Monitoring deep brain stimulation by measuring regional brain oxygen responses in freely moving mice.

BACKGROUND: Translational studies investigating the effects of deep brain stimulation (DBS) on brain function up to now mainly relied on BOLD responses measured with fMRI. However, fMRI studies in rodents face technical and practical limitations (e.g., immobilization, sedation or anesthesia, spatial and temporal resolution of data). Direct measurement of oxygen concentration in the brain using electrochemical sensors is a promising alternative to the use of fMRI. Here, we tested for the first time if such measurements can be combined with DBS. NEW METHOD: We combined bilateral DBS in the internal capsule (IC-DBS) with simultaneous amperometric measurements of oxygen in the medial prefrontal cortex (prelimbic area) and striatum of freely moving mice. Using a two-day within-animal experimental design, we tested the effects of DBS on baseline oxygen concentrations, and on novelty- and restraint-induced increases in oxygen concentration. RESULTS: Basal oxygen levels were stable across the daily sampling periods. Exposure to novelty and immobilization reproducibly increased oxygen concentrations in both areas. IC-DBS did not significantly alter basal oxygen, but reduced the novelty-induced increase in the striatum. COMPARISON WITH EXISTING METHOD(S): Amperometric detection of brain oxygen concentration with high temporal and spatial resolution can be performed in a number of key brain areas to study the effects of DBS in animal models of disease. The method is easily implemented and does not require expensive equipment or complicated data analysis processes. CONCLUSIONS: Direct and simultaneous measurement of brain oxygen concentration in multiple brain areas can be used to study the effects of bilateral DBS neuromodulation on brain activity in freely moving mice.

Simultaneous wireless and high-resolution detection of nucleus accumbens shell ethanol concentrations and free motion of rats upon voluntary ethanol intake.

Highly sensitive detection of ethanol concentrations in discrete brain regions of rats voluntarily accessing ethanol, with high temporal resolution, would represent a source of greatly desirable data in studies devoted to understanding the kinetics of the neurobiological basis of ethanol's ability to impact behavior. In the present study, we present a series of experiments aiming to validate and apply an original high-tech implantable device, consisting of the coupling, for the first time, of an amperometric biosensor for brain ethanol detection, with a sensor for detecting the microvibrations of the animal. This device allows the real-time comparison between the ethanol intake, its cerebral concentrations, and their effect on the motion when the animal is in the condition of voluntary drinking. To this end, we assessed in vitro the efficiency of three different biosensor designs loading diverse alcohol oxidase enzymes (AOx) obtained from three different AOx-donor strains: Hansenula polymorpha, Candida boidinii, and Pichia pastoris. In vitro data disclosed that the devices loading H. polymorpha and C. boidinii were similarly efficient (respectively, linear region slope [LRS]: 1.98 ± 0.07 and 1.38 ± 0.04 nA/mM) but significantly less than the P. pastoris-loaded one (LRS: 7.57 ± 0.12 nA/mM). The in vivo results indicate that this last biosensor design detected the rise of ethanol in the nucleus accumbens shell (AcbSh) after 15 minutes of voluntary 10% ethanol solution intake. At the same time, the microvibration sensor detected a significant increase in the rat's motion signal. Notably, both the biosensor and microvibration sensor described similar and parallel time-dependent U-shaped curves, thus providing a highly sensitive and time-locked high-resolution detection of the neurochemical and behavioral kinetics upon voluntary ethanol intake. The results overall indicate that such a dual telemetry unit represents a powerful device which, implanted in different brain areas, may boost further investigations on the neurobiological mechanisms that underlie ethanol-induced motor activity and reward.

A novel method for the determination of ascorbic acid and antioxidant capacity in Opuntia ficus indica using in vivo microdialysis.

A simple and rapid method was developed for in vivo simultaneous determination of ascorbic-acid and antioxidant capacity in microdialysates from cladodes of Opuntia ficus-indica (L.) Miller. The method is verified in water-stressed plants, as compared with a well-watered test controls. The microdialysis probe construction and insertion procedure was specifically developed to minimise the tissue trauma of the plant and to obtain optimal dialysis performance. Microdialysis was performed using a flow rate of 3 µL/min and the samples were analysed by HPLC coupled to electrochemical detection of ascorbic-acid and DPPH-determined antioxidant capacity. Our data indicate exponential decay of the concentrations of the analysed compounds as a function of microdialysis sampling time. Water-stressed Opuntia show decreased ascorbic acid levels and increased the others antioxidants.

Do on- and off-pump coronary bypass surgery differently affect perioperative peripheral tissue metabolism?

BACKGROUND: Microdialysis allows the in-vivo assessment of interstitial fluids. We studied the metabolic status of peripheral tissues (skeletal muscle) in patients undergoing coronary artery bypass surgery on- (CABG) or off-pump (OPCAB). METHODS: Twenty patients candidates to elective coronary bypass surgery were randomly assigned to undergo CABG or OPCAB. A microdialysis catheter was inserted in the left deltoid muscle before surgery and left in place for 24 hours, and metabolic markers of peripheral tissue perfusion (glucose, lactate, pyruvate, glycerol and lactate/pyruvate (L/P) ratio) were assessed before, at the end, and 24 hours after surgery. RESULTS: Preoperative clinical features were similar in both groups. Interstitial levels of glucose and lactate increased over time, being in both groups significantly higher than baseline 24 hours after surgery, whereas glycerol levels did not change over time and between groups. In addition, there was an increase over time of pyruvate levels which were significantly higher in CABG after surgery, whereas L/P ratio was significantly higher in OPCAB 24 hours after surgery. CONCLUSION: Metabolic changes after coronary bypass surgery occur with some differences related to CPB use. Overall, these changes suggest that, after coronary surgery, a certain degree of hypermetabolic state ensues, lasting up to 24 hours after surgery; the postoperative increase in pyruvate levels in CABG patients, together with the changes in L/P ratio occurring only in OPCAB patients implies an higher risk of tissue hypoperfusion/ischemia for patients submitted to OPCAB, although this does not lead to permanent cellular damage, as the markers of this complication (e.g., glycerol) do not change over time.