Katsushige Watanabe

Single-unit activity in the primate nucleus tegmenti pedunculopontinus related to voluntary arm movement

In the pedunculopontine tegmental nucleus (PPN), single-unit activity was recorded in two monkeys trained to manipulate an on-off lever with a hand. Among 280 neurons recorded, a change in the firing rate related to the lever-off movement was observed in 125 neurons for the contralateral limb movement (53%) and in 96 neurons for the ipsilateral limb movement (48%). The changes were an increase in the firing rate in 122 neurons and a decrease in 99 neurons. These changes in the firing rate related to the task often occurred for both the contralateral and ipsilateral limb movements. The change of activity preceded the movement onset for both contralateral and ipsilateral arm movements. These findings suggest that in primates the PPN contributes to coordination of upper limb movements on both sides.

Pathophysiology of central (thalamic) pain: combined change of sensory thalamus with cerebral cortex around central sulcus.

In 13 patients with central (thalamic) pain after stroke, CT, MRI, PET scan and intraoperative thalamic microrecordings were performed. Electrophysiological studies showed that irregular burst discharges were often encountered in the posterolateral thalamus. The more often the irregular burst discharges were encountered, the greater the decrease of sensory response in the posterolateral thalamus. Metabolic studies showed that regional cerebral glucose metabolism decreased in both the posterolateral thalamus and in the cortical postcentral area on the lesioned side in all cases. In the thalamic lesion cases in which many irregular burst discharges were found in the posterolateral thalamus, regional cerebral glucose metabolism and the relative value of glucose to oxygen metabolism increased in the cortical precentral area on the lesioned side. It was suggested that decreased activity with abnormal burst discharge in the posterolateral (sensory) thalamus associated with changes in cortical activity adjacent to the central sulcus might be related to the genesis of central (thalamic) pain. It is emphasized that cortical activity decreased in the postcentral area, but often increased in the precentral area.

Effect of electrical stimulation of the thalamic Vim nucleus on hand tremor during stereotactic thalamotomy

OBJECTIVE The aim of this study was to analyze the correlation between neuronal responses in the thalamic ventralis intermedius (Vim) nucleus to peripheral, natural stimulation and the modulation of tremor by electrical stimulation during stereotactic thalamotomy. DESIGN AND METHODS The authors studied 36 patients with hand tremor using a microelectrode. The responses of tremor to electrical stimulation were analysed electromyographically. Sixty stimulation sites were divided into three groups. RESULTS Group A (20 sites) where responses to stretching of the contralateral forearm muscles were recorded. Group B (26 sites) where responses to stretching of the other muscles of the upper extremity were recorded. Electrical stimulation at sites in groups A and B temporarily suppressed the contralateral tremor, but the minimum current intensity to suppress tremor at sites in group A was less than that in group B. Electrical stimulation in group C (14 sites), where kinesthetic responses of contralateral lower extremity were recorded, resulted in increased amplitude of hand tremor. Selective coagulation including the area of tremor suppression resulted in abolition of the tremor in all patients. CONCLUSIONS These results suggest that the most effective site for thalamotomy may also be suitable for chronic stimulation in the Vim nucleus.

Effect of Ventralis Intermedius Thalamotomy on the Area in the Sensorimotor Cortex Activated by Passive Hand Movements: fMR Imaging Study

Stereotactic ventralis intermedius (Vim) thalamotomy is effective for essential tremor (ET) of the limb, but the effect on the activity of the sensorimotor cortex is still unclear. The functional changes in this cortical area of patients with ET after Vim thalamotomy were investigated using functional magnetic resonance (fMR) imaging. Six patients underwent Vim thalamotomy for medically intractable ET, predominantly in the right hand. 1.5-tesla fMR imaging was performed using the blood oxygenation level-dependent sequence, before and after Vim thalamotomy, during passive movements with right wrist flexion and extension. Before and after images were analyzed using SPM99 software. Activation in the sensorimotor cortex and supplementary motor area evoked by wrist passive movement was observed both before and after surgery. Group analysis of changes in the blood oxygenation level-dependent response revealed a significantly smaller activated area postoperatively. Activation at the fundus of the central sulcus was characteristically decreased. All patients showed marked improvement in tremor after Vim thalamotomy. No patient experienced neurological deficits. fMR imaging showed that activation at the fundus of the central sulcus evoked by passive wrist movement was suppressed after Vim thalamotomy in ET patients, probably due to disruption of the thalamocortical pathway. The fundus of the central sulcus (Brodmann area 3a) is likely to be one of the key relays in the tremor circuit.

Use of a Frameless Isocentric Stereotactic System (NEURO-SAT) Combined with the Intraoperative Microrecording

Combining the frameless isocentric stereotactic system (NEURO-SAT) and intraoperative microrecording, we performed stereotactic biopsies of deep-seated brain tumors in two cases. Case 1 was a 58-year-old male suffering from a right thalamus to basal ganglia tumor and case 2 was a 29-year-old male suffering from brain stem tumor. In both cases, the border between the tumor and the normal tissue was ambiguous on neuroimagings. NEURO-SAT provides three-dimensional real-time surgical navigation by displaying the positional information on the MRI images, and intraoperative microrecording shows a clear delineation between the tumor and the normal tissue in both cases. Therefore, since this combined method provides real-time surgical navigation and clear delineation of the tumor and normal tissue, it is a promising method of accurate and reliable image-directed stereotactic biopsy of deep-seated brain tumor.

Neuronal Activity of Monkey Pedunculo-Pontine Tegmental Nucleus Area I

Anatomical studies have revealed dense connections between the pedunculopontine tegmental nucleus (PPN) and the basal ganglia (Figure 1). In primates, PPN receives massive afferents from the two output structures of the basal ganglia, that is, the substantia nigra pars reticulata and the internal pallidum. In turn, PPN projects profusely to the substantia nigra pars compacta and the subthalamic nucleus (Filion and Harnois, 1978; Harnois and Filion, 1980; Harnois and Filion, 1982; Parent and Hazrati, 1995). These ascending projections were found both ipsilaterally and contralaterally (Lavoie and Parent, 1994b). The existence of cerebello-tegmental projections, which are ipsilateral collaterals of the cerebello-thalamic projection, was also reported (Hazrati and Parent, 1992). Motor cortex (area 4) also sends fibers to PPN (Hartmann-Von Monakow et al., 1979; Moon Edley and Graybiel, 1983). PPN is a part of the mesencephalic locomotor region, from which locomotor movements are induced by its electrical stimulation (Garcia-Rill, 1986; Garcia-Rill, 1991).

Physiological Study of the Pallidal Neurons in Parkinson’s Disease

Although our understanding of the human basal ganglia (BG) is still relatively poor, the old type of pallidotomy (Svennilson et al., 1960: Narabayashi et al., 1956) is now modified and the revised type of pallidotomy has been widely accepted and its clinical benefit seems to be favorable to some extent (Sutton et al., 1995: Laitinen et al., 1992). Therefore, to elucidate the pathophysiological state of BG, particularly the internal segment of the globus pallidus (GPi), depth electrode recording during the course of stereotactic surgery as we have been using during thalamotomy for movement disorders, might also be useful.

Visualization of Dopamine Nerve Terminals in Monkey by Positron Emission Tomography Using 4-[18F]Fluoro-L-m-Tyrosine

4-[18F]Fluoro-L-m-tyrosine (FMT) is an L-Dopa analog that essentially follows the L-Dopa metabolic pathway, but without 3-O-methylation or extensive peripheral metabolism. As such, FMT may serve as a useful probe of striatal dopaminergic function with positron emission tomography (PET). FMT was synthesized, as previously described by Perlmutter et al. [Appl Radiat Isot 1990;41:801-807]. Scanning was undertaken with the SHR2000 positron tomograph (image spatial resolution, 3.5 x 4.5 x 6.5 mm). Two Macaca monkeys were anesthetized with ketamine (10 mg/kg) and pentobarbital (20 mg/kg). FMT was administered intravenously (5-6 mCi; specific activity 1-2 Ci/mmol) following carbidopa pretreatment (5 mg/kg i.v., 60 min before FMT administration). Dynamic image acquisition was done for 2 h immediately after tracer injection. This emission acquisition involved twelve 2-min frames followed by nine 4-min frames, and six 10-min images. Arterial blood samples were collected according to a schedule for assay of plasma [18F] radioactivity. Specific uptake of FMT in aromatic L-amino-acid-decarboxylase-rich areas of the monkey striatum was observed with PET imaging. The striatum-to-cerebellum ratio of the accumulation increased over time to 3.0 at 2 h. These results show the promise of FMT as a PET tracer in evaluating the CNS dopaminergic system.

Reliable and convenient method for the fixation of recording electrodes on nonshaved scalp for intraoperative electrophysiological monitoring: Technical note

BACKGROUND Difficulties with the intraoperative monitoring of evoked responses sometimes occur because of displacement or dislodgment of the recording electrodes during surgery, especially if placed on nonshaved scalp. METHODS An alternative fixation method of the recording electrode on the nonshaved scalp was developed. The sterile subdermal needle electrode was attached on the scalp by application of a transparent dressing (Tegaderm) over the electrode followed by fixing with a skin stapler. RESULTS The needle electrodes were easily, quickly, and firmly positioned even on the nonshaved scalp. The responses of the intraoperative evoked potentials were highly stable and reproducible throughout the operation. CONCLUSION This fixation method for subdermal needle electrodes on the scalp is safe, reliable, and convenient for intraoperative electrophysiological monitoring of evoked potentials, even if the scalp is not shaved.

EFFECTS OF REVERSIBLE BLOCKADE OF PEDUNCULOPONTINE TEGMENTAL NUCLEUS ON VOLUNTARY ARM MOVEMENT IN MONKEY

We examined the effects of a reversible blockade of pedunculopontine tegmental nucleus (PPN) in a monkey (macaca fuscata) which was trained to perform a lever-pull task with an arm. Neurons of PPN presented changes in their firing rate during arm movements. The changes were either an increase or a decrease. Muscimol (a γ-aminobutyric acid (GABA) agonist) was injected into PPN area to suppress its neuronal activity while the monkey was performing the task. The blockade of the activity of PPN neurons caused slowness of movements on the both sides of arms. The peak velocities of lever movement decreased and the reaction times increased. This work suggested that PPN had an excitatory effect to the initiation and the execution of voluntary movements of the limbs The monkey did not show any difficulty in performing the task and the success rates were kept high.