G. van Luijtelaar

Kappa opioid receptor agonists suppress absence seizures in WAG/Rij rats

Involvement of the kappa opioid receptor in the regulation of epileptic activity was studied in WAG/Rij rats, a genetic model of absence epilepsy. I.c.v. administration of the kappa agonists U50,488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide), U69,593 (5 alpha, 7 alpha, 8 beta)-(-)-N-methyl-(1-pyrrolidinyl)-1- oxaspiro(4,5)dec-8-yl)benzeneacetamide) or PD117,302 ((+/-)-trans-N-methyl-N-[2-(1-pyrrolidinyl)- cyclohexyl]benzo[b]thiophene-4-acetamide), 50 and 150 micrograms/5 microliter each, dose-dependently decreased the number and mean duration of spike wave discharges (SWD). Peripheral administration of U50,488H (10 and 30 mg/kg s.c.) also attenuated the seizure activity in this model. The specific kappa opioid receptor antagonist nor-binaltorphimine (Nor-BNI, 10 micrograms/5 microliters i.c.v., 18 h before EEG registration) moderately increased the number of SWD, which suggests that endogenous opioids acting through kappa receptors may tonically inhibit the seizure activity in these rats. In addition, the enhancement of an absence-like seizure activity induced by the specific mu opioid receptor agonist D-Ala2-N-methyl-Phe4-Gly5-ol-enkephalin (DAMGO, 0.7 microgram/5 microliters i.c.v.) was also attenuated in rats pretreated with U50,488H, U69,593 or PD117,302. These data indicate that activation of the kappa opioid receptor exerts an inhibitory effect on absence-like seizure activity in WAG/Rij rats.

Proenkephalin and prodynorphin mRNA level in brain of rats with absence epilepsy.

An in situ hybridization method was used to estimate the proenkephalin (PENK) and prodynorphin (PDYN) mRNA levels in the brain of epileptic 6-month-old WAG/Rij rats in comparison with non-epileptic: 3-month-old WAG/Rij rats, 3-month-old ACI rats and 6-month-old ACI rats. The epileptic rats had a significantly higher level of PENK mRNA in the striatum as compared to non-epileptic controls. The PDYN mRNA level was significantly elevated only in the hippocampus of epileptic rats, whereas age- or strain-related changes in the striatal and cortical PDYN mRNA levels were found in both epileptic and non-epileptic rats. The changes in the biosynthetic activity of endogenous opioid peptide systems may be important for the occurrence of epileptic discharges in these animals.

Effects of μ and δ opioid receptor agonists and antagonists on absence epilepsy in WAG/Rij rats

Abstract The effects of various types of opioid receptor agonists and antagonists were determined in a genetic rat model for generalized absence epilepsy. Rats of the WAG/Rij strain spontaneously showed several hundred spike-wave discharges per day. Intracerebroventricular (i.c.v.) injections of the selective μ agonist DAMGO (0.2, 0.7 μg) resulted in a dose-related increase in the number of spike-wave discharges, while the selective δ agonist DPDPE (20, 60 μg) was without effect. DAMGO reduced the duration of automatic behavior, enhanced the immobile behavior (after the low dose) and had no effect on exploratory behavior. On the other hand, DPDPE significantly enhanced the total time spent on exploration, but did not influence other behavioral parameters. There was no correlation between the ability of the drug to modulate the epileptic activity and behavioral changes. The nonselective antagonist naloxone, administered either i.p. (0.4, 2.0, 10 mg/kg) or i.c.v. (10, 50 μg), increased the number of spike-wave discharges in a dose-dependent way. The specific δ receptor antagonist naltrindole (0.3, 1 mg/kg) was without effect, as was the irreversible μ receptor antagonist β-funaltrexamine (β-FNA). Pretreatment with β-FNA diminished the action of DAMGO. These results clearly indicate that activation of the μ opioid receptor increases the number of spike-wave discharges, and that modulation of δ receptors is not effective. On the other hand, the naloxone-induced enhancement of spike-wave discharges, suggests a tonic control of the epileptic activity by another opioid system. These results point to an important role of the μ-, but not δ-, receptor in facilitation of the epileptic activity in WAG/Rij rats.

Anatomical and functional aspects of μ opioid receptors in epileptic WAG/Rij rats

Abstract Involvement of opioid systems in the pathogenesis of absence epilepsy has been postulated. However, the role of the μ opioid receptor has not been fully elucidated as yet. In the present study the role of this receptor in absence epilepsy was investigated autoradiographically and pharmacologically. The density of μ opioid receptors in discrete brain areas was quantified in WAG/Rij rats, which are regarded as a genetic model of primarily generalized absence epilepsy and in three control groups of non-epileptic rats. The autoradiographic study showed an abundance of μ opioid receptors (labelled with [ 3 H]DAMGO) in the structures involved in generation and propagation of spike-wave discharges, such as the thalamus, cortex and striatum. A significant decrease in the μ receptor density was found only in the frontal cortex of epileptic WAG/Rij rats. In the pharmacological study, the effect of μ opioid receptor activation in different brain structures of WAG/Rij rats on the number of complexes of spike-wave discharges was investigated. DAMGO (0.02 and 0.07 μ g/0.5 μ l) was bilaterally injected into the thalamus, striatum and frontal cortex. DAMGO resulted in a dose-related increase in the number of spike-wave discharges after intracortical and intrastriatal administration by ≈200–300% and after intrathalamic administration by ≈500%. The injection of DAMGO into those structures had no significant effect of any kind on the behavior measured, except for passive behavior which was reduced after intrastriatal injection. The high density of μ opioid receptors in the areas involved in the genesis of spike-wave discharges, as well as the highest responsiveness of thalamic μ opioid receptors to the epileptogenic effects of DAMGO, suggest involvement of μ receptors in the genesis of spike-wave discharges.

Method for diagnostics of characteristic patterns of observable time series and its real-time experimental implementation for neurophysiological signals

A method is proposed for analysis and automatic diagnostics of characteristic oscillatory patterns of the electric activity of the brain in real time on the basis of a continuous wavelet transformation. The results of experimental investigation of automatic recognition of epileptic activity episodes on experimental animals based on the proposed approach are considered.

Cytokines and Absence Seizures in a Genetic Rat Model

We investigated the role of two cytokines, IL-1β and TNF-α, in the development of absence seizures using a genetic model of absence epilepsy in WAG/Rij rats. We administered these cytokines to animals systemically and measured the number of spike-wave discharges (SWDs) in the EEG. We also coadministered IL-1β with the GABA reuptake inhibitor tiagabine and measured the levels of IL-1β and TNF-α in the brain and blood plasma of 2-, 4-, and 6-month-old WAG/Rij rats and animals that served as a non-epileptic control (ACI). We found that IL-1β induced a significant increase in SWDs 2-5 h after administration, while TNF-α enhanced SWDs much later. Both cytokines enhanced passive behavior; body temperature was elevated only after TNF-α. The action of tiagabine was potentiated by earlier IL-1β injection, even when IL-1β was no longer active. Young WAG/Rij rats showed higher levels of TNF-α in blood serum than young ACI rats; the effects in the brain tended to be opposite. The marked differences in timing of the increase in SWDs suggest different time scales for the action of both cytokines tested. It is proposed that the results found after TNF-α are due to the de novo synthesis of IL-1β. TNF-α may possess neuroprotective effects. IL-1β might increase GABA-ergic neurotransmission. The changes in the efficacy of antiepileptic drugs related to changes in the cytokine systems may have some clinical relevance.

Effects of diazepam on encoding processes

Benzodiazepines are known to induce amnesic effects. To specify these effects more precisely, 40 healthy volunteers were given 15 mg diazepam or placebo. Effects on a chain of encoding operations were investigated: activation of memory representations, spreading of activation, semantic encoding and organizational processes. The diazepam group performed tasks consistently slower, although spreading of activation and semantic encoding were not affected by diazepam. Rather, diazepam subjects benefited less from opportunities to organize to-be-learned material. It is suggested that cognitive processes are slowed down after diazepam intake. This may also have implications for the organization of to-be-learned material.

Connectivity analysis of generalized epileptic discharges

Adresses e-mail : sadeghiye hashem@yahoo.com, sadeghiye@ut.ac.it (H. Sadeghiyeh) The present study aimed to examine the gender differences in empathy for pain at a sensorimotor level. Previous studies using single-pulse TMS have shown a reduction in amplitude of motor-evoked potentials (MEPs) while subjects observing needles penetrating hand of a human model which was specific to the muscle subjects observed being pricked. Twenty-five subjects (thirteen females and twelve males) participated in the study. Their TMS-induced MEPs were recorded from their right first dorsal interosseus (FDI) muscle of index finger during watching various clips depicting needles penetrating the same FDI muscle of right hand of a model. There were twelve types of clips, including pictures of hands of a woman, a man, a child and an apple, which was either pinpricked by a needle, touched by a Q-tip or at rest. Each clip was shown to the subjects eighteen times in a completely random sequence. Electromyography signals were recorded through an amplifier of an ANT ERP recording system and analysed by ASA-Lab software. Results had been shown that women had larger MEP inhibited amplitude than men in all the stimuli. However, there were no significant differences between MEP amplitudes of different types of models’ hands. The gender differences of MEPs between subjects indicate greater sensorimotor empathy in women, which is in correspondence with greater subjective responses of women to the painful clips (state empathy), which were obtained through a Visual Analogue Scale. Therefore, upon these results, we can conclude that women’s stronger empathic response to observing pain in others go beyond just a subjective level and extend to a very automatic and sensorimotor level. Women are hard-wired to embody the pain of others more intensely, and this could prepare them to take action towards others’ pain more rapidly. Further reading

HORMONES AND GENDER | Hormones and Absence Epilepsy

Hormones have an extremely large impact on seizures and epilepsy. Stress and stress hormones are known to reinforce seizure expression, and gonadal hormones affect the number of seizures and even the seizure type. Moreover, hormonal concentrations change drastically over an individuals lifetime, especially in women. The prevailing view on steroid hormones is that estrogen and corticosteroid hormones are proconvulsant, whereas progesterone is anticonvulsant. The neuroactive steroids may exert some of their effects nongenomically through their action on classical GABA receptors. However, understanding the interaction between the GABA system and hormones in absence epilepsy is complicated by the peculiar pharmacological profile exhibited by absence epilepsy (which is opposite to the profile seen in other types of seizures). Moreover, absences are associated with hyperfunction of the GABAergic inhibitory system. Thus, the relations between hormones that modulate the GABA receptors and absence epilepsy must be given special attention. Outcomes of recent pharmacological studies with progesterone show that acute systemic administration exacerbates absence seizures, that absence seizures are virtually reduced during pregnancy when plasma levels are chronically elevated, and that intrahippocampal administration of progesterone reduces spike-wave discharges. This suggests a complicated relationship between progesterone and absence seizures. How progesterone affects absence seizures is an important, fascinating, and challenging question.

Biosynthesis of proenkephalin and prodynorphin in the brain of rats with genetic absence epilepsy

Endogenous opioid peptides are involved in the genesis or/and control of an epileptic activity in WAG/Rij rats - a genetic model of absence epilepsy. An in situ hybridization study showed that epileptic rats had a significantly higher level of proenkephalin (PENK) mRNA in the striatum and frontal cortex as compared with non-epileptic controls. In contrast to PENK, only age-related changes in PDYN mRNA in the cortex and, to the lesser extent in the striatum were detected in both epileptic and non-epileptic rats. In the hippocampus of epileptic rats, an elevated PDYN mRNA level and no differences in hippocampal PENK mRNA level were found