Anticonvulsant effects of four neuropeptides in the rat hippocampus during self-sustaining status epilepticus

Galanin and galanin receptors in epilepsy

The shift in the balance between the inhibition and the excitation in favor of the latter is a major mechanism of the evolvement of epileptic seizures. On the neurotransmitter level two major players contribute to such misbalance: an inhibitory transmitter gamma-aminobutyric acid, and an excitatory amino acid glutamate. Neuropeptides are powerful modulators of classical neurotransmitters, and thus represent an intriguing tool for restoring the balance between the inhibition and the excitation, through either blocking or activating peptide receptors depending on whether a peptide is pro- or anticonvulsant. Galanin, a 29-amino acid residues neuropeptide which inhibits glutamate release in the hippocampus, is a likely member of the anticonvulsant peptide family. During the past decade growing evidence has been suggesting that galanin is in fact a powerful inhibitor of seizure activity. This review summarizes the state of research of galanin in epilepsy, beginning with the first simple experiments which showed that central injection of galanin agonists inhibited seizures, and that seizures themselves affected galanin signaling in the hippocampus; exploring the impact of active manipulation with the expression of galanin and galanin receptors on seizures, using transgenic animals, antisense and peptide-expressing vector approaches; and concluding with the recent advances in pharmacology, which led to the synthesis of non-peptide galanin receptor agonists with anticonvulsant properties. We also address recently established functions of galanin in seizure-associated neuronal degeneration and neuronal plasticity.

Management of multifactorial idiopathic epilepsy in EL mice with caloric restriction and the ketogenic diet: role of glucose and ketone bodies

BACKGROUND: The high fat, low carbohydrate ketogenic diet (KD) was developed as an alternative to fasting for seizure management. While the mechanisms by which fasting and the KD inhibit seizures remain speculative, alterations in brain energy metabolism are likely involved. We previously showed that caloric restriction (CR) inhibits seizure susceptibility by reducing blood glucose in the epileptic EL mouse, a natural model for human multifactorial idiopathic epilepsy. In this study, we compared the antiepileptic and anticonvulsant efficacy of the KD with that of CR in adult EL mice with active epilepsy. EL mice that experienced at least 15 recurrent complex partial seizures were fed either a standard diet unrestricted (SD-UR) or restricted (SD-R), and either a KD unrestricted (KD-UR) or restricted (KD-R). All mice were fasted for 14 hrs prior to diet initiation. A new experimental design was used where each mouse in the diet-restricted groups served as its own control to achieve a 20-23% body weight reduction. Seizure susceptibility, body weights, and the levels of plasma glucose and beta-hydroxybutyrate were measured once/week over a nine-week treatment period. RESULTS: Body weights and blood glucose levels remained high over the testing period in the SD-UR and the KD-UR groups, but were significantly (p < 0.001) reduced in the SD-R and KD-R groups. Plasma beta-hydroxybutyrate levels were significantly (p < 0.001) increased in the SD-R and KD-R groups compared to their respective UR groups. Seizure susceptibility remained high in both UR-fed groups throughout the study, but was significantly reduced after three weeks in both R-fed groups. CONCLUSIONS: The results indicate that seizure susceptibility in EL mice is dependent on plasma glucose levels and that seizure control is more associated with the amount than with the origin of dietary calories. Also, CR underlies the antiepileptic and anticonvulsant action of the KD in EL mice. A transition from glucose to ketone bodies for energy is predicted to manage EL epileptic seizures through multiple integrated changes of inhibitory and excitatory neural systems.

Inhibition of nociceptin/orphanin FQ on penicillin-induced seizures in rats

The opioid peptides were thought to be involved in specific types of seizures. Nociceptin/Orphanin FQ (NC) is the endogenous ligand of the nociceptin opioid peptide (NOP) receptor and may play a role in epilepsy. However, accumulated evidences indicated that NC had both anti- and pro-convulsive effects, and the direct effect of NC in modulating epilepsy in the hippocampus still remained unclear. In this study, we investigated the effect of NC on penicillin-induced seizures (PIS) in rats. Seizure model was produced by intra-hippocampus injection of penicillin in anesthetized rats. The electroencephalography (EEG) was then observed and estimated by power spectrum analysis. Pretreatment of NC (intracerebroventricular, i.c.v.) depressed PIS in a dose-dependent manner at doses of 0.055, 0.55 and 5.5 nmol in 2 microl saline, respectively. [Nphe1]Nociceptin(1-13)NH2, a selective NOP receptor antagonist reversed the effect of NC against PIS, and this antagonist was inactive to PIS itself. These results indicated that NC had a receptor-specific preventive effect against PIS.

Neuropeptide Y and seizures: effects of exogenously applied ligands

The endogenous NPY system in the brain is centrally involved in seizure regulation. The present paper reviews the evidence that exogenously applied NPY receptor ligands can inhibit epileptic seizures in various rodent in vitro and in vivo models. Agonists at Y2 and/or Y5 receptors and antagonists at Y1 receptors appear to inhibit seizures, depending on the seizure model studied. Although progress has been made, further studies are needed using transgenic animals as well as novel selective agonists and antagonists to firmly identify the NPY receptors mediating antiepileptic effects. This may lead to the development of future antiepileptic drug treatments targeting the NPY system.

Anticonvulsant and antiepileptogenic effects mediated by adeno-associated virus vector neuropeptide Y expression in the rat hippocampus

Neuropeptide Y (NPY) inhibits seizures in experimental models and reduces excitability in human epileptic tissue. We studied the effect of long-lasting NPY overexpression in the rat hippocampus with local application of recombinant adeno-associated viral (AAV) vectors on acute kainate seizures and kindling epileptogenesis. Transgene expression was significantly increased by 7 d, reached maximal expression by 2 weeks, and persisted for at least 3 months. Serotype 2 AAV vector increased NPY expression in hilar interneurons, whereas the chimeric serotype 1/2 vector caused far more widespread expression, also including mossy fibers, pyramidal cells, and the subiculum. EEG seizures induced by intrahippocampal kainate were reduced by 50-75%, depending on the vector serotype, and seizure onset was markedly delayed. In rats injected with the chimeric serotype 1/2 vector, status epilepticus was abolished, and kindling acquisition was significantly delayed. Thus, targeted NPY gene transfer provides a potential therapeutic principle for the treatment of drug-resistant partial epilepsies.

Recombinant AAV-mediated expression of galanin in rat hippocampus suppresses seizure development

Galanin, a 29- or 30-amino acid neuropeptide, has been implicated in the modulation of seizures. In this study, we constructed a recombinant adeno-associated viral (AAV) vector to constitutively over-express galanin (AAV-GAL). The vector mediated efficient transduction of HEK 293 cells in vitro and robust galanin expression in vivo when injected into the rat dorsal hippocampus. Rats were administered kainic acid intrahippocampally 2.5 months following AAV-GAL or empty vector (AAV-Empty) injection to study the effect of vector-mediated galanin over-expression on seizures. AAV-GAL-injected rats showed a decreased number of seizure episodes and total time spent in seizures compared to AAV-Empty rats, despite similar latencies to development of the first EEG seizure and similar levels of neuronal damage in the CA3 region for both groups. These data show that recombinant AAV mediates strong and stable over-expression of galanin when injected into the rat hippocampus resulting in a significant anticonvulsive effect. The seizure suppression effect of galanin expression in the hippocampus by viral vectors may lead to novel therapeutic strategies for the treatment and management of intractable seizures with focal onset such as temporal lobe epilepsy.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).