1. Parkinsons Disease: Parkinsons disease (PD) affects over 700,000 people in the United States. Currently levodopa is the most effective medical treatment for PD. Exogenous levodopa replaces depleted dopamine stores and alleviates PD symptoms. While it is initially effective, the symptoms become refractory after 3 to 5 years of treatment and patients develop worsening on-off symptom fluctuations in which on periods are associated with hyperkinetic movements (e.g. dyskinesias) and off periods with hypokinetic movements (e.g. akinesia, bradykinesia) and gait difficulties.2. Convection-enhanced selective excitotoxic ablation of the neurons of the globus pallidus interna for treatment of primate parkinsonism: Selective treatment of central nervous system (CNS) structures holds therapeutic promise for many neurological disorders, including Parkinsons disease (PD). The ability to inhibit or augment specific neuronal populations within the CNS reliably by using present therapeutic techniques is limited. To overcome this problem, we modeled and developed a method in which convection was used to deliver compounds to deep brain nuclei in a reproducible, homogeneous, and targeted manner. The complications associated with chronic medical therapy of PD often respond to surgical treatment. The most common surgical therapy is stereotactic ablation of a portion of the Gpi by radiofrequency (thermal) lesioning, which can ameliorate the hypokinetic as well as the hyperkinetic symptoms, including levodopa-induced dyskinesias, in most patients with medically-intractable PD. Unfortunately, the non-specific nature of this form of tissue destruction can result in immediate or delayed damage to surrounding white matter tracts (i.e., internal capsule, optic tract) resulting in paralysis and visual loss. Moreover, the lesioning with radiofrequency energy of larger regions of tissue required for optimal efficacy is technically challenging and can increase the risks associated with this surgery. Due to the inherent problems associated with radiofrequency lesioning, attention has been focused on attempts to pharmacologically manipulate local neural circuits. At present there is no way to influence pathologic neuronal populations selectively, because currently-available central nervous system (CNS) drug distribution techniques rely on either systemic or intraventricular delivery. Systemic delivery is limited by toxicity and the inability of many compounds to cross the blood- brain barrier. Intraventricular delivery depends on diffusive- forces for distribution, which constrain tissue penetration and result in heterogeneous dispersion along an exponentially diminishing concentration gradient. Neither method can provide targeted delivery of therapeutic substances at effective and homogeneous levels. To overcome these problems, we modeled, then developed a method for convective delivery to the CNS, which showed that convection- enhanced infusion of an excitotoxin could be used to selectively lesion grey matter regions of the non-human primate brain. Because convection relies on bulk flow of infusate in the interstitial space, it can be used to distribute small or large molecular weight molecules in a homogenous, reproducible, and safe manner over clinically-useful brain volumes. These properties make convective delivery a potentially ideal method to target various nuclei or anatomic structures within the CNS for drug delivery. To determine the feasibility and clinical efficacy of convective drug delivery for treatment of a neurologic disorder, we selectively ablated globus pallidus interna (Gpi) neurons with an excitotoxin, quinolinic acid (QA), in the 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine (MPTP)-induced model of primate parkinsonism. After the parameters of convective distribution to the Gpi were confirmed by infusion of biotinylated-albumin into the Gpi of a primate (Macaca mulatta), primates were rendered parkinsonian by MPTP (n=5). Using convection-enhanced delivery to the Gpi, animals were infused with QA with substantial improvement of PD, manifest by a marked increase in activity monitor activity and dramatic improvement of parkinsonian clinical scores. In contrast, the controls did not improve. Histologic examination revealed selective neuronolysis of Gpi neurons (mean loss = 87%) with sparing of surrounding grey and white matter structures. Convection-enhanced delivery of QA permits selective, region- specific (Gpi), and safe lesioning of neuronal subpopulations with dramatic improvement in parkinsonian symptomatology. The properties of convection-enhanced delivery suggest that this method could be used for chemical neurosurgery for medically- refractory PD and that it may be ideal for cell-specific therapeutic ablation or trophic treatment of other targeted structures associated with the CNS disorders.3. Pathogenesis of dyskinesias associated with levo-dopa treatment:The functional status of the globus pallidus internal segment (Gpi) plays a key role in mediating the effects of antiparkinsonian drugs. The mechanism by which providing dopamine to a denervated striatum produces abnormal movements along with the expected reversal of parkinsonian features remains unknown. To address this issue we used single cell recording of the firing of GPi cells in 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-parkinsonian monkeys that developed dyskinesias after chronic levodopa treatment. The transition from the off to the on state was characterized by a decrease (most cells), no change, or an increase in firing rate of individual cells. During dyskinesias firing rates fell profoundly in almost all cells, with decrements as low as 97% in individual cells. These changes occurred only when dyskinesias were present.To avoid the risks associated with pooling activity from different functional groups of cells in the different states, we recorded single cells in the GPi of parkinsonian monkeys continuously through the off and on states, and 10-15 min later during on with or without dyskinesias, depending on two doses of levodopa. The transition from the off to the on state, with a complete reversal of parkinsonism, was characterized by a decrease (most cells), no changes or an increase in the firing rate of individual GPi cells. During dyskinesias firing rates fell profoundly in almost all cells, with decrements as low as 97% in individual cells. These changes occurred only when dyskinesias were present. The difference in GPi activity between on and on with dyskinesias suggests that normal motor function in Parkinson’s disease critically depends on fine tuning of the basal ganglia output. Dyskinesias result from an imbalanced low GPi discharge, a circumstance that may be susceptible to development of new therapeutic approaches. 4. Infrared Functional Mapping: It is important during neurosurgical procedures to identify and preserve eloquent functional cortex adjacent to a resectable lesion. Intraoperative real-time functional mapping techniques now available cannot be used in many surgical situations and are not sufficiently reliable in all cases in which they are used. We are examining an intraoperative approach that may permit lesion localization and brain functional mapping on-line with minimal risk. This approach makes use of infrared (IR) technology to identify functionally active cortex and may enhance differentiate abnormal tissue from normal cortex. To use the IR method most effectively in humans, we validated it in an OR situation. Rhesus monkeys were used to examine localization of the somatosensory cortex. An IR camera (sensitivity 0.01 degr.C; 3-5( wavelength) was positioned above the exposed cortex. Difference maps (stimulated minus control) defined topographic thermal features of the distribution of cortical activity. Physiological motion artifacts were reduced via gating and digital motion correction. Median nerve stimulation was used to evoke IR and high-resolution electrocorticographic (EcoG) maps (3.5 mm inter-electrode distance) of monkey somatosensory cortex were obtained intraoperatively to validate the coordinates and accuracy of the IR functional localization. Statistical analysis of single trials (Z-score test) reveal well-defined and reproducible temperature gradients in the somatosensory primary cortex and motor cortex. ECoG maps of the involved cortex revealed that IR signal accurately delineated the area of activated cortex.The mechanism of IR activation was explored by examining IR changes during systematic occlusion of cortical arteries. In experiments with temporary occlusion of cortical vessels we found that blood flow changes had an immediate and profound effect on the IR signal: local temperature decreased in area of vessel occlusion and multifocal temperature increases occurred in surrounding areas. Collateral flow was evaluated, and cortical steal was observed in a collateral vessel during reperfusion. The use of high-resolution, digital IR imaging permits real-time visualization of arterial flow and has the potential to provide the surgeon with a means to assess collateral flow during temporary vessel occlusion, and of directly visualizing flow in the parent arteries or persistent filling of an arteriovenous malformation or an aneurysm during surgery. We are also examining the IR camera during surgery of the exposed brain in humans. In 27 human cases with brain lesions (24 with tumors, 1 with CNS infection, and 2 patients with extractable epilepsy) infrared (IR) mapping of the cerebral cortex was performed at background and during functional activation. Activation paradigms included median nerve stimulation, hand movements, and speech/language production. Functional stimulation revealed cortical activation patterns in the form of evoked temperature gradients with a spatial resolution of 150 um. Neural activation elicited reproducible, rapid, focal temperature changes (0.04- 0.08 degr.C) in the primary somatosensory and motor cortex during repetitive hand movements and median nerve stimulation. Language production activated temperature changes in areas subsequently identified by cortical stimulation mapping as functionally significant for language/speech. Additional surrounding cortical areas were also activated, suggesting their involvement in the complex cognitive aspects of language/speech production. Discrete temperature gradients were found associated with surgically-verified lesions in all cases. Therefore, this method may provide intraoperative, accurate, real-time functional mapping of the cortex for neuro-navigation. Further, development of this IR imaging technique may provide a new approach to study neurophysiology in vivo. The high sensitivity and resolution of this approach may permit more accurate identification of the entire region of cortex activated during motor, sensory, and cognitive tasks than currently available approaches such as fMRI, PET, EcoG, and others.
