Comparison of the discriminative stimulus effects of dimethyltryptamine with different classes of psychoactive compounds in rats

RATIONALE

There has been increased recreational use of dimethyltryptamine (DMT), but little is known of its discriminative stimulus effects.

OBJECTIVES

The present study assessed the similarity of the discriminative stimulus effects of DMT to other types of hallucinogens and to psychostimulants.

METHODS

Rats were trained to discriminate DMT from saline. To test the similarity of DMT to known hallucinogens, the ability of (+)-lysergic acid diethylamide (LSD), (-)-2,5-dimethoxy-4-methylamphetamine (DOM), (+)-methamphetamine, or (+/-)3,4-methylenedioxymethyl amphetamine (MDMA) to substitute in DMT-trained rats was tested. The ability of DMT to substitute in rats trained to discriminate each of these compounds was also tested. To assess the degree of similarity in discriminative stimulus effects, each of the compounds was tested for substitution in all of the other training groups.

RESULTS

LSD, DOM, and MDMA all fully substituted in DMT-trained rats, whereas DMT fully substituted only in DOM-trained rats. Full cross-substitution occurred between DMT and DOM, LSD and DOM, and (+)-methamphetamine and MDMA. MDMA fully substituted for (+)-methamphetamine, DOM, and DMT, but only partially for LSD. In MDMA-trained rats, LSD and (+)-methamphetamine fully substituted, whereas DMT and DOM did not fully substitute. No cross-substitution was evident between (+)-methamphetamine and DMT, LSD, or DOM.

CONCLUSIONS

DMT produces discriminative stimulus effects most similar to those of DOM, with some similarity to the discriminative stimulus effects of LSD and MDMA. Like DOM and LSD, DMT seems to produce predominately hallucinogenic-like discriminative stimulus effects and minimal psychostimulant effects, in contrast to MDMA which produced hallucinogen- and psychostimulant-like effects.

Resolving mitochondrial protein complexes using nongradient blue native polyacrylamide gel electrophoresis

Blue native polyacrylamide gel electrophoresis (BN-PAGE) is a powerful technique for separation and proteomics analysis of high-molecular-weight protein complexes. It is often performed on gradient gels and is widely used for studying mitochondrial membrane complexes involved in electron transportation and oxidative phosphorylation. In this article, we present an alternative BN-PAGE method that uses highly porous, nongradient polyacrylamide gels for separation of rat brain mitochondrial protein complexes. Results demonstrate that this method not only resolves mitochondrial complexes I to V, allowing subsequent analysis by in-gel activity staining and mass spectrometry peptide sequencing, but also identifies Hsp60 polymers and dihydrolipoamide dehydrogenase (DLDH). Moreover, with this new method, it is shown for the first time that complex I and DLDH can be detected simultaneously on a single gel strip by in-gel activity staining. Overall, the method provides a simplified, nongradient gel electrophoretic approach that should be useful in functional proteomics studies.

Life span extension in mice by food restriction depends on an energy imbalance

In this study, our main objective was to determine whether energy restriction (ER) affects the rate of oxygen consumption of mice transiently or lastingly and whether metabolic rate plays a role in the ER-related extension of life span. We compared rates of resting oxygen consumption between C57BL/6 mice, whose life span is prolonged by ER, and the DBA/2 mice where it is not, at 6 and 23 mo of age, following 40% ER for 2 and 19 mo, respectively. Mice of the 2 strains that consumed food ad libitum (AL) had a similar body mass at the age of 4 mo and consumed similar amounts of food throughout the experiment; however, the body weight subsequently significantly increased (20%) in the C57BL/6 mice but did not increase significantly in the DBA/2 mice. The resting rate of oxygen consumption was normalized as per g body weight, lean body mass, organ weight, and per mouse. The resting rate of oxygen consumption at 6 mo was significantly higher in AL DBA/2 mice than the AL C57BL/6 mice for all of the criteria except organ weight. A similar difference in AL mice of the 2 strains was present at 23 mo when resting oxygen consumption was normalized to body weight. Resting oxygen consumption was lowered by ER in both age groups of each strain according to all 4 criteria used for normalization, except body weight in the C57BL/6 mice. The effect of ER on resting oxygen consumption was thus neither transient nor age or strain dependent. Our results suggest that ER-induced extension of life span occurs in the mouse genotype in which there is a positive imbalance between energy intake and energy expenditure.

Carisoprodol-mediated modulation of GABAA receptors: in vitro and in vivo studies

Carisoprodol is a frequently prescribed muscle relaxant. In recent years, this drug has been increasingly abused. The effects of carisoprodol have been attributed to its metabolite, meprobamate, a controlled substance that produces sedation via GABA(A) receptors (GABA(A)Rs). Given the structural similarities between carisoprodol and meprobamate, we used electrophysiological and behavioral approaches to investigate whether carisoprodol directly affects GABA(A)R function. In whole-cell patch-clamp studies, carisoprodol allosterically modulated and directly activated human alpha1beta2gamma2 GABA(A)R function in a barbiturate-like manner. At millimolar concentrations, inhibitory effects were apparent. Similar allosteric effects were not observed for homomeric rho1 GABA or glycine alpha1 receptors. In the absence of GABA, carisoprodol produced picrotoxin-sensitive, inward currents that were significantly larger than those produced by meprobamate, suggesting carisoprodol may directly produce GABAergic effects in vivo. When administered to mice via intraperitoneal or oral routes, carisoprodol elicited locomotor depression within 8 to 12 min after injection. Intraperitoneal administration of meprobamate depressed locomotor activity in the same time frame. In drug discrimination studies with carisoprodol-trained rats, the GABAergic ligands pentobarbital, chlordiazepoxide, and meprobamate each substituted for carisoprodol in a dose-dependent manner. In accordance with findings in vitro, the discriminative stimulus effects of carisoprodol were antagonized by a barbiturate antagonist, bemegride, but not by the benzodiazepine site antagonist, flumazenil. The results of our studies in vivo and in vitro collectively suggest the barbiturate-like effects of carisoprodol may not be due solely to its metabolite, meprobamate. Furthermore, the functional traits we have identified probably contribute to the abuse potential of carisoprodol.

Abuse Potential of Soma: the GABA(A) Receptor as a Target

Soma(®) (carisoprodol) is an increasingly abused, centrally-acting muscle relaxant. Despite the prevalence of carisoprodol abuse, its mechanism of action remains unclear. Its sedative effects, which contribute to its therapeutic and recreational use, are generally attributed to the actions of its primary metabolite, meprobamate, at GABA(A) receptors (GABA(A)R). Meprobamate is a controlled substance at the federal level; ironically, carisoprodol is not currently classified as such. Using behavioral and molecular pharmacological approaches, we recently demonstrated carisoprodol, itself, is capable of modulating GABA(A)R function in a manner similar to central nervous system depressants. Its functional similarities with this highly addictive class of drugs may contribute to the abuse potential of carisoprodol. The site of action of carisoprodol has not been identified; based on our studies, interaction with benzodiazepine or barbiturate sites is unlikely. These recent findings, when coupled with numerous reports in the literature, support the contention that the non-controlled status of carisoprodol should be reevaluated.

Dissociation of functional status from accrual of CML and RAGE in the aged mouse brain

The objectives of this study were: (i) to identify regions of the aged mouse brain in which advanced glycation end-products (AGEs) were increased, and (ii) assess the functional significance of AGEs by determining the extent to which they could predict age-related brain dysfunction. Densitometric analyses of immunoblots for N epsilon-(carboxymethyl)lysine (CML), a predominant AGE, and receptor for AGE (RAGE), were performed in different brain regions of mice aged 8 or 25 months. The 25-month-old mice were tested for ability to perform on tests of cognitive and psychomotor function prior to assessment of CML or RAGE, to determine if immunostaining results could predict functional impairment among the older mice. The amounts of CML increased with age in cortex, hippocampus, striatum, and midbrain, but were unchanged in the brainstem and cerebellum. Increases in RAGE were evident in all brain regions but the hippocampus, and were not linked to increased amounts of CML. Different statistical approaches each failed to reveal any strong association between the degree of age-related functional impairment among individual mice and amounts of CML or RAGE in any particular region of the brain. The findings from this study suggest that accrual of CML and expression of RAGE in different brain regions are time-related phenomena that do not account for individual differences in brain aging or cognitive decline.

Comparison of metabolic rate and oxidative stress between two different strains of mice with varying response to caloric restriction

Metabolic rate and parameters associated with oxidative stress were compared in two strains of mice, one of which, C57BL/6, exhibits an extension of life span in response to caloric restriction while the other, DBA/2, shows no such effect. Metabolic rate was higher in the DBA/2 than in the C57BL/6 mice, when measured at 5-6 months of age as in vivo and in vitro rates of oxygen consumption or body temperature. There were no remarkable inter-strain differences in activities of the antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase or in the rates of mitochondrial superoxide anion radical generation in heart or skeletal muscles. Comparison of glutathione redox state in the heart and skeletal muscles at 3 and 20 months of age indicated that the amount of glutathione (GSH) and the GSH:GSSG (glutathione disulfide) ratio were relatively higher in the young DBA/2 mice, but there were no inter-strain differences in the older mice. The age-related elevation in the level of oxidative stress reflected by GSH:GSSG ratio was greater in the C57BL/6 than DBA/2 mice. The energy balance, indicated by the gain/loss in body weight per unit of food consumed, is higher in C57BL/6 than DBA/2 mice. It is hypothesized that the genotype-specific extension of life span by caloric restriction may involve modulation of oxidative stress produced as a result of an interplay between metabolic rate and energy balance during aging.

Perforated appendicitis masquerading as acute pancreatitis in a morbidly obese patient

Diagnosis and treatment of common conditions in morbidly obese patients still pose a challenge to physicians and surgeons. Sometimes too much reliance is put on investigations that can lead to a misdiagnosis. This case demonstrates an obese woman admitted under the medical team with a presumed diagnosis of pneumonia, who was later found to have an acute abdomen and raised amylase, which led to an assumed diagnosis of pancreatitis. She died within 24 h of admission and post mortem confirmed the cause of death as systemic sepsis due to perforated appendicitis, with no evidence of pancreatitis. Significantly elevated serum amylase level may occur in non-pancreatitic acute abdomen.

Ethanol withdrawal provokes mitochondrial injury in an estrogen preventable manner

We investigated whether ethanol withdrawal (EW) oxidizes mitochondrial proteins and provokes mitochondrial membrane swelling and whether estrogen deprivation contributes to this problem. Ovariectomized female rats with or without 17beta-estradiol (E2)-implantation received a control diet or a liquid ethanol diet (6.5%) for 5 weeks and were sacrificed during EW. Protein oxidation was assessed by measuring carbonyl contents and was visualized by immunochemistry. Mitochondrial membrane swelling as an indicator of mitochondrial membrane fragility was assessed by monitoring absorbance at 540 nm and was compared with that of male rats. Compared to the control diet group and ovariectomized rats with E2-implantation, ovariectomized rats without E2-implantation showed higher carbonylation of mitochondrial proteins and more rapid mitochondrial membrane swelling during EW. Such rapid mitochondrial membrane swelling was comparable to that of male rats undergoing EW. These findings demonstrate that EW provokes oxidative injury to mitochondrial membranes in a manner that is exacerbated by estrogen deprivation.

Nicotine and methamphetamine share discriminative stimulus effects

BACKGROUND

Nicotine and methamphetamine are both abused in similar settings, sometimes together. Because there are known interactions between central nicotinic acetylcholine receptors and dopamine receptors, it is of interest to characterize the nature of the interaction of these two compounds in vivo.

METHODS

The purpose of this study was to characterize the extent to which these two compounds produce similar discriminative stimulus effects and to identify pharmacological mechanisms for their interaction. Male Sprague-Dawley rats were trained to discriminate methamphetamine or nicotine from saline. First, the ability of methamphetamine and nicotine to cross-substitute in rats trained to the other compound was tested. Subsequently, the ability of a dopamine antagonist (haloperidol) and a centrally acting nicotinic antagonist (mecamylamine) to block the discriminative stimulus effects of methamphetamine and nicotine were also tested.

RESULTS

Nicotine fully substituted in methamphetamine-trained rats, but methamphetamine only partially substituted in nicotine-trained rats. In nicotine-trained rats, mecamylamine fully antagonized the discriminative stimulus effects of nicotine, but haloperidol had no effect. The partial substitution of methamphetamine was partially attenuated by haloperidol, but not altered by mecamylamine. In methamphetamine-trained rats, mecamylamine failed to antagonize the discriminative stimulus effects of methamphetamine, but haloperidol fully blocked the methamphetamine cue. Mecamylamine blocked the ability of nicotine to substitute for methamphetamine, but haloperidol had no effect.

CONCLUSIONS

These results indicate that nicotine and methamphetamine share discriminative stimulus effects in some subjects and that the two compounds do not act at the same site, but produce their interaction indirectly. These findings suggest that these two compounds might be at least partially interchangeable in human users, and that there are potentially interesting pharmacological reasons for the commonly observed co-administration of nicotine and methamphetamine.

Mass spectrometry-based survey of age-associated protein carbonylation in rat brain mitochondria

There is a body of evidence lending credence to the idea that oxidative stress may be responsible for age-related deleterious changes in brain function, and that protein carbonylation is a potential marker for such changes. An investigation of oxidative damage to mitochondrial proteins from aged rat brains was done using gel electrophoresis coupled with carbonylation-specific immunostaining. Six proteins that appeared to be susceptible to oxidative modification were identified by in-gel trypsin digestion followed by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry. Two subunits of the H(+)-transporting ATP synthase, adenine nucleotide translocator, voltage-dependent anion channel, glutamate oxaloacetate transaminase, and aconitase were identified as likely targets of age-associated carbonylation.

Effect of long-term caloric restriction on oxygen consumption and body temperature in two different strains of mice

The hypothesis, that a decrease in metabolic rate mediates the life span prolonging effect of caloric restriction (CR), was tested using two strains of mice, one of which, C57BL/6, exhibits life span extension as a result of CR, while the other, DBA/2, shows little or no effect. Comparisons of the rate of resting oxygen consumption and body temperature were made between the strains after they were fed ad libitum (AL) or maintained under 40% CR, from 4 to 16 months of age. Ad libitum-fed mice of the two strains weighed the same when young and consumed similar amounts of food throughout the experiment; however, the C57BL/6 mice weighed 25% more than DBA/2 mice at 15 months of age. The rate of oxygen consumption was normalized as per gram body weight, lean body mass or organ weight as well as per animal. The body temperature and the rate of oxygen consumption, expressed according to all of the four criteria, were decreased in the DBA/2 mice following CR. The C57BL/6 mice also showed a CR-related decrease in body temperature and in the rate of oxygen consumption per animal and when normalized according to lean body mass or organ weight. The results of this study indicate that CR indeed lowers the rate of metabolism; however, this effect by CR does not necessarily entail the prolongation of the life span of mice.

Histochemical staining and quantification of dihydrolipoamide dehydrogenase diaphorase activity using blue native PAGE

Mammalian mitochondrial dihydrolipoamide dehydrogenase (DLDH, EC 1.8.1.4) catalyzes NAD(+)-dependent oxidation of dihydrolipoamide in vivo and can also act as a diaphorase catalyzing in vitro nicotinamide adenine dinucleotide (reduced form) (NADH)-dependent reduction of electron-accepting molecules such as ubiquinone and nitroblue tetrazolium (NBT). In this paper, we report a gel-based method for histochemical staining and quantification of DLDH diaphorase activity using blue native PAGE (BN-PAGE). Rat brain mitochondrial extracts, used as the source of DLDH, were resolved by nongradient BN-PAGE (9%), which was followed by diaphorase activity staining using NADH as the electron donor and NBT as the electron acceptor. It was shown that activity staining of DLDH diaphorase was both protein amount- and time-dependent. Moreover, this in-gel activity-staining method was demonstrated to be in good agreement with the conventional spectrophotometric method that measures DLDH dehydrogenase activity using dihydrolipoamide as the substrate. The method was applied to determine levels of DLDH diaphorase activity in several rat tissues other than the brain, and the results indicated a similar level of DLDH diaphorase activity for all the tissues examined. Finally, the effects of thiol-reactive reagents such as N-ethylmaleimide (NEM) and nitric oxide donors on DLDH diaphorase activity were evaluated, demonstrating that, with this method, DLDH diaphorase activity can be determined without having to remove these thiol-reactive reagents that may otherwise interfere with spectrophotometric measurement of DLDH dehydrogenase activity. The gel-based method can also be used as a means to isolate mitochondrial DLDH that is to be analyzed by mass spectral techniques in studying DLDH post-translational modifications.

Coenzyme Q, oxidative stress and aging

Coenzyme Q (CoQ) has three well-characterized functions in mitochondria, namely (i) transfer of reducing equivalents in the electron transport chain, (ii) generation of superoxide anion radical, O2*-, and (iii) quenching of free radicals. The main purpose of this review is to discuss the effects of CoQ10 intake for relatively prolonged periods on mitochondrial respiratory capacity, indicators of oxidative stress, and life span of animals, in context of the broader issue of whether or not the overall progression of the aging process can be modified by CoQ10 administration. Comparative studies on different mammalian species have indicated that the rate of mitochondrial superoxide anion radical generation is directly correlated with mitochondrial CoQ9 content and inversely related to amounts of CoQ10, particularly the CoQ10 bound to mitochondrial membrane proteins. Contrary to the historical view, dietary supplementation of mice and rats with CoQ10 has been demonstrated to augment the endogenous CoQ content (CoQ9 + CoQ10) in mitochondria and homogenates of various tissues, albeit to varying extent. Ingestion of CoQ10 results in the elevation of endogenous CoQ9, the predominant homologue in mice and rats. In our studies, there was no indication of a discernable effect of CoQ10 intake reflecting enhancement of mitochondrial respiratory activity, antioxidant capacity and pro-oxidant potentiation or prolongation of life span. The possibility that CoQ10 intake affects certain other biological functions by as yet unelucidated mechanisms cannot be ruled out as CoQ has been shown to broadly alter gene expression in mice.

Effects of monoamine oxidase inhibitors on cocaine discrimination in rats

This study tested the time course of the discriminative stimulus effects of inhibitors of monoamine oxidase alone or in combination with cocaine. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg, intraperitoneal) from saline using a two-lever choice methodology. The nonselective monoamine oxidase inhibitors tranylcypromine (0.01-5 mg/kg) and phenelzine (1-25 mg/kg), the monoamine oxidase-A selective compound clorgyline (1-25 mg/kg), and the monoamine oxidase-B selective compounds pargyline (0.005-50 mg/kg) and selegiline (1-25 mg/kg) were tested for substitution 15 min or 24 h following administration, and in combination with 10 mg/kg of cocaine 24 and 48 h after administration. At 15 min, selegiline fully substituted for the discriminative stimulus effects of cocaine, whereas all other compounds partially substituted. At 24 h, substitution of cocaine was diminished for all compounds except phenelzine, which produced a greater amount of substitution at 24 h than at 15 min. When cocaine was administered 24 h after clorgyline, selegiline, pargyline, and phenelzine, cocaine-appropriate responding was attenuated at intermediate doses of these drugs, whereas the highest doses did not alter cocaine-lever responding. All compounds except selegiline substantially decreased response rate and produced various adverse effects. At 48 h, the effects of all compounds except phenelzine were markedly reduced. Selectivity for monoamine oxidase-A or monoamine oxidase-B did not predict the ability to substitute for or attenuate the subjective effects of cocaine. These findings suggest that monoamine oxidase inhibitors can modulate the discriminative stimulus effects of cocaine for at least 24 h, and may be useful for treatment of cocaine abuse.

Effects of age and caloric intake on glutathione redox state in different brain regions of C57BL/6 and DBA/2 mice

The main purpose of the present study was to determine whether specific regions of the mouse brain exhibit different age-related changes in oxidative stress, as indicated by glutathione redox state and the level of protein-glutathionyl mixed disulfides. Comparison of 3- and 21-month-old mice indicated an age-related decrease in the ratio of reduced to oxidized glutathione (GSH/GSSG) as well as a pro-oxidizing shift in the calculated redox potential (ranging from 6 to 15 mV) in the cortex, hippocampus, striatum and cerebellum, whereas there was little change in the brainstem. This pro-oxidizing shift in redox state was due to a modest decrease in GSH content occurring in all the brain regions examined, and elevations in GSSG amount that were most pronounced in the striatum and cerebellum. The regional changes in glutathione redox state were paralleled by increases in the amounts of protein-mixed disulfides. A reduction of caloric intake by 40% for a short period (7 weeks), implemented in relatively old mice (17 months), increased the GSH/GSSG ratio and redox potential at 19 months in the same brain regions that exhibited age-related decreases. The effects of age and caloric restriction were qualitatively similar in C57BL/6 and DBA/2 mice. However, young DBA/2 mice, which do not show extension of life span in response to long-term caloric restriction, had lower GSH/GSSG ratios and higher protein-mixed disulfides than age-matched C57BL/6 mice. The current findings demonstrate that oxidative stress, as reflected by glutathione redox state, increases in the aging brain in regions linked to age-associated losses of function and neurodegenerative diseases.

Spatial learning and psychomotor performance of C57BL/6 mice: age sensitivity and reliability of individual differences

Two tests often used in aging research, the elevated path test and the Morris water maze test, were examined for their application to the study of brain aging in a large sample of C57BL/6JNia mice. Specifically, these studies assessed: (1) sensitivity to age and the degree of interrelatedness among different behavioral measures derived from these tests, (2) the effect of age on variation in the measurements, and (3) the reliability of individual differences in performance on the tests. Both tests detected age-related deficits in group performance that occurred independently of each other. However, analysis of data obtained on the Morris water maze test revealed three relatively independent components of cognitive performance. Performance in initial acquisition of spatial learning in the Morris maze was not highly correlated with performance during reversal learning (when mice were required to learn a new spatial location), whereas performance in both of those phases was independent of spatial performance assessed during a single probe trial administered at the end of acquisition training. Moreover, impaired performance during initial acquisition could be detected at an earlier age than impairments in reversal learning. There were modest but significant age-related increases in the variance of both elevated path test scores and in several measures of learning in the Morris maze test. Analysis of test scores of mice across repeated testing sessions confirmed reliability of the measurements obtained for cognitive and psychomotor function. Power calculations confirmed that there are sufficiently large age-related differences in elevated path test performance, relative to within age variability, to render this test useful for studies into the ability of an intervention to prevent or reverse age-related deficits in psychomotor performance. Power calculations indicated a need for larger sample sizes for detection of intervention effects on cognitive components of the Morris water maze test, at least when implemented at the ages tested in this study. Variability among old mice in both tests, including each of the various independent measures in the Morris maze, may be useful for elucidating the biological bases of different aspects of dysfunctional brain aging.

Endovascular middle cerebral artery occlusion in rats as a model for studying vascular dementia

Vascular dementia (VaD), incorporating cognitive dysfunction with vascular disease, ranks as the second leading cause of dementia in the United States, yet no effective treatment is currently available. The challenge of defining the pathological substrates of VaD is complicated by the heterogeneous nature of cerebrovascular disease and coexistence of other pathologies, including Alzheimer's disease (AD) types of lesion. The use of rodent models of ischemic stroke may help to elucidate the type of lesions that are responsible for cognitive impairment in humans. Endovascular middle cerebral artery (MCA) occlusion in rats is considered to be a convenient and reliable model of human cerebral ischemia. Both sensorimotor and cognitive dysfunction can be induced in the rat endovascular MCA occlusion model, yet sensorimotor deficits induced by endovascular MCA occlusion may improve with time, whereas data presented in this review suggest that in rats this model can result in a progressive course of cognitive impairment that is consistent with the clinical progression of VaD. Thus far, experimental studies using this model have demonstrated a direct interaction of cerebral ischemic damage and AD-type neuropathologies in the primary ischemic area. Further, coincident to the progressive decline of cognitive function, a delayed neurodegeneration in a remote area, distal to the primary ischemic area, the hippocampus, has been demonstrated in a rat endovascular MCA occlusion model. We argue that this model could be employed to study VaD and provide insight into some of the pathophysiological mechanisms of VaD.

Profiling psychomotor and cognitive aging in four-way cross mice

In part due to their genetic uniformity and stable characteristics, inbred rodents or their F1 progeny are frequently used to study brain aging. However, it is recognized that focus on a single genotype could lead to generalizations about brain aging that might not apply to the species as a whole, or to the human population. As a potential alternative to uniform genotypes, genetically heterogeneous (HET) mice, produced by a four-way cross, were tested in the current study to determine if they exhibit age-related declines in cognitive and psychomotor function similar to other rodent models of brain aging. Young (4 months) and older (23 months) CB6F1 × C3D2F1 mice were administered a variety of tests for cognitive, psychomotor, and sensory/reflexive capacities. Spontaneous locomotion, rearing, and ability to turn in an alley all decreased with age, as did behavioral measures sensitive to muscle strength, balance, and motor coordination. Although no effect of age was found for either startle response amplitude or reaction time to shock stimuli, the old mice reacted with less force to low intensity auditory stimuli. When tested on a spatial swim maze task, the old mice learned less efficiently, exhibited poorer retention after a 66-h delay, and demonstrated greater difficulty learning a new spatial location. In addition, the older mice were less able to learn the platform location when it was identified by a local visual cue. Because there was a significant correlation between spatial and cued discrimination performance in the old mice, it is possible that age-related spatial maze learning deficits could involve visual or motor impairments. Variation among individuals increased with age for most tests of psychomotor function, as well as for spatial swim performance, suggesting that four-way cross mice may be appropriate models of individualized brain aging. However, the analysis of spatial maze learning deficits in older CB6F1 × C3D2F1 mice may have limited applicability in the study of brain aging, because of a confounding with visually cued performance deficits.

Effect of coenzyme Q10 intake on endogenous coenzyme Q content, mitochondrial electron transport chain, antioxidative defenses, and life span of mice

The main purpose of this study was to determine whether intake of coenzyme Q10, which can potentially act as both an antioxidant and a prooxidant, has an impact on indicators of oxidative stress and the aging process. Mice were fed diets providing daily supplements of 0, 93, or 371 mg CoQ10 /kg body weight, starting at 3.5 months of age. Effects on mitochondrial superoxide generation, activities of oxidoreductases, protein oxidative damage, glutathione redox state, and life span of male mice were determined. Amounts of CoQ9 and CoQ10, measured after 3.5 or 17.5 months of intake, in homogenates and mitochondria of liver, heart, kidney, skeletal muscle, and brain increased with the dosage and duration of CoQ10 intake in all the tissues except brain. Activities of mitochondrial electron transport chain oxidoreductases, rates of mitochondrial O2-* generation, state 3 respiration, carbonyl content, glutathione redox state of tissues, and activities of superoxide dismutase, catalase, and glutathione peroxidase, determined at 19 or 25 months of age, were unaffected by CoQ10 administration. Life span studies, conducted on 50 mice in each group, showed that CoQ10 administration had no effect on mortality. Altogether, the results indicated that contrary to the historical view, supplemental intake of CoQ10 elevates the endogenous content of both CoQ9 and CoQ10, but has no discernable effect on the main antioxidant defenses or prooxidant generation in most tissues, and has no impact on the life span of mice.

GABAergic modulation of the discriminative stimulus effects of methamphetamine

To assess whether gamma-aminobutyric acid (GABA) modulation of dopamine is important in mediation of the discriminative stimulus effects of methamphetamine, the GABA compounds chlordiazepoxide (benzodiazepine site agonist), pentobarbital (barbiturate site agonist), bicuculline and pentylenetetrazol (GABA(A) receptor antagonists) were tested in Sprague-Dawley rats trained to discriminate methamphetamine (1 mg/kg, i.p.) from saline. Each of the compounds produced modest amounts of methamphetamine-appropriate responding (20-35%) when tested alone. When tested in combination with methamphetamine, the antagonists (bicuculline and pentylenetetrazol) failed to shift the methamphetamine dose-effect curve. In contrast, chlordiazepoxide (25 mg/kg, i.p.) reduced methamphetamine-appropriate responding at each dose of methamphetamine tested, and pentobarbital (10 mg/kg, i.p.) dose-dependently decreased the discriminative stimulus effects of 1 mg/kg methamphetamine. In conclusion, GABA(A) antagonists and positive modulators likely do not produce methamphetamine-like stimulus effects. However, activation of GABA(A) receptors can interfere with the discriminative stimulus effects of methamphetamine.

Concurrent administration of coenzyme Q10 and alpha-tocopherol improves learning in aged mice

The main purpose of this study was to determine whether supplemental intake of coenzyme Q10 (CoQ) (ubiquinone-10) or alpha-tocopherol, either alone or together, could improve brain function of aged mice, as reflected in their cognitive or psychomotor performance. Separate groups of aged mice (24 months) were administered either CoQ (123 mg/kg/day), or alpha-tocopherol acetate (200 mg/kg/day), or both, or the vehicle (soybean oil) via gavage for a period of 14 weeks. Three weeks following the initiation of these treatments, mice were given a battery of age-sensitive behavioral tests for the assessment of learning, recent memory, and psychomotor function. In a test that required the mice to rapidly identify and remember the correct arm of a T-maze, and to respond preemptively in order to avoid an electric shock, the intake of alpha-tocopherol plus CoQ resulted in more rapid learning compared to the control group. Learning was not significantly improved in the mice receiving CoQ or alpha-tocopherol alone. None of the treatments resulted in a significant improvement of psychomotor performance in the old mice. In a separate study, treatment with higher doses of CoQ alone (250 or 500 mg/kg/day) for 14 weeks failed to produce effects comparable to those of the combination of alpha-tocopherol and CoQ. The apparent interaction of CoQ and alpha-tocopherol treatments is consistent with the previous suggestion, based on biochemical studies, that coenzyme Q and alpha-tocopherol act in concert. Overall, the findings suggest that concurrent supplementation of alpha-tocopherol with CoQ is more likely to be effective as a potential treatment for age-related learning deficits than supplementation with CoQ or alpha-tocopherol alone.

Lifelong vitamin E intake retards age-associated decline of spatial learning ability in apoE-deficient mice

The potential for lifelong vitamin E supplementation to delay age-associated cognitive decline was tested in apoE-deficient and wild-type C57BL/6 mice. Beginning at eight weeks of age, the mice were maintained on a control diet or diets supplemented with dl-α-tocopheryl acetate yielding approximate daily intakes of either 20 or 200 mg/kg body weight. When 6 or 18 months of age, cognitive functioning of the mice was assessed using swim maze and discriminated avoidance testing procedures. For the mice maintained on control diets, the age-related declines in swim maze performance were relatively larger in apoE-deficient mice when compared with wild-type. On the other hand, age-associated declines in learning and working memory for discriminated avoidance were similar in the two genotypes. The 200-mg/kg dose of vitamin E prevented the accelerated decline in spatial learning apparent in 18-month-old apoE-deficient mice, but had no equivalent effect on performance declines attributable to normal aging in the wild-type mice. Vitamin E supplementation failed to prevent age-related impairments in learning and memory for discriminated avoidance observed in both the wild-type and apoE-deficient mice. The current findings are consistent with the hypothesis that apoE deficiency confers an accelerated, though probably selective, loss of brain function with age. This loss of function would appear to involve pathogenic oxidative mechanisms that can be prevented or offset by antioxidant supplementation.

Comparison of the actions of gamma-butyrolactone and 1,4-butanediol in Swiss-Webster mice

The abuse of gamma-hydroxybutyrate (GHB) and two of its precursors, gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are recognized as a public health concern. Here, we report dose-response and time-course analyses for effects of GBL and 1,4-BD on locomotor activity and body temperature in Swiss-Webster mice. Locomotor activity was measured for 2 h following a single injection of one of four doses of each agent plus a saline vehicle control. At 50 mg/kg, GBL produced an initial depression of locomotor activity which was followed by stimulation of locomotor activity. In contrast, 1,4-BD at 50 mg/kg stimulated locomotor activity without producing any depression of activity. At higher doses, GBL produced primarily a dose-dependent decrease in locomotor activity that returned to baseline within 50 min. In contrast, 1,4-BD produced an initial depression which was followed by stimulation of activity. Body temperature was measured rectally across a 2.5-h time course following injection with either agent. Both drugs produced hypothermia with peak effects occurring at 20 and 30 min for both drugs for the lower and higher dose, respectively. At 150 mg/kg, GBL produced a greater hypothermic response; however, no differences in hypothermic response were observed at 100 mg/kg. These studies demonstrate that the precursor drugs to GHB have some differential actions from each other.

Short-term vitamin E intake fails to improve cognitive or psychomotor performance of aged mice

The purpose of this study was to determine if relatively short-term vitamin E supplementation could reverse age-associated impairments in cognitive or motor function and the accumulated oxidative damage in the brain of aged mice. Separate groups of 5- or 20-month-old C57BL6 mice were placed on either a control diet or the same diet supplemented with alpha-tocopheryl acetate (1.65 g/kg). After 4 weeks on the diets, mice were tested for cognitive and motor functions over the next 8 weeks, during which the supplementation was maintained. Vitamin E supplementation increased the concentration of alpha-tocopherol in the cerebral cortex of both the young and old mice, but did not significantly affect oxidative damage to proteins and lipids in the brain cortex. When compared with young controls, the old control mice showed slower learning of a swim maze, longer reaction times, diminished auditory and shock-startle responsiveness, and diminished motor performance on tests of coordinated running and bridge walking. The vitamin E-administered old mice failed to show improvement of function relative to age-matched controls on any of the tests, but did show altered retention performance on the swim maze task and impaired performance in the test of coordinated running. The latter effects were not evident in young mice on the supplemented diet. Results of this study suggest that, when implemented in relatively old mice, supplementation of vitamin E is ineffective in reversing preexisting age-related impairments of cognitive or motor function, and has little effect on common measures of protein or lipid oxidative damage in the mouse brain. Moreover, the current findings indicate that vitamin E could have detrimental effects on some brain functions when implemented in older animals.

Proteomic identification of specific oxidized proteins in ApoE-knockout mice: relevance to Alzheimer's disease

We have examined oxidized proteins in the brain regions of wild-type (WT) and ApoE-knockout (KO) animals. Total protein oxidation in the hippocampus of young-KO (6 month) animals was approximately 2-fold greater than that of young-WT (6 month) animals and was similar to that of old-WT (18 month) and old-KO (18 month) animals. In the cortex of the same animals, the levels of total protein oxidation in all four groups were not significantly different. Two-dimensional electrophoresis (2-DE) coupled with immunostaining for protein carbonylation revealed six specific oxidation-sensitive proteins, the oxidation levels of which were increased in young-KO, old-WT, and old-KO mice compared with young-WT mice. These six oxidation-sensitive proteins were identified by mass spectrometry as glial fibrillary acidic protein, creatine kinase BB, disulfide isomerase, chaperonin subunit 5, dihydropyrimidase-related protein 2, and mortalin. These results indicate that the ApoE gene product offers protection against age-associated oxidative damage in the brain. Moreover, two of these proteins, creatine kinase and dihydropyrimidase-related protein 2, have recently been found to be oxidized in the brains of human subjects with Alzheimer's disease [Aksenov et al. J. Neurochem. 74: 2520-2527; 2000; Castegna et al. J. Neurochem. 82: 1524-1532; 2002]. These data suggest that the ApoE-knockout mouse serves as an appropriate model for studying pathogenic oxidative mechanisms influencing risk and progression of Alzheimer's disease.

Coenzyme Q intake elevates the mitochondrial and tissue levels of Coenzyme Q and alpha-tocopherol in young mice

The main objective of this study was to resolve the issue of whether the amounts of Coenzyme Q (CoQ), which is endogenously synthesized in cells, can be elevated in tissues and mitochondria of young mice by dietary supplementation with CoQ10. The prevalent view is that the uptake of exogenous CoQ by tissues other than plasma and liver either does not occur or is quite minimal. Mice, 6 mo of age, were fed 0, 148 or 654 mg CoQ10/(kg body x d) in their diets for 11 wk. CoQ10 intake enhanced both CoQ9 and CoQ10 homologues in the plasma, and in homogenates and mitochondria of liver, heart and skeletal muscle. CoQ was elevated in brain mitochondria, but not in the brain homogenate. The uptake of exogenous CoQ was higher in mitochondria of heart and skeletal muscle than those in liver. CoQ10 administration also elevated the alpha-tocopherol concentration in tissue homogenates and their mitochondria, thereby providing an in vivo indication of the "sparing" effect of CoQ on alpha-tocopherol. Results of this study demonstrate that, contrary to the historical view, both total and mitochondrial CoQ concentrations in the heart and skeletal muscle and in the mitochondria of brain of young mice can be augmented by dietary supplementation. Furthermore, CoQ intake enhances the antioxidative potential of tissues by elevating the endogenous amounts of alpha-tocopherol.

Effects of ethanol on cocaine discrimination in rats

Ethanol and cocaine are frequently abused in combination, but little is known about how the subjective effects of the two drugs interact. The ability of ethanol and other GABA(A)-active compounds to alter the discriminative stimulus effects of cocaine was tested. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg ip) from saline using either single- or cumulative-dosing methods. In single-dose testing, ethanol (0.1-0.5 g/kg) dose-dependently decreased cocaine-appropriate responding following the training dose of cocaine. Ethanol (0.5 g/kg) produced a rightward shift in the cocaine cumulative dose-effect curve. Ethanol (0.1-1.0 g/kg) failed to substitute for the discriminative stimulus effects of cocaine and the higher doses (1-2 g/kg) completely suppressed responding. Indirect GABA(A) agonists diazepam (benzodiazepine site) and pentobarbital (barbiturate site) did not block the discriminative stimulus effects of cumulative doses of cocaine. The GABA(A) antagonist pentylenetetrazol (PTZ) (10-40 mg/kg) did not substitute for cocaine. These findings suggest that ethanol can modulate the discriminative stimulus effects of cocaine, and that these effects may not be mediated by the actions of ethanol at the GABA(A) receptor.

Supplementation with vitamin E fails to attenuate oxidative damage in aged mice

The validity of the oxidative stress hypothesis of aging has sometimes been questioned because the administration of low molecular weight antioxidants such as alpha-tocopherol does not retard the aging process and extend maximum life span. Thus, the goal of the current study was to determine if increased oral intake of alpha-tocopheryl acetate indeed results in its augmentation in tissues or in their mitochondria, and whether or not this causes an attenuation of oxidative damage. Groups of relatively old (21 months) experimental mice were fed a diet supplemented with 1.65 g/kg alpha-tocopheryl acetate or the base diet (NIH-31), for 13 weeks. Supplementation with alpha-tocopheryl acetate increased alpha-tocopherol concentrations approximately 3-5-fold in plasma and in tissue homogenates and approximately 2-3-fold in mitochondria from liver, skeletal muscle and heart of the mice. However, supplementation affected neither the rate of heart mitochondrial H(2)O(2) generation nor products of lipid peroxidation (thiobarbituric acid-reactive substances) and protein oxidation (protein carbonyls). Thus, in contrast to life-extending interventions such as caloric restriction, that can produce relatively rapid decreases in oxidative damage, supplementation with alpha-tocopheryl acetate had little or no impact on the steady-state level of cellular oxidative damage. This difference could explain why alpha-tocopherol administration has been found to be ineffective in the extension of the life span.

Genotype and age influence the effect of caloric intake on mortality in mice

Long-term caloric restriction (CR) has been repeatedly shown to increase life span and delay the onset of age-associated pathologies in laboratory mice and rats. The purpose of the current study was to determine whether the CR-associated increase in life span occurs in all strains of mice or only in some genotypes and whether the effects of CR and ad libitum (AL) feeding on mortality accrue gradually or are rapidly inducible and reversible. In one experiment, groups of male C57BL/6, DBA/2, and B6D2F1 mice were fed AL or CR (60% of AL) diets beginning at 4 months of age until death. In the companion study, separate groups of mice were maintained chronically on AL or CR regimens until 7, 17, or 22-24 months of age, after which, half of each AL and CR group was switched to the opposite regimen for 11 wk. This procedure yielded four experimental groups for each genotype, namely AL-->AL, AL-->CR, CR-->CR, and CR-->AL, designated according to long-term and short-term caloric regimen, respectively. Long-term CR resulted in increased median and maximum life span in C57BL/6 and B6D2F1 mice but failed to affect either parameter in the DBA/2 mice. The shift from AL-->CR increased mortality in 17- and 24-month-old mice, whereas the shift from CR-->AL did not significantly affect mortality of any age group. Such increased risk of mortality following implementation of CR at older ages was evident in all three strains but was most dramatic in DBA/2 mice. Results of this study indicate that CR does not have beneficial effects in all strains of mice, and it increases rather than decreases mortality if initiated in advanced age.

Effects of coenzyme Q(10) administration on its tissue concentrations, mitochondrial oxidant generation, and oxidative stress in the rat

Coenzyme Q (CoQ(10)) is a component of the mitochondrial electron transport chain and also a constituent of various cellular membranes. It acts as an important in vivo antioxidant, but is also a primary source of O(2)(-*)/H(2)O(2) generation in cells. CoQ has been widely advocated to be a beneficial dietary adjuvant. However, it remains controversial whether oral administration of CoQ can significantly enhance its tissue levels and/or can modulate the level of oxidative stress in vivo. The objective of this study was to determine the effect of dietary CoQ supplementation on its content in various tissues and their mitochondria, and the resultant effect on the in vivo level of oxidative stress. Rats were administered CoQ(10) (150 mg/kg/d) in their diets for 4 and 13 weeks; thereafter, the amounts of CoQ(10) and CoQ(9) were determined by HPLC in the plasma, homogenates of the liver, kidney, heart, skeletal muscle, brain, and mitochondria of these tissues. Administration of CoQ(10) increased plasma and mitochondria levels of CoQ(10) as well as its predominant homologue CoQ(9). Generally, the magnitude of the increases was greater after 13 weeks than 4 weeks. The level of antioxidative defense enzymes in liver and skeletal muscle homogenates and the rate of hydrogen peroxide generation in heart, brain, and skeletal muscle mitochondria were not affected by CoQ supplementation. However, a reductive shift in plasma aminothiol status and a decrease in skeletal muscle mitochondrial protein carbonyls were apparent after 13 weeks of supplementation. Thus, CoQ supplementation resulted in an elevation of CoQ homologues in tissues and their mitochondria, a selective decrease in protein oxidative damage, and an increase in antioxidative potential in the rat.

Nitrones, their value as therapeutics and probes to understand aging

The nitrone-based free radical traps have significant potential in the treatment of neurodegenerative diseases as well as in the prolongation of life span. The mass action free radical trapping activity of these compounds is the property, which first brought them to the attention of the scientific community. Nevertheless extensive research has demonstrated that these reactions are not responsible for their therapeutic mechanistic basis of activity. Rather the mechanism of action in the case of their neuroprotective activity appears to involve the inhibition of enhanced signal transduction processes that mediate the upregulation of genes, which produce neurotoxic products. The most widely used compound in this series, alpha-phenyl-tert-butyl-nitrone (PBN), has been shown to extend life span in three published studies, i.e. two mouse models and one rat model. Significant prolongation of life span was noted in all three studies. We report the summary of a recent study with a novel nitrone, CPI-1429, which demonstrated the ability to extend life span even though administration of the compound was begun in older animals. Despite these promising studies, much more rigorous research examining the anti-aging activity of the nitrones needs to be conducted. It is not known exactly why the nitrones possess anti-aging activity. They have been shown to quell enhanced signal transduction processes associated with enhanced pro-inflammatory cytokine mediated events. The nitrones interfere in some unknown steps preventing receptor triggered MAP kinase phosphorylation cascades. Stabilization of phosphorylation networks associated with checkpoint proteins could slow cell cycle processes and this could be the basis of the nitrones anti-senescent activity.

Nitrones as neuroprotectants and antiaging drugs

Specific nitrones have been used for more than 30 years in analytical chemistry and biochemistry to trap and stabilize free radicals for the purpose of their identification and characterization. PBN (alpha-phenyl-tert-butyl nitrone), one of the more widely used nitrones for this purpose, has been shown to have potent pharmacologic activities in models of a number of aging-related diseases, most notably the neurodegenerative diseases of stroke and Alzheimer's disease. Studies in cell and animal models strongly suggest that PBN has potent antiaging activity. A novel nitrone, CPI-1429, has been shown to extend the life span of mice when administration was started in older animals. It has also shown efficacy in the prevention of memory dysfunction associated with normal aging in a mouse model. Mechanistic studies have shown that the neuroprotective activity of nitrones is not due to mass-action free radical-trapping activity, but due to cessation of enhanced signal transduction processes associated with neuroinflammatory processes known to be enhanced in several neurodegenerative conditions. Enhanced neuroinflammatory processes produce higher levels of neurotoxins, which cause death or dysfunction of neurons. Therefore, quelling of these processes is considered to have a beneficial effect allowing proper neuronal functioning. The possible antiaging activity of nitrones may reside in their ability to quell enhanced production of reactive oxygen species associated with age-related conditions. On the basis of novel ideas about the action of secretory products formed by senescent cells on bystander cells, it is postulated that nitrones will mitigate these processes and that this may be the mechanism of their antiaging activity.

Selection of putative immunogenic peptides by molecular modelling of the urease of Helicobacter pylori

Computational methods such as molecular modelling are becoming an increasingly useful means of rationalising experimental data and creating a hypothesis that can suggest new experiments. In this report we discuss the application of molecular modelling methods to aid the selection of feasible peptide epitopes of the urease enzyme from Helicobacter pylori, an important vaccine candidate. Surface exposure was chosen as a criterion for the selection of three peptides which each had different levels of accessibility according to the 3D model. Antibodies raised against these peptides were analysed for their immunoreactivity with the holo enzyme. Only one anti-peptide antibody showed good reactivity with the urease. Our findings emphasise that surface exposure of peptide is not the only important criterion for the selection of immunogenic peptides.

Dopamine transporter binding without cocaine-like behavioral effects: synthesis and evaluation of benztropine analogs alone and in combination with cocaine in rodents

RATIONALE

Previous SAR studies demonstrated that small halogen substitutions on the diphenylether system of benztropine (BZT), such as a para-Cl group, retained high affinity at the cocaine binding site on the dopamine transporter. Despite this high affinity, the compounds generally had behavioral effects different from those of cocaine. However, compounds with meta-Cl substitutions had effects more similar to those of cocaine.

OBJECTIVES

A series of phenyl-ring analogs of benztropine (BZT) substituted with 3'-, 4'-, 3',4"- and 4',4"-position Cl-groups were synthesized and their pharmacology was evaluated in order to assess more fully the contributions to pharmacological activity of substituents in these positions.

METHODS

Compounds were synthesized and their pharmacological activity was assessed by examining radioligand binding and behavioral techniques.

RESULTS

All of the compounds displaced [3H]WIN 35,428 binding with affinities ranging from 20 to 32.5 nM. Affinities at norepinephrine ([3H]nisoxetine) and serotonin ([3H]citalopram) transporters, respectively, ranged from 259 to 5120 and 451 to 2980 nM. Each of the compounds also inhibited [3H]pirenzepine binding to muscarinic M1 receptors, with affinities ranging from 0.98 to 47.9 nM. Cocaine and the BZT analogs produced dose-related increases in locomotor activity in mice. However, maximal effects of the BZT analogs were uniformly less than those produced by cocaine, and were obtained 2-3 h after injection compared to the relatively rapid onset (within 30 min) of cocaine effects. In rats trained to discriminate i.p. saline from 29 mumol/kg cocaine (10 mg/kg), cocaine produced a dose-related increase in responding on the cocaine lever, reaching 100% at the training dose; however, none of the BZT analogs fully substituted for cocaine, with maximum cocaine responding from 20 to 69%. Despite their reduced efficacy compared to cocaine in cocaine discrimination, none of the analogs antagonized the effects of cocaine. As has been reported previously for 4'-Cl-BZT, the cocaine discriminative-stimulus effects were shifted left-ward by co-administration of the present BZT analogs.

CONCLUSIONS

The present results indicate that although the BZT analogs bind with relatively high affinity and selectivity at the dopamine transporter, their behavioral profile is distinct from that of cocaine. The present results suggest that analogs of BZT may be useful as treatments for cocaine abuse in situations in which an agonist treatment is indicated. These compounds possess features such as reduced efficacy compared to cocaine and a long duration of action that may render them particularly useful leads for the development of therapeutics for cocaine abusers.

Reversible effects of long-term caloric restriction on protein oxidative damage

The age-associated increase in oxidative damage in ad libitum-fed mice is attenuated in mice fed calorically restricted (CR) diets. The objective of this study was to determine if this effect results from a slowing of age-related accumulation of oxidative damage, or from a reversible decrease of oxidative damage by caloric restriction. To address these possibilities, crossover studies were conducted in C57BL/6 mice aged 15 to 22 months that had been maintained, after 4 months of age, on ad libitum (AL) or a 60% of AL caloric regimen. One half of the mice in these groups were switched to the opposite regimen of caloric intake for periods up to 6 weeks, and protein oxidative damage (measured as carbonyl concentration and loss of sulfhydryl content) was measured in homogenates of brain and heart. In AL-fed mice, the protein carbonyl content increased with age, whereas the sulfhydryl content decreased. Old mice maintained continuously under CR had reduced levels of protein oxidative damage when compared with the old mice fed AL. The effects of chronic CR on the carbonyl content of the whole brain and the sulfhydryl content of the heart were fully reversible within 3-6 weeks following reinstatement of AL feeding. The effect of chronic CR on the sulfhydryl content of the brain cortex was only partially reversible. The introduction of CR for 6 weeks in the old mice resulted in a reduction of protein oxidative damage (as indicated by whole brain carbonyl content and cortex sulfhydryl), although this effect was not equivalent to that of CR from 4 months of age. The introduction of CR did not affect the sulfhydryl content of the heart. Overall, the current findings indicate that changes in the level of caloric intake may reversibly affect the concentration of oxidized proteins and sufhydryl content. In addition, chronic restriction of caloric intake also retards the age-associated accumulation of oxidative damage. The magnitude of the reversible and chronic effects appears to be dependent upon the tissue examined and the nature of the oxidative alteration.

Conformation and dynamics of heparin and heparan sulfate

The glycosaminoglycans heparin and heparan sulfate contain similar structural units in varying proportions providing considerable diversity in sequence and biological function. Both compounds are alternating copolymers of glucosamine with both iduronate- and glucuronate-containing sequences bearing N-sulfate, N-acetyl, and O-sulfate substitution. Protein recognition of these structurally-diverse compounds depends upon substitution pattern, overall molecular shape, and on internal mobility. In this review particular attention is paid to the dynamic aspects of heparin/heparan sulfate conformation. The iduronate residue possesses an unusually flexible pyranose ring conformation. This extra source of internal mobility creates special problems in rationalization of experimental data for these compounds. We present herein the solution-state NMR parameters, fiber diffraction data, crystallographic data, and molecular modeling methods employed in the investigation of heparin and heparan sulfate. Heparin is a useful model compound for the sulfated, protein-binding regions of heparan sulfate. The literature contains a number of solution and solid-state studies of heparin oligo- and polysaccharides for both isolated heparin species and those bound to protein receptors. These studies indicate a diversity of iduronate ring conformations, but a limited range of glycosidic linkage geometries in the repeating disaccharides. In this sense, heparin exhibits a well-defined overall shape within which iduronate ring forms can freely interconvert. Recent work suggests that computational modeling could potentially identify heparin binding sites on protein surfaces.

Molecular modelling study of HIV p17gag (MA) protein shell utilising data from electron microscopy and X-ray crystallography

The matrix protein p17gag (MA) is a product of proteolytic cleavage of the gag gene encoded polyprotein (pr55gag) and is formed when HIV particles undergo the process of maturation. The MA protein is associated with the inner surface of the viral membrane and determines the overall shape of the virion. Previous studies have shown the existence of trimers of MA in solution and in the crystalline state. Here, we used molecular modelling methods to identify feasible interactions between pairs of MA trimers and have related this to structural data from electron microscopy. A systematic search docking procedure was able to identify many energetically favourable conformations for a pair of trimers, including some which have been previously reported. These conformations were used to generate several networks of MA trimers, which were then evaluated against structural observations of the MA network. The model suggested here provides a good match with experimental data such as the spacing between gag protein rings, the number and disposition of glycoprotein (gp41-gp120) knobs and the number of copies of MA in a virus particle. It also rationalizes the observed distribution of sizes of virus particles and is consistent with the presence of icosahedral organisation in mature HIV. Energy minimisation performed with explicit water and counter ions, was used to identify residues participating in inter-trimer interactions. The nature of these interactions is discussed in relation to the conservation of these residues in reported variants of the HIV and SIV MA protein sequences.

Effects of NMDA receptor blockers on cocaine-stimulated locomotor activity in mice

Effects of MK-801 and ketamine, N-methyl-D-aspartate (NMDA) receptor blockers, on cocaine-stimulated locomotor activity were investigated in male Swiss-Webster mice. MK-801 (0.25, 0.5, 1.0 and 2.5 mg/kg), ketamine (10, 25 and 50 mg/kg) or saline was injected 20 min before cocaine (5, 10 and 20 mg/kg i.p.). Locomotor activity was measured for 30 min immediately following cocaine treatment. All doses of the drugs were also tested for ability to depress or stimulate locomotor activity in the naive (no cocaine-treated) mice. Cocaine produced a dose-dependent increase in locomotor activity that was blocked dose-dependently by MK-801 or ketamine. The blockade by MK-801 was more prominent than by ketamine. Our results may suggest that cocaine-induced locomotor stimulation in mice is modulated via NMDA receptor mediated mechanisms.

Effect of age and caloric restriction on bleomycin-chelatable and nonheme iron in different tissues of C57BL/6 mice

The objective of this study was to test the hypothesis that the widely observed age-associated increase in the amounts of macromolecular oxidative damage is due to an elevation in the availability of redox-active iron, that is believed to catalyze the scission of H2O2 to generate the highly reactive hydroxyl radical. Concentrations of bleomycin-chelatable iron and nonheme iron were measured in various tissues and different regions of the brain of mice fed on ad libitum (AL) or a calorically restricted (to 60% of AL) diet at different ages. The concentrations of these two pools of iron varied markedly as a function of tissue, age, and caloric intake. There was no consistent ratio between the amounts of nonheme and the bleomycin-chelatable iron pools across these conditions. Nonheme iron concentration increased with age in the liver, kidney, heart, striatum, hippocampus, midbrain and cerebellum of AL animals, whereas bleomycin-chelatable iron increased significantly with age only in the liver. Amounts of both nonheme and bleomycin-chelatable iron remained unaltered during aging in the cerebral cortex and hindbrain of AL mice. Caloric restriction had no effect on iron concentration in the brain or heart, but caused a marked increase in the concentration of both bleomycin-chelatable and nonheme iron in the liver and the kidney. The results do not support the hypothesis that accumulation of oxidative damage with age, or its attenuation by CR, are associated with corresponding variations in redox-active iron.

Effects of coenzyme Q10 and alpha-tocopherol administration on their tissue levels in the mouse: elevation of mitochondrial alpha-tocopherol by coenzyme Q10

Coenzyme Q (CoQ) was previously demonstrated in vitro to indirectly act as an antioxidant in respiring mitochondria by regenerating alpha-tocopherol from its phenoxyl radical. The objective of this study was to determine whether CoQ has a similar sparing effect on alpha-tocopherol in vivo. Mice were administered CoQ10 (123 mg/kg/day) alone, or alpha-tocopherol (200 mg/kg/day) alone, or both, for 13 weeks, after which the amounts of CoQ10, CoQ9 and alpha-tocopherol were determined by HPLC in the serum as well as homogenates and mitochondria of liver, kidney, heart, upper hindlimb skeletal muscle and brain. Administration of CoQ10 and alpha-tocopherol, alone or together, increased the corresponding levels of CoQ10 and alpha-tocopherol in the serum. Supplementation with CoQ10 also elevated the amounts of the predominant homologue CoQ9 in the serum and the mitochondria. A notable effect of CoQ10 intake was the enhancement of alpha-tocopherol in mitochondria. alpha-Tocopherol administration resulted in an elevation of alpha-tocopherol content in the homogenates of nearly all tissues and their mitochondria. Results of this study thus indicate that relatively long-term administration of CoQ10 or alpha-tocopherol can result in an elevation of their concentrations in the tissues of the mouse. More importantly, CoQ10 intake has a sparing effect on alpha-tocopherol in mitochondria in vivo.

Estimating age-related changes in psychomotor function: influence of practice and of level of caloric intake in different genotypes

This article presents a discussion of some key considerations in the measurement of age-related changes in psychomotor function of mice. We illustrate that "standard" measures of psychomotor performance, such as running speed on a rotorod task, are highly sensitive to practice effects. Examples are cited in which failure to assess practice effects can influence conclusions regarding the magnitude and rate of change in psychomotor capacity as a function of age. A second set of examples is focused on estimating the effect of an experimental intervention, caloric restriction, on age-related changes in psychomotor performance. These examples show that psychomotor performance at a given age may vary directly, and reversibly, with the level of caloric intake. Independent of such reversible effects, the level of caloric intake can also modulate the rate of change in capacity as a function of age. It is concluded that reversible, short-term effects must be considered in estimating the effect of an experimental intervention on the rate of age-associated change in psychomotor function.

Caloric restriction prevents age-associated accrual of oxidative damage to mouse skeletal muscle mitochondria

The purpose of this study was to understand the nature of the causes underlying the senescence-related decline in skeletal muscle mass and performance. Protein and lipid oxidative damage to upper hindlimb skeletal muscle mitochondria was compared between mice fed ad libitum and those restricted to 40% fewer calories--a regimen that increases life span by approximately 30-40% and attenuates the senescence-associated decrement in skeletal muscle mass and function. Oxidative damage to mitochondrial proteins, measured as amounts of protein carbonyls and loss of protein sulfhydryl content, and to mitochondrial lipids, determined as concentration of thiobarbituric acid reactive substances, significantly increased with age in the ad libitum-fed (AL) C57BL/6 mice. The rate of superoxide anion radical generation by submitochondrial particles increased whereas the activities of antioxidative enzymes superoxide dismutase, catalase, and glutathione peroxidase in muscle homogenates remained unaltered with age in the AL group. In calorically-restricted (CR) mice there was no age-associated increase in mitochondrial protein or lipid oxidative damage, or in superoxide anion radical generation. Crossover studies, involving the transfer of 18- to 22-month-old mice fed on the AL regimen to the CR regimen, and vice versa, indicated that the mitochondrial oxidative damage could not be reversed by CR or induced by AL feeding within a time frame of 6 weeks. Results of this study indicate that mitochondria in skeletal muscles accumulate significant amounts of oxidative damage during aging. Although such damage is largely irreversible, it can be prevented by restriction of caloric intake.

Differential responsiveness to cocaine in C57BL/6J and DBA/2J mice

The present study compared cocaine-induced hyperlocomotion and cocaine i.v. self-administration in DBA/2J and C57BL/6J mice. In the locomotor activity experiment, these strains were tested for hyperlocomotion after i.p. cocaine injection (0-60.0 mg/kg), using a Digiscan Animal Activity Monitoring System. In the cocaine i.v. self-administration experiment, they were compared for their ability to acquire and maintain cocaine self-administration in operant chambers with levers as the manipulanda. Animals were first trained to respond for food as a reinforcer (condensed milk solution); they were then submitted to surgical i.v. insertion of an in-dwelling catheter, and required to respond for i.v. cocaine (0.25-4.0 mg/kg per injection) as a reinforcer. DBA/2J mice showed significantly higher maximal cocaine-induced hyperlocomotion, more rapid acquisition of cocaine self-administration, and significantly lower rates of cocaine self-administration. Cocaine concentration in the brains of DBA/2J and C57BL/6J mice failed to differ following i.p. injection, suggesting that distribution factors were not involved in the differential responses to cocaine. Although not conclusive, this pattern of effects may suggest that cocaine has greater reinforcing efficacy in DBA/2J mice, confirming genetic make-up as a determinant factor in cocaine taking behavior.

Effect of age and caloric intake on protein oxidation in different brain regions and on behavioral functions of the mouse

The objective of this study was to determine if oxidative stress/damage is a possible causal factor in the senescence-related loss of brain functions in the mouse. If such a relationship indeed existed, it was expected that oxidative protein damage would increase with age within regions of the brain associated with senescence-related functional loss, and that calorie restriction, an intervention which retards certain aspects of age-associated functional loss, would reverse such increases. Dietary restriction was found to retard age-associated decline of sensorimotor coordination and improve performance of aged mice on an avoidance learning problem. Protein carbonyl concentration, one measure of protein oxidation, increased from 8 to 27 months of age in most regions of the mouse brain, with the most notable increases occurring in the striatum and hippocampus, regions of the brain strongly implicated in age-associated functional loss. Age-associated loss of protein sulfhydryls was more uniform across brain regions and did not involve the hippocampus. Dietary restriction resulted in reversal of the age-associated regional trends in carbonyl and sulfhydryl concentration, with the largest changes occurring within the striatum. Cross over studies in aged calorie restricted and ad libitum fed mice indicated that lowering of carbonyl content by calorie restriction could be induced or reversed within a time frame of 3 to 6 weeks. These findings suggest that the beneficial effects of dietary restriction upon brain function and life span may depend upon its ability to acutely reduce steady-state levels of oxidative stress.

Age-related losses of cognitive function and motor skills in mice are associated with oxidative protein damage in the brain

The hypothesis that age-associated impairment of cognitive and motor functions is due to oxidative molecular damage was tested in the mouse. In a blind study, senescent mice (aged 22 months) were subjected to a battery of behavioral tests for motor and cognitive functions and subsequently assayed for oxidative molecular damage as assessed by protein carbonyl concentration in different regions of the brain. The degree of age-related impairment in each mouse was determined by comparison to a reference group of young mice (aged 4 months) tested concurrently on the behavioral battery. The age-related loss of ability to perform a spatial swim maze task was found to be positively correlated with oxidative molecular damage in the cerebral cortex, whereas age-related loss of motor coordination was correlated with oxidative molecular damage within the cerebellum. These results support the view that oxidative stress is a causal factor in brain senescence. Furthermore, the findings suggest that age-related declines of cognitive and motor performance progress independently, and involve oxidative molecular damage within different regions of the brain.

Effect of the spin-trapping compound N-tert-butyl-alpha-phenylnitrone on protein oxidation and life span

N-tert-Butyl-alpha-phenylnitrone (PBN), a lipophilic spin-trapping compound, has been reported to decrease the concentration of protein carbonyls, the products of protein oxidation, in the brain of old gerbils to virtually the level found in the young gerbils (Carney, J. M., et al. (1991) Proc. Natl. Acad. Sci. USA 88, 3633-3636). The validity of this finding as well as that of the commonly used 2,4-dinitrophenylhydrazine procedure for the measurement of protein carbonyls was recently called into question by Cao and Cutler ((1995) Arch. Biochem. Biophys. 320, 106-114). The objective of the present study was to examine some of the relevant issues such as (a) whether the original findings on the effects of PBN can be confirmed, (b) whether similar effects of PBN occur in other species and tissues, and (c) whether PBN affects the life span of animals. Results of this study provide confirmation of the original finding that PBN indeed causes a decrease in protein carbonyl content in the gerbil brain cortex. However, a similar effect is not observed in the gerbil heart or the mouse brain cortex. Effects of PBN on protein carbonyls are thus variable depending upon tissue and species. PBN administration did not extend the life span of houseflies and at relatively high concentrations it was found to be toxic.

The benzodiazepine receptor inverse agonist RO 15-3505 reverses recent memory deficits in aged mice

The benzodiazepine receptor partial inverse agonist RO 15-3505 was tested for its ability to improve impaired recent memory of aged mice. All mice successfully acquired a learning set for accurate identification of the correct arm of a T-maze and could perform with nearly 100% accuracy after 1-min delays. However, performance of the aged mice approached chance levels after 2-h delays. When injected just before testing on a series of 2-h retention tests, RO 15-3505 (from 2.5-3505 (from 2.5-10.0 mg/kg) resulted in a marked improvement of response accuracy. These results confirm the role of benzodiazepine receptor mechanisms in the modulation of memory processes, and suggest that the memory-facilitating effects RO 15-3505 or similar benzodiazepine receptor ligands may be generalized to aged rodents with impaired memory function.