The effect of cycloheximide on the regulation of proenkephalin and prodynorphin gene expressions induced by kainic acid in rat hippocampus

Gastrodia elata modulated activator protein 1 via c-Jun N-terminal kinase signaling pathway in kainic acid-induced epilepsy in rats

Gastrodia elata (Orchidaceae) is a Chinese herb. Our previous study showed that Gastrodia elata is able to reduce epileptic seizures, oxygen free radicals, microglia activation, and apoptosis in kainic acid (KA)-treated rats. Activator protein 1 (AP-1) is involved in modulating the neuronal plasticity and apoptosis. Therefore, the aim of this study was to investigate the role of AP-1 in antiepileptic effect of Gastrodia elata. Gastrodia elata (0.5, 1.0g/kg) or valproic acid (VA, 250mg/kg) was administered orally in Sprague-Dawley rats for 1 week before and 2 weeks after intraperitoneal injection of KA. Protein levels of AP-1 were determined by measuring c-Jun and c-Fos proteins, and the mitogen-activated protein (MAP) kinases activations were determined by measuring the phosphorylations of extracellular signal-regulated kinases, p38, and c-Jun N-terminal kinases (JNKs) in the frontal cortex and the hippocampus of rat brain using Western blotting. These results indicated that pre-treatment with Gastrodia elata or VA activated JNK signal pathway and c-Jun expression, while post-treatment with Gastrodia elata or VA suppressed both the JNK signaling pathway and the c-Jun expression induced by KA. These findings suggested that Gastrodia elata regulated the AP-1 expression via the JNK signaling pathway in KA-induced epilepsy.

The dextromethorphan analog dimemorfan attenuates kainate-induced seizures via sigma1 receptor activation: comparison with the effects of dextromethorphan

In a previous study, we demonstrated that a dextromethorphan analog, dimemorfan, has neuroprotective effects. Dextromethorphan and dimemorfan are high-affinity ligands at sigma1 receptors. Dextromethorphan has moderate affinities for phencyclidine sites, while dimemorfan has very low affinities for such sites, suggesting that these sites are not essential for the anticonvulsant actions of dimemorfan. Kainate (KA) administration (10 mg kg(-1), i.p.) produced robust convulsions lasting 4-6 h in rats. Pre-treatment with dimemorfan (12 or 24 mg kg(-1)) reduced seizures in a dose-dependent manner. Dimemorfan pre-treatment also attenuated the KA-induced increases in c-fos/c-jun expression, activator protein (AP)-1 DNA-binding activity, and loss of cells in the CA1 and CA3 fields of the hippocampus. These effects of dimemorfan were comparable to those of dextromethorphan. The anticonvulsant action of dextromethorphan or dimemorfan was significantly counteracted by a selective sigma1 receptor antagonist BD 1047, suggesting that the anticonvulsant action of dextromethorphan or dimemorfan is, at least in part, related to sigma1 receptor-activated modulation of AP-1 transcription factors. We asked whether dimemorfan produces the behavioral side effects seen with dextromethorphan or dextrorphan (a phencyclidine-like metabolite of dextromethorphan). Conditioned place preference and circling behaviors were significantly increased in mice treated with phencyclidine, dextrorphan or dextromethorphan, while mice treated with dimemorfan showed no behavioral side effects. Our results suggest that dimemorfan is equipotent to dextromethorphan in preventing KA-induced seizures, while it may lack behavioral effects, such as psychotomimetic reactions.

Role of nicotinic acetylcholine receptors in the regulation of kainic acid-induced hippocampal cell death in mice

Kainic acid (KA) is a well-known excitatory, neurotoxic substance. In mice, morphological damage of hippocampus induced by KA administered intracerebroventricularly (i.c.v.) was markedly concentrated on the CA3 pyramidal neurons. In the present study, the possible role of nicotinic acetylcholine receptors (nAchRs) in hippocampal cell death induced by KA (0.1 microg) administered i.c.v. was examined. Methyllycaconitine (MC; nAchRs antagonist, 20 microg) attenuated KA-induced CA3 pyramidal cell death. KA increased immunoreactivities (IRs) of phorylated extracellular signal-regulated kinase (p-ERK; at 30 min), p-CaMK II (at 30 min), c-Fos (at 2 h), c-Jun (at 2 h), glial fibrillary acidic protein (GFAP at 1 day), and the complement receptor type 3 (OX-42; at 1 day) in hippocampal area. MC attenuated selectively KA-induced p-CaMK II, GFAP and OX-42 IR in the hippocampal CA3 region. Our results suggest that p-CaMK II may play as an important regulator responsible for the hippocampal cell death induced by KA administered i.c.v. in mice. Reactive astrocytes, which was meant by GFAP IR, and activated microglia, which was meant by OX-42 IR, may be a good indicator for measuring the cell death in hippocampal regions by KA-induced excitotoxicity. Furthermore, it is implicated that niconitic receptors appear to be involved in hippocampal CA3 pyramidal cell death induced by KA administered i.c.v. in mice.

Ginsenosides attenuate methamphetamine-induced behavioral side effects in mice via activation of adenosine A2A receptors: possible involvements of the striatal reduction in AP-1 DNA binding activity and proenkephalin gene expression

Current evidence suggests that ginsenosides inhibit methamphetamine (MA)-induced changes in behavior, but the precise mechanisms that underlie this effect are yet to be determined. We examined the role of adenosine receptors in the ginsenoside-induced changes in hyperlocomotion and conditioned place preference (CPP) in mice that occurred in response to administration of MA (2 mg/kg, i.p. x 1 or 2 mg/kg, i.p. x 6). Changes in circling behavior paralleled changes in CPP in the presence of MA. Pre-treatment with ginsenosides (50 or 150 mg/kg, i.p.) attenuated the MA-induced circling behavior and CPP. This attenuation was reversed by the adenosine A2A receptor antagonist 1,3,7-trimethyl-8-(3-chrostyryl)xanthine (CSC; 0.5 and 1.0 mg/kg) in a dose-dependent manner, but neither the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT; 0.5 and 1.0 mg/kg) nor the A2B receptor antagonist alloxazine (ALX; 1.5 and 3.0 mg/kg) had any such effect. MA-induced increases in activator protein (AP)-1 DNA binding activity, Fos-related antigen immunoreactivity (FRA-IR), proenkephalin mRNA expression, and proenkephalin-like immunoreactivity were reduced consistently in the striatum of animals that were pretreated with ginsenosides. These reductions were largely prevented by CSC, but not by CPT or ALX. Our results suggest that the stimulation of A2A receptors by ginsenosides attenuates the changes in behavior and the increases in AP-1 DNA binding activity, FRA-IR, and proenkephalin gene expression in mouse striatum that are induced by MA.

Roles of adenosine receptors in the regulation of kainic acid-induced neurotoxic responses in mice

Kainic acid (KA) is a well-known excitatory and neurotoxic substance. In ICR mice, morphological damage of hippocampus induced by KA administered intracerebroventricularly (i.c.v.) was markedly concentrated on the hippocampal CA3 pyramidal neurons. In the present study, the possible role of adenosine receptors in hippocampal cell death induced by KA (0.1 microg) administered i.c.v. was examined. It has been shown that 3,7-dimethyl-1-propargylxanthine (DMPX; A2 adenosine receptors antagonist, 20 microg) reduced KA-induced CA3 pyramidal cell death. KA dramatically increased the phosphorylated extracellular signal-regulated kinase (p-ERK) immunoreactivities (IR) in dentate gyrus (DG) and mossy fibers. In addition, c-Jun, c-Fos, Fos-related antigen 1 (Fra-1) and Fos-related antigen 2 (Fra-2) protein levels were increased in hippocampal area in KA-injected mice. DMPX attenuated KA-induced p-ERK, c-Jun, Fra-1 and Fra-2 IR. However, 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine (PACPX; A1 adenosine receptor antagonist, 20 microg) did not affect KA-induced p-ERK, c-Jun, Fra-1 and Fra-2 IR. KA also increased the complement receptor type 3 (OX-42) IR in CA3 region of hippocampus. DMPX, but not PACPX, blocked KA-induced OX-42 IR. Our results suggest that p-ERK and c-Jun may function as important regulators responsible for the hippocampal cell death induced by KA administered i.c.v. in mice. Activated microglia, which was detected by OX-42 IR, may be related to phagocytosis of degenerated neuronal elements by KA excitotoxicity. Furthermore, it is implicated that A2, but not A1, adenosine receptors appear to be involved in hippocampal CA3 pyramidal cell death induced by KA administered i.c.v. in mice.

Cycloheximide inhibits neurotoxic responses induced by kainic acid in mice

In the present study, we examined the effect of cycloheximide on various pharmacological responses induced by kainic acid (KA) administered intracerebroventricularly (i.c.v.) in mice. In a passive avoidance test, a 20-min cycloheximide (200mg/kg, i.p.) pretreatment prevented the memory impairment induced by KA. The morphological damage induced by KA (0.1microg) in the hippocampus was markedly concentrated in the CA3 pyramidal neurons and cycloheximide effectively prevented the KA-induced pyramidal cell death in CA3 hippocampal region. In immunohistochemical study, KA dramatically increased the phosphorylation of extracellular signal-regulated protein kinase (p-ERK), c-Jun N-terminal kinase 1 (p-JNK1), and calcium/calmodulin-dependent protein kinase II (p-CaMK II). Cycloheximide attenuated the increased p-ERK, p-JNK1, and p-CaMK II levels induced by KA. Furthermore, cycloheximide inhibited the increased c-Fos and c-Jun protein expression levels induced by KA in the hippocampus. The activation of microglia was detected in KA-induced CA3 cell death region by immunostaining with a monoclonal antibody against the OX-42. Cycloheximide inhibited KA-induced increase of OX-42 immunoreactivity. Our results suggest that the increased expression of the c-Fos, c-Jun, and phosphorylation of ERK, JNK1, and CaMK II proteins may play important roles in the memory impairment and the cell death in CA3 region of the hippocampus induced by i.c.v. KA administration in mice. Furthermore, the activated microglia may be related to phagocytosis of degenerated neuronal elements induced by KA.

Reassessment of the effects of cycloheximide on mossy fiber sprouting and epileptogenesis in the pilocarpine model of temporal lobe epilepsy

A feature of animal models of temporal lobe epilepsy and the human disorder is hippocampal sclerosis and Timm stain in the inner molecular layer (IML) of the dentate gyrus, which represents synaptic reorganization and may be important in epileptogenesis. We reassessed the hypothesis that pre-treatment with cycloheximide (CHX) prevents Timm staining in the IML following pilocarpine (PILO)-induced status epilepticus (a multifocal model of temporal lobe epilepsy), but allows epileptogenesis (i.e., chronic spontaneous seizures) after a latent period. Hippocampal slices from PILO-treated rats without Timm stain in the IML after CHX treatment were hypothesized to lack the electrophysiological abnormalities suggestive of recurrent excitation. The primary experimental groups were as follows: 1) CHX (1 mg/kg) 30-45 min prior to administration of PILO (320 mg/kg ip, 2) only PILO, and 3) only saline (0.5 ml, IP). The CHX pre-treatment significantly decreased the number of rats that responded to PILO with status epilepticus compared to rats that received only PILO. Pre-treatment with CHX did not significantly alter the spontaneous motor seizure rate post-treatment compared to treatment with PILO alone in those animals from each group that developed status epilepticus during PILO treatment. Timm stain in the IML was not significantly different between the PILO- and PILO+CHX-treated rats. Using quantitative methods, CHX did not prevent hilar, CA1, or CA3 neuronal loss compared to the PILO-treated rats. Extracellular responses to hilar stimulation in 30 microM bicuculline and 6 mM [K(+)](o) demonstrated all-or-none bursting in both the CHX+PILO- and PILO-treated rats but not in control rats. Whole cell recordings from granule cells, using glutamate flash photolysis to activate other granule cells, showed that both the CHX+PILO- and PILO-treated rats had excitatory synaptic interactions in the granule cell layer, which were not found after saline treatment. Some rats responded to PILO (with or without CHX pre-treatment) with only one or a few seizures at treatment, and some of these animals (n = 4) demonstrated spontaneous motor seizures within 2 mo after treatment. Timm staining and neuron loss in this group were not clearly different from saline-treated rats. These results suggest that in the PILO model, pre-treatment with CHX does not affect mossy fiber sprouting in the IML of epileptic rats and does not prevent the formation of recurrent excitatory circuits. However, the develoment of spontaneous motor seizures, in a small number of rats, could occur without detectable hippocampal neuron loss or mossy fiber sprouting, as assessed by the Timm stain method.

Effect of melatonin on the regulation of proenkephalin and prodynorphin mRNA levels induced by kainic acid in the rat hippocampus

The in vivo short-term effect of melatonin on kainic acid (KA)-induced proenkephalin (proENK) or prodynorphin (proDYN) mRNA, and on AP-1 protein levels in the rat hippocampus, were studied. Melatonin (5 mg/kg) or saline was administered intraperitoneally (i.p.) to rats 30 min prior to and immediately after i.p. injection of KA (10 mg/kg). Rats were sacrificed 1 and 3 h after KA injection. The proENK and proDYN mRNA levels were significantly increased 3 h after KA administration. The elevations of both proENK and proDYN mRNA levels induced by KA were significantly inhibited by the preadministration with melatonin. The increases of proENK and proDYN mRNA levels induced by KA were well-correlated with the increases of c-Fos, Fra-2, FosB, c-Jun, and JunB protein levels, which were significantly increased 3 h after KA administration and effectively inhibited by administration with melatonin. In an electrophoretic mobility shift assay, both AP-1 and ENKCRE-2 DNA binding activities were increased by KA, which were also attenuated by the administration of melatonin. In addition, cross-competition studies revealed that AP-1 or ENKCRE-2 DNA binding activity was effectively reduced by the 50x unlabeled cross-competitor. Therefore, these data suggest that melatonin has an inhibitory role in KA-induced gene expression, such as proENK and proDYN mRNA expression, and this may be due to a reduction of KA-induced AP-1 or ENKCRE-2 DNA binding activity.

The differential molecular mechanisms underlying proenkephalin mRNA expression induced by forskolin and phorbol-12-myristic-13-acetate in primary cultured astrocytes

In rat astrocytes, forskolin (FSK; 5 microM) and phorbol-12-myristic-13-acetate (PMA; 2.5 microM) increase the proenkephalin (proENK) mRNA level via different pathways. FSK-induced proENK mRNA expression is independent of protein de novo synthesis, and well correlated with CREB phosphorylation. This is in contrast to PMA-induced proENK mRNA expression that is dependent on protein de novo synthesis and is well correlated with the increase of AP-1 DNA binding activity rather than CREB phosphorylation. Differential regulation of AP-1 proteins by PMA and FSK was also observed. While c-Fos, Fra-2 and JunB were increased in response to either stimuli, only Fra-1, c-Jun and JunD were increased by PMA. The combined treatment with FSK and PMA additively increased the proENK mRNA level, which was correlated with AP-1 or ENKCRE-2 DNA binding activity, and CREB phosphorylation. Dexamethasone (DEX; 1 microM) further enhanced FSK- or PMA-induced proENK mRNA expression, which was not correlated with the activation of AP-1 expression and CREB phosphorylation, suggesting that synergistic interaction of glucocorticoid with PKA or PKC pathway for the regulation of proENK mRNA expression appears to be mediated by other pathways rather than CREB and AP-1 families.

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.

The modulatory role of nitric oxide in the regulation of proenkephalin and prodynorphin gene expressions induced by kainic acid in rat hippocampus

The effect of L-arginine (L-ARG), a nitric oxide donor, or Nomega-nitro-L-arginine (L-NAME), a nitric oxide synthase inhibitor, on the regulation of kainic acid (KA)-induced proenkephalin (proENK) and prodynorphin (proDYN) mRNA expressions in rat hippocampus was studied. The proENK and proDYN mRNA levels were markedly increased 6 h after KA (10 mg/kg, i.p.) administration. The elevations of both proENK and proDYN mRNA levels induced by KA was effectively inhibited by pre-administration of L-ARG (400 mg/kg, i.p.), but was not affected by pre-treatment with L-NAME (200 mg/kg, i.p.). The blockade of KA-induced proENK and proDYN mRNA levels by the pre-treatment with L-ARG was well correlated with proto-oncoprotein levels, such as c-Fos, Fra-2, FosB, JunD, JunB, and c-Jun, as well as AP-1 and ENKCRE-2 DNA binding activities. The pre-administration with L-NAME further increased KA-induced c-jun and c-fos mRNA levels in addition to their protein product levels, although the pre-treatment with L-NAME did not affect KA-induced FosB, Fra-2, JunB, and JunD protein levels at 6 h after treatment. In addition, the pre-administration with L-NAME further increased the KA-induced AP-1 and ENKCRE-2 DNA binding activities. Our results suggest that L-ARG plays an important role in inhibiting KA-induced proENK or proDYN mRNA expression, and its inhibitory action may be mediated through reducing the proto-oncoprotein levels, such as c-Fos, Fra-2, FosB, c-Jun, JunD, and JunB. In addition, L-NAME potentiated the c-Fos or c-Jun gene expression, as well as AP-1 or ENKCRE-2 DNA binding activity. However, these increases did not show the potentiative effect on KA-induced increases of proENK and proDYN mRNA level.

Intra-hippocampal administration of cycloheximide attenuates the restraint-induced exploratory deficit of an elevated plus maze

Rats submitted to 2 h of restraint stress show a reduced open arm exploration in the elevated plus maze 24 h later. The stress-induced exploratory deficit is prevented by i.c.v. pre-stress administration of cycloheximide (CHX), a protein synthesis inhibitor. The objective of the present work was to determine if the hippocampus could be involved in this effect. CHX (4 or 8 microg) was injected into the dorsal hippocampus of male Wistar rats (200-250 g), immediately before (n = 9-20 animals/group) a 2 h period of forced restraint. After 24 h the animals were tested in the elevated plus maze. Non-stressed, control groups, received saline (SAL) or cycloheximide (CHX, n = 6-12/group) and were tested 1 or 24 h later in the maze. Pre-stress microinjections of cycloheximide increased exploration of open arms in the elevated plus maze (percentage of entries, SAL = 10.3 +/- 2.7, CHX 4 microg = 24.5 +/- 4.6, CHX 8 microg = 28.2 +/- 4.8, percentage of time spent, SAL = 2.0 +/- 0.6, CHX 4 microg = 8.4 +/- 2.3, CHX 8 microg = 9.6 +/- 2.6, Duncan test, P < 0.05). No drug effect was observed in non stressed animals. These results suggest that blockade of protein synthesis in the dorsal hippocampus during the restraint period may attenuate the behavioural consequences of stress.

The stimulation of rat astrocytes with phorbol-12-myristate-13-acetate increases the proenkephalin mRNA: involvement of proto-oncogenes

The effect of phorbol-12-myristate-13-acetate (PMA) on the regulation of proenkephalin (proENK) mRNA level, ENKCRE-2 or AP-1 DNA binding activity, and the mRNA and protein levels of proto-oncogenes (c-fos, fra-1, and c-jun) in primary cultured rat astrocytes were studied. The proENK mRNA level was elevated at 4 h after the treatment of PMA (2.5 microM) without altering the intracellular proENK protein level, and this increase was attenuated by pre-treatment with cycloheximide (CHX; 15 microM), a protein synthesis inhibitor. Both AP-1 and ENKCRE-2 DNA binding activities were markedly increased at 1-4 h by PMA treatment and these PMA-induced responses were inhibited by pre-treatment with CHX, showing that the increase of proENK mRNA level was well correlated with the AP-1 and ENKCRE-2 DNA binding activities. In contrast, although the phospho-CREBP level was also increased by PMA at 0.5-1 h, the pre-treatment with CHX further increased the PMA-induced phospho-CREBP level. In addition, PMA caused the induction of c-fos, c-jun and fra-1 mRNA level and, especially, PMA-induced increase of fra-1 mRNA level was further enhanced by CHX treatment at 4 h. Furthermore, western immunoblot assay showed that PMA caused induction of c-Fos, Fra-1, and c-Jun protein levels. PMA-induced increases of proto-oncoproteins levels were also inhibited by CHX treatment. The results suggest that newly synthesized AP-1 proteins, such as c-Fos, Fra-1, and c-Jun may play important roles in the regulation of PMA-induced proENK gene expression in cultured rat astrocytes. Phospho-CREB protein appears not to be involved in the regulation of PMA-induced proENK gene expression.

Evidence for Fos involvement in the regulation of proenkephalin and prodynorphin gene expression in the rat hippocampus

For a long time Fos has been proposed to play some role in regulation of the proenkephalin (PENK) and prodynorphin (PDYN) gene expression. In recent years, however, evidence has accumulated that the transcription of both genes in several brain regions in vivo is transactivated by the transcription factor CREB rather than by Fos. In the present study, involvement of Fos in the mechanism of the PENK and PDYN gene induction in the hippocampal dentate gyrus during seizures elicited by kainic acid was studied using a knock-down technique. Pretreatment with an antisense oligonucleotide complementary to c-fos mRNA did not influence the kainic acid-elicited convulsions. It inhibited, by about 50%, the induction of Fos protein in the dentate gyrus during seizures. The subsequent induction of PENK and PDYN mRNAs was reduced by more than 60% by the c-fos antisense oligonucleotide, while constitutive expression of three other genes (alpha-tubulin, NMDA receptor-1, and GS protein alpha-subunit) was not affected. The obtained results support the view that Fos may be involved in regulation of the PENK and PDYN gene expression in the dentate gyrus during seizures, which further suggests that the mechanisms triggering the up-regulation of both these genes in the dentate gyrus may differ from these working in other brain regions, such as the striatum and hypothalamus.

Phenidone blocks the increases of proenkephalin and prodynorphin gene expression induced by kainic acid in rat hippocampus: involvement of Fos-related antigene protein

To determine the possible role of cyclooxygenase/lipoxygenase pathway in the regulation of proenkephalin (proENK) and prodynorphin (proDYN) gene expression induced by kainic acid (KA) in rat hippocampus, the effects of esculetin, aspirin, or phenidone on the seizure activity, proENK and proDYN mRNA levels, and the level of fos-related antigene (Fra) protein induced by KA in rat hippocampus were studied. Esculetin (5 mg/kg), aspirin (15 mg/kg), or phenidone (50 mg/kg) was administered orally five times every 12 h before the injection of KA (10 mg/kg, i.p.). Seizure activity induced by KA was significantly attenuated by phenidone. However, neither esculetin nor aspirin affected KA-induced seizure activity. The proENK and proDYN mRNA levels were markedly increased 4 and 24 h after KA administration. The elevations of both proENK and proDYN mRNA levels induced by KA were inhibited by pre-administration with phenidone, but not with esculetin and aspirin. ProENK-like protein level increased by KA administration was also inhibited by pre-administration with phenidone, but not with esculetin and aspirin. The increases of proENK and proDYN mRNA levels induced by KA were well correlated with the increases of Fra protein level. Additionally, the induction of Fra protein was inhibited by pre-administration with phenidone, but not with esculetin and aspirin. The results suggest that blockade of both cyclooxygenase and lipoxygenase pathways appears to be responsible for increases of proENK and proDYN mRNA levels induced by KA via inhibiting the induction of Fra protein in rat hippocampus.