(1/134) Cutaneous receptive field organization in the ventral posterior nucleus of the thalamus in the common marmoset.
The organization of cutaneous receptive fields in the ventroposterior (VP) thalamus of the common marmosets (Callithrix jacchus) was determined from single-unit recordings, and these data were correlated with the cytochrome oxidase (CO) histochemistry of the thalamus in the same animals. Under continuously maintained ketamine anesthesia, the receptive fields of a total of 192 single units were recorded from the right VP thalamus using 2 MOhms glass electrodes. After the receptive fields were mapped, the brains were reacted for CO histochemistry on 50-microm coronal frozen sections through the entire VP thalamus. The majority of units were localized to the CO-reactive regions that define the medial and lateral divisions of VP (VPm and VPl). Apart from the expected finding of the face being represented in VPm and the body in VPl, reconstructing the electrode tracks and unit locations in the histological sections revealed a general association between discrete regions of CO reactivity and the representation of specific body regions. Some low-threshold cutaneous units were apparently localized to VPi (the CO weak regions dorsal, ventral, and interdigitating with, the CO regions of VP). These VPi units were clearly part of the same representational map as the VPl and VPm units. We conclude that the low-threshold cutaneous receptive fields of the marmoset are organized in a single continuous representation of the contralateral body surface, and that this representation can most simply be interpreted as being folded or crumpled into the three-dimensional space of VP thalamus. The folded nature of the body map in VP may be related to the folded nature of VP as revealed by CO histochemistry. (+info)
(2/134) Changes in cerebral blood oxygenation of the frontal lobe induced by direct electrical stimulation of thalamus and globus pallidus: a near infrared spectroscopy study.
OBJECTIVE: Blood oxygenation level dependent (BOLD) contrast functional MRI images show activated cortical areas by detecting a reduced concentration of deoxyhaemoglobin (deoxy-Hb) during neuronal activity; however, near infrared spectroscopy (NIRS) has shown various patterns of cerebral blood oxygenation (CBO) changes in the frontal lobe during cognitive tasks. To determine if various patterns of CBO changes occur in the frontal lobe when the brain is directly stimulated, changes in CBO in the frontal lobe induced by deep brain stimulation in patients with implanted electrodes were evaluated. METHODS: Six patients were studied, including five with Parkinson's disease and one with essential tremor. To reduce tremor or rigidity, the electrodes were implanted at the thalamic nucleus ventralis intermedius (VIM: three Parkinson's disease and one essential tremor) or the globus pallidus internus (GPi: two Parkinson's disease). Using NIRS, changes of deoxy-Hb, oxyhaemoglobin (oxy-Hb) and total haemoglobin (total Hb) were measured in the bilateral frontal lobes during various stimulus conditions. RESULTS: High frequency (120 Hz) GPi stimulation consistently increased oxy-Hb and total Hb with a decrease of deoxy-Hb in an intensity and time dependent manner. Oxy-Hb and total Hb increased immediately after the onset of stimulation and then gradually decreased when stimulation was continued. By contrast, high frequency (120 Hz) VIM stimulation decreased oxy-Hb, deoxy Hb and total Hb in an intensity dependent manner. In the severe tremor patient with VIM stimulation, frequency response was examined by decreasing stimulus frequencies; deoxy-Hb increased at high frequencies (70-40 Hz), and then decreased below the control level at low frequencies (30-0 Hz), whereas oxy-Hb and total Hb increased consistently at high and low frequencies. CONCLUSION: The electrical stimulation of GPi and VIM caused various CBO changes in the frontal lobe, which were similar to those found during cognitive tasks. Such a multiplicity of CBO changes in the frontal lobe may be caused by complex neuronal circuits in the frontal lobe which has many neuronal connections to other cortical areas or the basal ganglia. (+info)
(3/134) Reorganization in the cutaneous core of the human thalamic principal somatic sensory nucleus (Ventral caudal) in patients with dystonia.
A wide range of observations suggest that sensory inputs play a significant role in dystonia. For example, the map of the hand representation in the primary sensory cortex (area 3b) is altered in monkeys with dystonia-like movements resulting from overtraining in a gripping task. We investigated whether similar reorganization occurs in the somatic sensory thalamus of patients with dystonia (dystonia patients). We studied recordings of neuronal activity and microstimulation-evoked responses from the cutaneous core of the human principal somatic sensory nucleus (ventral caudal, Vc) of 11 dystonia patients who underwent stereotactic thalamotomy. Fifteen patients with essential tremor who underwent similar procedures were used as controls. The cutaneous core of Vc was defined as the part of the cellular thalamic region where the majority of cells had receptive fields (RFs) to innocuous cutaneous stimuli. The proportion of RFs including multiple parts of the body was greater in dystonia patients (29%) than in patients with essential tremor (11%). Similarly, the percentage of projected fields (PFs) including multiple body parts was higher in dystonia patients (71%) than in patients with essential tremor (41%). A match at a thalamic site was said to occur if the RF and PF at that site included a body part in common. Such matches were significantly less prevalent in dystonia patients (33%) than in patients with essential tremor (58%). The average length of the trajectory where the PF included a consistent, cutaneous RF was significantly longer in patients with dystonia than in control patients with essential tremor. The findings of sensory reorganization in Vc thalamus are congruent with those reported in the somatic sensory cortex of monkeys with dystonia-like movements resulting from overtraining in a gripping task. (+info)
(4/134) Cytoarchitectonic and immunohistochemical characterization of a specific pain and temperature relay, the posterior portion of the ventral medial nucleus, in the human thalamus.
Previous studies in the macaque monkey have identified a thalamic nucleus, the posterior portion of the ventral medial nucleus (VMpo), as a dedicated lamina I spinothalamocortical relay for pain and temperature sensation. The dense plexus of calbindin-immunoreactive fibres that characterizes VMpo in primates enables its homologue to be identified in the human thalamus by immunohistochemical labelling for calbindin. We have now analysed in detail the cytoarchitectonic characteristics of VMpo and its relationship with immunoreactivity for calbindin, substance P and calcitonin gene-related peptide (CGRP) in the human thalamus. The area in the posterolateral thalamus in which dense calbindin-immunoreactive fibre terminations are present coincides nearly completely with a distinct region that contains small to medium-sized cells with round or oval shapes that are aggregated in clusters separated by cell sparse areas. This region, which we identify as VMpo, is located posteromedial to the ventral posterior lateral (VPL) and ventral posterior medial (VPM) nuclei, ventral to the anterior pulvinar and centre median nuclei, lateral to the limitans and parafascicular nuclei and dorsal to the medial geniculate nucleus. Calbindin-immunoreactive fibres enter VMpo from the spinal lemniscus and form large patches of dense terminal-like staining over clusters of VMpo neurons. A few of these clusters also display terminal-like substance P labelling. Small bursts of CGRP staining are intercalated between the calbindin-labelled clusters, but there is little or no overlap between these two markers. CGRP immunoreactivity is also present over small, non-clustered neurons in the calbindin-negative area that separates VMpo from the VPL and VPM nuclei, which we denote as the posterior nucleus (Po). These observations provide a concise description of VMpo in the human thalamus. Further, they suggest that the lamina I spinothalamic tract fibres (represented by calbindin and probably also substance P immunoreactivity) and vagal-solitary-parabrachial afferents (represented by CGRP immunoreactivity) form closely related, but separate, termination fields that can be considered to represent different aspects of enteroceptive information regarding the physiological status of the tissues and organs of the body. The location of VMpo and the adjacent Po fits with clinical descriptions of the thalamic area from which pain, temperature and visceral sensations can be evoked by microstimulation, and where nociceptive and thermoreceptive neurons have been recorded in humans. It also corresponds to the area in which infarcts cause analgesia and thermoanaesthesia and can lead to the paradoxical development of central pain. (+info)
(5/134) Regionally selective blockade of GABAergic inhibition by zinc in the thalamocortical system: functional significance.
The thalamocortical (TC) system is a tightly coupled synaptic circuit in which GABAergic inhibition originating from the nucleus reticularis thalami (NRT) serves to synchronize oscillatory TC rhythmic behavior. Zinc is colocalized within nerve terminals throughout the TC system with dense staining for zinc observed in NRT, neocortex, and thalamus. Whole cell voltage-clamp recordings of GABA-evoked responses were conducted in neurons isolated from ventrobasal thalamus, NRT, and somatosensory cortex to investigate modulation of the GABA-mediated chloride conductance by zinc. Zinc blocked GABA responses in a regionally specific, noncompetitive manner within the TC system. The regional levels of GABA blockade efficacy by zinc were: thalamus > NRT > cortex. The relationship between clonazepam and zinc sensitivity of GABA(A)-mediated responses was examined to investigate possible presence or absence of specific GABA(A) receptor (GABAR) subunits. These properties of GABARs have been hypothesized previously to be dependent on presence or absence of the gamma2 subunit and seem to display an inverse relationship. In cross-correlation plots, thalamic and NRT neurons did not show a statistically significant relationship between clonazepam and zinc sensitivity; however, a statistically significant correlation was observed in cortical neurons. Spontaneous epileptic TC oscillations can be induced in vitro by perfusion of TC slices with an extracellular medium containing no added Mg(2+). Multiple varieties of oscillations are generated, including simple TC burst complexes (sTBCs), which resemble spike-wave discharge activity. A second variant was termed a complex TC burst complex (cTBC), which resembled generalized tonic clonic seizure activity. sTBCs were exacerbated by zinc, whereas cTBCs were blocked completely by zinc. This supported the concept that zinc release may modulate TC rhythms in vivo. Zinc interacts with a variety of ionic conductances, including GABAR currents, N-methyl-D-aspartate (NMDA) receptor currents, and transient potassium (A) currents. D-2-amino-5-phosphonovaleric acid and 4-aminopyridine blocked both s- and cTBCs in TC slices. Therefore NMDA and A current-blocking effects of zinc are insufficient to explain differential zinc sensitivity of these rhythms. This supports a significant role of zinc-induced GABAR modulation in differential TC rhythm effects. Zinc is localized in high levels within the TC system and appears to be released during TC activity. Furthermore application of exogenous zinc modulates TC rhythms and differentially blocks GABARs within the TC system. These data are consistent with the hypothesis that endogenously released zinc may have important neuromodulatory actions impacting generation of TC rhythms, mediated at least in part by effects on GABARs. (+info)
(6/134) Convergent inputs from thalamic motor nuclei and frontal cortical areas to the dorsal striatum in the primate.
Current models of basal ganglia circuitry primarily associate the ventral thalamic nuclei with relaying basal ganglia output to the frontal cortex. However, some studies have demonstrated projections from the ventral anterior (VA) and ventral lateral (VL) thalamic nuclei to the striatum, suggesting that these nuclei directly modulate the striatum. VA/VL nuclei have specific connections with primary, supplementary, premotor, and cingulate motor cortices indicating their involvement in motor function. These areas mediate different aspects of motor control such as movement execution, motor learning, and sensorimotor integration. Increasing evidence indicates that functionally related motor areas have convergent projections to the dorsal striatum, suggesting that integration of different aspects of motor control occur at the level of the striatum. This study examines the organization of VA/VL thalamic inputs to the dorsal "motor" striatum to determine how this afferent projection is organized with respect to corticostriatal afferents from motor, premotor, and cingulate motor areas. Motor cortical projections to specific dorsal striatal regions arose from multiple areas, including components from primary motor, premotor, supplementary, and cingulate motor areas. Diverse motor cortical projections to a given dorsal striatal region indicated convergence of functionally related corticostriatal motor pathways. Most dorsal striatal sites received dense thalamic inputs from the VL pars oralis nucleus. Additional thalamostriatal projections arose from VA, VL pars caudalis, and ventral posterior lateral pars oralis nuclei and Olszewski's Area X. Our results provide evidence for convergent striatal projections from interconnected ventral thalamic and cortical motor areas, suggesting that these afferents modulate the same striatal output circuits. (+info)
(7/134) Progressive transneuronal changes in the brainstem and thalamus after long-term dorsal rhizotomies in adult macaque monkeys.
This study deals with a potential brainstem and thalamic substrate for the extensive reorganization of somatosensory cortical maps that occurs after chronic, large-scale loss of peripheral input. Transneuronal atrophy occurred in neurons of the dorsal column (DCN) and ventral posterior lateral thalamic (VPL) nuclei in monkeys subjected to cervical and upper thoracic dorsal rhizotomies for 13-21 years and that had shown extensive representational plasticity in somatosensory cortex and thalamus in other experiments. Volumes of DCN and VPL, number and sizes of neurons, and neuronal packing density were measured by unbiased stereological techniques. When compared with the opposite, unaffected, side, the ipsilateral cuneate nucleus (CN), external cuneate nucleus (ECN), and contralateral VPL showed reductions in volume: 44-51% in CN, 37-48% in ECN, and 32-38% in VPL. In the affected nuclei, neurons were progressively shrunken with increasing survival time, and their packing density increased, but there was relatively little loss of neurons (10-16%). There was evidence for loss of axons of atrophic CN cells in the medial lemniscus and in the thalamus, with accompanying severe disorganization of the parts of the ventral posterior nuclei representing the normally innervated face and the deafferented upper limb. Secondary transneuronal atrophy in VPL, associated with retraction of axons of CN neurons undergoing primary transneuronal atrophy, is likely to be associated with similar withdrawal of axons from the cerebral cortex and should be a powerful influence on reorganization of somatotopic maps in the somatosensory cortex. (+info)
(8/134) Temporary inactivation in the primate motor thalamus during visually triggered and internally generated limb movements.
To better understand the contribution of cerebellar- and basal ganglia-receiving areas of the thalamus [ventral posterolateral nucleus, pars oralis (VPLo), area X, ventral lateral nucleus, pars oralis (VLo), or ventral anterior nucleus, pars parvicellularis (VApc)] to movements based on external versus internal cues, we temporarily inactivated these individual nuclei in two monkeys trained to make visually triggered (VT) and internally generated (IG) limb movements. Infusions of lignocaine centered within VPLo caused hemiplegia during which movements of the contralateral arm rarely were performed in either task for a short period of time ( approximately 5-30 min). When VT responses were produced, they had prolonged reaction times and movement times and a higher incidence of trajectory abnormalities compared with responses produced during the preinfusion baseline period. In contrast, those IG responses that were produced remained relatively normal. Infusions centered within area X never caused hemiplegia. The only deficits observed were an increase in reaction time and movement amplitude variability and a higher incidence of trajectory abnormalities during VT trials. Every other aspect of both the VT and IG movements remained unchanged. Infusions centered within VLo reduced the number of movements attempted during each block of trials. This did not appear to be due to hemiplegia, however, as voluntary movements easily could be elicited outside of the trained tasks. The other main deficit resulting from inactivation of VLo was an increased reaction time in the VT task. Finally, infusions centered within VApc caused IG movements to become slower and smaller in amplitude, whereas VT movements remained unchanged. Control infusions with saline did not cause any consistent deficits. This pattern of results implies that VPLo and VLo play a role in the production of movements in general regardless of the context under which they are performed. They also suggest that VPLo contributes more specifically to the execution of movements that are visually triggered and guided, whereas area X contributes specifically to the initiation of such movements. In contrast, VApc appears to play a role in the execution of movements based on internal cues. These results are consistent with the hypothesis that specific subcircuits within the cerebello- and basal ganglio-thalamo-cortical systems preferentially contribute to movements based on external versus internal cues. (+info)