Rate of onset of dopamine transporter inhibitors assessed with intracranial self-stimulation and in vivo dopamine photometry in rats.

Drug self-administration and intracranial self-stimulation (ICSS) are two preclinical behavioral procedures used to predict abuse potential of drugs, and abuse-related drug effects in both procedures are thought to depend on increased mesolimbic dopamine (DA) signaling. Drug self-administration and ICSS yield concordant metrics of abuse potential across a diverse range of drug mechanisms of action. The "rate of onset," defined as the velocity with which a drug produces its effect once administered, has also been implicated as a determinant of abuse-related drug effects in self-administration procedures, but this variable has not been systematically examined in ICSS. Accordingly, this study compared ICSS effects produced in rats by three DA transporter inhibitors that have different rates of onset (fastest to slowest: cocaine, WIN-35428, RTI-31) and that produced progressively weaker metrics of abuse potential in a drug self-administration procedure in rhesus monkeys. Additionally, in vivo photometry using the fluorescent DA sensor dLight1.1 targeted to the nucleus accumbens (NAc) was used to assess the time course of extracellular DA levels as a neurochemical correlate of behavioral effects. All three compounds produced ICSS facilitation and increased DA levels assessed by dLight. In both procedures, the rank order of onset rate was cocaine > WIN-35428 > RTI-31; however, in contrast to monkey drug self-administration results, maximum effects did not differ across compounds. These results provide additional evidence that drug-induced increases in DA drive ICSS facilitation in rats and illustrate the utility of both ICSS and photometry to evaluate the time course and magnitude of abuse-related drug effects in rats.

Alterations of sarcoplasmic reticulum-mediated Ca2+ uptake in a model of premature ventricular contraction (PVC)-induced cardiomyopathy.

Premature ventricular contractions (PVCs) are the most frequent ventricular arrhythmias in the overall population. PVCs are known to acutely enhance contractility by the post-extrasystolic potentiation phenomenon, but over time persistent PVCs promote PVC-induced cardiomyopathy (PVC-CM), characterized by a reduction of the left ventricular (LV) ejection fraction. Ca2+ cycling in myocytes commands muscle contraction and in this process, SERCA2 leads the Ca2+ reuptake into the sarcoplasmic reticulum (SR) shaping cytosolic Ca2+ signal decay and muscle relaxation. Altered Ca2+ reuptake can contribute to the contractile dysfunction observed in PVC-CM. To better understand Ca2+ handling using our PVC-CM model (canines with 50% PVC burden for 12 weeks), SR-Ca2+ reuptake was investigated by measuring Ca2+ dynamics and analyzing protein expression. Kinetic analysis of Ca2+ reuptake in electrically paced myocytes showed a ~ 21 ms delay in PVC-CM compared to Sham in intact isolated myocytes, along with a ~ 13% reduction in SERCA2 activity assessed in permeabilized myocytes. Although these trends were not statistically significant between groups using hierarchical statistics, relaxation of myocytes following contraction was significantly slower in PVC-CM vs Sham myocytes. Western blot analyses indicate a 22% reduction in SERCA2 expression, a 23% increase in phospholamban (PLN) expression, and a 50% reduction in PLN phosphorylation in PVC-CM samples vs Sham. Computational analysis simulating a 20% decrease in SR-Ca2+ reuptake resulted in a ~ 22 ms delay in Ca2+ signal decay, consistent with the experimental result described above. In conclusion, SERCA2 and PLB alterations described above have a modest contribution to functional adaptations observed in PVC-CM.

Characterization of free fatty acid receptors expression in an obesity rat model with high sucrose diet.

INTRODUCTION/AIMS: In recent years, it has been shown that free fatty acids receptors (FFAR) of whose function in the cell surface plays a significant role in the regulation of cell function and nutrition as well are activated by various endogenous ligands, but mainly by fatty acids. Within FFAR of our interest are GPR 41, 43 and 120. The functions of these receptors are varied and dependent on the tissue where they are. The activation and signaling of these receptors, FFAR, are involved in many physiological processes, and currently the target of many drugs in metabolic disorders like obesity, diabetes and atherosclerosis. MATERIAL AND METHODS: Obesity was induced with hypercaloric diet (HD) in male Wistar rats for 20 weeks (n = 10). At the end, adipose tissue (abdominal and subcutaneous) was taken to perform assays for relative quantification mRNA expression by end-point RT-PCR and protein level expression by Western blot. RESULTS: These present data have shown for the first time that total mRNA isolation and protein expression from both adipose tissues (abdominal and subcutaneous) of rat in obesity condition yield significative statistical difference among the control versus obese groups, showing that the diet high in carbohydrates modifies the total presence of mRNA and protein level expression of the receptors GPR41, 43 and 120. CONCLUSIONS: Further comparative methods are in process to clarify whether or not the obesity changes the functional receptors in these two tissues for new pharmacological approaches.

Effects of topical capsaicin combined with moderate exercise on insulin resistance, body weight and oxidative stress in hypoestrogenic obese rats.

BACKGROUND: Hypoestrogenic (HE) women are one of the most vulnerable groups for the development of obesity and its complications. Capsaicin and exercise have demonstrated to reduce body weight and to improve insulin sensitivity in different animal models, but it is unknown whether their combination could be useful in HE obese females. METHODS: We investigated whether topical capsaicin, exercise or their combination had better therapeutic effects in an obesity-hypoestrogenism model. Ovariectomized Wistar rats were given a 30% sucrose solution (HE-Obese (HEOb)) or purified water (HE) during 28 weeks ad libitum; four experimental groups per each condition. After shaving the abdominal skin, cold cream vehicle was applied to the Sedentary groups (Sed) and capsaicin cream 0.075% (0.6 mg kg-1 per day) to the Capsaicin groups (Cap). Exercise (Ex) groups ran on a treadmill every day for 20 min at speeds from 9 to 18 m per min increased every 10 days; combination groups (Cap+Ex) were given topical capsaicin 90 min before exercise. The treatments were performed for 6 weeks, and caloric intake and body weight were monitored. At the end of the experimental protocol, glucose tolerance tests were performed, the animals were killed by decapitation; blood and organs were obtained to perform oxidative profile, histology, biochemical analyses and Western blot. RESULTS: In HEOb rats, the combined therapy reduced caloric intake, body weight and abdominal fat in a higher proportion than the individual treatments; it also decreased insulin resistance (IR), oxidative stress and pancreatic islet size. It was the only treatment that significantly increased p-AMPK levels in the soleus muscle. In HE rats, topical capsaicin was the only treatment that reduced glucose intolerance and improved the oxidative profile in a higher proportion than the combined therapy or Ex alone. CONCLUSIONS: Capsaicin per se or its combination with moderate exercise could be a useful therapy against complications linked to obesity-IR in HE females.