Propentophylline increases striatal dopamine release but dampens methamphetamine-induced dopamine dynamics: A microdialysis study.

While there are currently no medications approved for methamphetamine (METH) addiction, it has been shown that propentofylline (PPF), an atypical methylxanthine, can suppress the rewarding effects of methamphetamine (METH) in mice. This experiment studied the interactions of PPF with METH in striatal dopaminergic transmission. Herein, the impact of PPF (10-40mM, intrastriatally perfused (80min) on the effect of METH (5mg/kg, i.p.) on striatal dopamine (DA) release was evaluated using brain microdialysis in Sprague-Dawley adult rats. METH was injected at the 60min time point of the 80min PPF perfusion. The extracellular levels of DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined using high performance liquid chromatography with electrochemical detection (HPLC-ED). PPF induced a concentration-dependent increase in DA release beginning 30min after the onset of PPF perfusion. DA peak levels evoked by 40mM PPF were similar to those induced by 5mg/kg METH i.p. Only the highest concentration of PPF decreased the METH-induced DA peak (circa 70%). The significant decreases in extracellular levels of DOPAC and HVA evoked by METH were partially blocked by 10 and 20mM PPF. Although 40mM of PPF also partially blocked the METH-induced DOPAC decrease, it completely blocked HVA depletion after a transient increase in HVA levels in METH-treated rats. Data indicates for the first time that while PPF increases presynaptic striatal DA dynamics it attenuates METH-induced striatal DA release and metabolism.

Spatial memory impairments in a prediabetic rat model.

Diabetes is associated with an increased risk for brain disorders, namely cognitive impairments associated with hippocampal dysfunction underlying diabetic encephalopathy. However, the impact of a prediabetic state on cognitive function is unknown. Therefore, we now investigated whether spatial learning and memory deficits and the underlying hippocampal dysfunction were already present in a prediabetic animal model. Adult Wistar rats drinking high-sucrose (HSu) diet (35% sucrose solution during 9 weeks) were compared to controls' drinking water. HSu rats exhibited fasting normoglycemia accompanied by hyperinsulinemia and hypertriglyceridemia in the fed state, and insulin resistance with impaired glucose tolerance confirming them as a prediabetic rodent model. HSu rats displayed a poorer performance in hippocampal-dependent short- and long-term spatial memory performance, assessed with the modified Y-maze and Morris water maze tasks, respectively; this was accompanied by a reduction of insulin receptor-ß density with normal levels of insulin receptor substrate-1 pSer636/639, and decreased hippocampal glucocorticoid receptor levels without changes of the plasma corticosterone levels. Importantly, HSu animals exhibited increased hippocampal levels of AMPA and NMDA receptor subunits GluA1 and GLUN1, respectively, whereas the levels of protein markers related to nerve terminals (synaptophysin) and oxidative stress/inflammation (HNE, RAGE, TNF-α) remained unaltered. These findings indicate that 9 weeks of sucrose consumption resulted in a metabolic condition suggestive of a prediabetic state, which translated into short- and long-term spatial memory deficits accompanied by alterations in hippocampal glutamatergic neurotransmission and abnormal glucocorticoid signaling.

May exercise prevent addiction?

Amphetamines exert their persistent addictive effects by activating brain's reward pathways, perhaps through the release of dopamine in the nucleus accumbens (and/or in other places). On the other hand, there is a relationship between dopamine and all behavioural aspects that involve motor activity and it has been demonstrated that exercise leads to an increase in the synthesis and release of dopamine, stimulates neuroplasticity and promotes feelings of well-being. Moreover, exercise and drugs of abuse activate overlapping neural systems. Thus, our aim was to study the influence of chronic exercise in the mechanism of addiction using an amphetamine-induced conditioned-place-preference in rats.Adult male Sprague-Dawley rats were randomly separated in groups with and without chronic exercise. Chronic exercise consisted in a 8 week treadmill running program, with increasing intensity. The conditioned place preference test was performed in both groups using a procedure and apparatus previously established. A 2 mg.kg(-1) amphetamine or saline solution was administered intraperitonially according to the schedule of the conditioned place preference. Before conditioning none of the animals showed preference for a specific compartment of the apparatus. The used amphetamine dose in the conditioning phase was able to produce a marked preference towards the drug-associated compartment in the group without exercise. In the animals with exercise a significant preference by the compartment associated with saline was observed. These results lead us to conclude that a previous practice of regular physical activity may help preventing amphetamine addiction in the conditions used in this test.

Influence of the sample preparation method on the serotonin determination in plasma and platelets.

Plasma or platelet serotonin concentration is commonly used to provide information about the serotonergic activity in various psychiatric or neurological diseases. Some difficulties have been described in the measurement of serotonin (5-HT) levels in plasma or platelets. We describe an isocratic liquid-chromatographic assay with amperometric detection for determination of 5-HT in the platelet pellet and in platelet-rich and platelet-poor plasma (PRP and PPP) in sample sizes of 100 microL of plasma. The method uses an RP(18) column and an amperometric detector with a thin-layer type electrochemical fl ow cell, with glassy carbon electrode maintained at a potential of +0.600 V vs an Ag/AgCl reference electrode. Determinations were performed in the presence or in the absence of plasma, since the biological matrix may affect the results. Different validation parameters were analysed: selectivity, accuracy, precision, linearity and stability. Reference values for 5-HT concentration in healthy adults (n = 12) were 6.6 nmol/10(9) platelets, for the platelet pellet, and 5.5 nmol/10(9) platelets, for PRP. The 100 microL sample volume used for the preparation of PPP did not make possible the determination of 5-HT levels with accuracy and precision.

Cyclosporin effect on noradrenaline release from the sympathetic nervous endings of rat aorta.

Arterial hypertension is one of the main side effects of cyclosporin treatment and seems to be due to activation of the sympathetic nervous system. Some authors hypothesized that cyclosporin may act on the sympathetic nervous endings increasing catecholamine release, in agreement with our previous works which demonstrated an increase in rat plasma catecholamine levels after 30 mg/kg per day cyclosporin treatment for 7 weeks. Therefore, the aim of this work was to study the cyclosporin mechanism responsible for that increase in plasma catecholamines. Male Wistar rats were used. Noradrenaline release was performed in vitro experiments after loading rat aorta abdominal segments with 3H-noradrenaline (3H-NA). The release of 3H-NA was measured after electrical stimulation in the presence of 10(-6)M cyclosporin. In another set of experiments electrical stimulation was replaced by a pulse addition of cyclosporin (10(-6)M). Another group of rats was treated with 30 mg/kg per day cyclosporin for 7 weeks and catecholamine contents in aorta abdominal segments and adrenals were measured by high performance liquid chromatography system with electrochemical detection (HPLC-ECD). An increase in the 3H-NA release was observed in both types of in vitro experiments. Since cocaine abolished these cyclosporin effects, the obtained results suggest that cyclosporin may act on the catecholamine transporter across the membrane. In addition, after the 7 weeks of cyclosporin treatment, a significant decrease in catecholamine aorta contents was verified but in adrenals there was no difference regarding to controls. However, the dopamine synthesis/degradation ratio measured by the DA/DOPAC ratio suggests an increase in dopamine synthesis. These facts are in agreement with the enhanced plasma catecholamine levels and with the hypothesis of tissue catecholamine depletion. However, they do not explain the increase in plasma adrenaline levels, since adrenaline is a reflex of adrenal activity. The synthesized dopamine in adrenals seems to be unable to reach vesicles and to be metabolized in adrenaline. The observed decrease in HVA adrenal levels may be a consequence of extraneuronal uptake inhibition or inhibition by cyclosporin of the direct o-methylation of DOPAC. In conclusion, our results suggest that cyclosporin increases catecholamine release from the sympathetic nervous endings by a tyramine-like effect, i.e. by acting directly on the catecholamine transporter of the membrane.

Circadian and seasonal variation of endogenous ubiquinone plasma level.

Coenzyme Q10 (CoQ10) or ubiquinone, a redox component of the mitochondrial electron transport chains, is a powerful antioxidant and membrane stabilizer that may prevent cellular damage during myocardial ischemia and reperfusion therapy. Coenzyme Q10 has been used primarily as an adjuvant therapy for some cardiomyopathies. However, one of the main problems in CoQ10 administration is the high variability of endogenous plasma and tissue levels, which seems to be dependent on several factors. This work explores temporal 24h and seasonal variation as well as gender and racial differences in endogenous plasma ubiquinone concentration. Coenzyme Q10 measurements (quantified by HPLC-UV) of 16 healthy volunteers were done during the daytime hours of activity beginning at 09:00h one day and ending at 09:00h the next day (13 different determinations) in two distinct months. April and October, of the year. A statistically significant circadian rhythm in plasma ubiquinone concentration that includes only the fundamental 24h component was demonstrated both in the April and October data. Furthermore, the time-point means of the ubiquinone concentration in the October study were invariably higher than those obtained in the April study. No statistically significant differences were found in CoQ10 concentration between male and female subjects, both in April and in October. In addition, racial differences were demonstrated; lower plasma ubiquinone levels were found in Caucasian compared to African subjects. However, the latter small group of subjects failed to demonstrate a circadian rhythm, neither in the April nor in the October analysis.

The peripheral serotonergic system and platelet aggregation in cyclosporin A-induced hypertensive rats.

Cyclosporin A plays an important role in preventing rejection in allograft transplant recipients. However, the therapeutic use of cyclosporin A is associated with increased incidence of thromboembolic complications and drug-related hypertension. In order to study the mechanisms by which cyclosporin A induces these abnormal pathophysiological situations, we have assessed the platelet serotonin contents and whole blood platelet aggregation in control rats as well as in rats treated (orally) with 30 and 5 mg/kg/day of cyclosporin A, after 2 and 7 weeks of treatment. These doses correspond respectively to CsA "peak" and "trough" concentrations achieved in human blood in clinical practice (immediately following an intake of a daily dose of CsA and when the blood concentration stabilizes, respectively). Both trough and peak doses caused an increase in blood pressure after 2 and 7 weeks. Platelet serotonin content decreased in the cyclosporin-treated groups, in contrast with the control. Collagen-induced whole blood platelet aggregation increased drastically for the peak concentration-treated group, while adenosine 5'-diphosphate-induced platelet aggregation did not reach statistical significance. Finally, in vitro platelet thromboxane A2 generation increased in cyclosporin A concentrations when platelets were stimulated with either collagen or adenosine 5'-diphosphate. In conclusion, both tested cyclosporin A concentrations induced important changes in platelet serotonin and thromboxane content and aggregation, factors which may play a decisive role in the development and/or maintenance of hypertension and thrombotic complications.

Presynaptic dopamine receptors involved in the inhibition of noradrenaline and dopamine release in the human gastric and uterine arteries.

Electrical stimulation-induced depolarization releases both dopamine (DA) and noradrenaline (NA) from sympathetic neurones of the human gastric and uterine arteries. The overflow of catecholamines elicited by electrical stimulation was measured by using high performance liquid chromatography with electrochemical detection. The addition of yohimbine (0.01-10 microM), an alpha2-adrenoceptor antagonist, to the perfusion fluid increased, in a concentration-dependent manner, the electrically-evoked DA and NA overflow from gastric and uterine arteries. In the presence of sulpiride (0.01-10 microM), a dopamine D2-type receptor antagonist, the overflow of both amines was found to be increased in the uterine artery, but not in the gastric artery. Apomorphine (0.1-10 microM), a dopamine receptor agonist, produced a dose-dependent inhibition in the amount of DA and NA released from gastric and uterine arteries. SCH 23390 (0.1-10 microM), a dopamine D1 receptor antagonist, had no effect on the release of both amines in both preparations. The inhibitory effect of apomorphine was blocked by sulpiride in the gastric and uterine arteries but not by SCH 23390. The results presented suggest the existence of dopamine D2-type receptors in the human gastric and uterine arteries. They seem to have, in each artery, a different physiological importance.

Influence of 0.1 or 0.2% cholesterol-enriched diets on the induction of atherosclerosis and aorta reactivity in vitro.

Current knowledge of atherogenesis is largely based on animal models of hypercholesterolemia, which rarely show changes similar to the lesions described in humans. We studied the influence of two low cholesterol-enriched diets on the development of anatomopathologic lesions and on the reactivity of the isolated aorta in rabbits. Compared with controls (rabbits fed a normal diet), a 0.1% cholesterol-enriched diet over a 6- or 9-month period produced increases of the 5-hydroxytryptamine (5-HT)-induced contractile responses, as well as a decreases in acetylcholine (ACh)-induced relaxing response (endothelium-dependent, through the production of NO). Noradrenaline (NA)-induced contractions and relaxations elicited by sodium nitroprusside (SNP; endothelium independent) were not significantly modified. Because at 6 months, significant anatomopathologic intimal early lesions were not found, functional endothelial changes can explain such findings. There was a defect in NO synthesis, release, or diffusion; 5 HT, but not NA, may be responsible for inducing NO production. In 0.2% cholesterol-fed rabbits at 4 and 12 weeks, increases of 5-HT- and NA-induced contractile responses were found. In both cases, there was a decrease of ACh-induced relaxing effect, whereas responses to SNP remained unchanged. Intimal early and advanced lesions were present at both the 4- and 12-week periods. These data suggest abnormalities of the NO system. The effects obtained with NA may be explained by a possible decrease of catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO) activities or both or by decreased amine uptake. The extent to which NA may induce NO production is small, because changes in NA-induced contractions are verified only in the presence of significant alterations in the endothelium. The use of a 0.2% cholesterol diet for a short time may induce atherosclerotic lesions, whereas the 0.1% cholesterol diet for a 9-month period, besides being closer to the human diet, allows the detection of functional abnormalities before the evidence of structural lesions.