Effects of valproate on amino acid and monoamine concentrations in striatum of audiogenic seizure-prone Balb/c mice

Sudden unexpected death in epilepsy: Respiratory mechanisms

Epilepsy is one of the most common chronic neurologic diseases, with a prevalence of 1% in the US population. Many people with epilepsy live normal lives, but are at risk of sudden unexpected death in epilepsy (SUDEP). This mysterious comorbidity of epilepsy causes premature death in 17%-50% of those with epilepsy. Most SUDEP occurs after a generalized seizure, and patients are typically found in bed in the prone position. Until recently, it was thought that SUDEP was due to cardiovascular failure, but patients who died while being monitored in hospital epilepsy units revealed that most SUDEP is due to postictal central apnea. Some cases may occur when seizures invade the amygdala and activate projections to the brainstem. Evidence suggests that the pathophysiology is linked to defects in the serotonin system and central CO₂ chemoreception, and that there is considerable overlap with mechanisms thought to be involved in sudden infant death syndrome (SIDS). Future work is needed to identify biomarkers for patients at highest risk, improve ascertainment, develop methods to alert caregivers when SUDEP is imminent, and find effective approaches to prevent these fatal events.

Serotonergic mechanisms in the 6-Hz psychomotor seizures in mice

Serotonin (5-hydroxytrytamine (5-HT)) plays an important role in experimental seizures. Recently, we reported the depletion of 5-HT by parachlorophynylalanine (PCPA) in whole brain to enhance 6-Hz psychomotor seizures in mice. In the present work, we investigated the effect of 5-HT depletion in cortex and hippocampus, brain regions relevant for epilepsy, on behavioral and ultra-structural changes following 6-Hz psychomotor seizures in mice. In addition, we studied the effect of sodium valproate (SVP) on behavioral, biochemical, and ultra-structural effects induced by 6 Hz. Behavioral changes induced by 6 Hz stimulation were characterized as the increased duration of Straub's tail, stun position, twitching of vibrissae, forelimb clonus, and increased rearing and grooming. PCPA administration further enhanced while SVP reduced these behaviors in mice. The 6-Hz psychomotor seizure induced ultra-structural changes in both cortex and hippocampus in mice treated with PCPA. Furthermore, PCPA administrations followed by 6Hz-induced seizures were accompanied by reduced hippocampal and cortical 5-HT. SVP attenuated the PCPA-induced ultra-structural changes and alterations of 5-HT content in the mouse brain. The study suggests the involvement of 5-HT in the 6 Hz psychomotor seizures and in the mechanisms of action of SVP against such seizures in mice.

Modulation of antioxidant enzymatic activities by certain antiepileptic drugs (valproic acid, oxcarbazepine, and topiramate): evidence in humans and experimental models

It is estimated that at least 100 million people worldwide will suffer from epilepsy at some point in their lives. This neurological disorder induces brain death due to the excessive liberation of glutamate, which activates the postsynaptic N-methyl-D-aspartic acid (NMDA) receptors, which in turn cause the reuptake of intracellular calcium (excitotoxicity). This excitotoxicity elicits a series of events leading to nitric oxide synthase (NOS) activation and the generation of reactive oxygen species (ROS). Several studies in experimental models and in humans have demonstrated that certain antiepileptic drugs (AEDs) exhibit antioxidant effects by modulating the activity of various enzymes associated with this type of stress. Considering the above-mentioned data, we aimed to compile evidence elucidating how AEDs such as valproic acid (VPA), oxcarbazepine (OXC), and topiramate (TPM) modulate oxidative stress.

Intracellular pathways of antipsychotic combined therapies: implication for psychiatric disorders treatment

Dysfunctions in the interplay among multiple neurotransmitter systems have been implicated in the wide range of behavioral, emotional and cognitive symptoms displayed by major psychiatric disorders, such as schizophrenia, bipolar disorder or major depression. The complex clinical presentation of these pathologies often needs the use of multiple pharmacological treatments, in particular (1) when monotherapy provides insufficient improvement of the core symptoms; (2) when there are concurrent additional symptoms requiring more than one class of medication and (3) in order to improve tolerability, by using two compounds below their individual dose thresholds to limit side effects. To date, the choice of drug combinations is based on empirical paradigm guided by clinical response. Nonetheless, several preclinical studies have demonstrated that drugs commonly used to treat psychiatric disorders may impact common intracellular target molecules (e.g. Akt/GSK-3 pathway, MAP kinases pathway, postsynaptic density proteins). These findings support the hypothesis that convergence at crucial steps of transductional pathways could be responsible for synergistic effects obtained in clinical practice by the co-administration of those apparently heterogeneous pharmacological compounds. Here we review the most recent evidence on the molecular crossroads in antipsychotic combined therapies with antidepressants, mood stabilizers, and benzodiazepines, as well as with antipsychotics. We first discuss clinical clues and efficacy of such combinations. Then we focus on the pharmacodynamics and on the intracellular pathways underpinning the synergistic, or concurrent, effects of each therapeutic add-on strategy, as well as we also critically appraise how pharmacological research may provide new insights on the putative molecular mechanisms underlying major psychiatric disorders.

Identification of small molecules from human embryonic stem cells using metabolomics

Metabolomics enables the discovery of small molecules that may serve as candidate biomarkers of pharmacological efficacy or toxicity. Biochemical pathways of human development are likely active in human embryonic stem (hES) cells and derivatives, since they recapitulate organogenesis in vitro. We hypothesized that small molecules could be measured from undifferentiated hES cells and hES cell-derived neural precursors (hNPs) using metabolomics and that these compounds are altered in response to known disruptors of human development. Metabolite profiling was performed in hES cells and hNPs after exposure to valproate, an inducer of neurodevelopmental disorders. Kynurenine, an intermediate in tryptophan metabolism, and other small molecules in glutamate metabolism were significantly upregulated in response to valproate. Thus, for the first time, we have been able to measure and identify small molecules secreted from hES cells and cells derived from hES cells. The hES cell metabolome may thus serve as a source of candidate biomarkers to predict or measure pharmacological efficacy or toxic response.

Tryptophan breakdown pathway in bipolar mania

The upregulation of the initiating step of the kynurenine pathway was demonstrated in postmortem anterior cingulated cortex from individuals with schizophrenia and bipolar disorder. However, the tryptophan and kynurenine metabolism in bipolar mania patients especially in drug naïve state has not been clearly explored. This study explored the plasma tryptophan and its competing amino acids, kynurenine, kynurenic acid and 3-hydroxyanthranillic acid and their association with psychopathological scores in 39 drug naïve and drug-free bipolar manic patients in comparison with 80 healthy controls. When age and gender were controlled in multivariate analysis, bipolar manic patients have significantly lower tryptophan index than normal controls (f=9.779, p=0.004). The mean plasma tryptophan concentration and mean tryptophan index were reduced and mean tryptophan breakdown index was increased significantly after a 6-week treatment. The reduction in plasma tryptophan and reduction in tryptophan index showed significant negative correlation with reduction in YMRS score (r=-0.577, p=0.019 and r=-0.520, p=0.039 respectively). The reduction in YMRS also showed positive correlation with both plasma tryptophan concentration and tryptophan index both at the time of admission (r=0.464, p=0.019 and r=0.4, p=0.047 respectively) and discharged (r=0.529, p=0.035 and r=0.607, p=0.013 respectively). The reduction in BPRS score also showed positive correlation with tryptophan index at the time of discharge (r=0.406, p=0.044). These findings indicated the involvement of bi-directional tryptophan metabolism and kynurenine pathway in pathophysiology and response to medication in bipolar mania.

Prenatal exposure to an NMDA receptor antagonist, MK-801 reduces density of parvalbumin-immunoreactive GABAergic neurons in the medial prefrontal cortex and enhances phencyclidine-induced hyperlocomotion but not behavioral sensitization to methamphetamine in postpubertal rats

RATIONALE

Neurodevelopmental deficits of parvalbumin-immunoreactive gamma-aminobutyric acid (GABA)ergic interneurons in prefrontal cortex have been reported in schizophrenia. Glutamate influences the proliferation of this type of interneuron by an N-methyl-D-aspartate (NMDA)-receptor-mediated mechanism. The present study hypothesized that prenatal blockade of NMDA receptors would disrupt GABAergic neurodevelopment, resulting in differences in effects on behavioral responses to a noncompetitive NMDA antagonist, phencyclidine (PCP), and a dopamine releaser, methamphetamine (METH).

METHODS

GABAergic neurons were immunohistochemically stained with parvalbumin antibody. Psychostimulant-induced hyperlocomotion was measured using an infrared sensor.

RESULTS

Prenatal exposure (E15-E18) to the NMDA receptor antagonist MK-801 reduced the density of parvalbumin-immunoreactive neurons in rat medial prefrontal cortex on postnatal day 63 (P63) and enhanced PCP-induced hyperlocomotion but not the acute effects of METH on P63 or the development of behavioral sensitization. Prenatal exposure to MK-801 reduced the number of parvalbumin-immunoreactive neurons even on postnatal day 35 (P35) and did not enhance PCP-induced hyperlocomotion, the acute effects of METH on P35, or the development of behavioral sensitization to METH.

CONCLUSIONS

These findings suggest that prenatal blockade of NMDA receptors disrupts GABAergic neurodevelopment in medial prefrontal cortex, and that this disruption of GABAergic development may be related to the enhancement of the locomotion-inducing effect of PCP in postpubertal but not juvenile offspring. GABAergic deficit is unrelated to the effects of METH. This GABAergic neurodevelopmental disruption and the enhanced PCP-induced hyperlocomotion in adult offspring prenatally exposed to MK-801 may prove useful as a new model of the neurodevelopmental process of pathogenesis of treatment-resistant schizophrenia via an NMDA-receptor-mediated hypoglutamatergic mechanism.

Valproate blocks high-dose methamphetamine-induced behavioral cross-sensitization to locomotion-inducing effect of dizocilpine (MK-801), but not methamphetamine

RATIONALE

Our group has recently shown that methamphetamine (METH) (2.5 mg/kg) induced delayed increases in glutamate (Glu) levels in the rat nucleus accumbens (NAC), and that its repeated administration leads to behavioral cross-sensitization to a selective uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (MK-801).

OBJECTIVES

The present study aims to examine whether valproate (VPA) would inhibit the delayed increases in Glu levels and prevent METH (2.5 mg/kg)-induced behavioral cross-sensitization to MK-801 (0.2 mg/kg).

MATERIALS AND METHODS

We examined the effects of post-treated VPA (50 mg/kg) on METH (2.5 mg/kg)-induced delayed increases in Glu levels. We injected VPA (50 mg/kg) at 120 min after each METH (2.5 mg/kg, once every other day, total of five times) administration and measured locomotor activity induced by challenge with MK-801 (0.2 mg/kg) or METH (0.15 mg/kg) after sufficient withdrawal period. Finally, we measured locomotion induced by MK-801 (0.2 mg/kg) after pretreatment of a competitive NMDA receptor antagonist, CPP (30 mg/kg). Effects of VPA on extracellular Glu levels were examined by using in vivo microdialysis. Locomotor activity was measured by using an infrared sensor.

RESULTS

VPA administered 120 min after METH injection had no effect on METH-induced hyperlocomotion, and inhibited METH-induced delayed increases in Glu levels. Repeated VPA administration prevented METH-induced behavioral cross-sensitization to MK-801, but not sensitization to METH. MK-801-induced hyperlocomotion was enhanced when pretreated with the competitive NMDA receptor antagonist, CPP.

CONCLUSIONS

These results suggest that VPA inhibits high-dose METH-induced delayed increases in Glu levels to prevent development of behavioral cross-sensitization to an NMDA antagonist, but not sensitization to METH.

Effects of divalproex and atypical antipsychotic drugs on dopamine and acetylcholine efflux in rat hippocampus and prefrontal cortex

Mood stabilizers (e.g., valproic acid) and antipsychotic drugs (APDs) are commonly co-administered in the treatment of bipolar disorder and schizophrenia. The basis for any synergism between these classes of drugs in either group of disorders has been little studied. Previous studies have shown that atypical APDs (e.g., clozapine) preferentially increases dopamine (DA) and acetylcholine (ACh) efflux in rat medial prefrontal cortex (mPFC) and hippocampus (HIP), both of which have been suggested to contribute to their ability to improve cognition in patients with schizophrenia. We have recently reported that the anticonvulsant mood stabilizers (AMS), valproic acid, carbamazepine, and zonisamide, but not lithium, also preferentially increase DA efflux in the rat mPFC, and that, at subthreshold doses, the AMS also augment the ability of the atypical APDs clozapine and risperidone to increase DA but not ACh efflux in the mPFC. The present study examined the ability of divalproex (DVX), which is chemically related to valproic acid, to enhance DA and ACh efflux in the HIP and to augment the effect of atypical APDs on ACh efflux in the HIP and mPFC. DVX, 500 mg/kg, significantly increased DA and ACh efflux in the HIP, and DA, but not ACh, efflux in the mPFC, whereas a lower dose of DVX, 50 mg/kg, had no effect on DA or ACh in either region. However, DVX, 50 mg/kg, combined with the atypical APDs olanzapine (1.0 mg/kg) or aripiprazole (0.3 mg/kg) significantly potentiated the effect of both APDs on DA, but not ACh efflux in the HIP and mPFC. Pretreatment of olanzapine or aripiprazole with the selective serotonin 5-HT(1A) antagonist, WAY100635 (1.0 mg/kg) partially but significantly blocked the effect of the combination of DVX, 50 mg/kg, and olanzapine or aripiprazole, on DA efflux in both the HIP and mPFC. WAY100635 did not affect the ability of the combination of olanzapine or aripiprazole and DVX to enhance ACh efflux in the HIP or mPFC. Subchronic administration of the combination of DVX, 50 mg/kg, and risperidone, produced significantly greater increases in DA and ACh efflux in the mPFC, but these increases were not significantly different from those following the acute administration of the combination of risperidone and DVX. These results provide further evidence that the AMS, DVX, augments the ability of atypical APDs to increase DA or ACh efflux in either the HIP or mPFC or both. The clinical significance of this potentiation for the beneficial clinical effects of this combination of agents and the differences between AMS in this regard warrants further study.

Bipolar mania and plasma amino acids: increased levels of glycine

Previous studies have suggested that the N-methyl-d-aspartate (NMDA) glutamate receptor complex is implicated in the pathophysiology of several neuropsychiatric disorders. Especially the glycine coagonist site of this receptor has been proposed as a therapeutic target. It has been hypothesized that the NMDA receptor and the serotonergic system, which function is compromised in affective disorders, are functionally coupled. Furthermore, several studies suggest that peripheral levels of amino acids are associated with psychotic symptomatology. We therefore measured plasma levels of glutamate, glycine, tryptophan and the tryptophan ratio in 20 bipolar-I patients during the manic phase and at remission of symptomatology. Data were compared to a matched group of healthy controls and a group of euthymic bipolar-I patients. During the manic phase, a significant increase of both glutamate and glycine was found, that persisted at remission. Tryptophan and the tryptophan ratio were decreased in manic patients. Subsequent analysis showed that changes in glutamate, tryptophan and tryptophan ratio could be attributed to the use of anticonvulsants. The increased glycine, however, was not related to the use of mood stabilizers. Although the exact relationship between peripheral measures of amino acids, e.g., glycine is not fully clear, the results of this study suggest an involvement of glycine and/or its coagonist site of the NMDA receptor in a manic relapse of patients with a bipolar-I disorder.

The ketogenic diet; fatty acids, fatty acid-activated receptors and neurological disorders

This review outlines the molecular sensors that reprogram cellular metabolism in response to the ketogenic diet (KD). Special emphasis is placed on the fasting-, fatty acid- and drug-activated transcription factor, peroxisome proliferator-activated receptor alpha (PPARalpha). The KD causes a switch to ketogenesis that is coordinated with an array of changes in cellular lipid, amino acid, carbohydrate and inflammatory pathways. The role of both liver and brain PPARalpha in mediating such changes will be examined, with special reference to the anti-epileptic effects not only of the KD but a range of synthetic anti-epileptic drugs such as valproate. Finally, the implications of the KD and activated brain PPARalpha will be discussed in the context of their potential involvement in a range of disorders of neuro-degeneration and neuro-inflammation.

Convergent effects of lithium and valproate on the expression of proteins associated with large dense core vesicles in NGF-differentiated PC12 cells

Lithium and valproate are chemically unrelated compounds that are used to treat manic-depressive illness. Previously, we reported that lithium ions upregulate genes encoding proteins primarily associated with large dense core vesicles (LDCV) in nerve growth factor (NGF)-differentiated PC12 cells, but not in undifferentiated PC12 cells. Moreover, lithium did not alter the expression of proteins associated with small-clear, synaptic-like vesicles (SSV) in these cells. Based on these observations, we investigated whether valproate had actions similar to those of lithium in PC12 cells. Thus, undifferentiated or NGF-differentiated PC12 cells were exposed to lithium (1 mM) or valproate (1 mM) for 48 h. Extracts from these cells were submitted to semiquantitative Northern and Western analyses. In NGF-differentiated cells, both agents increased the expression of proteins associated with LDCV, the vesicular monoamine transporter 1 (VMAT1), and cysteine string protein (CSP). These same treatments did not alter the expression of proteins primarily associated with SSV, the vesicular acetylcholine transporter (VAChT), and synaptophysin (SY). Furthermore, neither drug affected the expression of these proteins in undifferentiated cells. Interestingly, secretion of (3)H-dopamine was increased in cells exhibiting the increase of VMAT1 and csp. Taken together, the convergent effects of these chemically diverse compounds suggest that altered dynamics of LDCV may play a vital role in the biochemical pathway, leading to the relief of the symptoms of manic depression.

Anticonvulsant properties of N-salicyloyltryptamine in mice

A new tryptamine analogue, N-salicyloyltryptamine (STP), a potential central nervous system (CNS) depressant, was tested in the pentylenetetrazol (PTZ) and maximal electroshock (MES) models of epilepsy in mice. When administered concurrently, STP (100 mg/kg ip) significantly reduced the number of animals that exhibited PTZ-induced seizures and eliminated the extensor reflex of maximal electric-induced seizures test in 50% of the experimental animals. In addition, it showed protection in the PTZ test by diminishing the death rate.

Monoamine neurotransmitters in resected hippocampal subparcellations from neocortical and mesial temporal lobe epilepsy patients: in situ microvoltammetric studies

It is known that epilepsy patients diagnosed with neocortical temporal lobe epilepsy (NTLE), differ from those diagnosed with mesial temporal lobe epilepsy (MTLE), e.g., in hippocampal (HPC) pathology. In the present studies, we tested the hypothesis that NTLE and MTLE subtypes of human epilepsy might differ in regards to their HPC monoamine neurochemistry. Monoamine neurotransmitters were studied in separate signals and within s with semiderivative microvoltammetry, used in combination with stearate indicator, Ag-AgCl reference and stainless steel auxiliary microelectrodes. Anterior HPC specimens from the patients' epileptogenic zone, defined by electrocorticography, were resected neurosurgically from 13 consecutive patients with intractable temporal lobe epilepsy. Four patients were diagnosed with NTLE and nine with MTLE. The criteria for the diagnosis of NTLE versus MTLE was absence versus presence of HPC sclerosis, respectively, based on MRI examination of resected tissue. In addition, NTLE patients demonstrated seizure onset in anterolateral temporal neocortex on electroencephalography (EEG). HPC subparcellations studied were: (a) Granular Cells of the Dentate Gyrus (DG), (b) Polymorphic Layer of DG and (c) Pyramidal Layer: subfields, CA1 and CA2. Dopamine (DA), serotonin (5-HT), norepinephrine (NE) and ascorbic acid (AA) (co-factor in DA to NE synthesis), exhibited separate and characteristic half-wave potentials in millivolts. Each half-wave potential, i.e., the potential at which maximum current was generated, was experimentally established in vitro. Concentrations of neurotransmitters found in HPC subparcellations were interpolated from calibration curves derived in vitro from electrochemical detection of monoamines and AA in saline phosphate buffer. Significant differences between subtypes in concentration of monoamines were analyzed by the Mann Whitney rank sum test and those differences in probability distribution of monoamines were analyzed by the Fisher Exact test; in each case, P<0.01 was the criteria selected for determining statistical significance. DA concentrations were higher in NTLE compared with MTLE in each HPC subparcellation [P=0.037, 0.024 and 0.007, respectively (P<0.01)] and DA occurred more frequently in NTLE in the Pyramidal Layer [P=0.077 (P<0.01)]. AA was present in one NTLE patient. NE concentrations were higher in MTLE vs. NTLE in each subparcellation [P=0.012, 0.067 and 0.07, respectively (P<0.01)] and NE occurred more frequently in MTLE in Granular Cells of DG and Pyramidal Layer [P=0.052 and 0.014, respectively (P<0.01)]. In MTLE, NE concentrations in the CA1 subfield of the Pyramidal Layer were decreased vs. the CA2 subfield [P=0.063 (P<0.01)]. Serotonin was found in every HPC subparcellation of each subtype but 5-HT concentrations were higher in NTLE vs. MTLE in the Granular Cells of DG and the Pyramidal Layer (CA1 subfield) [P=0.076 and 0.095, respectively (P<0.01)]. Thus, this preliminary study showed that marked differences in HPC monoamine neurochemistry occurred in NTLE patients as compared with MTLE patients.

GABA levels within the medial preoptic area: effects of chronic administration of sodium valproic acid

Sodium valproic acid (VPA) is a widely prescribed anticonvulsant medication that has been shown to interfere with pubertal maturation of the reproductive system, and induce endocrine abnormalities in adults, within a subset of the clinical population. While VPA's mechanism of action is still poorly understood, it may exert its anti-reproductive effects by enhancing GABAergic inhibition of the GnRH neuronal population within the medial preoptic area (mPOA). The purpose of this study was to determine if chronic administration of VPA alters GABA levels within the mPOA region. In Experiment 1, the mPOA, caudate, and arcuate nucleus regions were harvested from VPA-treated and control mice. Analysis of whole tissue content of GABA revealed that levels were lower in the caudate and arcuate nucleus regions of VPA-treated animals, whereas there were no group differences for the mPOA region. Collapsing across drug group, there was also a trend for males having overall higher levels of GABA as compared to females. In Experiments 2 and 3, mice were implanted with microdialysis probes within the mPOA region and sampled for extracellular GABA levels. Females (Exp. 3) were sampled either on diestrous, proestrous, or estrous. Results from males (Exp. 2) revealed that VPA enhanced extracellular GABA levels in the mPOA region compared with controls. However, GABA levels for both groups remained stable across the sampling period. Conversely, in Exp. 3, females showed cyclical release of GABA across the sampling period. For control females, GABA levels increased during the afternoon on all cycle days, but the rise on proestrus was smaller than on other cycle days. VPA-treated animals showed an overall reduction in GABA levels compared with controls. Furthermore, while GABA increased over sampling time on estrus and diestrus days of the cycle, there was not a significant rise in GABA on proestrus. These data indicate: (1) regional specificity in VPA effects upon GABA levels, (2) a sex difference in the effects of VPA on GABA levels within the mPOA, and (3) GABA levels increase on the afternoon of all days of the estrous cycle with VPA attenuating the rise seen on the afternoon of proestrus. These results provide evidence that VPA effects upon the reproductive axis may involve changes in GABA release, and that males and females show different patterns of neurochemical response to the drug.

Valproate: a reappraisal of its pharmacodynamic properties and mechanisms of action

Valproate is currently one of the major antiepileptic drugs with efficacy for the treatment of both generalized and partial seizures in adults and children. Furthermore, the drug is increasingly used for therapy of bipolar and schizoaffective disorders, neuropathic pain and for prophylactic treatment of migraine. These various therapeutic effects are reflected in preclinical models, including a variety of animal models of seizures or epilepsy. The incidence of toxicity associated with the clinical use of valproate is low, but two rare toxic effects, idiosyncratic fatal hepatotoxicity and teratogenicity, necessitate precautions in risk patient populations. Studies from animal models on structure-relationships indicate that the mechanisms leading to hepatotoxicity and teratogenicity are distinct and also differ from the mechanisms of anticonvulsant action of valproate. Because of its wide spectrum of anticonvulsant activity against different seizure types, it has repeatedly been suggested that valproate acts through a combination of several mechanisms. As shown in this review, there is substantial evidence that valproate increases GABA synthesis and release and thereby potentiates GABAergic functions in some specific brain regions, such as substantia nigra, thought to be involved in the control of seizure generation and propagation. Furthermore, valproate seems to reduce the release of the epileptogenic amino acid gamma-hydroxybutyric acid and to attenuate neuronal excitation induced by NMDA-type glutamate receptors. In addition to effects on amino acidergic neurotransmission, valproate exerts direct effects on excitable membranes, although the importance of this action is equivocal. Microdialysis data suggest that valproate alters dopaminergic and serotonergic functions. Valproate is metabolized to several pharmacologically active metabolites, but because of the low plasma and brain concentrations of these compounds it is not likely that they contribute significantly to the anticonvulsant and toxic effects of treatment with the parent drug. By the experimental observations summarized in this review, most clinical effects of valproate can be explained, although much remains to be learned at a number of different levels of valproate's mechanisms of action.

Lamotrigine inhibits the in situ activity of tyrosine hydroxylase in striatum of audiogenic seizure-prone and audiogenic seizure-resistant Balb/c mice

Lamotrigine (LTG), an anticonvulsive drug, was tested for its effects on striatal content of DA and its metabolites, DOPAC and HVA, in audiogenic seizure-resistant (ER) and audiogenic seizure-prone (EP) lines of Balb/c mice. A single dose of LTG (20 mg/kg) prevented audiogenic seizures in seizure-prone mice, while reducing substantially the striatal content of the DA metabolite, DOPAC (to less than 50% of saline-injected controls) in both seizure-resistant and seizure-prone mice. LTG administration also resulted in significant reduction of striatal content of HVA. The in situ activity of tyrosine hydroxylase (TH) in extracts of striatum was significantly reduced by LTG administration in both ER and EP mice. These data show that DA synthesis in the striatum of mice is substantially reduced by LTG administration.

Effects of subchronic treatment with valproate on L-5-HTP-induced cortisol responses in mania: evidence for increased central serotonergic neurotransmission

The mechanisms underlying the acute and prophylactic antimanic properties of valproate have remained elusive. There are some reports that treatment with valproic acid may increase brain serotonergic neurotransmission in the rodent. This study was carried out in order to investigate the effects of subchronic therapy with valproate on central serotonin metabolism in manic patients. Toward this end, the authors examined plasma cortisol responses to 200 mg (orally) L-5-hydroxy-tryptophan (L-5-HTP) in 10 manic patients both before and after subchronic treatment with valproate. Administration of L-5-HTP resulted in significantly increased cortisol responses both before and after treatment with valproate. The L-5-HTP-induced cortisol responses were significantly higher after treatment with valproate than before treatment. It is suggested that valproate may increase central serotonergic neurotransmission and that this stimulation may play a role in the antimanic effects of valproate.

Effect of valproate on the metabolism of the central nervous system

The effects of valproate on brain energy and lipid metabolism is reviewed. Increasing evidence suggests that valproate uses the monocarboxylic acid carrier in order to cross the blood brain barrier (BBB) and the neural cell plasma membranes. The uptake of valproate into the brain through this mechanism would compete with the uptake of energy precursors, such as the monocarboxylic acids 3-hydroxybutyrate, lactate or pyruvate and with some amino acids, but not with glucose. This could impair brain fuel utilization, specially during the neonatal period or childhood, when lactate or 3-hydroxybutyrate furnishes alternative substrates to glucose for the brain. It is concluded that valproate interference with energy metabolism may have implications for the therapeutic action of the drug, stressing the possibility that valproate-mediated alterations in brain lipid synthesis may contribute to the pharmacological action of the drug.