Chronic Electroconvulsive Seizures Down–Regulate Expression of the Immediate-Early Genes c-fos and c-jun in Rat Cerebral Cortex

Acute seizures and other stimuli that increase neuronal activity cause a rapid induction of the immediate-early genes c-fos and c-jun, also referred to as nuclear proto-oncogenes, in the nervous system. In the present study, rats were administered one or more electroconvulsive seizures (ECS) and the responsiveness of c-fos and c-jun to an acute, "test" seizure was examined. Four hours after a single ECS, the induction of c-fos mRNA by a test seizure was blocked, in agreement with earlier findings, but by 18 h the levels of c-fos mRNA could be reinduced by the test seizure, suggesting that 1 day is sufficient to "reset" the responsiveness of this system. However, it was found that chronic, daily ECS treatments resulted in a time-dependent decrease in the expression of c-fos mRNA in response to a test seizure administered 18 h after the last daily ECS; this effect was maximal after 8-10 days of treatment, at which time the induction of c-fos mRNA by the test seizure was blocked dramatically. Chronic ECS also blocked the induction of c-jun in response to an acute, test seizure. The effect of chronic ECS on levels of Fos protein was also investigated. It was found that basal levels of Fos protein were reduced after chronic (10 days) ECS and were not induced by a test seizure. Because levels of Fos protein remain elevated 4 h after a single seizure this finding suggests that the mechanisms by which acute (4 h) and chronic (8-10 days) ECS block the induction of c-fos may differ.     

Amygdala Kindling Potentiates Seizure-Stimulated Immediate-Early Gene Expression in Rat Cerebral Cortex

Kindling induces long-term adaptations in neuronal function that lead to a decreased threshold for induction of seizures. In the present study, the influence of amygdala kindling on levels of mRNA for the immediate-early genes (IEGs) c-fos, c-jun, and NGF1-A were examined both before and after an acute electroconvulsive seizure (ECS). Although amygdala kindling did not significantly influence resting levels of c-fos mRNA in cerebral cortex, ECS-stimulated levels of c-fos mRNA (examined 45 min after ECS) were approximately twofold greater in the cerebral cortex of kindled rats relative to sham-treated controls. The influence of kindling on IEG expression was dependent on the time course of kindling, as ECS-stimulated levels of c-fos mRNA were not significantly increased in stage 2 kindled animals. ECS-stimulated levels of c-jun and NGF1-A mRNA were also significantly increased in cerebral cortex of kindled rats relative to sham-treated controls. The influence of kindling on IEG expression was long-lasting because an acute ECS stimulus significantly elevated levels of c-fos and c-jun mRNA in the cerebral cortex of animals that were kindled 5 months previously. In contrast to these effects in cerebral cortex, kindling did not influence ECS-stimulated levels of c-fos mRNA in hippocampus. Finally, immunohistochemical studies revealed lamina-specific changes in the cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mouse Brain c-fos mRNA Distribution Following a Single Electroconvulsive Shock

The regional distribution of c-fos mRNA in the mouse brain has been investigated by in situ hybridization autoradiography after seizures induced by an acute electroconvulsive shock (ECS). ECS led to a widespread induction of the proto-oncogene c-fos in the brain, with highest concentrations in discrete areas within the limbic system and also in the hypothalamus and cerebellum. The mild stress of sham treatment in earclipped animals induced a weaker and qualitatively different pattern of c-fos mRNA expression involving the cortex, hippocampus, and cerebellum. These data suggest the usefulness of c-fos in situ hybridization as a marker of neuronal stimulation and in mapping a range of effects from a mild stress to the robust changes of an electroconvulsive seizure.     

Expression of c-fos, c-jun and HSP70 mRNA in rat brain following high acceleration stress

Rats exposed to high +Gz forces in a small animal centrifuge (SAC) exhibit loss of neuronal function (isoelectric EEG), termed G-induced loss of consciousness (G-LOC). This phenomenon is presumably due to a reduction in cerebral blood flow (CBF) or ischemia. Ischemia induces various metabolic and physiologic changes including expression of immediate early genes (IEGs) in the brain. Expression of IEGs have been suggested to be reliable markers for neuronal response to external stimuli or stress. In the present study expression of IEGs c-fos, c-jun and stress response gene HSP70 were measured in the brains of rats subjected to six 30 s exposures of +22.5Gz in a small animal centrifuge. The level of c-fos, HSP70 and beta-actin mRNA were measured by both Northern blot and RT-PCR. Expression of c-jun was measured only by RT-PCR. Expression of c-fos and c-jun was significantly stimulated at 0.5, 15, 30 and 60 min post-centrifugation. The level of HSP70 mRNA was significantly higher only at 60 and 180 min post-centrifugation. Measurement of metabolities showed a significant increase in lactate and a decrease in Cr-P level at 30 s and 15 min post-centrifugation, respectively. Lactate, but not Cr-P and ATP levels were restored to control levels by 60 min post-centrifugation. It is concluded that the transient expression of c-fos, c-jun and HSP70 mRNA is stimulated by repeated ischemic/reperfusion episodes induced by high acceleration stress.     

Roles of prostaglandin synthesis in excitotoxic brain diseases

Cyclooxygenase (COX) is a rate-limiting enzyme in prostaglandin synthesis. COX consists of two isoforms, constitutive COX-1 and inducible COX-2. We have first found that COX-2 expression in the brain is tightly regulated by neuronal activity under physiological conditions, and electroconvulsive seizure robustly induces COX-2 mRNA in the brain. Our recent in-depth studies reveal COX-2 expression is divided into two phases, early in neurons and late in non-neuronal cells, such as endothelial cells or astrocytes. In this review, we present that early synthesized COX-2 facilitates the recurrence of hippocampal seizures in rapid kindling model, and late induced COX-2 stimulates hippocampal neuron loss after kainic acid treatment. Hence, we consider the potential role of COX-2 inhibitors as a new therapeutic drug for a neuronal loss after seizure or focal cerebral ischemia. The short-term and sub-acute medication of selective COX-2 inhibitors that suppresses an elevation of prostaglandin E(2) (PGE(2)) may be an effective treatment to prevent neuronal loss after onset of neuronal excitatory diseases. This review also discusses a novel role of vascular endothelial cells in brain diseases. We found that these cells produce PGE(2) by synthesizing COX-2 and microsomal prostaglandin E synthase-1 (mPGES-1) in response to excitotoxicity and neuroinflammation. We also show a possible mechanisms of neuronal damage associated with seizure via astrocytes and endothelial cells. Further analysis of the interaction among neurons, astrocytes and endothelial cells may provide a better understanding of the processes of neuropathological disorders, as well as facilitating the development of new treatments.     

Effects of ionizing radiation and beta-adrenergic stimulation on the expression of early response genes in rat parotid glands.

There is little known about the regulation of gene expression in rat parotid glands after exposure to ionizing radiation. The present studies investigate the effects of in vivo ionizing radiation, with subsequent stimulation of beta-adrenergic receptors by isoproterenol, on parotid gland function and on the expression of the early response genes, c-fos, c-jun, and jun B. Ionizing radiation diminished parotid gland weight and saliva output. Treatment of irradiated rats with isoproterenol increased the gland weight to levels similar to those in nonirradiated rats. However, such treatment had no effect on saliva output as indicated by measurements of parotid salivary flow rate. Irradiation alone increased the expression of c-fos, c-jun, and jun B. The combination of irradiation and isoproterenol had an additional effect on the levels of c-fos and jun B mRNAs and proteins particularly at earlier experimental times (1 to 8 h). Isoproterenol alone induced high levels of c-fos and jun B mRNA but not of c-jun mRNA. However, c-jun mRNA was induced markedly by radiation and 8 h of isoproterenol treatment, indicating a combined effect on c-jun gene expression. These observations suggest that the expression of the proto-oncogenes c-fos, c-jun, and jun B is probably regulated through differential signal transduction pathways which may be activated by these external stimuli and may be associated with functional changes induced in the rat parotid gland by ionizing radiation and by ionizing radiation and isoproterenol.     

Influence of Ivabradine on the Anticonvulsant Action of Four Classical Antiepileptic Drugs Against Maximal Electroshock-Induced Seizures in Mice

Although the role of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in neuronal excitability and synaptic transmission is still unclear, it is postulated that the HCN channels may be involved in seizure activity. The aim of this study was to assess the effects of ivabradine (an HCN channel inhibitor) on the protective action of four classical antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) against maximal electroshock-induced seizures in mice. Tonic seizures (maximal electroconvulsions) were evoked in adult male albino Swiss mice by an electric current (sine-wave, 25 mA, 0.2 s stimulus duration) delivered via auricular electrodes. Acute adverse-effect profiles of the combinations of ivabradine with classical antiepileptic drugs were measured in mice along with total brain antiepileptic drug concentrations. Results indicate that ivabradine (10 mg/kg, i.p.) significantly enhanced the anticonvulsant activity of valproate and considerably reduced that of phenytoin in the mouse maximal electroshock-induced seizure model. Ivabradine (10 mg/kg) had no impact on the anticonvulsant potency of carbamazepine and phenobarbital in the maximal electroshock-induced seizure test in mice. Ivabradine (10 mg/kg) significantly diminished total brain concentration of phenytoin and had no effect on total brain valproate concentration in mice. In conclusion, the enhanced anticonvulsant action of valproate by ivabradine in the mouse maximal electroshock-induced seizure model was pharmacodynamic in nature. A special attention is required when combining ivabradine with phenytoin due to a pharmacokinetic interaction and reduction of the anticonvulsant action of phenytoin in mice. The combinations of ivabradine with carbamazepine and phenobarbital were neutral from a preclinical viewpoint.