Valproate reduced excitatory postsynaptic currents in hippocampal CA1 pyramidal neurons

Translational genomics and beyond in bipolar disorder

Genome-wide association studies (GWAS) have revealed multiple genomic loci conferring risk of bipolar disorder (BD), providing hints for its underlying pathobiology. However, there are still remaining questions to answer. For example, discordance exists between BD heritability estimated with earlier epidemiological evidence and that calculated based on common GWAS variations. Where is the "missing heritability"? How can we explain the biology of the disease based on genetic findings? In this review, we summarize the accomplishments and limitations of current BD GWAS, and discuss potential reasons for the "missing heritability." In addition, progresses of research for the biological mechanisms underlying BD genetic risk using brain tissues, reprogrammed cells, and model animals are reviewed. While our knowledge of BD genetic basis is significantly promoted by these efforts, the complexities of gene regulation in the genome, the spatial-temporal heterogeneity during brain development, and the limitations of different experimental models should always be considered. Notably, several genes have been widely studied given their relatively well-characterized involvement in BD (e.g., CACAN1C and ANK3), and findings of these genes are summarized to both outline possible biological mechanisms of BD and describe examples of translating GWAS discoveries into the pathophysiology.

Valproic acid induces nuclear factor erythroid 2-related factor 2 expression in fetal and neonatal brains but not in adult brain: evidence of the gamma-aminobutyric acid-shift hypothesis

The gamma-aminobutyric acid (GABA)-shift hypothesis proposes that GABA agonist action is excitatory early in development and transitions to an inhibitory role later in life. In experiment 1, the nonspecific GABA agonist, valproic acid (VPA), was administered to pregnant C57BL/6 mice on embryonic day 13. Fetal and maternal brains were harvested 2 h post-VPA exposure and assayed for nuclear factor erythroid 2-related factor 2 (NRF2) and H3 expression through western blot analysis. In experiment 2, VPA was administered to neonatal pups on P14 and adult mice on P60. In both experiments, it was observed that NRF2 expression was increased in fetal and neonatal brains, but not in the adult brain. Because NRF2 expression is activated by oxidative stress, these results imply support of the GABA-shift hypothesis in that VPA may exert its developmental damage in the fetal and neonatal periods through excitotoxicity.

Cell Proliferation in the Isolated Brains of Adult Zebrafish Incubated in Artificial Cerebrospinal Fluid

The high rate of cell proliferation in the zebrafish brain allows one to perform reliable studies on cellular molecules associated with cell proliferation. In this study, we show that 5-bromo-2'-deoxyuridine (BrdU)-labeled cells were detected in the isolated brains of adult zebrafish that were incubated in oxygenated artificial cerebrospinal fluid (aCSF) in vitro. The number of BrdU-labeled cells shown in the in vitro preparation was close to that in the in vivo study and was modified by treatment with various pharmacological agents, such as valproic acid. In parallel to cell proliferation, protein expression and neural activity could also be measured in the isolated brains maintained in aCSF.

Valproic acid potently inhibits interictal-like epileptiform activity in prefrontal cortex pyramidal neurons

Valproic acid has a long-standing reputation of effectively treating the symptoms of not only epilepsy but also psychiatric conditions. In the latter, the exact mechanism by which valproate exerts its effect remains unclear. In this study, epileptiform bursts were recorded from pyramidal neurons in the prefrontal cortex (the brain region thought to be involved in psychiatric disorders) using the patch-clamp technique. An extracellular solution with no magnesium ions and elevated potassium levels that is known to induce epileptiform activity in vitro was used. Because of their short durations, the epileptiform bursts were regarded as interictal-like epileptiform activity, which is believed to be involved in cognitive impairment. Interictal discharges occur in many neuropsychiatric disorders as well as in healthy population. Epileptic activity in prefrontal cortex pyramidal neurons was potently inhibited by two therapeutic concentrations of valproic acid (20 μM and 200 μM). Moreover, valproate suppressed spontaneous excitatory postsynaptic potentials. Epileptiform bursts were fully inhibited by NMDA receptor antagonist, which suggests that epileptiform activity is driven by NMDA receptors. The inhibition of excitability in prefrontal cortex pyramidal neurons by valproate was also shown. This study shows that it is possible to evoke NMDA-dependent epileptiform activity in prefrontal cortex pyramidal neurons in vitro. We suggest that the prefrontal cortex is a good region for studying the influence of drugs on interictal epileptiform activity.

Excitatory and inhibitory synaptic dysfunction in mania: an emerging hypothesis from animal model studies

Bipolar disorder (BD) is a common psychiatric disorder characterized by recurrent mood swings between depression and mania, and is associated with high treatment costs. The existence of manic episodes is the defining feature of BD, during which period, patients experience extreme elevation in activity, energy, and mood, with changes in sleep patterns that together severely impair their ability to function in daily life. Despite some limitations in recapitulating the complex features of human disease, several rodent models of mania have been generated and characterized, which have provided important insights toward understanding its underlying pathogenic mechanisms. Among the mechanisms, neuronal excitatory and inhibitory (E/I) synaptic dysfunction in some brain regions, including the frontal cortex, hippocampus, and striatum, is an emerging hypothesis explaining mania. In this review, we highlight recent studies of rodent manic models having impairments in the E/I synaptic development and function. We also summarize the molecular and functional changes of E/I synapses by some mood stabilizers that may contribute to the therapeutic efficacy of drugs. Furthermore, we discuss potential future directions in the study of this emerging hypothesis to better connect the outcomes of basic research to the treatment of patients with this devastating mental illness.

Studies in rodents offer insights into bipolar disorder that may help understanding and treatment of this common and debilitating condition. Kihoon Han and colleagues at Korea University in Seoul review research using mice and rats to model the episodes of mania in patients with bipolar disorder. The research supports an emerging hypothesis implicating specific problems with nervous transmission in the brain in the onset of mania. The hypothesis suggests that the transmission of signals between particular nerve cells whose normal function is either to excite or to inhibit other nerve cells may be involved. It also indicates regions of the brain most involved in manic episodes. Changes at the affected nerve junctions—called synapses—brought about by mood-stabilizing drugs are examined. The hypothesis suggests new approaches to treatment options for researchers to explore.

Perturbation of the Vacuolar ATPase: A NOVEL CONSEQUENCE OF INOSITOL DEPLETION

Depletion of inositol has profound effects on cell function and has been implicated in the therapeutic effects of drugs used to treat epilepsy and bipolar disorder. We have previously shown that the anticonvulsant drug valproate (VPA) depletes inositol by inhibiting myo-inositol-3-phosphate synthase, the enzyme that catalyzes the first and rate-limiting step of inositol biosynthesis. To elucidate the cellular consequences of inositol depletion, we screened the yeast deletion collection for VPA-sensitive mutants and identified mutants in vacuolar sorting and the vacuolar ATPase (V-ATPase). Inositol depletion caused by starvation of ino1Δ cells perturbed the vacuolar structure and decreased V-ATPase activity and proton pumping in isolated vacuolar vesicles. VPA compromised the dynamics of phosphatidylinositol 3,5-bisphosphate (PI3,5P2) and greatly reduced V-ATPase proton transport in inositol-deprived wild-type cells. Osmotic stress, known to increase PI3,5P2 levels, did not restore PI3,5P2 homeostasis nor did it induce vacuolar fragmentation in VPA-treated cells, suggesting that perturbation of the V-ATPase is a consequence of altered PI3,5P2 homeostasis under inositol-limiting conditions. This study is the first to demonstrate that inositol depletion caused by starvation of an inositol synthesis mutant or by the inositol-depleting drug VPA leads to perturbation of the V-ATPase.

Long-term valproate treatment increases brain neuropeptide Y expression and decreases seizure expression in a genetic rat model of absence epilepsy

The mechanisms by which valproate, one of the most widely prescribed anti-epileptic drugs, suppresses seizures have not been fully elucidated but may involve up-regulation of neuropeptide Y (NPY). We investigated the effects of valproate treatment in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) on brain NPY mRNA expression and seizure control. GAERS were administered either valproate (42 mg.kg⁻¹ hr⁻¹) or saline continuously for 5 days. Electroencephalograms were recorded for 24 hrs on treatment days 1, 3 and 5 and the percentage of time spent in seizure activity was analysed. NPY mRNA expression was measured in different brain regions using qPCR. Valproate treatment suppressed seizures by 80% in GAERS (p<0.05) and increased NPY mRNA expression in the thalamus (p<0.05) compared to saline treatment. These results demonstrate that long-term valproate treatment results in an upregulation of thalamic expression of NPY implicating this as a potential contributor to the mechanism by which valproate suppresses absence seizures.

Evaluation of the antiepileptic effect of curcumin and Nigella sativa oil in the pilocarpine model of epilepsy in comparison with valproate

The present study aimed to investigate the effect of curcumin and Nigella sativa oil (NSO) on amino acid neurotransmitter alterations and the histological changes induced by pilocarpine in the hippocampus and cortex of rats. Epilepsy was induced by i.p. injection of pilocarpine, and the animals were left for 22 days to establish spontaneous recurrent seizures. They were then treated with curcumin, NSO or valproate for 21 days. Pilocarpine induced a significant increase in hippocampal aspartate and a significant decrease in glycine and taurine levels. In the cortex, a significant increase in aspartate, glutamate, GABA, glycine, and taurine levels was obtained after pilocarpine injection. Treatment of pilocarpinized rats with curcumin and valproate ameliorated most of the changes in amino acid concentrations and reduced the histopathological abnormalities induced by pilocarpine. N. sativa oil failed to improve the pilocarpine-induced abnormalities. This may explain the antiepileptic effect of curcumin and suggest its use as an anticonvulsant.

Effect of valproic acid through regulation of NMDA receptor-ERK signaling in sleep deprivation rats

Although the effect of mood stabilizer valproic acid (VPA) through multiple signaling pathways has been shown, its therapeutic mechanism is still largely unknown. We investigated the effect of VPA (200 mg/kg, every 12 h) in sleep deprivation (SD) rats (72 h), the manic-like animal model, focusing on the N-methyl-D: -aspartic acid (NMDA) receptor and signaling mediators of synaptic plasticity such as extracellular signal-regulated protein kinase (ERK), cAMP response element-binding protein (CREB), B cell chronic lymphocytic leukemia/lymphoma 2 (BCL2), and brain-derived neurotrophic factor (BDNF). SD reduced the expression of the NR2B subunit of the NMDA receptor in the frontal cortex and hippocampus but did not affect the expression of NR1 and NR2A subunits. In comparison, VPA inhibited the SD-induced reduction of NR2B expression in both brain regions. In addition, SD attenuated ERK phosphorylation in the frontal cortex and hippocampus, whereas VPA prevented the attenuation. VPA also protected the SD-induced decrease of CREB phosphorylation, BCL2 expression, and BDNF expression in the frontal cortex but not in the hippocampus. These results indicate that VPA could regulate NMDA receptor-ERK signaling in SD rats, preventing the SD-induced decrease of the expression of NR2B subunit and the activation of ERK signaling mediators such as ERK, CREB, BCL2, and BDNF.

IRS-2 Deficiency impairs NMDA receptor-dependent long-term potentiation

The beneficial effects of insulin and insulin-like growth factor I on cognition have been documented in humans and animal models. Conversely, obesity, hyperinsulinemia, and diabetes increase the risk for neurodegenerative disorders including Alzheimer's disease (AD). However, the mechanisms by which insulin regulates synaptic plasticity are not well understood. Here, we report that complete disruption of insulin receptor substrate 2 (Irs2) in mice impairs long-term potentiation (LTP) of synaptic transmission in the hippocampus. Basal synaptic transmission and paired-pulse facilitation were similar between the 2 groups of mice. Induction of LTP by high-frequency conditioning tetanus did not activate postsynaptic N-methyl-D-aspartate (NMDA) receptors in hippocampus slices from Irs2(-/-) mice, although the expression of NR2A, NR2B, and PSD95 was equivalent to wild-type controls. Activation of Fyn, AKT, and MAPK in response to tetanus stimulation was defective in Irs2(-/-) mice. Interestingly, IRS2 was phosphorylated during induction of LTP in control mice, revealing a potential new component of the signaling machinery which modulates synaptic plasticity. Given that IRS2 expression is diminished in Type 2 diabetics as well as in AD patients, these data may reveal an explanation for the prevalence of cognitive decline in humans with metabolic disorders by providing a mechanistic link between insulin resistance and impaired synaptic transmission.

Effects of sodium valproate on synaptic transmission and neuronal excitability in rat hippocampus

1. Valproate (VPA) has long been used in the treatment of both generalized and partial seizures. However, its cellular mechanisms of action remain unclear. 2. In the present study, the effects of VPA on synaptic transmission and neuronal excitability were examined in the hippocampal CA1 region using whole-cell patch clamp recordings. 3. Perfusion with VPA, at therapeutically attainable concentrations (i.e. 0.3 and 0.6 mmol/L), significantly increased the frequency (112 +/- 2 and 133 +/- 2% of control, respectively; n = 5; both P < 0.05), but not the average amplitude, of miniature inhibitory post-synaptic currents (mIPSCs). Perfusion with VPA had no effect on either the amplitude or the frequency of miniature excitatory post-synaptic currents (mEPSCs). 4. In acutely dissociated CA1 pyramidal neurons, VPA had no effect on 10 micromol/L GABA-induced currents. Furthermore, following the administration of 0.3 and 0.6 mmol/L VPA, the frequency of action potential firing was significantly reduced from 18.0 +/- 1.1 to 15.3 +/- 0.9 and from 18.6 +/- 0.9 to 12.6 +/- 0.6, respectively (n = 8; both P < 0.05). In contrast, 0.3 and 0.6 mmol/L VPA significantly increased spike frequency adaptation from 4.02 +/- 0.47 to 4.72 +/- 0.55 and from 3.47 +/- 0.41 to 4.48 +/- 0.58, respectively (n = 8; P < 0.05). 5. The results of the present study suggest that VPA presynaptically increases inhibitory synaptic activity without modifying excitatory synaptic transmission and reduces neuronal excitability. Any or all of these effects may contribute to its anticonvulsant action.

Chronic administration of valproic acid reduces brain NMDA signaling via arachidonic acid in unanesthetized rats

Evidence that brain glutamatergic activity is pathologically elevated in bipolar disorder suggests that mood stabilizers are therapeutic in the disease in part by downregulating glutamatergic activity. Such activity can involve the second messenger, arachidonic acid (AA, 20:4n - 6). We tested this hypothesis with regard to valproic acid (VPA), when stimulating glutamatergic N-methyl-D: -aspartate (NMDA) receptors in rat brain and measuring AA and related responses. An acute subconvulsant dose of NMDA (25 mg/kg i.p.) or saline was administered to unanesthetized rats that had been treated i.p. daily with VPA (200 mg/kg) or vehicle for 30 days. Quantitative autoradiography following intravenous [1-(14)C]AA infusion was used to image regional brain AA incorporation coefficients k*, markers of AA signaling. In chronic vehicle-pretreated rats, NMDA compared with saline significantly increased k* in 41 of 82 examined brain regions, many of which have high NMDA receptor densities, and also increased brain concentrations of the AA metabolites, prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)). VPA pretreatment reduced baseline concentrations of PGE(2) and TXB(2), and blocked the NMDA induced increases in k* and in eicosanoid concentrations. These results, taken with evidence that carbamazepine and lithium also block k* responses to NMDA in rat brain, suggest that mood stabilizers act in bipolar disorder in part by downregulating glutamatergic signaling involving AA.

Screening for the effects of antiepileptic drugs on short term plasticity using a time efficient bioassay

Screening for changes in the short-term plasticity (STP) characteristics induced by antiepileptic drugs (AEDs) can be accelerated using a novel in vitro bioassay. The bioassay is based on the analysis of varying population spike (PS) amplitudes recorded in the CA1 region of the hippocampal slice in response to Poisson distributed random electrical stimuli. Three antiepileptic drugs (phenytoin 100 microM, carbamazepine 100 microM, and valproate 700 microM) were tested at maximal effective therapeutic concentrations. The data were analyzed using an advanced nonlinear approach that is more specific and time-efficient than the conventional paired pulse and fixed frequency train methods. STP was quantified by the first and the second order Volterra kernels. The first order kernel (k1) represented the mean PS amplitude while the second order kernel (k2) quantified the effect on the current PS amplitude of the interaction between the current stimulus impulse and each past stimulus impulse within a time (memory) window mu. The mean PS (k1 decreased by 15%, 10%, and 7% when phenytoin, carbamazepine, and valproate were added respectively. Phenytoin caused an increase in the k2 peak facilitation in the high frequency domain. Carbamazepine impaired frequency facilitation in the theta frequency range by causing a left shift in the second order kernel.

Lamotrigine inhibits postsynaptic AMPA receptor and glutamate release in the dentate gyrus

PURPOSE

The dentate gyrus (DG) is a gateway that regulates seizure activity in the hippocampus. We investigated the site of action of lamotrigine (LTG), an effective anticonvulsant, in the regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and N-methyl-D-aspartic acid (NMDA) receptor-mediated excitatory synaptic transmission on DG.

METHODS

Evoked AMPA and NMDA receptor-mediated excitatory postsynaptic currents (eEPSCampa and eEPSCnmda) were recorded by whole-cell patch-clamp recording from the granule cells of DG in brain slice preparation of young Wistar rats (60-120 g). Exogenously applied AMPA and NMDA-induced currents and AMPA receptor-mediated miniature EPSC (mEPSCampa) were recorded in the presence of specific antagonists.

RESULTS

LTG inhibited both eEPSCampa and eEPSCnmda, and had no effect on exogenously applied NMDA-induced current indicating LTG inhibited glutamate release. Previous studies demonstrated that alteration in glutamate concentration in synaptic cleft causes parallel changes of eEPSCampa and eEPSCnmda. Our results showed that LTG inhibited eEPSCampa significantly more than eEPSCnmda (p < 0.05), suggesting that LTG may also have blocked the postsynaptic AMPA receptor. The hypothesis is further supported by the facts that; (1) LTG (30-100 microM) inhibited direct exogenously applied AMPA-induced currents (to 90%), (2) LTG significantly reduced the amplitude, but not the frequency of mEPSCampa and asynchronous (EPSC), and (3) LTG-induced reduction of eEPSCampa was not associated with a modification of the paired-pulse ratio. To sum up, LTG exerts a postsynaptic inhibitory mechanism on the AMPA receptor.

CONCLUSIONS

Our results demonstrate that LTG suppresses postsynaptic AMPA receptors and reduces glutamate release in granule cells of DG. The postsynaptic effect can be one of the underlying mechanisms of LTG's anticonvulsant action.

Antiepileptic drugs in migraine: from clinical aspects to cellular mechanisms

Migraine and epilepsy share several clinical features, and epilepsy is a comorbid condition of migraine. Clinical studies have shown that some antiepileptic drugs are effective at preventing migraine attacks. A rationale for their use in migraine prophylaxis is the hypothesis that migraine and epilepsy share several common pathogenetic mechanisms. An imbalance between excitatory glutamate-mediated transmission and GABA-mediated inhibition in specific brain areas has been postulated in these two pathological conditions. Moreover, abnormal activation of voltage-operated ionic channels has been implicated in both migraine and epilepsy. Cortical spreading depression has been found to be involved in the pathophysiology of epilepsy, in addition to the generation of migraine aura.

Chronic lithium administration attenuates up-regulated brain arachidonic acid metabolism in a rat model of neuroinflammation

Neuroinflammation, caused by a 6-day intracerebroventricular infusion of lipopolysaccharide (LPS) in rats, is associated with the up-regulation of brain arachidonic acid (AA) metabolism markers. Because chronic LiCl down-regulates markers of brain AA metabolism, we hypothesized that it would attenuate increments of these markers in LPS-infused rats. Incorporation coefficients k* of AA from plasma into brain, and other brain AA metabolic markers, were measured in rats that had been fed a LiCl or control diet for 6 weeks, and subjected in the last 6 days on the diet to intracerebroventricular infusion of artificial CSF or of LPS. In rats on the control diet, LPS compared with CSF infusion increased k* significantly in 28 regions, whereas the LiCl diet prevented k* increments in 18 of these regions. LiCl in CSF infused rats increased k* in 14 regions, largely belonging to auditory and visual systems. Brain cytoplasmic phospholipase A(2) activity, and prostaglandin E(2) and thromboxane B(2) concentrations, were increased significantly by LPS infusion in rats fed the control but not the LiCl diet. Chronic LiCl administration attenuates LPS-induced up-regulation of a number of brain AA metabolism markers. To the extent that this up-regulation has neuropathological consequences, lithium might be considered for treating human brain diseases accompanied by neuroinflammation.

Anti-convulsants and anti-depressants

Damage to a nerve should only lead to sensory loss. While this is common, the incidence of spontaneous pain, allodynia and hyperalgesia indicate marked changes in the nervous system that are possible compensations for the loss of normal function that arises from the sensory loss. Neuropathic pain arises from changes in the damaged nerve which then alter function in the spinal cord and the brain and lead to plasticity in areas adjacent to those directly influenced by the neuropathy. The peripheral changes drive central compensations so that the mechanisms involved are multiple and located at a number of sites. Nerve damage increases the excitability of both the damaged and undamaged nerve fibres, neuromas and the cell bodies in the dorsal root ganglion. These peripheral changes are substrates for the ongoing pain and the efficacy of excitability blockers such as carbamazepine, lamotrigine and mexiletine, all anti-convulsants. A better understanding of ion channels at the sites of injury has shown important roles of particular sodium, potassium and calcium channels in the genesis of neuropathic pain. Within the spinal cord, increases in the activity of calcium channels and the receptors for glutamate, especially the N-methyl-D-aspartate (NMDA) receptor, trigger wind-up and central hyperexcitability. Increases in transmitter release, neuronal excitability and receptive field size result from the damage to the peripheral nerves. Ketamine and gabapentin/pregabalin, again with anti-convulsant activity, may interact with these mechanisms. Ketamine acts on central spinal mechanisms of excitability whereas gabapentin acts on a subunit of calcium channels that is responsible for the release of pain transmitters into the spinal cord. In addition to these spinal mechanisms of hyperexcitability, spinal cells participate in a spinal-supraspinal loop that involves parts of the brain involved in affective responses to pain but also engages descending excitatory and inhibitory systems that use the monoamines. These pathways become more active after nerve injury and are the site of action of anti-depressants. This chapter reviews the evidence and mechanisms of drugs, both anti-depressants and anti-convulsants, that are believed to be effective in pain control, with a major emphasis on the neuropathic state.

17beta-estradiol attenuates excitatory neurotransmission and enhances the excitability of rat parabrachial neurons in vitro

The steroid hormone 17beta-estradiol and its respective receptors have been found in several cardiovascular nuclei in the central nervous system including the parabrachial nucleus. In a previous study, we provided evidence that 17beta-estradiol attenuated an outward potassium conductance in parabrachial neurons of male rats, using an in vitro slice preparation. In this study we sought to enhance the comprehensive information provided previously on estradiol's postsynaptic effects in the parabrachial nucleus by directly examining whether 17beta-estradiol application will modulate excitatory synaptic neurotransmission. Using a pontine slice preparation and whole-cell patch-clamp recording, bath application of either 17beta-estradiol (20-100 muM) or BSA-17beta-estradiol (50 muM) decreased the amplitude of evoked excitatory postsynaptic currents (from 30-60% of control) recorded from neurons in the parabrachial nucleus. The paired pulse ratio was not significantly affected and suggests a post-synaptic site of action. The inhibitory effect on the synaptic current was relatively long-lasting (non-reversible) and was blocked by the selective estrogen receptor antagonist, ICI 182,780. Furthermore, 17beta-estradiol reduced the maximum current elicited by a ramp protocol, increased the input resistance measured between resting membrane potential and action potential threshold and caused an increase in the firing frequency of the cells under current-clamp. In summary, 17beta-estradiol caused 3 effects: first, a depolarization; second, a reduction in evoked excitatory postsynaptic potentials; and third, an enhancement of action potential firing frequency in neurons of the parabrachial nucleus. These observations are consistent with our previous findings and support a role for estrogen in modulating neurotransmission in this nucleus.

Excitability of the human epileptic cortex after chronic valproate: A reappraisal

We explored the action of chronic valproic acid (VPA) on the human epileptic cortex by means of transcranial magnetic stimulation (TMS). TMS is an emerging biomarker for neurotropic drugs. We had 15 drug-naive patients with different epileptic syndromes. Interictally, we measured several TMS indexes of cortical excitability before commencing VPA and 3 months later. At that time, all patients were clinical responders to the drug, whose plasma levels were in the "therapeutic range". We then compared the two conditions, while 18 healthy subjects, of whom 12 were retested at a similar delay, acted as controls. In the pooled patients, the baseline resting motor threshold to TMS was similar to that of controls, but it increased significantly (P < 0.05) after VPA. Intracortical facilitation, another index of cortical excitability, was abnormally enhanced at baseline but decreased significantly after VPA (P < 0.05). On splitting patients according to their diagnosis, the threshold increase was significant (P < 0.05) among partial, but not generalized epilepsies. The reverse was true for changes in intracortical facilitation. TMS phenomena had no linear relation to VPA serum levels. Based on the known pharmacology of TMS effects, VPA reduced the intrinsic membrane excitability of motor cortical neurons, possibly through changes in Na+ channel activity. Then, VPA corrected a transmitter-mediated interneuronal hyper-excitability of the primary motor cortex. The former effect was best seen in partial, and the latter in generalized epilepsy patients.

Animal models for the development of new neuropharmacological therapeutics in the status epilepticus

Status epilepticus (SE) is a major medical emergency associated with significant morbidity and mortality. SE is best defined as a continuous, generalized, convulsive seizure lasting > 5 min, or two or more seizures during which the patient does not return to baseline consciousness. The relative efficacy and safety of different drugs in the treatment of human SE should be determined in a prospective, randomized, blinded study. However, complementary animal models of SE are required to answer important questions concerning the treatment of SE because of the obvious difficulties of setting up such studies in clinical emergency conditions. This review offers an overview of the implementation and characteristics of some of the most prevalent animal models of SE currently in use. A description is also provide about how animal models of SE may facilitate the use of neurobiological techniques to successfully address critical questions in the drug treatment of SE. In particular, the experience with recently introduced drugs such as intravenous valproate will be addressed. Finally, the importance of some animal models and pharmacological approaches is explained and we discuss their impact in the development of therapeutic strategies to improve pharmacological treatment for SE is discussed.

Progress in pharmaceutical development presentation with improved pharmacokinetics: a new formulation for valproate

Successful long-term treatment of patients with epilepsy requires selection of an appropriate antiepileptic regimen, optimal dosing and patient compliance. Recent advances in our understanding of the biological basis of epilepsy and in the choice of treatment options are transforming the global management of these patients. If the achievement of seizure freedom remains the primary goal of any antiepileptic treatment, issues associated with drug acceptability and tolerability, and with quality of life of patients, have gained increasing attention as major determinants of ultimate therapeutic success. Sustained-release formulations of antiepileptic drugs can be very helpful in achieving treatment objectives. Stable serum levels without marked peak-to-trough fluctuations, reduced frequency of dosing and the possibility of dosing flexibility may all improve compliance, patient satisfaction and ultimately quality of life. The efficacy of sodium valproate for the treatment of most types of epilepsy has been demonstrated extensively and this drug remains the mainstay of treatment for many clinical situations. Among the various valproate formulations, extended-release tablets have shown improved patient compliance and satisfaction. However, the tablet size and the limited dosing flexibility could be unsuitable for individualized treatment in special populations such as children, the elderly and patients with swallowing difficulties. A new sustained-release formulation of sodium valproate consisting of tasteless microspheres that can be sprinkled on semi-solid food such as yoghurt or jam has been developed. A stick pack presentation allows individualized dosing and greater convenience.

Stabilizing effects of extracellular ATP on synaptic efficacy and plasticity in hippocampal pyramidal neurons

The role of adenosine triphosphate (ATP) as a neurotransmitter and extracellular diffusible messenger has recently received considerable attention because of its possible participation in the regulation of synaptic plasticity. However, the possible contribution of extracellular ATP in maintaining and regulating synaptic efficacy during intracellular ATP depletion is understudied. We tested the effects of extracellular ATP on excitatory postsynaptic currents (EPSCs) evoked in CA1 pyramidal neurons by Schaffer collateral stimulation. In the absence of intracellular ATP, EPSC rundown was neutralized when a low concentration of ATP (1 microm) was added to the extracellular solution. Adenosine and ATP analogues did not prevent the EPSC rundown. The P(2) antagonists piridoxal-5'-phosphate-azophenyl 2',4'-disulphonate (PPADS) and reactive blue-2, and the P(1) adenosine receptor antagonist 8-cyclopentyltheophylline (CPT) had no detectable effects in cells depleted of ATP. However, the protective action of extracellular ATP on synaptic efficacy was blocked by extracellular application of the protein kinase inhibitors K252b and staurosporine. In contrast, K252b and staurosporine per se did not interfere with synaptic transmission in ATP loaded cells. Without intracellular ATP, bath-applied caffeine induced a transient (< 35 min) EPSC potentiation that was transformed into a persistent long-term potentiation (> 80 min) when 1 microm ATP was added extracellularly. An increased probability of transmitter release paralleled the long-term potentiation induced by caffeine, suggesting that it originated presynaptically. Therefore, we conclude that extracellular ATP may operate to maintain and regulate synaptic efficacy and plasticity in conditions of abnormal intracellular ATP depletion by phosphorylation of a surface protein substrate via activation of ecto-protein kinases.

Stressor-related impairment of synaptic transmission in hippocampal slices from α-synuclein knockout mice

The role of alpha-synuclein (alpha-Syn) has recently received considerable attention because it seems to play a role in Parkinson's disease (PD). Missense mutations in the alpha-Syn gene were found in autosomal dominant PD and alpha-Syn was shown to be a major constituent of protein aggregates in sporadic PD and other synucleinopathies. Under normal conditions, alpha-Syn protein is found exclusively in synaptic terminals. However, the potential participation of alpha-synuclein in maintaining and regulating synaptic efficacy is unknown. We have investigated the excitatory synaptic modulation of alpha-synuclein in CA1 pyramidal neurons, using the in vitro hippocampal slice technique. The 4-aminopyridine-induced increase of both spontaneous excitatory postsynaptic current (EPSC) frequency and amplitude was significantly higher in alpha-Syn wild-type than knockout mice, whereas basal spontaneous EPSC frequency and amplitude was similar in both animals. As the spontaneous synaptic activity was abolished by tetrodotoxin, which indicates that it was a result of action potential-mediated transmitter release from presynaptic terminals, spontaneous EPSC changes observed in alpha-Syn knockout mice suggest that these animals present a modification of synaptic transmission with a presynaptic origin. Presynaptic depression of evoked EPSCs by hypoxia or adenosine was significantly larger in alpha-Syn knockout than in wild-type mice, further supporting the hypothesis of regulation of synaptic transmission by alpha-Syn. Together, these observations indicate that the loss of alpha-Syn reduces synaptic efficacy when the probability of transmitter release is modified. We conclude that alpha-Syn might have important actions on the maintenance of the functional integrity of synaptic transmission and its regulation in hippocampus.

Valproate reduced synaptic activity increase induced by 4-aminopyridine at the hippocampal CA3-CA1 synapse

PURPOSE

We investigated the effects of valproate (VPA) on excitatory synaptic transmission changes induced by 4-aminopyridine (4-AP) to determine whether the antiepileptic effects shown by VPA can be ascribed to a modulation of spontaneous excitatory postsynaptic currents (sEPSCs) in the CA3-CA1 synapse.

METHODS

Rat hippocampal slices were prepared and maintained in vitro with standard methods. Whole-cell current and voltage-clamp recordings were obtained from CA1 pyramidal neurons by using the "blind" patch-clamp technique in an immersion recording chamber. Increase in the spontaneous excitatory synaptic activity was induced by addition of 4-AP to the medium.

RESULTS

Perfusion with VPA significantly counteracted the increase of frequency and amplitude of the sEPSCs induced by application of 4-AP and suppressed the epileptiform activity.

CONCLUSIONS

We conclude that VPA decreases the 4-AP-induced enhancement of excitatory synaptic activity at the CA3-CA1 synapse, and that this reduction of excitation input to CA1 contributes to the anticonvulsant effects of VPA.