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The possible role of glutamate in the pathophysiology and treatment of depression is of intense current interest. Proton magnetic resonance spectroscopy (MRS) enables the detection of glutamate in the living human brain and meta-analyses of previous MRS studies in depressed patients have suggested that glutamate levels are decreased in anterior brain regions. Nevertheless, at conventional magnetic field strengths [1.5–3 Tesla (T)], it is difficult to separate glutamate from its metabolite and precursor, glutamine, with the two often being measured together as Glx. In contrast, MRS at 7 T allows clear spectral resolution of glutamate and glutamine.
We studied 55 un-medicated depressed patients and 50 healthy controls who underwent MRS scanning at 7 T with voxels placed in anterior cingulate cortex, occipital cortex and putamen (PUT). Neurometabolites were calculated using the unsuppressed water signal as a reference.
Compared with controls, depressed patients showed no significant difference in glutamate in any of the three voxels studied; however, glutamine concentrations in the patients were elevated by about 12% in the PUT (p < 0.001).
The increase in glutamine in PUT is of interest in view of the postulated role of the basal ganglia in the neuropsychology of depression and is consistent with elevated activity in the descending cortical glutamatergic innervation to the PUT. The basal ganglia have rarely been the subject of MRS investigations in depressed patients and further MRS studies of these structures in depression are warranted.
Three specific deep brain stimulation (DBS) targets are currently in widespread use for the treatment of specific movement disorders. These are ventral intermediate nucleus (VIM) for the treatment of tremor (Parkinsonian or essential), subthalamic nucleus (STN) for Parkinson's disease (PD), and globus pallidus internus (GPi) for PD and for dystonia. All DBS surgeries currently require some form of stereotaxy, which is a means of translating information from two-dimensional (2D) brain images to the three-dimensional (3D) operative field. Two types of stereotactic approaches are available for DBS surgery. The success of DBS surgery is critically dependent on accurate localization of the target structure of interest. Two different approaches to initial target localization exist, and frequently are combined in the operating room: indirect and direct targeting. Ultra-high-field magnetic resonance imaging (MRI) systems are proving invaluable for basic science research and neuroscience applications.
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