Intracerebral microdialysis during deep brain stimulation surgery.

BACKGROUND: This report describes the use of microdialysis in conjunction with deep brain stimulation (DBS) surgery to assess extracellular levels of neurotransmitters within the human basal ganglia (BG). Electrical stimulation of the subthalamic nucleus (STN) is an efficacious treatment for advanced Parkinson's disease, yet the mechanisms of STN DBS remain poorly understood. Measurement of neurotransmitter levels within the BG may provide insight into mechanisms of DBS, but such an approach presents technical challenges. METHODS: After microelectrode recordings confirmed location of STN, a custom microdialysis guide cannula was inserted. A CMA (Stockholm, Sweden) microdialysis probe was then positioned to the same depth as the microrecording electrode in STN or 2mm inferiorly to record in the substantia nigra. The catheter was perfused at a rate of 2.0 microL/min with a sterile mock CSF solution and samples of extracellular fluid were collected at regular intervals. Dialysate samples were analyzed using high-pressure liquid chromatography (HPLC) detection procedures for quantitation of glutamate, gamma-aminobutyric acid (GABA), and dopamine. RESULTS: Levels of neurotransmitters were reliably identified in dialysate samples using HPLC. By monitoring concentrations of glutamate, GABA and dopamine, we were able to demonstrate what seemed to be a steady state baseline within approximately 30 min. CONCLUSION: Microdialysis during DBS surgery is a feasible method for assessing levels of glutamate, GABA and dopamine within the human BG. Obtaining a steady state baseline of neurotransmitter levels appears feasible, thus making future studies of intraoperative microdialysis during DBS meaningful.

Feasibility of an operational standardized checklist for movement disorder surgery. A pilot study.

Despite the clinical success of deep brain stimulation (DBS), it remains to be elucidated where within the work process the surgical result could diverge from the surgical plan. We sought to determine this. We implemented a standardized checklist to detect and remediate procedural errors. A consecutive series of 13 patients was studied. Revisions, explantations and thermal lesions were excluded. We tabulated the number and type of errors that could occur when implementing a surgical plan. Errors were categorized as minor or major. The elapsed time was also assessed. A mean of two errors per case were identified: 1.15 major errors/case and 0.85 minor errors per case. The total number of errors identified per case did not change significantly over the course of the series. Time to complete the checklist decreased monotonically from 4 min 5 s to 1 min 10 s. The checklist applied in this scenario is a useful tool to identify and remediate errors during DBS, adding minimal additional operative time and consistently identifying errors.

Relative adrenal insufficiency in patients with acute spinal cord injury.

INTRODUCTION: Relative adrenal insufficiency has been shown to occur in the settings of critical illness and septic shock, impairing the body's ability to respond to stress. Studies have demonstrated that the treatment of adrenal insufficiency (AI) results in shock reversal, hemodynamic stability, and a subsequent decrease in mortality. Endocrine changes and AI have been reported in patients with spinal cord injuries during their extended courses of rehabilitation. DISCUSSION: We describe two cases of patients with cervical spine injuries who presented with acute adrenal insufficiency following their injuries. With the addition of low-dose corticosteroids, each patient had symptom resolution and demonstrated clinical improvement. CONCLUSION: Patients with spinal cord injuries are at risk for AI, both in the acute and chronic settings following injury prompting the need for an increased awareness of this condition. Although variability exists in the exact criteria for the diagnosis of AI, the combination of clinical symptoms, depressed serum cortisol concentrations, and responsiveness to exogenous steroid therapy should all contribute to the diagnosis of this condition.

Aminophylline for the treatment of symptomatic bradycardia and asystole secondary to cervical spine injury.

INTRODUCTION: Bradycardia is a common complication of cervical spine damage in the weeks following injury, occurring in up to 100% of patients in some studies. Cardiac arrest and asystole have been reported in as many as 15% of these patients and cardiac events are the main cause of death within the first year. We describe the case of a 25-year-old African-American male involved in a motor vehicle collision who suffered C6-C7 subluxation. METHODS: Following cervical discectomy and spinal fusion the patient began to develop progressive bradycardia culminating on hospital day 20 with two asystolic events requiring atropine administration. In an attempt to prevent further events and generate hemodynamic stability, aminophylline therapy was initiated. RESULTS: Following day two of therapy, the patient's bradycardia resolved, and no further asystolic events occurred. CONCLUSION: There is limited evidence for the use of methylxanthines in the treatment of bradycardia associated with spinal cord injury. In patients with recurrent asystolic events or symptomatic bradycardia the use of these agents should be considered.

Dynamic gain control of dopamine delivery in freely moving animals.

Activity changes in a large subset of midbrain dopamine neurons fulfill numerous assumptions of learning theory by encoding a prediction error between actual and predicted reward. This computational interpretation of dopaminergic spike activity invites the important question of how changes in spike rate are translated into changes in dopamine delivery at target neural structures. Using electrochemical detection of rapid dopamine release in the striatum of freely moving rats, we established that a single dynamic model can capture all the measured fluctuations in dopamine delivery. This model revealed three independent short-term adaptive processes acting to control dopamine release. These short-term components generalized well across animals and stimulation patterns and were preserved under anesthesia. The model has implications for the dynamic filtering interposed between changes in spike production and forebrain dopamine release.