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PubMed1994

Differential foci and synaptic organization of the principal and spinal trigeminal projections to the thalamus in the rat.

The thalamus is known to receive single-whisker 'lemniscal' inputs from the trigeminal nucleus principalis (PrV) and multiwhisker 'paralemniscal' inputs from the spinal trigeminal nucleus (SpV), yet the responses of cells in the thalamic ventroposteromedial nucleus (VPM) are most similar to and contingent upon inputs from PrV. This may reflect a differential termination pattern, density and/or synaptic organization of PrV and SpV projections. This hypothesis was tested in adult rats using anterograde double-labelling with fluorescent dextrans, horseradish peroxidase (HRP) and choleragenoid, referenced against parvalbumin and calbindin immunoreactivity. The results indicated that PrV's most robust thalamic projection is to the whisker-related barreloids of VPM. The SpV had robust projections to non-barreloid thalamic regions, including the VPM 'shell' encapsulating the barreloid area, a caudal and ventral region of VPM that lacks barreloids and PrV inputs, the posterior thalamic nucleus, nucleus submedius and zona incerta. Within the barreloid portion of VPM, SpV projections were sparse relative to those from PrV, and most terminal labelling occurred in the peripheral fringes of whisker-related patches and in interbarreloid septae. Thus, PrV and SpV have largely complementary projection foci in the thalamus. Intra-axonal staining of a small sample of trigeminothalamic axons with whisker or guard hair receptive fields revealed highly localized and somatotopic terminal aggregates in VPM that spanned areas no larger than that of a single barreloid. In the electron microscopic component of this study, HRP transport to the barreloid region of VPM from left SpV and right PrV in the same cases revealed PrV terminals contacting dendrites with a broad range of minor axis diameters (mean +/- SD: 1.51 +/- 0.10 microns). SpV terminals were indistinguishable from those of PrV, but they had a disproportionate number of contacts on narrow dendrites (1.27 +/- 0.07 microns, P < 0.01). PrV endings were also more likely to contact VPM somata (11.0 +/- 4.2% of all labelled terminals) than those from SpV (3.0 +/- 1.0%, P < 0.01). Insofar as primary dendrites are thicker than distal dendrites in VPM, these data suggest a differential distribution of PrV and SpV inputs onto VPM cells that may account for their relative efficacies in dictating the responses of VPM cells to whisker stimulation. Multiwhisker receptive fields in VPM may also reflect direct transmission of convergent inputs from PrV.

Animals↗
PubMed2006

Evidence for a direct, short latency projection from the dorsal cochlear nucleus to the auditory thalamus in the guinea pig.

The auditory thalamus (medial geniculate body, MGB) receives its main ascending input from the inferior colliculus (IC), which was considered to be an obligatory relay for all auditory inputs to the MGB. However, recent anatomical evidence in the rat [ (Malmierca et al. 2002) J. Neurosci., 22, 10891-10897] has confirmed the presence of a direct pathway from the dorsal cochlear nucleus (DCN) to the medial MGB, bypassing the IC, as previously suggested in the chimpanzee [ (Strominger et al. 1977) J. Comp. Neurol., 172, 349-366]. We show that this direct pathway is also present in the guinea pig and apparently results in short latency responses in the thalamus. Injection of anterograde tracer into the DCN of five adult guinea pigs revealed terminal boutons and axonal swellings distributed throughout the medial MGB, but absent from all other MGB subdivisions. Electrophysiological recordings made from 39 adult guinea pigs (24 male & 15 female) showed neurons in the medial MGB responded with significantly shorter latencies to acoustic clicks (7.8 ms) than those from the ventral (11.0 ms), dorsal (14.4 ms), or shell (16.5 ms) MGB, consistent with the direct pathway from the DCN. The function of the direct pathway is not known but may be related to the fast responses and the role of the medial MGB in integrating combined somatosensory and auditory inputs. Short latency responses may be important in priming the auditory cortex to prepare it for rapid analysis and in recruiting the amygdala for rapid emotional responses such as fear.

Acoustic Stimulation↗
PubMed1994

Lemniscal and non-lemniscal synaptic transmission in rat auditory thalamus.

1. The central auditory pathway linking the inferior colliculus (IC) and the medial geniculate body (MGB) of the thalamus consists of a segregated ventral lemniscal and dorsal non-lemniscal projection whose synaptic transmission mechanisms remain unknown. Extracellular and intracellular recordings combined with axonal tract tracing and cell staining were made from lemniscal and non-lemniscal divisions of adult rat MGB maintained acutely in in vitro explants containing parallel tectothalamic projections. 2. Biocytin deposition within the brachium of the IC revealed dense axonal fibres projecting to the MGB. Thin axonal terminals were found throughout the ventral (MGv) and dorsal (MGd) divisions of the MGB. Bushy cells with tufted or bitufted dendritic branches were primarily found in the MGv. In the MGd, cells were mainly seen as stellate neurones having a radiate dendritic arbor. 3. Electrical stimulation of the brachium of IC invariably elicits fast, excitatory synaptic potentials in both MGv and MGd cells. The evoked responses occurred monosynaptically and were exclusively mediated by glutamate acting on both N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Non-lemniscal MGd neurones recorded extracellularly exhibited a strong tendency to discharge in bursts in response to brachium stimulation. In contrast, a large proportion of ventral lemniscal cells tended to discharge in single or dual spikes. Intracellularly, MGd cells, but not MGv cells, showed a predominant, slow synaptic potential mediated by NMDA receptors. 4. It is concluded that the central auditory circuitry linking the tectum and the thalamus is connected monosynaptically via glutamatergic synapses. Lemniscal and non-lemniscal thalamic neurones possess distinct response properties which cannot be accounted for by a differential transmitter system or polysynaptic delays as postulated previously.

Animals↗
PubMed2004

Electrical stimulation of the posteromedial thalamus modulates breathing in unanesthetized fetal sheep.

Having previously shown that lesions in the posteromedial group of thalamic nuclei abolish hypoxic inhibition of fetal breathing, we devised this study to identify thalamic loci that depress breathing by focal stimulation of specific sectors of the caudal thalamus and adjacent structures. Multipolar electrode arrays consisting of a series of eight stimulation contacts at 1.25-mm intervals were implanted vertically through guide cannulae into the caudal diencephalon of 12 chronically catheterized fetal sheep (>0.8 term), and central neural tissue was stimulated between adjacent contacts. Each site was stimulated repeatedly with increasing current searching for spatial and stimulus strength parameters for a reliable alteration in respiratory rate. Respiratory period increased when stimulation involved areas of the parafascicular nuclear complex (Pf), which more than doubled the mean period compared with the baseline of 0.90 +/- 0.19 s. The change in respiratory period was due to an increase in expiratory time, whereas inspiratory time and breath amplitude were not significantly affected. Breathing period and expiratory time were also increased when the stimulations involved the intralaminar wing surrounding the mediodorsal nucleus, the rostral central gray, zona incerta, and ventral tegmental area. Reductions in respiratory frequency occurred less consistently, with stimulation involving surrounding zones including the sub-Pf, ventromedial nucleus, and ventrobasal nuclear complex. These findings support the hypothesis that a restricted area of the posteromedial thalamus (principally Pf) constitutes part of a neuronal circuitry that modulates respiratory motoneurons.

Animals↗
PubMed2005

Effect of amiloride on gustatory responses in the ventroposteromedial nucleus of the thalamus in rats.

The existence of gustatory neuron types has been demonstrated in the chorda tympani nerve and the nucleus of the solitary tract (NTS) of rats and hamsters through the oral application of amiloride, a sodium channel blocker. At these lower-order levels, amiloride was shown to reduce the response to sodium and lithium salts in sodium- and sugar-oriented cells, while leaving those of acid- and quinine-oriented neurons unmodified. We extended this investigation to higher-order levels by determining whether amiloride suppressed the responses of cells at the 4th-order gustatory relay in the thalamus, which neurons were affected, the degree of suppression, and whether the subsequent neural code for sodium was altered. We stimulated the whole oral cavity of anesthetized rats with a variety of tastants while recording the responses of 42 single thalamic neurons before and after the application of amiloride. The results revealed a similar pattern to that reported in the NTS. Amiloride inhibited only sodium- and sugar-oriented neurons, and specifically their responses to sodium- or lithium-containing stimuli. Moreover, there was a significant relationship between the degree of sodium specificity of a neuron and its sensitivity to inhibition by amiloride. These results demonstrate a relationship between a cell's response profile and its susceptibility to amiloride, and so offer evidence that gustatory neuron types exist through the level of the thalamus in rats. Thus membership in a neuronal group retains functional significance based on a receptor event 4 synapses away.

Action Potentials↗
PubMed1978

Nociceptive responses of neurons in medial thalamus and their relationship to spinothalamic pathways.

1. An extracellular study of the cat medial thalamus has revealed four types of somatosensory neurons. These were located primarily in the n. parafascicularis, n. subparafascicularis, and n. centralis lateralis; none were found in the n. centrum medianum. There was no functional segregation of neurons within each nucleus or between nuclei. Each type of neuron had large and often bilateral receptive areas. No somatotopic organization of neurons was found within the medial thalamus. 2. Noxious (N) and noxious-tap (NT) neurons comprising 72% of the sample (78 of 109 total) were considered to be nociceptive. N cells responded exclusively to noxious mechanical stimulation of skin, muscle fascia, tendons, and joints, and to direct stimulation of A-delta- and C-fiber groups in cutaneous, articular, and muscle nerves. NT cells responded to noxious and tap stimulation in a differential manner and to stimulation of the entire spectrum of A- and C-fibers. N and NT cells accurately signaled the duration of noxious mechanical stimulation. Their nociceptive responses were also graded as a function of both noxious stimulus intensity and the number of activated A-delta- and C-fibers. Stimulation of A- and C-fibers evoked, respectively, an inital burst and a late burst of discharges. A brief period of inhibition intervened between the initial and late bursts of NT cells. Prolonged afterdischarge was often observed following noxious natural stimulation or stimulation of A-delta- and C-fibers. The phenomenon of discharge "windup" was observed during iterative stimulation of C-fibers. 3. Tap (T) neurons (10%) responded only to brisk but innocuous taps applied to skin or underlying tissue. These cells were driven only by activation of A-alpha- and A-beta-fibers. The response to such stimulation was seen as an initial burst of discharges followed by an inhibitory period. 4. Inhibited (I) neurons (18%) had resting discharges that were inhibited by noxious stimuli and stimulation of A-beta- and C-fiber groups. 5. The results obtained from monitoring the peripherally evoked responses of nociceptive N and NT neurons before and after selective lesions of the spinal cord strongly suggested that the spinothalamic tracts were the only spinal projections mediating A- and C-fiber input to these cells. Each spinothalamic tract apparently carried information originating from both sides of the body.

Animals↗
PubMed1984

Functional organization of trigeminal subnucleus interpolaris: nociceptive and innocuous afferent inputs, projections to thalamus, cerebellum, and spinal cord, and descending modulation from periaqueductal gray.

In view of continuing uncertainties concerning the organization, afferent inputs, and projection sites of neurons in the subnucleus interpolaris of the trigeminal (V) spinal tract nucleus, the characteristics of 222 single neurons in and adjacent to the subnucleus were examined electrophysiologically in adult cats anesthetized with chloralose. Neurons were tested for orthodromic responsiveness to a variety of stimuli that included nonnoxious tactile stimuli, noxious mechanical and radiant-heat stimuli, and graded electrical stimulation of the skin, mucosa, tooth pulp, and masseter nerve. Antidromic activation techniques were also used to determine if the functionally identified neurons projected directly to the contralateral posterior thalamus, ipsilateral cerebellum, or cervical spinal cord. In addition, the periaqueductal gray matter (PAG) was stimulated to test for conditioning influences from the PAG on orthodromic responses to noxious and nonnoxious oral-facial stimuli. Interpolaris neurons were somatotopically arranged in subnucleus interpolaris in a pattern conforming in general to the medially facing, inverted-head representation characteristic of other parts of the V brain stem sensory nuclear complex. On the basis of their responsiveness to cutaneous stimuli, the neurons could be functionally classified as either cutaneous nociceptive or low-threshold mechanoreceptive (LTM) neurons. The LTM neurons constituted the major neuron type, accounting for over 75% of our neuron sample. Most of them had a localized mechanoreceptive field of less than 100 mm2 in area that was restricted to one V division, and they had skin-evoked response latencies indicative of afferent input predominantly from A-beta cutaneous afferents. A population of nociceptive neurons was also encountered in the lateral, marginal region of interpolaris and at its medial or ventral border with the reticular formation. These neurons were of two types: nociceptive-specific (NS) neurons, which did not respond to nonnoxious stimuli but which required noxious stimuli for their activation; and wide dynamic range ( WDR ) neurons, which responded to both noxious and nonnoxious stimuli applied to the facial skin. Most had an ipsilateral receptive field that was greater than 100 mm2 in area and that often involved two or three V divisions. Their properties generally conformed to those previously described for nociceptive neurons in the medullary dorsal horn (V subnucleus caudalis) and spinal cord dorsal horn. Interpolaris neurons of all classes (LTM, WDR , and NS) were found to have direct axonal projections to the thalamus, cerebellum, and spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1986

Response characteristics of neurons in the ventral posterior lateral nucleus of the monkey thalamus.

The activity of 132 neurons in the caudal part of the ventral posterior lateral nucleus (VPLc) of the thalamus was recorded from 23 anesthetized monkeys. All single thalamic units that could be excited by electrical search stimuli applied to the contralateral sciatic nerve were investigated. Responses of these cells to mechanical, thermal, and electrical stimuli applied in the periphery indicated that at least half of the sampled cells were nociceptive. Based on responses to graded mechanical stimuli applied to the periphery, 110 of the sampled cells that received a predominant input from cutaneous receptive fields were classified. There were 56 low-threshold, 39 wide dynamic range, and 15 high-threshold cells. The same neurons were also classified into five mechanical types based on a cluster analysis: types 1-5 contained 25, 34, 17, 10, and 24 cells, respectively. The fact that about half the population of cells belonged to either the wide dynamic or the high threshold group (or mechanical types 3-5) suggested that a large population of VPLc neurons respond to mechanical nociceptive stimuli either exclusively or preferentially. Responses of 63 thalamic neurons were tested to noxious heat pulses applied to their cutaneous receptive fields with a contact thermostimulator. Of these, 47 cells were excited, whereas only 16 cells did not respond. The peripheral nerve that innervated the receptive field of each of 82 thalamic neurons was stimulated with graded strengths to activate A fibers only or both A and C fibers. All tested cells responded to peripheral A fiber volleys. In addition, 42 of these cells responded to peripheral C fiber volleys. The C fiber responses could be either short lasting (a few hundreds of milliseconds) or long lasting (up to several seconds). The recording sites of 80 cells were reconstructed. Of these, 78 were in the VPLc nucleus and the remaining two were in the reticular nucleus of the thalamus. No obvious relationship between the response characteristics and the locations of the cells within the VPLc nucleus was found. Sampled thalamic units had a variety of sources of input from the periphery, including both cutaneous and/or deep tissue receptive fields. The majority of the cells, however, had exclusively cutaneous receptive fields. The sizes of the cutaneous receptive fields were often very small, so that nearly half (41%) of the receptive fields of cells sampled occupied an area of skin smaller than half the foot.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1994

Physiologic properties and somatotopic organization of the primate motor thalamus.

1. To examine the functional organization of the primate "motor" thalamus, neuronal activity was studied systematically in awake behaving monkeys throughout the nucleus ventralis lateralis, pars oralis (VLo), nucleus ventralis posterior lateralis, pars oralis (VPLo), ventralis lateralis, pars caudalis (VLc), and portions of ventralis anterior (VA) and Area X. In addition, portions of the sensory nucleus ventralis posterior lateralis, pars caudalis (VPLc) were explored. Isolated neurons were examined for their responses to somatosensory examination and active movement (n = 919) and for their response to torque-induced joint displacements (n = 375). A total of 684 neurons was determined histologically to lie within specific subnuclei of the motor (n = 574) or sensory (n = 110) thalamus. 2. The sensorimotor response properties of neurons in the thalamic subnuclei showed clear differences in their response to somatosensory examination. In order of decreasing frequency, the percent of neurons responding to passive somatosensory examination in each subnucleus were as follows: VPLc, 96% (106/110), VPLo, 93% (252/270), VLc, 77% (43/56), VLo, 37% (59/155), Area X, 22% (12/53), and VA, 12% (5/40). Conversely, neurons that responded only to active movement were most frequent in VLo, 44% (68/155), VA, 45% (18/40), and Area X, 40% (21/53) and relatively infrequent in VLc 11% (6/56) and VPLo, 3% (7/270). In VPLc, no neurons were found that responded only to active movement (0/110). 3. A well-defined somatotopic organization was found in VLo, VPLo, and VPLc and was suggested strongly for VLc. Individual body regions were represented in a series of lamellae, organized in a partial onion skin-like arrangement with the leg represented in the outermost lamella, and the trunk, arm, and orofacial regions represented in successively deeper lamellae. In general the body representations, although present for each subnucleus thoroughly examined, i.e., VLo, VPLo, and VPLc, also were contiguous across subnuclei. Based on the available data, a clear somatotopic picture could not be discerned for Area X or VA. 4. Responses to torque application were more common in neurons in VPLo (77%; 60/78) and VLc (73%; 16/22) than in VLo (44%; 12/27). Mean latencies were shortest for neurons in VPLo (25 +/- 14 ms; mean +/- SD) and the bordering (shell) region of VPLc (22 +/- 15 ms) and were approximately twice as long in VLc (51 +/- 23 ms) and VLo (47 +/- 21 ms).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1999

Neuronal activity in the primate motor thalamus during visually triggered and internally generated limb movements.

Single-unit recordings were made from the basal-ganglia- and cerebellar-receiving areas of the thalamus in two monkeys trained to make arm movements that were either visually triggered (VT) or internally generated (IG). A total of 203 neurons displaying movement-related changes in activity were examined in detail. Most of these cells (69%) showed an increase in firing rate in relation to the onset of movement and could be categorized according to whether they fired in the VT task exclusively, in the IG task exclusively, or in both tasks. The proportion of cells in each category was found to vary between each of the cerebellar-receiving [oral portion of the ventral posterolateral nucleus (VPLo) and area X] and basal-ganglia-receiving [oral portion of the ventral lateral nucleus (VLo) and parvocellular portion of the ventral anterior nucleus (VApc)] nuclei that were examined. In particular, in area X the largest group of cells (52%) showed an increase in activity during the VT task only, whereas in VApc the largest group of cells (53%) fired in the IG task only. In contrast to this, relatively high degree of task specificity, in both VPLo and VLo the largest group of cells ( approximately 55%) burst in relation to both tasks. Of the cells that were active in both tasks, a higher proportion were preferentially active in the VT task in VPLo and area X, and the IG task in VLo and VApc. In addition, cells in all four nuclei became active earlier relative to movement onset in the IG task compared with the VT task. These results demonstrate that functional distinctions do exist in the cerebellar- and basal-ganglia-receiving portions of the primate motor thalamus in relation to the types of cues used to initiate and control movement. These distinctions are most clear in area X and VApc, and are much less apparent in VPLo and VLo.

Animals↗
PubMed2000

Auditory thalamus neurons during sleep: changes in frequency selectivity, threshold, and receptive field size.

The present study describes how the frequency receptive fields (RF) of auditory thalamus neurons are modified when the state of vigilance of an unanesthetized animal naturally fluctuates among wakefulness (W), slow-wave sleep (SWS), and paradoxical sleep (PS). Systematic quantification of several RF parameters-including strength of the evoked responses, response latency, acoustic threshold, shape of rate-level function, frequency selectivity, and RF size-was performed while undrugged, restrained guinea pigs presented spontaneous alternances of W, SWS, and PS. Data are from 102 cells recorded during W and SWS and from 53 cells recorded during W, SWS, and PS. During SWS, thalamic cells behaved as an homogeneous population: as compared with W, most of them (97/102 cells) exhibited decreased evoked spike rates. The frequency selectivity was enhanced and the RF size was reduced. In contrast during PS, two populations of cells were identified: one (32/53 cells) showed the same pattern of changes as during SWS, whereas the other (21/53 cells) expressed values of evoked spike rates and RF properties that did not significantly differ from those in W. These two populations were equally distributed in the different anatomical divisions of the auditory thalamus. Last, during both SWS and PS, the responses latency was longer and the acoustic threshold was higher than in W but the proportion of monotonic versus nonmonotonic rate-level functions was unchanged. During both SWS and PS, no relationship was found between the changes in burst percentage and the changes of the RF properties. These results point out the dual aspect of sensory processing during sleep. On the one hand, they show that the auditory messages sent by thalamic cells to cortical neurons are reduced both in terms of firing rate at a given frequency and in terms of frequency range. On the other hand, the fact that the frequency selectivity and the rate-level function are preserved suggests that the messages sent to cortical cells are not deprived of informative content, and that the analysis of complex acoustic sounds should remain possible. This can explain why, although attenuated, reactivity to biologically relevant stimuli is possible during sleep.

Acoustic Stimulation↗
PubMed2002

Stereotactic interstitial radiosurgery with a miniature X-ray device in the minimally invasive treatment of selected tumors in the thalamus and the basal Ganglia.

The aim of this study was to evaluate the role of interstitial radiosurgery (IR) using the photon radiosurgery system (PRS) in the treatment of selected tumors within the thalamus and the basal ganglia. The PRS is a miniature X-ray generator that was developed for interstitial irradiation. This series included 14 patients (5 with glioblastomas, 4 with low-grade astrocytomas and 5 with metastases) harboring spheroidal lesions with dimensions ranging from 13 to 42 mm (mean 30 mm). After stereotactic biopsy, a radiation dose ranging from 6 to 15.4 Gy (mean 11.3 Gy) was delivered at the target volume margins. Follow-up varied from 3 to 26 months (mean 10.2 months). In the group of glioblastomas, 3 patients died (3-12 months after the procedure) because of tumor progression, while the remaining had tumor control. Two patients with metastases died from systemic disease (4-9 months after the treatment), and 3 were alive and well at the end of the study. Local control was achieved in all metastases. Patients with low-grade astrocytomas were well and imaging studies showed tumor control PRS IR is a minimally invasive procedure for the treatment of selected glial or secondary brain tumors. Compared to conventional radiosurgery (brachytherapy and external radiosurgery), PRS IR presents dose delivery characteristics useful for the treatment of tumors in the thalamus and basal ganglia, without inconveniences such as handling radioisotopes, the need of expensive facilities and radiation protection measures. Although the clinical value needs further investigations, PRS IR seems to be effective in metastases while it provides less benefit in malignant gliomas. PRS IR could have a major role in the treatment of low-grade astrocytomas.

Adolescent↗
PubMed1994

Plasticity in human somatosensory thalamus as a result of deafferentation.

Experimental studies indicate that deafferentation results in reorganization of the somatosensory map at various levels of the CNS, such that the representation of a body part adjacent to a region that is denervated expands into the deafferented area. Recent data suggest that in the human this occurs at the cortical level, but subcortical structures have not been systematically investigated. To test the hypothesis that the human thalamus is capable of significant reorganization as a result of changes in afferent input, microelectrode recording and stimulating techniques were used to define thalamic somatotopy in 61 patients undergoing stereotactic procedures. Five groups were compared: those with pain in the deafferented body part, face (n = 9), arm/hand (n = 4), leg/foot (n = 8) and hemibody (n = 5) and those with neither pain nor deafferentation, i.e., movement disorder (n = 24). Trunk representation, as determined from receptive fields, was significantly larger in patients with leg/foot deafferentation than in patients without deafferentation (1.8 +/- 0.7 vs. 0.5 +/- 0.2 mm; p < 0.01). Also, microstimulation induced paraesthesiae in the face from a significantly larger region of thalamus in the facially denervated group compared to the movement disorder group (13.8 +/- 2.8 vs. 3.7 +/- 0.6 mm; p < 0.001). There were no significant differences in the representation of other body parts in the five groups. The results in the leg-deafferented group agree with conclusions reached from animal studies; however, the human situation is more complex. There appear to be different patterns and degrees of somatotopic reorganization in the human, all of which may be associated with pain syndromes.

Afferent Pathways↗
PubMed1990

Structural and connectional diversity of the primate motor thalamus: experimental light and electron microscopic studies in the rhesus monkey.

In this study we analyzed neuronal and synaptic organization of nigral and cerebellar afferent territories in the rhesus monkey motor thalamus using a variety of electron microscopic techniques. Significant qualitative and quantitative differences were revealed between the two regions with respect to features of nerve cells, their relationships to one another, and organization of afferent inputs on them. The data suggest that information arriving to the thalamus via nigral and cerebellar afferents is processed by different mechanisms.

Afferent Pathways↗
PubMed1993

The primate motor thalamus analysed with reference to subcortical afferent territories.

This paper analyses the internal organisation of the primate motor thalamus. A topographic study of the three main subcortical afferent territories (the cerebellar, pallidal and nigral territories) gives a much simpler and more functionally relevant partitioning of the thalamus than consideration of conflictual cytoarchitectonic nuclei.

Afferent Pathways↗
PubMed1993

Unit activity of nucleus ventralis lateralis of human thalamus during voluntary movements.

The dynamics of change of single VL neurons of human thalamus during voluntary movements was investigated in the course of stereotactic operations on dyskinetic patients. Two basic types of units (A and B cells), reacting to the voluntary movement with different discharge patterns, revealed the common dynamics and a transient time-connectivity of responses correlated with certain phases of the performance of motor acts. It is supposed that these findings reflect the dynamic conjugation of two functionally different cellular subsystems in the human thalamus, which perform collaborative processing and transmitting of information during voluntary movements.

Humans↗
PubMed1994

Brainstem reticular nuclei that project to the thalamus in rats: a retrograde tracer study.

The precise nuclear origins of projections from the brainstem reticular formation to the thalamus were identified in rats using two retrograde tracing substances: wheat germ agglutinin-horseradish peroxidase conjugate, and Fluoro-Gold. Injections of these tracers were made into a variety of thalamic nuclei, including the intralaminar nuclei (most of these also involved the lateral part of the mediodorsal nucleus), the central part of the mediodorsal nucleus, the ventrolateral/ventromedial nuclei, and the ventral posterolateral/ventral posteromedial nuclei. Counts of retrogradely labeled cells were done on a large sample of select cases. The data generated by these cell counts indicate that brainstem reticular projections to the intralaminar/lateral mediodorsal complex are fairly strong, as are those to the ventrolateral/ventromedial nuclear complex. Ascending reticular projections to the mediodorsal nucleus per se are somewhat weaker, while those to the ventrobasal complex (or at least the ventral posterolateral nucleus) are weaker still. As a whole, reticular neurons projecting to the thalamus are by far most numerous in the midbrain, and then decline gradually at successively caudal levels through the pons and medulla. Midbrain reticular groups evincing very strong ascending projections include nucleus reticularis (n.r.) pedunculopontinus (particularly its pars compactus), n.r. cuneiformis and n.r. subcuneiformis (together known as the deep mesencephalic nucleus). Strong thalamic projections arise from the medial part of n.r. pontis oralis, the medial (beta) part of n.r. pontis caudalis, and the mid-pontine dorsomedial tegmental area. Within the medullary reticular formation, a 'trans-nuclear field' of neurons encompassing n.r. paragigantocellularis dorsalis and dorsal parts of n.r. gigantocellularis and n.r. parvocellularis was consistently labeled contralateral to the injection site. In general, ascending reticulothalamic projections are largely ipsilateral from midbrain reticular groups, bilateral from pontine reticular groups, and contralateral from medullary reticular groups. Within individual reticular nuclei, the morphology of labeled neurons is identical to that reported previously by this laboratory subsequent to spinal, cortical, or cerebellar tracer injections, thus strengthening our hypothesis that the various brainstem reticular nuclei can be distinguished on the basis of neuronal morphology. As a whole, thalamic-projecting reticular neurons are mostly small or medium-sized cells.

Animals↗
PubMed2004

Abnormal glucose metabolism in the mediodorsal nucleus of the thalamus in schizophrenia.

OBJECTIVE: Three thalamic nuclei--the mediodorsal nucleus, pulvinar, and centromedian nucleus--each have unique reciprocal circuitry with cortical and subcortical areas known to be affected in schizophrenia. To determine if the disorder is also associated with dysfunction in the mediodorsal nucleus, pulvinar, and centromedian nucleus, relative glucose metabolism in these regions was measured in a large group of unmedicated patients with schizophrenia. METHOD: [18F]-deoxyglucose positron emission tomography (PET) and matching T1-weighted magnetic resonance imaging (MRI) scans were obtained for 41 unmedicated patients with schizophrenia and 60 age- and sex-matched healthy subjects. The PET and MRI images for each subject were coregistered, and the whole thalamus, mediodorsal nucleus, pulvinar, and centromedian nucleus were traced on the MRI image. Relative glucose metabolism in these regions was assessed. RESULTS: Patients with schizophrenia showed significantly lower relative glucose metabolism in the mediodorsal nucleus and the centromedian nucleus and significantly higher relative glucose metabolism in the pulvinar, compared with the healthy subjects. Lower relative glucose metabolism in the total thalamus, mediodorsal nucleus, and pulvinar was associated with greater overall clinical symptoms as measured by the Brief Psychiatric Rating Scale. Lower relative glucose metabolism in the pulvinar was associated with more hallucinations and more positive symptoms, while lower relative glucose metabolism in the mediodorsal nucleus was associated with more negative symptoms. CONCLUSIONS: The findings suggest that patients with schizophrenia exhibit dysfunction in thalamic subdivisions with distinct cortical connections and that these thalamic subdivisions have specific associations with clinical symptoms.

Adolescent↗