Adverse effects of phenobarbital on morphological and biochemical development of fetal mouse spinal cord neurons in culture

Neonatal seizures: an update on mechanisms and management

The lifespan risk of seizures is highest in the neonatal period. Current therapies have limited efficacy. Although the treatment of neonatal seizures has not changed significantly in the last several decades, there has been substantial progress in understanding developmental mechanisms that influence seizure generation and responsiveness to anticonvulsants. This article provides an overview of current approaches to the diagnosis and treatment of neonatal seizures, and some of the recent insights about the pathophysiology of neonatal seizures that may provide the foundation for better treatment are identified.

The 2008 Judith Hoyer lecture: epilepsy in children: listening to mothers

The incidence of epilepsy is significantly higher in children than adults. When faced with the diagnosis of epilepsy, parents have many questions regarding cause, treatment, and prognosis. Although the majority of children with epilepsy have an excellent prognosis and respond well to therapy, some children are refractory to therapy and suffer from cognitive decline. Animal models are now providing insights into the mechanisms responsible for the high incidence of seizures during development and age-dependent seizure-induced damage. One of the causes of the increased susceptibility of the young brain to seizures is the depolarizing effects of GABA secondary to high intracellular concentrations of chloride in young neurons. Although cell loss is not a feature of seizures in the young brain, recurrent seizures do result in aberrant sprouting of mossy fibers, reduce neurogenesis, and alter excitatory and inhibitory neurotransmitter receptor structure and function. Behavioral consequences of early-life seizures include impaired spatial cognition, which now can be assessed using single-cell recordings from the hippocampus. Antiepileptic drugs have had a tremendous positive influence in epilepsy management, although there are now a number of studies demonstrating that antiepileptic drugs at therapeutic concentrations can impair cognition and result in increased apoptosis. While clinical judgment and experience are paramount when discussing the consequences of seizures and their treatment, awareness of studies from animals can provide the clinician with guidance in addressing these important issues with parents.

Neonatal seizures

In childhood, the risk for seizures is greatest in the neonatal period. Currently used therapies have limited efficacy. Although the treatment of neonatal seizures has not significantly changed in the past several decades, there has been substantial progress in understanding developmental mechanisms that influence seizure generation and responsiveness to anticonvulsants. This review includes an overview of current approaches to the diagnosis and treatment of neonatal seizures, identifies some of the critical factors that have limited progress, and highlights recent insights about the pathophysiology of neonatal seizures that may provide the foundation for better treatment.

Postnatal concerns in children born to women with epilepsy

Infants born to mothers with epilepsy are at substantial risk for neurocognitive and behavioral disorders. Although exposure of the child to antiepileptic drugs (AEDs) during pregnancy and postnatally through breast milk has been implicated in disorders of higher cortical function, there have been relatively few clinical or animal studies examining the long-term effects of AEDs on cognition in the developing brain. In the limited animal studies done thus far, drug-specific effects on cognitive function have been identified. Phenobarbital, in particular, has been found to lead to adverse cognitive outcomes, whereas the newer AEDs have generally had more favorable outcomes. Although the pathophysiological mechanisms responsible for these deficits remain largely unknown, there is evidence that AEDs can adversely effect neuronal proliferation and migration, and increase apoptosis. While animal studies can provide valuable information regarding mechanism of AED-induced developmental pathology, they do not provide insight into cortical functions unique to humans, such as speech and language. Understanding the full spectrum of AED-induced effects on the developing brain will require both rigorous basic science and clinical studies.

Mechanisms of action for the commonly used antiepileptic drugs: relevance to antiepileptic drug-associated neurobehavioral adverse effects

Antiepileptic drugs exert their anticonvulsant effects by interfering with brain processes that involve structures that are also involved in learning, memory, and emotional behavior. Thus, modulation of ion channels, neurotransmitters, second messengers, and other processes by antiepileptic drugs, although helpful in controlling seizures, can interfere with normal brain function in undesired ways. The specific mechanism(s) of action of an antiepileptic drug can increase the risk for particular types of adverse events. In this review, we examine the cognitive and behavioral effects of antiepileptic drugs in animal models. Although animal studies, in many respects, do not mimic clinical experience, the data suggest a connection between certain mechanisms of antiepileptic action and the occurrence of cognitive adverse effects. Specifically, antiepileptic drugs with traditional gamma-aminobutyric acid (GABA)ergic mechanisms have the most detrimental effects on cognitive function, possibly because they impair attention. Conversely, drugs with the predominant effects at Na+ channels appear to have minimal impact on cognition. Levetiracetam, with its nonconventional GABAergic and Ca2+ channel effects, has shown positive cognitive effects in animal studies. Antiglutamatergic drugs have the potential to be a double-edged sword: they can interfere with consolidation of learning and memory but can also provide neuroprotection in addition to their antiseizure effects.

Neonatal seizures and neonatal epileptic syndromes

The neonatal period is defined as the first 28 days of life of a term infant; for premature infants the limit of this period is 44 completed weeks of the infant's conceptional age (CA)-defined as the chronological age plus gestational age (GA) at birth. The clinical and electroencephalographic (EEG) manifestations of seizures during this period are determined primarily by the development features of the immature brain at the time of seizure onset, but are also related to the type and diversity of etiologies and risk-factors for seizures neonates may face early in life. Neonatal seizures may be strikingly different from the clinical and electrical seizures of older children and adults. In addition, findings from basic science investigations suggest that immature animals are more likely to experience seizures in response to injury than more mature animals, although the developing brain is less susceptible to seizure-induced injury.

Special considerations in treating children with epilepsy

The incidence of seizures is high in infants and children. Many epileptic syndromes have their onset early in life. The increase in seizure susceptibility of the immature brain may be due to several factors, including an imbalance between excitatory and inhibitory processes, age-specific differences in ionic transport and clearance systems, high incidence of epileptogenic stimuli early in life, and the age-specific expression of pre- and perinatal brain anomalies. All of these factors must be taken into account when developing safe and effective age-specific antiepileptic drugs (AEDs). The use of developmental epilepsy models, followed by clinical trials in children, may help identify such AEDs.

Acute and chronic effects of seizures in the developing brain: lessons from clinical experience

Seizures in the neonate are often considered a form of status epilepticus (SE) because they are relatively prolonged, difficult to control with antiepileptic drugs (AEDs), and may be associated with significant morbidity and mortality. Despite their clinical importance, there is still no clear understanding of how seizures may affect the developing brain. Although both basic neuroscience and clinical research have addressed these issues, there are difficulties in the design and analysis of each type of investigation. Animal studies should reflect the human condition, the most relevant studies being those that consider neocortical rather than hippocampal seizures. Clinical investigations should be based on precise, age-specific definitions of seizures of epileptic origin and of SE. Treatment strategies should be standardized with defined rationale and end points. Outcome measures are best when defined and quantifiable. The relative effects of underlying CNS injuries that coexist with the onset of neonatal seizures may be difficult to differentiate from the effects of the seizures themselves or their treatment. Current clinical studies suggest that the overriding factors in determining the outcome of neonates with seizures are the cause, the degree, and the distribution of brain injury at the time of seizure occurrence. However, such studies have limitations and may not yet employ methodology sensitive enough to detect a full range of adverse effects of seizures themselves.

Late cognitive effects of early treatment with phenobarbital

We previously reported that IQ was significantly lowered in a group of toddler-aged children randomly assigned to receive phenobarbital or placebo for febrile seizures and there was no difference in the febrile seizure recurrence rate. We retested these children 3-5 years later, after they had entered school, to determine whether those effects persisted over the longer term and whether later school performance might be affected. On follow-up testing of 139 (of the original n = 217) Western Washington children who had experienced febrile seizures, we found that the phenobarbital group scored significantly lower than the placebo group on the Wide Range Achievement Test (WRAT-R) reading achievement standard score (87.6 vs 95.6; p = 0.007). There was a nonsignificant mean difference of 3.71 IQ points on the Stanford-Binet, with the phenobarbital-treated group scoring lower (102.2 vs 105.7; p = 0.09). There were five children in our sample with afebrile seizures during the 5-year period after the end of the medication trial. Two had been assigned to phenobarbital, and three had been in the placebo group. We conclude there may be a long-term adverse cognitive effect of phenobarbital on the developmental skills (language/verbal) being acquired during the period of treatment and no beneficial effect on the rate of febrile seizure recurrences or later nonfebrile seizures.

Epilepsy in the developing brain: lessons from the laboratory and clinic

Children with epilepsy present unique challenges to the clinician. In addition to having differences in clinical and EEG phenomena, children differ from adults in regard to etiological factors, response to antiepileptic drugs (AEDs), and outcome. It is now recognized that the immature brain also differs from the mature brain in the basic mechanisms of epileptogenesis and propagation of seizures. The immature brain is more prone to seizures due to an imbalance between excitation and inhibition. gamma-Aminobutyric acid (GABA), the major CNS inhibitory neurotransmitter in the mature brain, can lead to depolarization in the hippocampal CA3 region in very young rats. There are also age-related differences in response to GABA agonists and antagonists in the substantia nigra, a structure important in the propagation of seizures. These age-related differences in response to GABAergic agents provide further evidence that the pathophysiology of seizures in the immature brain differs from that in the mature brain. Although prolonged seizures can cause brain damage at any age, the extent of brain damage after prolonged seizures is highly age dependent. Far less histological damage and fewer disturbances in cognition result from prolonged seizures in the immature brain than from seizures of similar duration and intensity in mature animals. However, detrimental effects of AEDs may be greater in the immature brain, than in the mature brain. These lessons from the animal laboratory raise questions about the appropriateness of current therapeutic approaches to childhood seizure disorders.

Antiepileptic drug treatment in pregnancy: drug side effects in the neonate and neurological outcome

Antiepileptic drugs taken by pregnant epileptic women are known human teratogens. They may also cause pharmacological side effects in the newborn, i.e. sedation and or withdrawal symptoms. We examined the relationship between the maternal antiepileptic therapy, neonatal behaviour and later neurological functions in infancy. The study comprised 40 children exposed in utero to a single antiepileptic drug (phenobarbitone, phenytoin, valproic acid). Valproic-acid-exposed children were the highest compromised, except for apathy, which was most profound in phenobarbitone-exposed neonates. Valproic acid serum concentrations at birth correlated with the degree of neonatal hyper-excitability and neurological dysfunction when children were re-examined 6 years later. We suggest that valproic acid may not only cause malformations but also cerebral dysfunction immediate and long term.

Neonatal seizures and electrographic analysis: evaluation and outcomes

Issues exist in the diagnosis, evaluation, management, and outcome of neonatal seizures. Electroencephalographic data are essential in the characterization, description, and classification of these events, as clinical inspection alone may lead to significant errors in underestimation or overestimation of seizures. This review discusses ictal characteristics of neonatal seizures as well as electrographic status epilepticus. The long-term benefit of treatment of electrographic seizures has never been proved. Prognosis is of critical concern in neonates with seizures and electroencephalographic data yield significant predictive information. Background analysis is most reliable in infants with normal or markedly abnormal recordings. Other ictal features may provide insight into specific outcomes (e.g., development of cerebral palsy). Mortality and neurologic morbidity (including postnatal epilepsy) remain major risks.

Effects of chronic prenatal, neonatal and adult exposure to barbiturates on mitochondrial benzodiazepine receptors in mouse testis

In the present study we investigated the effect of chronic exposure to phenobarbital, administered to mice during the prenatal or neonatal period, as well as to adult mice, on mitochondrial benzodiazepine receptors in the testis. Three modes of treatment were investigated: (1) offspring of pregnant mice receiving food containing 3 g/kg phenobarbital until gestational day 18 were killed at 22 or 50 days of age and assayed for receptor binding (prenatal group); (2) offspring of untreated mice were injected subcutaneously once daily with 50 mg/kg phenobarbital on days 2-21 of age and killed at 22 or 50 days of age (neonatal group); (3) adult mice were injected subcutaneously once daily for 3 weeks with 50 or 100 mg/kg phenobarbital (adult group). Prenatal or neonatal exposure to phenobarbital did not alter the testicular weight in all groups (except for the neonatally exposed group killed at 22 days of age), or the mitochondrial benzodiazepine receptor binding characteristics. However, the maximal number of these receptors in the testes of mice in the adult group receiving 100 mg/kg phenobarbital was significantly increased (42%, P < 0.05), compared to controls. The administration of 50 mg/kg phenobarbital to the adult group also induced an increase (27%, non-significant) in testicular mitochondrial benzodiazepine receptors. Phenobarbital administration did not affect the receptor affinity values or the weight of the testis. It is unclear whether these receptor alterations due to chronic phenobarbital exposure of adult mice reflect functional changes in the testis.

Effects of phenobarbital and phenytoin on cortical glial cells in culture

Studies were undertaken to determine the effects of 7-day phenobarbital and phenytoin exposure on 14-day-old glial cell cultures of fetal murine cortex. Biochemical markers monitored were Ro5-4684-displaceable 3H-flunitrazepam binding, 3H-beta-alanine uptake, glutamine synthetase activity, and protein content. Phenobarbital concentrations were 30, 60, and 120 micrograms/ml and phenytoin concentrations 15, 30, 60 micrograms/ml. There were no discernible phase microscopic changes at any concentration of either drug. Phenobarbital produced no significant changes in the biochemical measures monitored. Exposure to phenytoin produced no biochemical changes at 15 micrograms/ml, but did produce significant changes at 30 and 60 micrograms/ml. There was an increase in Ro5-4684-displaceable 3H-flunitrazepam binding signifying increased binding or an increase in the number of binding sites and perhaps an increased population of glial cells although, the unchanged protein content suggests that the number of glial cells was not increased. There was a decrease with 30 and 60 micrograms/ml phenytoin of 3H-beta-alanine uptake suggesting interference with normal membrane transport of this compound. The latter effect may well mirror changes in GABA uptake in glial cells in the presence of phenytoin.

Phenobarbital for febrile seizures--effects on intelligence and on seizure recurrence

Phenobarbital is widely used in the treatment of children with febrile seizures, although there is concern about possible behavioral and cognitive side effects. In 217 children between 8 and 36 months of age who had had at least one febrile seizure and were at heightened risk of further seizures, we compared the intelligence quotients (IQs) of a group randomly assigned to daily doses of phenobarbital (4 to 5 mg per kilogram of body weight per day) with the IQs of a group randomly assigned to placebo. After two years, the mean IQ was 7.03 [corrected] points lower in the group assigned to phenobarbital than in the placebo group (95 percent confidence interval, -11.52 to -2.5, P = 0.0068 [corrected]). Six months later, after the medication had been tapered and discontinued, the mean IQ was 5.2 points lower in the group assigned to phenobarbital (95 percent confidence interval, -10.5 to 0.04, P = 0.052). The proportion of children remaining free of subsequent seizures did not differ significantly between the treatment groups. We conclude that phenobarbital depresses cognitive performance in children treated for febrile seizures and that this disadvantage, which may outlast the administration of the drug by several months, is not offset by the benefit of seizure prevention.

Controversies concerning neonatal seizures

Five issues are discussed with respect to the diagnosis, etiology, treatment, prognosis, and pathogenesis of neonatal seizures. The presentation of a newborn with seizures represents a true emergency and frequently indicates significant neurologic dysfunction or damage to the immature nervous system. Despite the urgency to establish a diagnosis, several unique aspects of neonatal seizures impede prompt recognition. In addition, several etiologic possibilities may be associated with seizures. The efficacy of antiepileptic drugs and the prediction of outcome of patients with neonatal seizures are controversial. Experimental research in developing animals suggests both a selective vulnerability and resistance of the brains of immature animals subjected to neonatal seizures.

Differential effects of prenatal exposure to phenobarbital on the behaviour and neurochemistry of CBA and C57BL/6J mice

Pregnant C57BL/6J and CBA mice were administered 60 mg/kg phenobarbital intraperitoneally from days 10 to 16 of gestation. On day 18 of pregnancy half of the control and drug-treated mice were killed and the embryonic brains removed for cell cultures. The remaining mice were allowed to have their litter. After cross-fostering the mice were used for behavioural studies. Pups born to drug-treated CBA mice had birth-weights similar to controls, but their weights had fallen behind controls by day 18 after birth. They were slower at attaining mature responses in tests for sensory motor development and became progressively more hyperactive (three times more active at day 18) compared to controls. Drug-exposed C57 pups also had birth weights similar to controls. After cross-fostering, 19% of control and 31% of drug-exposed pups died, but the remaining drug-exposed pups showed no deficits in weight gain. In contrast to drug-treated CBA pups, drug-exposed C57 pups were slightly quicker in attaining mature responses in some tests. There was no difference in activity between them and their controls. In neurochemical analyses, uptake of neurotransmitters by cerebral cultures from CBA showed that uptake of GABA was increased by 5%, choline by 95%, dopamine 120%, serotonin 165% and noradrenaline by 160% in cultures from drug exposed embryos compared to controls. In cerebral cultures from C57, GABA uptake was reduced by 18%, choline 33%, dopamine 35% and noradrenaline by 25%. Only serotonin uptake was increased by 182% compared to controls. Differences between C57 and CBA were also apparent in the uptake of neurotransmitters by neuronal cultures from the mesencephalon.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of anticonvulsants on cholinergic and GABAergic properties in the neuronal cell clone NG108-15

The effects of anticonvulsant drugs on growth, cholinergic, and GABAergic properties were examined in the neuronal cell clone NG108-15. Cells were exposed for 4 days to valproic acid, phenobarbital, phenytoin, or carbamazepine in concentrations equivalent to therapeutic free levels in human serum. Experiments were also performed with varying concentrations of a recently proposed antiepileptic, gamma-vinyl GABA. Of these five anticonvulsants, cell growth (total protein and cell counts) was decreased with valproic acid and phenytoin but only valproic acid and gamma-vinyl GABA altered neurotransmitter markers. Therapeutic concentrations of valproic acid increased choline acetyltransferase activity to 142% of control but had no effect on either the activity of glutamate decarboxylase or the level of GABA. The effects of a higher (toxic) concentration of valproic acid (200 micrograms/ml) were similar to those induced by the differentiating agent dibutyryl cyclic AMP: both decreased cell growth, enhanced the activity of choline acetyltransferase and reduced the activity of glutamate decarboxylase. Gamma-vinyl GABA had no effect on cholinergic markers but, at 1300 micrograms/ml, increased GABA levels to 135% of control despite the reduction of glutamate decarboxylase to 68% of control. In the NG108-15 cell clone, anticonvulsants have varying effects on cell growth, differentiation, and neurotransmitter systems. Our findings do not support the proposal that the mechanism of action for valproic acid, phenobarbital, phenytoin, and carbamazepine is via alteration of GABA levels.

Effects of chronic phenobarbital exposure on cultured mouse spinal cord neurons

The anticonvulsant phenobarbital (PB), at concentrations of 20, 40, and 90 micrograms/ml, was chronically applied to cell cultures of mouse spinal cord from day 2 or day 14 after initial plating, and the effects of this exposure on neuronal density and morphological characteristics were determined. Neuronal morphological characteristics were analyzed quantitatively following intracellular injection of the fluorescent dye Lucifer yellow. Cultures exposed to PB for 6 weeks, from day 14 after plating, showed concentration-dependent reductions in neuronal density; both large and small neurons were equally affected. PB exposure also reduced dendritic branching frequency, and the length of dendrites, of remaining large neurons. A higher percentage of these neurons had a bipolar branching pattern than was normally the case. Neurons in cultures exposed to PB from day 2 after plating, compared with those exposed from day 14, showed significantly less alteration in terms of density and morphological characteristics. Effects on neuronal morphological characteristics increased with duration of drug exposure. Equimolar concentrations of barbituric acid produced effects similar to those produced by PB. Chronic exposure to PB adversely affects survival and morphological characteristics of mammalian central neurons grown in cell culture. Curiously, exposure from the time of initial plating appears to be less deleterious than exposure initiated 2 weeks later. To the extent that neuronal development in vitro can be compared to the situation in vivo, these results, and those of other investigators, raise concerns about long-term exposure of the developing human nervous system to PB.

Neonatal seizures: a commentary on selected aspects

Despite the immaturity of the newborn brain, the neonatal period is reported to have a very high frequency of seizures. This review concludes that many of the neonatal events that are called seizures probably originate from subcortical structures, have little in common with cortical seizures seen in older individuals, and may not benefit from conventional anticonvulsant treatment. Many studies of anticonvulsants in the newborn have important methodologic problems, compounded by the fact that the seizures tend to spontaneously remit with the resolution of the acute hypoxic-ischemic encephalopathy that is most often the cause. Randomized trials of anticonvulsants in this setting have not been carried out. Even in many of these seizures do not originate in the cortex, they still imply profound cortical disturbance and are associated with high mortality and morbidity. It is unknown if the type and duration of treatment influence the long-term, overall outcome. The seizures usually stop in the newborn period, and anticonvulsants beyond hospital discharge seem unwarranted because they are unlikely to prevent subsequent epilepsy. Newer investigations, including video-EEG and nuclear magnetic resonance studies, may clarify the real significance of neonatal seizures.

Effects of anticonvulsants on cell growth and enzymatic and receptor binding activity in a neuroblastoma x glioma hybrid cell culture

The effects of anticonvulsants on markers of growth, intracellular enzymes, and synaptic functions were evaluated using a rapidly dividing cholinergic neuroblastoma x glioma hybrid cell-line (NG108-15). Cell cultures were exposed for 4 days to phenobarbital, phenytoin, carbamazepine, or valproic acid. Anticonvulsant concentrations added to the media were selected to produce free levels in the cell media that were equivalent to free levels in humans ranging from therapeutic to very toxic. Free levels of anticonvulsants in the toxic range affected cell number, protein content, and neurochemical markers. However, only valproic acid and phenytoin reduced cell growth at therapeutic free drug concentrations. Valproic acid was the only medication to act as a differentiating agent, significantly increasing the activity of choline acetyltransferase, beta-galactosidase, and muscarinic cholinergic receptor binding. These results emphasize the importance of performing drug studies at appropriate free drug concentrations and suggest that valproic acid differs from other commonly prescribed anticonvulsants by having both a growth-suppressing and a differentiating effect.

Astrocytes convert the parkinsonism inducing neurotoxin, MPTP, to its active metabolite, MPP+

The ability of astrocytes to convert 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP) to its toxic metabolite 1-methyl-4-phenylpyridinium ion (MPP+) was directly tested. Cultured astrocytes rapidly converted MPTP (25 micrograms/ml) to MPP+; after 6 h MPP+ concentrations reached 1.5 micrograms/ml, within the toxic range for neurons. MPTP (above 10 micrograms/ml) reduced glial density after 5 days of exposure. This toxic effect was blocked by pargyline, a monoamine oxidase inhibitor; pargyline also reduced the conversion of MPTP to MPP+ by 85%. When neurons were added to astrocyte cultures, MPTP conversion to MPP+ was not enhanced. Astrocytes appear critical in converting MPTP to MPP+, and are damaged by chronic exposure to MPTP.

Epileptogenesis and the immature brain

Epidemiological studies indicate that the incidence of seizures is highest early in life. This report discusses the experimental data derived from studies of focal epileptogenesis of the immature brain in tandem with ongoing maturational changes. During development, neurons have characteristic neurophysiological properties. Local interictal discharges are long in duration, lack a stereotypic morphology, and have limited fields. Yet the immature brain is very susceptible to the development of bilateral, although asynchronous, seizures and status epilepticus induced by amygdala kindling or by convulsant drugs. This increased seizure susceptibility may be due to a functional immaturity of a substantia nigra, GABA-sensitive output system. The morbidity of convulsions occurring early in life may not be as grave as previously thought in terms of subsequent acquisition of "normal" developmental milestones. The propensity to develop recurrent convulsions in adulthood is not related to the severity of a single seizure in infancy. Although multiple severe seizures may predispose animals to the development of seizures later in life, this is not a unique feature of the immature brain, since it also occurs in the adult brain. Finally, there is evidence that the immature brain may respond to anticonvulsant drugs differently from its mature counterpart; these findings emphasize the need to develop new antiepileptic therapies that take into account the maturational state of the brain.

Effects of prenatal phenobarbital on benzodiazepine receptor development

Phenobarbital (PB) was administered to pregnant mice during days 9-21 of gestation. Forebrain and cerebellar [3H]flunitrazepam ([3H]FLU) binding was assayed in the offspring at birth and at 21 days of age. Prenatal treatment produced a decrease in the number (Bmax) of [3H]FLU receptors in both the forebrain and cerebellum at birth. A small decrease in the [3H]FLU dissociation constant (KD) values in the forebrain was also detected at birth, but no changes were seen in the [3H]FLU KD values in the cerebellum. No changes were observed in forebrain and cerebellar [3H]FLU Bmax or KD values at 21 days of age, indicating that the effects of prenatal exposure to PB on [3H]FLU binding are eliminated during the postnatal development of the forebrain and cerebellum. The receptor affinity for the triazolopyridazine CL 218,872, which distinguishes the type I and type II benzodiazepine (BDZ) receptors, was not altered by prenatal PB treatment. The coupling of the BDZ receptor to the gamma-aminobutyric acid and pentobarbital binding sites was unaffected by exposure to PB in utero.

Long-term exposure of cortical cell cultures to clonazepam reduces benzodiazepine receptor binding

To determine if reduced drug efficacy after long-term exposure to clonazepam may be a consequence of benzodiazepine receptor alterations, cerebral cortical cell cultures were exposed to the drug (200 nM) for 14 days. Receptor binding was assayed on living cells in situ. After drug exposure, binding in experimental cultures differed markedly from controls with respect to total, specific, and clonazepam-displaceable (neuronal) benzodiazepine binding (60%, 53%, and 6% of control values, respectively) but recovered within 96 h of drug removal. RO5-4864-displaceable (nonneuronal) binding was modestly reduced at 0 time (72% of control), but returned to control values in 24 h. The differences in binding could be attributable to a relatively reduced affinity of the high-affinity binding site (Kd approximately 18 nM for controls and approximately 30 nM for drug-exposed cultures) but not to changes in the low-affinity binding site or to reduced numbers of receptors.

A case for long-term treatment with anticonvulsants

Seizures occurring in the neonatal period are one of the most significant discriminating factors in predicting childhood neurologic mortality and morbidity (epilepsy, cerebral palsy and mental retardation). Data derived from retrospective and prospective studies indicate that different variables, such as cause and severity of seizure activity, birth weight, neurologic examination and electroencephalogram, help predict which of these children will be severely affected. Most physicians treat such children with an anticonvulsant (phenobarbital) for the first year of life on the supposition that this therapy will minimize mortality and long-term morbidity. There are no controlled studies to indicate whether anticonvulsant therapy affects the outcome in children with neonatal seizures. It may now be possible to select those who are at significantly higher risk for neurologic morbidity, and these infants may benefit from anticonvulsant prophylaxis with phenobarbital.

Anticonvulsant therapy after neonatal seizures--how long should it be continued? I. A case for early discontinuation of anticonvulsants

The risk of epilepsy or afebrile seizures after convulsions in the neonatal period is compared with the benefits and risks of chronic use of anticonvulsants in infants. The best predictor of later seizures appears to be the presence of moderate to severe neurologic damage. In the absence of such deficits, the risk is below 10%, but increases to 50-70% when damage is severe. A comparison of reports indicates no difference in seizure recurrence rates when anticonvulsants are stopped early in the neonatal period or when treatment is longer, even in the high-risk group. After phenobarbital is discontinued and the plasma concentration falls below the therapeutic range, seizures usually recur within a few days or not for several months. Only 50% of these seizure types are expected to be controlled with phenobarbital. Long-term phenobarbital use is associated with impaired cognitive function in infants and toddlers, and retarded brain growth in rodent studies.

Differential toxicity of chronic exposure to phenytoin, phenobarbital, or carbamazepine in cerebral cortical cell cultures

The effects of phenytoin (30 micrograms/ml), phenobarbital (64 micrograms/ml), and carbamazepine (24 micrograms/ml) were assessed in cerebral cortical cell cultures. After antiepileptic drug exposure for eleven days, cultures were assayed for total protein, number of neurons, tetanus toxin fixation, high-affinity uptake of gamma-aminobutyric acid and beta-alanine, activity of choline acetyltransferase, and benzodiazepine binding. Carbamazepine-exposed cultures demonstrated minimal effects, whereas highly significant deficits related to generalized toxicity were observed in cultures exposed to phenytoin or phenobarbital.

Reduced benzodiazepine receptor binding in cerebral cortical cultures chronically exposed to diazepam

Fetal mouse cerebral cortex in culture was exposed chronically to diazepam, and benzodiazepine (BDZ) receptor activity was assayed on the intact cell. Results have indicated: (1) minimal evidence of generalized drug toxicity, determined by choline acetyltransferase activity, tetanus labeling, high-affinity uptakes of gamma-aminobutyric acid and beta-alanine, protein, and light microscopy; (2) a significant dose-dependent reduction (down-regulation) of BDZ receptor activity that occurs after chronic exposure to clinically relevant concentrations of the drug; (3) a disproportionate suppression of the neuronal portion of the receptor after both acute and chronic exposure; and (4) recovery patterns of the BDZ receptor that differ substantially after acute versus chronic treatment. The latter finding may partially explain the observed clinical manifestations of drug tolerance and reduced anticonvulsant efficacy after prolonged use of this class of drugs.

Long-lasting effects of early barbiturates on central nervous system and behavior

Forty years of prescribing barbiturates to pregnant women and infants, and thirty years of animal research have shown that barbiturates affect the developing central nervous system (CNS) and behavior. This paper compiles and reviews animal and selected human literature in this research area. Early barbiturate exposure in animals reduces brain weight with related changes in brain biochemistry and neuromorphology. Significant changes may be found in surviving adult offspring. Evidence of CNS and behavioral damage in human beings due to early barbiturate exposure is not clearcut, however, confounded by the conditions for which the drugs are prescribed. In animals, early drug exposure significantly reduces levels of hormones, vitamins, and other biologically active macromolecules via (long-lasting) induction of hepatic metabolizing enzymes. Whether or not in humans treated with barbiturates, hormone levels remain within the normal range (by-feed-back regulation) and, also, if vitamin deficiencies can be simply corrected by supplements is still being debated. Early barbiturates administered to animals is associated with long-lasting disturbances in activity, learning performance, sexual behavior, and reproductive function, but not in a simple dose-exposure related manner. Animal studies show that long-lasting functional tolerance to drugs develops following early barbiturate exposure. Although infants become "passively addicted" following in utero exposure, there is as yet no data on subsequent development of human adult tolerance. Drug related damage must, in any case, be weighed against therapeutic benefits of drug administration and the results of failure to treat.

Toxic effect of phenytoin on developing cortical neurons in culture

Studies were undertaken to determine the effect of chronic phenytoin exposure on developing neurons. Cerebral cortex from 16-day fetal mice was utilized to prepare primary dissociated cell cultures. Phenytoin was added to the cultures 10 days after plating and the cultures were harvested on day 17. Cortical cultures were assayed for neuronal cell number by phase microscopy and for high-affinity uptake of 3H-labeled gamma-aminobutyric acid (GABA) by both radioautography and scintillation spectrometry. Neuronal cell counts demonstrated a highly significant decrement in the number of neurons in cultures exposed to phenytoin at 15, 25, and 50 micrograms/ml. 3H-GABA-labeled neurons constituted 13% of the neurons present in both control and phenytoin-exposed cultures. These data indicate that phenytoin is toxic to cortical neurons in culture and that GABAergic neurons are affected to the same extent as the total neuronal population.

Electrophysiological techniques in dissociated tissue culture

The application of electrophysiological techniques to tissue culture is still evolving. We have attempted in this chapter to give a practical summary of intracellular recording techniques used in our laboratory, as well as give some examples of new experimental strategies and electrophysiological methods that should provide further information on a number of interesting neurobiological questions. The combination of an increasing knowledge of the cell biology of cultured neurons and advances in electrophysiology should continue to be a fruitful interaction.

Behavioural effects of phenobarbitone. 1. Effects in the offspring of laboratory mice

Phenobarbitone at a concentration of 187.5 mg/l in drinking fluid of breeding mice and their offspring after weaning did not affect gestation period, litter size, litter weight or pup development before weaning, although a slight retardation of weight gain after weaning occurred. This level of phenobarbitone given to mice after weaning did not affect weight gain. The average daily intake of phenobarbitone ranged from 30 to 52 mg/kg body weight depending on age and sex. Behaviour of offspring and mice treated after weaning was examined by ethological analysis of encounters between unfamiliar mice of the same sex and treatment group in a neutral enclosure. After lifelong exposure to phenobarbitone mice at 5 and 15 weeks of age showed an increased amount of scanning and exploration of the unfamiliar cage coupled with a decrease of time spent in immobility. Difference from control levels was more pronounced at 15 than at 5 weeks of age, in part because controls showed more immobility and explored less as they matured. No behavioural changes were detected in mice treated with this level of phenobarbitone after weaning. Lifelong exposure to phenobarbitone did not affect agonistic behaviour in pair-housed males at 30 weeks of age, and under these circumstances no longer stimulated exploration to a significant extent.

A method for large-scale production of mouse brain cortical cultures

Fetal cerebral cortex can be grown for several weeks in dissociated cell culture using a relatively simple protocol for culture preparation. It is possible to establish large numbers of very similar cultures which serve as an effective test system for studies of toxicity and mechanism of action of neuroactive compounds. Light microscopic and ultrastructural studies document the neuronal component of the cultures as well as the developmental sequence. Cell counts, protein concentration and choline acetyltransferase activity demonstrate the reproducibility of the cultures from dish to dish.