Electrophysiological localization of the substantia nigra in the parkinsonian nonhuman primate

Simplified adaptor for stereotactic surgery in non-human primates

BACKGROUND

It is challenging for researchers performing stereotactic procedures to transition from small animals to non-human primate (NHP) experiments. The NHP stereotactic atlas is based on ear-bar zero (EBZ), which is an anatomical reference frame that is not visible during surgery. Most current NHP stereotactic systems require high-cost MRI or CT imaging and complex computer processing to determine the stereotactic coordinates, limiting the procedure to those with significant expertise.

NEW METHOD

We have designed a simplified adaptor consisting of a circular arc for coronal tilt, a carrier for electrodes or cannulas, and an anchor to attach the adaptor to a conventional stereotactic frame. Our adaptor allows easy identification of the EBZ with the help of an anchor notch, and provides digital distance sensors without the need for imaging data or computer processing. Our system enables the use of trajectories that avoid injury to important structures and vessels.

RESULTS

We tested the accuracy of our system using simulated targeting with phantoms, and demonstrated sub-millimeter accuracy. Infusion of methylene blue also showed satisfactory staining in target structures deep in the brain.

COMPARISON WITH EXISTING METHODS

This system does not require high-cost imaging and extra training to determine EBZ. Once EBZ is set automatically by the system itself, targeting is similar to that in small animal stereotactic procedure.

CONCLUSION

Our simple adaptor will aid researchers who plan to conduct experiments involving stereotactic surgery in NHPs.

Relationship between oscillatory activity in the cortico-basal ganglia network and parkinsonism in MPTP-treated monkeys

Parkinsonism is associated with changes in oscillatory activity patterns and increased synchronization of neurons in the basal ganglia and cortex in patients and animal models of Parkinson's disease, but the relationship between these changes and the severity of parkinsonian signs remains unclear. We examined this relationship by studying changes in local field potentials (LFPs) in the internal pallidal segment (GPi) and the subthalamic nucleus (STN), and in encephalographic signals (EEG) from the primary motor cortex (M1) in Rhesus monkeys which were rendered progressively parkinsonian by repeated systemic injections of small doses of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Observations during wakefulness and sleep (defined by EEG and video records) were analyzed separately. The severity of parkinsonism correlated with increases in spectral power at frequencies below 15.5Hz in M1 and GPi and reductions in spectral power at frequencies above 15.6Hz with little change in STN. The severity of parkinsonism also correlated with increases in the coherence between M1 EEG and basal ganglia LFPs in the low frequency band. Levodopa treatment reduced low-frequency activity and increased high-frequency activity in all three areas, but did not affect coherence. The state of arousal also affected LFP and EEG signals in all three structures, particularly in the STN. These results suggest that parkinsonism-associated changes in alpha and low-beta band oscillatory activity can be detected early in the parkinsonian state in M1 and GPi. Interestingly, oscillations detectable in STN LFP signals (including oscillations in the beta-band) do not appear to correlate strongly with the severity of mild-to-moderate parkinsonism in these animals. Levodopa-induced changes in oscillatory M1 EEG and basal ganglia LFP patterns do not necessarily represent a normalization of abnormalities caused by dopamine depletion.

The impact of multichannel microelectrode recording (MER) in deep brain stimulation of the basal ganglia

Deep brain stimulation (DBS) of the basal ganglia (Ncl. subthalamicus, Ncl. ventralis intermedius thalami, globus pallidus internus) has become an evidence-based and well-established treatment option in otherwise refractory movement disorders. The Ncl. subthalamicus (STN) is the target of choice in Parkinson's disease.However, a considerable discussion is currently ongoing with regard to the necessity for micro-electrode recording (MER) in DBS surgery.The present review provides an overview on deep brain stimulation and (MER) of the STN in patients with Parkinson's disease. Detailed description is given concerning the multichannel MER systems nowadays available for DBS of the basal ganglia, especially of the STN, as a useful tool for target refinement. Furthermore, an overview is given of the historical aspects, spatial mapping of the STN by MER, and its impact for accuracy and precision in current functional stereotactic neurosurgery.The pros concerning target refinement by MER means on the one hand, and cons including increased bleeding risk, increased operation time, local or general anesthesia, and single versus multichannel microelectrode recording are discussed in detail. Finally, the authors favor the use of MER with intraoperative testing combined with imaging to achieve a more precise electrode placement, aiming to ameliorate clinical outcome in therapy-resistant movement disorders.

Deep brain stimulation of the substantia nigra pars reticulata improves forelimb akinesia in the hemiparkinsonian rat

Deep brain stimulation (DBS) employing high-frequency stimulation (HFS) is commonly used in the globus pallidus interna (GPi) and the subthalamic nucleus (STN) for treating motor symptoms of patients with Parkinson's disease (PD). Although DBS improves motor function in most PD patients, disease progression and stimulation-induced nonmotor complications limit DBS in these areas. In this study, we assessed whether stimulation of the substantia nigra pars reticulata (SNr) improved motor function. Hemiparkinsonian rats predominantly touched with their unimpaired forepaw >90% of the time in the stepping and limb-use asymmetry tests. After SNr-HFS (150 Hz), rats touched equally with both forepaws, similar to naive and sham-lesioned rats. In vivo, SNr-HFS decreased beta oscillations (12-30 Hz) in the SNr of freely moving hemiparkinsonian rats and decreased SNr neuronal spiking activity from 28 ± 1.9 Hz before stimulation to 0.8 ± 1.9 Hz during DBS in anesthetized animals; also, neuronal spiking activity increased from 7 ± 1.6 to 18 ± 1.6 Hz in the ventromedial portion of the thalamus (VM), the primary SNr efferent. In addition, HFS of the SNr in brain slices from normal and reserpine-treated rat pups resulted in a depolarization block of SNr neuronal activity. We demonstrate improvement of forelimb akinesia with SNr-HFS and suggest that this motor effect may have resulted from the attenuation of SNr neuronal activity, decreased SNr beta oscillations, and increased activity of VM thalamic neurons, suggesting that the SNr may be a plausible DBS target for treating motor symptoms of DBS.

The subcortical hidden side of focal motor seizures: evidence from micro-recordings and local field potentials

Focal motor seizures are characterized by transient motor behaviour that occurs simultaneously with paroxystic activity in the controlateral motor cortex. The implication of the basal ganglia has already been shown for generalized seizure but the propagation pathways from the motor cortex towards the basal ganglia during focal motor seizures are largely unknown. With a better knowledge of those pathways, a therapeutic modulation for reducing drug resistant motor epilepsy could be considered. Here, we recorded single-unit activities and local field potentials in the basal ganglia of two Macaca fascicularis in which acute focal motor seizures were induced by the injection of penicillin over the arm motor cortex territory. Each neuron was characterized using its mean firing rate and its type of firing pattern during interictal periods and seizures. Time-frequency analyses of local field potentials and electroencephalographic signals were used to assess dynamic changes occurring during seizure at a larger spatial level. The firing rate of neurons of input stages of basal ganglia (subthalamic nucleus and putamen) and those from the external part of the globus pallidus were significantly higher during seizures as compared to interictal periods. During seizures, the proportion of oscillatory neurons in subthalamic nucleus (71%), external globus pallidus (45%) and putamen (53%) significantly increased in comparison to interictal periods. Rhythmic activity was synchronized with ictal cortical spikes in external globus pallidus and subthalamic nucleus, but not in the putamen which oscillated faster than motor cortex. In contrast, no significant modification of the firing rate of the output stages of basal ganglia (internal part of the globus pallidus, substantia nigra pars reticulata) could be found during seizures. The local field potentials of subthalamic nucleus and external globus pallidus changed abruptly at the onset of the seizure, showing synchronization with the cortical activity throughout the seizure. In putamen, the synchronization appeared only by the end of seizures and for the two output structures, despite some increase of the oscillatory activity, the synchronization with the cortex was not significant. Our results suggest that the subthalamo-(external)-pallidal pathway is the main subcortical route involved during ictal motor seizures. Surprisingly, ictal activity did not propagate to the output structure of basal ganglia in that model. This finding may be important for clinical decisions of targeting when considering anti-epileptic neuromodulation in human beings suffering from disabling, drug resistant motor epilepsy.

Mapping of microstimulation evoked responses and unit activity patterns in the lateral hypothalamic area recorded in awake humans. Technical note

Major contributions to the understanding of human brain function have come from detailed clinical reports of responses evoked by electrical stimulation and specific brain regions during neurosurgical procedures in awake humans. In this study, microstimulation evoked responses and extracellular unit recordings were obtained intraoperatively in 3 awake patients undergoing bilateral implantation of deep brain stimulation electrodes in the lateral hypothalamus. The microstimulation evoked responses exhibited a clear anatomical distribution. Anxiety was most reliably evoked by stimulation directed ventromedially within or adjacent to the ventromedial nucleus of the hypothalamus, nausea was most reliably evoked by stimulation directed at the center of the lateral hypothalamus, and paresthesias were most reliably evoked by stimulation at the border of the lateral hypothalamus and basal nuclei. Regarding the unit recordings, the firing rates of individual neurons did not have an anatomical distribution, but a small subpopulation of neurons located at the border of the lateral hypothalamus and basal nuclei exhibited a fast rhythmically bursting behavior with an intraburst frequency of 200-400 Hz and an interburst frequency of 10-20 Hz. Based on animal studies, the lateral hypothalamic area and surrounding hypothalamic nuclei are putatively involved with a variety of physiological, behavioral, and sensory functions. The lateral hypothalamus is situated to play a dynamic and complex role in human behavior and this report further shows that to be true. In addition, this report should serve as a valuable resource for future intracranial work in which accurate targeting within this region is required.

The effects of chronic levodopa treatments on the neuronal firing properties of the subthalamic nucleus and substantia nigra reticulata in hemiparkinsonian rhesus monkeys

Dopamine replacement therapy with levodopa (LD) is currently the most effective pharmacological treatment for Parkinson's disease (PD), a neurodegenerative disorder characterized by dysfunction of basal ganglia electrophysiology. The effects of chronic LD treatments on the electrophysiological activity of the subthalamic nucleus (STN) and the substantia nigra reticulata (SNR) in parkinsonism are not clear. In the present study we examined the effects of chronic LD treatments on the firing rate and firing pattern of STN and SNR neurons in the stable hemiparkinsonian monkey model of PD. We also evaluated local field potentials of both nuclei before and after LD treatments. In a stable hemiparkinsonian state, STN and SNR had a mean firing rate of 42.6 ± 3.5H z (mean ± SEM) and 52.1 ± 5.7 Hz, respectively. Chronic intermittent LD exposure induced marked amelioration of parkinsonism with no apparent drug-induced motor complications. LD treatments did not significantly change the mean firing rate of STN neurons (41.3 ± 3.3 Hz) or bursting neuronal firing patterns. However, LD treatments induced a significant reduction of the mean firing rates of SNR neurons to 36.2 ± 3.3 Hz (p<0.05) and a trend toward increased burstiness. The entropy of the spike sequences from STN and SNR was unchanged by LD treatment, while there was a shift of spectral power into higher frequency bands in the LFPs. The inability of chronic LD treatments to reduce the bursty firing patterns in the STN and SNR should be further examined as a potential pathophysiological mechanism for PD symptoms that are refractory to LD treatments.

Ultrastructural localization and function of dopamine D1-like receptors in the substantia nigra pars reticulata and the internal segment of the globus pallidus of parkinsonian monkeys

The motor symptoms of Parkinson's disease (PD) are commonly attributed to striatal dopamine loss, but reduced dopamine innervation of basal ganglia output nuclei, the internal globus pallidus (GPi) and the substantia nigra pars reticulata (SNr) may also contribute to symptoms and signs of PD. Both structures express dopamine D1 and D5 receptors under normal conditions, and we have recently demonstrated that their local activation reduces neuronal discharge rates and enhances bursts and oscillatory activity in both nuclei of normal monkeys [M.A. Kliem et al. (2007)J. Neurophysiol., 89, 1489-1500]. Here, we determined the ultrastructural localization and function of D1-like receptors in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys. In both normal and MPTP-treated monkeys, most of the D1 and D5 receptor immunoreactivity was associated with unmyelinated axons, but we also found significant postsynaptic D5 receptor immunostaining in dendrites of GPi and SNr neurons. A significant proportion of axonal D1 immunostaining was bound to the plasma membrane in both normal and MPTP-treated monkeys. Local microinjections of the D1/D5 receptor agonist SKF82958 significantly reduced discharge rates in GPi and SNr neurons, while they increased burst firing and oscillatory activity in the 3-15-Hz band in SNr, but not in GPi, of parkinsonian monkeys. Together with our recent findings from normal monkeys, these data provide evidence that functional D1/D5 receptors are expressed in GPi and SNr in both normal and parkinsonian states, and that their activation by endogenous dopamine (under normal conditions) or dopamine receptor agonists (in parkinsonism) may regulate basal ganglia outflow.

Microelectrode recording in the posterior hypothalamic region in humans

INTRODUCTION

Deep brain stimulation of the posterior hypothalamic region (PHR) is an emerging technique for the treatment of medically intractable cluster headache. Few reports have analyzed single unit neuronal recordings in the human PHR. We report properties of spontaneous neuronal discharge in PHR for 6 patients who underwent DBS for cluster headaches.

METHODS

Initial target coordinates, determined by magnetic resonance imaging stereotactic localization, were 2 mm lateral, 3 mm posterior, and 5 mm inferior to the midpoint of the anterior commissure-posterior commissure plane. A single microelectrode penetration was performed beginning 10 mm above the anatomic target, without systemic sedation. Single units were discriminated off-line by cluster cutting in principal components space. Discharge rates, interspike intervals, and oscillatory activity were analyzed and compared between ventromedial thalamic and hypothalamic units.

RESULTS

Six patients and 24 units were evaluated. Units in the PHR had a slow, regular spontaneous discharge with wide, low-amplitude action potentials. The mean discharge rate of hypothalamic neurons was significantly lower (mean +/- standard deviation, 13.2 +/- 12.2) than that of medial thalamic units (28.0 +/- 8.2). Oscillatory activity was not detected. Microelectrode recording in this region caused no morbidity.

CONCLUSION

The single-unit discharge rate of neurons in the PHR of awake humans was 13.2 Hz and was significantly lower than medial thalamic neurons recorded dorsal to the target. The findings will be of use for microelectrode localization of the cluster headache target and for comparison with animal studies.

Neuronal activity of the red nucleus in Parkinson's disease

Precise placement of the electrodes for stimulation of the subthalamic nucleus (STN) in Parkinson's disease (PD) is crucial for the therapeutic benefit. As a result of the mistargeting and misplacement of the electrodes during surgery in 2 patients with PD, we have characterized the neuronal firing in the red nucleus (RN) and observed the effects of stimulation of this nucleus. Although the neuronal firing (mean +/- SD) of the RN (34 +/- 4.4 Hz) resembles that described for the STN (33.1 +/- 16.6 Hz), a higher proportion of cells responded to the movement of the contralateral limbs (70-80%). Stimulation in the area of the RN-induced intolerable side effects without motor improvement. We conclude that the STN and RN have some similar neurophysiological features but can be distinguished intraoperatively. This initial description of the physiological characteristics of the RN in humans will draw attention to the possibility of confusing the RN and STN during intraoperative recording.

Method of construction of a MRI-based tabular database of 3D stereotaxic co-ordinates for individual structures in the basal ganglia of Macaca mulatta

Primate models are commonly used in Parkinson's disease research to study stereotaxic strategies that demand accurate localization of the structures in basal ganglia. We demonstrate a method to construct an extensive tabular database of 3D stereotaxic co-ordinates of various basal ganglia structures from high-quality magnetic resonance (MR) images of 47 adult female 3-5 kg rhesus monkeys. For each animal, the structures in the basal ganglia were traced as they appeared on the axial MR images. Their maximal outlines were projected in the axial plane to create a stack of images and X, Y, Z co-ordinates were calculated for margins of each structure. These co-ordinates and the outlines of the individual nuclei help delineate a "common area," which was further narrowed down to a point that represents the 'most reliable target point' (MRTP) in subthalamic nucleus, globus pallidum, caudate and putamen on both sides. Common area and MRTP represent the region that can most definitely be associated with a structure and hence the most definite target for a given structure. The goal of this study is to demonstrate the method of construction, discuss the feasibility and usefulness of such a tabular database that could potentially add to accuracy of localization while using atlas-based stereotaxy. Though use of MRI remains a standard practice and advances in imaging have made targeting for functional surgery more accurate, in developing countries that implies prohibitive costs per procedure. Population based human databases similar to the monkey database described here, when used along with less expensive imaging modalities can reduce the costs considerably as well as add to the accuracy of targeting.

Somatotopy in the basal ganglia: experimental and clinical evidence for segregated sensorimotor channels

Growing experimental and clinical evidence supports the notion that the cortico-basal ganglia-thalamo-cortical loops proceed along parallel circuits linking cortical and subcortical regions subserving the processing of sensorimotor, associative and affective tasks. In particular, there is evidence that a strict topographic segregation is maintained during the processing of sensorimotor information flowing from cortical motor areas to the sensorimotor areas of the basal ganglia. The output from the basal ganglia to the motor thalamus, which projects back to neocortical motor areas, is also organized into topographically segregated channels. This high degree of topographic segregation is demonstrated by the presence of a well-defined somatotopic organization in the sensorimotor areas of the basal ganglia. The presence of body maps in the basal ganglia has become clinically relevant with the increasing use of surgical procedures, such as lesioning or deep brain stimulation, which are selectively aimed at restricted subcortical targets in the sensorimotor loop such as the subthalamic nucleus (STN) or the globus pallidus pars interna (GPi). The ability to ameliorate the motor control dysfunction without producing side effects related to interference with non-motor circuits subserving associative or affective processing requires the ability to target subcortical areas particularly involved in sensorimotor processing (currently achieved only by careful intraoperative microelectrode mapping). The goal of this article is to review current knowledge about the somatotopic segregation of basal ganglia sensorimotor areas and outline in detail what is known about their body maps.

Implantation of deep brain stimulators into the subthalamic nucleus: technical approach and magnetic resonance imaging-verified lead locations

OBJECT

Chronic deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a procedure that is rapidly gaining acceptance for the treatment of symptoms in patients with Parkinson disease (PD), but there are few detailed descriptions of the surgical procedure itself. The authors present the technical approach used to implant 76 stimulators into the STNs of patients with PD and the lead locations, which were verified on postoperative magnetic resonance (MR) images.

METHODS

Implantation procedures were performed with the aid of stereotactic MR imaging, microelectrode recording (MER) in the region of the stereotactic target to define the motor area of the STN, and intraoperative test stimulation to assess the thresholds for stimulation-induced adverse effects. All patients underwent postoperative MR imaging, which was performed using volumetric gradient-echo and T2-weighted fast-spin echo techniques, computational reformatting of the MR image into standard anatomical planes, and quantitative measurements of lead location with respect to the midcommissural point and the red nucleus. Lead locations were statistically correlated with physiological data obtained during MER and intraoperative test stimulation.

CONCLUSIONS

The authors' approach to implantation of DBS leads into the STN was associated with consistent lead placement in the dorsolateral STN, a low rate of morbidity, efficient use of operating room time, and robust improvement in motor function. The mean coordinates of the middle of the electrode array, measured on postoperative MR images, were 11.6 mm lateral, 2.9 mm posterior, and 4.7 mm inferior to the midcommissural point, and 6.5 mm lateral and 3.5 mm anterior to the center of the red nucleus. Voltage thresholds for several types of stimulation-induced adverse effects were predictive of lead location. Technical nuances of the surgery are described in detail.

Comparison of atlas- and magnetic resonance imaging-based stereotactic targeting of the globus pallidus internus in the performance of deep brain stimulation for treatment of dystonia

OBJECT

To assess the validity of relying on atlases during stereotactic neurosurgery, the authors compared target coordinates in the globus pallidus internus (GPi) obtained using magnetic resonance (MR) imaging with those determined using an atlas. The targets were used in deep brain stimulation (DBS) for the treatment of generalized dystonia.

METHODS

Thirty-five patients, who were treated using bilateral DBS of the GPi, were included in this study. The target was selected on three-dimensional MR images by direct visual recognition of the GPi. The coordinates were automatically recorded using dedicated software. They were translated into the anterior commissure-posterior commissure (AC-PC) coordinate system by using a matrix transformation process. The same GPi target was defined, based on the locations of brain structures shown in the atlases of Schaltenbrand and Talairach. Magnetic resonance imaging-based GPi target coordinates were statistically compared with the corresponding atlas-based coordinates by applying the Student t-test. A significant difference (p < 0.001) was demonstrated in x, y, and z directions between MR imaging-based and Schaltenbrand atlas-derived target coordinates. The comparison with normalized Talairach atlas coordinates demonstrated a significant difference (p < 0.01) in the y and z directions, although not in the x direction (p = 0.12). No significant correlation existed between MR imaging-based target coordinates and patient age (p > 0.1). No significant correlation was observed between MR imaging-based target coordinates and patient sex in the y and z directions (p > 0.9), although it was significant in the x direction (p < 0.05). A significant variation in coordinates and the length of the AC-PC line was revealed only in the y direction (p < 0.005).

CONCLUSIONS

A significant difference was found between target coordinates obtained by direct visual targeting on MR images (validated by postoperative clinical results) and those obtained by indirect targeting based on atlases.

Radiosurgery performed with the aid of a 3-mm collimator in the subthalamic nucleus and substantia nigra of the vervet monkey

OBJECT

Radiosurgery for functional neurosurgery performed using a linear accelerator (LINAC) has not been extensively characterized in preclinical studies. In the present study, the properties of a newly designed 3-mm-diameter collimator were evaluated in a dedicated LINAC, which produced lesions in the basal ganglia of vervet monkeys. Lesion formation was determined in vivo in three animals by examining magnetic resonance (MR) images to show the dose-delivery precision of targeting and the geometry and extent of the lesions. Postmortem immunohistochemical studies were conducted to determine the extent of lesion-induced radiobiological effects.

METHODS

In three male vervet monkeys, the subthalamic nucleus (STN; one animal) and the pars compacta of the lateral substantia nigra (SN; two animals) were targeted by a Novalis Shaped Beam Surgery System that included a 3-mm collimator and delivered a maximum dose of 150 Gy. Magnetic resonance images obtained 4, 5, and 9 months posttreatment were reviewed, and the animals were killed so that immunohistological characterizations could be made.

CONCLUSIONS

The generation of precise radiosurgical lesions by a 3-mm collimator was validated in studies that targeted the basal ganglia of the vervet monkey. The extent of the lesions created in all animals remained restricted in diameter (< 3 mm) throughout the duration of the studies, as assessed by reviewing MR images. Histological studies showed that the lesions were contained within the STN and SN target areas and that there were persistent increases in glial fibrillary acidic protein immunoreactivity. Increases in immunoreactivity for tyrosine hydroxylase, the serotonin transporter, and the GluR1 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate glutamate receptor in penumbral regions of the lesion were suggestive of compensatory neuronal adaptations. This radiosurgical approach may be of particular interest for the induction of lesions of the STN and SN in studies of experimental parkinsonism, as well as for the development of potential radiosurgical treatments for Parkinson disease.

Antiparkinsonian and behavioral effects of inactivation of the substantia nigra pars reticulata in hemiparkinsonian primates

Altered activity in one of the output nuclei of the basal ganglia, the internal segment of the globus pallidus, is known to play an important role in the generation of parkinsonism. These inactivation studies tested the hypothesis that altered activity in the second major output nucleus of the basal ganglia, the substantia nigra pars reticulata (SNr), also contributes to parkinsonian motor signs. To this end, three rhesus monkeys were rendered hemiparkinsonian by intracarotid injections of MPTP. The animals then received intra-SNr injections of the GABA(A) receptor agonist muscimol to inactivate small portions of the SNr. Before and after these injections, parkinsonian motor signs were evaluated with a battery of behavioral observation methods. Injections into the centrolateral SNr reduced contralateral limb akinesia and bradykinesia in two animals. By contrast, medial injections induced generalized activation, contralateral turning, and saccadic eye movements in all animals. Injections in the most lateral and posterior portions of the nucleus had no effects. Two of the animals also received ibotenic acid lesions of the SNr, followed by a series of similar observations. These injections induced improvements in limb akinesia, postural improvements, and turning. The experiments suggest that the anterolateral "motor" territory of the SNr is involved in the development of appendicular parkinsonian motor signs.