Indeed, it’s been shownin vitrothat the depolarizing effects of HFS are eliminated by glutamate receptor antagonist drugs,25supporting the hypothesis that glutamate release is crucial to HFS function. with the vesicular H+-ATPase inhibitor, bafilomycin, and the calcium chelator, BAPTA-AM. Furthermore, electrical stimulation of purified primary astrocytic cultures was able to evoke intracellular calcium transients and glutamate release, and bath application of BAPTA-AM inhibited glutamate release in this setting. == Conclusion == These results suggest that vesicular astrocytic neurotransmitter release may be an important mechanism by which DBS is able to achieve clinical benefits. Keywords:astrocytes, adenosine, deep brain stimulation, glia, glutamate, high frequency stimulation == Introduction == Deep brain stimulation (DBS) is an effective and increasingly popular treatment for a variety of disorders including Parkinson’s Disease,1dystonia,2-4tremor,5,6epilepsy7,8and chronic pain,9as well as Compound E psychiatric disorders, like Tourette syndrome,10obsessivecompulsive disorder,11-13and depression.14-16For the treatment of tremor and epilepsy, specific thalamic nuclei have been the preferential target for implanted electrodes, while the subthalamic nucleus (STN) is the favored target for the treatment of Parkinson’s disease.17Intra-operative recordings from patients have shown that tremor neurons in the thalamus discharge rhythmically, either prior to or in synchrony with the 3-6 Hz oscillatory muscular tremor.18High frequency stimulation (HFS) applied to the area of the thalamus containing tremor cells leads to immediate tremor arrest, and the tremor rapidly returns when stimulation ceases.19Absence seizures are also associated with oscillatory phenomena in the thalamus. They are associated with Compound E 3 Hz spike and wave oscillations in the EEG and are likely to represent a perverse form of thalamo-cortical activity that is related to the normal generation of spindle waves.20Spontaneous normal spindle activity and abnormal absence-seizure-like activity can be recorded even in reduced preparations such as ferret thalamic brain slices.21Thus, the ferret thalamic slice is an ideal model for testing the functional consequences of HFS-mediated neurotransmitter release. Previously, it has been demonstrated that HFS of the STN22or the thalamus23,24results in neurotransmitter release. Indeed, it has been shownin vitrothat the depolarizing effects of HFS are eliminated by glutamate receptor antagonist drugs,25supporting the hypothesis that glutamate release is crucial to HFS function. Furthermore, Bekar et al.26have also shown that thalamic DBS is associated with a marked increase in extracellular adenosine and that adenosinergic mechanisms are important in tremor control.26Here, we employed an enzyme-linked glutamate sensor system and fast scan cyclic voltammetry (FSCV) to directly measure the extracellular glutamate and adenosine levels during HFS, respectively.27-31There are two potential sources of glutamate and adenosine in the brain: astrocytes32and neurons. There are large pools of glutamate and adenosine32,33stored in astrocytes that can be released by mechanical stimulation.34,35In addition, astrocytes release glutamate and adenosine through a Ca2+-dependent mechanism, establishing an important reciprocal interaction with neurons.36-38Despite these results, HFS mediated neurotransmitter release is assumed to be of neuronal origin, and the possibility that the neurotransmitter may come from astrocytes has thus far been ignored. Here, we test the hypotheses that HFS results in glutamate and adenosine release, that this neurotransmitter release has the functional consequence of abolishing neural network oscillations, and that the neurotransmitter release may, at least in part, be of astrocytic origin. == Methods == == In vitrothalamic slice preparation == The following experiments were approved by Institutional Animal Care and Use Committees in accordance with National Institute of Health guidelines for use of animals in teaching and research. For the preparation of slices, 3-4 month old male ferrets (Mustela putorious furo; Rabbit Polyclonal to PSMD6 Marshall Farms; North Rose, New York) were deeply anesthetized with sodium pentobarbital (30-40mg/kg) and killed by decapitation. The forebrain was rapidly removed, and the hemispheres were separated with a midline incision. Four hundred micron thick slices were cut using a vibratome (Ted Pella, Inc.) in the sagittal plane. During the preparation of slices, the tissue was placed in a solution (5 C) in which NaCl was replaced with sucrose while maintaining an osmolarity of 307mOsm to increase tissue viability.39Slices Compound E were placed in an interface style recording chamber (Fine Sciences Tools) maintained at 34 1 C and allowed at least two hours to recover. The bath was perfused with artificial cerebrospinal fluid (aCSF) which contained (126mM NaCl; 2.5mM KCl; 1.2mM MgSO4; 1.25mM NaH2PO4; 2mM CaCl2; 26mM NaHCO3; 10mM dextrose and was aerated with 95% O2, 5% CO2to a final pH of 7.4. For the first 20 minutes of perfusion, the bathing medium contained an equal mixture of aCSF and the sucrose-substituted solution. Glutamate electrochemistry in slices were performed using glutamate biosensors (Pinnacle Technology Inc., Lawrence, KS), as described below. ==.
Indeed, it’s been shownin vitrothat the depolarizing effects of HFS are eliminated by glutamate receptor antagonist drugs,25supporting the hypothesis that glutamate release is crucial to HFS function
