Neurochemical changes after acute binge toluene inhalation in adolescent and adult rats: A high-resolution magnetic resonance spectroscopy study

Inhalant abuse in young people is a growing public health concern. We reported previously that acute toluene intoxication in young rats, using a pattern of exposures that approximate abuse patterns of inhalant use in humans, significantly altered neurochemical measures in select brain regions. In this study, adolescent and young adult rats were exposed similarly to an acute (2 × 15 min), high dose (8000–12,000 ppm) of toluene and high-resolution magic angle spinning proton magnetic resonance spectroscopy (HR-MAS ¹H-MRS) was used to assess neurochemical profiles of tissue samples from a number of brain regions collected immediately following solvent exposure. The current investigation focused on N-acetyl-aspartate (NAA), choline-containing compounds, creatine, glutamate, GABA, and glutamine. Contrary to our predictions, no significant alterations were found in the levels of NAA, choline, creatine, glutamate, or glutamine in adolescent animals. In contrast to these minimal effects in adolescents, binge toluene exposure altered several neurochemical parameters in young adult rats, including decreased levels of choline and GABA in the frontal cortex and striatum and lowered glutamine and NAA levels in the frontal cortex. One of the more robust findings was a wide-ranging increase in lactate after toluene exposure in adult animals, an effect not observed in adolescents. These age-dependent effects of toluene are distinct from those reported previously in juvenile rats and suggest a developmental difference in vulnerability to the effects of inhalants. Specifically, the results suggest that the neurochemical response to toluene in adolescents is attenuated compared to adults, and imply an association between these neurochemical differences and age-influenced differences in solvent abuse in humans.     

Binge toluene exposure alters glutamate, glutamine and GABA in the adolescent rat brain as measured by proton magnetic resonance spectroscopy

Despite the high incidence of toluene abuse in adolescents, little is known regarding the effect of binge exposure on neurochemical profiles during this developmental stage. In the current study, the effects of binge toluene exposure during adolescence on neurotransmitter levels were determined using high-resolution proton magnetic resonance spectroscopy ex vivo at 11.7T. Adolescent male Sprague-Dawley rats were exposed to toluene (0, 8000, or 12,000 ppm) for 15 min twice daily from postnatal day 28 (P28) through P34 and then euthanized either 1 or 7 days later (on P35 or P42) to assess glutamate (GLU), glutamine, and GABA levels in intact tissue punches from the medial prefrontal cortex (mPFC), anterior striatum and hippocampus. In the mPFC, toluene reduced GLU 1 day after exposure, with no effect on GABA, while after 7 days, GLU was no longer affected but there was an increase in GABA levels. In the hippocampus, neither GABA nor GLU was altered 1 day after exposure, whereas 7 days after exposure, increases were observed in GABA and GLU. Striatal GLU and GABA levels measured after either 1 or 7 days were not altered after toluene exposure. These findings show that 1 week of binge toluene inhalation selectively alters these neurotransmitters in the mPFC and hippocampus in adolescent rats, and that some of these effects endure at least 1 week after the exposure. The results suggest that age-dependent, differential neurochemical responses to toluene may contribute to the unique behavioral patterns associated with drug abuse among older children and young teens.     

Maternal and fetal blood and organ toluene levels in rats following acute and repeated binge inhalation exposure

Inhalation of organic solvents is a persistent form of drug abuse with particular concern being the abuse of inhalants by women of child-bearing age. While studies have begun assessing postnatal outcomes of offspring exposed prenatally to inhalants, relatively little is known about the distribution of toluene in blood and body tissues of pregnant, inhalant-abusing women, or in the fetuses. The present study assessed the tissue toluene levels attained following brief toluene exposures using a pre-clinical rat model of maternal inhalant abuse. Timed-pregnant Sprague–Dawley rats were exposed to toluene at 8000 or 12,000 parts per million (ppm) for 15, 30 or 45 min/exposure. Exposures occurred twice each day from gestational day 8 (GD8) through GD20. Immediately following the second exposure on GD8, GD14 and GD20 blood was taken from the saphenous vein of the dams. Following saphenous vein blood collection on GD20, dams were sacrificed and trunk blood was collected along with maternal tissue specimens from cerebellum, heart, lung, kidney and liver. The placenta, amniotic fluid and fetal brain were also collected. Results demonstrated that maternal saphenous blood toluene levels increased as the inhaled concentration of toluene and duration of exposure increased. The maternal cerebellum, heart, kidney and liver appeared to be saturated after 30 min on GD20 such that toluene levels in those organs were equivalent across all ambient concentrations of inhaled toluene. Toluene levels also increased in fetal brain as the inhaled concentration of toluene increased and in placenta and amniotic fluid as the duration of exposure increased. Toluene levels in all tissues at GD20, except maternal lung and amniotic fluid, were higher than in maternal saphenous blood suggesting that toluene concentrated in those organs. Measurement of toluene levels in blood and other tissues following repeated toluene exposure demonstrated that toluene readily reaches a variety of potential sites of action throughout the maternal–placental–fetal unit.     

Maternal and fetal blood and organ toluene levels in rats following acute and repeated binge inhalation exposure

Inhalation of organic solvents is a persistent form of drug abuse with particular concern being the abuse of inhalants by women of child-bearing age. While studies have begun assessing postnatal outcomes of offspring exposed prenatally to inhalants, relatively little is known about the distribution of toluene in blood and body tissues of pregnant, inhalant-abusing women, or in the fetuses. The present study assessed the tissue toluene levels attained following brief toluene exposures using a pre-clinical rat model of maternal inhalant abuse. Timed-pregnant Sprague–Dawley rats were exposed to toluene at 8000 or 12,000 parts per million (ppm) for 15, 30 or 45 min/exposure. Exposures occurred twice each day from gestational day 8 (GD8) through GD20. Immediately following the second exposure on GD8, GD14 and GD20 blood was taken from the saphenous vein of the dams. Following saphenous vein blood collection on GD20, dams were sacrificed and trunk blood was collected along with maternal tissue specimens from cerebellum, heart, lung, kidney and liver. The placenta, amniotic fluid and fetal brain were also collected. Results demonstrated that maternal saphenous blood toluene levels increased as the inhaled concentration of toluene and duration of exposure increased. The maternal cerebellum, heart, kidney and liver appeared to be saturated after 30 min on GD20 such that toluene levels in those organs were equivalent across all ambient concentrations of inhaled toluene. Toluene levels also increased in fetal brain as the inhaled concentration of toluene increased and in placenta and amniotic fluid as the duration of exposure increased. Toluene levels in all tissues at GD20, except maternal lung and amniotic fluid, were higher than in maternal saphenous blood suggesting that toluene concentrated in those organs. Measurement of toluene levels in blood and other tissues following repeated toluene exposure demonstrated that toluene readily reaches a variety of potential sites of action throughout the maternal–placental–fetal unit.     

Nonprotein sulfhydryl alterations in F-344 rats following acute methyl chloride inhalation

This study examined the effect of acute methyl chloride (MeCl) inhalation on F-344 rat tissue nonprotein sulfhydryl (NPSH), largely reduced glutathione. Rats were exposed to MeCl concentrations of 1500, 500, or 100 ppm. A 6-hr exposure to 1500 ppm of MeCl decreased the NPSH content of liver, kidney, and lungs to 17, 27, and 30% of control values, respectively, while 500 ppm MeCl lowered the liver, kidney, and lung NPSH to 41, 59, and 55% of control values, respectively, demonstrating a concentration-related effect. Blood NPSH did not differ from controls in either of these groups. No statistically significant changes from controls in tissue or blood NPSH were observed following a 100-ppm MeCl exposure. The extent of tissue NPSH loss was dependent on exposure duration. Liver and kidney NPSH returned to control NPSH concentrations within 8 hr following exposure of 1500 ppm MeCl. Pretreatment of rats with Aroclor-1254 or SKF-525A did not alter the MeCl-induced decrease in tissue NPSH. These data indicate that MeCl reacts extensively with tissue NPSH in vivo in a concentration-related fashion following acute inhalation exposure. The most likely NPSH constituent with which MeCl reacts is reduced glutathione. The finding that blood NPSH was not affected, in contrast to liver, kidney, or lung NPSH, indicates a tissue-specific reaction between MeCl and sulfhydryl groups, a reaction in which the tissue enzyme glutathione-S-alkyltransferase may play a role.     

Regional alterations of brain biogenic amines and GABA/glutamate levels in rats following chronic lead exposure during neonatal development

Wistar rat pups were administered either a high dose of lead acetate (400 g lead/g body weight/day) or a low dose (100 g lead/g body weight/day) by gastric intubation, from 2 days through 60 days of age. The rats on both these doses exhibited statistically significant decreases in body and brain weights throughout the lead treatment period. A group of rats on high dose was also rehabilitated by discontinuing the lead from 60 days of age. In these rats, at 160 days of age, the body weight but not the brain weight recovered to normal levels. During the lead intake, the rats on high dose revealed significant elevations in the levels of noradrenaline (NA) in the hippocampus (HI), cerebellum (CE), hypothalamus (HY), brainstem (BS), and accumbens-striatum (SA). The elevated levels in all the above regions except in the HY persisted even after rehabilitation. The dopamine (DA) levels changed significantly in opposite directions in HY (elevation) and BS (reduction) during the lead treatment, and the HY recovered after rehabilitation. Under lead, the serotonin (5HT) levels were elevated significantly in the HI, BS and MC (motor cortex), while after rehabilitation the abnormality persisted only in the MC. Low dose lead treatment was also effective on the same areas of brain. In the low dose group, estimation of the levels of GABA and glutamate were also done, and a significant decrease of GABA in CE and glutamate in MC was observed. The differences observed in the neurotoxic effects (none or significant) of lead in the different regions for each of the transmitters (NA, DA, 5HT) supports the interesting conclusion that the vulnerability of the axon terminals of any given type is dependent on some regional factors, although the projections of the different regions originate from an apparently similar category of neurons in the brain stem.     

磁共振波谱分析银杏叶提取物对大鼠急性脑缺血的影响

目的:研究银杏叶提取物(GbE)对大鼠急性脑缺血的干预影响。方法:大鼠随机分成假手术组、缺血组、预防组和治疗组。用磁共振波谱分析动态观测脑缺血后48小时内生化代谢的变化及GbE(100mg/kg,ip,qd)的干预影响。结果:(1)大鼠急性脑缺血后90min梗塞区出现乳酸峰,并随着时间的延长而持续上升。预防组乳酸峰轻度升高(P<0.01,n=6);治疗组较预防组升高(P<0.05,n=6)。(2)缺血组在缺血后4h内N-乙酰基天门冬氨酸下降(P<0.05,n=6)并持续降低(P<0.01,n=6);治疗组及预防组24h后N-乙酰基天门冬氨酸略下降(P<0.05,m=6)。(3)缺血后24h缺血组及治疗组胆碱略升高(P<0.05,n=6),肌酸略降低(P<0.05,n=6);预防组在48h后才发生上述变化。结论:GbE对脑缺血具有预防及治疗作用,预防给药效果较佳。     

Pulmonary microsomal alterations following short-term low level inhalation of p-xylene in rats

Rats exposed to 300 ppm para-xylene vapor for 1, 3 or 5 days, 6 h/day, exhibited alterations in pulmonary microsomal membrane structural and metabolic parameters. Following 1 day of exposure, conjugated diene levels were elevated while total phospholipid levels, P-450 content, benzyloxyresorufin O-dealkylase activity and 2-aminofluorene N-hydroxylase activity were decreased. Core and leaflet membrane fluidity, ethoxyresorufin O-deethylase activity and aryl hydrocarbon hydroxylase (AHH) activity were unchanged at this time. Altered parameters began to return to control values by day 3 of exposure except for 2-aminofluorene N-hydroxylase activity, which remained decreased throughout the time course, and core membrane fluidity which was increased following 3 days of exposure. After 5 days of exposure, all parameters returned to control levels with the exception of AHH activity which was increased 41% at this time. Extracellular surfactant levels were also decreased by 1 and 3 days of exposure but returned to control values after 5 days. Initial pulmonary alterations produced by low level p-xylene exposure may be mediated by a peroxidative process. The initial damage triggers an adaptive response in lung tissue which possibly involves enzyme induction and/or cell proliferation. The increase in AHH activity after 5 days of exposure could have important consequences on the metabolism of co-administered xenobiotics.     

Steroidogenic alterations in testes and sera of rats exposed to formulated Fenvalerate by inhalation

Fenvalerate (Fen) is a synthetic pyrethroid, which is commonly used for destroying a variety of insect pests damaging several vegetable, fruit, and cotton crops. This insecticide is also used to mitigate household insects like flies, cockroaches, mosquitoes, and so forth. Human beings are exposed to formulated Fen preparations mostly by inhalation during spraying in fields for crop protection, for control of household insects, and also during handling and packaging at manufacturing plants. Limited online information is available regarding toxic effects of formulated Fen exposure on mammalian reproductive system. The present study has been undertaken to investigate male reproductive toxic effects of a formulated preparation of Fen (20% EC) particularly in relation to steroidogenic alterations in testes and sera of rats exposed by nose-only inhalation for (4 hours/day and five days a week) for three months. The results indicate significant reduction in the weight of testes, epididymal sperm counts, and sperm motility, along with decrease in marker testicular enzymes for testosterone biosynthesis viz. 17-beta-hydroxy steroid dehydrogenase (17-beta-HSD) and glucose-6-phosphate dehydrogenase (G6PDH), leading to net decrease in serum testosterone concentration in group of rats exposed to one-fifth LC50 of Fen (20% EC) by inhalation (4 hours/day, five days a week) subchronically for three months. These results for the first time indicate the role of testosterone in Fen (20% EC)-induced male reproductive toxicity of rats subchronically exposed by inhalation probably due to neuroendocrine-mediated phenomenon and hormone-disrupting property of the insecticide.     

Differential effect of CDP-choline on brain cytosolic choline levels in younger and older subjects as measured by proton magnetic resonance spectroscopy

Phosphatidylcholine (PtdCho), which is essential for membrane integrity and repair, is reduced in brain cell membranes with age. Evidence from both animal and in vitro studies indicates that cytidine 5′ diphosphate choline (CDP-choline) can increase the synthesis of PtdCho; however, the effect of CDP-choline on brain choline metabolism has not previously been studied in human subjects. In this study, in vivo proton magnetic resonance spectroscopy (¹H-MRS) was used to measure brain levels of cytosolic, cholinecontaining compounds before and after single oral doses of CDP-choline. Three hours after dosing, plasma choline increased similarly in younger (mean age 25 years) and older subjects (mean age 59 years). However, while the choline resonance in brain increased by 18% on average in younger subjects, it decreased by almost 6% in older subjects (P=0.028). These results may be explained by a previously observed decrease in brain choline uptake, but not cytidine uptake, in older subjects. Additional intracellular cytidine following the administration of CDP-choline should lead to the increased incorporation of choline already present in brain into membrane PtdCho, which is not MRS-visible, consequently lowering the brain choline resonance below that of pre-treatment values. These results suggest that the cytidine moiety of CDP-choline stimulates phosphatidylcholine synthesis in human brain cell membranes in older subjects.     

Tissue cadmium and locomotor behavior following acute inhalation exposure to cadmium aerosol in rats

Rats were exposed for 1 h to increasing concentrations of cadmium (Cd) through inhalation of cadmium chloride aerosol using nose-only inhalation chambers and depositions of Cd in lungs, liver and kidneys were measured. Changes in spontaneous locomotor activities were recorded 2 and 7 d after cessation of exposure. A concentration dependent increase in Cd in lungs, liver and kidneys was accompanied by significant alterations in spontaneous locomotor response that was dependent on the air Cd concentrations and the postexposure duration. The study shows decreased spontaneous locomotor activity due to Cd accumulation in tissues.     

Neuropathology of aluminum toxicity in rats (glutamate and GABA impairment).

To get better insights into the pathological and biochemical defects underlying aluminum toxicity in brain tissue, we exposed male albino rats for 35 days to aluminum sulfate by gavage. Tissue aluminum level of brain was assessed, histological sections of brain were examined and amino acid transmitters contents were detected by reversed phase high performance liquid chromatography.Aluminum levels were high in brain specimens of the treated groups comparing to the control and it was dose-dependent. Marked increase in glutamate and glutamine levels was noticed while GABA level was significantly decreased.The most pronounced changes in brain tissue included spongioform changes in the neurons specially those of hippocampus, nuclear deformity, and neurofibrillary degeneration, similar to neurofibrillary tangles in Alzheimer's disease. It is concluded that accumulated aluminum in brain and altered amino acid neurotransmitters are important mechanisms of aluminum neurotoxicity.     

A proton magnetic resonance spectroscopy investigation of the dorsolateral prefrontal cortex in acute mania

BACKGROUND: Several neurochemical abnormalities have been reported in bipolar disorder (BD), but the exact mechanisms that underlie its pathophysiology remain to be elucidated. Proton magnetic resonance spectroscopy (1HMRS) allows in vivo measurements of certain neurometabolites in the human brain. 1HMRS was used to investigate the dorsolateral prefrontal cortex (DLPFC) in bipolar subjects during a manic or mixed phase. N-acetyl-L-aspartate (NAA), choline-containing molecules (Cho), creatine plus phosphocreatine (Cr) and myoinositol (Ino) were measured. METHOD: Ten bipolar patients (nine manic, one mixed), diagnosed by a semi-structured clinical interview (SCID), and ten age- and gender-matched healthy volunteers were studied. Absolute neurometabolites levels were measured from two 8 cm3 voxels placed in left and right DLPFC using a short TE 1HMRS method at 1.5 T. T1- and T2-weighted anatomical magnetic resonance imaging was performed to exclude any neuroanatomical abnormality. RESULTS: No significant differences were found for NAA, Cho, Cr, Ino, NAA/Cr, Cho/Cr or Ino/Cr between patients and controls. Manic/mixed patients had significantly higher left-to-right myoinositol ratios in DLPFC (p = 0.044). CONCLUSIONS: Increased left-to-right myoinositol ratios in the DLPFC in bipolar patients during acute mania may represent a dysfunction in the phosphoinositide-signaling pathway. Longitudinal studies with larger samples of unmedicated patients assessing pre- and post-treatment times will be required for further clarification of the time course of these abnormalities and the relationship with treatment effects.     

Regional levels of GABA and glutamate in mouse brain following exposure to pain

Based on previous studies from this laboratory, a study of the effects of pain on regional brain levels of GABA and glutamate were performed using male CFl mice. Gas-chromatographic analysis revealed no significant differences in these substrates in “subcortical” areas. In the “cortical” areas, pain produced a significant elevation of GABA levels and a small, but significant, decrease in glutamate levels. Neither of these changes was observed in animals pretreated with morphine before exposure to pain. Restraint stress failed to produce the same changes. The ratio of GABA to glutamate was a reliable index of exposure to pain.