Rapid volume pulsations of the extracellular space accompany epileptiform activity in trauma-injured neocortex and depend on the sodium-bicarbonate cotransporter NBCe1

Post traumatic epilepsy (PTE) is a treatment-resistant consequence of traumatic brain injury (TBI). Recently, it has been revealed that epileptiform activity in acute chemoconvulsant seizure models is accompanied by transient shrinkages of extracellular space (ECS) called rapid volume pulsations (RVPs). Shrinkage of the ECS surrounding neurons and glia may contribute to ictogenic hyperexcitability and hypersynchrony during the chronic phase of TBI. Here, we identify the phenomenon of RVPs occurring spontaneously in rat neocortex at ≥ 3 weeks after injury in the controlled cortical impact (CCI) model for PTE. We further report that blocking the electrogenic action of the astrocytic cotransporter NBCe1 with 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) eliminates both RVPs and epileptiform activity in ex-vivo CCI neocortical brain slices. We conclude that NBCe1-mediated extracellular volume shrinkage may represent a new target for therapeutic intervention in PTE.

4-AP challenge reveals that early intervention with brivaracetam prevents posttraumatic epileptogenesis in rats

PURPOSE

There are currently no clinical treatments to prevent posttraumatic epilepsy (PTE). Recently, our group has shown that administration of levetiracetam (LEV) or brivaracetam (BRV) shortly after cortical neurotrauma prevents the development of epileptiform activity in rats, as measured ex vivo in neocortical slices. Due to the low incidence of spontaneous seizures in rodent-based models of traumatic brain injury (TBI), chemoconvulsants have been used to test injured animals for seizure susceptibility. We used a low dose of the voltage-gated potassium channel blocker 4-aminopyridine (4-AP) to evaluate posttraumatic epileptogenesis after controlled cortical impact (CCI) injury. We then used this assessment to further investigate the efficacy of BRV as an antiepileptogenic treatment.

METHODS

Sprague-Dawley rats aged P24-35 were subjected to severe CCI injury. Following trauma, one group received BRV-21 mg/kg (IP) at 0-2 min after injury and the other BRV-100 mg/kg (IP) at 30 min after injury. Four to eight weeks after injury, animals were given a single, low dose of 4-AP (3.0-3.5 mg/kg, IP) and then monitored up to 90 min for stage 4/5 seizures.

RESULTS

The chemoconvulsant challenge revealed that within four to eight weeks, CCI injury led to a two-fold increase in percentage of rats with 4-AP induced stage 4-5 seizures relative to sham-injured controls. Administration of a single dose of BRV within 30 min after trauma significantly reduced injury-induced seizure susceptibility, bringing the proportion of CCI-rats that exhibited evoked seizures down to control levels.

CONCLUSIONS

This study is the first to use a low dose of 4-AP as a chemoconvulsant challenge to test epileptogenicity within the first two months after CCI injury in rats. Our findings show that a single dose of BRV administered within 30 min after TBI prevents injury-induced increases in seizure susceptibility. This supports our hypothesis that early intervention with BRV may prevent PTE.

Efficient Delivery of FMR1 across the Blood Brain Barrier Using AAVphp Construct in Adult FMR1 KO Mice Suggests the Feasibility of Gene Therapy for Fragile X Syndrome

Background Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and autism. Gene therapy may offer an efficient method to ameliorate the symptoms of this disorder. Methods An AAVphp.eb-hSyn-mFMR1IOS7 vector and an empty control were injected into the tail vein of adult Fmr1 knockout (KO) mice and wildtype (WT) controls. The KO mice were injected with 2 × 1013 vg/kg of the construct. The control KO and WT mice were injected with an empty vector. Four weeks following treatment, the animals underwent a battery of tests: open field, marble burying, rotarod, and fear conditioning. The mouse brains were studied for levels of the Fmr1 product FMRP. Results: No significant levels of FMRP were found outside the CNS in the treated animals. The gene delivery was highly efficient, and it exceeded the control FMRP levels in all tested brain regions. There was also improved performance in the rotarod test and partial improvements in the other tests in the treated KO animals. Conclusion: These experiments demonstrate efficient, brain-specific delivery of Fmr1 via peripheral administration in adult mice. The gene delivery led to partial alleviation of the Fmr1 KO phenotypical behaviors. FMRP oversupply may explain why not all behaviors were significantly affected. Since AAV.php vectors are less efficient in humans than in the mice used in the current experiment, studies to determine the optimal dose using human-suitable vectors will be necessary to further demonstrate feasibility.

Brivaracetam prevents the development of epileptiform activity when administered early after cortical neurotrauma in rats

OBJECTIVES

There is no effective therapy to prevent the development of posttraumatic epilepsy (PTE). Recently, we reported that administration of the antiseizure medication (ASM) levetiracetam (LEV) shortly after trauma prevented the development of epileptiform activity in two experimental models of neurotrauma. However, the time window for effective intervention with LEV may be too narrow for most clinical settings. Using the controlled cortical impact (CCI) injury model, the current study tested whether early administration of brivaracetam (BRV), an ASM with 20 times the affinity of LEV for the SV2A synaptic vesicle protein, could improve upon the antiepileptogenic action observed with LEV.

METHODS

Rats (postnatal day [P] 24-32) subjected to CCI injury were given a single dose of BRV (21 or 100 mg/kg, i.p.) at one of three post-injury time points: immediately (0-2 minutes), 30 minutes, or 60 minutes. Control animals received only vehicle (0.9% saline). Posttraumatic electrographic epileptiform activity was assayed ex vivo from coronal neocortical slices collected proximal to the injury (four per rat) 3-4 weeks after injury. In this model, ictal-like burst discharges occur spontaneously or can be evoked in an "all or none" manner with applied electrical stimulation within the first 2 weeks after injury.

RESULTS

A single dose of BRV administered to rats up to 60 minutes after traumatic brain injury (TBI) significantly reduced the development of posttraumatic epileptiform activity by (1) inhibiting the development of both evoked and spontaneous epileptiform activity, (2) raising the threshold for stimulus-evoked epileptiform discharges, and (3) reducing the intensity of epileptiform bursts that arise after cortical neurotrauma.

SIGNIFICANCE

Clinically there has been little success preventing the development of posttraumatic epilepsy. The results of this study support the hypothesis that early intervention with BRV has the potential to prevent or reduce posttraumatic epileptogenesis, and that there may be a limited time window for successful prophylactic intervention.

Development of a Quantitative FMRP Assay for Mouse Tissue Applications

Fragile X syndrome results from the absence of the FMR1 gene product—Fragile X Mental Retardation Protein (FMRP). Fragile X animal research has lacked a reliable method to quantify FMRP. We report the development of an array of FMRP-specific monoclonal antibodies and their application for quantitative assessment of FMRP (qFMRPm) in mouse tissue. To characterize the assay, we determined the normal variability of FMRP expression in four brain structures of six different mouse strains at seven weeks of age. There was a hierarchy of FMRP expression: neocortex > hippocampus > cerebellum > brainstem. The expression of FMRP was highest and least variable in the neocortex, whereas it was most variable in the hippocampus. Male C57Bl/6J and FVB mice were selected to determine FMRP developmental differences in the brain at 3, 7, 10, and 14 weeks of age. We examined the four structures and found a developmental decline in FMRP expression with age, except for the brainstem where it remained stable. qFMRPm assay of blood had highest values in 3 week old animals and dropped by 2.5-fold with age. Sex differences were not significant. The results establish qFMRPm as a valuable tool due to its ease of methodology, cost effectiveness, and accuracy.

Rapid volume pulsation of the extracellular space coincides with epileptiform activity in mice and depends on the NBCe1 transporter

KEY POINTS

Extracellular space (ECS) rapid volume pulsation (RVP) accompanying epileptiform activity is described for the first time. Such RVP occurs robustly in several in vitro and in vivo mouse models of epileptiform activity. In the in vitro 4-aminopyridine model of epileptiform activity, RVP depends on the activity of the electrogenic Na⁺ /HCO₃ ^- cotransporter (NBCe1). NBCe1 pharmacological inhibition suppresses RVP and epileptiform activity. Inhibition of changes in ECS volume may be a useful target in epilepsy patients who are resistant to current treatments. ​ ABSTRACT: The extracellular space (ECS) of the brain shrinks persistently by approximately 35% during epileptic seizures. Here we report the discovery of rapid volume pulsation (RVP), further transient drops in ECS volume which accompany events of epileptiform activity. These transient ECS contractions were observed in multiple mouse models of epileptiform activity both in vivo (bicuculline methiodide model) and in vitro (hyaluronan synthase 3 knock-out, picrotoxin, bicuculline and 4-aminopyridine models). By using the probe transients quantification (PTQ) method we show that individual pulses of RVP shrank the ECS by almost 15% in vivo. In the 4-aminopyridine in vitro model, the individual pulses of RVP shrank the ECS by more than 4%, and these transient changes were superimposed on a persistent ECS shrinkage of 36% measured with the real-time iontophoretic method. In this in vitro model, we investigated several channels and transporters that may be required for the generation of RVP and epileptiform activity. Pharmacological blockages of Na⁺ /K⁺ /2Cl^- cotransporter type 1 (NKCC1), K⁺ /Cl^- cotransporter (KCC2), the water channel aquaporin-4 (AQP4) and inwardly rectifying potassium channel 4.1 (Kir4.1) were ineffective in halting the RVP and the epileptiform activity. In contrast, pharmacological blockade of the electrogenic Na⁺ /HCO₃ ^- cotransporter (NBCe1) by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) eliminated both the RVP and the persistent ECS shrinkage. Importantly, this blocker also stopped the epileptiform activity. These results demonstrate that RVP is closely associated with epileptiform activity across several models of epileptiform activity and therefore the underlying mechanism could potentially represent a novel target for epilepsy management and treatment.

Early intervention with levetiracetam prevents the development of cortical hyperexcitability and spontaneous epileptiform activity in two models of neurotrauma in rats

This study examined the antiepileptogenic potential of the antiseizure drug (ASD) levetiracetam (LEV) using the in vitro traumatized-slice and in vivo controlled cortical impact (CCI) models of traumatic brain injury (TBI) in rats when administered early after the injury. For the in vitro model, acute coronal slices (400-450 μm) of rat neocortex (P21-32) were injured via a surgical cut that separated the superficial layers from the deeper regions. Persistent stimulus-evoked epileptiform activity developed within 1-2 h after trauma. In randomly selected slices, LEV (500 μM) was bath-applied for 1 h starting immediately or delayed by 30-80 min after injury. Treated and untreated slices were examined for epileptiform activity via intracellular and extracellular recordings. For the in vivo model, rats (P24-32) were subjected to a non-penetrating, focal, CCI injury targeting the neocortex (5.0 mm diameter; 2.0 mm depth). Immediately after injury, rats were given either a single dose of LEV (60-150 mg/kg, i.p.) or the saline vehicle. At 2-3 weeks after the injury, ex vivo cortical slices were examined for epileptiform activity. The results from the traumatized-slice experiments showed that in vitro treatment with LEV within 60 min of injury significantly reduced (> 50%) the proportion of slices that exhibited stimulus-evoked epileptiform activity. LEV treatment also increased the stimulus intensity required to trigger epileptiform bursts in injured slices by 2-4 fold. Consistent with these findings, LEV treatment of CCI-injured rats (n = 15) significantly reduced the proportion of animals that exhibited spontaneous and stimulus-evoked epileptiform bursts in ex vivo cortical slices compared to saline-treated controls (n = 15 rats), and also significantly increased the stimulus intensity required to evoke epileptiform bursts. These results suggest that early administration of LEV has the potential to prevent or reduce posttraumatic epileptogenesis and that there may be a narrow therapeutic window for successful prophylactic intervention.

Persistent Increases of PKMζ in Sensorimotor Cortex Maintain Procedural Long-Term Memory Storage

Procedural motor learning and memory are accompanied by changes in synaptic plasticity, neural dynamics, and synaptogenesis. Missing is information on the spatiotemporal dynamics of the molecular machinery maintaining these changes. Here we examine whether persistent increases in PKMζ, an atypical protein kinase C (PKC) isoform, store long-term memory for a reaching task in rat sensorimotor cortex that could reveal the sites of procedural memory storage. Specifically, perturbing PKMζ synthesis (via antisense oligodeoxynucleotides) and blocking atypical PKC activity (via zeta inhibitory peptide [ZIP]) in S1/M1 disrupts and erases long-term motor memory maintenance, indicating atypical PKCs and specifically PKMζ store consolidated long-term procedural memories. Immunostaining reveals that PKMζ increases in S1/M1 layers II/III and V as performance improved to an asymptote. After storage for 1 month without reinforcement, the increase in M1 layer V persists without decrement. Thus, the persistent increases in PKMζ that store long-term procedural memory are localized to the descending output layer of the primary motor cortex.

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Perturbing PKMζ synthesis in S1/M1 slows the formation of skilled motor memory

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Blocking PKMζ activity specifically erases memories maintained without reinforcement

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Skilled motor learning induces the increase of PKMζ in S1/M1 layers II/III and V

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PKMζ sustains the engram for procedural motor memory in M1 layer V

Neuroanatomical characterization of the cellular and axonal architecture of subcortical band heterotopia in the BXD29-Tlr4lps-2J/J mouse cortex

Subcortical band heterotopia (SBH) are malformations of the human cerebral cortex typically associated with epilepsy and cognitive delay/disability. Rodent models of SBH have demonstrated strong face validity as they are accompanied by both cognitive deficits and spontaneous seizures or reduced seizure threshold. BXD29-Tlr4^lps-2J/J recombinant inbred mice display striking bilateral SBH, partial callosal agenesis, morphological changes in subcortical structures of the auditory pathway, and display sensory deficits in behavioral tests (Rosen et al., 2013; Truong et al., 2013, 2015). Surprisingly, these mice show no cognitive deficits and have a higher seizure threshold to chemi-convulsive treatment (Gabel et al., 2013) making them different than other rodent SBH models described previously. In the present report, we perform a detailed characterization of the cellular and axonal constituents of SBH in BXD29-Tlr4^lps-2J/J mice and demonstrate that various types of interneurons and glia as well as cortical and subcortical projections are found in SBH. In addition, the length of neuronal cilia was reduced in SBH compared to neurons in the overlying and adjacent normotopic cortex. Finally, we describe additional and novel malformations of the hippocampus and neocortex present in BXD29-Tlr4^lps-2J/J mice. Together, our findings in BXD29-Tlr4^lps-2J/J mice are discussed in the context of the known neuroanatomy and phenotype of other SBH rodent models.

Subcortical band heterotopia in rat offspring following maternal hypothyroxinaemia: structural and functional characteristics

Thyroid hormones (TH) play crucial roles in brain maturation and are important for neuronal migration and neocortical lamination. Subcortical band heterotopia (SBH) represent a class of neuronal migration errors in humans that are often associated with childhood epilepsy. We have previously reported the presence of SBH in a rodent model of low level hypothyroidism induced by maternal exposure to the goitrogen, propylthiouracil (PTU). In the present study, we report the dose-response characteristics of this developmental malformation and the connectivity of heterotopic neurones with other brain regions, as well as their functionality. Pregnant rats were exposed to varying concentrations of PTU through the drinking water (0-10 p.p.m.) beginning on gestational day 6 to produce graded levels of TH insufficiency. Dose-dependent increases in the volume of the SBH present in the corpus callosum were documented in the adult offspring, with a clear presence at concentrations of PTU that resulted in minor (< 15%) reductions in maternal serum thyroxine as measured when pups were weaned. SBH contain neurones, oligodendrocytes, astrocytes and microglia. Monoaminergic and cholinergic processes were prevalent and many of the axons were myelinated. Anatomical connectivity of SBH neurones to cortical neurones and the synaptic functionality of these anatomical connections was verified by ex vivo field potential recordings. SBH persisted in adult offspring despite a return to euthyroid status on termination of exposure and these offspring displayed an increased sensitivity to seizures. Features of this model are attractive with respect to the investigation of the molecular mechanisms of cortical development, the effectiveness of therapeutic intervention in hypothyroxinaemia during pregnancy and the impact of the very modest TH imbalance that accompanies exposure to environmental contaminants.

Aging-induced Seizure-related Changes to the Hippocampal Mossy Fiber Pathway in Forebrain Specific BDNF Overexpressing Mice

Aging confers an increased risk for developing seizure activity, especially within brain regions that mediate learning and synaptic plasticity. Brain derived neurotrophic factor (BDNF) is a member of the neurotrophin family that has an important role in regulating growth and development of the nervous system. BDNF is upregulated after pharmacological seizure induction and this upregulation contributes to enhanced excitability of the hippocampal mossy fiber-CA3 pathway, which is accompanied by neuropeptide Y (NPY) upregulation. Mice overexpressing a BDNF transgene in forebrain neurons provide an avenue for understanding the role of neurotrophic support in the aged hippocampus. In this study BDNF transgenic (TG) mice were utilized to determine whether increased BDNF expression through genetic manipulation resulted in age-related changes in hippocampal excitability and NPY expression. Spontaneous behavioral seizures were observed in TG mice, but not WT mice, past 5 months of age and the severity of behavioral seizures increased with age. Electrophysiological investigation of hippocampal CA3 activity indicated that slices from aged TG mice (86%), but not age-matched WT mice, or young TG mice, showed epileptiform activity in response to either repeated paired pulse or high frequency (tetanic) stimulation. Electrophysiological results were supported by the observation of robust ectopic NPY immunoreactivity in hippocampal mossy fibers of most aged TG mice (57%), which was absent in age-matched WT mice and young TG mice. The results from this study indicate that forebrain restricted BDNF overexpression produces age-related changes in hyperexcitability and NPY immunoreactivity in mossy fiber-CA3 pathway. Together, these data suggest that the capability for BDNF to promote epileptogenesis is maintained, and may be enhanced, in the aging hippocampus.

Spontaneous epileptiform activity in rat neocortex after controlled cortical impact injury

A hallmark of severe traumatic brain injury (TBI) is the development of post-traumatic epilepsy (PTE). However, the mechanisms underlying PTE remain poorly understood. In this study, we used a controlled cortical impact (CCI) model in rats to examine post-traumatic changes in neocortical excitability. Neocortical slices were prepared from rats at 7-9 days (week 1) and 14-16 days (week 2) after CCI injury. By week 2, we observed a substantial gray matter lesion with a cavity that extended to the hippocampal structure. Fluoro-Jade B staining of slices revealed active neuronal degeneration during weeks 1 and 2. Intracellular and extracellular recordings obtained from layer V revealed evoked and spontaneous epileptiform discharges in neocortices of CCI-injured rats. At week 1, intracellular recordings from pyramidal cells revealed evoked epileptiform firing that was synchronized with population events recorded extracellularly, suggestive of increased excitability. This activity was characterized by bursts of action potentials that were followed by recurrent, repetitive after-discharges. At week 2, both spontaneous and evoked epileptiform firing were recorded in slices from injured rats. The evoked discharges resembled those observed at week 1, but with longer burst durations. Spontaneous activity included prolonged, ictal-like discharges lasting up to 8-10 sec, and briefer interictal-like burst events (<1 sec). These results indicate that during the first 2 weeks following severe CCI injury, there is a progressive development of neocortical hyperexcitability that ultimately leads to spontaneous epileptiform firing, suggesting a rapid epileptogenic process.

Vascular endothelial growth factor is up-regulated after status epilepticus and protects against seizure-induced neuronal loss in hippocampus

Vascular endothelial growth factor (VEGF) is a protein factor which has been found to play a significant role in both normal and pathological states. Its role as an angiogenic factor is well-established. More recently, VEGF has been shown to protect neurons from cell death both in vivo and in vitro. While VEGF's potential as a protective factor has been demonstrated in hypoxia-ischemia, in vitro excitotoxicity, and motor neuron degeneration, its role in seizure-induced cell loss has received little attention. A potential role in seizures is suggested by Newton et al.'s [Newton SS, Collier EF, Hunsberger J, Adams D, Terwilliger R, Selvanayagam E, Duman RS (2003) Gene profile of electroconvulsive seizures: Induction of neurotrophic and angiogenic factors. J Neurosci 23:10841-10851] finding that VEGF mRNA increases in areas of the brain that are susceptible to cell loss after electroconvulsive-shock induced seizures. Because a linear relationship does not always exist between expression of mRNA and protein, we investigated whether VEGF protein expression increased after pilocarpine-induced status epilepticus. In addition, we administered exogenous VEGF in one experiment and blocked endogenous VEGF in another to determine whether VEGF exerts a neuroprotective effect against status epilepticus-induced cell loss in one vulnerable brain region, the rat hippocampus. Our data revealed that VEGF is dramatically up-regulated in neurons and glia in hippocampus, thalamus, amygdala, and neocortex 24 h after status epilepticus. VEGF induced significant preservation of hippocampal neurons, suggesting that VEGF may play a neuroprotective role following status epilepticus.

Modest thyroid hormone insufficiency during development induces a cellular malformation in the corpus callosum: a model of cortical dysplasia

There is a growing body of evidence that subtle decreases in maternal thyroid hormone during gestation can impact fetal brain development. The present study examined the impact of graded levels of thyroid hormone insufficiency on brain development in rodents. Maternal thyroid hormone insufficiency was induced by exposing timed-pregnant dams to propylthiouracil (PTU) at doses of 0, 1, 2, 3, and 10 ppm in the drinking water from gestational d 6 through weaning on postnatal d 30. An examination of Nissl-stained sections of the brains from developmentally hypothyroid offspring killed on postnatal d 23 revealed the presence of a heretofore unreported bilateral cellular malformation, a heterotopia, positioned within the white matter of the corpus callosum of both hemispheres. Immunohistochemical techniques were used to determine that this heterotopia primarily consists of neurons born between gestational d 17-19 and exhibits a dose-dependent increase in size with decreases in thyroid hormone levels. Importantly, this structural abnormality is evident at modest levels of maternal thyroid hormone insufficiency ( approximately 45% reductions in T(4) with no change in T(3)), persists in adult offspring despite a return to normal hormonal status, and is dramatically reduced in size with prenatal thyroid hormone replacement. Developmental exposure to methimazole, another goitrogen, also induced formation of this heterotopia. Whereas the long-term consequence of this cortical malformation on brain function remains to be determined, the presence of the heterotopia underscores the critical role thyroid hormone plays in brain development during the prenatal period and provides a new model in which to study mechanisms of cortical development and cortical dysplasia.

Thyroid hormone insufficiency during brain development reduces parvalbumin immunoreactivity and inhibitory function in the hippocampus

Thyroid hormones are necessary for brain development. gamma-Amino-butyric acid (GABA)ergic interneurons comprise the bulk of local inhibitory circuitry in brain, many of which contain the calcium binding protein, parvalbumin (PV). A previous report indicated that severe postnatal hypothyroidism reduces PV immunoreactivity (IR) in rat neocortex. We examined PV-IR and GABA-mediated synaptic inhibition in the hippocampus of rats deprived of thyroid hormone from gestational d 6 until weaning on postnatal d 30. Pregnant dams were exposed to propylthiouracil (0, 3, 10 ppm) via the drinking water, which decreased maternal serum T(4) by approximately 50-75% and increased TSH. At weaning, T(4) was reduced by approximately 70% in offspring in the low-dose group and fell below detectable levels in high-dose animals. PV-IR was diminished in the hippocampus and neocortex of offspring killed on postnatal d 21, an effect that could be reversed by postnatal administration of T(4). Dose-dependent decreases in the density of PV-IR neurons were observed in neocortex and hippocampus, with the dentate gyrus showing the most severe reductions (50-75% below control counts). Altered staining persisted to adulthood despite the return of thyroid hormones to control levels. Developmental cross-fostering and adult-onset deprivation studies revealed that early postnatal hormone insufficiency was required for an alteration in PV-IR. Synaptic inhibition of the perforant path-dentate gyrus synapse evaluated in adult offspring, in vivo, revealed dose-dependent reductions in paired pulse depression indicative of a suppression of GABA-mediated inhibition. These data demonstrate that moderate degrees of thyroid hormone insufficiency during the early postnatal period permanently alters interneuron expression of PV and compromises inhibitory function in the hippocampus.

Kynurenate and 7-chlorokynurenate formation in chronically epileptic rats

PURPOSE

The tryptophan metabolite kynurenic acid (KYNA) and its synthetic derivative, 7-chlorokynurenic acid (7-Cl-KYNA), are antagonists of the glycine co-agonist ("glycine(B)") site of the N-methyl-D-aspartate (NMDA)-receptor. Both compounds have neuroprotective and anticonvulsive properties but do not readily penetrate the blood-brain barrier. However, KYNA and 7-Cl-KYNA can be formed in, and released from, astrocytes after the peripheral administration of their transportable precursors kynurenine and 4-chlorokynurenine, respectively. The present study was designed to examine these biosynthetic processes, as well as astrogliosis, in animals with spontaneously recurring seizures.

METHODS

The fate and formation of KYNA and 7-Cl-KYNA was studied in vivo (microdialysis) and in vitro (tissue slices) in rats exhibiting chronic seizure activity (pilocarpine model) and in appropriate controls. Neuronal loss and gliosis in these animals were examined immunohistochemically.

RESULTS

In vivo microdialysis revealed higher ambient extracellular KYNA levels and enhanced de novo formation of 7-Cl-KYNA in the entorhinal cortex and hippocampus in epileptic rats. Complementary studies in tissue slices showed increased neosynthesis of KYNA and 7-Cl-KYNA in the same two brain areas. Microscopic analysis revealed pronounced astrocytic reactions in entorhinal cortex and hippocampus in epileptic animals.

CONCLUSIONS

These results demonstrate that the epileptic brain can synthesize glycine(B) receptor antagonists in situ. Astrogliosis probably accounts for their enhanced production in chronically epileptic rats. These results bode well for the use of 4-chlorokynurenine in the treatment of chronic seizure disorders.

Seizure susceptibility in intact and ovariectomized female rats treated with the convulsant pilocarpine

Despite numerous neuroendocrinological studies of seizures, the influence of estrogen and progesterone on seizures and epilepsy remains unclear. This may be due to the fact that previous studies have not systematically compared distinct endocrine conditions and included all relevant controls. The goal of the present study was to conduct such a study using pilocarpine as chemoconvulsant. Thus, age and weight-matched, intact or ovariectomized rats were tested to determine incidence of status epilepticus and to study events leading to status. Intact female rats were sampled at each cycle stage (proestrus, estrus, metestrus, or diestrus 2). Convulsant was administered at the same time of day, 10:00-10:30 a.m. Statistical analysis showed that there was a significantly lower incidence of status on the morning of estrus, but differences were attenuated in older animals. Ovariectomized rats were distinct in their rapid progression to status. These results show that the incidence of status in female rats following pilocarpine injection, and the progression to pilocarpine-induced status, are influenced by reproductive state as well as age. The hormonal milieu present specifically on the morning of estrus appears to decrease susceptibility to pilocarpine-induced status, particularly at young ages. In contrast, the chronic absence of reproductive steroids that characterizes the ovariectomized rat leads to a more rapid progression to status. This dissociation between incidence vs. progression provides new insight into the influence of estrogen and progesterone on seizures.

Neuropeptide Y stimulates neuronal precursor proliferation in the post-natal and adult dentate gyrus

Adult dentate neurogenesis is important for certain types of hippocampal-dependent learning and also appears to be important for the maintenance of normal mood and the behavioural effects of antidepressants. Neuropeptide Y (NPY), a peptide neurotransmitter released by interneurons in the dentate gyrus, has important effects on mood, anxiety-related behaviour and learning and memory. We report that adult NPY receptor knock-out mice have significantly reduced cell proliferation and significantly fewer immature doublecortin-positive neurons in the dentate gyrus. We also show that the neuroproliferative effect of NPY is dentate specific, is Y1-receptor mediated and involves extracellular signal-regulated kinase (ERK)1/2 activation. NPY did not exhibit any effect on cell survival in vitro but constitutive loss of the Y1 receptor in vivo resulted in greater survival of newly generated neurons and an unchanged total number of dentate granule cells. These results show that NPY stimulates neuronal precursor proliferation in the dentate gyrus and suggest that NPY-releasing interneurons may modulate dentate neurogenesis.

Chronic developmental lead exposure reduces neurogenesis in adult rat hippocampus but does not impair spatial learning

The dentate granule cell (DG) layer of the hippocampal formation has the distinctive property of ongoing neurogenesis that continues throughout adult life. Although the function of these newly generated neurons and the mechanisms that control their birth are unknown, age, activity, diet and psychosocial stress have all been demonstrated to regulate this type of neurogenesis. Little information on the impact of environmental insults on this process has appeared to date. Developmental lead (Pb) exposure has been well documented to impair cognitive function in children and animals and reduce activity-dependent synaptic plasticity in the hippocampus of rodents. Therefore, we examined the effects of this classic environmental neurotoxicant on hippocampal-dependent learning and adult neurogenesis in the hippocampus. Pregnant rats were exposed to a low level of Pb-acetate (0.2%) via the drinking water from late gestation (GD 16) until weaning on postnatal day 21 (PN 21). At weaning, half of the Pb-exposed animals were weaned to control drinking water and the remainder were maintained on Pb water until termination of the study. Animals were paired- housed and on PN 75 were administered a series of injections of a thymidine analog bromodeoxyuridine (BrdU), a marker of DNA synthesis that labels proliferating cells and their progeny. At 12-h intervals for 12 days, rats received an ip injection of BrdU (50 mg/kg). Subjects were sacrificed and perfused 24 h and 28 days after the last injection. Spatial learning was assessed in an independent group of animals beginning on PN 110 using a Morris water maze. No Pb-induced impairments were evident in water maze learning. Immunohistochemistry for the detection of BrdU-labeled cells was performed on 40-microm coronal sections throughout the hippocampus. Continuous exposure to Pb (Life) reduced the total number of BrdU-positive cells at 28 days without affecting the total number of labeled cells evident 24 h after the last injection. No differences in the number of progenitor cells labeled or surviving were seen between control and treated animals whose Pb exposure was terminated at weaning. Double labeling with BrdU and the glial specific marker, glial acidic fibrillary protein (GFAP) indicated that the bulk of the surviving cells were of a neuronal rather than a glial phenotype. These data reveal that chronic low-level Pb exposure reduces the capacity for neurogenesis in the adult hippocampus. Despite deficits in synaptic plasticity previously reported from our laboratory, and now structural plasticity, no significant impact on spatial learning was detected.

Preemptive Low-frequency Stimulation Decreases the Incidence of Amygdala-kindled Seizures

PURPOSE

The use of electrical stimulation as a therapy for epilepsy is currently being studied in experimental animals and in patients with epilepsy. This study examined the effect of preemptive, low-frequency, 1-Hz sine wave stimulation (LFS) on the incidence of amygdala-kindled seizures in the rat.

METHODS

Electrodes were implanted into the basolateral amygdalae of adult male rats. All animals received a kindling stimulus of 60-Hz, 400-microA, sine wave for 1 s twice a day. Experimental animals received an additional LFS consisting of 1 Hz, 50 microA for 30 s immediately before the kindling stimulus. Afterdischarge (AD) duration, behavioral seizure score, the number of stimulations required to elicit the first stage five seizure and to become fully kindled were measured. After 20 stimulations, a crossover procedure was performed. Fully kindled rats from each group were switched, so that the original controls received LFS plus the kindling stimulus, and the original experimental rats received only the kindling stimulus.

RESULTS

During kindling acquisition, LFS induced a significant decrease in AD duration. A significant increase in the number of times the kindling stimulus failed to elicit an AD was noted. Control rats exhibited an AD 99% of the time compared with 70% in experimental rats (p < 0.0001; Fisher's Exact test). In fully kindled animals, the incidence of stage five seizures in the original controls significantly decreased from 98% to 42% (p < 0.0001) when the LFS was added to the kindling paradigm.

CONCLUSIONS

The dramatic decrease in the incidence of stage 5 seizures in fully kindled animals after preemptive LFS strongly suggests that LFS may be an effective therapy for the prevention of seizures in patients with epilepsy.

Perforant path activation of ectopic granule cells that are born after pilocarpine-induced seizures

Granule cells in the dentate gyrus are born throughout life, and various stimuli can affect their development in the adult brain. Following seizures, for instance, neurogenesis increases greatly, and some new cells migrate to abnormal (ectopic) locations, such as the hilus. Previous electrophysiological studies of this population have shown that they have intrinsic properties that are similar to normal granule cells, but differ in other characteristics, consistent with abnormal integration into host circuitry. To characterize the response of ectopic hilar granule cells to perforant path stimulation, intracellular recordings were made in hippocampal slices from rats that had pilocarpine-induced status epilepticus and subsequent spontaneous recurrent seizures. Comparisons were made with granule cells located in the granule cell layer of both pilocarpine- and saline-treated animals. In addition, a few ectopic hilar granule cells were sampled from saline-treated rats. Remarkably, hilar granule cells displayed robust responses, even when their dendrites were not present within the molecular layer, where perforant path axons normally terminate. The evoked responses of hilar granule cells were similar in several ways to those of normally positioned granule cells, but there were some differences. For example, there was an unusually long latency to onset of responses evoked in many hilar granule cells, especially those without molecular layer dendrites. Presumably this is due to polysynaptic activation by the perforant path. These results indicate that synaptic reorganization after seizures can lead to robust activation of newly born hilar granule cells by the perforant path, even when their dendrites are not in the terminal field of the perforant path. Additionally, the fact that these cells can be found in normal tissue and develop similar synaptic responses, suggests that seizures, while not necessary for their formation, strongly promote their generation and the development of associated circuits, potentially contributing to a lowered seizure threshold.

Electrophysiological evidence of monosynaptic excitatory transmission between granule cells after seizure-induced mossy fiber sprouting

Mossy fiber sprouting is a form of synaptic reorganization in the dentate gyrus that occurs in human temporal lobe epilepsy and animal models of epilepsy. The axons of dentate gyrus granule cells, called mossy fibers, develop collaterals that grow into an abnormal location, the inner third of the dentate gyrus molecular layer. Electron microscopy has shown that sprouted fibers from synapses on both spines and dendritic shafts in the inner molecular layer, which are likely to represent the dendrites of granule cells and inhibitory neurons. One of the controversies about this phenomenon is whether mossy fiber sprouting contributes to seizures by forming novel recurrent excitatory circuits among granule cells. To date, there is a great deal of indirect evidence that suggests this is the case, but there are also counterarguments. The purpose of this study was to determine whether functional monosynaptic connections exist between granule cells after mossy fiber sprouting. Using simultaneous recordings from granule cells, we obtained direct evidence that granule cells in epileptic rats have monosynaptic excitatory connections with other granule cells. Such connections were not obtained when age-matched, saline control rats were examined. The results suggest that indeed mossy fiber sprouting provides a substrate for monosynaptic recurrent excitation among granule cells in the dentate gyrus. Interestingly, the characteristics of the excitatory connections that were found indicate that the pathway is only weakly excitatory. These characteristics may contribute to the empirical observation that the sprouted dentate gyrus does not normally generate epileptiform discharges.

Brain Stimulation As a Therapy for Epilepsy

The failure of current antiepileptic therapies to adequately treat a significant number of epileptic patients highlights the need for the development of new treatments for the disorder. A new strategy that is currently being developed is to deliver electrical stimulation directly to the brain to decrease or prevent seizure activity. Clinical evidence that electrical stimulation could interfere with seizure activity was initially reported in the 1930's. However, many of these early studies consisted of case reports or were poorly controlled. In addition, there were a number of studies that failed to observe any beneficial effect of brain stimulation on seizures. More recently, deep brain stimulation has been used successfully to treat patients with movement disorders and vagus nerve stimulation has been shown to effectively decrease seizure activity in a select population of epilepsy patients. These advances have led to a reexamination of the potential therapeutic benefits of deep brain stimulation for the treatment of epilepsy. There is now experimental and clinical evidence that direct electrical stimulation of the brain can prevent or decrease seizure activity. However, several fundamental questions remain to be resolved. They include where in the brain the stimulus should be delivered and what type of stimulation would be most effective. One goal of this research is to combine the beneficial aspects of electrical stimulation with seizure detection technology in an implantable responsive stimulator. The device will detect the onset of a seizure and deliver an electrical stimulus that will safely block seizure activity without interfering with normal brain function.

Vascular endothelial growth factor (VEGF) in seizures: a double-edged sword

Vascular endothelial growth factor (VEGF) is a vascular growth factor which induces angiogenesis (the development of new blood vessels), vascular permeability, and inflammation. In brain, receptors for VEGF have been localized to vascular endothelium, neurons, and glia. VEGF is upregulated after hypoxic injury to the brain, which can occur during cerebral ischemia or high-altitude edema, and has been implicated in the blood-brain barrier breakdown associated with these conditions. Given its recently-described role as an inflammatory mediator, VEGF could also contribute to the inflammatory responses observed in cerebral ischemia. After seizures, blood-brain barrier breakdown and inflammation is also observed in brain, albeit on a lower scale than that observed after stroke. Recent evidence has suggested a role for inflammation in seizure disorders. We have described striking increases in VEGF protein in both neurons and glia after pilocarpine-induced status epilepticus in the brain. Increases in VEGF could contribute to the blood-brain barrier breakdown and inflammation observed after seizures. However, VEGF has also been shown to be neuroprotective across several experimental paradigms, and hence could potentially protect vulnerable cells from damage associated with seizures. Therefore, the role of VEGF after seizures could be either protective or destructive. Although only further research will determine the exact nature of VEGF's role after seizures, preliminary data indicate that VEGF plays a protective role after seizures.

Hippocampal excitability increases during the estrous cycle in the rat: a potential role for brain-derived neurotrophic factor

To test the hypothesis that induction of BDNF may contribute to changes in hippocampal excitability occurring during the female reproductive cycle, we examined the distribution of BDNF immunoreactivity and changes in CA1 and CA3 electrophysiology across the estrous cycle in rats. Hippocampal BDNF immunoreactivity increased on the day of proestrus as well as on the following morning (estrus), relative to metestrus or ovariectomized animals. Changes in immunoreactivity were clearest in mossy fiber axons of dentate gyrus granule cells, which contain the highest concentration of BDNF. Increased immunoreactivity was also apparent in the neuropil-containing dendrites of CA1 and CA3 neurons. Electrophysiological recordings in hippocampal slices showed robust cycle-dependent differences. Evoked responses of CA1 neurons to Schaffer collateral stimulation changed over the cycle, with larger maximum responses at both proestrus and estrus relative to metestrus. In area CA3, repetitive hilar stimuli frequently evoked multiple population spikes at proestrus and estrus but only rarely at other cycle stages, and never in slices of ovariectomized rats. Hyperexcitability in area CA3 at proestrus was blocked by exposure to the high-affinity neurotrophin receptor antagonist K252a, or an antagonist of the alpha7 nicotinic cholinergic receptor, whereas it was induced at metestrus by the addition of BDNF to hippocampal slices. These studies suggest that hippocampal BDNF levels change across the estrous cycle, accompanied by neurophysiological responses that resemble the effects of BDNF treatment. An estrogen-induced interaction of BDNF and alpha7 nicotinic receptors on mossy fibers seems responsible for estrous cycle changes in area CA3. Periovulatory changes in hippocampal function may, thus, involve estrogen-induced increases in BDNF expression.

Structural and functional asymmetry in the normal and epileptic rat dentate gyrus

The rat dentate gyrus is usually described as relatively homogeneous. Here, we present anatomic and physiological data which demonstrate that there are striking differences between the supra- and infrapyramidal blades after status epilepticus and recurrent seizures. These differences appear to be an accentuation of a subtle asymmetry present in normal rats. In both pilocarpine and kainic acid models, there was greater mossy fiber sprouting in the infrapyramidal blade. This occurred primarily in the middle third of the hippocampus. Asymmetric sprouting was evident both with Timm stain as well as antisera to brain-derived neurotrophic factor (BDNF) or neuropeptide Y (NPY). In addition, surviving NPY-immunoreactive hilar neurons were distributed preferentially in the suprapyramidal region of the hilus. Extracellular recordings from infrapyramidal sites in hippocampal slices of pilocarpine-treated rats showed larger population spikes and weaker paired-pulse inhibition in response to perforant path stimulation relative to suprapyramidal recordings. A single stimulus could evoke burst discharges in infrapyramidal granule cells but not suprapyramidal blade neurons. BDNF exposure led to spontaneous epileptiform discharges that were larger in amplitude and longer lasting in the infrapyramidal blade. Stimulation of the infrapyramidal molecular layer evoked larger responses in area CA3 than suprapyramidal stimulation. In slices from the temporal pole, in which anatomic evidence of asymmetry waned, there was little evidence of physiological asymmetry either. Of interest, some normal rats also showed signs of greater evoked responses in the infrapyramidal blade, and this could be detected with both microelectrode recording and optical imaging techniques. Although there were no signs of hyperexcitability in normal rats, the data suggest that there is some asymmetry in the normal dentate gyrus and this asymmetry is enhanced by seizures. Taken together, the results suggest that supra- and infrapyramidal blades of the dentate gyrus could have different circuit functions and that the infrapyramidal blade may play a greater role in activating the hippocampus.

Spontaneous recurrent seizures after pilocarpine-induced status epilepticus activate calbindin-immunoreactive hilar cells of the rat dentate gyrus

Although it is now established that neurogenesis of dentate gyrus granule cells increases after experimental seizures, little is currently known about the function of the new granule cells. One question is whether they become integrated into the network around them. Recent experiments that focused on the newly born granule cells in the hilus showed that indeed the new cells appear to become synchronized with host hippocampal neurons [Scharfman et al. (2000) J. Neurosci. 20, 6144-6158]. To address this issue further, we asked whether the new hilar granule cells were active during spontaneous limbic seizures that follow status epilepticus induced by pilocarpine injection. Thus, we perfused rats after spontaneous seizures and stained sections using antibodies to c-fos, a marker of neural activity, and calbindin, a marker of the newly born hilar granule cells [Scharfman et al. (2000) J. Neurosci. 20, 6144-6158]. We asked whether calbindin-immunoreactive hilar neurons were also c-fos-immunoreactive.C-fos was highly expressed in calbindin-immunoreactive hilar neurons. Approximately 23% of hilar cells that expressed c-fos were double-labeled for calbindin. In addition, other types of hilar neurons, i.e. those expressing parvalbumin or neuropeptide Y, also expressed c-fos. Yet other hippocampal neurons, including granule cells and pyramidal cells, had weak expression of c-fos at the latency after the seizure that hilar neuron expression occurred. In controls, there was very little c-fos or calbindin expression in the hilus.These results indicate that calbindin-immunoreactive hilar cells are activated by spontaneous seizures. Based on the evidence that many of these cells are likely to be newly born, the data indicate that new cells can become functionally integrated into limbic circuits involved in recurrent seizure generation. Furthermore, they appear to do so in a manner similar to many neighboring hilar neurons, apparently assimilating into the local environment. Finally, the results show that a number of hilar cell types are activated during chronic recurrent seizures in the pilocarpine model, a surprising result given that many hilar neurons are thought to be damaged soon after pilocarpine-induced status epilepticus.

Spontaneous limbic seizures after intrahippocampal infusion of brain-derived neurotrophic factor

The results of several studies have contributed to the hypothesis that BDNF promotes seizure activity, particularly in adult hippocampus. To test this hypothesis, BDNF, vehicle (phosphate-buffered saline, PBS), or albumin was infused directly into the hippocampus for 2 weeks using osmotic minipumps. Rats were examined behaviorally, electrophysiologically, and anatomically. An additional group was tested for sensitivity to the convulsant pilocarpine. Spontaneous behavioral seizures were observed in BDNF-infused rats (8/32; 25%) but not in controls (0/20; 0%). In a subset of six animals (three BDNF, three albumin), blind electrophysiological analysis of scalp recordings contralateral to the infused hippocampus demonstrated abnormalities in all BDNF rats; but not controls. Neuronal loss in BDNF-treated rats was not detected relative to PBS- or albumin-treated animals, but immunocytochemical markers showed a pattern of expression in BDNF-treated rats that was similar to rats with experimentally induced seizures. Thus, BDNF-infused rats had increased expression of NPY in hilar neurons of the dentate gyrus relative to control rats. NPY and BDNF expression was increased in the mossy fiber axons of dentate gyrus granule cells relative to controls. The increase in NPY and BDNF expression in BDNF-treated rats was bilateral and occurred throughout the septotemporal axis of the hippocampus. Mossy fiber sprouting occurred in five BDNF-treated rats but no controls. In another group of infused rats that was tested for seizure sensitivity to the convulsant pilocarpine, BDNF-infused rats had a shorter latency to status epilepticus than PBS-infused rats. In addition, the progression from normal behavior to severe seizures was faster in BDNF-treated rats. These data support the hypothesis that intrahippocampal BDNF infusion can facilitate, and potentially initiate, seizure activity in adult hippocampus.

Electrophysiological effects of exogenous and endogenous kynurenic acid in the rat brain: studies in vivo and in vitro

In this review, recent studies on the electrophysiological effects of de novo synthesized ("endogenous") kynurenic acid (KYNA) are discussed. Endogenous KYNA is normally formed as a byproduct of tryptophan metabolism. Evidence for a physiological role in neuronal excitability has not been strong, in part because brain levels are much lower than the KD of KYNA at the glycine site of the NMDA receptor, where KYNA is thought to exert its most potent effect. The results suggest that, unexpectedly, even low concentrations of endogenous KYNA have physiological consequences. These levels of KYNA reduced the number of hippocampal slices with spontaneous epileptiform discharges after exposure to buffer lacking magnesium. However, effects on evoked responses to single afferent stimuli were not detected. Taken together, the data argue for a potentially important role of endogenous KYNA in suppression of seizure-like activity, and suggest a novel approach to anticonvulsant drug development that could have few side effects.

Survival of dentate hilar mossy cells after pilocarpine-induced seizures and their synchronized burst discharges with area CA3 pyramidal cells

The clinical and basic literature suggest that hilar cells of the dentate gyrus are damaged after seizures, particularly prolonged and repetitive seizures. Of the cell types within the hilus, it appears that the mossy cell is one of the most vulnerable. Nevertheless, hilar neurons which resemble mossy cells appear in some published reports of animal models of epilepsy, and in some cases of human temporal lobe epilepsy. Therefore, mossy cells may not always be killed after severe, repeated seizures. However, mossy cell survival in these studies was not completely clear because the methods did allow discrimination between mossy cells and other hilar cell types. Furthermore, whether surviving mossy cells might have altered physiology after seizures was not examined. Therefore, intracellular recording and intracellular dye injection were used to characterize hilar cells in hippocampal slices from pilocarpine-treated rats that had status epilepticus and recurrent seizures ('epileptic' rats). For comparison, mossy cells were also recorded from age-matched, saline-injected controls, and pilocarpine-treated rats that failed to develop status epilepticus. Numerous hilar cells with the morphology, axon projection, and membrane properties of mossy cells were recorded in all three experimental groups. Thus, mossy cells can survive severe seizures, and those that survive retain many of their normal characteristics. However, mossy cells from epileptic tissue were distinct from mossy cells of control rats in that they generated spontaneous and evoked epileptiform burst discharges. Area CA3 pyramidal cells also exhibited spontaneous and evoked bursts. Simultaneous intracellular recordings from mossy cells and pyramidal cells demonstrated that their burst discharges were synchronized, with pyramidal cell discharges typically beginning first. From these data we suggest that hilar mossy cells can survive status epilepticus and chronic seizures. The fact that mossy cells have epileptiform bursts, and that they are synchronized with area CA3, suggest a previously unappreciated substrate for hyperexcitability in this animal model.

Boron neutron capture therapy of brain tumors: biodistribution, pharmacokinetics, and radiation dosimetry sodium borocaptate in patients with gliomas

OBJECTIVE

The purpose of this study was to obtain tumor and normal brain tissue biodistribution data and pharmacokinetic profiles for sodium borocaptate (Na2B12H11SH) (BSH), a drug that has been used clinically in Europe and Japan for boron neutron capture therapy of brain tumors. The study was performed with a group of 25 patients who had preoperative diagnoses of either glioblastoma multiforme (GBM) or anaplastic astrocytoma (AA) and were candidates for debulking surgery. Nineteen of these patients were subsequently shown to have histopathologically confirmed diagnoses of GBM or AA, and they constituted the study population.

METHODS

BSH (non-10B-enriched) was infused intravenously, in a 1-hour period, at doses of 15, 25, and 50 mg boron/kg body weight (corresponding to 26.5, 44.1, and 88.2 mg BSH/kg body weight, respectively) to groups of 3, 3, and 13 patients, respectively. Multiple samples of tumor tissue, brain tissue around the tumors, and normal brain tissue were obtained at either 3 to 7 or 13 to 15 hours after infusion. Blood samples for pharmacokinetic studies were obtained at times up to 120 hours after termination of the infusion. Sixteen of the patients underwent surgery at the Beijing Neurosurgical Institute and three at The Ohio State University, where all tissue samples were subsequently analyzed for boron content by direct current plasma-atomic emission spectroscopy.

RESULTS

Blood boron values peaked at the end of the infusion and then decreased triexponentially during the 120-hour sampling period. At 6 hours after termination of the infusion, these values had decreased to 20.8, 29.1, and 62.6 microg/ml for boron doses of 15, 25, and 50 mg/kg body weight, respectively. For a boron dose of 50 mg/kg body weight, the maximum (mean +/- standard deviation) solid tumor boron values at 3 to 7 hours after infusion were 17.1+/-5.8 and 17.3+/-10.1 microg/g for GBMs and AAs, respectively, and the mean tumor value averaged across all samples was 11.9 microg/g for both GBMs and AAs. In contrast, the mean normal brain tissue values, averaged across all samples, were 4.6+/-5.1 and 5.5+/-3.9 microg/g and the tumor/normal brain tissue ratios were3.8 and 3.2 for patients with GBMs and AAs, respectively. The large standard deviations indicated significant heterogeneity in uptake in both tumor and normal brain tissue. Regions histopathologically classified either as a mixture of tumor and normal brain tissue or as infiltrating tumor exhibited slightly lower boron concentrations than those designated as solid tumor. After a dose of 50 mg/kg body weight, boron concentrations in blood decreased from 104 microg/ml at 2 hours to 63 microg/ml at 6 hours and concentrations in skin and muscle were 43.1 and 39.2 microg/g, respectively, during the 3- to 7-hour sampling period.

CONCLUSION

When tumor, blood, and normal tissue boron concentrations were taken into account, the most favorable tumor uptake data were obtained with a boron dose of 25 mg/kg body weight, 3 to 7 hours after termination of the infusion. Although blood boron levels were high, normal brain tissue boron levels were almost always lower than tumor levels. However, tumor boron concentrations were less than those necessary for boron neutron capture therapy, and there was significant intratumoral and interpatient variability in the uptake of BSH, which would make estimation of the radiation dose delivered to the tumor very difficult. It is unlikely that intravenous administration of a single dose of BSH would result in therapeutically useful levels of boron. However, combining BSH with boronophenylalanine, the other compound that has been used clinically, and optimizing their delivery could increase tumor boron uptake and potentially improve the efficacy of boron neutron capture therapy.

Granule-like neurons at the hilar/CA3 border after status epilepticus and their synchrony with area CA3 pyramidal cells: functional implications of seizure-induced neurogenesis

A group of neurons with the characteristics of dentate gyrus granule cells was found at the hilar/CA3 border several weeks after pilocarpine- or kainic acid-induced status epilepticus. Intracellular recordings from pilocarpine-treated rats showed that these "granule-like" neurons were similar to normal granule cells (i. e., those in the granule cell layer) in membrane properties, firing behavior, morphology, and their mossy fiber axon. However, in contrast to normal granule cells, they were synchronized with spontaneous, rhythmic bursts of area CA3 pyramidal cells that survived status epilepticus. Saline-treated controls lacked the population of granule-like cells at the hilar/CA3 border and CA3 bursts. In rats that were injected after status epilepticus with bromodeoxyuridine (BrdU) to label newly born cells, and also labeled for calbindin D(28K) (because it normally stains granule cells), many double-labeled neurons were located at the hilar/CA3 border. Many BrdU-labeled cells at the hilar/CA3 border also were double-labeled with a neuronal marker (NeuN). Taken together with the recent evidence that granule cells that are born after seizures can migrate into the hilus, the results suggest that some newly born granule cells migrate as far as the CA3 cell layer, where they become integrated abnormally into the CA3 network, yet they retain granule cell intrinsic properties. The results provide insight into the physiological properties of newly born granule cells in the adult brain and suggest that relatively rigid developmental programs set the membrane properties of newly born cells, but substantial plasticity is present to influence their place in pre-existing circuitry.

Kynurenergic manipulations influence excitatory synaptic function and excitotoxic vulnerability in the rat hippocampus in vivo

Competing enzymatic mechanisms degrade the tryptophan metabolite L-kynurenine to kynurenate, an inhibitory and neuroprotective compound, and to the neurotoxins 3-hydroxykynurenine and quinolinate. Kynurenine 3-hydroxylase inhibitors such as PNU 156561 shift metabolism towards enhanced kynurenate production, and this effect may underlie the recently discovered anticonvulsant and neuroprotective efficacy of these drugs. Using electrophysiological and neurotoxicological endpoints, we now used PNU 156561 as a tool to examine the functional interplay of kynurenate, 3-hydroxykynurenine and quinolinate in the rat hippocampus in vivo. First, population spike amplitude in area CA1 and the extent of quinolinate-induced excitotoxic neurodegeneration were studied in animals receiving acute or prolonged intravenous infusions of L-kynurenine, PNU 156561, (L-kynurenine+PNU 156561) or kynurenate. Only the latter two treatments, but not L-kynurenine or PNU 156561 alone, caused substantial inhibition of evoked responses in area CA1, and only prolonged (3h) infusion of (L-kynurenine+PNU 156561) or kynurenate was neuroprotective. Biochemical analyses in separate animals revealed that the levels of kynurenate attained in both blood and brain (hippocampus) were essentially identical in rats receiving extended infusions of L-kynurenine alone or (L-kynurenine+PNU 156561) (4 and 7microM, respectively, after an infusion of 90 or 180min). However, addition of the kynurenine 3-hydroxylase inhibitor resulted in a significant decrement in the formation of 3-hydroxykynurenine and quinolinate in both blood and brain. These data suggest that the ratio between kynurenate and 3-hydroxykynurenine and/or quinolinate in the brain is a critical determinant of neuronal excitability and viability. The anticonvulsant and neuroprotective potency of kynurenine 3-hydroxylase inhibitors may therefore be due to the drugs' dual action on both branches of the kynurenine pathway of tryptophan degradation.

Improved survival after boron neutron capture therapy of brain tumors by Cereport-mediated blood-brain barrier modulation to enhance delivery of boronophenylalanine

OBJECTIVE

Cereport (Alkermes, Inc., Cambridge, MA), or, as it has been previously called, RMP-7 (receptor-mediated permeabilizer-7), is a bradykinin analog that has been shown to produce a transient, pharmacologically mediated opening of the blood-brain barrier. The purpose of the present study was to determine whether the efficacy of boron neutron capture therapy (BNCT) could be enhanced by means of intracarotid (i.c.) infusion of Cereport, in combination with intravenous (i.v.) injection or i.c. infusion of boronophenylalanine (BPA) in the F98 rat glioma model.

METHODS

For biodistribution studies, Fischer rats bearing intracerebral implants of the F98 glioma received i.v. or i.c. injections of 300 or 500 mg/kg body weight (b.w.) of BPA with or without i.c. infusion of 1.5 microg/kg b.w. of Cereport. For therapy studies, BNCT was initiated 14 days after intracerebral implantation of 10(3) F98 cells. The i.v. or i.c. injection of BPA (500 mg/kg b.w.) was given with or without Cereport, and the animals were irradiated 2.5 hours later at the Brookhaven Medical Research Reactor with a collimated beam of thermal neutrons delivered to the head.

RESULTS

At a BPA dose of 500 mg/kg b.w., tumor boron concentrations (mean +/- standard deviation) were 55.7 +/- 9.6 microg/g with Cereport versus 33.6 +/- 3.9 microg/g without Cereport at 2.5 hours after i.c. infusion of BPA, and concentrations were 29.4 +/- 9.9 microg/g with Cereport versus 15.4 +/- 3.5 microg/g without Cereport (P < 0.05) after i.v. injection of BPA. After i.c. administration of BPA and Cereport, the tumor-to-blood ratio was 5.4 +/- 0.6, and the tumor-to-brain ratio was 5.2 +/- 2.4. After BNCT with BPA at a dose of 500 mg/kg, the survival time was 50 +/- 16 days for i.c. administration of BPA with Cereport versus 40 +/- 6 days without Cereport (P = 0.05), 38 +/- 4 days for i.v. administration of BPA with Cereport versus 34 +/- 3 days without Cereport (P = 0.02), 28 +/- 5 days for irradiated controls, and 23 +/- 3 days for untreated controls. Compared with untreated controls, there was a 117% increase in lifespan in rats that received an i.c. infusion of Cereport and then BPA, and an 86% increase in lifespan in rats that received i.c. administration of BPA without Cereport.

CONCLUSION

These studies have established that i.c. administration of Cereport can not only increase tumor uptake of BPA, but also enhance the efficacy of BNCT.

Boron neutron capture therapy of brain tumors: enhanced survival and cure following blood-brain barrier disruption and intracarotid injection of sodium borocaptate and boronophenylalanine

PURPOSE

Boronophenylalanine (BPA) and sodium borocaptate (Na(2)B(12)H(11)SH or BSH) have been used clinically for boron neutron capture therapy (BNCT) of high-grade gliomas. These drugs appear to concentrate in tumors by different mechanisms and may target different subpopulations of glioma cells. The purpose of the present study was to determine if the efficacy of BNCT could be further improved in F98-glioma-bearing rats by administering both boron compounds together and by improving their delivery by means of intracarotid (i.c.) injection with or without blood-brain barrier disruption (BBB-D).

METHODS AND MATERIALS

For biodistribution studies, 10(5) F98 glioma cells were implanted stereotactically into the brains of syngeneic Fischer rats. Eleven to 13 days later animals were injected intravenously (i.v.) with BPA at doses of either 250 or 500 mg/kg body weight (b.w.) in combination with BSH at doses of either 30 or 60 mg/kg b.w. or i.c. with or without BBB-D, which was accomplished by i.c. infusion of a hyperosmotic (25%) solution of mannitol. For BNCT studies, 10(3) F98 glioma cells were implanted intracerebrally, and 14 days later animals were transported to the Brookhaven National Laboratory (BNL). They received BPA (250 mg/kg b.w.) in combination with BSH (30 mg/kg b.w. ) by i.v. or i.c. injection with or without BBB-D, and 2.5 hours later they were irradiated with a collimated beam of thermal neutrons at the BNL Medical Research Reactor.

RESULTS

The mean tumor boron concentration +/- standard deviation (SD) at 2.5 hours after i. c. injection of BPA (250 mg/kg b.w.) and BSH (30 mg/kg b.w.) was 56. 3 +/- 37.8 microgram/g with BBB-D compared to 20.8 +/- 3.9 microgram/g without BBB-D and 11.2 +/- 1.8 microgram/g after i.v. injection. Doubling the dose of BPA and BSH produced a twofold increase in tumor boron concentrations, but also concomitant increases in normal brain and blood levels, which could have adverse effects. For this reason, the lower boron dose was selected for BNCT studies. The median survival time was 25 days for untreated control rats, 29 days for irradiated controls, 42 days for rats that received BPA and BSH i.v., 53 days following i.c. injection, and 72 days following i.c. injection + BBB-D with subsets of long-term survivors and/or cured animals in the latter two groups. No histopathologic evidence of residual tumor was seen in the brains of cured animals.

CONCLUSIONS

The combination of BPA and BSH, administered i.c. with BBB-D, yielded a 25% cure rate for the heretofore incurable F98 rat glioma with minimal late radiation-induced brain damage. These results demonstrate that using a combination of boron agents and optimizing their delivery can dramatically improve the efficacy of BNCT in glioma-bearing rats.

Preoperative antibiotics and steroids in vestibular schwannoma excision

OBJECTIVE

To examine the benefits of preoperative admission for intravenous steroids and antibiotics for patients undergoing vestibular schwannoma excision.

STUDY DESIGN

Retrospective cohort study.

METHODS

One hundred twenty patients with pathologically confirmed vestibular schwannoma followed for at least 1 year after surgery were included. Sixty patients were assigned to the preoperative admission group and 60 patients to the same-day-admission surgery group. The preoperative admission group was given intravenous dexamethasone (0.1 mg/kg) and intravenous cefazolin (1 g) beginning 12 hours before surgery. The same-day-surgery group received the same dosage of medication beginning at induction of anesthesia.

OUTCOMES

Facial nerve function, meningitis, and wound infection rates, duration of hospital stay, and readmission rates were examined.

RESULTS

There was no statistical difference in facial nerve function between the groups when controlling for tumor size. Likewise, there was no difference in meningitis or wound infection rates in the groups. As expected, hospital stay was significantly reduced but readmission rates were not affected.

CONCLUSIONS

There are no apparent facial nerve function or infection control benefits to 1-day preoperative admission for intravenous steroids and antibiotics for patients undergoing vestibular schwannoma excision.

Actions of brain-derived neurotrophic factor in slices from rats with spontaneous seizures and mossy fiber sprouting in the dentate gyrus

This study examined the acute actions of brain-derived neurotrophic factor (BDNF) in the rat dentate gyrus after seizures, because previous studies have shown that BDNF has acute effects on dentate granule cell synaptic transmission, and other studies have demonstrated that BDNF expression increases in granule cells after seizures. Pilocarpine-treated rats were studied because they not only have seizures and increased BDNF expression in granule cells, but they also have reorganization of granule cell "mossy fiber" axons. This reorganization, referred to as "sprouting," involves collaterals that grow into novel areas, i.e., the inner molecular layer, where granule cell and interneuron dendrites are located. Thus, this animal model allowed us to address the effects of BDNF in the dentate gyrus after seizures, as well as the actions of BDNF on mossy fiber transmission after reorganization. In slices with sprouting, BDNF bath application enhanced responses recorded in the inner molecular layer to mossy fiber stimulation. Spontaneous bursts of granule cells occurred, and these were apparently generated at the site of the sprouted axon plexus. These effects were not accompanied by major changes in perforant path-evoked responses or paired-pulse inhibition, occurred only after prolonged (30-60 min) exposure to BDNF, and were blocked by K252a. The results suggest a preferential action of BDNF at mossy fiber synapses, even after substantial changes in the dentate gyrus network. Moreover, the results suggest that activation of trkB receptors could contribute to the hyperexcitability observed in animals with sprouting. Because human granule cells also express increased BDNF mRNA after seizures, and sprouting can occur in temporal lobe epileptics, the results may have implications for understanding temporal lobe epilepsy.

Kindled seizures activate both branches of the autonomic nervous system

Amygdaloid kindled seizures in the rat induce an abrupt elevation of blood pressure accompanied by a significant decrease in heart rate. The autonomic pharmacology of this response was examined in unanesthetized kindled rats. Muscarinic receptor blockade with atropine (1 mg/kg, intravenous (i.v.)) abolished the seizure-induced bradycardia. The seizure-induced hypertension was unaffected by beta-adrenergic blockade with timolol (1 mg/kg, i.v.), but was reduced by phentolamine (5 mg/kg, subcutaneous (s.c.)), an alpha-adrenergic receptor antagonist. A chemical sympathectomy was induced with 6-hydroxydopamine (100 mg/kg, i.v.), an agent that does not cross the blood-brain barrier. This eliminated the pressor response but did not completely block the seizure-induced bradycardia. The effectiveness of 6-hydroxydopamine was tested with tyramine (0.5 mg/kg, i.v.) an agent that releases endogenous catecholamines. These results indicate amygdaloid kindled seizures activate both branches of the autonomic nervous system. The bradycardia was mediated by the parasympathetic system; the pressor response was caused by an increase in peripheral resistance due to alpha-adrenergic receptor activation. More important, these findings show that kindling is a useful seizure model for future studies on the effect of seizures on cardiovascular function and possible mechanisms of seizure-related sudden unexplained death.

Boron neutron capture therapy of brain tumors: an emerging therapeutic modality

Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when boron-10, a stable isotope, is irradiated with low-energy thermal neutrons to yield alpha particles and recoiling lithium-7 nuclei. For BNCT to be successful, a large number of 10B atoms must be localized on or preferably within neoplastic cells, and a sufficient number of thermal neutrons must be absorbed by the 10B atoms to sustain a lethal 10B (n, alpha) lithium-7 reaction. There is a growing interest in using BNCT in combination with surgery to treat patients with high-grade gliomas and possibly metastatic brain tumors. The present review covers the biological and radiobiological considerations on which BNCT is based, boron-containing low- and high-molecular weight delivery agents, neutron sources, clinical studies, and future areas of research. Two boron compounds currently are being used clinically, sodium borocaptate and boronophenylalanine, and a number of new delivery agents are under investigation, including boronated porphyrins, nucleosides, amino acids, polyamines, monoclonal and bispecific antibodies, liposomes, and epidermal growth factor. These are discussed, as is optimization of their delivery. Nuclear reactors currently are the only source of neutrons for BNCT, and the fission reaction within the core produces a mixture of lower energy thermal and epithermal neutrons, fast or high-energy neutrons, and gamma-rays. Although thermal neutron beams have been used clinically in Japan to treat patients with brain tumors and cutaneous melanomas, epithermal neutron beams now are being used in the United States and Europe because of their superior tissue-penetrating properties. Currently, there are clinical trials in progress in the United States, Europe, and Japan using a combination of debulking surgery and then BNCT to treat patients with glioblastomas. The American and European studies are Phase I trials using boronophenylalanine and sodium borocaptate, respectively, as capture agents, and the Japanese trial is a Phase II study. Boron compound and neutron dose escalation studies are planned, and these could lead to Phase II and possibly to randomized Phase III clinical trials that should provide data regarding therapeutic efficacy.

Enhanced delivery of boronophenylalanine for neutron capture therapy of brain tumors using the bradykinin analog Cereport (Receptor-Mediated Permeabilizer-7)

OBJECTIVE

Using the well-characterized F98 rat glioma model, the purpose of the present study was to determine whether the delivery of boronophenylalanine (BPA) could be enhanced by prior administration of the bradykinin analog Cereport (Alkermes, Inc., Cambridge, MA) (previously known as Receptor-Mediated Permeabilizer-7), which produces a transient, pharmacologically mediated opening of the blood-brain barrier.

METHODS

Two series of experiments were performed in F98 glioma-bearing rats that had received either intracarotid (i.c.) or intravenous infusions of Cereport (at doses ranging from 1.5 to 7.5 microg/kg of body weight), followed by i.c. (or intravenous) injection of BPA (300 mg/kg of body weight). Animals were killed 0.5, 2.5, or 4 hours later, samples of blood, skin, muscle, and eye were obtained, brains were removed, and tumors were excised for boron determination by direct current plasma-atomic emission spectroscopy.

RESULTS

Averaged over all time points, i.c. infusion of Cereport significantly enhanced tumor boron uptake (P = 0.0001), compared with the excipient (saline) control values. Tumor boron values were equivalent at 0.5 (36.0 microg/g) and 2.5 hours (38.5 microg/g) after i.c. administration of Cereport and BPA and then decreased by 33% (to 25.7 microg/g) at 4 hours. These tumor boron uptake values were significantly different (alpha = 0.05), compared with values measured at the corresponding times after i.c. administration of BPA without Cereport (22.6, 21.8, and 15.3 microg/g, respectively). Although no time-related effects were observed, i.c. administration of Cereport followed by intravenous administration of BPA also significantly enhanced (alpha = 0.05) tumor boron uptake at 0.5, 2.5, and 4 hours (27.4, 30.3, and 28.0 microg/g, respectively), compared with values obtained without Cereport (11.3, 13.4, and 15.2 microg/g, respectively). Boron levels in normal brain tissue from tumor-bearing and non-tumor-bearing cerebral hemispheres and in blood were not significantly different from those measured in saline-treated control animals.

CONCLUSION

This study established that i.c. infusion of Cereport significantly increased delivery of BPA to F98 rat gliomas, and this could enhance the efficacy of boron neutron capture therapy of this tumor.

Chronic changes in synaptic responses of entorhinal and hippocampal neurons after amino-oxyacetic acid (AOAA)-induced entorhinal cortical neuron loss

Chronic changes in synaptic responses of entorhinal and hippocampal neurons after amino-oxyacetic acid (AOAA)-induced entorhinal neuron loss. J. Neurophysiol. 80: 3031-3046, 1998. Synaptic responses of entorhinal cortical and hippocampal neurons were examined in vivo and in vitro, 1 mo to 1.5 yr after a unilateral entorhinal lesion caused by a focal injection of amino-oxyacetic acid (AOAA). It has been shown previously that injection of AOAA into the medial entorhinal cortex produces cell loss in layer III preferentially. Although behavioral seizures stopped approximately 2 h after AOAA treatment, abnormal evoked responses were recorded as long as 1.5 yr later in the entorhinal cortex and hippocampus. In the majority of slices from AOAA-treated rats, responses recorded in the superficial layers of the medial entorhinal cortex to white matter, presubiculum, or parasubiculum stimulation were abnormal. Extracellularly recorded responses to white matter stimulation were prolonged and repetitive in the superficial layers. Intracellular recordings showed that residual principal cells in superficial layers produced prolonged, repetitive excitatory postsynaptic potentials (EPSPs) and discharges in response to white matter stimulation compared with brief EPSPs and a single discharge in controls. Responses of deep layer neurons of AOAA-treated rats did not differ from controls in their initial synaptic response. However, in a some of these neurons, additional periods of excitatory activity occurred after a delay. Abnormal responses were recorded from slices ipsilateral as well as contralateral to the lesioned hemisphere. Recordings from the entorhinal cortex in vivo were abnormal also, as demonstrated by prolonged and repetitive responses to stimulation of the area CA1/subiculum border. Evoked responses of hippocampal neurons, recorded in vitro or in vivo, demonstrated abnormalities in selected pathways, such as responses of CA3 neurons to hilar stimulation in vitro. There was a deficit in the duration of potentiation of CA1 population spikes in response to repetitive CA3 stimulation in AOAA-treated rats. Theta activity was reduced in amplitude in area CA1 and the dentate gyrus of AOAA-treated rats, although evoked responses to angular bundle stimulation could not be distinguished from controls. The results demonstrate that a preferential lesion of layer III of the entorhinal cortex produces a long-lasting change in evoked and spontaneous activity in parts of the entorhinal cortex and hippocampus. Given the similarity of the lesion produced by AOAA and entorhinal lesions in temporal lobe epileptics, these data support the hypothesis that preferential damage to the entorhinal cortex contributes to long-lasting changes in excitability, which could be relevant to the etiology of temporal lobe epilepsy.

Effects of central and peripheral administration of kynurenic acid on hippocampal evoked responses in vivo and in vitro

Kynurenic acid is an excitatory amino acid antagonist with preferential activity at the N-methyl-D-aspartate subtype of glutamate receptors. It is produced endogenously in the brain, but is synthesized more effectively in the periphery. The influence of peripheral kynurenic acid on brain function is unclear because kynurenic acid is likely to penetrate the blood-brain barrier poorly. To determine the potential central effects of peripheral kynurenic acid, we compared its effects in the hippocampus after peripheral or direct administration. The hippocampus of the rat was chosen as a test system because this region receives glutamatergic inputs, and because responses to stimulation of these inputs can be compared after peripheral drug administration in vivo, and after direct administration of drugs in vitro. Peripherally-administered kynurenic acid was injected via a catheter in the jugular vein. Bath-application to hippocampal slices was used to test effects of direct administration. Area CA1 pyramidal cells and dentate gyrus granule cells were examined by extracellular recording and stimulation of area CA3 or the perforant path, respectively. Pairs of identical stimuli were used to assess paired-pulse inhibition and paired-pulse facilitation. Kynurenic acid decreased evoked responses in area CA1 and the dentate gyrus, both in vivo and in vitro. Effective concentrations were in the low micromolar range, and therefore were likely to be mediated by antagonism of N-methyl-D-aspartate receptors. In both preparations, area CA1 was more sensitive than the dentate gyrus, and paired-pulse facilitation was affected, but not paired-pulse inhibition. Control solutions had no effect. We conclude that kynurenic acid can enter the brain after peripheral administration, and that peripheral and direct effects in the hippocampus are qualitatively similar. Therefore, we predict that effects of endogenous kynurenic acid that was synthesized peripherally or centrally would be similar. Furthermore, the results suggest that modulation of the glycine site of the N-methyl-D-aspartate receptor, for example by kynurenic acid, may vary considerably among different brain areas.

Middle fossa transpetrosal approach for petroclival and brainstem tumors

OBJECTIVE

The purpose of the study was to demonstrate the utility of the middle fossa transpetrosal approach with anterior petrosectomy for difficult-to-access petroclival and pontine lesions.

STUDY DESIGN

Retrospective case review in academic tertiary referral center.

METHODS

Patients for inclusion had pontine and prepontine lesions of the petroclival region. Middle fossa transpetrosal approach with anterior petrosectomy with excision or biopsy of the lesion was performed. The main outcome measure was postoperative neurologic status including motor and cranial nerve function.

RESULTS

No patient experienced neuromuscular compromise or cranial nerve deficits as a direct result of the surgical procedure. Complications consisted of a subdural temporal lobe hemorrhage and one case of cerebrospinal fluid rhinorrhea.

CONCLUSIONS

The middle fossa transpetrosal approach with anterior petrosectomy was utilized for five patients with petroclival or pontine tumors. In this small series, it served well to spare cranial nerves and allowed avoidance of serious vascular injury. To our knowledge, this is the first reported use of this procedure for pontine venous angiomas.

Interpretive risks: the use of the Hopkins Symptom Checklist 90-Revised (SCL 90-R) with brain tumour patients

Patients with brain tumours often report distress. Interpretive problems ensue when measures normed on healthy persons are utilized to quantify distress. This study investigated potentially spurious elevations on the Hopkins Symptom Checklist 90 Revised (SCL 90-R). Responses of 17 patients were obtained prior to aggressive chemotherapy. Traditional interpretation indicated that 47% of the patients endorsed clinical levels of somatization, 53% obsessive-compulsive and 59% psychotic disorders. Elevations were attributable to common consequences of brain tumours, medication and the emotional reaction to prognosis. Conventional interpretation would lead to inappropriate classifications. The majority of SCL 90-R item endorsements were significantly different than those of the norm group. Appropriate interpretation of scores is discussed.

Maxillary removal and reinsertion for anterior cranial base tumors: long-term results

OBJECTIVE

To evaluate complications and sequelae of maxillary removal and reinsertion for anterior cranial base tumors.

DESIGN

A retrospective review of patients who underwent maxillary removal and reinsertion from 1990 to 1996.

SETTING

The Arthur G. James Cancer Hospital and Research Institute at The Ohio State University, Columbus.

PATIENTS

A consecutive sample of 46 patients who underwent maxillary removal and reinsertion. The patients ranged in age from 11 to 77 years and were followed up for as long as 6 years after surgery. There were 16 benign and 30 malignant lesions.

MAIN OUTCOME MEASURES

Intraoperative, postoperative (1-10 days), short-term (11 days through 3 months), and long-term (>3 months) complications; survival status of patients; and adjuvant therapy.

RESULTS

Four patients (9%) had undergone previous radiotherapy; 9 (20%) received intraoperative radiation therapy; and 23 (50%) received planned postoperative radiotherapy. No intraoperative complications were noted. The most common short-term complication found was transient diplopia, affecting 9 patients (20%). Diplopia resolved within 3 months in all but 2 patients, in whom the condition was permanent. There were 4 patients (9%) who required removal of the nasal dorsum plate, and 4 (9%) who required removal of maxillary plates that were exposed intranasally. Midface asymmetry as reported by the patient or noted on the physical examination was documented in only 2 patients. The most common long-term complication was nasal asymmetry, affecting 13 patients (28%).

CONCLUSIONS

Maxillary removal allows improved visualization and access to anterior skull base lesions, while reinsertion of the maxillary fragment provides functional preservation and excellent cosmesis with few short- or long-term complications, even when adjuvant radiotherapy is used.

The rationale and requirements for the development of boron neutron capture therapy of brain tumors

The dismal clinical results in the treatment of glioblastoma multiforme despite aggressive surgery, conventional radiotherapy, and chemotherapy, either alone or in combination has led to the development of alternative therapeutic modalities. Among these is boron neutron capture therapy (BNCT). This binary system is based upon two key requirements: (1) the development and use of neutron beams from nuclear reactors or other sources with the capability for delivering high fluxes of thermal neutrons at depths sufficient to reach all tumor foci, and (2) the development and synthesis of boron compounds that can penetrate the normal bloodbrain barrier, selectively target neoplastic cells, and persist therein for suitable periods of time prior to irradiation. The earlier clinical failures with BNCT related directly to the lack of tissue penetration by neutron beams and to boron compounds that showed little specificity for and low retention by tumor cells, while attaining high concentrations in blood. Progress has been made both in neutron beam and compound development, but it remains to be determined whether these are sufficient to improve therapeutic outcomes by BNCT in comparison with current therapeutic regimens for the treatment of malignant gliomas.

Enhanced survival of glioma bearing rats following boron neutron capture therapy with blood-brain barrier disruption and intracarotid injection of boronophenylalanine

Boronophenylalanine (BPA) has been used for boron neutron capture therapy (BNCT) of brain tumors in both experimental animals and humans. The purpose of the present study was to determine if the efficacy of BNCT could be enhanced by means of intracarotid (i.c.) injection of BPA with or without blood-brain barrier disruption (BBB-D) and neutron irradiation using a rat brain tumor model. For biodistribution studies, F98 glioma cells were implanted stereotactically into the brains of Fischer rats, and 12 days later BBB-D was carried out by i.c. infusion of 25% mannitol (1.373 mOsmol/ml), followed immediately by i.c. administration of 300, 500 or 800 mg of BPA/kg body weight (b.w.). At the 500 mg dose a fourfold increase in tumor boron concentration (94.5 micrograms/g) was seen at 2.5 hours after BBB-D. compared to 20.8 micrograms/g in i.v. injected animals. The best composite tumor to normal tissue ratios were observed at 2.5 hours after BBB-D, at which time the tumor: blood (T: Bl) ratio was 10.9, and the tumor: brain (T:Br) ratio was 7.5, compared to 3.2 and 5.0 respectively for i.v. injected rats. In contrast, animals that had received i.c. BPA without BBB-D had T : Bl and T:Br ratios of 8.5 and 5.9, respectively, and the tumor boron concentration was 42.7 micrograms/g. For therapy experiments, initiated 14 days after intracerebral implantation of F98 glioma cells, 500 mg/kg b.w. of BPA were administered i.v. or i.c. with or without BBB-D, and the animals were irradiated 2.5 hours later at the Brook-haven Medical Research Reactor with a collimated beam of thermal neutrons delivered to the head. The mean survival time for untreated control rats was 24 +/- 3 days, 30 +/- 2 days for irradiate controls, 37 +/- 3 days for those receiving i.v. BPA, 52 +/- 15 days for rats receiving i.c. BPA without BBB-D, and 95 +/- 95 days for BBB-D followed by i.c. BPA and BNCT. The latter group had a 246% increase in life span (ILS) compared to untreated controls and a 124% ILS compared to that of i.v. injected animals. These survival data are the best ever obtained with the F98 glioma model and suggest that i.c. administration of BPA with or without BBB-D may be useful as a means to increase the efficacy of BNCT.

Boron neutron capture therapy of brain tumors: enhanced survival following intracarotid injection of either sodium borocaptate or boronophenylalanine with or without blood-brain barrier disruption

The purpose of the present study was to determine whether the efficacy of boron neutron capture therapy could be enhanced by means of intracarotid (i.c.) injection of sodium borocaptate (BSH) or boronophenylalanine (BPA) with or without blood-brain barrier disruption (BBB-D). For biodistribution studies, F98 glioma-bearing rats were injected i.v. or i.c. with either BSH (30 mg of boron/kg of body weight) or BPA (24 mg of boron/kg of body weight) with or without mannitol-induced, hyperosmotic BBB-D and killed 2.5 h later. The highest tumor boron concentrations for BSH and BPA were attained following i.c. injection with BBB-D (48.6 and 94.0 microg/g, respectively) compared to i.c. (30.8 and 42.7 microg/g) and i.v. injection (12.9 and 20.8 microg). Using the same doses of BSH and BPA, therapy experiments were initiated 14 days after intracerebral implantation of F98 glioma cells. Animals were irradiated 2.5 h after i.v. or i.c. administration of the capture agent with or without BBB-D using a collimated beam of thermal neutrons at the Brookhaven Medical Research Reactor. The median survival times of rats given BSH or BPA i.c. were 52 and 69 days, respectively, for rats with BBB-D; 39 and 48 days for rats without BBB-D; 33 and 37 days for i.v. injected rats; 29 days for irradiated controls; and 24 days for untreated controls. i.c. injection of either BSH or BPA resulted in highly significant enhancement (P = 0.01 and P = 0.0002, respectively) of survival times compared to i.v. injection, and this was further augmented by BBB-D (P = 0.02 and P = 0.04, respectively) compared to i.c. injection. Normal brain tissue tolerance studies were carried out with non-tumor-bearing rats, which were treated in the same way as tumor-bearing animals. One year after irradiation, the brains of these animals showed only minimal radiation-induced changes in the choroid plexus, but no differences were discernible between irradiated controls and those that had BBB-D followed by i.c. injection of either BSH or BPA. Our data clearly show that the route of administration, as well as BBB-D, can enhance the uptake of BSH and BPA, and, subsequently, the efficacy of boron neutron capture therapy.

Boron neutron capture therapy of brain tumors: enhanced survival following intracarotid injection of sodium borocaptate with or without blood-brain barrier disruption

PURPOSE

Sodium borocaptate (Na2B12H11SH or BSH) has been used clinically for boron neutron capture therapy (BNCT) of patients with primary brain tumors. The purpose of the present study was to determine if tumor uptake of BSH and efficacy of BNCT could be enhanced in F98 glioma-bearing rats by intracarotid (i.c.) injection of the compound with or without blood-brain barrier disruption (BBB-D).

METHODS AND MATERIALS

For biodistribution studies 100,000 F98 glioma cells were implanted stereotactically into the brains of Fischer rats, and 12 days later BBB-D was carried out by i.c. infusion of 25% mannitol, followed immediately thereafter by i.c. injection of BSH (30 mg B/kg body weight). Animals were killed 1, 2.5, and 5 h later, and their brains were removed for boron determination. For BNCT experiments, which were initiated 14 days after intracerebral implantation of 1000 F98 cells, BSH (30 mg B/kg b.wt. was administered intravenously (i.v.) without BBB-D, or i.c. with or without BBB-D. The animals were irradiated 2.5 h later with a collimated beam of thermal neutrons at the Brookhaven National Laboratory Medical Research Reactor.

RESULTS

The mean tumor boron concentration after i.c. injection with BBB-D was 48.6 +/- 17.2 microg/g at 2.5 h compared with 30.8 +/- 12.2 microg/g after i.c. injection without BBB-D and 12.9 +/- 4.2 microg/g after i.v. injection. The best composite tumor to normal tissue ratios were observed at 2.5 h after BBB-D, at which time the tumor:blood (T:B1) ratio was 5.0, and the tumor: brain (T:Br) ratio was 12.3, compared to 1.1 and 4.6, respectively, in i.v. injected rats. The mean survival time for untreated control rats was 24 +/- 3 days, 29 +/- 4 days for irradiated controls, 33 +/- 6 days for those receiving i.v. injection of BSH, 40 +/- 8 days for rats receiving i.c. BSH without BBB-D, and 52 +/- 13 days for BBB-D followed by BNCT (p = 0.003 vs. i.v. injected BSH).

CONCLUSIONS

Intracarotid administration of BSH with or without BBB-D significantly increased tumor uptake of BSH and enhanced survival of F98 glioma-bearing rats following BNCT. BBB-D may be a useful way to enhance the delivery of both low and high molecular weight boron compounds to brain tumors. Further studies are in progress to assess this approach with other boron delivery agents.

Basal expression and induction of glutamate decarboxylase and GABA in excitatory granule cells of the rat and monkey hippocampal dentate gyrus

The excitatory, glutamatergic granule cells of the hippocampal dentate gyrus are presumed to play central roles in normal learning and memory, and in the genesis of spontaneous seizure discharges that originate within the temporal lobe. In localizing the two GABA-producing forms of glutamate decarboxylase (GAD65 and GAD67) in the normal hippocampus as a prelude to experimental epilepsy studies, we unexpectedly discovered that, in addition to its presence in hippocampal nonprincipal cells, GAD67-like immunoreactivity (LI) was present in the excitatory axons (the mossy fibers) of normal dentate granule cells of rats, mice, and the monkey Macaca nemestrina. Using improved immunocytochemical methods, we were also able to detect GABA-LI in normal granule cell somata and processes. Conversely, GAD65-LI was undetectable in normal granule cells. Perforant pathway stimulation for 24 hours, which evoked population spikes and epileptiform discharges in both dentate granule cells and hippocampal pyramidal neurons, induced GAD65-, GAD67-, and GABA-LI only in granule cells. Despite prolonged excitation, normally GAD- and GABA-negative dentate hilar neurons and hippocampal pyramidal cells remained immunonegative. Induced granule cell GAD65-, GAD67-, and GABA-LI remained elevated above control immunoreactivity for at least 4 days after the end of stimulation. Pre-embedding immunocytochemical electron microscopy confirmed that GAD67- and GABA-LI were induced selectively within granule cells; granule cell layer glia and endothelial cells were GAD- and GABA-immunonegative. In situ hybridization after stimulation revealed a similarly selective induction of GAD65 and GAD67 mRNA in dentate granule cells. Neurochemical analysis of the microdissected dentate gyrus and area CA1 determined whether changes in GAD- and GABA-LI reflect changes in the concentrations of chemically identified GAD and GABA. Stimulation for 24 hours increased GAD67 and GABA concentrations sixfold in the dentate gyrus, and decreased the concentrations of the GABA precursors glutamate and glutamine. No significant change in GAD65 concentration was detected in the microdissected dentate gyrus despite the induction of GAD65-LI. The concentrations of GAD65, GAD67, GABA, glutamate and glutamine in area CA1 were not significantly different from control concentrations. These results indicate that dentate granule cells normally contain two "fast-acting" amino acid neurotransmitters, one excitatory and one inhibitory, and may therefore produce both excitatory and inhibitory effects. Although the physiological role of granule cell GABA is unknown, the discovery of both basal and activity-dependent GAD and GABA expression in glutamatergic dentate granule cells may have fundamental implications for physiological plasticity presumed to underlie normal learning and memory. Furthermore, the induction of granule cell GAD and GABA by afferent excitation may constitute a mechanism by which epileptic seizures trigger compensatory interictal network inhibition or GABA-mediated neurotrophic effects.