Evaluation of different procedure involved in the Transcranial Direct Current Stimulation (tDCS) technique experimental application

Introduction: The transcranial direct current stimulation (tDCS) is a non-invasive technique, which induces neuroplastic changes in the central nervous system of animals and humans. Furthermore, tDCS has been suggested as a therapeutic tool for pain management. The aim of this study was to standardize a non-invasive tDCS technique indexed by the nociceptive response of rats submitted to different conditions necessary to the tDCS application. Method: 60-day-old male Wistar rats (n=65), divided into 6 groups: control(C); non-active sham (NAS); active-sham (AS); active-sham restrained (ASR); non-active sham restrained (NASR); active tDCS treatment. Animals received treatment during 30 seconds (sham-active) or 20 minutes (restraint and tDCS)/8 days. Nociceptive threshold was assessed by Hot Plate test at baseline, immediately and 24h after the first session, immediately and 24h after the last session. Variance analysis of repeated measurements followed by Bonferroni was performed for intra-group comparison. Results: Physical restraint and 30 seconds stimulation (sham-tDCS) increased pain sensitivity (P≤0.05), and tDCS treatment was able to prevent the thermal hyperalgesia. Our original tDCS montage is similar to that used in the procedure with humans, because it is not an invasive technique. The electrodes are positioned on the head, and the animals are immobilized during the 20-minute treatment. As this procedure could involve behavior and neurochemical alterations due to stress induced by restriction (thus, it creates a research bias), we hypothesized that a 30-second electrical stimulus application (sham-tDCS) and the physical restriction used during tDCS treatment might alter nociceptive response in rats. Conclusion: There are methodological limitations in the present tDCS-technique. Although active-tDCS treatment is able to prevent these harmful effects, interference of these factors has to be considered during the results' analysis. Future adaptations of the tDCS-technique in rats are required to evaluate its therapeutic effects (AU)

Cafeteria diet increases liquid intake and serum creatinine levels in rats

Introduction: Important changes in human dietary pattern occurred in recent decades. Increased intake of processed foods leads to obesity, which is related with the development of chronic diseases such as type 2 diabetes mellitus, hypertension, as well as cardiovascular and chronic kidney diseases. The prevalence of hypertension has also dramatically increased in recent years, and high sodium intake contributes to this scenario. In healthy individuals, kidneys are the primary end-organs that regulate sodium homeostasis. This study aims to evaluate renal function parameters and systolic blood pressure measurements in an animal model of obesity. Methods: Sixty-day-old male Wistar rats (n=30) were divided into two groups: standard (SD) and cafeteria diet (CD). Cafeteria diet was altered daily and was composed by crackers, wafers, sausages, chips, condensed milk, and soda. All animals had free access to water and chow and the experiment was carried out for 6 weeks. Weight gain, sodium and liquid intake control, systolic blood pressure measurements, and renal function parameters were evaluated. Results: Animals exposed to cafeteria diet had an increase of 18% in weight compared to the control group. Sodium intake was increased by cafeteria diet and time (F(1,28)=773.666, P=0.001 and F(5,28)=2.859, P=0.02, respectively) and by the interaction of both factors (F(6,28)=2.859, P=0.02). On liquid intake occurred only effect of cafeteria diet and time (F(1,28)=147.04, P=0.001 and F(5,28)=3.996, P=0.003, respectively). Cafeteria diet exposure also induced an increase on creatinine serum levels (P=0.002), however this effect was not observed on creatinine urine levels (P>0.05) nor on systolic pressure measurements (Students' t test, P>0.05). Conclusions: Obesity induced by cafeteria diet exposure increases liquid intake and alters creatinine serum levels, an important renal function marker. Considering the high consumption of hypercaloric food currently in the world, further studies are required to elucidate the modifications on renal function triggered by this diet over time (AU)

Melatonin as a potential counter-effect of hyperalgesia induced by neonatal morphine exposure.

Morphine administration in the neonatal period can induce long-term effects in pain circuitry leading to hyperalgesia induced by the opioid in adult life. This study explored a new pharmacological approach for reversing this effect of morphine. We focused on melatonin owing its well-known antinociceptive and anti-inflammatory effects, and its ability to interact with the opioid system. We used the formalin test to assess the medium and long-term effects of melatonin administration on hyperalgesia induced by morphine in early life. Newborn rats were divided into two groups: the control group, which received saline, and the morphine group, which received morphine (5µg subcutaneously [s.c.]) in the mid-scapular area, once daily for 7days, from P8 (postnatal day 8) until P14. At postnatal days 30 (P30) and 60 (P60), both groups were divided in two subgroups, which received melatonin or melatonin vehicle 30min before the formalin test. The nociceptive responses were assessed by analyzing the total time spent biting, flicking, and licking the formalin-injected hind paw; these responses were recorded during the first 5min (neurogenic/acute phase) and from 15 to 30min (inflammatory/tonic phase). Initially, animals in the morphine/vehicle group showed increased nociceptive behavior in phase II (inflammatory) of the formalin test at P30, and in the neurogenic and inflammatory phases at P60. These increased nociceptive responses were fully reversed by melatonin administration at either age. These findings show that melatonin administration is a potential means for countering hyperalgesia induced by neonatal morphine exposure in young and adult rats.