A New Rat Model of Thalamic Pain Produced by Administration of Cobra Venom to the Unilateral Ventral Posterolateral Nucleus

BACKGROUND

Thalamic pain is a neuropathic pain syndrome that occurs as a result of thalamic damage. It is difficult to develop therapeutic interventions for thalamic pain because its mechanism is unclear. To better understand the pathophysiological basis of thalamic pain, we developed and characterized a new rat model of thalamic pain using a technique of microinjecting cobra venom into the ventral posterolateral nucleus (VPL) of the thalamus.

OBJECTIVES

This study will establish a new thalamic pain rat model produced by administration of cobra venom to the unilateral ventral posterolateral nucleus.

STUDY DESIGN

This study used an experimental design in rats.

SETTING

The research took place in the laboratory at the Aviation General Hospital of China Medical University and Beijing Institute of Translational Medicine.

METHODS

Male Sprague-Dawley rats were subjected to the administration of cobra venom or saline into the left VPL. The development of mechanical hyperalgesia and changes in pain-related behaviors and motor function were measured after intrathalamic cobra venom microinjection using the von Frey test, video recording, and cylinder test, respectively. On postoperative days 7 to 35, both electroacupuncture and pregabalin (PGB) were administered to verify that the model reproduced the findings in humans. Moreover, the organizational and structural alterations of the thalamus were examined via transmission electron microscopy (TEM).

RESULTS

The threshold for mechanical stimuli in the left facial skin was significantly decreased on day 3 after thalamic pain modeling as compared with pre-venom treatment. Furthermore, the ultrastructural alterations of neurons such as indented neuronal nuclei, damaged mitochondria and endoplasmic reticulum, and dissolved surrounding tissues were observed under TEM. Moreover, electroacupuncture treatment ameliorated mechanical hyperalgesia, pain-like behaviors, and motor dysfunction, as well as restore normal structures of neurons in the thalamic pain rat model. However, no such beneficial effects were noted when PGB was administered.

LIMITATIONS

The pathophysiological features were different from the present model and the patients in clinical practice (in most cases strokes, either ischemic or hemorrhagic).

CONCLUSION

The cobra venom model may provide a reasonable model for investigating the mechanism of thalamic pain and for testing therapies targeting recovery and pain after thalamic lesions.

KEY WORDS

Thalamic pain, cobra venom, electroacupuncture, pregabalin, indented neuronal nuclei, damaged mitochondria, dissolved endoplasmic reticulum, golgi body.

Recurrent cerebral microbleeds with acute stroke symptoms: A case report

RATIONALE

Cerebral microbleeds are lesions that appear as round low signal intensity areas with a diameter of 2-5 mm on gradient echo T2-weighted sequence magnetic resonance imaging. Cerebral microblees are hemorrhages found in the brain parenchyma and they are caused by the extravasation of the blood. Although more patients with ischemic stroke are found to have cerebral microbleeds, only a few studies have evaluated other neurologic abnormalities outside of cognitive dysfunction due to cerebral microbleeds.

PATIENT CONCERNS

A 73-year-old female patient had only a lacunar infarction with the development of a new microbleed whenever a new neurologic symptom occurred, without the occurrence of acute ischemic stroke.

DIAGNOSES

A 73-year-old female patient diagnosed symptomatic cerebral microbleeds.

INTERVENTIONS

Brain magnetic resonance imaging was taken within a few hours of the occurrence of a new symptom and we confirmed increased cerebral microbleeds in the ventral-posterolateral area of the thalamus, consistent with the symptoms.

OUTCOMES

This case study is meaningful because it proves that repeated occurrences of cerebral microbleeds in a specific area can induce acute ischemic stroke-like symptoms.

LESSONS

Cerebral microbleeds have been considered to be asymptomatic lesions thus far. However, recent studies have reported the association of cerebral microbleeds with neurological symptoms including cognitive dysfunction. This study confirmed the presence of newly formed cerebral microbleeds through imaging follow-ups whenever a symptom occurred.

Selective downregulation of vesicular glutamate transporter2 in ventral posterolateral nucleus of thalamus attenuates neuropathic mechanical allodynia in mice

Vesicular glutamate transporters (VGLUTs) transport glutamate into synaptic vesicles prior to exocytotic release. The expression pattern of VGLUT2 and studies of genetically modified mice have revealed that VGLUT2 contributes to neuropathic pain. We previously showed that VGLUT2 is upregulated in supraspinal regions including the thalamus in mice following spared nerve injury (SNI), and blocking VGLUTs using the VGLUT inhibitor CSB6B attenuated mechanical allodynia. To further evaluate the role of VGLUT2 in neuropathic pain, in this study, we developed a lentiviral vector expressing small hairpin RNAs (shRNAs) against mouse VGLUT2, which was injected into the ventral posterolateral (VPL) nucleus of the thalamus in the presence or absence of SNI. The administration of VGLUT2 shRNAs result in downregulation of VGLUT2 mRNA and protein expression, and decreased extracellular glutamate release in primary cultured neurons. We also showed that VGLUT2 shRNAs attenuated SNI-induced mechanical allodynia, in accordance with knockdown of VGLUT2 in the VPL nucleus in mice. Accordingly, our study supports the essential role of supraspinal VGLUT2 in neuropathic pain in adult mice and, thereby, validates VGLUT2 as a potential target for neuropathic pain therapy.

Lesions of the ventral midline thalamus produce deficits in reversal learning and attention on an odor texture set shifting task

The nucleus reuniens (RE) of the ventral midline thalamus is strongly reciprocally connected with the hippocampus (HF) and the medial prefrontal cortex (mPFC) and has been shown to mediate the transfer of information between these structures. It has become increasingly well established that RE serves a critical role in mnemonic tasks requiring the interaction of the HF and mPFC, but essentially not tasks relying solely on the HF. Very few studies have addressed the independent actions of RE on prefrontal executive functioning. The present report examined the effects of lesions of the ventral midline thalamus, including RE and the dorsally adjacent rhomboid nucleus (RH) in rats on attention and behavioral flexibility using the attentional set shifting task (AST). The task uses odor and tactile stimuli to test for attentional set formation, attentional set shifting, behavioral flexibility and reversal learning. By comparison with sham controls, lesioned rats were significantly impaired on reversal learning and intradimensional (ID) set shifting. Specifically, RE/RH lesioned rats were impaired on the first reversal stage of the task which required a change in response strategy to select a previously non-rewarded stimulus for reward. RE/RH lesioned rats also exhibited deficits in the ability to transfer or generalize rules of the task which requires making the same modality-based choices (e.g., odor vs. tactile) to different sets of stimuli in the ID stage of the task. These results demonstrate that in addition to its role in tasks dependent on HF-mPFC interactions, nucleus reuniens is also critically involved cognitive/executive functions associated with the medial prefrontal cortex. As such, the deficits in the AST task produced by RE/RH lesions suggest the ventral midline thalamus directly contributes to flexible goal directed behavior.

The non-motor complications in Parkinson's disease - what can we learn from animal models?

Sporadic Parkinson's disease is a widespread human disease that has never been reported in non-human vertebrates. The etiopathogenesis of the non-motor symptoms in the disease is not well understood and it is difficult to interpret the roles of affected neurotransmitters in currently available animal models. Most of the non-motor symptoms do not correlate with the stage of motor deficits and precede the development of motor symptoms by many years, before the permanent loss of dopaminergic neurons in the basal ganglia. The aim of this review is to briefly summarize the advantages and limitations of the well-recognized mammalian animal models with special regard to the non-motor complications of the prodromal and early stage Parkinson's disease.

Forelimb amputation-induced reorganization in the ventral posterior lateral nucleus (VPL) provides a substrate for large-scale cortical reorganization in rat forepaw barrel subfield (FBS)

In this study, we examined the role of the ventral posterior lateral nucleus (VPL) as a possible substrate for large-scale cortical reorganization in the forepaw barrel subfield (FBS) of primary somatosensory cortex (SI) that follows forelimb amputation. Previously, we reported that, 6 weeks after forelimb amputation in young adult rats, new input from the shoulder becomes expressed throughout the FBS that quite likely has a subcortical origin. Subsequent examination of the cuneate nucleus (CN) 1 to 30 weeks following forelimb amputation showed that CN played an insignificant role in cortical reorganization and led to the present investigation of VPL. As a first step, we used electrophysiological recordings in forelimb intact adult rats (n=8) to map the body representation in VPL with particular emphasis on the forepaw and shoulder representations and showed that VPL was somatotopically organized. We next used stimulation and recording techniques in forelimb intact rats (n=5) and examined the pattern of projection (a) from the forelimb and shoulder to SI, (b) from the forepaw and shoulder to VPL, and (c) from sites in the forepaw and shoulder representation in VPL to forelimb and shoulder sites in SI. The results showed that the projections were narrowly focused and homotopic. Electrophysiological recordings were then used to map the former forepaw representation in forelimb amputated young adult rats (n=5) at 7 to 24 weeks after amputation. At each time period, new input from the shoulder was observed in the deafferented forepaw region in VPL. To determine whether the new shoulder input in the deafferented forepaw VPL projected to a new shoulder site in the deafferented FBS, we examined the thalamocortical pathway in 2 forelimb-amputated rats. Stimulation of a new shoulder site in deafferented FBS antidromically-activated a cell in the former forepaw territory in VPL; however, similar stimulation from a site in the original shoulder representation, outside the deafferented region, in SI did not activate cells in the former forepaw VPL. These results suggest that the new shoulder input in deafferented FBS is relayed from cells in the former forepaw region in VPL. In the last step, we used anatomical tracing and stimulation and recording techniques in forelimb intact rats (n=9) to examine the cuneothalamic pathway from shoulder and forepaw receptive field zones in CN to determine whether projections from the shoulder zone might provide a possible source of shoulder input to forepaw VPL. Injection of biotinylated dextran amine (BDA) into physiologically identified shoulder responsive sites in CN densely labeled axon terminals in the shoulder representation in VPL, but also gave off small collateral branches into forepaw VPL. In addition, microstimulation delivered to forepaw VPL antidromically-activated cells in shoulder receptive field sites in CN. These results suggest that forepaw VPL also receives input from shoulder receptive sites in CN that are latent or subthreshold in forelimb intact rats. However, we speculate that following amputation these latent shoulder inputs become expressed, possibly as a down-regulation of GABA inhibition from the reticular nucleus (RTN). These results, taken together, suggest that VPL provides a substrate for large-scale cortical reorganization that follows forelimb amputation.

A pilot study of focused ultrasound thalamotomy for essential tremor

BACKGROUND

Recent advances have enabled delivery of high-intensity focused ultrasound through the intact human cranium with magnetic resonance imaging (MRI) guidance. This preliminary study investigates the use of transcranial MRI-guided focused ultrasound thalamotomy for the treatment of essential tremor.

METHODS

From February 2011 through December 2011, in an open-label, uncontrolled study, we used transcranial MRI-guided focused ultrasound to target the unilateral ventral intermediate nucleus of the thalamus in 15 patients with severe, medication-refractory essential tremor. We recorded all safety data and measured the effectiveness of tremor suppression using the Clinical Rating Scale for Tremor to calculate the total score (ranging from 0 to 160), hand subscore (primary outcome, ranging from 0 to 32), and disability subscore (ranging from 0 to 32), with higher scores indicating worse tremor. We assessed the patients' perceptions of treatment efficacy with the Quality of Life in Essential Tremor Questionnaire (ranging from 0 to 100%, with higher scores indicating greater perceived disability).

RESULTS

Thermal ablation of the thalamic target occurred in all patients. Adverse effects of the procedure included transient sensory, cerebellar, motor, and speech abnormalities, with persistent paresthesias in four patients. Scores for hand tremor improved from 20.4 at baseline to 5.2 at 12 months (P=0.001). Total tremor scores improved from 54.9 to 24.3 (P=0.001). Disability scores improved from 18.2 to 2.8 (P=0.001). Quality-of-life scores improved from 37% to 11% (P=0.001).

CONCLUSIONS

In this pilot study, essential tremor improved in 15 patients treated with MRI-guided focused ultrasound thalamotomy. Large, randomized, controlled trials will be required to assess the procedure's efficacy and safety. (Funded by the Focused Ultrasound Surgery Foundation; ClinicalTrials.gov number, NCT01304758.).

Use of laser microdissection in the investigation of facial motoneuron and neuropil molecular phenotypes after peripheral axotomy

The mechanism underlying axotomy-induced motoneuron loss is not fully understood, but appears to involve molecular changes within the injured motoneuron and the surrounding local microenvironment (neuropil). The mouse facial nucleus consists of six subnuclei which respond differentially to facial nerve transection at the stylomastoid foramen. The ventromedial (VM) subnucleus maintains virtually full facial motoneuron (FMN) survival following axotomy, whereas the ventrolateral (VL) subnucleus results in significant FMN loss with the same nerve injury. We hypothesized that distinct molecular phenotypes of FMN existed within the two subregions, one responsible for maintaining cell survival and the other promoting cell death. In this study, we used laser microdissection to isolate VM and VL facial subnuclear regions for molecular characterization. We discovered that, regardless of neuronal fate after injury, FMN in either subnuclear region respond vigorously to injury with a characteristic "regenerative" profile and additionally, the surviving VL FMN appear to compensate for the significant FMN loss. In contrast, significant differences in the expression of pro-inflammatory cytokine mRNA in the surrounding neuropil response were found between the two subnuclear regions of the facial nucleus that support a causative role for glial and/or immune-derived molecules in directing the contrasting responses of the FMN to axonal transection.

[Cerebral palsy]

Great advances have been made in the causes, lesions and symptoms of cerebral palsy over the years. Children with athetosis have lesions of the ventral lateral nuclei of the thalamus and putamen. Cocontraction and overflow are considered essential problems in athetosis. Some patients with a lesion of the ventral lateral nucleus of the thalamus do not show any involuntary movements. Children with periventricular leukomalacia demonstrate various patterns of the hip, knee and ankle in response to bearing body weight. Some of these patients exhibit ataxia, tremor and mouth opening triggered by voluntary movements. They have various central visual disorders or visual cognitive disorders. They also exhibit paroxysmal ocular downward deviation. In early infancy with spastic diplegia, there is no isolated extension of the knee or leg elevation. Hemiplegia results from stroke of the middle cerebral artery or venous infarction during the fetal or neonatal period. Border-zone infarction results from partial asphyxia.

Prognostic value of posteromedial cortex deactivation in mild cognitive impairment

BACKGROUND

Normal subjects deactivate specific brain regions, notably the posteromedial cortex (PMC), during many tasks. Recent cross-sectional functional magnetic resonance imaging (fMRI) data suggests that deactivation during memory tasks is impaired in Alzheimer's disease (AD). The goal of this study was to prospectively determine the prognostic significance of PMC deactivation in mild cognitive impairment (MCI).

METHODOLOGY/PRINCIPAL FINDINGS

75 subjects (34 MCI, 13 AD subjects and 28 controls) underwent baseline fMRI scanning during encoding of novel and familiar face-name pairs. MCI subjects were followed longitudinally to determine conversion to AD. Regression and analysis of covariance models were used to assess the effect of PMC activation/deactivation on conversion to dementia as well as in the longitudinal change in dementia measures. At longitudinal follow up of up to 3.5 years (mean 2.5+/-0.79 years), 11 MCI subjects converted to AD. The proportion of deactivators was significantly different across all groups: controls (79%), MCI-Nonconverters (73%), MCI-converters (45%), and AD (23%) (p<0.05). Mean PMC activation magnitude parameter estimates, at baseline, were negative in the control (-0.57+/-0.12) and MCI-Nonconverter (-0.33+/-0.14) groups, and positive in the MCI-Converter (0.37+/-0.40) and AD (0.92+/-0.30) groups. The effect of diagnosis on PMC deactivation remained significant after adjusting for age, education and baseline Mini-Mental State Exam (p<0.05). Baseline PMC activation magnitude was correlated with change in dementia ratings from baseline.

CONCLUSION

Loss of physiological functional deactivation in the PMC may have prognostic value in preclinical AD, and could aid in profiling subgroups of MCI subjects at greatest risk for progressive cognitive decline.

Modulation of thalamic nociceptive processing after spinal cord injury through remote activation of thalamic microglia by cysteine cysteine chemokine ligand 21

Spinal cord injury (SCI) results in the generation and amplification of pain caused in part by injury-induced changes in neuronal excitability at multiple levels along the sensory neuraxis. We have previously shown that activated microglia, through an ERK (extracellular signal-regulated kinase)-regulated PGE(2) (prostaglandin E(2)) signaling mechanism, maintain neuronal hyperexcitability in the lumbar dorsal horn. Here, we examined whether microglial cells in the thalamus contribute to the modulation of chronic pain after SCI, and whether microglial activation is governed by spinally mediated increases in the microglial activator cysteine-cysteine chemokine ligand 21 (CCL21). We report that CCL21 is upregulated in dorsal horn neurons, that tissue levels are increased in the dorsal horn and ventral posterolateral (VPL) nucleus of the thalamus 4 weeks after SCI, and that the increase can be differentially reduced by spinal blockade at T1 or L1. In intact animals, electrical stimulation of the spinothalamic tract induces increases in thalamic CCL21 levels. Recombinant CCL21 injected into the VPL of intact animals transiently activates microglia and induces pain-related behaviors, effects that could be blocked with minocycline. After SCI, intra-VPL antibody-mediated neutralization of CCL21 decreases microglial activation and evoked hyperexcitability of VPL neurons, and restores nociceptive thresholds to near-normal levels. These data identify a novel pathway by which SCI triggers upregulation of the neuroimmune modulator CCL21 in the thalamus, which induces microglial activation in association with pain phenomena.

Evaluating posterolateral linearization of the putaminal margin with magnetic resonance imaging to diagnose the Parkinson variant of multiple system atrophy

The objective was to develop a simple method for evaluating putaminal atrophy in patients with the Parkinson variant of multiple system atrophy (MSA-P). We used magnetic resonance imaging to study 9 patients with MSA-P, 24 patients with cerebellar variants of multiple system atrophy (MSA-C), 38 patients with Parkinson's disease (PD), and 27 healthy control subjects. Posterolateral linearization of the putaminal margin was semiquantitatively scored and the putaminal area per intracranial area was calculated as the adjusted putaminal area. There was a negative correlation between the linearization scores and adjusted putaminal areas (r = -0.43, P < 0.001), such that the mean adjusted putaminal area in the group without putaminal linearization (0.0148 +/- 0.0022) was greater than that of the group with linearization (0.0124 +/- 0.0029, P < 0.005). Moreover, the occurrence of putaminal linearization was significantly higher in MSA-P patients (88.8%) than in MSA-C (8.3%), PD (7.9%) and healthy subjects (7.4%; P < 0.005). Putaminal linearization was a highly sensitive (0.89) and specific (0.91) measure for differentiating MSA-P. Our results suggest that evaluating posterolateral putaminal linearization is useful for assessing putaminal atrophy and for differentiating MSA-P from MSA-C, PD, and healthy subjects.

Lesions limited to the human thalamic principal somatosensory nucleus (ventral caudal) are associated with loss of cold sensations and central pain

Central pain is neuropathic pain resulting from a lesion of the CNS, such as a stroke [poststroke central pain (CPSP)]. Lesions involving the posterior thalamus lead to reduction or loss of sensation and to CPSP, although the responsible nuclei have not been identified. We now examine the hypotheses that thalamic lesions must extend posterior to the ventral caudal nucleus (Vc) and include ventral medial posterior nucleus (VMpo), to result in loss of cold sensibility and CPSP. Patients with small thalamic strokes associated with CPSP were evaluated by atlas-based mapping of magnetic resonance imaging scans, and by somatosensory testing. All lesions involved posterior Vc; two lesions also involved nuclei posterior to Vc, but not VMpo. All patients tested had alterations of cold pain sensation and tactile sensation, as measured by von Frey hairs. Three patients had altered cool sensation, and the patient with the least involvement of Vc had normal cool thresholds, suggesting that a critical volume of Vc must be involved before cool sensation is impaired. Perception of warm was impaired only in lesions involving nuclei posterior to Vc. Heat pain perception was never affected. In a subject with cold allodynia, a single-subject protocol PET study measured the responses to immersion of either hand in a 20 degrees C waterbath. The scan during stimulation of the affected hand was characterized by intense activation of contralateral sensorimotor cortex. Therefore, there are modality-specific subnuclear structures in the posterior thalamus, but lesions of Vc not involving VMpo are sufficient to impair cold sensibility and to produce CPSP.

[Correction of changes induced by toluene in the cortical and subcortical structures of albino rat brain]

The number and weight of cells in the cortical and subcortical structures of the cerebral and cerebellar motor system in albino rats after a long-term exposure to toluene. Toluene intoxication proved to kill projection neurons and interneurons in the sensorimotor cortex, ventrolateral thalamic nucleus, caudate nucleus, pallidum, red nucleus, and inferior olivary complex. The decreased number of cerebellar cells was mediated by atrophic changes as indicated by the decrease in the area and dry weight of Purkinje cells. The addition of plaferon LB to the diet attenuated the cytotoxic effect of toluene.

Nogo-A is involved in secondary axonal degeneration of thalamus in hypertensive rats with focal cortical infarction

We investigate whether Nogo-A is involved in the secondary axonal degeneration in the thalamus after distal middle cerebral artery occlusion (MCAO) in stroke-prone renovascular hypertensive rats (RHRSP). The expression of Nogo-A in ipsilateral ventroposterior nucleus (VPN) of the thalamus in RHRSP was observed at 1, 2 and 4 weeks after distal MCAO. In addition, intracerebroventricular infusion of NEP1-40, a Nogo-66 receptor (NgR) antagonist peptide, was administered starting 24 h after MCAO and continued for 1, 2 and 4 weeks, respectively. Axonal damage and regeneration were evaluated by analysis of the immunoreactivity (IR) of amyloid betaA4 precursor protein (APP), growth associated protein 43 (GAP-43) and microtubule associated protein 2 (MAP-2) in ipsilateral VPN of the thalamus at 1, 2 and 4 weeks after distal MCAO. Following ischemia, the expression of Nogo-A in oligodendrocytes increased persistently and its localization became redistributed around damaged axons and dendrites. Administration of NEP1-40 downregulated the expression of Nogo-A, reduced axonal injury and enhanced axonal regeneration. Our data suggest that Nogo-A is involved in secondary axonal degeneration and that inhibition of Nogo-A can reduce neuronal damage in the thalamus after distal MCAO.

Involvement of the anterior lobe of the cerebellar vermis in perinatal profound hypoxia

BACKGROUND AND PURPOSE

We report abnormal high T2 signal intensity in the anterior lobe of the cerebellar vermis that we believe was the result of profound hypoxic ischemic encephalopathy in the perinatal period in term infants. We tested the hypothesis that this sign was associated with other signs of significant perinatal hypoxic damage.

METHODS

Thirty patients with clinically and radiologically confirmed perinatal profound hypoxia close to term were included in the study. The cranial MR images were reviewed by 2 pediatric neuroradiologists and were scored for the presence and severity of hypoxia/ischemia in the regions typically affected by profound hypoxia. The presence or absence of high T2 signal intensity in the vermis and other sites was correlated with the extent of damage in typically affected regions.

RESULTS

Eighteen of 30 patients had high T2 signal intensity in the vermis. The presence of vermian damage correlated positively with radiologic evidence of severe hypoxic damage and extremely poor (0 or 1) 1-minute Apgar scores.

CONCLUSIONS

High T2 signal intensity in the anterior lobe of the vermis probably represents gliosis secondary to hypoxia/ischemia and is related to the severity of damage in the term infant.

Three-tesla magnetic resonance imaging of the ventrolateral thalamus: a correlative anatomical description

Object

Surgery for tremor targets the ventrolateral nuclei of the thalamus. An initial radiological estimation of this target can be further refined through intraoperative physiological confirmation. Direct visualization of these nuclei has not yet been described. The improved signal-to-noise ratio associated with 3-tesla (3T) magnetic resonance (MR) imaging makes increased spatial resolution possible, which may aid in the identification of subtle morphological features. This study was conducted to describe the anatomy of the nuclei and fiber projections within the ventral thalamus by using 3T MR imaging.

Methods

Using a commercially available 3T MR unit, the authors obtained images of a formalin-fixed, paraffin-embedded brain. Slices with a 2-mm thickness and 0.2-mm gap were obtained parallel to the anterior commissure–posterior commissure (AC–PC) line. The brain was then sectioned through the cerebral hemispheres to obtain tissue slices encompassing the same levels. Adjacent 10-μm paraffin sections from the middle of each level were stained with Luxol fast blue and cresyl violet. The MR image and histological sections at the level of the AC–PC line were then compared in detail. In a separate study, the human thalamus was scanned in vivo using 3T and 1.5T MR imaging for anatomical comparison.

Conclusions

The anatomy of the nuclei and fiber projections within the ventrolateral thalamus in humans can be described using 3T MR imaging. The findings were reproducible in vivo with 3T but not 1.5T MR imaging. Additional studies are needed to confirm the accuracy of this observation for clinical purposes.

[Neuronal activities in the ventrolateral thalamus and basal ganglia in relation to Parkinson's disease]

OBJECTIVE

To investigate the neuronal activities in the ventrolateral thalamus (VL), internal globus pallidus (GPi), and subthalamic nucleus (STN) in relation to parkinsonian symptoms.

METHODS

Twenty-seven patients with Parkinson's disease, 17 males and 10 females, aged 59 +/- 8, received stereotactic surgical treatment on the VL (n = 10), GPi (n = 10), or STN (n = 7) respectively. Microelectrode recording in the three nuclei and electromyography (EMG) on the limbs contralateral to the surgical side were performed intraoperatively. All patients were evaluated with the unified Parkinson's disease rating scale (UPDRS) in "off" medication state pre-and post-operatively. Single unit analysis and cross-correlation analysis were carried out to explore the relationship among the neuronal activities and limb EMG. One-way ANOVA was performed to study the numbers of neuron in these 3 nuclei in different discharge patterns and the improvement of the 3 main symptoms of Parkinson's disease.

RESULTS

Three hundred and sixty-one neurons were obtained from 27 microrecording trajectories (146 for VL, 139 for GPi, and 76 for STN). Three patterns of neuronal activities were identified: tremor-related activities ("tremor cells", n = 159); tonic neuronal activities (n = 134), and irregular neuronal activities (n = 68). The rhythm of the tremor-related activities was correlated with the frequency of limb tremor in VL (r(2) = 0.8, P < 0.01), GPi (r(2) = 0.7, P < 0.01), and STN (r(2) = 0.5, P < 0.01). The average number of cells in each tract of VL, GPi, and STN were 9.0, 4.9, and 3.0 for tremor-related activities (ANOVA, P < 0.05); 4.2, 6.2 and 4.3 for tonic neuronal activities (ANOVA, P > 0.05) and 1.4, 2.8 and 3.7 for irregular neuronal activities (ANOVA, P < 0.05). The UPDRS revealed that VL had the highest effect on tremor improvement (91.7%) as compared to GPi (84.8%) and STN (62.7%), whereas STN and GPi had significant effects on bradykinesia improvement (70.8% and 62.3% respectively) as compared to VL (36.9%). However there was no significant difference in the improvement of rigidity among VL, GPi, and STN (56.2%, 71.3%, and 68.8% respectively, all P > 0.05).

CONCLUSION

Different patterns of neuronal activities in VL, GPi and STN are likely to associate with parkinsonian symptoms. The results are important not only for the target selection, but also for understanding of neurophysiological basis underlying Parkinson's disease.

Degeneration of cholecystokinin-immunoreactive afferents to the VPL thalamus in a mouse model of Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a progressive neurological disorder of lipid metabolism. The Balb/C npc1 mutant strain is a genetically authentic murine model of NPC, which reproduce the clinical and histologic features of human NP-C. In the present study, we show that cholecystokinin (CCK)-immunoreactive fibers in the thalamic VPL nuclei, which are densely distributed in controls, degenerate in NPC mice. This degeneration is associated with the appearance of CCK-immunoreactive axonal spheroids containing characteristic intracellular inclusions of NP-C. These observations provide supportive evidence of the occurrence of dying-back axonopathy of neurons in the dorsal column nuclei in this mouse model.

Allodynia in the flank after thalamic stroke

Lesions responsible for thalamic pain are often thought to involve the ventral posteromedial nucleus and ventral posterolateral nucleus of the thalamus. We describe two patients with allodynia and hyperpathia in the contralateral flank caused by a small lesion in the posteroventral part of the thalamus. When considered with the literature, involvement of the ventral posteroinferior nucleus may be responsible for this unique post-stroke pain syndrome.

Staged bilateral stereotactic pallidothalamotomy for life-threatening dystonia in a child with Hallervorden-Spatz disease

Hallervorden-Spatz disease (HSD) is a rare disorder characterized by progressive motor dysfunction and dementia. Dystonia is the most prominent and disabling symptom, responding only to a modest extent to pharmacological therapy. At the moment, only a few cases have been reported to improve dystonia and even fewer to resolve status dystonicus for a longer period in children. The authors present the case of a 10-year-old boy who had progressive generalized dystonia, resulting in spontaneous femur fracture and life-threatening swallowing and respiratory disability. As a rescue solution, staged bilateral pallidothalamotomy was performed. Postoperatively, Burke-Fahn-Marsden Dystonia Rating Scale and Dystonia Disability Rating Scale improved (from 116 and 30 points to 41 and 18 points, respectively) and painful dystonia was resolved, which was still continuous 4 years later (47 and 20 points). Stereotactic staged bilateral pallidothalamotomy should be considered as a potential treatment in the management of life-threatening generalized dystonia related to HSD.

A comparison of degeneration in motor thalamus and cortex between progressive supranuclear palsy and Parkinson's disease

Changes in motor cortical activation are associated with the major symptoms observed in both Parkinson's disease and progressive supranuclear palsy (PSP). While research has concentrated on basal ganglia abnormalities as central to these cortical changes, several studies in both disorders have shown pathology in the thalamus and motor cortices. In particular, we recently reported an 88% loss of corticocortical projection neurones in the pre-supplementary motor (pre-SMA) cortex in Parkinson's disease. Further analysis of the degree of neuronal loss and pathology in motor cortices and their thalamocortical relays in Parkinson's disease and PSP is warranted. Six cases with PSP, nine cases with Parkinson's disease and nine controls were selected from a prospectively studied brain donor cohort. alpha-Synuclein, ubiquitin and tau immunohistochemistry were used to identify pathological lesions. Unbiased stereological methods were used to analyse atrophy and neuronal loss in the motor thalamus [ventral anterior, ventrolateral anterior and ventrolateral posterior (VLp) nuclei] and motor cortices (primary motor, dorsolateral premotor and pre-SMA cortices). Analysis of variance and post hoc testing was used to determine differences between groups. In Parkinson's disease, the motor thalamus and motor cortices (apart from the pre-SMA) were preserved containing only rare alpha-synuclein-positive and ubiquitin-positive Lewy bodies. In contrast, patients with PSP had significant atrophy and neuronal loss in VLp (22 and 30%, respectively), pre-SMA (21 and 51%, respectively) and primary motor cortices (33 and 54%, respectively). In the primary motor cortex of PSP cases, neuronal loss was confined to inhibitory interneurones, whereas in the pre-SMA both interneurones (reduced by 26%) and corticocortical projection neurones (reduced by 82%) were affected. Tau-positive neurofibrillary and glial tangles were observed throughout the motor thalamus and motor cortices in PSP. These non-dopaminergic lesions in motor circuits are likely to contribute to the pathogenesis of both PSP and Parkinson's disease. The selective involvement of the VLp and primary motor cortex in PSP implicates these cerebellothalamocortical pathways as differentiating this disease, possibly contributing to the early falls.

Motor cortex excitability after thalamic infarction

OBJECTIVE

We examined 8 patients with hemihypesthesia due to an ischemic thalamic lesion to explore the effects of a central sensory dysfunction on motor cortex excitability.

METHODS

Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Motor function was evaluated by the Nine-Hole-Peg Test and measurement of hand grip strength. The affected side was compared with the non-lesioned side and with an age-matched control group.

RESULTS

Patients had a loss of inhibition and an increase of facilitation in the motor cortex of the affected side. The silent period was prolonged and motor function was impaired on the affected side.

CONCLUSIONS

A thalamic lesion can modulate motor cortical excitability.

SIGNIFICANCE

This study suggests that, under normal conditions, somatosensory afferents influence inhibitory and excitatory properties in the motor cortex.

Pronounced cell death in the absence of NMDA receptors in the developing somatosensory thalamus

Genetic deletion of NMDA glutamate receptors disrupts development of whisker-related neuronal patterns in the somatosensory system. Independent studies have shown that NMDA receptor antagonists increase cell death among developing neurons. Here, we report that a dramatic feature of the developing somatosensory system in newborn NMDA receptor 1 (NMDAR1) knock-out mice is increased cell death in the ventrobasal nucleus (VB) of the thalamus. Sections were subject to terminal deoxynucleotidyl transferase dUTP nick end labeling staining for apoptotic DNA fragmentation, thionine staining for pyknotic nuclei, silver staining for degenerating cells, and immunostaining for caspase-3. All four methods demonstrated that deletion of NMDAR1 causes a large (on the order of threefold to fivefold) increase in cell death in the VB. The NMDA receptor antagonists dizocilpine maleate (MK-801) and phencyclidine also increase cell death in this structure. The onset of increased cell death in the VB in the absence of NMDA receptor function is approximately the time of birth, overlaps with naturally occurring cell death and synaptogenesis, and displays some anatomical specificity. For example, there was no increase in cell death in the hippocampus or neocortex of NMDAR1 knock-out mice at any of the time points examined: embryonic day 15.5 (E15.5), E17.5, and postnatal day 0. We also report a significant reduction in the size of the VB that is evident starting at E17.5. The results indicate that NMDA receptors play a major role in cell survival during naturally occurring cell death in the VB and demonstrate that cell death is a consideration in NMDA receptor knock-out studies.

The role of the human thalamus in processing corollary discharge

Corollary discharge signals play an important role in monitoring self-generated movements to guarantee spatial constancy. Recent work in macaques suggests that the thalamus conveys corollary discharge information of upcoming saccades passing from the superior colliculus to the frontal eye field. The present study aimed to investigate the involvement of the thalamus in humans by assessing the effect of thalamic lesions on the processing of corollary discharge information. Thirteen patients with selective thalamic lesions and 13 healthy age-matched control subjects performed a saccadic double-step task in which retino-spatial dissonance was induced, i.e. the retinal vector of the second target and the movement vector of the second saccade were different. Thus, the subjects could not rely on retinal information alone, but had to use corollary discharge information to correctly perform the second saccade. The amplitudes of first and second saccades were significantly smaller in patients than in controls. Five thalamic lesion patients showed unilateral deficits in using corollary discharge information, as revealed by asymmetries compared with the other patients and controls. Three patients with lateral thalamic lesions including the ventrolateral nucleus (VL) were impaired contralaterally to the side of damage and one patient with a lesion in the mediodorsal thalamus (MD) was impaired ipsilaterally to the lesion. The largest asymmetry was found in a patient with a bilateral thalamic lesion. The results provide evidence for a thalamic involvement in the processing of corollary discharge information in humans, with a potential role of both the VL and MD nuclei.

Gamma knife thalamotomy for movement disorders: evaluation of the thalamic lesion and clinical results

Object.The authors studied the effects of gamma knife thalamotomy (GKT) on Parkinson disease-related tremor and essential tremor before and after reloading of radioactive cobalt.

Methods.Based on experience in stereotactic thalamotomy aided by depth microrecording, the target was located at the lateral border of the thalamic ventralis intermedius nucleus (VIM). For more precise targeting, the percentage representation of the thalamic VIM in relation to the entire thalamic length is useful. The location of the target was determined on magnetic resonance (MR) imaging and computerized tomography scanning. A maximum dose of 130 Gy was delivered to the target by using a single isocenter with the 4-mm collimator. In more recent cases, a systematic follow-up examination was performed at 3, 6, 12, 18, and 24 months after GKT.

Since 1993, the authors have treated 70 patients with PD. Throughout the series the same dosimetric technique has been used. The course after GKT was compared between the 25 cases with PD treated before reloading and the 35 cases treated after reloading. In the majority (80–85%) treated after reloading, tremor and rigidity were reduced around 6 months after GKT. In the cases treated before reloading this effect took approximately 1 year. The thalamic reaction on MR imaging showed the same two lesion types in both series: a restricted and a diffuse. After reloading the restricted lesion was more frequent and the lesion volume was smaller.

Conclusions.The shorter delay in clinical improvement and smaller lesion size may be related to an increased radiation dose.

Functional Neurosurgery in the MRI Environment

OBJECTIVE

The purpose of this study was to evaluate the feasibility of microelectrode recording, electrical stimulation, and electrode position checking during functional neurosurgical procedures (DBS, lesion) in the interventional magnetic resonance imaging (iMRI) environment.

METHODS

Seventy-six surgical procedures for DBS implant or radiofrequency lesion were performed in an open 0.2 T MRI operating room. DBS implants were performed in 54 patients (72 surgical procedures) and unilateral radiofrequency lesions in three for a total of 76 surgeries in 57 patients. Electrophysiological studies including macrostimulation and microelectrode recordings for localization were obtained in the 0.5 to 10 mT fringes of the magnetic field in 51 surgeries. MRI confirmation of the electrode position during the procedure was performed after electrophysiological localization.

RESULTS

The magnetic field associated with the MRI scanner did not contribute significant noise to microelectrode recordings. Anatomical confirmation of electrode position was possible within the MRI artifact from the DBS hardware. Symptomatic hemorrhage was detected in two (2.6 %) patients during the operation. Image quality of the 0.2 T MRI scan was sub-optimal for anatomical localization. However, image fusion with pre-operative scans permitted excellent visualization of the DBS electrode tip in relation to the higher quality 1.5 T MRI anatomical scans.

CONCLUSION

This study shows that conventional stereotactic localization, microelectrode recordings, electrical stimulation, implant of DBS hardware, and radiofrequency lesion placement are possible in the open 0.2 T iMRI environment. The convenience of having an imaging modality that can visualize the brain during the operation is ideal for stereotactic procedures.

Allodynia in patients with post-stroke central pain (CPSP) studied by statistical quantitative sensory testing within individuals

The disinhibition hypothesis of post-stroke central pain (CPSP) suggests that 'the excessive response (dysesthesia/hyperalgesia/allodynia) is accompanied by a em leader loss of sensation' resulting from a lesion of a 'lateral nucleus' of thalamus or of 'cortico-thalamic paths' [Brain 34 (1911) 102]. One recent elaboration of this hypothesis proposes a submodality specific relationship, such that injury to a cool-signaling lateral thalamic pathway disinhibits a nociceptive medial thalamic pathway, thereby producing both burning, cold, ongoing pain and cold allodynia. The current study quantitatively evaluated the sensory loss and sensory abnormalities to discern submodality relationships between these sensory features of CPSP. The present results were statistically tested within individuals so that sensory loss and sensory abnormality are directly related by occurrence in the same individual. The results demonstrate that individuals with CPSP and normal tactile detection thresholds experience tactile allodynia significantly more often than those with tactile hypoesthesia. Most patients (11/13) exhibited hypoesthesia for the perception of cool stimuli, but few of these (2/11) showed cold allodynia. The most dramatic case of cold allodynia occurred in a patient who had a normal detection threshold for cold. Individuals with cold hypoesthesia, strictly contralateral to the cerebro-vascular accident (CVA or stroke), were often characterized by the presence of burning, cold, ongoing pain, and by the absence, not the presence, of cold allodynia. Overall, these results in CPSP suggest that tactile allodynia occurs in disturbances of thermal/pain pathways that spare the tactile-signaling pathways, and that cold hypoesthesia is neither necessary nor sufficient for cold allodynia.

Differential responses in three thalamic nuclei in moderately disabled, severely disabled and vegetative patients after blunt head injury

In vivo imaging techniques have indicated for many years that there is loss of white matter after human traumatic brain injury (TBI) and that the loss is inversely related to cognitive outcome. However, correlated, quantitative evidence for loss of neurons from either the cerebral cortex or the diencephalon is largely lacking. There is some evidence in models of TBI that neuronal loss occurs within the thalamus, but no systematic studies of such loss have been undertaken in the thalamus of humans after blunt head injury. We have undertaken a stereological analysis of changes in numbers of neurons within the dorsomedial, ventral posterior and lateral posterior thalamic nuclei in patients assessed by the Glasgow Outcome Scale as moderately disabled (n = 9), severely disabled (n = 12) and vegetative (n = 10) head-injured patients who survived between 6 h and 3 years, and controls (n = 9). In histological sections at the level of the lateral geniculate body, the cross-sectional area of each nucleus and the number and the mean size of neurons within each nucleus was quantified. A statistically significant loss of cross-sectional area and number of neurons occurred in the dorsomedial nucleus in moderately disabled, and both the dorsomedial and ventral posterior thalamic nuclei in severely disabled and vegetative head-injured patients. However, there was no change in neuronal cell size. In the lateral posterior nucleus, despite a reduction in mean cell size, there was not a significant change in either nuclear area or number of neurons in cases of moderately disabled, severely disabled or vegetative patients. We posit, although detailed neuropsychological outcome for the patients included within this study was not available, that neuronal loss in the dorsomedial thalamus in moderately and severely disabled and vegetative patients may be the structural basis for the clinical assessment in the Glasgow Outcome Scale. In severely disabled and vegetative patients, loss of neurons from the ventral posterior thalamic nucleus may also reflect loss of response to afferent stimuli.

Deep brain stimulation for dystonia confirming a somatotopic organization in the globus pallidus internus

Object. In patients with dystonia, symptoms vary greatly in their extent and severity. The efficacy of pallidal stimulation is now established, but an interindividual variability in the responses to this treatment exists. A retrospective analysis of postoperative magnetic resonance (MR) images demonstrated millimetric variations in the positions of electrode contacts inside the posterolateroventral portion of the globus pallidus internus (GPi). It therefore seemed very likely that there is a somatotopic organization within the GPi. The goal of this study was to examine the positions of specific electrode contacts according to patients' clinical evolution, so that a somatotopic organization within the GPi could be defined.

Methods. This study included 19 patients (17 of whom were right handed) with generalized dystonia who were treated by bilateral stimulation of the GPi. Patients were examined pre- and postoperatively by using the Burke-Fahn-Marsden Dystonia Rating Scale. Dividing the patient's body into three parts—cervicoaxial area, superior limb, and inferior limb—we determined the following: 1) where the dystonic symptoms started; 2) where symptoms predominated at the time of surgery; and 3) where the highest postoperative improvement was observed.

Variations in clinical response were correlated to the positions of the electrode contacts. All activated electrode contacts were in the posterolateroventral portion of the GPi (Laitinen target). A correlation between the contact location measured longitudinally and the part of the body in which the highest improvement was observed (three different areas; p = 0.004) showed that a location more anterior for the inferior limb and one more posterior for the superior limb were delineated for the right side, but not for the left side.

Conclusions. Inside the posterolateroventral subvolume of the GPi on the right side, three statistically different locations of electrode contacts were determined to be primary deep brain stimulation treatment sites for particular body parts in cases of dystonia.

Partial lesion of thalamic ventral intermediate nucleus after chronic high-frequency stimulation

A 73-year-old man with Parkinson's disease underwent thalamic stimulation for disabling tremor with excellent results only when stimulation on. Post-mortem neuropathology (7 years postoperatively) revealed 60% cell loss within 0.5 mm of the electrode tip. Tremor improvement was attributable to chronic stimulation, not microthalamotomy.

[Neurophysiologic and neuropathological analysis of Parkinson's disease and its treatment with stereotaxic method]

Complete stopping of tremor or its essential reduction have been achieved in 55 of 66 patients with Parkinson's disease. In 3 cases, there was a fatal outcome. The microstructural changes of nigrostriatal, thalamus and neocortex neurons are presented, and biopotentials led from these structures, along with clinical and neurophysiological effects of electrostimulation of thalamic and subthalamic regions, are evaluated. The results obtained in the study are used for explanation of tremor mechanism.

[HIV related Foix-Chavany-Marie syndrome]

Automatic-voluntary motor dissociation of the face and lower cranial nerves of brainstem is the hallmark of Foix-Chavany-Marie syndrome (biopercular syndrome). It is commonly caused by ischemic strokes. We present a biopercular syndrome associated with HIV. A 41 year old female who presents a progressive automatic- voluntary motor dissociation of face and lower cranial nerves with later involvement of limbs. She was immunodepressed as a result of HIV. MRI showed bilateral lesions in opercular areas and ventrolateral thalamic nucleus, likely as a result of retrograde neuronal degeneration. Automatic-voluntary dissociation occur after biopercular lesions with sparing of motor pathway proceeding from the cingulate cortex.

Chronic cognitive impairment following laterothalamic infarcts: a study of 9 cases

BACKGROUND

The occlusion of the lateral thalamic arteries leads to infarcts of ventrolateral thalamic nuclei, the ventroposterior nucleus, and the rostrolateral part of pulvinar, and produces hemisensory loss with or without hemiataxia. Cognitive impairment after such strokes has not been systematically studied.

OBJECTIVE

To determine the nature and the extent of long-lasting cognitive deficits following lateral thalamic strokes.

DESIGN

Case series.

SETTING

Neurology department, Lausanne University Hospital, Lausanne, Switzerland.

PATIENTS

Nine patients with hemisensory loss due to an isolated laterothalamic infarct.

MAIN OUTCOME MEASURES

Three to 6 months after stroke onset, standard neuropsychologic evaluation, including testing of language, ideomotor and constructive praxis, visual gnosis, spatial attention, learning abilities, and executive functions.

RESULTS

Six of 9 patients showed some degree of cognitive impairment. Executive functions tasks, particularly verbal fluency, were impaired in 5 patients (4 with right and 1 with left lesion). Learning and delayed recall in visuospatial and verbal tasks, but not in recognition, were impaired in 3 patients (2 with right and 1 with left lesion). Difficulties in visual gnosia were observed in 1 patient with right lesion while word-finding difficulties were observed in 1 patient with left lesion.

CONCLUSIONS

Our observations show that while learning, naming, and gnosic difficulties fit with the classical verbal/nonverbal dichotomy (left and right hemisphere, respectively), executive dysfunctions, including verbal fluency tasks, were more dominant after right thalamic infarcts. Although the observed deficits appeared to be less severe than those generally found with dorsomedial and polar thalamic strokes, the dominance of executive dysfunction suggests that ventrolateral thalamic lesions may disrupt frontothalamic subcortical loops.

Ventralis intermedius thalamotomy can succeed when ventralis intermedius thalamic stimulation fails: report of 2 cases for tremor

In 2 patients with essential tremor, thalamotomy in the ventralis intermedius (VIM) provided lasting tremor relief after thalamic stimulation of the VIM failed. These cases illustrate that the effects of deep brain stimulation might not be those of simple inhibition, and that thalamotomy should be considered when deep brain stimulation does not succeed.

Thalamic stuttering: a distinct clinical entity?

A 38-year-old right-handed male with no history of speech or language problems presented with neurogenic stuttering following an ischaemic lesion of the left thalamus. He stuttered severely in propositional speech (conversation, monologue, confrontation naming, and word retrieval) but only slightly in non-propositional speech (automatic speech, sound, word and sentence repetition, and reading aloud). It is suggested that thalamic stuttering may constitute a distinct clinical entity.

Vulnerability of the thalamic somatosensory pathway after prolonged global hypoxic-ischemic injury

The aim of this study was to test the hypothesis that under prolonged global ischemic injury, the somatosensory thalamus and the cortex would manifest differential susceptibility leading to varying degrees of thalamo-cortical dissociation. The thalamic electrical responses displayed increasing suppression with longer durations of ischemia leading to a significant thalamo-cortical electrical dissociation. The data also point to a selective vulnerability of the network oscillations involving the thalamic relay and reticular thalamic neurons. An adult rat model of asphyxial cardiac arrest involving three cohorts with 3 min (G1, n=5), 5 min (G2, n=5) and 7 min (G3, n=5) of asphyxia respectively was used. The cortical evoked response, as quantified by the peak amplitude at 20 ms in the cortical evoked potential, recovers to more than 60% of baseline in all the cases. The multi-unit responses to the somatosensory stimuli recorded from the thalamic ventral posterior lateral (VPL) nuclei consists typically of three components: (1). the ON response (<30 ms after stimulus), (2). the OFF response (period of inhibition, from 30 ms to 100 ms after stimulus) and (3). rhythmic spindles (beyond 100 ms after stimulus). Asphyxia has a significant effect on the VPL ON response at 30 min (P<0.025), 60 min (P<0.05) and 90 min (P<0.05) after asphyxia. Only animals in G3 show a significant suppression (P<0.05) of the VPL ON response when compared to the sham group at 30 min, 60 min and 90 min after asphyxia. There was no significant reduction in somatosensory cortical N20 (negative peak in the cortical response at 20 ms after stimulus) amplitude in any of the three groups with asphyxia indicating a thalamo-cortical dissociation in G3. Further, rhythmic spindle oscillations in the thalamic VPL nuclei that normally accompany the ON response recover either slowly after the recovery of ON response (in the case of G1 and G2) or do not recover at all (in the case of G3).We conclude that there is strong evidence for selective vulnerability of thalamic relay neurons and its network interactions with the inhibitory interneurons in the somatosensory pathway leading to a thalamo-cortical dissociation after prolonged durations of global ischemia.

Somatosensory input to the ventrolateral thalamic region in the macaque monkey: potential substrate for parkinsonian tremor

In the present study, we determined the anatomic relationships between somatosensory and motor pathways within ventrolateral (VL) thalamic nuclei of the motor thalamus of macaque monkeys. In labeling experiments, four macaque monkeys (Macaca mulatta) received injections of biotinylated dextran amine and wheat germ agglutinin conjugated to horseradish peroxidase into the cerebellar nuclei or internal segment of the globus pallidus and cervical segments of the spinal cord, respectively. Each tracer was visualized in brain sections by sequentially using a different chromogen. Labeled terminals were plotted and superimposed on adjacent brain sections processed for Nissl substance, acetylcholinesterase, and the antigens for calbindin and Cat-301 to reveal thalamic nuclei. The labeled cerebellar terminals were distributed throughout the posterior VL (VLp), whereas the labeled pallidothalamic terminals were concentrated in the anterior VL and the ventral anterior nucleus. The spinothalamic input was directed mostly to the ventral posterior complex and cells just caudal to it. In addition, the patches of spinothalamic terminations intermingled and partly overlapped with the cerebellothalamic, but not with the pallidothalamic terminations within VLp. The regions of overlap of somatosensory and cerebellar inputs within the VLp of the present study appear to correspond to the reported locations of the tremor-related cells in parkinsonian patients. Thus, the overlapping spinothalamic and cerebellar inputs may provide a substrate for the altered activity of motor thalamic neurons in such patients.

The window of opportunity for administration of magnesium therapy following focal brain injury is 24 h but is task dependent in the rat

The present study was conducted to establish the window of opportunity for the administration of a regimen of MgCl2 pharmacotherapy following focal injury to the brain. Rats were subjected to unilateral electrolytic lesions of the sensorimotor cortex (SMC) and administered a regimen of MgCl2 (1.0 mmol/kg) or 0.9% saline (1.0 ml/kg) beginning either 15 min, 8 h or 24 h after injury. Subsequent injections were administered 24 and 72 h after the initial treatment. Behavioral testing assessed recovery of function on several sensorimotor behaviors for 24 days following injury. The results of the present study suggest that treatment with a regimen of MgCl2 significantly facilitated recovery of function on the forelimb-->forelimb and vibrissae-->forelimb placing tests when administered 15 min, 8 h or 24 h after injury compared with saline-treated rats. Recovery of locomotor placing was significantly facilitated at 15 min and 8 h but not at 24 h compared with saline-treated rats. In addition, the ability of MgCl2 to limit neuronal loss in the ipsilateral ventral posterior lateral (VPL) nucleus of the thalamus was seen at only the 15-min treatment interval. These results suggest that the window of opportunity for MgCl2 pharmacotherapy is 24 h, task dependent and is much shorter for protecting neurons in the VPL.

Imaging of subthalamic nucleus and ventralis intermedius of the thalamus

The techniques of targeting the subthalamic nucleus (STN) and the ventralis intermedius nucleus (Vim) are similar, only the coordinates are different. Targeting ideally consists of gathering all data about a target and positioning the electrode correctly within that target. The electrode should be positioned within a statistical range of coordinates, where the neuronal firing fits a given pattern and responds to external stimuli, particularly to proprioceptive inputs, in a somatotopically organized manner. Moreover, final placement should provide the best clinical improvement of symptoms under the stimulation parameters expected to be used in the long term. This latter criterion is by far the most important, because intraoperative findings indicate the functional benefit for the patient, which is the ultimate purpose of this surgery. A variety of radiological modalities are available to provide data for electrode placement, but each type has its drawbacks. Ventriculography, although safe when performed accordingly to strict technical procedure, is the most precise method but provides more indirect targeting and is more invasive than magnetic resonance imaging (MRI). MRI is the best method for visualizing the STN and, to some extent, for discerning the Vim, but it is plagued with unpredictable and nonreproducible deformations that induce a systematic distortion. These shortcomings no doubt will be corrected in the near future, and the technologies will better assist us in the proper placement of electrodes, which will provide the patient with the highest possible benefit.

Neuronal activity in the monkey motor thalamus during bicuculline-induced dystonia

Recent data suggest that a decreased basal ganglia output may occur in dystonia, resulting in an increased thalamic drive to the mesial premotor cortex. In a previous work we found that injection of the GABAA antagonist bicuculline into the rostral motor thalamus induced contralateral dystonic postures, whereas myoclonic jerks were frequent after injection into the caudal motor thalamus. In the present study, we performed electrophysiological recordings in the rostral and caudal parts of the ventrolateral thalamus of two cynomolgus monkeys before and after bicuculline injections or saline injections. Discharge frequencies of thalamic neurons were increased after bicuculline injections vs. controls. Their discharge pattern was more bursty in the caudal part in which bursts of neuronal activity were correlated with myoclonic jerks. After bicuculline injection, neurons responded more frequently and less selectively to passive limb movements in both parts of the motor thalamus. Conversely, the response to microstimulation increased after bicuculline injection, particularly in the caudal part. Our data show that acute bicuculline-induced dystonia is associated with a reversible overactivity and disorganization of neuronal activity in the motor thalamus. Such a phenomenon might induce an overspreading of cortical activity leading to dystonia. We postulate that the distinct clinical syndromes observed after bicuculline injections into the rostral and caudal motor thalamus are due to differences both in the neuronal circuitry within each thalamic nucleus and in segregated cortical projections.

Normotopic and heterotopic cortical representations of mystacial vibrissae in rats with subcortical band heterotopia

The tish rat is a neurological mutant exhibiting bilateral cortical heterotopia similar to those found in certain epileptic patients. Previous work has shown that thalamocortical fibers originating in the ventroposteromedial nucleus, which in normal animals segregate as 'barrel' representations for individual whiskers, terminate in both normotopic and heterotopic areas of the tish cortex (Schottler et al., 1998). Thalamocortical innervation terminates as barrels in layer IV and diffusely in layer VI of the normotopic area. Discrete patches of terminals are also observed in the underlying heterotopic area suggesting that representations of individual vibrissa may be present in the heterotopic somatosensory areas. The present study examines this issue by investigating the organization of the vibrissal somatosensory system in the tish cortex. Staining for cytochrome oxidase or Nissl substance reveals a normal complement of vibrissal barrels in the normotopic area of the tish cortex. Dense patches of cytochrome oxidase staining are also found in the underlying lateral portions of the heterotopic area (i.e. the same area that is innervated by the ventroposteromedial nucleus). Injections of retrograde tracers into vibrissal areas of either the normotopic or heterotopic area produce topographically organized labeling of neurons restricted to one or a small number of barreloids within the ventroposteromedial nucleus of the thalamus. Physical stimulation of a single whisker (D3 or E3) elicits enhanced uptake of [(14)C]2-deoxyglucose in restricted zones of both the normotopic and heterotopic areas, demonstrating that single whisker stimulation can increase functional activity in both normotopic and heterotopic neurons. These findings indicate that the barrels are intact in the normotopic area and are most consistent with the hypothesis that at least some of the individual vibrissae are 'dually' represented in normotopic and heterotopic positions in the primary somatosensory areas of the tish cortex.

The ventral lateral posterior nucleus of the thalamus in schizophrenia: a post-mortem study

The ventral lateral posterior thalamic nucleus (VLp) is an integral part of both the cerebello-thalamocortical and the basal ganglia-thalamocortical circuit. Although both circuits are thought to be involved in the pathophysiology of schizophrenia, the VLp has not yet been examined in schizophrenia. Using stereological techniques in the brains of eight patients with schizophrenia and in eight age- and sex-matched controls, we measured the nuclear volume of the VLp and obtained estimates of the total number of neurons in this nucleus. Whole brain volume did not differ between the schizophrenia group and the control group and was not correlated to the volume of the right VLp or left VLp. The volume (minus sign25%) and the total neuron number (minus sign27%) of the left VLp were significantly reduced in the schizophrenia group. There were no significant differences in the nuclear volume, neuron density and total neuron number in the right VLp between the schizophrenia group and the control group. There were no significant correlations between length of illness and the nuclear volume, neuron density and total neuron number of the left and right VLp. The present results suggest that the total neuron number of the left VLp is reduced in the schizophrenia group, which may reflect disturbed cerebello-thalamocortical and basal ganglia-thalamocortical circuits in this disease.

Protracted expression of serotonin transporter and altered thalamocortical projections in the barrelfield of hypothyroid rats

In humans, thyroid hormone deficiency during development causes severe neurological diseases but the underlying mechanisms are unclear. We have examined the effects of thyroid hormones on the development of somatosensory thalamocortical projections, by inducing hypothyroidism in rats by methimazole treatment at embryonic day 13 and subsequent thyroidectomy at postnatal day 6 (P6). Initial development of the thalamocortical projections and their tangential and laminar patterning were similar in normal and hypothyroid rats from birth to P4. The tangential spread of the thalamocortical arbors is reduced in hypothyroid rats after P4, paralleling the overall cortical atrophy. Anterograde tracing and single axon reconstructions indicate that thalamic afferents reached layer IV but that they had fewer and shorter branches, with a 42% reduction in the number of boutons. The transient serotonin (5-HT) immunostaining and 5-HT transporter (5-HTT) expression were both prolonged by 5 days in hypothyroid rats. This does not reflect a delayed maturation of the thalamus because other transiently expressed genes such as the vesicular monoamine transporter and the 5-HT1B receptor are not modified. Protracted 5-HTT expression also occurred in other areas with transient expression, but no changes were observed in the raphe nuclei where the 5-HTT is expressed permanently. Thus, thyroid hormones appear to be important in regulating the extinction of the 5-HTT in nonserotoninergic neurons. The transient stabilization of 5-HT reuptake in hypothyroid rats could affect the growth of thalamic axons. Our data stress the importance of maternal and foetal thyroid hormones for the normal development of sensory systems.

Expressions of neuropilin-1, neuropilin-2 and semaphorin 3A mRNA in the rat brain after middle cerebral artery occlusion

This study investigated the spatial and temporal expressions of mRNA encoding neuropilin (Npn)-1, Npn-2 and semaphorin3A (Sema3A) in the rat brain after occlusion of the middle cerebral artery (MAC) distal to the striate branches. The expression of Npn-1 mRNA was transiently upregulated in layers V and VI of the parietal cortex not entering infarction on the lesion side from 3 to 6 h after MCA occlusion. The transient up-regulation of Npn-1 mRNA expression was presumably accompanied by an increase in Npn-1 protein as shown by immunohistochemistry in combination with in situ hybridization histochemistry. Intense Npn-2 mRNA expression was noted temporarily in layer II of the parietal cortex on the lesion side from 1 to 6 h after MCA occlusion. The expression of Sema3A mRNA was upregulated in layer VI of the non-infarcted parietal cortex on the lesion side at 6 h after MCA occlusion. The above increases in mRNA expression were no longer observed at 12 h after MCA occlusion. The expressions of Npn-1, -2 and Sema3A mRNA were not detected in the ventroposterior thalamic nucleus undergoing secondary degeneration after MCA occlusion. In the infarct lesion or ischemic core, neuronal expressions of Npn-1, -2 and Sema3A disappeared by 3 days after MCA occlusion as the neurons in situ entered apoptosis or necrosis. In contrast, ED-1-positive microglia/macrophages with Npn-1 and Npn-2 mRNA were observed in the infarct lesion at 1 week after MCA occlusion. These findings suggest that the temporal up-regulation of Npn-1 and Sema 3A mRNA expressions in the non-infarcted parietal cortex on the lesion side is insufficient to induce neuronal cell death possibly because the up-regulated mRNA molecules are not fully translated and that the overexpression of Npn-1 and/or Npn-2 in the ischemic core with degenerating neurons enables activated microglial cells to contact the damaged neurons in situ for phagocytosis.

Somatotopic reorganization in the brainstem and thalamus following peripheral nerve injury in adult primates

Injury-induced reorganization of central somatotopic maps is a phenomenon that has proven to be useful for elucidating the mechanisms and time course of neural plasticity. To date, the overwhelming majority of this line of research has focused on such plastic events in cortical areas, at the expense of subcortical structures. In this study, we used multi-unit electrophysiological recording techniques to assess the somatotopic organization of brainstem and thalamic areas following chronic survival from paired median and ulnar nerve section in adult squirrel monkeys. We report that the extent of cutaneously-driven reorganization in both the cuneate nucleus of the brainstem and the ventroposterior lateral nucleus of the thalamus is comparable to that previously documented for area 3b of cortex. These observations are consistent with those previously reported in thalamus, and are unique for brainstem.

Progressive neuronal loss in the ventral posterior lateral and medial nuclei of thalamus in Niemann-Pick disease type C mouse brain

Niemann-Pick disease type C (NP-C) disease is a progressive and fatal neurological disorder characterized by accumulation of cholesterol and glycosphingolipids in peripheral tissues and that of glycosphingolipids in the brain. A C57BL/KsJ-npc1(spm) mutant strain is a genetically authentic model of NP-C. This study investigated neuronal cell loss and lipid accumulation in the npc1(spm) mouse brain. Nissl-staining revealed abundant swollen neurons in the neocortex, piriform cortex, hippocampus and basal ganglia at 3-4 wk of age. In addition to loss of the Purkinje cells, we found a conspicuous cell loss in the ventral posterial lateral (VPL) and medial (VPM) nuclei of thalamus, which became apparent after 4-5 wk. Biochemical analyses revealed no increase of cholesterol in the lipid extracts whereas a substantial accumulation of cholesterol was detectable in most of the large neurons by filipin staining in the brain of homozygous mice. In contrast to the diffuse staining pattern in normal brains, the neuropils of the neurons in the brain of homozygous mice were stained in a punctate pattern. The ubiquitous accumulation excludes a direct role of cholesterol in the progressive neuronal loss in the Purkinje cell layer and in the VPL and VPM of the thalamus.

Thalamic stimulation for essential tremor activates motor and deactivates vestibular cortex

BACKGROUND

The functional effects of deep brain stimulation in the nucleus ventralis intermedius (VIM) of the thalamus on brain circuitry are not well understood. The connectivity of the VIM has so far not been studied functionally. It was hypothesized that VIM stimulation would exert an effect primarily on VIM projection areas, namely motor and parietoinsular vestibular cortex.

METHODS

Six patients with essential tremor who had electrodes implanted in the VIM were studied with PET. Regional cerebral blood flow was measured during three experimental conditions: with 130 Hz (effective) and 50 Hz (ineffective) stimulation, and without stimulation.

RESULTS

Effective stimulation was associated with regional cerebral blood flow increases in motor cortex ipsilateral to the side of stimulation. Right retroinsular (parietoinsular vestibular) cortex showed regional cerebral blood flow decreases with stimulation.

CONCLUSIONS

Beneficial effects of VIM stimulation in essential tremor are associated with increased synaptic activity in motor cortex, possibly due to nonphysiologic activation of thalamofrontal projections or frequency-dependent neuroinhibition. Retroinsular regional cerebral blood flow decreases suggest an interaction of VIM stimulation on vestibular-thalamic-cortical projections that may explain dysequilibrium, a common and reversible stimulation-associated side effect.

[Stereotactic thalamotomy for Parkinsonian and others types of tremor. Experiences of thalamic multiunit burst activity by means of semimicroelectrode]

INTRODUCTION

Better understanding of the basic mechanism of disorders of movement, together with improvements in surgery and electrophysiological techniques have led to a resurge of interest in the surgical treatment of patients with tremor. Ventrolateral thalamotomy has been considered to be an alternative neurosurgical treatment for disabled persons including those with drug-resistant Parkinson s disease and other types of tremor.

PATIENTS AND METHODS

Thirty four of 47 patients had Parkinson s disease (n= 23), essential tremor (n= 4), multiple sclerosis (n= 5), olivopontocerebellar lesion (n= 1) and posttraumatic tremor (n= 1) and did not show satisfactory improvement after drug treatment. The lesions were made in the thalamic nucleus. In 26 patients simultaneous recordings were made of nerve activity in the thalamus and of burst activity.

RESULTS

In 23% of the cases the appropriate site for the final lesion could not be determined in accordance with electrostimulation of the empirical objective. In these patients the objective was determined after observation of the electrophysiological activity localized to the burst activity seen during the operation. The patients were followed-up for 6-24 months (average 12 months); 88% of them had no tremor or moderate contralateral tremor. The patients were assessed on a modified Fahn scale. Average scoring fell from a preoperative evaluation of 73.8 points to 34.0 after three months; 30.7 after six months, 32.0 after 9 months, 37.1 after 12 months and 35.2 points after 18 months.

CONCLUSION

Of 47 thalamotomies done, 13 (29%) were successful and 5 (10%) maintained their original state, but no cases became worse or had serious complications.