Central actions of valproic acid in man and in experimental models of epilepsy

Role of environmental factors and epigenetics in autism spectrum disorders

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder thought to be caused by predisposing high-risk genes that may be altered during the early development by environmental factors. The impact of maternal challenges during pregnancy on the prevalence of ASD has been widely studied in clinical and animal studies. Here, we review some clinical and pre-clinical evidence that links environmental factors (i.e., infection, air pollution, pesticides, valproic acid and folic acid) and the risk of ASD. Additionally, certain prenatal environmental challenges such as the valproate and folate prenatal exposures allow us to study mechanisms possibly linked to the etiology of ASD, for instance the epigenetic processes. These mechanistic pathways are also presented and discussed in this chapter.

Activity of several GABAergic agents on the behavioral “despair” test in rats

The present study was conducted to investigate whether several GABAergic drugs could affect immobility in the behavioral “despair” test (swimming test). The subacute (3 injections) treatment with the GABA-B agonist baclofen 0.5 mg/kg (BC05) partially antagonised the antiimmobility action of imipramine (IMI), whereas muscimol 0.00125 mg/kg (MU ; GABA-A agonist) did not affect the imipramine effect on immobility. The highest doses of baclofen alone increased immobility time, and no effect of muscimol alone was observed on this measure. Other experiments indicated that different doses of δ-α-aminovaleric acid (a GABA-B antagonist and GABA-A agonist) or progabide (a GABA A/B agonist with clinical antidepressive properties) did not modify immobility time. On the other hand, sodium valproate (VPA), chronically administered, was effective in reducing the time of immobility of rats in the swimming test, at doses which did not alter motor activity in an open field test. Since there is evidence indicating that valproate can be considered as a GABA-mimetic agent, the present data is consistent with other results showing an antidepressant-like activity of agents which enhance GABAergic transmission.

Dietary betaine supplementation improves meat quality of transported broilers through altering muscle anaerobic glycolysis and antioxidant capacity

BACKGROUND

To investigate the effect of dietary betaine supplementation on growth performance, meat quality, muscle anaerobic glycolysis and antioxidant capacity of transported broilers, 1-day-old partridge-shank-broiler-chickens (n = 192) were randomly divided into three groups for a 50-day feeding trial. The broilers in the control group were fed a basal diet, and experienced 0.75-h transport before slaughter. The broilers in the other three groups were fed a basal diet supplemented with 0, 500 or 1000 mg kg^-1 betaine, respectively, and experienced 3-h transport before slaughter (T, T + BET₅₀₀ or T + BET₁₀₀₀ groups).

RESULTS

Dietary betaine supplementation increased (P < 0.05) average daily gain of broilers, and feed conversion ratio was also improved (P < 0.05) by 500 mg kg^-1 betaine supplementation. Compared with the control group, 3-h transport increased (P < 0.05) live weight loss, serum corticosterone and cortisol concentrations, as well as muscle lactate and malondialdehyde (MDA) contents, and decreased (P < 0.05) muscle pH_24h , glycogen content and total superoxide dismutase activity. Compared with the T group, betaine supplementation decreased (P < 0.05) serum corticosterone and cortisol concentrations and muscle MDA content, and increased (P < 0.05) muscle a*_24 h . In addition, 1000 mg kg^-1 betaine supplementation further decreased (P < 0.05) muscle drip loss, lactate content and lactate dehydrogenase activity, and increased (P < 0.05) muscle glutathione content and glutathione peroxidase activity.

CONCLUSION

Betaine supplementation not only improved growth performance of broilers, but also alleviated meat quality deterioration of transported broilers through altering muscle anaerobic glycolysis and antioxidant capacity. © 2020 Society of Chemical Industry.

Neither cortisol nor brain-derived neurotrophic factor is associated with serotonin transporter in bipolar disorder

Converging evidence indicates the hypothalamus-pituitary-adrenal axis and serotonergic neurons exert reciprocal modulatory actions. Likewise, brain-derived neurotrophic factor (BDNF) has been implicated as a growth and differentiation factor in the development of serotonergic neurons. The aim of this study was to examine the interaction of cortisol and BDNF on serotonin transporter (SERT) in bipolar disorder (BD). Twenty-eight BD and 28 age- and gender-matched healthy controls (HCs) were recruited. (123)I-ADAM with single-photon emission computed tomography (SPECT) was applied for measurement of SERT availability in the brain, which included the midbrain, thalamus, putamen and caudate. Ten milliliters of venous blood was withdrawn, when the subject underwent SPECT, for the measurement of the plasma concentration of cortisol and BDNF. SERT availability was significantly decreased in the midbrain and caudate of BD compared with HCs, whereas plasma concentration of cortisol and BDNF did not show a significant difference. The linear mixed-effect model revealed that there was a significant interaction of group and cortisol on SERT availability of the midbrain, but not BDNF. Linear regression analyses by groups revealed that cortisol was associated with SERT availability in the midbrain in the HCs, but not in BD. Considering previous studies, which showed a significant association of cortisol with SERT availability in the HCs and major depressive disorder (MDD), our result replicated a similar finding in HCs. However, the negative finding of the association of cortisol and SERT availability in BD, which was different from MDD, suggests a different role for cortisol in the pathophysiology of mood disorder.

Phenomenology and treatment of tremor disorders

Tremor is classified according to anatomic distribution among body parts, and by frequency and amplitude during rest, postural maintenance, movement, intention, and the performance of specific tasks. Key historical features include age at onset, progression over time, family history, exacerbating and remitting factors and behaviors, response to alcohol and medications, and additional neurological signs and symptoms. Accurate diagnosis is a critical factor in predicting the natural history and response to treatment.

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.

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.

Magnesium valproate attenuates hyperactivity induced by dexamphetamine-chlordiazepoxide mixture in rodents

A mixture of dexamphetamine and chlordiazepoxide induces hyperactivity in both mice and rats. This type of hyperactivity has been proposed as an animal model of mania. Magnesium valproate itself had little influence on the activity of normal mice and rats. Acute pretreatment of mice with magnesium valproate (75-300 mg/kg p.o., 37.5-150 mg/kg i.v.) attenuated the mixture-induced hyperactivity. Pretreatment of rats with a single dose of magnesium valproate (75-300 mg/kg, p.o. or i.p.) also counteracted the locomotor hyperactivity caused by the mixture. The effects of magnesium valproate in the mixture-treated mice and rats could be abolished by bicuculline and picrotoxin, but not isoniazid. These findings suggest that the antimanic effect of valproate may be related to its ability to enhance the postsynaptic effects of gamma-aminobutyric acid (GABA).

Valproate potentiates and picrotoxin antagonizes the anxiolytic action of ethanol in a nonshock conflict task

The purpose of this study was to examine the effects of the indirect GABA agonist valproate and the indirect GABA antagonist picrotoxin on the anxiolytic (anti-conflict) activity of ethanol in a behavioral conflict task that does not employ electroshock. This task (negative contrast) quantifies how animals respond to an abrupt, unexpected reduction in reward. Treatment with valproate alone did not elevated depressed behavior engendered by abrupt reduction in reward. However, when administered together with a sub-effective dose of ethanol (0.5 g/kg), valproate (50-200 mg/kg) dose-dependently potentiated the anxiolytic action of ethanol. Picrotoxin (2 mg/kg) antagonized the anxiolytic effects of a larger dose of ethanol (1.0 g/kg) given alone, as well as the ability of valproate to enhance the anxiolytic effects of smaller dose of ethanol (0.5 g/kg). As such, these data support a role for GABA in mediating the anxiolytic activity of ethanol.

Sodium valproate reduces immobility in the behavioral 'despair' test in rats

The present study was conducted to investigate whether sodium valproate could affect immobility in the 'behavioral despair' test in rats. Acute (one injection), subacute (three injections) and chronic treatment with sodium valproate reduced the immobility time in this test, whereas a stimulation of motor activity in the open-field test was not observed with the same drug treatments. The anti-immobility activity of valproate was partially counteracted by the administration of bicuculline (2 mg/kg) or picrotoxin (1.4 mg/kg) before the immobility test. The data agree with previous findings from several animal models of depression of an antidepressant-like activity of GABA mimetics or agents which stimulate GABAergic function.

Marked increase in anticonvulsant activity but decrease in wet-dog shake behaviour during short-term treatment of amygdala-kindled rats with valproic acid

The anticonvulsant activity of valproic acid (VPA) was determined in amygdala-kindled rats after single and repeated (total of 7 injections given 3 times per day) administration of 200 mg/kg i.p. After a single injection, VPA significantly reduced the severity and duration of the kindled seizures and decreased the duration of after-discharges recorded from the stimulated amygdala, but only 12% of the animals were totally protected from seizures. The percentage of animals totally protected increased to 88% after 7 doses. This pronounced increase in the anticonvulsant activity was not related to alterations in the plasma concentrations of VPA or its major active metabolites. Furthermore, determination of VPA and its metabolites in the substantia nigra after a single and repeated administration yielded the same data, again indicating that the increase in the anticonvulsant activity was not due to drug accumulation. In contrast to the marked increase in the anticonvulsant efficacy of VPA during short-term treatment, wet-dog shake behaviour induced by a single injection of the drug was significantly attenuated after repeated dosing, indicating that the anticonvulsant effect of VPA and the wet-dog shake behaviour induced by the drug were not mediated by the same mechanism. This was substantiated by experiments with one of the major metabolites of VPA in rat plasma, trans-2-en-VPA, which had approximately the same anticonvulsant efficacy as VPA but did not induce wet-dog shakes in rats.

The effect of sodium valproate on tardive dyskinesia--revisited

As a treatment for tardive dyskinesia, sodium valproate was tested in a double-blind placebo-controlled parallel group trial, with 6-week base-line observation period followed by 6 weeks of treatment. Sodium valproate was not found to be an effective treatment for either tardive dyskinesia or drug-induced Parkinsonism, and did not affect mental state or behaviour.

Mechanisms of anticonvulsant drug action. II. Drugs primarily used for absence epilepsy

The usefulness of the anticonvulsant drugs is determined by the mechanisms by which the agent acts and its pharmacokinetics. The general mechanisms of action of these agents include (1) effects on neurotransmitter action, (2) effects on repetitive neuronal firing mechanisms, (3) effects on neuronal networks, and (4) effects on neuronal ionic transport. Ethosuximide, valproic acid and clonazepam are used primarily in absence epilepsy. Valproic acid is also effective against generalized tonic-clonic epilepsy. Diazepam is used primarily in status epilepticus. Valproic acid enhances gamma aminobutyric acid (GABA)-mediated inhibition, reduces repetitive firing, and reduces both inhibition and excitation in neuronal networks. Clonazepam and diazepam enhance the inhibitory action of GABA, decrease inhibition in neuronal networks and affect calcium ion transport with lesser effects on repetitive firing. Ethosuximide reduces inhibition in neuronal networks, may interact with dopamine, and possibly affects sodium and potassium ion transport. Further work is needed to assess the degree of involvement of these effects in the anticonvulsant action versus the adverse effects of these agents.

Development of kindling: whole-brain stimulation in rats

Previous studies have demonstrated that low-intensity electrical stimulation of some specific brain regions in several animal species leads to gradual changes in behavior, culminating in generalized seizures (kindling). We found that repeated whole-brain stimulation in rats with electrical currents of 5 and 3 mA elicited progressive behavioral changes and finally triggered convulsive seizures.

An update on sodium valproate

Sodium valproate has been in clinical use for the treatment of epilepsy in Great Britain since 1973 and in the United States since 1978. It is chemically quite different from the existing antiepileptic drugs. Although most authorities concentrate on its modification of GABAergic inhibitory transmission in the central nervous system, its mechanism of action remains obscure. It has been shown to be an effective antiepileptic drug in a wide variety of seizure types, but clinically, its major use to date has been in generalized seizures. It is particularly effective in photosensitive epilepsy and myoclonus. Most adverse reactions to sodium valproate are mild and reversible, but with increasing experience, the drug's rare, idiosyncratic, adverse effects are becoming apparent, particularly hepatotoxicity and teratogenicity. The role of therapeutic drug monitoring in the management of patients taking sodium valproate is controversial.

Effect of valproic acid on 5-hydroxytryptamine turnover in mouse brain

The effect of the antiepileptic drug valproic acid (di-n-propylacetic acid, 200 mg kg-1) on brain 5-hydroxytryptamine (5-HT) synthesis during monoamine oxidase inhibition by pargyline hydrochloride (120 mg kg-1) was studied in mice. Valproic acid increased 5-HT synthesis and elevated 5-hydroxyindoleacetic acid level in brain indicating that turnover of 5-HT is increased. The possible significance of this effect in relation to anticonvulsant action of valproic acid is discussed.

Failure of the GABAergic drug, sodium valproate, to reduce basal plasma prolactin secretion in chronic schizophrenia

The psychoneuroendocrinology of schizophrenia derives from the presumption that neurotransmitter or receptor abnormalities in the limbic regions might extend to or influence the hypothalamus, which plays a role in the regulation of prolactin (PRL) secretion from the anterior pituitary gland. Since a GABA disturbance has been recently proposed in the pathogenesis of certain schizophrenic symptoms, and since a tuberoinfundibular-GABA (TI-GABA) system has been shown to modulate PRL secretion in humans, we tested the activity of this system both in controls and in chronic schizophrenic women. For this purpose the GABAergic drug sodium valproate (800 mg) was administered orally to 20 healthy women and 18 chronic schizophrenic women. Plasma PRL levels were measured before and after the drug administration. Sodium valproate decreased PRL concentrations only in the healthy women. Although the hypothesis of a GABA disturbance in schizophrenia at present is only speculative, these results might suggest a defect of the TI-GABA system in chronic schizophrenia.

Evidence for a GABAergic control of the exercise-induced rise in GH in man

The effect of the GABAergic drug sodium valproate (SV) on the exercise-induced release of growth hormone (GH) was investigated in 10 healthy males. The exercise test consisted of using a stationary bicycle ergometer at 450 kg/min for 20 min. SV 600 mg blunted the increase in GH induced by the exercise, suggesting GABAergic regulation of GH secretion in man, at least under certain physiological conditions.

Reversal of the anti-conflict action of valproate by various GABA and benzodiazepine antagonists

The effects of RO 15-1788, RO 5-3663, picrotoxin and bicuculline on the anti-conflict properties of valproate were studied in rats using a modified Vogel 's conflict test procedure. A low dose of the benzodiazepine (BDZ) antagonist, RO 15-1788 (5 mg/kg), blocked the anti-punishment properties of valproate (400 mg/kg), whereas no antagonism was observed after a high dose (25 mg/kg) of the BDZ antagonist. High doses of RO 5-3663 or picrotoxin also reversed the anti-conflict action of valproate. Bicuculline did not change the effects of valproate in this test situation. The suppressive effect of valproate on locomotor activity was reversed by a low dose (5 mg/kg) of RO 15-1788, but not by the other antagonists. RO 5-3663 was the only antagonist which effectively reversed the muscle relaxant effects of valproate observed in a Rotarod performance test. These findings indicate that various pharmacological actions of valproate may be due to a complex interplay with several sites at the GABA-BDZ-receptor complex.

Lack of ACTH lowering effect of sodium valproate in patients with ACTH hypersecretion

The effect of an oral dose of 200 or 400 mg sodium valproate (DPA) on ACTH and cortisol secretion was assessed in 11 patients with Cushing's disease (3 bilaterally adrenalectomized), 3 patients with Nelson's syndrome and 6 patients with Addison's disease. In none of the patients examined DPA induced changes in ACTH (and cortisol) levels appreciably different from the fluctuations recorded after placebo administration. The effect of a long term administration of sodium valproate (600-1000 mg/day) was evaluated in 2 patients with active Cushing's disease and in 1 patient with Nelson's syndrome (3 weeks, 3, 9 months respectively); in the 2 patients with Cushing's disease ACTH and cortisol secretion, 17-hydroxy-corticosteroids (17-OHCS) urinary excretion did not change during DPA treatment. Similarly the cortisol response to hypoglycemia and the 17-OHCS urinary excretion after dexamethasone were not normalized. Long term DPA administration did not induce either clinical or hormonal modifications in the patient with Nelson's syndrome. These findings do not support the possibility that a deficiency of a GABAergic system plays a role in the pathogenesis of ACTH hypersecretion. DPA does not seem to be of therapeutical value in the medical management of Cushing's disease and Nelson's syndrome.

GABAergic mechanisms in antinociception

GABAergic mechanisms appear to be involved in antinociceptive processes. Generally, peripheral administration of GABAergic agents increases the antinociceptive effect of morphine, but central administration inhibits this effect, suggesting that multiple interactions may occur. GABAergic agents also can produce antinociception directly. Muscimol and THIP (GABAA agonists) act at supraspinal sites to produce antinociception, but do not appear to interact with bicuculline sensitive receptors. Baclofen (a GABAB agonist) acts at both supraspinal and spinal sites. Supraspinal mechanisms include inhibition of ascending noradrenergic and dopaminergic pathways but activation of descending noradrenergic pathways. The spinal mechanism may involve postsynaptic inhibition of the effect of substance P. D-Baclofen is an antagonist at spinal baclofen receptors. Antinociception produced by inhibitors of GABA-transaminase is not reduced by bicuculline in most studies, while manipulations which increase the antinociceptive effect of baclofen do not alter or block the effect of GABA-transaminase inhibitors. An understanding of the role of GABAA and GABAB receptors in antinociception will require clarification of some curious pharmacological actions of bicuculline and the use of a specific GABAB receptor antagonist.

Inhibition of oxidative phosphorylation in hepatic and cerebral mitochondria of sodium valproate-treated rats

Rats were treated with intraperitoneal injections of sodium valproate (VPA), either acutely, one injection VPA 200 mg/kg, or chronically, VPA 600 mg/kg/day for 5 days, and the oxygen consumption, MO2, of isolated hepatic and cerebral mitochondria measured. For hepatic mitochondria, Stade IV MO2 decreased by more than 20%, and Stage III MO2 by more than 50%, in the presence of succinate or glutamate-malate substrates. A decoupling agent intensified this inhibition. With cerebral mitochondria, the effects were similar but weaker, for pyruvate-malate or glutamate-malate substrates. These findings suggest that VPA, a short-chain fatty acid, may affect the properties of the internal mitochondrial membrane, although an action on substrate carriers, or on indispensable mitochondrial metabolites, is not excluded. Inhibition of oxidative phosphorylation cannot, however, alone account for hepatotoxicities seen in VPA-treated subjects. These are rare, whereas inhibition of mitochondrial respiration by VPA is consistently observed.

Studies on the role of serotonin in different regions of the rat central nervous system on pentylenetetrazol-induced seizures and the effect of di-n-propylacetate

5,7-Dihydroxytryptamine (5,7-DHT) injections which caused selective depletion of serotonin in the forebrain enhanced the seizures caused by pentylenetetrazol (PTZ 90 mg/kg s.c.) in rats. No effect was observed in rats with 5,7-DHT-induced depletion of spinal serotonin or treated with metergoline (1 mg/kg i.p.) or methysergide (10 mg/kg i.p.). The various procedures aimed at decreasing serotonin transmission did not significantly modify the effect of di-n-propylacetate (DPA) on tonic seizures and mortality caused by PTZ but significantly reduced the DPA-induced increase in the latency to the first convulsion. More animals with clonic seizures were seen in the DPA-treated group which had been subjected to selective depletion of spinal serotonin or treated with methysergide than in DPA-treated controls. Combined treatment with d-fenfluramine (1.25 mg/kg i.p.) and DPA (75 mg/kg i.p.), doses which by themselves had no significant effect, reduced tonic seizures and mortality caused by PTZ. The results show that a diffuse deficit in forebrain serotonin enhances PTZ-induced seizures. Serotonin does not play an important role in the effect of DPA against PTZ-DPA on clonic convulsions. Agents increasing serotonin transmission may enhance the anticonvulsant activity of DPA.

[Sodium valproate: a hyperammonemic drug. Study in the epileptic and healthy volunteer]

Sodium valproate (VPA) consistently induces an arterial hyperammonemia in epileptics tolerant of this drug and in normal subjects. The hyperammonemia appears with the first oral or intravenous dose of the drug, 15-25 mg/kg, and is established within minutes following drug absorption. In 20 epileptics treated with VPA alone for 4 days, the mean arterial ammonemia measured 2-3 h after breakfast and the day's first VPA dose was 72 +/- 9 mumols/l in non-alcoholics, and 77 +/- 7 mumols/l in alcoholics. Hyperammonemia persisted during chronic treatment; in 10 epileptics who had had received only VPA for over a month, the mean hyperammonemia was 87 +/- 6 mumols/l (normal value means +/- 2 SD = 28 +/- 12 mumols/l). The ammonemia varied in the course of the day; sharp peaks 7 or more times the base value were observed. These variations, differing among subjects, depended on the VPA plasma concentration, and above all on the meal composition and the relative timing of the meal and the drug administration. No secondary effects were seen; in particular, hepatic and pancreatic tests were normal. The hyperammonemia would seem to be due to physiopathological mechanisms other than those giving rise to the hepatic complications occasionally observed with VPA. The permanence and the extent of the hyperammonemia raise questions as to its origin, its relation to the stuporous states induced by VPA, and its eventual repercussions on the functioning of neurons.

The role of different types of adrenergic receptors in pentylenetetrazol-induced seizures and the effect of di-n-propylacetate in the rat

Selective depletion of forebrain noradrenaline has been shown to potentiate various types of experimentally induced seizures. This study was aimed at exploring the role of different types of adrenergic receptors in pentylenetetrazol (PTZ)-induced seizures in rats and the anticonvulsive effect of di-n-propylacetate (DPA). Piperoxane (10 and 20 mg/kg, IP) significantly potentiated PTZ-induced tonic seizures and mortality. Similar effects were observed after 6-hydroxydopamine (6-OHDA)-induced depletion of forebrain noradrenaline, whereas no effects were found in animals with depletion of spinal noradrenaline. Neither phenoxybenzamine (20 mg/kg, IP) nor prazosin (1 and 10 mg/kg, IP) nor propranolol (2 and 5 mg/kg, IP) modified tonic seizures and mortality caused by PTZ. Combined treatment with propranolol (5 mg/kg, IP) and prazosin (10 mg/kg, IP) had no effect either. Various agents used to increase central serotonin transmission (d-fenfluramine, 5 mg/kg, IP; quipazine, 10 mg/kg, IP; m-chlorophenylpiperazine, 3 mg/kg, IP) did not alter the effect of piperoxane on PTZ-induced seizures. None of the conditions used to diminish central adrenergic function significantly affected the inhibitory effect of DPA on tonic seizures and mortality caused by PTZ. Combined treatment with subthreshold doses of clonidine (0.1 mg/kg, IP) and DPA (75 mg/kg, IP) significantly reduced tonic seizures and mortality caused by PTZ. The data suggest that alpha 2 type adrenoceptors are involved in the control of PTZ-induced seizures in rats. The peculiarity of the role of these receptors in the effect of PTZ is discussed.

Dissociation between epileptic seizures induced by convulsant drugs and alteration in the concentrations of pyridoxal phosphate in rat brain regions

Allylglycine increased the concentration of pyridoxal phosphate in cerebral cortex from 1011.4 +/- 25.0 to 1318.0 +/- 66.3 and decreased it in cerebellum from 1289.0 +/- 49 to 1147.7 +/- 119.4 ng/g wet tissue during the preictal period. Mercaptopropionic acid increased the concentration of pyridoxal phosphate in cerebellum from 1525 +/- 91 to 1985.7 +/- 275 ng/g wet tissue. Similar effects were noted in hippocampus and cerebral cortex. Picrotoxin increased the concentration of pyridoxal phosphate in hippocampus from 938.7 +/- 44 to 1043 +/- 118 but decreased it in cerebral cortex from 1124.52 +/- 124 to 979.4 +/- 15 ng/g wet brain. The effects of strychnine were identical to those of allylglycine. Bicuculline reduced the concentration of pyridoxal phosphate in cerebral cortex from 1184 +/- 61 to 1075.14 +/- 78 ng/g wet brain.

In vivo uptake of valproic acid into brain

The pharmacokinetics of valproic acid (VPA) penetration into the central nervous system of cats were studied. VPA levels in cortical gray matter and plasma were measured at timed intervals after rapid intravenous drug infusion. Brain uptake of the drug was maximal at 1 min postinfusion and decayed rapidly with a mean elimination half-life of 41 min. After a rapid distribution phase, plasma VPA levels remained stable for 90 min. The brain:plasma ratio was maximal at 1 min and also declined rapidly. The volume of distribution was 0.125 1/kg. The small volume of distribution, low brain:plasma ratios and rapid clearance from brain indicate that VPA is not significantly bound in cerebral cortex after a single dose.