Gene modulation in total brain induced by exposure to the bicyclic phosphorus ester trimethylolpropane phosphate (TMPP).

The effect of a single subconvulsive dose of the GABAergic convulsant trimethylolpropane phosphate (TMPP) on gene expression in total rat brain was examined using cDNA array analysis. Using threshold criteria that reduce the number of false positives to <1 gene per 3551 actively transcribed genes on the cDNA array, 41 genes/EST sequences were reproducibly modulated in response to 0.25 mg/kg TMPP. Several genes that were consistent with epileptogenesis and/or neuronal damage and repair mechanisms, such as trkB, alphaB-crystallin, and decorin, were modulated by TMPP exposure in the absence of clinical convulsions. Previous research indicates that rats exposed to subconvulsive doses of TMPP exhibit both "absence-like" EEG paroxysms and persisting central nervous system (CNS) sensitization, as evidenced by increased susceptibility to audiogenic seizures (AGS). Results of this study suggest that cDNA arrays can be used to identify gene modulation events induced by low-level exposure to a chemical convulsant in a reproducible manner.

Effects of repeated exposure to JP-8 jet fuel vapor on learning of simple and difficult operant tasks by rats.

Groups of 16 Sprague-Dawley rats each were exposed by whole-body inhalation methods to JP-8 jet fuel at the highest vapor concentration without formation of aerosol (1,000 +/- 10% mg/m3); to 50% of this concentration (500 +/- 10% mg/m3); or to treated room air (70 +/- 81 L/min) for 6 h/d, 5 d/wk, for 6 wk (180 h). Although two subjects died of apparent kidney complications during the study, no other change in the health status of exposed rats was observed, including rate of weight gain. Following a 65-d period of rest, rats were evaluated for their capacity to learn and perform a series of operant tasks. These tasks ranged in difficulty from learning of a simple food-reinforced lever pressing response, to learning a task in which subjects were required to emit up to four-response chains of pressing three different levers (e.g., press levers C, R, L, then C). It was shown that repeated exposure to 1,000 mg/m3 JP-8 vapor induced significant deficits in acquisition or performance of moderately difficult or difficult tasks, but not simple learning tasks, as compared to those animals exposed to 500 mg/m3. Learning/performance of complex tasks by the 500-mg/m3 exposure group generally exceeded the performance of control animals, while learning by the 1,000-mg/m3 group was nearly always inferior to controls, indicating possible "neurobehavioral" hormesis. These findings appear consistent with some previously reported data for operant performance following acute exposure to certain hydrocarbon constituents of JP-8 (i.e., toluene, xylenes). There has, however, been little previously published research demonstrating long-term learning effects for repeated hydrocarbon fuel exposures. Examination of regional brain tissues from vapor-exposed rats indicated significant changes in levels of dopamine in the cerebral cortex and DOPAC in the brainstem, measured as long as 180 d postexposure, as compared to controls.

Effects of repeated exposure of rats to JP-5 or JP-8 jet fuel vapor on neurobehavioral capacity and neurotransmitter levels.

The U.S. Naval Service is anticipating transition from the nearly exclusive use of JP-5 jet fuel to predominant use of JP-8, consistent with the primary utilization by the U.S. Army, U.S. Air Force, and the militaries of most NATO countries. To compare the relative risk of repeated exposure to JP-5 versus JP-8 vapor, groups of 32 male Sprague-Dawley rats each were exposed for 6 h/d, 5 d/wk for 6 wk (180 h) to JP-8 jet fuel vapor (1,000 +/- 10% mg/m3), IP-5 vapor (1,200 +/- 10% mg/m3), or room air control conditions. Following a 65-d rest period, rats completed 10 tests selected from the Neurobehavioral Toxicity Assessment Battery (NTAB) to evaluate changes in performance capacity. Repeated exposure to JP-5 resulted in significant effects on only one test, forelimb grip strength (FGS), while exposure to JP-8 vapor resulted in a significant difference versus controls on appetitive reinforcer approach sensitization (ARAS). Rats were further evaluated for concentrations of major neurotransmitters and metabolites in five brain regions and in the blood serum. Levels of dopamine, the dopamine metabolite dihydroxyphenylacetic acid (DOPAC), and the serotonin metabolite homovanillic acid (HVA) were significantly modulated in various brain regions, as measured 85+ d postexposure. Similarly, serum levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) were differentially modulated following JP-8 or JP-5 exposure. Results are compared to previously published research evaluating the neurotoxicity of repeated exposure to other hydrocarbon fuels and solvents.

A review of the neurotoxicity risk of selected hydrocarbon fuels.

Over 1.3 million civilian and military personnel are occupationally exposed to hydrocarbon fuels, emphasizing gasoline, jet fuel, diesel fuel, or kerosene. These exposures may occur acutely or chronically to raw fuel, vapor, aerosol, or fuel combustion exhaust by dermal, respiratory inhalation, or oral ingestion routes, and commonly occur concurrently with exposure to other chemicals and stressors. Hydrocarbon fuels are complex mixtures of 150-260+ aliphatic and aromatic hydrocarbon compounds containing varying concentrations of potential neurotoxicants including benzene, n-hexane, toluene, xylenes, naphthalene, and certain n-C9-C12 fractions (n-propylbenzene, trimethylbenzene isomers). Due to their natural petroleum base, the chemical composition of different hydrocarbon fuels is not defined, and the fuels are classified according to broad performance criteria such as flash and boiling points, complicating toxicological comparisons. While hydrocarbon fuel exposures occur typically at concentrations below permissible exposure limits for their constituent chemicals, it is unknown whether additive or synergistic interactions may result in unpredicted neurotoxicity. The inclusion of up to six performance additives in existing fuel formulations presents additional neurotoxicity challenge. Additionally, exposures to hydrocarbon fuels, typically with minimal respiratory or dermal protection, range from weekly fueling of personal automobiles to waist-deep immersion of personnel in raw fuel during maintenance of aircraft fuel tanks. Occupational exposures may occur on a near daily basis for from several months to over 20 yr. A number of published studies have reported acute or persisting neurotoxic effects from acute, subchronic, or chronic exposure of humans or animals to hydrocarbon fuels, or to certain constituent chemicals of these fuels. This review summarizes human and animal studies of hydrocarbon fuel-induced neurotoxicity and neurobehavioral consequences. It is hoped that this review will support ongoing attempts to review and possibly revise exposure standards for hydrocarbon fuels.

Reduction of motor seizures in rats induced by the ethyl bicyclophosphate trimethylolpropane phosphate (TMPP).

1. Trimethylolpropane phosphate (TMPP) is a potent cage convulsant, reported to act through binding to the picrotoxinin and/or benzodiazepine receptor sites of the gamma-aminobutyricA (GABA(A)) ionophore complex. 2. Adult male Fischer-344 rats were pretreated by intraperitoneal (i.p.) injection with either diazepam (DZP) [0.5-5.0 mg/kg], Phenobarbital (PB) [5-20 mg/kg], dizocilpine maleate (MK-801) [0.5-3.0 mg/kg], Tiagabine (TGB) [0.5-5.0 mg/kg], 6,7-dinitro-quinoxaline-2,3-dione (DNQX), [5-20 mg/kg], or scopolamine [SCP] (0.25-1.0 mg/kg) 30 min prior to i.p. injection with a convulsive dose of TMPP (0.6 mg/kg). 3. Rats were rated for occurrence of convulsive activity for 120 min post-injection. Time from TMPP injection to observation of subclinical seizures, generalized (tonic-clonic) seizures, and lethality was rated for each pretreatment group. 4. In general, DZP = PB > TGB in reduction of TMPP subclinical and/or clinical seizures. MK-801, at dose levels inducing near sedation, was also effective in modulation of TMPP-induced seizures. SCP or DNQX were generally ineffective in reducing or eliminating TMPP-induced seizures.

Behavioral sensitization following exposure to low doses of trimethylolpropane phosphate.

Behavioral sensitization is commonly studied within the context of drugs known to directly increase activity in the brain's dopamine system, particularly drugs of abuse. However, the present research suggests such behavioral changes can also be observed following exposure to other compounds that indirectly affect the dopamine system. One such compound is trimethylolpropane phosphate (TMPP), a bridged organophosphate that can be produced by the partial pyrolysis of certain synthetic lubricants used on military ships and aircraft. Although TMPP is a potent convulsant, it has been demonstrated that treatment with doses below seizure threshold results in long-term behavioral sensitization. The effect has been demonstrated with a number of neurobehavioral endpoints, particularly those assessing appetitive responding. More specifically, sensitization has been observed in acquisition of schedule-induced polydipsia (SIP), appetitive reinforcer approach sensitization (ARAS) and social interaction as measured in neonatal ultrasonic vocalizations, juvenile play and adult conspecific approach. Overall, the rats demonstrated a heightened appetitive response pattern. More specifically, TMPP reliably reduced the number of SIP sessions necessary to induce asymptotic drinking level and increased the time spent investigating (sniffing) a food reinforcer as measured in the ARAS task. Specific effects of TMPP on social interaction were an increase in ultrasonic vocalizations when the neonate was isolated from the dam and littermates and an increase in both measures of juvenile play (pins and dorsal contacts). A complex set of interactions emerged for the measures of adult social investigation where the drug effect was modulated by such factors as sex and neutral vs. stress-inducing experiences coincident with the drug treatment. In contrast to the above results, no behavioral changes were recorded for measures in the elevated plus maze and open field exploration. These results suggest that TMPP produces neurophysiological changes that persist much longer than the pharmacological effect of the compound, particularly in the neural correlates for appetitive behavior.

Acute neurobehavioral effects in rats from exposure to HFC 134a or CFC 12.

1,1,1,2-Tetrafluoroethane (HFC 134a), a chlorine-free hydrofluoroalkane, is internationally replacing billions of pounds of dichlorodifluoromethane (CFC 12) for coolant, refrigerant and aerosol propellant applications. The ALC50 for HFC 134a in rats is 567,000 ppm for 4 h; its potential for cardiac epinephrine sensitization in beagle dogs is acceptable (75,000 ppm); and its capacity to induce carcinogenicity or developmental disorders in animals is minimal. HFC 134a, with a serum half life estimated at 4-11 min, has been accepted for use as a propellant in metered-dose inhalant products, implying a low human toxicity risk from periodic brief exposures. There has been little published human or animal research evaluating possible neurobehavioral toxicity from longer HFC 134a exposures, as may be expected to occur in operational scenarios. In this study, male Wistar rats were exposed to various concentrations of HFC 134a or CFC 12 for up to 30 min while performing in either a rotarod/motorized running wheel apparatus or in an operant chamber The relative neurobehavioral toxicity of CFC 12 and its ozone-depleting substance replacement HFC 134a was assessed by comparing both gross motor system incapacitation and more subtle changes in ability to perform an operant discrimination task. It was shown that exposure to HFC 134a or CFC 12 concentrations from 40,000 to 470,000 ppm, for up to 30 min, induced neurobehavioral deficits in every subject, ranging from reduced operant efficiency to apparent anesthesia. For neurobehavioral endpoints examined in these experiments, HFC 134a inhalation was shown to induce deficits more rapidly, and at lower concentrations when compared to CFC 12 exposure.

Trimethylolpropane phosphate induces epileptiform discharges in the CA1 region of the rat hippocampus.

The actions of trimethylolpropane phosphate (TMPP), an ethyl bicyclophosphate convulsant produced during the partial pyrolysis of some phosphate ester-based lubricants, were tested on CA1 neurons of rat hippocampal slices using intracellular recording techniques. Bath application of TMPP (0.1-100 microM) induced spontaneous paroxysmal depolarizing shifts and the associated spontaneous epileptiform bursts followed by after-hyperpolarizations in 63% of neurons tested. The TMPP-induced epileptiform bursts were blocked by muscimol, a gamma-aminobutyric acid A (GABA(A)) receptor agonist, diazepam (DZP), a GABA(A)-benzodiazepine ionophore complex agonist, or baclofen, a GABA(B) receptor agonist. While bath application of muscimol, DZP, or baclofen suppressed spontaneous activity in CA1 neurons not previously exposed to TMPP, subsequent application of TMPP (10 microM) reversed the actions of muscimol and diazepam, but not baclofen. TMPP (0.1-100 microM) also induced membrane hyperpolarization associated with an increase in peak input resistance and inward rectification in 33% of neurons tested or membrane depolarization associated with an increase in input resistance in 17% of neurons tested. In summary, TMPP induced epileptiform activities in hippocampal CA1 neurons. The epileptogenic effects of TMPP are consistent with its interaction with GABA(A)-benzodiazepine receptors.

A review of the effects of uranium and depleted uranium exposure on reproduction and fetal development.

Depleted uranium (DU) is used in armor-penetrating munitions, military vehicle armor, and aircraft, ship and missile counterweighting/ballasting, as well as in a number of other military and commercial applications. Recent combat applications of DU alloy [i.e., Persian Gulf War (PGW) and Kosovo peacekeeping objective] resulted in human acute exposure to DU dust, vapor or aerosol, as well as chronic exposure from tissue embedding of DU shrapnel fragments. DU alloy is 99.8% 238Uranium, and emits approximately 60% of the alpha, beta, and gamma radiation found in natural uranium (4.05 x 10(-7) Ci/g DU alloy). DU is a heavy metal that is 160% more dense than lead and can remain within the body for many years and slowly solubilize. High levels of urinary uranium have been measured in PGW veterans 10 years after exposure to DU fragments and vapors. In rats, there is strong evidence of DU accumulation in tissues including testes, bone, kidneys, and brain. In vitro tests indicate that DU alloy may be both genotoxic and mutagenic, whereas a recent in vivo study suggests that tissue-embedded DU alloy may be carcinogenic in rats. There is limited available data for reproductive and teratological deficits from exposure to uranium per se, typically from oral, respiratory, or dermal exposure routes. Alternatively, there is no data available on the reproductive effects of DU embedded. This paper reviews published studies of reproductive toxicity in humans and animals from uranium or DU exposure, and discusses ongoing animal research to evaluate reproductive effects in male and female rats embedded with DU fragments, and possible consequences in F1 and F2 generations.

Identification of target genes responsive to JP-8 exposure in the rat central nervous system.

Concern for the health risk associated with occupational exposure to jet fuel has emerged in the Department of Defense. Jet propulsion fuel-8 (JP-8) is the fuel used in most US and North Atlantic Treaty Organization (NATO) jet aircraft, and will be the predominant fuel both for military land vehicles and aircraft into the twenty-first century. JP-8 exhibits reduced volatility and lower benzene content as compared to JP-4, the predominant military aircraft fuel before 1992, possibly suggesting greater occupational exposure safety. However, the higher rates of occupational exposure through fueling and maintenance of increasingly larger numbers of aircraft/vehicles raise concerns with respect to toxicity. Clinical studies of workers experiencing long-term exposure to certain jet fuels demonstrated deficits in CNS function, including fatigue, neurobehavioral changes, psychiatric disorders, and abnormal electroencephalogram (EEG). In the present study, cDNA nylon arrays (Atlas Rat 1.2 Array, Clontech Laboratories, Palo Alto, CA) were utilized to measure changes in gene expression in whole brain tissue of rats exposed repeatedly to JP-8, under conditions that simulated possible real-world occupational exposure (6 h/day for 91 days) to JP-8 vapor at 1,000 mg/m3. Gene expression analysis of the exposure group compared to the control group revealed a modulation of several genes, including glutathione S-transferase Yb2 subunit (GST Yb2); cytochrome P450 IIIAl (CYP3A1); glucose-dependent insulinotropic peptide (GIP); alpha1-proteinase inhibitor (alpha1-AT); polyubiquitin; GABA transporter 3 (GAT-3); and plasma membrane Ca2+-transporting ATPase (brain isoform 2) (PMCA2). The implications of these vapor-induced changes in gene expression are discussed.

Toxicity of chemical mixtures: proteomic analysis of persisting liver and kidney protein alterations induced by repeated exposure of rats to JP-8 jet fuel vapor.

Male Sprague-Dawley rats were exposed by whole body inhalation to 1000 mg/m3 +/- 10% JP-8 jet fuel vapor or room air control conditions for 6 h/day, 5 days/week for six consecutive weeks. Following a rest period of 82 days rats were sacrificed, and liver and kidney tissues examined by proteomic methods for both total protein abundance and protein charge modification. Kidney and lung samples were solubilized and separated via large scale, high resolution two-dimensional electrophoresis (2-DE) and gel patterns scanned, digitized and processed for statistical analysis. Through the use of peptide mass fingerprinting, confirmed by sequence tag analysis, three altered proteins were identified and quantified. Numerical, but not significantly different increases were found in total abundance of lamin A (NCBI Accession No. 1346413) in the liver, and of 10-formyltetrahydrofolate dehydrogenase (10-FTHF DH, #1346044) and glutathione-S-transferase (GST; #2393724) in the kidneys of vapor-exposed subjects. Protein charge modification index (CMI) analysis indicated significant alterations (P < 0.001) in expressed lamin A and 10-FTHF DH. These persisting changes in liver and kidney proteins are discussed in terms of possible alterations in the functional capacity of exposed subjects.

Application of neurobehavioral toxicology methods to the military deployment toxicology assessment program.

The military Tri-Service (Army, Navy & Marines, Air Force) Deployment Toxicology Assessment Program (DTAP) represents a 30-year (1996-2026) planning effort to implement comprehensive systems for the protection of internationally deployed troops against toxicant exposures. A major objective of DTAP is the implementation of a global surveillance system to identify chemicals with the potential to reduce human performance capacity. Implementation requires prior development of complex human risk assessment models, known collectively as the Neurobehavioral Toxicity Evaluation Instrument (NTEI), based on mathematical interpolation of results from tissue-based and in vivo animal studies validated by human performance assessment research. The Neurobehavioral Toxicity Assessment Group (NTAG) at the Naval Health Research Center Detachment-Toxicology (NHRC-TD), Dayton, OH, and associated academic institutions are developing and cross-validating cellular-level (NTAS), laboratory small animal (NTAB), nonhuman primate (GASP), and human-based (GASH) toxicity assessment batteries. These batteries will be utilized to develop and evaluate mathematical predictors of human neurobehavioral toxicity, as a function of laboratory performance deficits predicted by quantitative structural analysis relationship (QSAR-like) properties of potential toxicants identified by international surveillance systems. Finally, physiologically-based pharmacokinetic (PBPK) and pharmacodynamic (PBPD) modeling of NTAS, NTAB, GASP, GASH data will support multi-organizational development and validation of the NTEI. The validated NTEI tool will represent a complex database management system, integrating global satellite surveillance input to provide real-time decision-making support for deployed military personnel.

Inhibition of spontaneous GABAergic transmission by trimethylolpropane phosphate.

Trimethylolpropane phosphate (TMPP) is a neuroactive organophosphate generated during partial pyrolysis of a synthetic ester turbine engine lubricant. While TMPP had been shown to have little affinity for acetylcholinesterase, previous binding studies and 6Cl- flux measurements have implicated TMPP as an antagonist of GABA, receptor/Cl- channels. Using the whole-cell patch clamp method, spontaneous inhibitory postsynaptic currents (sIPSCs) mediated by bicuculline-sensitive GABA(A) receptors were measured in neurons cultured from the rat embryonic hippocampus for 13-21 days. Experiments were conducted in the presence of tetrodotoxin and 6-cyano-7-nitroquinoxaline to inhibit spontaneous presynaptic action potentials and glutamate transmission, respectively, thus isolating GABAergic sIPSCs for study. TMPP induced a concentration-dependent inhibition of sIPSC amplitude and frequency suggesting both postsynaptic and presynaptic actions. Administration of 5 microM TMPP reversibly diminished sIPSC amplitude by 23 +/- 8% (mean SEM, n=5 cells) while markedly decreasing the mean sIPSC frequency by 40 +/- 2% (n=5). The mean time constant of sIPSC decay was reversibly decreased by 20 +/- 4% (n=3) in the presence of 20 microM TMPP, suggesting an increase in the rate of inactivation. To directly verify the blockade of ionotropic GABA receptors by TMPP, the effects of TMPP were examined on whole-cell Cl- current responses activated by exogenous GABA. Administration of TMPP (5 microM) depressed peak whole-cell GABA-induced currents to 73 1% (n=4) of control levels, consistent with the results on sIPSC amplitude. Our data directly demonstrate that TMPP directly inhibits GABA(A) receptor function, as indicated by the blockade of whole-cell GABA-mediated Cl- current and the reduction in sIPSC amplitude. Furthermore, TMPP exerts a presynaptic effect on GABAergic transmission, as evidenced by the reduction in sIPSC frequency, which may be independent of a GABA(A) receptor. The molecular basis for the presynaptic action of TMPP remains to be elucidated.

Repeated exposure of rats to JP-4 vapor induces changes in neurobehavioral capacity and 5-HT/5-HIAA levels.

Thirty-two Sprague-Dawley rats were exposed for 6 h/d for 14 consecutive days to JP-4 jet fuel vapor (2 mg/L) or room air control conditions. Following a 14- or 60-d recovery period, rats completed a battery of 8 tests selected from the Navy Neurobehavioral Toxicity Assessment Battery (NTAB) to evaluate changes in performance capacity. Exposure to JP-4 vapor resulted in significant changes in neurobehavioral capacity on several tests that varied as a function of the duration of the recovery period. Rats were evaluated for major neurotransmitter and metabolite levels in five brain regions and in the blood serum. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were shown to be significantly elevated in several brain regions as well as in the blood serum in the vapor-exposed groups. Results of the rat study are compared to previously reported neurobehavioral evaluations of European manufacturing personnel exposed chronically to jet fuel vapor.

Repeated exposure to trimethylolpropane phosphate induces central nervous system sensitization and facilitates electrical kindling.

Trimethylolpropane phosphate (TMPP), pentylenetetrazol (PTZ) and N-methyl-beta-carboline-3-carboxamide (FG-7142) were evaluated and compared for facilitation of electrical kindling in freely moving rats. Stimulating/recording electrodes were implanted in the left amygdala (LAD), right amygdala (RAD) and left bed nucleus (LBN) of the stria terminalis. TMPP (0.275 mg/kg), PTZ (20 mg/kg), FG-7142 (7.5 mg/kg) or vehicle was administered intraperitoneally (i.p.) to separate groups of rats 3 times/week for 10 weeks. Stimulation of the LAD (0.1 Hz, 0.1-ms duration, 280-1500 microA, 20 pulses) 24 h following the drug administration evoked epileptiform after-discharges (ADs) in the LBN and RAD of 12.5% and 17% of rats after the seventh dose of TMPP and PTZ, respectively, and in 20% of rats from the LBN and RAD after the ninth and nineteenth dose of FG-7142, respectively. The same stimulation also induced myoclonic jerks after nine doses of TMPP or PTZ, or after thirteen doses of FG-7142 in 25%, 30% and 20% of animals tested, respectively. Chemically kindled clonic seizures were observed in 100% of TMPP or FG-7142 and 50% of PTZ treated rats by the thirtieth dosing. Control animals exhibited neither behavioral nor electrographic seizures to vehicle injection or to the LAD stimulation. Kindling stimulation applied to the LAD (60 Hz, 2-s train duration, 20-1500 microA, 0.1-ms pulse duration) 4 weeks following the completion of drug treatments evoked epileptic after-discharges from the LAD, LBN and RAD in all treated groups, with generally decreased threshold and latency to onset of after-discharges, compared to vehicle controls. The present study suggests that repeated exposure of rats to sub-convulsive doses of TMPP, PTZ and FG-7142 induces long-term central nervous system sensitization that may be related to both chemical kindling and the facilitation of electrical kindling.

Tissue distribution, metabolism, and clearance of the convulsant trimethylolpropane phosphate in rats.

The distribution, metabolism, and clearance of trimethylolpropane phosphate (TMPP), a potent, bicyclophosphate, gamma-aminobutyric acid-ergic convulsant, were studied in male Fischer-344 rats. Intraperitoneal administration of TMPP was compared with oral gavage with respect to rates of absorption, distribution, and clearance. Distribution of TMPP to major body tissues was evaluated for the first 24 hr after administration or, in the case of regional brain distribution, immediately after the first TMPP-induced clinical seizure. Samples purified from the urine, feces, and bile of rats exposed to TMPP, as well as from rat liver microsomes incubated with TMPP in vitro, were analyzed for possible phase I and phase II metabolism, using HPLC. The disposition and clearance of TMPP in the blood and major body tissues were measured. TMPP was found to be well distributed to highly vascularized tissue compartments, with little retention >24 hr after administration. TMPP was eliminated through the urine and feces as the parent compound, with no evidence of phase I or phase II metabolism. TMPP was rapidly cleared from the blood during the first 30 min after exposure, with slower clearance of >87% of the drug during the following 8-hr period and >99.5% clearance by 100 hr after injection. Repeated daily exposure to TMPP for up to 5 successive days resulted in no measurable accumulation in the brain or other major tissue compartments. Possible mechanisms for TMPP-induced, short- and long-term, neurobehavioral modulation are discussed.

Acute effects of a bicyclophosphate neuroconvulsant on monoamine neurotransmitter and metabolite levels in the rat brain.

Naive male Sprague-Dawley rats were injected intraperitoneally (i.p.) with the bicyclophosphate convulsant trimethylolpropane phosphate (TMPP) at dose levels from 0.2 to 0.6 mg/kg. Rats were observed for convulsive activity, and were sacrificed 15 min posttreatment. Levels of the monoamine neurotransmitters norepinephrine (NE), epinephrine (EPI), dopamine (DA), and serotonin (5-HT) and the major metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were assayed in forebrain, midbrain, hindbrain, cerebellum and brainstem regions. Neurotransmitter and metabolite levels were compared between control rats and rats that did and did not experience seizures. TMPP administration induced significant decreases in levels of measured neurotransmitters that varied as a function of brain region, dose, and expression of the seizure activity. These results show that tonic or tonic-clonic seizures induced by TMPP administration (0.6 mg/kg) are reliably associated with regional decreases in serotonin, dopamine, and norepinephrine. Convulsive activity resulting from lower dose administrations (0.2-0.4 mg/kg) of TMPP result only in decreased regional levels of serotonin.

Trimethylolpropane phosphate (TMPP) perfusion into the nucleus accumbens of the rat: electroencephalographic, behavioral and neurochemical correlates.

The infusion (0.13 mumol/infusion) of the convulsant trimethylolpropane phosphate (TMPP) into the nucleus accumbens (NA) of adults Sprague-Dawley rats reliably induced subclinical seizures, hyperlocomotor activity, and integrated stereotypies. Observation of these behaviors was temporally correlated with the appearance of EEG paroxysms, as well as with significant decreases in extracellular concentrations of both dopamine (DA) and norepinephrine (NE) in the NA. Repeated perfusion of TMPP revealed significant increases in stereotypic behavior during subsequent pre-drug baseline testing.

An overview of the development, validation, and application of neurobehavioral and neuromolecular toxicity assessment batteries: potential applications to combustion toxicology.

Currently, there are few alternatives to the use of animals in toxicology for human risk assessment. Neurobehavioral toxicology is an emerging area in which complex performance capacity is evaluated during or following toxicological exposure. While a number of single tests and a few more complex neurobehavioral batteries exist, no fully validated and comprehensive neurobehavioral toxicity assessment battery has yet been developed. The Neurobehavioral Toxicity Assessment Battery (NTAB) is a multi-test battery being developed by the Naval Medical Research Institute Detachment (Toxicology) (NMRI/TD) to categorize the potential neurobehavioral toxicity of compounds of Navy interest, especially those found in combustion atmospheres. The NTAB is intended to identify specific areas of deficit (e.g. motivational, sensory, motor, and cognitive) from complex changes in performance induced by toxic exposures, as well as to provide a mechanism to evaluate recovery of neurobehavioral integrity. Portions of the NTAB have been successfully used to assess the risk of brief exposure to low concentrations of combustion gases, including smoke from electrical aircraft fires, ozone-depleting substances and their replacements, and the novel neuroconvulsant trimethylolpropane phosphate. The goal of the NMRI/TD Neurobehavioral Toxicology Group and the Tri-Service Toxicology Consortium's neurobehavioral toxicology program is the incorporation of more molecular techniques involving neurophysiology, neuropharmacology, in vivo electrochemistry, and real-time microdialysis for correlative use with the neurobehavioral battery in human risk assessment. This overview discusses the application of neurobehavioral and neuromolecular endpoint test batteries to combustion toxicology.