Adrian C. Michael

Voltammetric study of extracellular dopamine near microdialysis probes acutely implanted in the striatum of the anesthetized rat.

Establishing in vivo microdialysis methods for the quantitative determination of dopamine concentrations in the extracellular space of the brain is an important yet challenging objective. The source of the challenge is the difficulty in directly measuring the microdialysis recovery of dopamine during an in vivo experiment. The recovery value is needed for quantitative microdialysis, regardless of whether conventional or no-net-flux methods are used. Numerical models of microdialysis that incorporate both diffusion and active transport processes suggest that dopamine recovery is strongly affected by processes occurring in the tissue closest to the probe. Some evidence suggests that the tissue adjacent to the probe becomes disrupted during probe implantation. Hence, the objective of the present study was to further identify whether the tissue adjacent to the probe is disrupted and, if so, whether that disruption might affect dopamine recovery. The experiments were conducted with microdialysis probes implanted acutely in the striatum of rats anesthetized with chloral hydrate. Carbon fiber voltammetric microelectrodes were used to monitor extracellular dopamine at three sites near the probes; immediately adjacent to the probe, 220-250 microm from the probe, and 1 mm from the probe. Probes were lowered slowly over a 30 min period, so that dialysate dopamine levels were stable, in the low nanomolar range, and partially TTX-sensitive by the time experiments began. Starting 2h after probe implantation, dopamine was monitored by fast-scan cyclic voltammetry during electrical stimulation of the medial forebrain bundle and during administration of the dopamine uptake inhibitor, nomifensine. The findings of this study show that a gradient of dopamine release and uptake activity extends at least 220 microm from microdialysis probes implanted acutely in the striatum of the anesthetized rat.

Electrochemical Methods for Neuroscience

Introduction to Electrochemical Methods in Neuroscience, L. M. Borland and A. C. Michael Rapid Dopamine Release in Freely Moving Rats, D. L. Robinson and R. M. Wightman Presynaptic Regulation of Extracellular Dopamine as Studied by Continuous Amperometry in Anesthetized Animals, M. Benoit-Marand, M.F. Suaud-Chagny, and F. Gonon Fast Scan Cyclic Voltammetry of Dopamine and Serotonin in Mouse Brain Slices, C. E. John and S. R. Jones High-Speed Chronoamperometry to Study Kinetics and Mechanisms for Serotonin Clearance in vivo, L. C. Daws and G. M. Toney Using High-Speed Chronoamperometry Coupled with Local Dopamine Application to Assess Dopamine Transporter Function, J. M. Gulley, G. A. Larson, and N. R. Zahniser Determining Serotonin and Dopamine Uptake Rates in Synaptosomes Using High-Speed Chronoamperometry, X. A. Perez, A. J. Bressler, and A. Milasincic Andrews Using Fast-Scan Cyclic Voltammetry to Investigate Somatodendritic Dopamine Release, S. Threlfell and S. J. Cragg From Interferant Anion to Neuromodulator: Ascorbate Oxidizes Its Way to Respectability, G. V. Rebec Biophysical Properties of Brain Extracellular Space Explored with Ion-Selective Microelectrodes, Integrative Optical Imaging and Related Techniques, S. Hrabtova and C. Nicholson Hydrogen Peroxide as a Diffusible Messenger: Evidence from Voltammetric Studies of Dopamine Release in Brain Slices, M. E. Rice, M. V. Avshalumov, and J. Patel In Vivo Voltammetry with Telemetry, P. A. Garris, P. G. Greco, S. G. Sandberg, G.Howes, S. Pongmaytegul, B. A. Heidenreich, J. M. Casto, R. Ensman, J. Poehlman, A. Alexander, and G. V. Rebec Oxidative Stress at the Single Cell Level, C. Amatore and S. Arbault Electrochemistry at the Cell Membrane/Solution Interface, N. Wittenberg, M. Maxson, Daniel Eves, A.S. Cans, and A. G. Ewing The Patch Amperometry Technique: Design of a Method to Study Exocytosis of Single Vesicles, G. Dernick, G. Alvarez de Toledo, and M. Lindau Amperometric Detection of Dopamine Exocytosis from Synaptic Terminals, R.G.W. Staal, S. Rayport, and D. Sulzer Scanning Electrochemical Microscopy as a Tool in Neuroscience, A. Schulte and W. Schuhmann Principles, Development and Applications of Self-Referencing Electrochemical Microelectrodes to the Determination of Fluxes at Cell Membranes, P.J.S. Smith, R. H. Sanger, and M. A. Messerli Second-by-Second Measures of L-Glutamate and Other Neurotransmitters Using Enzyme-Based Microelectrode Arrays, K. N. Hascup, E. C. Rutherford, J. E. Quintero, B. K. Day, J. R. Nickell, F. Pomerleau, P. Huettl, J. J. Burmeister, and G. A. Gerhardt Telemetry for Biosensor Systems, D. A. Johnson and G. S. Wilson The Principles, Development and Application of Microelectrodes for the in vivo Determination of Nitric Oxide, M. J. Serpe and X. Zhang In vivo Fast-scan Cyclic Voltammetry of Dopamine near Microdialysis Probes, H. Yang and A. C. Michael

Brain tissue responses to neural implants impact signal sensitivity and intervention strategies.

Implantable biosensors are valuable scientific tools for basic neuroscience research and clinical applications. Neurotechnologies provide direct readouts of neurological signal and neurochemical processes. These tools are generally most valuable when performance capacities extend over months and years to facilitate the study of memory, plasticity, and behavior or to monitor patients’ conditions. These needs have generated a variety of device designs from microelectrodes for fast scan cyclic voltammetry (FSCV) and electrophysiology to microdialysis probes for sampling and detecting various neurochemicals. Regardless of the technology used, the breaching of the blood–brain barrier (BBB) to insert devices triggers a cascade of biochemical pathways resulting in complex molecular and cellular responses to implanted devices. Molecular and cellular changes in the microenvironment surrounding an implant include the introduction of mechanical strain, activation of glial cells, loss of perfusion, secondary metabolic injury, and neuronal degeneration. Changes to the tissue microenvironment surrounding the device can dramatically impact electrochemical and electrophysiological signal sensitivity and stability over time. This review summarizes the magnitude, variability, and time course of the dynamic molecular and cellular level neural tissue responses induced by state-of-the-art implantable devices. Studies show that insertion injuries and foreign body response can impact signal quality across all implanted central nervous system (CNS) sensors to varying degrees over both acute (seconds to minutes) and chronic periods (weeks to months). Understanding the underlying biological processes behind the brain tissue response to the devices at the cellular and molecular level leads to a variety of intervention strategies for improving signal sensitivity and longevity.

Controlled cortical impact injury affects dopaminergic transmission in the rat striatum

The therapeutic benefits of dopamine (DA) agonists after traumatic brain injury (TBI) imply a role for DA systems in mediating functional deficits post‐TBI. We investigated how experimental TBI affects striatal dopamine systems using fast scan cyclic voltammetry (FSCV), western blot, and d‐amphetamine‐induced rotational behavior. Adult male Sprague–Dawley rats were injured by a controlled cortical impact (CCI) delivered unilaterally to the parietal cortex, or were naïve controls. Amphetamine‐induced rotational behavior was assessed 10 days post‐CCI. Fourteen days post‐CCI, animals were anesthetized and underwent FSCV with bilateral striatal carbon fiber microelectrode placement and stimulating electrode placement in the medial forebrain bundle (MFB). Evoked DA overflow was assessed in the striatum as the MFB was electrically stimulated at 60 Hz for 10 s. In 23% of injured animals, but no naïve animals, rotation was observed with amphetamine administration. Compared with naïves, striatal evoked DA overflow was lower for injured animals in the striatum ipsilateral to injury (p < 0.05). Injured animals exhibited a decrease in Vmax (52% of naïve, p < 0.05) for DA clearance in the hemisphere ipsilateral to injury compared with naïves. Dopamine transporter (DAT) expression was proportionally decreased in the striatum ipsilateral to injury compared with naïve animals (60% of naïve, p < 0.05), despite no injury‐related changes in vesicular monoamine transporter or D2 receptor expression (DRD2) in this region. Collectively, these data appear to confirm that the clinical efficacy of dopamine agonists in the treatment of TBI may be related to disruptions in the activity of subcortical dopamine systems.

Voltammetric study of the control of striatal dopamine release by glutamate

The central dopamine systems are involved in several aspects of normal brain function and are implicated in a number of human disorders. Hence, it is important to understand the mechanisms that control dopamine release in the brain. The striatum of the rat receives both dopaminergic and glutamatergic projections that synaptically target striatal neurons but not each other. Nevertheless, these afferents do form frequent appositional contacts, which has engendered interest in the question of whether they communicate with each other despite the absence of a direct synaptic connection. In this study, we used voltammetry in conjunction with carbon fiber microelectrodes in anesthetized rats to further examine the effect of the ionotropic glutamate antagonist, kynurenate, on extracellular dopamine levels in the striatum. Intrastriatal infusions of kynurenate decreased extracellular dopamine levels, suggesting that glutamate acts locally within the striatum via ionotropic receptors to regulate the basal extracellular dopamine concentration. Infusion of tetrodotoxin into the medial forebrain bundle or the striatum did not alter the voltammetric response to the intrastriatal kynurenate infusions, suggesting that glutamate receptors control a non‐vesicular release process that contributes to the basal extracellular dopamine level. However, systemic administration of the dopamine uptake inhibitor, nomifensine (20 mg/kg i.p.), markedly decreased the amplitude of the response to kynurenate infusions, suggesting that the dopamine transporter mediates non‐vesicular dopamine release. Collectively, these findings are consistent with the idea that endogenous glutamate acts locally within the striatum via ionotropic receptors to control a tonic, impulse‐independent, transporter‐mediated mode of dopamine release. Although numerous prior in vitro studies had suggested that such a process might exist, it has not previously been clearly demonstrated in an in vivo experiment.

Direct comparison of the response of voltammetry and microdialysis to electrically evoked release of striatal dopamine

Abstract: Carbon fiber microelectrodes either were implanted directly into striatal tissue or were mounted into the outlet of microdialysis probes that were implanted into striatal tissue. This allowed voltammetry and microdialysis to be used under identical in vivo experimental conditions to monitor extracellular dopamine levels during electrical stimulation of the medial forebrain bundle both before and after uptake inhibition with nomifensine. The marked differences between the results obtained with each technique cannot be explained on the basis of their inherent analytical attributes (sensitivity, temporal response, etc.). The results demonstrate that the microdialysis recovery factor for endogenous dopamine increases after uptake inhibition, an observation that stands in contradiction to the existing theory and practice of the microdialysis technique. The observations led to the development of a numerical model that rationalizes the observations reported herein and that allows in vivo voltammetry and in vivo microdialysis results to be interpreted within a single theoretical framework.

Ultrastructure at carbon fiber microelectrode implantation sites after acute voltammetric measurements in the striatum of anesthetized rats

This work seeks to establish the feasibility of characterizing the ultrastructure of brain tissue disruption associated with the implantation of carbon fiber voltammetric microelectrodes. In vivo recording was performed by fast scan cyclic voltammetry in conjunction with carbon fiber microelectrodes (3.5 microm radius) in the striatum of rats anesthetized with chloral hydrate. After 4 h of in vivo recording, the microelectrodes were removed from the brain and the animals underwent intracardial perfusion. Brain tissue was collected and sectioned in the horizontal plane perpendicular to the axis of the microelectrodes. With microelectrodes of a conventional single barreled design, the tissue tracks were often too small to be followed by light microscopy to the point of deepest penetration, which would correspond to the implantation site of the carbon fiber itself. The enlarged tissue tracks formed by the implantation of double barreled electrodes, however, could be followed to their termination by light microscopy. Anatomical mapping was used to identify the fields laying 100 microm deeper than the deepest trace of such tracks. Electron microscopy of these fields revealed a spot of tissue damage presumed to be associated with the implantation site of the carbon fiber microelectrode. The spot of maximal tissue damage had a radius of 2.5 microm and was surrounded by an annular region with a width of 4 microm that contained a mix of healthy and damaged elements. Beyond this annular region, i.e. beyond 6.5 microm from the center of the spot of maximal damage, signs of microelectrode-associated damage were rare and consisted primarily of neurons with darkened cytoplasm.

Coupled effects of mass transfer and uptake kinetics on in vivo microdialysis of dopamine.

Abstract: Voltammetric microelectrodes and microdialysis probes were used simultaneously to monitor extracellular dopamine in rat striatum during electrical stimulation of the medial forebrain bundle. Microelectrodes were placed far away (1 mm) from, immediately adjacent to, and at the outlet of microdialysis probes. In drug‐naive rats, electrical stimulation (45 Hz, 25 s) evoked a robust response at microelectrodes far away from the probes, but there was no response at microelectrodes adjacent to and at the outlet of the probes. After nomifensine administration (20 mg/kg i.p.), stimulation evoked robust responses at all three microelectrode placements. These results demonstrate first that evoked release in tissue adjacent to microdialysis probes is suppressed in comparison with evoked release in tissue far away from the probes and second that equilibration of the dopamine concentration in the extracellular fluid adjacent to and far away from the probes is prevented by the high‐affinity dopamine transporter. Hence, models of microdialysis, which assume the properties of tissue to be spatially uniform, require modification to account for the distance that separates viable sites of evoked dopamine release from the probe. We introduce new mass transfer resistance parameters that qualitatively explain the observed effects of uptake inhibition on stimulation responses recorded with microdialysis and voltammetry.

Invasive consequences of using micro-electrodes and microdialysis probes in the brain

The ability to monitor the concentration of neurotransmitters in the extracellular space of living brain is crucial to improving our understanding of the neurochemical aspects of brain function and the dysfunction associated with numerous neurological disorders. Microdialysis probes and electrochemical microsensors are often used for in-vivo neurotransmitter monitoring, but these are invasive devices that are implanted directly into brain tissue. Although the selectivity, sensitivity, and temporal resolution of these devices have been characterized in detail, less attention has been paid to the impact of the trauma that they inflict on the tissue or the effect of any such trauma on the outcome of the measurements that they are used to perform. In this paper, we describe emerging evidence that suggests trauma effects deserve closer consideration than they have received to date.

Chronic Methylphenidate Treatment Enhances Striatal Dopamine Neurotransmission After Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) results in functional deficits that often are effectively treated clinically with the neurostimulant, methylphenidate (MPH). We hypothesized that daily MPH administration would reverse striatal neurotransmission deficits observed in the controlled cortical impact (CCI) model of TBI. CCI or naïve rats received daily injections of MPH (5 mg/kg) or saline for 14 days and were assessed on day 15 using fast scan cyclic voltammetry. Dopamine (DA) transporter (DAT) localization, DA‐related proteins, and transcription factor (c‐fos) expression were also assessed. CCI resulted in reduced electrically evoked overflow of DA and maximal velocity of DA clearance (Vmax). In contrast, CCI was associated with a decrease in the apparent KM of DAT. Daily dose of MPH after CCI resulted in robust increases in evoked DA overflow and Vmax as well as increased apparent KM. Reductions in total striatal DAT expression occurred after CCI and were not further affected by MPH. In contrast, membrane‐bound striatal DAT levels were increased in both CCI groups. MPH post‐CCI significantly increased striatal c‐fos levels compared with saline. These results support the hypothesis that daily MPH improves striatal DA neurotransmission after CCI. DAT expression and transcriptional changes affecting DA protein function may underlie the injury and MPH‐induced alterations in neurotransmission observed.