Long-term reduction in spontaneous alternations after early exposure to phenobarbital

Early life phenobarbital exposure dysregulates the hippocampal transcriptome

Introduction: Phenobarbital (PB) and levetiracetam (LEV) are the first-line therapies for neonates with diagnosed seizures, however, a growing body of evidence shows that these drugs given during critical developmental windows trigger lasting molecular changes in the brain. While the targets and mechanism of action of these drugs are well understood-what is not known is how these drugs alter the transcriptomic landscape, and therefore molecular profile/gene expression during these critical windows of neurodevelopment. PB is associated with a range of neurotoxic effects in developing animals, from cell death to altered synaptic development to lasting behavioral impairment. LEV does not produce these effects. Methods: Here we evaluated the effects of PB and Lev on the hippocampal transcriptome by RNA sequencing. Neonatal rat pups were given a single dose of PB, Lev or vehicle and sacrificed 72 h later-at time at which drug is expected to be cleared. Results: We found PB induces broad changes in the transcriptomic profile (124 differentially expressed transcripts), as compared to relatively small changes in LEV-treated animals (15 transcripts). PB exposure decreased GABAergic and oligodendrocyte markers pvalb and opalin, and increased the marker of activated microglia, cd68 and the astrocyte- associated gene vegfa. These data are consistent with the existing literature showing developmental neurotoxicity associated with PB, but not LEV. Discussion: The widespread change in gene expression after PB, which affected transcripts reflective of multiple cell types, may provide a link between acute drug administration and lasting drug toxicity.

Adeno-Associated Virus-Mediated Gene Therapy in the Mashlool, Atp1a3Mashl/+, Mouse Model of Alternating Hemiplegia of Childhood

Alternating Hemiplegia of Childhood (AHC) is a devastating autosomal dominant disorder caused by ATP1A3 mutations, resulting in severe hemiplegia and dystonia spells, ataxia, debilitating disabilities, and premature death. Here, we determine the effects of delivering an extra copy of the normal gene in a mouse model carrying the most common mutation causing AHC in humans, the D801N mutation. We used an adeno-associated virus serotype 9 (AAV9) vector expressing the human ATP1A3 gene under the control of a human Synapsin promoter. We first demonstrated that intracerebroventricular (ICV) injection of this vector in wild-type mice on postnatal day 10 (P10) results in increases in ouabain-sensitive ATPase activity and in expression of reporter genes in targeted brain regions. We then tested this vector in mutant mice. Simultaneous intracisterna magna and bilateral ICV injections of this vector at P10 resulted, at P40, in reduction of inducible hemiplegia spells, improvement in balance beam test performance, and prolonged survival of treated mutant mice up to P70. Our study demonstrates, as a proof of concept, that gene therapy can induce favorable effects in a disease caused by a mutation of the gene of a protein that is, at the same time, an ATPase enzyme, a pump, and a signal transduction factor.

Neonatal phenobarbital exposure disrupts GABAergic synaptic maturation in rat CA1 neurons

OBJECTIVE

Phenobarbital is the most commonly utilized drug for the treatment of neonatal seizures. The use of phenobarbital continues despite growing evidence that it exerts suboptimal seizure control and is associated with long-term alterations in brain structure, function, and behavior. Alterations following neonatal phenobarbital exposure include acute induction of neuronal apoptosis, disruption of synaptic development in the striatum, and a host of behavioral deficits. These behavioral deficits include those in learning and memory mediated by the hippocampus. However, the synaptic changes caused by acute exposure to phenobarbital that lead to lasting effects on brain function and behavior remain understudied.

METHODS

Postnatal day (P)7 rat pups were treated with phenobarbital (75 mg/kg) or saline. On P13-14 or P29-37, acute slices were prepared and whole-cell patch-clamp recordings were made from CA1 pyramidal neurons.

RESULTS

At P14 we found an increase in miniature inhibitory postsynaptic current (mIPSC) frequency in the phenobarbital-exposed as compared to the saline-exposed group. In addition to this change in mIPSC frequency, the phenobarbital group displayed larger bicuculline-sensitive tonic currents, decreased capacitance and membrane time constant, and a surprising persistence of giant depolarizing potentials. At P29+, the frequency of mIPSCs in the saline-exposed group had increased significantly from the frequency at P14, typical of normal synaptic development; at this age the phenobarbital-exposed group displayed a lower mIPSC frequency than did the control group. Spontaneous inhibitory postsynaptic current (sIPSC) frequency was unaffected at either P14 or P29+.

SIGNIFICANCE

These neurophysiological alterations following phenobarbital exposure provide a potential mechanism by which acute phenobarbital exposure can have a long-lasting impact on brain development and behavior.

Brief postnatal exposure to phenobarbital impairs passive avoidance learning and sensorimotor gating in rats

Phenobarbital is the most commonly utilized drug for the treatment of neonatal seizures. However, mounting preclinical evidence suggests that even brief exposure to phenobarbital in the neonatal period can induce neuronal apoptosis, alterations in synaptic development, and long-lasting changes in behavioral functions. In the present report, we treated neonatal rat pups with phenobarbital and evaluated behavior in adulthood. Pups were treated initially with a loading dose (80 mg/kg) on postnatal day (P)7 and with a lower dose (40 mg/kg) on P8 and P9. We examined sensorimotor gating (prepulse inhibition), passive avoidance, and conditioned place preference for cocaine when the animals reached adulthood. Consistent with our previous reports, we found that three days of neonatal exposure to phenobarbital significantly impaired prepulse inhibition compared with vehicle-exposed control animals. Using a step-though passive avoidance paradigm, we found that animals exposed to phenobarbital as neonates and tested as adults showed significant deficits in passive avoidance retention compared with matched controls, indicating impairment in associative memory and/or recall. Finally, we examined place preference conditioning in response to cocaine. Phenobarbital exposure did not alter the normal conditioned place preference associated with cocaine exposure. Our findings expand the profile of behavioral toxicity induced by phenobarbital.

Long term reduction in eight arm maze performance after early exposure to phenobarbital

Performance in the hippocampal eight arm maze was studied in mice after early exposure to phenobarbital (PhB). since previous studies suggested that these animals suffered neural deficits in the hippocampus. For prenatal exposure pregnant mothers were fed 3 g PhB/kg milled food on gestation days 9-18. Neonates were injected daily with 50 mg PhB/kg. on postnatal days 2-21. After a week of water deprivation, the animals were tested at age 50 days for 5 days preceded by 1 day of habituation. Deficits in eight arm maze performance were demonstrated in early treated mice on every testing day. For example, on day 5 of testing the number of correct entries during the first eight attempts in the prenatally treated group were 12% below control level (P<0.01), the respective reduction in the neonatal group was 10% (P< 0.001). The number of trials needed to enter all arms on day 5 was 27% above control level among prenatally treated mice (P< 0.001), and 13% in neonatally treated mice (P< 0.05). It took prenatal PhB animals twice the time to reach criterion than their controls (P< 0.001) and four times as long for neonatally treated mice (P< 0.001).

Neonatal exposure to phenobarbital potentiates schizophrenia-like behavioral outcomes in the rat

Previous work has indicated an association between seizures early in life and increased risk of psychiatric disorders, including schizophrenia. However, because early-life seizures are commonly treated with antiepileptic drugs (AEDs) such as phenobarbital, the possibility that drug treatment may affect later-life psychiatric outcomes needs to be evaluated. We therefore tested the hypothesis that phenobarbital exposure in the neonatal rat increases the risk of schizophrenia-like behavioral abnormalities in adulthood. Thus, in this study, we examined the effects of a single acute neonatal exposure to phenobarbital on adult behavioral outcomes in the rat neonatal ventral hippocampal (nVH) lesion model of schizophrenia. We compared these outcomes to those in rats a) without nVH lesions and b) with nVH lesions, without phenobarbital. The tasks used for behavioral evaluation were: amphetamine-induced locomotion, prepulse inhibition, elevated plus-maze, and novel object recognition task. We found that neonatal phenobarbital treatment (in the absence of nVH lesions) was sufficient to disrupt sensorimotor gating (as tested by prepulse inhibition) in adulthood to an extent equivalent to nVH lesions. Additionally, neonatal phenobarbital exposure enhanced the locomotor response to amphetamine in adult animals with and without nVH lesions. Our findings suggest that neonatal exposure to phenobarbital can predispose to schizophrenia-like behavioral abnormalities. Our findings underscore the importance of examining AED exposure early in life as a potential risk factor for later-life neuropsychiatric abnormalities in clinical populations.

Cell signaling as a target and underlying mechanism for neurobehavioral teratogenesis

A wide variety of drugs and chemicals elicit neurobehavioral teratogenesis. Surprisingly, however, despite the obvious differences among unrelated compounds, the behavioral outcomes often display striking similarities, such as cognitive and attentional deficits. Recent studies of drugs of abuse (heroin, nicotine, barbiturates) and environmental toxins (environmental tobacco smoke, pesticides, metals) suggest that, regardless of the originating mechanism for perturbation of brain development, disparate neuroteratogens converge downstream on common families of alterations, characterized by changes in the expression and/or activity of the cell-signaling molecules that are essential to neuronal differentiation and synaptic communication. Identification of these common targets may help in the design of pharmacologic interventions that, administered in adulthood, can reverse the impact of exposure to neurobehavioral teratogens.

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.

Alterations in hippocampal hemicholinium-3 binding and related behavioural and biochemical changes after prenatal phenobarbitone exposure

Previous studies demonstrated postsynaptic septohippocampal cholinergic alterations after early exposure to phenobarbital. The present study was designed to ascertain possible corresponding presynaptic alterations while confirming the known behavioral deficits and extending previous findings on postsynaptic cholinergic alterations. Pregnant heterogeneous mice received milled mouse food containing 3 g/kg phenobarbital on gestation days 9-18. At age 50 days, [3H]hemicholinium-3 binding, which labels the presynaptic transporter for high affinity choline uptake, was increased in treated mice by 100% (P < 0.001). This change was not accompanied by a change in the affinity of the transporter to the ligand. Another group of offspring was tested for hippocampus-related behaviors. Consistent with our previous studies in the Morris maze, treated animals took longer to reach the platform in the place test as compared to control, and swam fewer times over the missing platform location in the spatial probe test. In the eight-arm maze, the treated offspring needed more entries than control to visit all the arms. In the spontaneous alternation test, the treated mice showed fewer alternations than controls. Biochemically, as in our previous results, prenatal phenobarbital exposure resulted in an increase in the degree of stimulation of inositol phosphate formation by carbachol (P < 0.05), an action presumed to occur at postsynaptic muscarinic receptors. While the present results show that the effect of a combination of raised K+ in the presence of physostigmine and carbachol was significantly greater in barbiturate-treated mice (P < 0.05), the action of K+ in the presence of physostigmine, but without carbachol, was not affected by the phenobarbital treatment. The results point to the uniqueness of outcome of early insults where alterations along nerve conduction cascades do not necessarily follow the common rules in that upregulation could simultaneously occur both pre- and post synaptically.

Hippocampal gamma-aminobutyric acid and benzodiazepine receptors after early phenobarbital exposure

Mice were exposed to phenobarbital (PhB) prenatally (PreB offspring) by feeding their mothers 3 g/kg PhB in milled food on gestation days 9-18, or neonatally by directly injecting pups of intact mothers with daily dose of 50 mg PhB on postnatal days 2-21 (NeoB offspring). At age 22 or 50 days, the offspring were tested for gamma-aminobutyric acid (GABA) up take in the hippocampus and in the rest of the brain. In addition, [3H]muscimol and [3H]flunitrazepam binding in the hippocampus and cortex were measured in the offspring at age 22 and 50 days. Long-term decrease in GABA uptake was found in the NeoB group. A 23% decrease was found in 22-day-old mice (P < 0.001) and a 22% decrease in 50-day-old mice (P < 0.05). In addition, there was a 22% decrease in GABA uptake in the brain of 22-day-old PreB mice (P < 0.05). An increase of 52% in [3H]muscimol binding (P < 0.001) and 45% (P < 0.001) in [3H]flunitrazepam binding were measured in the hippocampus in the 22-day-old NeoB mice; no differences were found in affinity. The differences were short-term and could no longer be detected at age 50 days. No differences were found in the cortex; unlike NeoB, PreB mice did not differ from controls. The results suggest upregulation of the GABAergic system in early PhB exposed mice.

Hippocampal cholinergic alterations and related behavioral deficits after early exposure to phenobarbital

Mice were exposed to phenobarbital (PhB) prenatally and neonatally. Prenatal exposure was accomplished by feeding the mother PhB (3 g/kg milled food) on gestation days 9-18. Neonatal exposure was accomplished by daily injections of 50 mg/kg sodium PhB directly to the pups on days 2-21. Long-term biochemical alterations in the pre- and postsynaptic septohippocampal system, as well as related behavioral deficits, were assessed in the treated animals. Significant increase in B(max) values for binding of [3H]QNB to muscarinic cholinergic receptors was obtained on both ages 22 and 50 in prenatally (40-90%, respectively, p less than 0.001) and neonatally exposed (58-89%, p less than 0.001) mice whereas Kd remained normal. Similarly, a significant increase of inositol phosphate (IP) formation in response to carbachol was found after both prenatal and neonatal exposure to PhB (p less than 0.05). No alterations in choline acetyltransferase (ChAT) activity were observed in the prenatally or neonatally treated animals. The early exposed mice showed deficits in the performance in Morris water maze, a behavior related to the septohippocampal pathway. The results suggest that early exposure to PhB induces alterations in postsynaptic components of the hippocampal cholinergic system and concomitantly to impairment in hippocampus-related behavior.

Consequences of chronic phenobarbital treatment on local cerebral glucose utilization in the developing rat

The influence of a chronic phenobarbital (PhB) treatment on postnatal evolution of local cerebral metabolic rates for glucose (LCMRglc) was studied in 58 cerebral structures of freely moving rats. The animals received a daily subcutaneous injection of PhB at a dose of 50 mg/kg between days 2 and 35 or an equivalent volume of saline for controls and were studied at 5 postnatal stages, i.e. 10, 14, 17, 21 and 35 days, and at the adult stage. Body and brain weights were both reduced by 6-21% over the whole period studied. PhB exposure induced significant decreases in LCMRglc during the period of pharmacological treatment, i.e. until 35 days, except at the stage of 17 days as well as long-term reductions in LCMRglc of adult rats in 36 out of the 58 brain regions studied. These decreases affected all systems studied, sensory systems as well as limbic, hypothalamic, motor and white matter areas. In addition to a growth retardation, PhB also seemed to be able to induce a delay in the acquisition of auditory function which matures early during postnatal life. The long-term deficits in cerebral energy metabolism due to PhB in the adult rat also confirm the behavioral deficits which have been shown previously after early PhB exposure.

Influence of early neonatal phenobarbital exposure on cerebral energy metabolism and behavior

The influence of an early chronic phenobarbital (PhB) exposure on local cerebral glucose utilization (LCGU) and on behavior was studied in the rat. The animals were treated from Postnatal Day 2 to Postnatal Day 35 by a daily injection of 50 mg/kg PhB or by saline and tested between 10 and 35 days for short-term effects of the drug on LCGU and between 70 and 90 days for long-term effects of PhB on LCGU and behavior. PhB induced short- and long-lasting reductions in the overall rates of LCGU in hippocampal and cerebellar areas, but no significant changes in LCGU in the different cell layers of these two cerebral areas. PhB also changed the pattern of maturation of the rates of LCGU as compared to control subjects. The barbiturate treatment induced a decrease in the exploratory behavior of PhB- as compared to saline-treated rats in the open field, as well as a significant 25% decrease in the rate of spontaneous alternation with delay. In addition, PhB-treated rats needed significantly more time than control animals to perform their trials in the nonrewarded T maze testing. However, the neonatal barbiturate exposure did not induce changes in performances of adult rats in the rewarded eight arm maze. The results of the present study show that there is no apparent correlation between the rates of energy metabolism in the hippocampus and the impairment of learning abilities of adult rats in behavioral tests related to the hippocampus.

Studies into the mechanisms of strain differences in hippocampus-related behaviors

The heterogeneous mouse stocks HS/Ibg and SABRA/HUC and the inbred strains C57BL/6J, CBA/LAC, and BALB/Crgl were employed in an investigation of strain differences in delayed spontaneous alteration (SA) and eight-arm maze performance (EAM). Intact male mice were tested for SA at age 41 days for 2 consecutive days and for EAM at age 50-54 days, under conditions of water deprivation that commenced on day 43. In SA, BALB mice had a lower score than all other strains on day 1 but differed significantly only from SABRA; performance on day 2 was not consistent with that on day 1. In EAM, HS was first, CBA second, C57 third, SABRA fourth, and BALB fifth. HS was superior to the other strains, while BALB fell far below all other strains in both tests. Except for these two strains, the correlation between the two tests across the other strains was low. A study was undertaken to investigate the role of the hippocampus in the deficits in the performance of BALB mice in the two behaviors. Noradrenergic neurons were transplanted to hippocampus or cortex, and cholinergic neurons to their hippocampus. There were no significant differences in performance between the control and transplanted mice. The possibility was discussed that the behavioral differences are the outcome of variability in the neurotransmitters systems of the hippocampus but probably not the noradrenergic system.

Effects of early chronic phenobarbital treatment on the maturation of energy metabolism in the developing rat brain. II. Incorporation of beta-hydroxybutyrate into amino acids

The influence of phenobarbital (PhB) on the utilization of beta-hydroxybutyrate by the cerebral cortex and the cerebellum was studied in rats during postnatal maturation. The animals were treated from day 2 to day 35 after birth either by a daily injection of 50 mg/kg PhB or by saline. The rats were studied at 5 postnatal stages: 7, 10, 14, 21 and 35 days. Plasma beta-hydroxybutyrate and acetoacetate levels reached their peak values between 10 and 14 days after birth. The concentration of both ketone bodies was significantly higher in PhB- than in saline-treated rats between 10 and 35 days after birth. The total incorporation of [3-14C]beta-hydroxybutyrate into amino acids reached a peak value at 14 days after birth and was down to very low values at 35 days. It was higher in PhB- than in saline-treated rats. The specific radioactivity values of glutamate, glutamine, aspartate and GABA were significantly higher in PhB- than in saline-treated especially at 10 days after birth. These results demonstrate that a PhB treatment induces an increase in brain ketone body utilization in neonate rats, which is likely to balance the decrease in brain glucose utilization induced by this pharmacological treatment.

Normal zinc and iron concentrations in mice after early exposure to phenobarbital

Zinc and iron levels were studied in mice with early (pre/neonatal) exposure to phenobarbital, as the levels of these trace metals are known to be correlated with specific behaviors shown in our previous and present experiment to be affected by early phenobarbital administration. Mice were exposed to phenobarbital prenatally or neonatally. At adulthood they showed marked reduction from control in all parameters of eight-arm maze performance (P less than 0.001). Since zinc is known to be correlated with this behavior, it was subsequently studied in barbiturate exposed animals. The differences between barbiturate exposed and control offspring for zinc levels in plasma, brain and hippocampus did not reach statistical significance. Our previous studies have shown that the number of dopamine receptors and the resulting apomorphine-induced climbing behavior is altered after early exposure to phenobarbital. The effect of iron level on dopamine receptors is now well established. Subsequently, a group of mice were tested for iron levels in their brain and liver. No significant differences were found. It is suggested that deficits in the hippocampal behaviors, mainly eight-arm maze, after early exposure to phenobarbital are not related to changes in zinc levels. Similarly, early phenobarbital-induced alternation in dopamine receptors and the resulting dopaminergic behaviors are not related to changes in iron levels.

Studies on noradrenergic alterations in relation to early phenobarbital-induced behavioral changes

Mice were exposed to phenobarbital prenatally (B offspring) by feeding their mother 3 g/kg phenobarbital in milled food on gestation days 9-18; control dams received unadulterated milled food. At age 50 days, B offspring had fewer fluorescing noradrenergic (NE) cells in the locus coeruleus than control (P less than 0.001). Hippocampal NE levels were also lower in B than in control offspring, while the cerebellar NE levels of B offspring remained normal. Since B offspring are known to be deficient in their hippocampal eight-arm maze behavior, an attempt was made to reverse the behavioral deficit by transplantation of normal embryonic locus coeruleus NE cells into the impaired hippocampus of B offspring. While sham and NE-transplanted controls needed approximately 2 days to reach criterion in the maze, sham-transplanted B required approximately 5 days to reach criterion (P less than 0.01). The scores of NE-transplanted B mice were similar to B and differed significantly from control (P less than 0.01). Thus, it appears that the hippocampal behavioral deficits studied may not be related to alterations in locus coeruleus-hippocampal NE innervations.

Early phenobarbital-induced alterations in hippocampal acetylcholinesterase activity and behavior

Early exposure to phenobarbital (PhB) causes marked destruction of large neurons which are then forming both in the hippocampus and in the cerebellum. Such exposure to PhB also reduces the achievements of mice in hippocampus-related behaviors such as radial 8-arm maze performance. Experimental evidence suggests that these behaviors are partially mediated by cholinergic transmission. We studied the performance of mice, exposed to PhB prenatally or neonatally, in radial 8-arm maze. Both treatments caused significant impairments in the animals' performance in the maze. Acetylcholinesterase (AChE) and pseudocholinesterase (pChE) activities were studied in the hippocampus and cerebellum of mice who were exposed to PhB prenatally or neonatally. These enzymes are involved both in cholinergic transmission and in neuronal development. A significant decrease (13-16%, P less than 0.01) in hippocampal AChE specific activity was found between days 15 and 22 in animals exposed to PhB neonatally. The total hippocampal activity of AChE was also greatly reduced (25-39%, P less than 0.01) during that period as a result of both the reduction in specific activity and a reduction in hippocampal weight of the treated animals. These alterations were transient and were not detected in adulthood. No changes in hippocampal AChE or pChE activities were found in animals treated prenatally. Cerebellar AChE and pChE activities were not altered after prenatal nor after neonatal exposure to PhB. It is possible that the short-term effect of neonatal treatment on AChE specific activity might mediate the long-term impairments in hippocampus-related behaviors.