The protein kinase C activators, phorbol 12-myristate,13-acetate and phorbol 12,13-dibutyrate, are convulsant in the pico-nanomolar range in mice

Effects of the putative lithium mimetic ebselen on pilocarpine-induced neural activity

Lithium, commonly used to treat bipolar disorder, potentiates the ability of the muscarinic agonist pilocarpine to induce seizures in rodents. As this potentiation by lithium is reversed by the administration of myo-inositol, the potentiation may be mediated by inhibition of inositol monophosphatase (IMPase), a known target of lithium. Recently, we demonstrated that ebselen is a 'lithium mimetic' in regard to behaviours in both mice and man. Ebselen inhibits IMPase in vitro and lowers myo-inositol in vivo in the brains of mice and men, making ebselen the only known inhibitor of IMPase, other than lithium, that penetrates the blood-brain barrier. Our objective was to determine the effects of ebselen on sensitization to pilocarpine-induced seizures and neural activity. We administered ebselen at different doses and time intervals to mice, followed by injection of a sub-seizure dose of pilocarpine. We assessed seizure and neural activity by a subjective seizure rating scale, by monitoring tremors, and by induction of the immediate early gene c-fos. In contrast to lithium, ebselen did not potentiate the ability of pilocarpine to induce seizures. Unexpectedly, ebselen inhibited pilocarpine-induced tremor as well as pilocarpine-induced increases in c-fos mRNA levels. Both lithium and ebselen inhibit a common target, IMPase, but only lithium potentiates pilocarpine-induced seizures, consistent with their polypharmacology at diverse molecular targets. We conclude that ebselen does not potentiate pilocarpine-induced seizures and instead, reduces pilocarpine-mediated neural activation. This lack of potentiation of muscarinic sensitization may be one reason for the lack of side-effects observed with ebselen treatment clinically.

Assessing Specialized Metabolite Diversity in the Cosmopolitan Plant Genus Euphorbia L

Coevolutionary theory suggests that an arms race between plants and herbivores yields increased plant specialized metabolite diversity and the geographic mosaic theory of coevolution predicts that coevolutionary interactions vary across geographic scales. Consequently, plant specialized metabolite diversity is expected to be highest in coevolutionary hotspots, geographic regions, which exhibit strong reciprocal selection on the interacting species. Despite being well-established theoretical frameworks, technical limitations have precluded rigorous hypothesis testing. Here we aim at understanding how geographic separation over evolutionary time may have impacted chemical differentiation in the cosmopolitan plant genus Euphorbia. We use a combination of state-of-the-art computational mass spectral metabolomics tools together with cell-based high-throughput immunomodulatory testing. Our results show significant differences in specialized metabolite diversity across geographically separated phylogenetic clades. Chemical structural diversity of the highly toxic Euphorbia diterpenoids is significantly reduced in species native to the Americas, compared to Afro-Eurasia. The localization of these compounds to young stems and roots suggest a possible ecological relevance in herbivory defense. This is further supported by reduced immunomodulatory activity in the American subclade as well as herbivore distribution patterns. We conclude that computational mass spectrometric metabolomics coupled with relevant ecological data provide a strong tool for exploring plant specialized metabolite diversity in a chemo-evolutionary framework.

Potential aversive compounds in leafy spurge for ruminants and rats

Several wild and domestic ruminant species and horses apparently will not consume leafy spurge (Euphorbia esula) while grazing range and pasture lands. It has been demonstrated that leafy spurge can elicit conditioned food aversions in cattle and sheep, and the aversion-eliciting capacity of leafy spurge may account for why cattle seldom graze this nutritious plant and why sheep may not readily consume it at some locations. The identity of the aversive compound(s) in leafy spurge is unknown, but several different diterpenoid ingenol esters have been isolated from its tissues, and we suspect that one or more ingenol esters may be aversion-eliciting compounds in leafy spurge. The objectives of this study were to determine whether or not leafy spurge is aversive to laboratory rats and if a crude acetone extract of leafy spurge, presumably containing ingenol esters and other phytochemicals, could generate an aversive response in sheep and laboratory rats. An additional objective was to determine whether or not a particular ingenol monobenzoate, which may be similar to ingenol esters in leafy spurge, might also elicit an aversive response from rats. Rats exhibited food aversions associated with leafy spurge (P < 0.05). An acetone extract of leafy spurge induced conditioned food aversions in both sheep and rats (P < 0.01). The ingenol 3-monobenzoate also induced conditioned food aversions in rats (P < 0.01). Our interpretation of these data is that rats can be used as a model for cattle and sheep with respect to their aversion to leafy spurge ingestion. Additionally, we suggest that one or more ingenol esters may be aversion-inducing agents in leafy spurge. However, others may exist in leafy spurge that are also aversive or are the only or prime aversive chemicals.

Protein kinase associated with gating and closing transmission mechanisms in temporoammonic pathway

The entorhinal cortex (EC) is a major source of afferent input to the hippocampus via the perforant and temporoammonic pathways; however, the detailed transmission mechanism in the temporoammonic pathway remains to be clarified. Thus, we determined interaction among GABA(A), AMPA/glutamate receptors and protein kinases (PKA and PKC) in the exocytosis of GABA and glutamate using multiprobe microdialysis, as well as propagation of neuronal excitability using optical recording in the EC-Hippocampal formation. Multiprobe microdialysis demonstrated that EC-evoked GABA release in ventral CA1 was predominantly regulated by the PKC-related rather than PKA-related exocytosis mechanism and was augmented by the activation of glutamatergic transmission. Contrary to GABA release, EC-evoked glutamate release was predominantly regulated by PKA-related rather than PKC-related mechanisms and was suppressed by activation of GABAergic transmission. Optical recording demonstrated that there are two sub-pathways in the temporoammonic pathway; direct projects from EC layers (II-IV) to dendrites on pyramidal cells and GABAergic interneurons in ventral hippocampal CA1. PKC activation enhanced trisynaptic transmission, whether the GABA(A) receptor was functional or blocked, whereas PKC activation enhanced and inhibited temporoammonic transmission when the GABA(A) receptor was functional and blocked, respectively. Thus, GABAergic inhibition, which is regulated by PKC activity, in the temporoammonic pathway is more significant than that in the trisynaptic pathway.

A cDNA microarray analysis of gene expression profiles in rat hippocampus following a ketogenic diet

The ketogenic diet (KD) is an effective therapy for medically intractable epilepsy, but its anticonvulsant mechanisms are unknown. Few studies to date have addressed the molecular changes following treatment with a KD. In the present study, we fed juvenile rats either a standard diet or a KD for 1 month, and then determined changes in hippocampal gene expression using cDNA microarray analysis (Clontech). To validate the microarray expression results, we also performed Northern blot and RT-PCR analysis on a small subset of affected genes. Among a total of 1176 cDNAs, 42 genes were strongly up- or down-regulated (>2-fold change over controls) by a KD. We found that the expression of mitochondrial ATP synthase beta subunit, mitochondrial ATP synthase D subunit (ATP5H) and mitochondrial ATP synthase beta subunit precursor (ATP5F) were especially increased in KD-treated group, whereas the KD down-regulated protein kinase C (PKC) beta and epsilon isoforms. Thus, the most prominent changes were seen in genes encoding proteins involved in mitochondrial metabolic and intracellular signal transduction pathways. Our data provide some insights into the complex cascade of cellular changes in the hippocampus induced by a KD, some of which may contribute to its anticonvulsant effects.

Acetyl-L-carnitine requires phospholipase C-IP3 pathway activation to induce antinociception

The cellular events involved in acetyl-L-carnitine (ALCAR) analgesia were investigated in the mouse hot plate test. I.c.v. pretreatment with aODNs against the alpha subunit of G(q) and G(11) proteins prevented the analgesia induced by ALCAR (100 mg kg(-1) s.c. twice daily for 7 days). Administration of the phospholipase C (PLC) inhibitors U-73122 and neomycin, as well as the injection of an aODN complementary to the sequence of PLCbeta(1), antagonized the increase of the pain threshold induced by ALCAR. Pretreatment with U-73343, an analogue of U-73112 inactive on PLC, did not modify ALCAR analgesic effect. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or pretreatment with TMB-8, a blocker of Ca(++) release from intracellular stores, the antinociception induced by ALCAR was dose-dependently antagonized. I.c.v. treatment with heparin, an IP(3) receptor antagonist, prevented the increase of pain threshold induced by the investigated compound, analgesia that was restored by co-administration of D-myo-inositol. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitors calphostin C and cheleritryne, resulted in a dose-dependent potentiation of ALCAR antinociception. The administration of PKC activators, such as PMA and PDBu, dose-dependently prevented the ALCAR-induced increase of pain threshold. Neither aODNs nor pharmacological treatments produced any behavioral impairment of mice as revealed by the rota-rod and hole board tests. These results indicate that central ALCAR analgesia in mice requires the activation of the PLC-IP(3) pathway. By contrast, the simultaneous activation of PKC may represent a pathway of negative modulation of ALCAR antinociception.

H1-receptor stimulation induces hyperalgesia through activation of the phospholipase C-PKC pathway

The supraspinal cellular events involved in H(1)-mediated hyperalgesia were investigated in a condition of acute thermal pain by means of the mouse hot-plate test. I.c.v. administration of the phospholipase C (PLC) inhibitors U-73122 and neomycin antagonized the hyperalgesia induced by the selective H(1) agonist FMPH. By contrast, U-73343, an analogue of U-73122 used as negative control, was unable to modify the reduction of the pain threshold induced by FMPH. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or treatment with heparin, an IP(3)-receptor antagonist, the hyperalgesia induced by the H(1)-receptor agonist remained unchanged. Similarly, pretreatment with D-myo inositol did not alter the H(1)-induced hypernociceptive response. Neither i.c.v. pretreatment with TMB-8, a blocker of Ca(2+) release from intracellular stores, nor pretreatment with thapsigargin, a depletor of Ca(2+) intracellular stores, prevented the decrease of pain threshold induced by FMPH. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitors calphostin C and chelerytrine resulted in a dose-dependent prevention of the H(1)-receptor agonist-induced hyperalgesia. The administration of PKC activators, such as PMA and PDBu, did not produce any effect on FMPH effect. The pharmacological treatments employed did not produce any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate a role for the PLC-PKC pathway in central H(1)-induced hyperalgesia in mice. Furthermore, activation of PLC-IP(3) did not appear to play a major role in the modulation of pain perception by H(1)-receptor agonists.

The phospholipase C-IP3 pathway is involved in muscarinic antinociception

The cellular events involved in muscarinic analgesia were investigated in the mouse hot-plate test. Intracerebroventricular (i.c.v.) pretreatment with antisense oligonucleotides (aODNs) against the alpha subunit of G(q) and G(11) proteins prevented the analgesia induced by physostigmine and oxotremorine. Furthermore, administration of the phospholipase C (PLC) inhibitor U-73122, as well as the injection of an aODN complementary to the sequence of PLCbeta(1), antagonized the increase of the pain threshold induced by both cholinomimetic drugs. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or treatment with heparin, an IP(3) receptor antagonist, the antinociception induced by physostigmine and oxotremorine was dose-dependently antagonized. I.c.v. pretreatment with TMB-8, a blocker of Ca(2+) release from intracellular stores, prevented the increase of pain threshold induced by the investigated cholinomimetic drugs. Coadministration of Ca(2+) restored the muscarinic analgesia in LiCl, heparin, and TMB-8-preatreated mice. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitor calphostin C, resulted in a dose-dependent enhancement of physostigmine- and oxotremorine-induced antinociception. The administration of PKC activators, such as PMA and PDBu, dose dependently prevented the cholinomimetic drug-induced increase of pain threshold. Neither aODNs nor pharmacological treatments employed produced any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate a role for the PLC-IP(3) pathway in central muscarinic analgesia in mice. Furthermore, activation of PKC by cholinomimetic drugs may represent a pathway of negative modulation of muscarinic antinociception.

Excitatory amino acid-elicited tonic convulsions in mice and N-methyl-D-aspartate receptor activation: role of Ca(2+) influx and involvement of intracellular Ca(2+)-dependent biochemical processes

Intravenously administered nimodipine (an L-type Ca(2+) antagonist) as well as dizocilpine (an N-methyl-D-aspartate--NMDA--antagonist) showed a wide spectrum of anticonvulsant activity in intracerebroventricular mouse models for excessive activation of excitatory amino acid receptors. The duration of Bay k-8644 (L-type Ca(2+) agonist; intracerebroventricular administration) caused seizures was significantly reduced by intravenously administered nimodipine. Intracisternal administration of Bay k-8644 lowered the convulsion threshold of an intracerebroventricular injection of NMDA. Intracisternal administration of omega-conotoxin GVIA (N-type Ca(2+) antagonist) only tended to inhibit the NMDA-induced tonic convulsions. Intracisternal administration of staurosporine (a protein kinase C inhibitor) or calmidazolium (a calmodulin antagonist) was effective in inhibiting the NMDA-induced tonic convulsions. Calmidazolium, unlike staurosporine, produced side effects at a dose showing its anticonvulsant activity. From these results, it is suggested that excessive activation of excitatory amino acid receptors results in tonic convulsions by virtue of a massive increase of Ca(2+) influx mainly through NMDA receptor channels, and at least in part through L-type Ca(2+) channels, and in subsequent activation of protein kinase C and possibly calmodulin.

Selective up-regulation of protein kinase C epsilon in granule cells after kainic acid-induced seizures in rat

Kainate-induced seizure activity causes persistent changes in the hippocampus that include synaptic reorganization and functional changes in the mossy fibers. Using in situ hybridization histochemistry, the expression of PKC alpha, PKC beta, PKC gamma, PKC delta and PKC epsilon mRNAs was investigated in the hippocampus of adult rats following seizures induced by a s.c. injection of kainic acid. In CA1 and CA3, we found a significant decrease in PKC gamma mRNA 1 day after kainic acid which persisted for a 2nd day in CA1. None of the other PKC isoform mRNAs were altered in CA1 or CA3. In granule cells, a significant up-regulation specific to PKC epsilon mRNA was observed. One week after kainic acid administration, a marked increase in PKC epsilon immunoreactivity was found that persisted 2 months after kainic acid administration. PKC epsilon immunoreactivity was found associated with mossy fibers projecting to the hilus of the dentate gyrus and to the stratum lucidum of the CA3 field and presumably with the newly sprouted mossy fibers projecting to the supragranular layer. These data provide the first evidence for a long-lasting increase of the PKC epsilon in the axons of granule cells caused by kainate-induced seizures and suggest that PKC epsilon may be involved in the functional and/or structural modifications of granule cells that occur after limbic seizures.

Phorbol ester intracerebroventricularly induces a behavioral hypoactivity that is not affected by chronic or acute lithium

Chronic lithium treatment in rats has been reported to decrease protein kinase C alpha isozyme in hippocampal membranes. We gave phorbol ester, a protein kinase C activator, i.c.v. to rats treated with acute or chronic lithium. Low dose phorbol ester causes a marked hypoactivity and high dose phorbol ester causes a barrel rolling behavior, but no behavioral interactions with lithium treatment were observed.

Status epilepticus may be caused by loss of adenosine anticonvulsant mechanisms

The inhibitory neuromodulator adenosine is an endogenous anticonvulsant that terminates brief seizures in the brain and it has been proposed that loss of adenosine or adenosine-mediating systems may play a major role in the development of status epilepticus, a seizure condition characterized by prolonged and/or recurrent seizures that last by definition, at least 20 min. In this study, the effect of specific A1-adenosine agonists and antagonists were tested for their ability to prevent and cause status epilepticus in two electrical stimulation models in rats. In a recurrent electrical stimulation model, whereas no vehicle-treated animals developed status epilepticus after 20 recurrent electrical stimulations, rats injected with 10 mg/kg of the specific A1-adenosine antagonist 8-cyclopentyl-1,3-dimethylxanthine intraperitoneally developed status epilepticus after stimulation. 8-(p-Sulphophenyl)-theophylline, which has limited penetrability into the brain when administered peripherally, did not cause status epilepticus when injected intraperitoneally. However, when 200 micrograms of 8-(p-sulphophenyl)-theophylline were administered intracerebroventricularly, status epilepticus developed in all animals, suggesting status epilepticus developed as a result of central adenosine receptor antagonism. In the second study, whereas all vehicle-treated animals developed status epilepticus after constant electrical stimulation, administration of N6-cyclohexyladenosine and N6-cyclopentyladenosine prior to stimulation suppressed the development of status epilepticus. N6-Cyclohexyladenosine was also effective in terminating status epilepticus after it had progressed for 20 min. The effects of a selective A2-agonist was also tested on both stimulation models and had no anticonvulsant effects. An electrical stimulus given to rats pretreated three days prior to stimulation with pertussis toxin, a compound which inactivates Gi-proteins, also resulted in generalized status epilepticus, suggesting that impairment of G-protein-linked receptors is involved in the development of status epilepticus. The effects of a GABAB antagonist, phaclofen, and a GABAB agonist, baclofen, were also tested in the recurrent stimulation model, as GABAB receptors are also coupled to the same subset of K+ channels as the A1-receptor. Rats given phaclofen did not develop status epilepticus after recurrent electrical stimulation, although baclofen was effective at preventing the induction of status epilepticus in the constant stimulation model. These results, together with some preliminary data obtained showing that the GABAA antagonist picrotoxin did not cause status epilepticus after recurrent stimulation, suggest that loss of GABAergic inhibition only has a minor role in status epilepticus development in our models. Brains from all animals were also assessed for brain injury.(ABSTRACT TRUNCATED AT 400 WORDS)