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

Anti-seizure medication-induced developmental cell death in neonatal rats is unaltered by history of hypoxia

BACKGROUND

Many anti-seizure medications (ASMs) trigger neuronal cell death when administered during a confined period of early life in rodents. Prototypical ASMs used to treat early-life seizures such as phenobarbital induce this effect, whereas levetiracetam does not. However, most prior studies have examined the effect of ASMs in naïve animals, and the degree to which underlying brain injury interacts with these drugs to modify cell death is poorly studied. Moreover, the degree to which drug-induced neuronal cell death differs as a function of sex is unknown.

METHODS

We treated postnatal day 7 Sprague Dawley rat pups with vehicle, phenobarbital (75 mg/kg) or levetiracetam (200 mg/kg). Separate groups of pups were pre-exposed to either normoxia or graded global hypoxia. Separate groups of males and females were used. Twenty-four hours after drug treatment, brains were collected and processed for markers of cell death.

RESULTS

Consistent with prior studies, phenobarbital, but not levetiracetam, increased cell death in cortical regions, basal ganglia, hippocampus, septum, and lateral thalamus. Hypoxia did not modify basal levels of cell death. Females - collapsed across treatment and hypoxia status, displayed a small but significant increase in cell death as compared to males in the cingulate cortex, somatosensory cortex, and the CA1 and CA3 hippocampus; these effects were not modulated by hypoxia or drug treatment.

CONCLUSION

We found that a history of graded global hypoxia does not alter the neurotoxic profile of phenobarbital. Levetiracetam, which does not induce cell death in normal developing animals, maintained a benign profile on the background of neonatal hypoxia. We found a sex-based difference, as female animals showed elevated levels of cell death across all treatment conditions. Together, these data address several long-standing gaps in our understanding of the neurotoxic profile of antiseizure medications during early postnatal development.

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.

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.

Therapeutic strategies to avoid long-term adverse outcomes of neonatal antiepileptic drug exposure

Antiepileptic drugs (AEDs) such as phenobarbital, phenytoin, and valproic acid, when given in therapeutic doses to neonatal rats, cause pronounced neuronal apoptotic cell death. This effect is especially pronounced in the striatum and cortex during the second postnatal week, a period corresponding to the "brain growth spurt" (third trimester of gestation and early infancy) in humans. Of particular concern is the fact that phenobarbital is the most frequently used therapy for neonatal epilepsy. If AED-induced neuronal cell death leads to long-term functional impairment, then it becomes crucial to find therapies that avoid this neurotoxicity in the sensitive period. Herein we examine short- and long-term functional effects following exposure of neonatal rat pups to phenobarbital; the functions tested include striatal gamma-aminobutyric acid (GABA)ergic synaptic responses and reflex development in pups, and fear conditioning, emotionality, and sensory-motor gating in adults. In all cases, phenobarbital exposure during the second postnatal week was sufficient to cause significant impairment. In contrast, adult animals exposed as pups to lamotrigine (given in a dose that does not cause apoptotic neuronal death) were not impaired on the tasks we examined. Our data suggest that treatments devoid of proapoptotic actions may be promising therapies for avoiding adverse outcomes after neonatal exposure. In addition, our findings identify early exposure to certain AEDs as an important potential risk factor contributing to psychiatric and neurologic abnormalities later in life.

Prenatal effects of antiepileptic drugs

Antiepileptic drugs (AEDs) target ion channels and neurotransmitter systems in the brain; these same targets are responsible for regulation of processes essential for brain development. In this review, experimental findings on adverse effects of AEDs in the developing mammalian brain will be presented, including interference with physiological apoptotic cell death, cell proliferation and migration, neurogenesis, axonal arborization, synaptogenesis, and synaptic plasticity.

Effects of the endocannabinoid noladin ether on body weight, food consumption, locomotor activity, and cognitive index in mice

We have investigated the effect of 2-arachidonylglyceryl-ether (Noladin) on food consumption, weight, activity, and cognitive function in mice during diet restriction for 17 days and subsequent ad libitum feeding for 32 days. Female Sabra mice were given food for 2.5 h/day (equal to 60% diet restriction), received Noladin (0.001, 0.01, 0.1 mg/(kg day) intraperitonially (i.p.)) with or without the CB1 antagonist SR141716A (1 mg/kg i.p.) during days 3-17. Noladin (0.001 mg/kg) significantly increased food consumption without a change in body weight, probably due to increased activity and there was no change in cognitive function. A higher dose (0.1 mg/kg) did not affect food consumption, but increased activity and slightly decreased weight 32 days after termination of Noladin administration; however, cognitive deterioration was observed. At all doses tested, Noladin did not affect weight during the diet-restriction period, whereas the CB1 antagonist (with or without Noladin) caused a very significant decline in weight in this phase. Weight catch-up was observed 1 month after administration of Noladin was discontinued. Weight at day 32 after the termination of Noladin (0.1 mg/(kg day)) treatment was 5% less than control. Female C57BL/6 mice (same protocol, with 0.001 mg/(kg day) Noladin) gave similar results to 0.1 mg/kg in Sabra mice as regards weight. CB1 antagonist treatment caused very significant decline in both weight and food consumption; cognition and activity were unchanged. These results indicate that Noladin has a significant dose-dependent effect on food consumption, cognition and weight maintenance after weight loss. Low doses of Noladin may possibly allow an increase in food intake without a gain in weight after dieting. Thus, Noladin could be of potential clinical benefit in treating disorders of body weight. Noladin seems to signal food consumption and weight through CB1 receptors based on effects observed with the CB1 antagonist, while the cognition and activity are probably mediated by non-cannabinoid receptors.

Structural Effects and Neurofunctional Sequelae of Developmental Exposure to Psychotherapeutic Drugs: Experimental and Clinical Aspects

The advent of psychotherapeutic drugs has enabled management of mental illness and other neurological problems such as epilepsy in the general population, without requiring hospitalization. The success of these drugs in controlling symptoms has led to their widespread use in the vulnerable population of pregnant women as well, where the potential embryotoxicity of the drugs has to be weighed against the potential problems of the maternal neurological state. This review focuses on the developmental toxicity and neurotoxicity of five broad categories of widely available psychotherapeutic drugs: the neuroleptics, the antiepileptics, the antidepressants, the anxiolytics and mood stabilizers, and a newly emerging class of nonprescription drugs, the herbal remedies. A brief review of nervous system development during gestation and following parturition in mammals is provided, with a description of the development of neurochemical pathways that may be involved in the action of the psychotherapeutic agents. A thorough discussion of animal research and human clinical studies is used to determine the risk associated with the use of each drug category. The potential risks to the fetus, as demonstrated in well described neurotoxicity studies in animals, are contrasted with the often negative findings in the still limited human studies. The potential risk fo the human fetus in the continued use of these chemicals without more adequate research is also addressed. The direction of future research using psychotherapeutic drugs should more closely parallel the methodology developed in the animal laboratories, especially since these models have already been used extremely successfully in specific instances in the investigation of neurotoxic agents.

Developmental neuropathology of environmental agents

The developing central nervous system (CNS) is more vulnerable to injury than the adult one. Although a great deal of research has been devoted to subtle effects of developmental exposure, such as neurobehavioral changes, this review instead focuses on a number of chemicals that have been shown, in several experimental models as well as humans, to cause morphological changes in the developing nervous system. Chemicals that are discussed include methylmercury (MeHg), lead (Pb), antiepileptic drugs, and ethanol. Additionally, the issue of silent neurotoxicity, i.e., persistent morphological and/or biochemical injury that remains clinically unapparent until later in life, is discussed.

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.

Primidone-induced embryolethality and DRL deficits in surviving offspring

Pregnant Sprague-Dawley rats were administered primidone (PRM) by oral gavage on gestation days 8-20 in doses of 0 or 120 mg/kg. This dose did not produce body weight differences in the dams during the dosing period nor were there differences in the birth weights of the offspring. PRM was embryolethal with only 43% of drug-treated dams maintaining their pregnancies, whereas 100% of the pregnant controls produced offspring. An analysis of resorption sites in PRM-treated dams that did not deliver showed a nearly identical number of implantation sites (12.6) compared to the litter size of controls (12.8) that delivered pups. There were no overall differences in exploratory activity levels between PRM-treated and control animals. However, in the PRM-treated females there was an absence of the sexually dimorphic increase in activity seen in control females when compared to control males. The PRM-treated males showed an impairment in the acquisition of a DRL-20 (differential reinforcement of low rates) operant schedule over a 9-week acquisition period. There were no differences in the total response rates between the groups, suggesting that this is a specific learning deficit and not a performance deficit. The results of these experiments provide evidence that prenatal PRM exposure can be embryolethal and also impair behavior in the surviving rat offspring.

Developmental and behavioral effects of prenatal primidone exposure in the rat

Pregnant Sprague-Dawley rats were administered primidone (PRM) by oral gavage on gestation days 8-17 in doses of 0.40, and 80 mg/kg. Although these doses of PRM did not produce significant differences in litter size, birth weight, mortality, date of attainment of developmental landmarks or measures of preweaning reflex and motor development, there were a number of significant differences that developed as the animals approached and entered adulthood. When tested as adults, the 80 mg/kg male rats showed a deficit in the performance of an eight-arm radial maze task. These same animals showed a significant reduction in open field activity when tested as adults. In addition, both male and female PRM-treated animals showed reduced body weights at different periods corresponding to onset of sexual maturation during development. These findings are consistent with the larger body of literature reporting on the neurobehavioral teratology of phenobarbital, including its ability to produce lesions in the hippocampus and endocrine dysfunction resulting in reproductive deficits. These results suggest that PRM produces its adverse effects as a result of its metabolism to phenobarbital, which in turn affects the limbic system.

Neural grafting as a tool for the study and reversal of neurobehavioral birth defects

The transplantation of fetal neurons has gained notoriety in recent years for its perceived potential to reverse neurological deficits caused by loss of one or another neuronal population. The present paper describes a neural grafting approach employed by our laboratory to gain more insight into the drug-induced neurobehavioral teratogenicity. Mice were exposed prenatally to phenobarbital by feeding the barbiturate to the pregnant dam on gestation days 9-18. Heroin exposure was accomplished by injecting dams during the same gestational period. At maturity, the drug-exposed offspring displayed profound deficits in specific behavioral tasks, suggesting alterations in the septohippocampal cholinergic pathway. Biochemically, we observed increased presynaptic activity in the pathway, which was not accompanied by a corresponding reduction in postsynaptic activity. Rather, there was a general hyperactivation along the different postsynaptic phases. In contrast, we noted a desensitization of protein kinase C activity in response to the exposure of a cholinergic agonist to the drug-exposed offspring. Subsequent transplantation of embryonic cholinergic cells from normal mice to the impaired hippocampus reversed the behavioral deficits, whereas sham-operated controls exhibited no improvement. Concomitantly, all the biochemical alterations studied, both presynaptic and postsynaptic, were either partially or completely reversed following grafting.

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.

Reversal of early phenobarbital-induced cholinergic and related behavioral deficits by neuronal grafting

The present experiment was performed to assess the possible restoration of normal maze behavior, as well as parallel muscarinic receptor binding capabilities, in mice pre- or neonatally exposed to phenobarbital. Mice were exposed to phenobarbital prenatally by feeding the mother phenobarbital (3 gkg milled food) on gestation days 9-18 (PreB mice), or neonatally, by daily injections of 50 mg/kg Na phenobarbital to the pups on days 2-21 (NeoB). At adulthood, PreB and NeoB mice were 61.3% and 65% deficient, respectively, in the hippocampus-related Morris maze behavior, as compared to control. Both groups had a 58% increase in their hippocampal muscarinic receptors maximal binding (Bmax) (p < 0.001); the dissociation constant (Kd) was not affected by the phenobarbital exposure. Treated animals and their respective controls received septal cholinergic embryonic graft into the hippocampus. The viability of the transplants was confirmed by AChE histochemistry. Nine weeks later the grafted mice showed significant improvement in the Morris maze (52% for both PreB and NeoB (p < 0.001)). Their Bmax was also reduced from early phenobarbital exposed animals' levels by 15% for PreB and by 25% for NeoB (p < 0.001). The results suggest that early phenobarbital-induced behavioral deficit and their related biochemical alterations can be partially corrected by the appropriate neural grafting, and thus provide further support to the apparent relationship between the early phenobarbital-induced septohippocampal cholinergic alterations and the hippocampus-related behavioral deficits.

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.

Eight-arm maze performance, neophobia, and hippocampal cholinergic alterations after prenatal oxazepam in mice

Outbred CD-1 mice were exposed to oxazepam (15 mg/kg PO twice/day) on days 12-16 of fetal life, i.e., at a critical ontogenetic stage of Type II benzodiazepine (BDZ) receptor increase, and fostered at birth to untreated dams. At adulthood, radial arm maze performance, activity-habituation test in an open-field arena (either single 15-min test or three 5-min sessions at 24-h intervals), approach to a novel stimulus object, and amphetamine or scopolamine effects thereon were assessed in male progeny. Overall, the oxazepam exposed (OX) mice were much less efficient in the radial arm maze task than the vehicle exposed (VEH) animals. Pre-test scopolamine injection, but not amphetamine, significantly impaired the arm maze performance of OX mice when compared with the corresponding VEH-scopolamine animals. In separate nonlearned behavioral tasks, prenatal oxazepam did not affect either baseline activity levels in the open field or the response to the amphetamine and the scopolamine challenge, while it considerably increased the latency of first approach to a novel object and produced a deficit of habituation in the course of the subsequent exploratory period. Concomitant investigation at the neurochemical level showed that the adult OX animals had a significant increase in both Bmax and in the affinity (Kd) of cholinergic muscarinic receptors in the hippocampal formation when compared to the vehicle-exposed controls.

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.

Effect of prenatal and neonatal chronic exposure to phenobarbital on central and peripheral benzodiazepine receptors

Phenobarbital (PhB) was administered to pregnant mice during days 9-18 of gestation. [3H]Muscimol binding to cerebellum, [3H]flunitrazepam binding to cerebellum and olfactory bulb, and [3H]PK 11195 binding to olfactory bulb, heart and kidney were assay in the of offspring at 22 and 50 days of age. The chronic prenatal administration of PhB did not affect either gamma-aminobutyric acid (GABA) receptors, central benzodiazepine receptors (CBR), or peripheral benzodiazepine binding sites (PBS) in these tissues. In the next stage of the study, we investigated a possible modulatory effect of chronic postnatal PhB treatment during days 2-21 of age on the same receptors measured at 22 and 50 days of age. PhB exposure of neonates resulted in a significant down-regulation of GABA receptors and CBR in the cerebellum and of PBS in the heart. The effects were demonstrated on day 22 of age and were undetectable by day 50 of age. CBR at the olfactory bulb and PBS at the olfactory bulb and kidney were not altered by the drug treatment. It is concluded that in utero exposure to PhB does not affect benzodiazepine receptor ontogenesis, and the effects of postnatal treatment are transitory only.

Neuromorphological changes in mouse olfactory bulb after neonatal exposure to phenobarbital

Heterogeneous Sabra mice pups were injected daily with 50 mg/kg phenobarbital (B50) or 40 mg/kg (B40) from postnatal day 2 (P2) to P21. Control litter mates (C) received vehicle injections. All animals were killed on P50 and their brains removed for histological analysis. The volumetric growth of the main olfactory bulb (MOB) was assessed in hematoxylin and eosin-stained serial sections cut in the sagittal plane. The volume of MOB was reduced 20 to 25% in barbiturate-treated mice. The greatest reductions in volume were seen in the external layers of the bulb (20 to 28%). There were moderate reductions in the internal granular layer (IGL, 6 to 20%) and no reductions in the subependymal layer that contains the migrating and immature cells. The number of prenatally-formed mitral cell neurons was unaffected by the treatment while the number of the pre- and postnatally generated granule cells was significantly reduced in the B40 group. There were no treatment effects on the sizes or packing densities of the mitral or granule cells. Like the hippocampus and the cerebellum, the developing MOB is vulnerable to barbiturate-exposure.

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.

Neuron transplantation reverses phenobarbital-induced behavioral birth defects in mice

Mice were exposed to phenobarbital prenatally on gestation days 9-18 (B mice), and were tested at adulthood for behavioral changes. B mice showed deficits in the eight-arm maze, a behavior related to the septohippocampal pathways. Consequently, transplantation of septal (mostly cholinergic) and locus coeruleus (mostly noradrenergic) neurons was applied to reverse the behavioral deficits. Most (75%) of the controls but none of the B mice reached a specific criterion in the eight-arm maze. However, transplantation of fetal septal tissue into the hippocampus of B mice enabled 55% of them to reach criterion. Transplantation of locus coeruleus tissue did not improve the performance of B mice. The viability of the transplants was confirmed in cytochemical studies. The results suggest that transplantation of neurons can be applied to reverse phenobarbital-induced behavioral birth defects.

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.