Effect of valproic acid on brain serotonin metabolism in isolated and grouped rats

Serotonin and sudden unexpected death in epilepsy

Epilepsy is a highly prevalent disease characterized by recurrent, spontaneous seizures. Approximately one-third of epilepsy patients will not achieve seizure freedom with medical management and become refractory to conventional treatments. These patients are at greatest risk for sudden unexpected death in epilepsy (SUDEP). The exact etiology of SUDEP is unknown, but a combination of respiratory, cardiac, neuronal electrographic dysfunction, and arousal impairment is thought to underlie SUDEP. Serotonin (5-HT) is involved in regulation of breathing, sleep/wake states, arousal, and seizure modulation and has been implicated in the pathophysiology of SUDEP. This review explores the current state of understanding of the relationship between 5-HT, epilepsy, and respiratory and autonomic control processes relevant to SUDEP in epilepsy patients and in animal models.

Divalproex sodium in the treatment of adults with bipolar disorder

Divalproex sodium (Depakote, Abbott Laboratories) is an anticonvulsant with well-established efficacy in the treatment of bipolar I disorder, manic or mixed episode. Over the past 10 years, an increased number of studies indicate that divalproex has a broad spectrum of activity in the treatment of bipolar depression and rapid cycling, psychotic symptoms, impulsive aggression and post-traumatic stress disorder. Newer formulations of divalproex, namely the extended-release formulation, are now available. The improved tolerability and convenience of the once-daily extended-release formulation has a significant potential to improve patient compliance and thus, clinical and functional outcomes. The use of divalproex in the treatment of bipolar and other related psychiatric disorders is reviewed.

Divalproex sodium in the treatment of pediatric psychiatric disorders

Divalproex sodium is an anticonvulsant that is used extensively in adults with indications for epilepsy, acute mania and migraine prophylaxis. It has been used in children and adolescents as a first-line agent for mania in bipolar disorder. Its efficacy as a mood stabilizer has been established, and there have been studies outlining its efficacy as an agent effective in the treatment of conduct disorder, disruptive behavior disorders, aggression and explosive disorder. Longer-acting formulations are now available that cause less gastrointestinal side effects and can also be taken once a day, thus potentially increasing adherence, an important factor in this patient population. Future directions would include developing a more potent valproic acid formulation with fewer side effects, completing randomized controlled trials to establish the efficacy of divalproex sodium in various other pediatric psychiatric disorders, establishing the relative efficacy of the compound in head-to-head comparisons with other mood stabilizers, examining systematically the value of the compound in multimodal pediatric psychiatric treatment packages, and complete effectiveness trials that demonstrate the short- and long-term effectiveness of the compound in the real world of clinicians. In this drug profile, divalproex sodium and its uses in the pediatric population for psychiatric conditions are reviewed.

Effect of D-cycloserine and valproic acid on the extinction of reinstated fear-conditioned responses and habituation of fear conditioning in healthy humans: a randomized controlled trial

RATIONALE

Although the effects of D: -cycloserine (DCS) and valproic acid (VPA) on the facilitation of the extinction of fear-conditioned memory have been elucidated in animals, these effects have not been clearly confirmed in humans.

OBJECTIVE

This study aimed to determine the effect of DCS (100 mg) and VPA (400 mg) on the facilitation of the extinction and acquisition of fear-conditioned memory in humans.

METHODS

We performed a randomized, blind, placebo-controlled, four-arm clinical trial in 60 healthy adults. Visual cues and electric shocks were used as the conditioned stimulus (CS) and unconditioned stimulus (US), respectively.

RESULTS

The extinction or acquisition effect was not observed in the simple recall after the extinction or acquisition of coupled CS-US; however, the extinction and habituation effects but not the acquisition effects were presented after the unexpected re-exposure of coupled CS-US (reinstatement stimuli). Extinction and habituation effects were facilitated by either a single dose of DCS or VPA or a combination of DCS and VPA. However, we did not observe the expected synergistic effect of the combined treatment on the extinction or habituation of fear conditioning.

CONCLUSION

A single dose of DCS or VPA might enhance exposure-based cognitive therapy of anxiety disorders by reducing the vulnerability to reinstatement and preventing relapses of fear-conditioned responses.

Comprehensive review of the psychiatric uses of valproate

The therapeutic effects of valproate in psychiatric conditions are most substantially recognized in bipolar disorder. However, this well-tolerated medication may be beneficial in the treatment of other mental illnesses. In this article, the authors comprehensively review studies of valproate as treatment for psychiatric conditions, including bipolar, depressive, anxiety, and psychotic disorders; alcohol withdrawal and dependence; tardive dyskinesia; agitation associated with dementia; and borderline personality disorder. Valproate shows the most promising efficacy in treating mood and anxiety disorders, with possible efficacy in the treatment of agitation and impulsive aggression, and less convincing therapeutic response in treating psychosis and alcohol withdrawal or dependence. The authors conclude with a brief summary of its mechanism of action and therapeutic spectrum.

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.

Valproate and its major metabolite E-2-en-valproate induce different effects on behaviour and brain monoamine metabolism in rats

The antiepileptic drug valproate has previously been shown to increase serotonin and dopamine turnover in certain brain regions, but the role of these alterations in the diverse pharmacodynamic effects of valproate is not known. For instance, monoamines have been implicated in the 'wet dog' shake behaviour induced by valproate in rats. E-2-en-valproate, a major metabolite of valproate, exhibits the same profile and potency of anticonvulsant activity as valproate, but does not induce wet dog shakes in rats. When administered at about equipotent anticonvulsant doses, both valproate and E-2-en-valproate increased serotonin metabolism in several brain regions of rats, although wet dog shakes were only seen after valproate, thus indicating that wet dog shake behaviour in response to valproate is not mediated by alterations in serotonin. Dopamine metabolism was differentially altered by the two compounds, with marked increases in 3,4-dihydroxyphenylacetic acid or homovanillic acid seen in frontal cortex and brainstem after valproate but not E-2-en-valproate, while the latter drug but not valproate significantly increased 3,4-dihydroxyphenylacetic acid in the amygdala. Levels of noradrenaline were not significantly altered in any of the 8 brain regions examined.

Valproic acid-induced rapid changes of met-enkephalin levels in rat brain. Probable association with abstinence behavior and anticonvulsant activity

Valproic acid (VPA) induces abstinence behavior and analgesia and displays an anticonvulsant effect, but its exact mechanism of action is not yet clear. In order to view whether proenkephalin derived-peptides are involved in the mechanism of VPA-induced behavior, we analyzed immunoreactive-met-enkephalin (IR-ME) in rat striatum, midbrain, and amygdala 10, 20, and 45 min after i.p. injection of 200 mg/kg of VPA. VPA induced body shakes that peaked within 5 to 10 min. IR-ME increased in the striatum and decreased in the midbrain at 10, 20, and 45 min, reaching the highest and lowest levels at 10 and 20 min, respectively. No changes occurred in the amygdala. Gel filtration chromatography followed by HPLC of striatum extracts showed that the increased IR-ME levels corresponded to low molecular weight peptides, including ME. These results indicate that VPA produced rapid changes of IR-ME levels in rat brain and suggest peptide participation in the mechanisms of VPA-induced behavior. The anticonvulsant effect of VPA was tested in rats treated with pentylenetetrazol (70 mg/kg) 30 min after VPA (400 mg/kg) administration, and IR-ME was analyzed in striatum 15 min later. No changes in striatal IR-ME levels occurred in protected rats (no behavioral convulsions), compared with those treated only with VPA, but a significant decrease appeared in unprotected animals (clonic convulsions). These results suggest that striatal ME may participate in the mechanism of VPA-induced abstinence behavior and in the anticonvulsant effect. Otherwise, midbrain ME might be involved in other VPA behaviors such as analgesia.

Regional effects of sodium valproate on extracellular concentrations of 5-hydroxytryptamine, dopamine, and their metabolites in the rat brain: an in vivo microdialysis study

The effects of sodium valproate (VPA; 100, 200, and 400 mg/kg, i.p.) on ventral hippocampal and anterior caudate putamen extracellular levels of dopamine (DA) and 5-hydroxytryptamine (5-HT) were examined using in vivo microdialysis. VPA induced dose-related increases in dialysate DA, 3,4-dihydroxyphenylacetic acid, and 5-HT in the ventral hippocampus. Anterior caudate putamen dialysate 5-HT was also dose dependently elevated by the drug, whereas DA levels tended to decrease with increasing VPA dose. In contrast, VPA (200, 400, and 800 mg/kg, i.p.) produced no significant elevation of DA in posterior caudate putamen dialysates, although 5-HT levels were significantly elevated at the 400- and 800-mg/kg doses. In all three regions studied, dialysate concentrations of 5-hydroxyindoleacetic acid and homovanillic acid remained at basal levels following VPA treatments. The results are discussed with regard to the possible anticonvulsant mode of action of VPA.

Inhibition of mouse killing behavior by serotonin-mimetic drugs: effects of partial alterations of serotonin neurotransmission

Rats which do not kill mice and which acquire mouse killing behavior after partial lesion of the serotonin neurotransmission, either by p-chlorophenylalanine treatment or by electrolytical lesions of dorsal and median raphe nucleus, were treated by IP injection of serotonin-mimetics. The following drugs were used: 5-methoxy-N-N-dimethyl-tryptamine and 8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide, serotonin-agonists, fluoxetine and citalopram, inhibitors of serotonin uptake. All these serotonin-mimetics inhibit mouse killing behavior without apparent secondary effects. When these compounds were tested on killer rats, a stronger antimuricidal effect was observed in rats having altered serotonin neurotransmission. These results support a role for the serotoninergic supersensitivity in a model of aggressive behavior.

Sodium valproate: effects on social behaviour and physical development in the mouse

Sodium valproate given in drinking fluid at 600 mg/l (160-180 mg/kg daily) to breeding mice did not affect fertility, birth weights or physical development of pups. Postnatal and postweaning administration of this dose also had no effects upon development or weight gain. The offspring ingested 103-158 mg/kg valproate daily after weaning. Behaviour was examined in a neutral enclosure by ethological methods. Offspring exposed to valproate in utero and throughout postnatal life showed no behavioural changes at 5 weeks, although at 15 weeks Immobility was reduced in females and Social Investigation increased. At 25 weeks when encountering mice of the opposite sex, treated males showed increase in Social Investigation and treated females increases in Other Non-social Activity. Postnatal and postweaning treatment with valproate caused behavioural changes both in juveniles and adults. After postnatal exposure, reduced Immobility with increased Social Investigation and Explore and Scan occurred at 5 and 15 weeks, at 25 weeks valproate increased Social Investigation in males encountering females and at 30 weeks enhanced Aggression in pair-housed males. Stimulation of Social Investigation was the only significant behavioural effect after postweaning exposure. Overall valproate appears to enhance behaviour stimulated by the test situation; urinary pheromones do not appear to play a part in this behavioural action.

Disinhibition of muricide and irritability by intraseptal muscimol

In two experiments we have found and replicated the observation that intraseptal muscimol profoundly facilitates muricide. It also increases irritability (response to handling). These effects are specific to aggressive behaviors in that the drug affects neither activity nor chocolate chip acceptance. The effects of the GABA synthesis inhibitor thiosemicarbazide depend upon the site of injection within the septum; in more anterior loci the drug produces the expected increase in muricide latency; in more posterior sites it produces an anomalous facilitation of muricide. The serotonergic agents quipazine and metergoline have no significant effect when injected into any of these sites. These results suggest that the septal neurons mediating the muricide-inhibitory effect of electrical stimulation [29] are subject to local, GABAergic, control. Inhibition of these neurons by muscimol produces a net disinhibition of muricide.