MicroPET/CT assessment of FDG uptake in brain after long-term methylphenidate treatment in nonhuman primates.

Methylphenidate (MPH) is a psychostimulant commonly used for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). Since the long-term effects of this drug on the central nervous system (CNS) are not well understood, we conducted microPET/CT scans on young adult male rhesus monkeys (n=4/group) to gather information on brain metabolism using the uptake of [(18)F]Fluoro-2-deoxy-2-d-glucose (FDG) as a marker. Approximately two-year old, male rhesus monkeys were treated orally with MPH twice per day, five days per week (M-F) over a 6-year period. Subjects received MPH at either 2.5 or 12.5mg/kg/dose or vehicle (Prang). To minimize the acute effects of MPH on FDG uptake, microPET/CT scans were scheduled on Mondays before their first daily dosing of the week (approximately 68h since their last treatment). FDG (370±8.88MBq) was injected intravenously and 30min later microPET/CT images were obtained over 60min. Radiolabeled tracer accumulation in regions of interest (ROIs) in the prefrontal cortex, temporal cortex, striatum and cerebellum were converted into Standard Uptake Values (SUVs). Compared to the control group, the uptake of FDG in the cerebellum was significantly decreased in both the low and high dose groups. These preliminary data demonstrate that microPET imaging is capable of distinguishing differences in retention of FDG in the brains of NHPs treated chronically with MPH and suggests that this approach may provide a minimally invasive biomarker for exploring the effects of chronic MPH treatment on aspects of brain function.

MicroPET imaging of ketamine-induced neuronal apoptosis with radiolabeled DFNSH.

Recent reports indicate that 6-12 h of ketamine anesthesia can trigger neuronal apoptosis in postnatal day (PND) 7 rats. In vitro, ex vivo, and confocal fluorescent imaging studies suggest that dansyl compounds can accumulate within the cytoplasm of the apoptotic cell. High-resolution positron emission tomography (microPET) imaging has been proposed as a minimally invasive method for detecting apoptosis in the rat brain. Compared with [(18)F]-labeled annexin V, which binds to externalized phosphatidylserine (PS) on the outer membrane of apoptotic cells, intracellular uptake of the dansylhydrazone of p-fluorobenzaldehyde (DFNSH) may lead to improved target-to-background contrast ratios. In this study, the effect of ketamine on the uptake and retention of [(18)F]-DFNSH in the rat brain was investigated using microPET imaging. On PND 7, rat pups in the experimental group were exposed, at 2-h intervals, to six subcutaneous injections of ketamine (20 mg/kg) and control rat pups received six injections of saline. On PND 35, [(18)F]-DFNSH (37 MBq) was injected into the tail vein of rats and microPET images were obtained over 2 h following the injection. Radiolabeled tracer accumulation in the region of interest (ROI) in the frontal cortex was converted into standard uptake values (SUVs). The radiotracer was quickly distributed into the brains of both ketamine- and saline-treated rats. Compared with the control group, the uptake of [(18)F]-DFNSH was significantly increased in the ROI, frontal cortex area of ketamine-treated rats. In addition, the wash-out duration of the tracer was prolonged in the ketamine-treated animals. This study demonstrates that microPET imaging is capable of distinguishing differences in retention of [(18)F]-DFNSH in ROI and suggests that this compound may serve as a minimally invasive biomarker of neuronal apoptosis in rodents.

Expression of genes related to oxidative stress in the mouse brain after exposure to silver-25 nanoparticles.

Nanoparticles are small scale substances (<100 nm) used in biomedical applications, electronics, and energy production. Increased exposure to nanoparticles being produced in large-scale industry facilities elicits concerns for the toxicity of certain classes of nanoparticles. This study evaluated the effects of silver-25 nm (Ag-25) nanoparticles on gene expression in different regions of the mouse brain. Adult-male C57BL/6N mice were administered (i.p.) 100mg/kg, 500 mg/kg or 1,000 mg/kg Ag-25 and sacrificed after 24h. Regions from the brain were rapidly removed and dissected into caudate nucleus, frontal cortex and hippocampus. Total RNA was isolated from each of the three brain regions collected and real-time RT-PCR analysis was performed using Mouse Oxidative Stress and Antioxidant Defense Arrays. Array data revealed the expression of genes varied in the caudate nucleus, frontal cortex and hippocampus of mice when treated with Ag-25. The data suggest that Ag-25 nanoparticles may produce neurotoxicity by generating free radical-induced oxidative stress and by altering gene expression, producing apoptosis and neurotoxicity.

Selective alterations of transcription factors in MPP+-induced neurotoxicity in PC12 cells.

MPP(+) (1-methyl-4-phenylpyridinium; the active metabolite of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine)) depletes dopamine (DA) content and elicits cell death in PC12 cells. However, the mechanism of MPP(+)-induced neurotoxicity is still unclear. In this study, the dose response and time-course of MPP(+)-induced DA depletion and decreased cell viability were determined in nerve growth factor (NGF)-differentiated PC12 cells. The alteration of transcription factors (TFs) induced by MPP(+) from a selected dose level and time point was then evaluated using protein/DNA-binding arrays. K-means clustering analysis identified four patterns of protein/DNA-binding changes. Three of the 28 TFs identified in PC12 cells increased by 100% (p53, PRE, Smad SBE) and 2 decreased by 50% (HSE, RXR(DR1)) of control with MPP(+) treatment. In addition, three TFs decreased within the range of 33-50% (TFIID, E2F1, CREB) and two TFs increased within the range of 50-100% (PAX-5, Stat4). An electrophoretic mobility shift assay (EMSA) was used to confirm the changes of p53 and HSE. The observed changes in TFs correlated with the alterations of DA and cell viability. The data indicates that selective transcription factors are involved in MPP(+)-induced neurotoxicity and it provides mechanistic information that may be applicable to animal studies with MPTP and clinical studies of Parkinson's disease.

Acute changes in dopamine release and turnover in rat caudate nucleus following a single dose of methamphetamine.

Acute changes in dopamine (DA) turnover were studied in the caudate nucleus (CN) of adult male rats between 0-24 h after a single injection of Methamphetamine (20 mg/kg, ip). A single dose of METH-induced an increase in DA turnover [(DOPAC + HVA)/DA] concomitant with an acute DA release followed by transient DA and DOPAC depletion in the rat CN.

Assessing the potential toxicity of MK-801 and remacemide: chronic exposure in juvenile rhesus monkeys.

The present experiment examined the effects of chronic exposure to either 0.1 or 1.0 mg/kg MK-801 [a selective N-methyl-D-aspartate (NMDA) receptor antagonist] or 20.0 or 50.0 mg/kg remacemide (an NMDA receptor antagonist which also blocks fast sodium channels) in juvenile rhesus monkeys. Endpoints were monitored to provide a general index of subjects' health and included measures of clinical chemistry, hematology, ophthalmology, spontaneous home-cage behavior, and peak drug plasma levels. In general, both drugs were well tolerated and produced no treatment-related effects during 2 years of dosing and assessment. Periodic plasma drug level determinations provided limited evidence that both compounds may induce their own metabolism. The present results contrast sharply with previously reported effects of long-lasting impairments in the acquisition of incremental learning and in the development of color and position discrimination in these same subjects. These observations highlight the importance of collecting a broad range of toxicology data, including tests of cognitive function, to make comprehensive assessments of new drug safety. In the present case, the less obvious effects of these drugs on cognition defined the toxicologic response.

Methamphetamine-induced dopaminergic neurotoxicity: role of peroxynitrite and neuroprotective role of antioxidants and peroxynitrite decomposition catalysts.

Oxidative stress, reactive oxygen (ROS), and nitrogen (RNS) species have been known to be involved in a multitude of neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Both ROS and RNS have very short half-lives, thereby making their identification very difficult as a specific cause of neurodegeneration. Recently, we have developed a high performance liquid chromatography/electrochemical detection (HPLC/EC) method to identify 3-nitrotyrosine (3-NT), an in vitro and in vivo biomarker of peroxynitrite production, in cell cultures and brain to evaluate if an agent-driven neurotoxicity is produced by the generation of peroxynitrite. We show that a single or multiple injections of methamphetamine (METH) produced a significant increase in the formation of 3-NT in the striatum. This formation of 3-NT correlated with the striatal dopamine depletion caused by METH administration. We also show that PC12 cells treated with METH has significantly increased formation of 3-NT and dopamine depletion. Furthermore, we report that pretreatment with antioxidants such as selenium and melatonin can completely protect against the formation of 3-NT and depletion of striatal dopamine. We also report that pretreatment with peroxynitrite decomposition catalysts such as 5, 10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and 5, 10, 15, 20-tetrakis (2,4,6-trimethyl-3,5-sulfonatophenyl) porphinato iron III (FETPPS) significantly protect against METH-induced 3-NT formation and striatal dopamine depletion. We used two different approaches, pharmacological manipulation and transgenic animal models, in order to further investigate the role of peroxynitrite. We show that a selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), significantly protect against the formation of 3-NT as well as striatal dopamine depletion. Similar results were observed with nNOS knockout and copper zinc superoxide dismutase (CuZnSOD)-overexpressed transgenic mice models. Finally, using the protein data bank crystal structure of tyrosine hydroxylase, we postulate the possible nitration of specific tyrosine moiety in the enzyme that can be responsible for dopaminergic neurotoxicity. Together, these data clearly support the hypothesis that the reactive nitrogen species, peroxynitrite, plays a major role in METH-induced dopaminergic neurotoxicity and that selective antioxidants and peroxynitrite decomposition catalysts can protect against METH-induced neurotoxicity. These antioxidants and decomposition catalysts may have therapeutic potential in the treatment of psychostimulant addictions.

Peroxynitrite plays a role in methamphetamine-induced dopaminergic neurotoxicity: evidence from mice lacking neuronal nitric oxide synthase gene or overexpressing copper-zinc superoxide dismutase.

The use of methamphetamine (METH) leads to neurotoxic effects in mammals. These neurotoxic effects appear to be related to the production of free radicals. To assess the role of peroxynitrite in METH-induced dopaminergic, we investigated the production of 3-nitrotyrosine (3-NT) in the mouse striatum. The levels of 3-NT increased in the striatum of wild-type mice treated with multiple doses of METH (4 x 10 mg/kg, 2 h interval) as compared with the controls. However, no significant production of 3-NT was observed either in the striata of neuronal nitric oxide synthase knockout mice (nNOS -/-) or copper-zinc superoxide dismutase overexpressed transgenic mice (SOD-Tg) treated with similar doses of METH. The dopaminergic damage induced by METH treatment was also attenuated in nNOS-/- or SOD-Tg mice. These data further confirm that METH causes its neurotoxic effects via the production of peroxynitrite.

Transplacental pharmacokinetics and fetal distribution of 2', 3'-didehydro-3'-deoxythymidine (d4T) and its metabolites in late-term rhesus macaques.

BACKGROUND: The overall goal of human immunodeficiency virus (HIV) therapy during pregnancy is to maintain maternal health and reduce the probability of vertical transmission during gestation and delivery, while keeping toxicity risks low. Azidothymidine (AZT) is currently recommended for pregnant women infected with HIV; however, many pregnant women are unable to tolerate AZT because of toxicity. In the present study, the placental transfer and fetal accumulation of the anti-HIV compound 2',3'-didehydro-3'-deoxythymidine (d4T) and its active (triphosphorylated) and inactive (thymine and beta-aminoisobutyric acid) metabolites were examined at steady state in late-term rhesus macaques. METHODS: On the day of the hysterotomy, the mother was administered an intravenous loading dose of d4T, followed by a 3-hr steady-state intravenous infusion that also included [(3)H]d4T as a tracer. After 3 hr of infusion, the fetus was delivered by cesarean section under halothane/N(2)O anesthesia. Plasma, amniotic fluid, and tissues were analyzed for d4T and its inactive metabolites by HPLC; tissue samples were analyzed for d4T and active (phosphorylated) metabolites by strong anion-exchange HPLC. RESULTS: Maternal steady-state plasma concentrations of d4T were 1-2 microg/ml, with a fetal-to-maternal plasma ratio of 0.85 +/- 0.09. The fetal tissue distribution of radioactivity was highest in the kidney and lowest in the brain. D4T, thymine, and beta-aminoisobutyric acid were detected in all fetal tissues examined. CONCLUSIONS: Our data indicate that d4T readily crosses the placenta and is present in the fetus as parent compound or its inactive metabolites after maternal infusion. Although fetal plasma concentrations of d4T were similar to clinical d4T concentrations, no phosphorylated metabolites were detected. Teratology 62:93-99, 2000. Published 2000 Wiley-Liss, Inc.

An evaluation of l-ephedrine neurotoxicity with respect to hyperthermia and caudate/putamen microdialysate levels of ephedrine, dopamine, serotonin, and glutamate.

l-Ephedrine is an active ingredient in several herbal formulations with a mechanism of action similar to amphetamine and methamphetamine. However, its potential to damage dopaminergic terminals in the caudate/putamen (CPu) has yet to be fully evaluated. The studies here used in vivo brain microdialysis experiments to determine the systemic doses and extracellular brain levels of l-ephedrine necessary to produce similar increases in CPu extracellular dopamine and marked hyperthermia that were previously shown necessary for amphetamine-induced neurotoxicity in male Sprague-Dawley rats. At an environmental temperature of 23 degrees C, a single 40 mg/kg intraperitoneal (ip) dose of l-ephedrine produced marked hyperthermia (>/= 40 degrees C), peak microdialysate ephedrine levels of 7.3 +/- 1.2 microM, and a 20-fold increase in microdialysate dopamine levels. Twenty-five mg/kg produced a lesser degree of hyperthermia, peak microdialysate ephedrine levels of 2.6 +/- 0.4 microM, and a 10-fold increase in dopamine levels. Three doses of 40 mg/kg given at 3-h intervals or 4 doses of 25 mg/kg l-ephedrine given at 2-h intervals were compared with 4 doses of 5 mg/kg d-amphetamine given at 2-h intervals. Multiple doses of either ephedrine or amphetamine caused severe hyperthermia (>/= 41.3 degrees C) but striatal tissue levels of dopamine 7 days after dosing were reduced only 25% or less by ephedrine compared to the 75% reductions produced by amphetamine. The increases in CPu microdialysate levels of serotonin produced by either 4 x 25 mg/kg l-ephedrine or 4 x 5 mg/kg d-amphetamine did not significantly differ, but elevation of dopamine levels by d-amphetamine were over 2-fold times the level caused by l-ephedrine. Microdialysate glutamate levels were elevated to the same extent by either 25 mg/kg l-ephedrine or 4 x 5 mg/kg d-amphetamine. l-Ephedrine may not be as neurotoxic to dopaminergic terminals as d-amphetamine, because non-lethal doses of l-ephedrine do not sufficiently increase the CPu dopamine levels within nerve terminals or the extracellular space to those necessary for a more pronounced long-term dopamine depletion.

Methamphetamine generates peroxynitrite and produces dopaminergic neurotoxicity in mice: protective effects of peroxynitrite decomposition catalyst.

Methamphetamine (METH)-induced dopaminergic neurotoxicity is believed to be produced by oxidative stress and free radical generation. The present study was undertaken to investigate if METH generates peroxynitrite and produces dopaminergic neurotoxicity. We also investigated if this generation of peroxynitrite can be blocked by a selective peroxynitrite decomposition catalyst, 5, 10,15, 20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and protect against METH-induced dopaminergic neurotoxicity. Administration of METH resulted in the significant formation of 3-nitrotyrosine (3-NT), an in vivo marker of peroxynitrite generation, in the striatum and also caused a significant increase in the body temperature. METH injection also caused a significant decrease in the concentration of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) by 76%, 53% and 40%, respectively, in the striatum compared with the control group. Treatment with FeTMPyP blocked the formation of 3-NT by 66% when compared with the METH group. FeTMPyP treatment also provided significant protection against the METH-induced hyperthermia and depletion of DA, DOPAC and HVA. Administration of FeTMPyP alone neither resulted in 3-NT formation nor had any significant effect on DA or its metabolite concentrations. These findings indicate that peroxynitrite plays a role in METH-induced dopaminergic neurotoxicity and also suggests that peroxynitrite decomposition catalysts may be beneficial for the management of psychostimulant abuse.

Ibogaine blocked methamphetamine-induced hyperthermia and induction of heat shock protein in mice.

Body temperature changes and heat shock protein (HSP-72) induction in the caudate nucleus were studied in female C57BL/6N mice pretreated with ibogaine (50 mg/kg) and sacrificed 48 h. after a single dose of methamphetamine (20 mg/kg). Methamphetamine injection resulted in hyperthermia and induced HSP-72 expression, whereas treatment with ibogaine alone produced hypothermia. The ibogaine followed by methamphetamine injection showed no hyperthermia and decreased HSP-72 expression. These data indicate that pretreatment with ibogaine can completely block methamphetamine-induced hyperthermia and HSP-72 expression in the striatum.

Selenium, an antioxidant, protects against methamphetamine-induced dopaminergic neurotoxicity.

Dopaminergic changes were studied in the caudate nucleus of adult female mice after pre- and post-treatment with an antioxidant, selenium, 72 h after the multiple injections of methamphetamine (METH, 4x10 mg/kg, i.p. at 2-h interval) or an equivalent volume of saline. Selenium treatment prevented the depletion of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in caudate nucleus resulting from the METH treatment. These data suggest that METH-induced neurotoxicity is mediated by free radical and selenium plays a protective role against METH-induced dopaminergic neurotoxicity.

Effect of manganese on the concentration of amino acids in different regions of the rat brain.

The present study was designed to determine if chronic exposure of weanlings and adult rats to Mn produces significant alterations in amino acid concentrations in different regions of the rat brain. Weanling (30 day old) and adult (90 day old) male rats were exposed to 10 and 20 mg Mn/kg body weight per day, by gavage, for 30 days. Forty-eight hours after the last dose, animals were sacrificed by decapitation and brains were dissected into different regions to determine the concentration of amino acids by HPLC/EC. A dose dependent decrease in body weight gain was found in the adult, but not in the weanling rats. Significant increases occurred in concentrations of aspartate, glutamate, glutamine, taurine and gamma-aminobutyric acid (GABA) in the cerebellum of the adult rats dosed with 20 mg/kg per day, Mn. A significant decrease in the concentration of glutamine was observed in caudate nucleus and hippocampus of weanling rats dosed with 10 mg/kg, Mn. These data suggest that chronic Mn exposure can produce a decrease in body weight gain in adult rats and alterations in amino acids in different regions of weanling and adult rat brains.

Fenfluramine and norfenfluramine levels in brain microdialysate, brain tissue and plasma of rats administered doses of d-fenfluramine known to deplete 5-hydroxytryptamine levels in brain.

The relationship between dose, frontal cortex (brain) microdialysate and brain tissue levels of fenfluramine (FEN) and norfenfluramine (NF), as well as the effect that these levels have on body temperature, was determined after systemic d-FEN. FEN and NF levels were monitored continuously in the microdialysate of adult male Sprague-Dawley rats dosed with 3 x 5 mg/kg s.c. (spaced 2 hr apart), 1 x 2 mg/kg s.c. or 1 x 10 mg/kg i.p. d-FEN (at ambient temperatures of either 23 degrees C or 27 degrees C). Drug concentrations in plasma and brain regions were also determined 1 hr after one or three doses of 5 mg/kg of d-FEN and 1 and 8 hr after 10 mg/kg d-FEN, and the levels of 5-hydroxytryptamine and 5-hydroxyindole acetic acid in the frontal cortex of FEN and controls were determined 4 days after dosing. Peak microdialysate FEN levels, occurring between 40 and 60 min after the first dose, were 0.24 +/- 0.07 microM after 2 mg/kg, 0.33 +/- 0.04 microM after 5 mg/kg and 1.65 microM after 10 mg/kg. After multiple doses of 5 mg/kg FEN the time-to-peak level was greater than 80 min with peaks of 0.68 +/- 0.04 microM after the second dose and 1.20 +/- 0.07 microM after the third dose. There was a positive correlation between combined (FEN + NF) peak levels in microdialysate and the increase in body temperature after 10 mg/kg d-FEN at 27 degrees C; however, the group mean and peak levels of FEN and NF in microdialysate were statistically the same at either 23 degrees C or 27 degrees C. The indole-depleting effect of d-FEN at 4 days after dosing was exacerbated at 27 degrees C when hyperthermia occurred. Thus, hyperthermia does not affect the pharmacokinetics of d-FEN but pharmacokinetics can influence the degree of hyperthermia in a 27 degrees C environment. Plasma levels, brain extracellular and brain levels of approximately 1 microM, 2.5 microM and 50 microM FEN (respectively), or greater, result from 5-hydroxytryptamine-depleting doses of 5 mg/kg s.c. FEN.

Quantitative analysis of free sphingoid bases in the brain and spinal cord tissues by high-performance liquid chromatography with a fluorescence detection.

The o-phthaldialdehyde precolumn derivatives of psychosine, sphinganine and sphingosine extracted from brain and spinal cord tissues were determined by high-performance liquid chromatography-fluorescence detection. This method was developed with the purpose of detecting an endogenous amount of psychosine, sphingosine and sphinganine using small aliquots of brain tissues and spinal cord in rats. These sphingolipid bases were extracted in various ratios of chloroform-methanol and several pH values. Recovery of the method is about 81% in 12 ng/tube (final volume, 320 microl), 90-95% in 45 ng/tube of sphingosine and sphinganine within 2-12% relative standard deviation. Detection limits of these sphingoid bases were about 0.05 pmol/mg brain tissue. In the forebrain, brainstem and spinal cord of rats at three different ages of postnatal days (PND) 1, PND 13 and 6 months old, the endogenous concentrations of psychosine, sphingosine and sphinganine were determined. From these results, this method is suitable for the determination of sphingoid bases in small aliquot of brain and spinal cord tissues.

Determination of D-fenfluramine, D-norfenfluramine and fluoxetine in plasma, brain tissue and brain microdialysate using high-performance liquid chromatography after precolumn derivatization with dansyl chloride.

A HPLC method is described for the simultaneous determination of D-fenfluramine (FEN), D-norfenfluramine (NF) and fluoxetine (FLX) using fluorometric detection after precolumn derivatization with dansyl-chloride. The method has limits of quantitation of 200 fmol for FEN and NF, 500 fmol for FLX in brain microdialysate, and 1 pmol for NF and FEN, and 2 pmol for FLX in plasma. Brain tissue standards were linear between 5 and 200 pmol/mg for all three compounds. The inter-assay variability (relative standard deviation) was 6.6%, 6.9% and 9.3% for FEN, 4.6%, 3.7% and 7.9% for NF and 10.4%, 4.9% and 12.2% for FLX, for brain microdialysate (2 pmol/microl), plasma (2 pmol/ microl) and brain tissue (50 pmol/mg), respectively. Intra-assay variability was always lower, typically several times lower than inter-assay variability. Extraction recovery was 108% and 48% for FEN, 105% and 78% for NF and 94% and 45% for FLX, in plasma (2 pmol/microl) and brain tissue (5 pmol/mg), respectively. Due to the stability of the dansyl-chloride derivatives this method is well suited for an autoinjector after manual derivatization with dansyl chloride at room temperature for 4 h.

Neuroendocrine and neurochemical effects of acute ibogaine administration: a time course evaluation.

Ibogaine (IBO) is an indole alkaloid that is reported to facilitate drug abstinence in substance abusers. Despite considerable investigation, the mechanism of IBO action in vivo and its suitability as a treatment for drug addiction remains unclear. The present study was designed to evaluate the time-course effects of acute IBO on neuroendocrine and neurochemical indices. Adult male rats were treated with i.p. saline or 50 mg/kg IBO and sacrificed 15, 30, 60, 120 min and 24 h later. Trunk blood was collected for hormone measures and brains were dissected for neurochemical analyses. IBO produced a rapid elevation in plasma prolactin that declined to control levels by 60 min. Corticosterone levels increased 15 min after drug administration, continued to increase for 120 min, but returned to control levels 24 h after dosing. IBO decreased dopamine (DA) concentrations in the striatum and frontal cortex at 30, 60 and 120 min after injection while DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were elevated over the same time period. 24 h after IBO, DOPAC concentrations in striatum and HVA levels in the frontal cortex were below control values. Serotonin (5-HT) and its metabolite 5-hydroxyindole acetic acid (5-HIAA) were decreased at 60 min after IBO administration only in the striatum. These data indicate that a single injection of IBO produces a spectrum of effects that includes: (1) elevation of plasma prolactin and corticosterone, (2) short- and long-term effects on DA neurotransmission, and (3) modest, transient effects of 5-HT neurotransmission. The effects of IBO reported herein may have relevance to the anti-addictive properties of this drug, and this proposal warrants further investigation.

Individual differences in dopamine release but not rotational behavior correlate with extracellular amphetamine levels in caudate putamen in unlesioned rats.

It has been postulated that differences in pharmacokinetics do not contribute to the well-known individual variability in response to amphetamine (AMPH), but this is yet to be investigated thoroughly. Therefore, rotational behavior of outbred rats (Sprague-Dawley, 4 months old) was recorded during microdialysis sessions and striatal microdialysate was analyzed concomitantly for AMPH and dopamine concentrations after a single injection of 2.5 mg/kg AMPH SC. Three hours later these rats received three doses of 5 mg/kg AMPH SC (spaced 2 h apart) and their brain temperature was recorded every 20 min. The most important findings were: 1) the increase in extracellular dopamine was highly correlated with the corresponding peak AMPH levels in the microdialysate; 2) the peak dopamine level in response to 2.5 mg/kg AMPH was predictive of the hyperthermic response observed during 3 x 5 mg/kg AMPH and 3) high versus low rotators differed neither in their AMPH nor in their dopamine extracellular striatal concentrations.

Methamphetamine-induced dopaminergic toxicity in mice. Role of environmental temperature and pharmacological agents.

1. Multiple injections of METH (4 x 10 mg/kg, i.p.) at room temperature (23 degrees C) produced a significant depletion of dopamine (DA) and its metabolites DOPAC and HVA in striatum at 24 and 72 hr, and 1 and 2 wk. 2. Three days post 4 x 10 mg/kg METH at 23 degrees C, an 80% decrease in striatal dopamine (DA) occurred, while the same dose at 4 degrees C produced only a 20% DA decrease, and 4 x 20 mg/kg METH at 4 degrees C produced a 54% DA decrease. A similar pattern in the decreases of the DA metabolites DOPAC and HVA was observed after METH administration. 3. At 23 degrees C (+)MK-801 completely blocked while phenobarbital (40% decrease) and diazepam (65% decrease) partially blocked decreases in striatal DA produced by 4 x 10 mg/kg METH. Decreases in DOPAC and HVA were similar to the decreases in DA after METH and antagonists. 4. Multiple injections of METH (4 x 10 mg/kg, i.p.) at room temperature also produced a significant depletion of serotonin (5-HT) in striatum at 24 and 72 hr, and 1 and 2 wk. The depletion of 5-HT metabolite 5-HIAA was found only at 72 hr post-dosing. 5. This depletion of 5-HT and its metabolite 5-HIAA at room temperature was blocked either by changing the environmental temperature to 4 degrees C, or by pretreatment with MK-801, diazepam and phenobarbital after METH treatment. 6. Therefore, these data suggest that drugs that block METH toxicity, such as haloperidol (D2 receptors), pentobarbital and phenobarbital (chloride channels) and MK-801 (NMDA/glutamate receptors), do not necessarily have the same mechanism of action but may either induce hypothermia or block induction of hyperthermia. 7. In summary, these studies show that in the mouse, environmental temperature greatly influences METH neurotoxicity, and that the protective effects of compounds such as diazepam, phenobarbital and MK-801 may be mediated by blockade of METH-induced hyperthermia.