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.

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.

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.

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.

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.

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.

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.

Enhanced delivery of boronophenylalanine for neutron capture therapy by means of intracarotid injection and blood-brain barrier disruption

There has been increasing interest in the possible use of boronophenylalanine as a capture agent for boron neutron capture therapy of brain tumors. The purpose of the present study was to determine whether the uptake of boronophenylalanine in F98 glioma-bearing rats could be enhanced by means of intracarotid (i.c.) injection with or without blood-brain barrier disruption (BBB-D). Glioma cells (10(5)) were stereotactically implanted into the right cerebral hemisphere of Fischer rats, and 12 days later, BBB-D was performed by infusing 25% mannitol (1.373 mOsmol/ml) into the right carotid artery and then immediately injecting L-boronophenylalanine (300 mg/kg of body weight) intracarotidly. The animals were killed 0.5, 1, 2.5, and 4 hours later, and the brains were removed for boron determination by direct current plasma atomic emission spectroscopy. BBB-D was assessed by the intravenous injection of Evans blue or horseradish peroxidase, and the barrier-disrupted hemispheres and tumors showed intense staining with each. The mean tumor boron concentration after i.c. injection and BBB-D was 34.8 +/- 6.8 micrograms/g at 2.5 hours compared with 20.3 +/- 6.2 micrograms/g after i.c. injection without BBB-D and 10.7 +/- 0.7 micrograms/g after intravenous injection. No significant differences in boron concentration in muscle, skin, and eye were observed among the different groups. Boron concentrations in the ipsilateral, disrupted hemisphere increased transiently but rapidly returned to background levels by 2.5 hours after BBB-D. The tumor:brain and tumor:blood ratios were 5.2 and 5.6, respectively, compared to 3.2 and 2.1 for intravenous injection groups at 2.5 hours. The present study is the first to show that BBB-D combined with i.c. injection can enhance the tumor uptake of boron compounds for boron neutron capture therapy.

Apoptosis and necrosis induced in different hippocampal neuron populations by repetitive perforant path stimulation in the rat

Patients experiencing spontaneous seizures of temporal lobe origin often exhibit a shrunken hippocampus, which results from the loss of dentate granule cells, hilar neurons, and hippocampal pyramidal cells. Although experimental attempts to replicate the human pattern of hippocampal sclerosis in animals indicate that prolonged seizures cause prominent injury to dentate hilar neurons and hippocampal pyramidal cells, dentate granule cells of animals are generally regarded as relatively resistant to seizure-induced injury. By evaluating pathology shortly after hippocampal seizure discharges were induced electrically, we discovered that some granule cells are highly vulnerable to prolonged excitation and that they exhibit acute degenerative features distinct from those of other vulnerable cell populations. Intermittent perforant path stimulation for 24 hours induced acute degeneration of dentate granule cells, dentate hilar neurons, and hippocampal pyramidal cells. However, stimulation for 8 hours, which was insufficient to injure hilar neurons and hippocampal pyramidal cells, was nonetheless sufficient to induce bilateral granule cell degeneration. Degenerating granule cells were consistently more numerous in the infrapyramidal than the suprapyramidal blade, and were consistently more numerous in the rostral than caudal dentate gyrus. Depending on the nature of the insult, acutely degenerating neurons exhibit distinct morphological features that are classifiable as either apoptosis or necrosis, although the degree of possible overlap is unknown. Light and electron microscopic analysis of the acute pathology caused by prolonged afferent stimulation revealed that degenerating hilar neurons and pyramidal cells exhibited the morphological features of necrosis, which is characterized in part by early cytoplasmic vacuolization before nuclear changes occur. However, acutely degenerating granule cells exhibited the clearly distinct morphological features of apoptosis, which include an early coalescence of nuclear chromatin into multiple nuclear bodies, compaction of the cytoplasm, cell shrinkage, and budding-off of 'apoptotic bodies' that are engulfed by glia. Whereas pyramidal cell debris persisted for months, granule cell debris disappeared rapidly. This observation may explain why significant granule cell vulnerability has not been described previously. These data document for the first time that dentate granule cells are among the cell types most vulnerable to seizure-induced injury, and demonstrate that whereas hilar neurons and pyramidal cells undergo a typically necrotic degenerative process, granule cells simultaneously exhibit morphological features that more closely resemble the degenerative process of apoptosis. This finding implies that the type of cell death induced by excessive excitation may be determined postsynaptically by the way in which different target cells 'interpret' an excitatory insult. This experimental model may be useful for identifying the biochemical mechanisms that initiate and mediate neuronal apoptosis and necrosis, and for developing strategies to prevent or induce these presumably distinct forms of neuronal death.

Selective modulation of elements of the immune system by low molecular weight nucleosides

To optimally modulate a system as complex as the immune system, one must ultimately control its elements individually. Up to this time, use of polyclonal immune stimulants has necessarily involved modulation of a block of immune functions, frequently including undesired activities as well as the activity of interest. We now report selective modulation of individual elements of the immune system by low molecular weight nucleosides, within the context of a fully functional immune system. Loxoribine (7-allyl-8-oxoguanosine) is a well characterized pleiotropic agonist of the immune system in a variety of species, including mouse and humans. In B-cells it binds to soluble cytoplasmic binding proteins, which upregulate transcription upon translocation to the nucleus. By altering specific portions of the loxoribine molecule, multiple distinct, bioactivity profiles have now been obtained. These include: 1) selective augmentation of antibody responses without effects on B-cell proliferation or NK-cell activity; 2) selective enhancement of NK-cell activity and B-cell proliferation in the absence of antibody responses; and 3) selective enhancement of NK-cell activity and antibody responses without B-cell proliferation. Predominant NK-cell responses with minimal B-cell activity of either type also can be generated. The pattern of cytokine mRNA transcription induced is consistent with the spectrum of cellular activities observed. Thus, it is possible to modulate selective activities of the immune system by relatively minor structural modifications of a broad-spectrum immunomodulator in an unseparated cell system.

Adjunctive treatment of cranial base malignacies

The indications for skull base tumor surgery have increased in recent years primarily because of improving surgical techniques and adjunctive treatment modalities. In this article we review current and future adjunctive treatment for cranial base malignancies. Surgically clear tumor margins are often difficult to achieve in skull base surgery because of unacceptable morbidity to surrounding structures. Current phase I and II trials of adjunctive radiation and chemotherapy are discussed. Future advances in radiation therapy and chemotherapy are introduced.

Topology of the loxoribine binding site. Studies with inactive loxoribine analogues

We have previously described a class of immunostimulatory ribonucleoside, exemplified by loxoribine (7-allyl-8-oxoguanosine) and 8-bromoguanosine, that act on cycling B cells to promote nonspecific proliferation and differention, and that synergize with Ag to recruit quiescent Ag-reactive B cells to undergo differentiation and high level Ab production. In murine B cells, two distinct binding activities have been characterized that have dissociation constants that parallel their distinctive dose-response profiles. The SJL mouse strain, which is hypo-responsive to the B cell proliferative properties of these molecules, exhibits a dissociation constant of 10- to 20-fold lower affinity than that of normal murine strains; its Kd for the higher affinity-binding interaction, however, is essentially normal. These observations suggested the existence of two distinct binding activities. Recently, immunoselective subgroups of loxoribine have been described, with an ability to stimulate individual components of the immune response that correlates with specific changes in discrete domains of the nucleoside molecule. By using a panel of nonstimulatory loxoribine analogues as inhibitors, we now report further evidence for the existence of unique sites on loxoribine binding proteins that recognize distinct domains on nucleoside analogues; changes in these regions confer immunologic selectivity. These data confirm the conclusions of previous studies, extend our understanding of the topology of subsites that are otherwise silent, and provide insight into the binding site mediating adjuvanticity. These results allow more profound appreciation of the nature of structural changes that will permit a tighter fit between ligand and binding site, ultimately promoting the design of more potent immunoselective agents.

Topology of the loxoribine binding site. Studies with inactive loxoribine analogues

We have previously described a class of immunostimulatory ribonucleoside, exemplified by loxoribine (7-allyl-8-oxoguanosine) and 8-bromoguanosine, that act on cycling B cells to promote nonspecific proliferation and differention, and that synergize with Ag to recruit quiescent Ag-reactive B cells to undergo differentiation and high level Ab production. In murine B cells, two distinct binding activities have been characterized that have dissociation constants that parallel their distinctive dose-response profiles. The SJL mouse strain, which is hypo-responsive to the B cell proliferative properties of these molecules, exhibits a dissociation constant of 10- to 20-fold lower affinity than that of normal murine strains; its Kd for the higher affinity-binding interaction, however, is essentially normal. These observations suggested the existence of two distinct binding activities. Recently, immunoselective subgroups of loxoribine have been described, with an ability to stimulate individual components of the immune response that correlates with specific changes in discrete domains of the nucleoside molecule. By using a panel of nonstimulatory loxoribine analogues as inhibitors, we now report further evidence for the existence of unique sites on loxoribine binding proteins that recognize distinct domains on nucleoside analogues; changes in these regions confer immunologic selectivity. These data confirm the conclusions of previous studies, extend our understanding of the topology of subsites that are otherwise silent, and provide insight into the binding site mediating adjuvanticity. These results allow more profound appreciation of the nature of structural changes that will permit a tighter fit between ligand and binding site, ultimately promoting the design of more potent immunoselective agents.

Small-molecule immunostimulants. Synthesis and activity of 7,8-disubstituted guanosines and structurally related compounds

A series of 7,8-disubstituted guanosine derivatives was designed and prepared as potential B-cell-selective activators of the humoral immune response. These compounds were evaluated for their ability to act as B-cell mitogens and to augment the antibody response of B cells to sheep red blood cell (SRBC) challenge (adjuvanticity). In addition, they were tested for their ability to stimulate the natural killer (NK) cell response in murine in vitro cell assays. Certain of the compounds demonstrated in vivo activity when administered either intravenously, subcutaneously, or orally. Analogues with a medium-length alkyl chain (2-4 carbons, 5-7) on the 7-position of 7-alkyl-8-oxoguanosines were found to be particularly potent. Compounds bearing hydroxyalkyl, aminoalkyl, or substituted aminoalkyl substituents on this 7-position were weakly active. However, benzyl groups, including those substituted with heteroatoms (e.g., p-nitrobenzyl, 14), were active. Oxo, thioxo, and seleno groups on C-8 of the guanosine ring all imparted strong activity, whereas other larger substituents did not (e.g., N = CN). Stereochemical inversion of the 2'-hydroxyl on the ribose ring in this series, giving arabinose analogue 70, lessened activity. However, removal of the 2'-hydroxyl, either with (64) or without (73) removal of the 3'-hydroxyl, resulted in excellent activity and improved solubility; 64 also displayed good oral in vivo activity as well. A series of ketals involving the 2',3'-hydroxyls were prepared; certain of the nonpolar ketals (e.g., 48) were remarkably active, pointing to an ancillary hydrophobic binding region that can augment activity. 5'-Phosphate derivative 57 was fairly active, and acyclovir analogue 90 displayed good NK-selective activity: other N-9 sugar mimetics were also active (97-104), although this activity did not carry over into the human B-cell assay. A total of 80 compounds were prepared and evaluated for their immunostimulating activity. Within this group, compounds could be divided into those that were active in all three assays, those that displayed some measure of selectivity for the adjuvanticity assay, and those that preferentially activated NK responses. Because of its overall biological profile and ease of synthesis, 7-allyl-8-oxoguanosine (6; loxoribine, RWJ-21757) was chosen for further development. It is among the most potent compounds evaluated in the three biological assays.

Cocaine neurotoxicity and altered neuropeptide Y immunoreactivity in the rat hippocampus; a silver degeneration and immunocytochemical study

Neuroanatomical methods were used to determine if cocaine irreversibly injures neurons. Despite acute and chronic high-dose treatments for months that produced stereotyped behavior and seizures, and the use of a sensitive silver impregnation method, we were unable to find any evidence of neuronal damage anywhere in the brain. Since expression of the inducible 72 kDa heat shock protein (HSP72) is a sensitive indicator of potentially toxic neuronal stress, we next determined if cocaine evoked HSP72 expression. Even high doses of cocaine that evoked seizures did not induce HSP72 immunoreactivity anywhere within the brain, whereas kainic acid produced widespread HSP72 immunoreactivity and irreversible injury. Having failed to find indications of frank neurotoxicity, we examined peptide and protein cell marker immunoreactivities in search of cocaine-induced changes. Although cocaine treatment had no obvious effects on the patterns of hippocampal calbindin-D28K, somatostatin-, tyrosine hydroxylase- and parvalbumin immunoreactivities, cocaine reliably altered neuropeptide Y-like immunoreactivity (NPY-LI). Most notably, NPY-LI was expressed in hippocampal dentate granule cells and pyriform cortical neurons, which do not normally express it. Conversely, we noted decreased NPY-LI in dentate hilar neurons that normally do express it. Since both changes in NPY-LI were seen only in cocaine-treated rats that exhibited seizures, the role of seizure activity per se in producing the NPY changes was addressed in normal rats by electrical stimulation of the perforant path. Like cocaine, perforant path stimulation for as little as 15min evoked NPY-LI in granule cells but did not replicate the cocaine-induced decrease in hilar cell NPY-LI. These results suggest that cocaine does not irreversibly injure neurons in the rat, even at doses that induce seizures. However, cocaine produces long-lasting changes in NPY expression that are of unknown functional significance. Our inability to demonstrate cocaine-induced neuronal damage in rats should in no way be taken as evidence of its safety in humans.

Calbindin-D28k immunoreactivity and selective vulnerability to ischemia in the dentate gyrus of the developing rat

Hippocampal dentate granule cells normally express the calcium-binding protein calbindin-D28k and, in the adult, are the hippocampal neurons least vulnerable to an ischemic insult. We evaluated hippocampal structure 2-3 days after hypoxic/ischemic insult at postnatal day 7-10, and discovered that, unlike adult granule cells, developing granule cells were irreversibly injured. Localization of calbindin-D28k-like immunoreactivity (LI) revealed that the vulnerable cells were the immature granule cells at the base of the cell layer that were not yet calbindin-immunoreactive. Adjacent granule cells that did not die in response to the hypoxic/ischemic insult were calbindin-immunoreactive. Whether the lack of calbindin-LI in immature granule cells is causally related to their vulnerability, or is a coincidental reflection of cellular immaturity, remains to be determined.

Maxillary removal and reinsertion for improved access to anterior cranial base tumors

Portions or all of the maxillae are oftentimes removed solely to provide access to certain cranial base tumors rather than because they are involved directly with disease. The purpose of this report is to describe an approach that involves removal of one or both maxillae to improve tumor exposure with subsequent reinsertion as free bone grafts which are stabilized with titanium craniofacial fixation plates. The titanium permits postoperative imaging studies and radiotherapy. Eleven patients ranging from 10 to 69 years of age have undergone 12 operations using this technique for resection of 4 benign and 8 malignant tumors at The Ohio State University. Seven of the 8 patients with malignancies underwent postoperative radiation therapy. There have been no permanent complications and no evidence of bone resorption in this group after follow-up of up to 15 months.

Evidence for commissurally projecting parvalbumin-immunoreactive basket cells in the dentate gyrus of the rat

The fluorescent retrograde tracer, fluorogold, was used to identify commissurally projecting neurons in the hippocampus and dentate gyrus. After injection of fluorogold into the hippocampus, the contralateral hippocampus was evaluated for fluorogold-immunoreactive or fluorescent neurons. In addition to observing labeled hilar neurons and CA3 pyramidal cells that previously have been reported to send commissurally projecting axons to the contralateral hippocampus, the authors unexpectedly found a population of fluorogold-labeled cells in the granule cell layer with the morphology and location of GABA-immunoreactive basket cells. Immunocytochemical staining revealed that all fluorogold-labeled cells of the granule cell layer were immunoreactive for parvalbumin. However, not all parvalbumin cells, shown previously to be a subset of GABA neurons, were fluorogold-labeled. The association between fluorogold transport and parvalbumin immunoreactivity was unique for these cells of the granule cell layer. In the adjacent hilus, relatively few of the many fluorogold-labeled cells were parvalbumin- or GABA-immunoreactive. These results (1) identify a population of presumed inhibitory neurons that apparently form commissural projections; (2) document that all of these cells contain the calcium-binding protein parvalbumin; and (3) indicate that the vast majority of commissurally projecting hilar neurons are neither parvalbumin- nor GABA-immunoreactive.

Inhibition of tumor growth in a glioma model treated with boron neutron capture therapy

This investigation attempts to determine whether increased survival time seen when the F98 glioma model is treated with boron neutron capture therapy (BNCT) is a result of inhibition of tumor growth caused by radiation-induced alterations in endothelial cells and normal tissue components. This indirect effect of radiation has been called the tumor bed effect. A series of tumor-bearing rats was studied, using a standardized investigational BNCT protocol consisting of 50 mg/kg of Na2B12H11SH injected intravenously 14 to 17 hours before neutron irradiation at 4 x 10(12) n/cm2. Ten rats, serving as controls, received no treatment either before or after tumor implantation. A second group of 10 rats was treated with BNCT 4 days before tumor implantation; these animals received no further treatment. The remaining group of 10 rats received no pretreatment but was treated with BNCT 10 days after implantation. Histological and ultrastructural analyses were performed in 2 animals from each group 17 days after implantation. Survival times of the untreated control animals (mean, 25.8 days) did not differ statistically from the survival times of the rats in the pretreated group (mean, 25.5 days). The rats treated with BNCT after implantation survived significantly longer (P less than 0.02; mean, 33.2 days) than the controls and the preirradiated animals. Tumor size indices calculated from measurements taken at the time of death were similar in all groups. These results indicate that, with this tumor model, BNCT does not cause a tumor bed effect in cerebral tissue. The therapeutic gains observed with BNCT result from direct effects on tumor cells or on the peritumoral neovascularity.

Kindled seizures elevate blood pressure and induce cardiac arrhythmias

The effect of kindled seizures on the cardiovascular system was examined in amygdaloid kindled rats. The most prominent cardiovascular response during a generalized kindled seizure was an abrupt 50% increase in mean arterial pressure (MAP) lasting 20-30 s after initiation of the seizure. Superimposed on this change in blood pressure (BP) was a profound bradycardia characterized by a rate about half that recorded before stimulation. Changes in heart rate (HR) and BP observed during amygdaloid kindled seizures were similar to those observed during secondary spontaneous seizures. These effects apparently are independent of the kindling stimulus because stimulus-induced cardiovascular changes were not present at the beginning of the kindling process. These results suggest that the kindling seizure model is useful to study the underlying mechanisms of seizure-induced cardiac arrhythmias and possibly the clinical phenomenon of sudden unexplained death in epileptic patients.

Theoretical basis and clinical methodology for stereotactic interstitial brain tumor irradiation using iododeoxyuridine as a radiation sensitizer and 145Sm as a brachytherapy source

A technique to produce radiation enhancement during interstitial brain tumor irradiation by using a radiation sensitizer (iododeoxyuridine-IdUrd) and by stimulation of Auger electron cascades through absorption of low-energy photons in iodine is described. Clinical studies using iododeoxyuridine, 192Ir as a brachytherapy source, and external radiation have produced promising results. Substituting 145Sm for 192Ir in this protocol is planned to evaluate the enhanced dose resulting from photon activation therapy.

Boron neutron capture therapy of a rat glioma

The purpose of the present study was to utilize a well-established rat glioma to evaluate boron neutron capture therapy for the treatment of malignant brain tumors. Boron-10 (10B) is a stable isotope which, when irradiated with thermal neutrons, produces a capture reaction yielding high linear energy transfer particles (10B + 1nth----[11B]----4He(alpha) + 7Li + 2.79 MeV). The F98 tumor is an anaplastic glioma of CD Fischer rat origin with an aggressive biological behavior similar to that of human glioblastoma multiforme. F98 cells were implanted intracerebrally into the caudate nuclei of Fischer rats. Seven to 12 days later the boron-10-enriched polyhedral borane, Na2B12H11SH, was administered intravenously at a dose of 50 mg/kg body weight at varying time intervals ranging from 3 to 23.5 hours before neutron irradiation. Pharmacokinetic studies revealed blood 10B values ranging from 0.33 to 10.5 micrograms/ml depending upon the time after administration, a T1/2 of 6.2 hours, normal brain 10B concentrations of 0.5 microgram/g, and tumor values ranging from 1.1 to 12.8 micrograms/g. No therapeutic gain was seen if the capture agent was given at 3 or 6 hours before irradiation with 4 x 10(12) n/cm2 (10 MW-min; 429 cGy). A 13.5-hour preirradiation interval resulted in a mean survival of 37.8 days (P less than 0.01), compared to 30.5 days (P less than 0.03) for irradiated controls and 22.1 days for untreated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The surgery of benign and malignant neoplasms adjacent to or involving the skull base

A group of patients who have undergone resection of benign and malignant neoplasms, either adjacent to or through the skull base, were evaluated to determine whether the long-term results justify the risks of such surgery. A total of 37 patients underwent 55 operations in a 6.5-year period from December 1979 to July 1986 at The Ohio State University. An analysis of the operative, perioperative, and long-term complications demonstrates that surgery is well-tolerated. The disease-free interval and survival rates for both benign and malignant neoplasms are encouraging and demonstrate curative potential even for those patients presenting with recurrent malignancies extending through the base of the skull. The interdisciplinary approach evaluated in this study is an effective modality in the treatment of skull base tumors, conferring a favorable risk-benefit ratio.

Ultrastructural microvascular response to boron neutron capture therapy in an experimental model

A CD 344 rat glioma model currently used to investigate boron neutron capture therapy (BNCT) was used to demonstrate an increased survival rate after thermal neutron irradiation enhanced by administration of 10B-enriched polyhedral borane, Na2B12H11SH. To investigate the possible effects of BNCT on normal and tumor microvasculature, we subjected animals to sublethal neutron irradiation with and without intravenous injection of 50 mg/kg of enriched 10B and performed histological and ultrastructural analyses. In the rats that did not undergo tumor transplantation, minimal detectable morphological changes in the microvasculature of the central nervous system were observed after treatment, both in the immediate posttreatment phase and at 10 months. Light microscopy of cerebral cortex and caudate nucleus showed normal cytoarchitecture with no evidence of vessel occlusion, hyalinization, thickening, or reactive gliosis. Electron microscopy demonstrated that the junctional complexes of the endothelial cells, the basal lamina, and the perivascular glia were comparable in both treated and control animals. In those animals examined at 18 months, pathological membrane-bound clusters of electron-dense vesicles were seen in pericytes. In the rats implanted with gliomas, vascular proliferation with evidence of breakdown of the blood-brain barrier and vasogenic edema occurred. In the irradiated animals, we noted increased peritumoral edema 3 days after treatment. At seven days, both increased peritumoral edema and necrosis were noted in the rats treated with BNCT. These observations show that the normal microvasculature of the central nervous system tolerates BNCT at the treatment parameters used in our experimental model; the progressive edema and necrosis found in the peritumoral region after BNCT indicate a pathological endothelial response.

Pre-clinical studies on boron neutron capture therapy

The present report provides an overview of the multidisciplinary research effort on BNCT that currently is in progress at The Ohio State University. Areas under investigation include the preparation of boron containing monoclonal antibodies, the synthesis of boron containing derivatives of promazines and phathalocyanines, the development of a rat model for the treatment of glioblastoma by means of BNCT, the design of an accelerator-based neutron irradiation facility, and 10B concentration measurements using alpha track autoradiographic methods. Progress in each of these areas is described and the direction of future research is indicated.

Endurance of the kindling effect is independent of the degree of generalization

The endurance of the effect of amygdaloid kindling was studied in rats kindled to stages 1-4, then left unstimulated for 45 days prior to resumption of kindling. Afterdischarge duration and behavioral stages upon resumption of kindling revealed retention of the full kindling effect. Endurance of the localized effect of kindling appears to be independent of the degree of generalization prior to interruption of kindling.