum of anesthetized rats depressed the electrical activity of the neurons of the substantia nigra pars compacta while the infusion of bromocriptine had an excitatory or inhibitory effect. These data suggest that:1) the action of the two dopamine agonists on the striato-nigral pathway is different; 2) the striatum might contain dopaminergic receptors located on cells projecting to the substantia nigra with different roles in the feedback regulation of the latter; 3) the inhibitory action of systemically injected apomorphine is not simply due to a stimulation of dopamine “autoreceptors” but also to an action mediated by fibers descending from the striatum to the substantia nigra.     

Role of dopamine receptors in the mechanism of formation of stress-induced stomach lesions

Experiments on rats with the use of different exposures to stress (generalized electrization and "social stress") have demonstrated that stimulation of dopamine receptors localized in the central nervous system is one of the reasons for stress-induced gastric lesions, particularly for massive hemorrhages. Stimulation of peripheral dopamine receptors seems to have a gastroprotective action. As judged from the intensity of the effects of the dopamine agonists, apomorphine and L-DOPA, on stress-induced lesions of the gastric mucosa, stimulation of D2- rather than of D1-dopamine receptors is of greater importance in stress.     

The anticonvulsive effect of non-NMDA antagonist GYKI 52466 on 3-aminopyridine-induced primary and secondary cortical ictal activity in rat

The effect of GYKI 52466, a selective, non-competitive antagonist of the AMPA glutamate receptor subtype was investigated on the development, expression and propagation of 3-aminopyridine-induced cortical ictal activity, both in the primary and secondary focus. In one group of animals GYKI 52466 was administered intraperitoneally, 20 minutes prior to the local application of the convulsant the surface of the cortex of anaesthetized rats. Control animals were injected by physiological solution. Different parameters of electrographic ictal discharges were measured under the influence of the antagonist and compared to control values. The results demonstrate that GYKI 52466 exerts anticonvulsive effects on both the induction and the expression of primary and secondary electrical ictal activity, by delaying the onset of the first ictal period, shortening the duration of ictal activity and decreasing the amplitudes of epileptiform discharges. However, the seizure propagation was not influenced significantly. It is suggested that the initiation, maintenance and the propagation of spontaneous seizures may be controlled by separate mechanisms and that changes can occur in one of the procedures without parallel changes in others. The observations of the present study extend those reported previously by others, namely that activation of non-NMDA receptors is significantly involved in the initiation and maintenance of cortical epileptiform activity.     

Effects of the potential neuroleptic peptide des-tyrosine1-γ-endorphin and haloperidol on apomorphine-induced behavioural syndromes in rats and mice

The effects of haloperidol and Des-Tyr¹-γ-endorphin (DTγE) were studied on climbing induced in mice by high doses of apomorphine and on the yawning syndrome induced in rats by low doses of apomorphine. Haloperidol in a dose of 0.0046 mg/kg s.c. potentiated climbing whereas at higher doses climbing was inhibited (ED₅₀=0.03 mg/kg). DTγE had no effect on climbing under normal conditions in doses up to 2 mg/kg s.c.. After three days of handling and saline pre-injections DTγE potentiated climbing in doses from 0.1 to 1 mg/kg.Haloperidol inhibited yawning induced by low doses of apomorphine (ED₅₀=0.01 mg/kg). DTγE, on the other hand, potentiated yawning induced by low apomorphine at doses of 0.02 and 0.04 mg/kg s.c.. From the point of view that low doses of apomorphine predominantly activate presynaptic dopamine autoreceptors while higher doses predominantly activate postsynaptic dopamine receptors the following tentative conclusions are drawn. 1) Haloperidol blocks presynaptic dopamine autoreceptors at low doses and postsynaptic dopamine receptors at higher doses. 2) DTγE sensitizes presynaptic dopamine autoreceptors at low doses, thereby strengthening the local feedback mechanism at the dopaminergic nerve ending, and sensitizes postsynaptic dopamine receptors at higher doses.     

Effects of centrally injected amylin on sexually behavior of male rats.

Amylin (AMY) is a peptide of pancreatic origin principally involved in the carbohydrate metabolism, but that may interfere with central and peripheral dopamine (DA) pathways. The peptide, injected intracerebroventricularly (ICV) at the dose of 2.5 microg/rat, induced a decrease of copulatory activity in good copulators (GCO) and sluggish (SLU) male rats. The dose of 0.1 microg/rat did not affect significantly the sexual behavior of GCO rats, whereas AMY 0.5 microg/rat increased only the latency and reduced the frequency of ejaculation. At the dose of 2.5 microg/rat AMY antagonized the activation of sexual behavior induced by the DA receptor agonist, apomorphine administered subcutaneously (SC) at the dose of 100 microg/kg. Moreover, this inhibitory effect was blocked by the calcitonin gene-related peptide and AMY receptor antagonist, CGRP (8-37) fragment (injected ICV at the dose of 1 microg/rat). These data suggest that AMY may exert inhibitory effects on male sexual behavior in rats, probably interfering with central DA neurotransmission and with CGRP receptors.     

A spatially extended model for macroscopic spike-wave discharges

Spike-wave discharges are a distinctive feature of epileptic seizures. So far, they have not been reported in spatially extended neural field models. We study a space-independent version of the Amari neural field model with two competing inhibitory populations. We show that this competition leads to robust spike-wave dynamics if the inhibitory populations operate on different time-scales. The spike-wave oscillations present a fold/homoclinic type bursting. From this result we predict parameters of the extended Amari system where spike-wave oscillations produce a spatially homogeneous pattern. We propose this mechanism as a prototype of macroscopic epileptic spike-wave discharges. To our knowledge this is the first example of robust spike-wave patterns in a spatially extended neural field model.     

The effect of dopamine receptor stimulation on the motor and stereotypic activities of mice with different genotypes]

On mice of 8 highly inbred strains--BALB/c, DBA/2, C57B1/6, CBA, DD, CC57Br, C3H/He, A/He--the role was studied of dopamine receptors of the first and second types (D1 and D2) in the regulation of the general motor activity and stereotypic climbing. Significant dependence was shown of these types of dopamine-dependent behaviour on the genotype. Agonist of D1/D2 receptors, apomorphine decreased the motor activity of animals of the all studied strains, and this effect significantly depended on the genotype. The inhibition of locomotion after selective stimulation of D2 receptors (by LY 171555) was significant. Distribution of mouse strains according to expressiveness of climbing after administration of apomorphine differed from their distribution by the level of motor activity. Selective stimulation of D1 receptors, on the whole, elicited climbing of lesser intensity than D1/D2 activation (excluding CBA strain), and administration of D2 agonist did not induce it at all. Probably, for full expression of behavioural reactions the interaction between D1 and D2 receptors is required.