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PubMed1994

Projection of visuotopically organized afferents to the dorsal thalamus in the opossum, Monodelphis domestica.

Retrogradely transported dyes, Fluorogold and Fast Blue were injected into both sides of the dorsal thalamus in the Monodelphis opossum. Projection of the presumed primary visual cortical area, superior colliculus and parabigeminal nucleus to the dorsal lateral geniculate nucleus and the lateral posterior--lateral intermedius nuclear complex were described. They show close similarities to the homologous projections in the North American Opossum, insectivores and some rodents. In comparison with rat, cortico-thalamic and tecto-thalamic projections in the Monodelphis are less numerous. The peculiarity of cytoarchtitectonics of cortical layer 6 is described and discussed.

Animals↗
PubMed1994

Squirrel monkey lateral thalamus. I. Somatic nociresponsive neurons and their relation to spinothalamic terminals.

The incidence and response properties of nociresponsive neurons, their locations relative to spinothalamic terminals, and their relations to cytoarchitectonic borders were studied in the lateral thalamus of the squirrel monkey. Nociceptive neurons were found in ventral posterior inferior nucleus (VPI), in the lateral and medial nuclei (VPL and VPM) of the ventral posterior complex (VP = VPL + VPM), as well as the posterior complex (PO). The overall incidence of nociresponsive cells was 19% (50 of 270 cells). The proportion of nociresponsive neurons within VPI was 50% (23 of 46), 38% in PO (8 of 21), and 10% in VP (19 of 203). Most nociresponsive cells (90%) in VP were of wide-dynamic-range type, while within VPI 43% of nociresponsive cells were nociceptive-specific type. Most of these nociresponsive cells had thermal and mechanical responses, and a small number also responded to cooling. The receptive fields of nociresponsive cells in VPL were in continuity, in both size and body location, with surrounding low-threshold units. The receptive fields of VPI and PO nociresponsive cells were larger than those in VPL. The probability of encountering nociresponsive cells located within 100 microns of spinothalamic terminations was high in VPI (73%) and low in VPL (33%). On the other hand, the probability of encountering non-nociceptive cells located within 100 microns of spinothalamic terminals was low in both VPI (20%) and VPL (26%). The results indicate segregation of nociresponsive cell types across VP, VPI, and PO and suggest that VPI, and perhaps PO, is an important region for discriminative processing and perception of painful stimuli.

Animals↗
PubMed1976

Altered response of blood thyroxine level after its acute depletion by isovolemic exchange transfusion in rats with lesions in hypothalamus and thalamus.

Bilateral electrolytic lesions were made in various areas of hypothalamus or thalamus on the 6th day of a period of daily radioiodide injections (1 or 5 muCi125I-daily per animal) in male rats weighing about 350 g. Such injections were continued for another 4 days and after 2 days of intermission the blood thyroid hormone was acutely depleted by isovolemic exchange transfusion of thyroid hormone free blood cell suspension. Relative changes of plasma thyroxine level were measured with the aid of paper chromatography in small aliquots of plasma frequently taken from the animals under maintaining isovolemia by replacing the removed plasma. It was found that in animals with various bilateral electrolytic lesions in hypothalamus (suprachiasmatic and paraventricular areas) the response of blood thyroxine level after the transfusion is similar as in sham-operated controls bearing unilateral subcortical lesion or in normal animals observed previously. On the other hand, the response in animals with thalamic lesions was repeatedly found to resemble that observed previously in thyroidectomized animals. Since the response of blood thyroxine level presumably results from changes of pituitary thyrotropic activity, it is concluded that in rats with thalamic lesions the normal response of hypothalamo-pituitary-thyroid axis was prevented. The mechanism of this action, however, remains to be elucidated.

Animals↗
PubMed1996

Nucleus-specific expression of GABA(A) receptor subunit mRNAs in monkey thalamus.

Expression of 10 GABAA receptor subunit genes was examined in monkey thalamus by in situ hybridization using cRNA probes specific for alpha 1, alpha 2, alpha 3, alpha 4, alpha 5, beta 1, beta 2, beta 3, gamma 1, and gamma 2 subunit mRNAs. These displayed unique hybridization on patterns with significant differences from rodents. Alpha 1, beta 2, and gamma 2 transcripts were expressed at high levels in all dorsal thalamic nuclei, but expression was significantly higher in sensory relay nuclei-especially the dorsal lateral geniculate nucleus. Other transcripts showed nucleus-specific differences in levels of expression and in the range expressed. Alpha 5 and alpha 4 subunit transcripts were expressed in all nuclei except the intralaminar nuclei. Levels of alpha 2, alpha 3, beta 1, beta 3, and gamma 1 expression were very low, except in intralaminar nuclei. In the reticular nucleus, most subunit transcripts were not expressed, and only gamma 2 transcripts were consistently detected at modest levels. Thalamic GABAA receptors may be assembled from nucleus-specific groupings of subunit polypeptides.

Animals↗
PubMed1996

[Gamma knife treatment of AVM of the basal ganglia and thalamus].

Arteriovenous malformatios (AVMs) in the basal ganglia (BG) and thalamus (Thal) are difficult to treat by microsurgery or intravascular embolization alone, and the role of stereotactic gamma radiosurgery (gamma knife) of these AVMs is discussed. We have treated 324 cases of AVM with gamma knife since May 1991, and in 71 of these cases (19%) the AVM was in the BG or Thal. The results of gamma radiosurgery on AVMs of the BG and Thal were compared with the results of treating AVMs at other intracranial locations by gamma radiosurgery. The nidi were small (mean diameter: 16.4 mm), and they were treated with a mean maximum dose of 36.4 Gy and marginal dose of 19.9 Gy. The results were evaluated angiographically in 39 (55%) of the 71 cases, with a mean follow-up period of 23 months. The complete obliteration rate of AVMs in the BG and Thal 1 and 2 years after treatment was 54.3% and 92.0%, respectively, and the rate at the other locations was 42.9% and 76.0%, respectively. Adverse effects of this treatment in the AVM cases overall were rebleeding from the nidus in 5 cases (1.5%) and radiation necrosis in 4 cases (1.2%). In conclusion, AVMs of the BG and Thal were effectively and safely treated with the gamma knife, and stereotactic radiosurgery is a definitive alternative treatment for deep seated AVMs.

Adolescent↗
PubMed1996

Non-invasive imaging of neuronal population dynamics in human thalamus.

Waveforms for early thalamic and cortical population responses to unilateral median nerve stimulation at the wrist were determined non-invasively for six subjects from 122-channel magnetoencephalographic data. Biphasic responses in contralateral ventral thalamus were obtained in 9 hemispheres similar to depth-electrode results reported for patients. Thalamic responses occurred at 15.1-17.4 and at 19.2-24 ms. Responses in contralateral sensorimotor cortex began at 16.3-18.8 ms.

Evoked Potentials↗
PubMed1996

Delayed-onset hemidystonia and chorea following contralateral infarction of the posterolateral thalamus. A case report.

A 68 year-old man developed progressive hemidystonia and chorea 8 months after a contralateral thalamic stroke. The neurological examination also showed a right pyramidal syndrome without hemiparesis, a right horizontal sectoranopia, and a right hemihypesthesia for all sensory modalities. The MRI revealed infarctions in the left medial temporo-occipital lobes and left posterolateral thalamus, corresponding to the vascular territories of both the thalamo-geniculate and posterolateral choroidal arterial pedicles. The thalamic lesion involved the pulvinar, the lateral geniculate body, and the ventro-postero-lateral, dorso-lateral, posterolateral, and dorso-medial nuclei, but apparently did not extent to the ventrolateral thalamic nucleus, and the subthalamic and midbrain regions. Thalamic and striatopallidal dystonia have not a common pathophysiological mechanism. The involvement of the pulvinar nucleus and of the strategic crossing of proprioceptive, cerebellar, pyramidal, and subthalamic pathways may play a role in the genesis of the posterolateral thalamic dystonia.

Aged↗
PubMed1997

Interconnected parallel circuits between rat nucleus accumbens and thalamus revealed by retrograde transynaptic transport of pseudorabies virus.

One of the primary outputs of the nucleus accumbens is directed to the mediodorsal thalamic nucleus (MD) via its projections to the ventral pallidum (VP), with the core and shell regions of the accumbens projecting to the lateral and medial aspects of the VP, respectively. In this study, the multisynaptic organization of nucleus accumbens projections was assessed using intracerebral injections of an attenuated strain of pseudorabies virus, a neurotropic alpha herpesvirus that replicates in synaptically linked neurons. Injection of pseudorabies virus into different regions of the MD or reticular thalamic nucleus (RTN) produced retrograde transynaptic infections that revealed multisynaptic interactions between these areas and the basal forebrain. Immunohistochemical localization of viral antigen at short postinoculation intervals confirmed that the medial MD (m-MD) receives direct projections from the medial VP, rostral RTN, and other regions previously shown to project to this region of the thalamus. At longer survival intervals, injections confined to the m-MD resulted in transynaptic infection of neurons in the accumbens shell but not in the core. Injections that also included the central segment of the MD produced retrograde infection of neurons in the lateral VP and the polymorph (pallidal) region of the olfactory tubercle (OT) and transynaptic infection of a small number of neurons in the rostral accumbens core. Injections in the lateral MD resulted in retrograde infection in the globus pallidus (GP) and in transynaptic infection in the caudate-putamen. Viral injections into the rostroventral pole of the RTN infected neurons in the medial and lateral VP and at longer postinoculation intervals, led to transynaptic infection of scattered neurons in the shell and core. Injection of virus into the intermediate RTN resulted in infection of medial VP neurons and second-order infection of neurons in the accumbens shell. Injections in the caudal RTN or the lateral MD resulted in direct retrograde labeling of cells within the GP and transynaptic infection of neurons in the caudate-putamen. These results indicate that the main output of VP neurons receiving inputs from the shell of the accumbens is heavily directed to the m-MD, whereas a small number of core neurons appear to influence the central MD via the lateral VP. Further segregation in the flow of information to the MD is apparent in the organization of VP and GP projections to subdivisions of the RTN that give rise to MD afferents. Collectively, these data provide a morphological basis for the control of the thalamocortical system by ventral striatal regions, in which parallel connections to the RTN may exert control over activity states of cortical regions.

Animals↗
PubMed1997

Analgesia by dihydrocodeine is not due to formation of dihydromorphine: evidence from nociceptive activity in rat thalamus.

Dihydrocodeine is increasingly used in slow-release preparations for the treatment of chronic pain on step 2 of the "analgesic ladder" of the World Health Organization. Dihydrocodeine is suggested to act after O-demethylation to dihydromorphine. To test this possibility, experiments were carried out on rats under urethane anesthesia in which nociceptive activity was evoked by electrical stimulation of afferent C fibers in the sural nerve and recorded from neurons in the ventrobasal complex of the thalamus. Dihydrocodeine administered by intravenous injection reduced the evoked nociceptive activity in a dose-dependent manner. Like morphine, dihydrocodeine was capable of completely suppressing the evoked activity. Maximum depression was caused by 2 mg/kg, and the ED50 is 0.47 mg/kg. Naloxone (0.2 mg/kg) reversed the effect of dihydrocodeine (2 mg/kg). To inhibit O-demethylation of dihydrocodeine to dihydromorphine, metyrapone or cimetidine (50 mg/kg) was injected intraperitoneally 20 min before dihydrocodeine (1 and 2 mg/kg). This failed to markedly reduce the effect of dihydrocodeine. Dihydromorphine injected intravenously also reduced the evoked activity in a dose-dependent way. Maximum depression occurred at a dose of 4 mg/kg, and the ED50 is 0.97 mg/kg. Dihydrocodeine and dihydromorphine were equieffective when administered by intrathecal injection at a dose of 100 microg. It is concluded that dihydrocodeine causes analgesia independent of biotransformation to dihydromorphine.

Analgesics, Opioid↗
PubMed1998

[Disorders of higher mental functions in localization of separate infarctions in the optic thalamus and in the region of thalamo-frontal tracts].

The paper presents 9 patients (5 women, 4 men, average age 58 years) with small infarctions located in either thalamus (T) or in the region of thalamofrontal ways. Such infarctions resulted in acute development of mental disorders which corresponded to dementia in 7 cases and to slight cognitive disorders in 2 cases. The complex of mental disorders resembled one in "Frontal Syndrome" and was characterised mainly by aspontaneity, adynamia, hypersomnia, disorientation, memory impairment, attention deficit, delay of all mental processes, lack of criticism and adequacy. Accompanying focal neurologic symptoms were slight in 7 patients, moderate or pronounced in 2 cases. In 5 patients the manifestation of mental disorders decreased gradually. Computer tomography revealed small infarctions in anterior or medial areas of T in 7 cases, and in thalamofrontal routes in 2 patients. Infarctions were located in dominant hemisphere of brain in 5 patients, in nondominant one--in 3 cases, in both hemispheres--in one patient. Location of all the foci corresponded to the structures through which the routes passed and connected T and reticular formation localized lower with frontal lobes of brain. It was suggested that separation of these routes resulted in cognitive disorders or dementia because of functional inactivation of the cortex of frontal lobes of brain.

Adult↗
PubMed1998

[The activity of neurons of the thalamus and brain cortex hemispheres during EEG complexes "slow wave-spindle wave" in rabbits].

Neurons of the medial thalamus and some cortical neurons revealed the same activity upon the spindle wave as upon the slow wave. The membrane potential was changing in a similar way. The data obtained suggests that the slow wave mechanism is analogous to the mechanism of the spindle waves, whereas the rhythm of complexes occurrence or their common with the "spontaneous" sleep spindles rhythm, are determined by a different mechanism.

Animals↗
PubMed1976

Vestibular projections to the thalamus of the pigeon.

Microelectrode recording in the thalamus of pigeons subjected to tilt and sinusoidal rotational stimuli around the vertical, longitudinal and transversal axes revealed vestibularly driven units in two thalamic nuclei, the nucleus posteroventralis and the nucleus principalis precommissuralis. Many of these units responded in a complex manner suggesting that inputs from contralateral and ipsilateral cupulae and maculae converged on them. A few units received additional visual or proprioceptive information. The homology relationship with a mammalian vestibular thalamic nucleus is discussed briefly.

Action Potentials↗
PubMedDate not supplied

[Long-term potentiation of the neuronal activity in the motor cortex induced by simultaneous stimulation of the thalamus and somatosensory cortex in cats].

Long-lasting potentiation of the cat motor cortex units induced by tetanic stimulation of the VL + SCx led to an increase of the motor cortex unit discharge rate. The findings suggest that co-activation of cortico-cortical and thalamo-cortical afferents modifies neuronal activity of the motor cortex at the specific site which receives convergent sensory input from the thalamus and the somatosensory cortex.

Animals↗
PubMed1998

Mediodorsal thalamus plays a critical role in the development of limbic motor seizures.

Limbic motor seizures in animals, analogous to complex partial seizures in humans, result in a consistent activation of the mediodorsal thalamus (MD) and, with prolonged seizures, damage to MD. This study examined the functional role of MD in focally evoked limbic motor seizures in the rat. GABA- and glutamate (Glu)-mediated synaptic transmissions in MD were evaluated for an influence on seizures evoked from area tempestas (AT), a discrete epileptogenic site in the rostral piriform cortex. A GABAA receptor agonist, Glu receptor antagonists, or a GABA-elevating agent were focally microinfused into MD before evoking seizures by focal application of bicuculline methiodide into the ipsilateral AT. Focal pretreatment of MD with the GABAA agonist muscimol (190 pmol) protected against seizures evoked from AT. Seizure protection was also obtained with the focal application of 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) (500 pmol), an antagonist of the AMPA subtype of Glu receptors, into MD. In contrast, focal pretreatment of MD with a competitive antagonist of the NMDA receptor 2-amino-7-phosphonoheptanoic acid (500 pmol) did not attenuate seizures. The anticonvulsant effects achieved with intra-MD injections of muscimol and NBQX were site-specific, because no seizure protection was obtained with injections placed 2 mm ventral or lateral to MD. Prolonged seizure protection was obtained following GABA elevation in MD after the application of the GABA transaminase inhibitor vigabatrin (194 nmol). These results suggest the following: (1) MD is a critical participant in the generation of seizures elicited focally from piriform cortex; (2) transmission via AMPA receptors, but not NMDA receptors, in MD regulates limbic seizure propagation; and (3) a GABA-mediated system exists within MD, the enhancement of which protects against focally evoked limbic motor seizures.

2-Amino-5-phosphonovalerate↗
PubMed1983

Anterograde memory deficits for visuospatial material after infarction of the right thalamus.

A patient with a discrete lesion in the region of the right dorsomedial thalamic nucleus had anterograde memory impairment for visuospatial material. The thalamus may be critical for memory function because of its reciprocal connections with dorsolateral and orbitofrontal cortex and also because of its participation in both basolateral and medial limbic systems.

Cerebral Infarction↗
PubMed1987

Normal memory after damage to medial thalamus.

We studied two patients with nonhemorrhagic infarcts of the thalamus and assessed their cognitive functions comprehensively using standardized neuropsychological probes. Neither patient had any discernible memory impairment for verbal or nonverbal material. Analysis of magnetic resonance images with a stereotaxic method revealed that one subject had a right-sided lesion involving about 15% of the dorsomedial nucleus (DM). The other had bilateral lesions that affected about 15% of the left DM and less than 5% of the right DM. The mamillothalamic tract appeared intact in both patients. Considering that medial thalamic lesions commonly cause amnesia in human beings as well as nonhuman primates, there are two possible reasons, alone or in combination, that may explain why these patients failed to have amnesia: the amount of DM damage was less than required to cause amnesia; or the amnesia related to thalamic lesions requires damage to a second structure, such as the mamillothalamic tract or the anterior nucleus.

Adult↗
PubMed1996

Three-dimensional analysis of cerebellar terminals and their postsynaptic components in the ventral lateral nucleus of the cat thalamus.

Relationships among cerebellar terminals (CTs), dendrites of thalamocortical projection neurons (TCNs), and dendrites of local circuit neurons in the ventral lateral nucleus of the cat thalamus were analyzed quantitatively by observing several series of serial ultrathin sections and by using a computer-assisted program for the three-dimensional reconstruction from serial ultrathin sections. In pentobarbital-anesthetized cats, CTs were labeled either by injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the cerebellar nuclei or by intra-axonal injection of HRP after electrophysiological identification. By using two series of 133 and 73 serial sections, mutual relationships between 43 WGA-HRP-labeled CTs and their postsynaptic structures were analyzed based on their synaptic specializations and shapes of synaptic vesicles. Thirty-nine of these CTs formed a synapse with one TCN dendrite, whereas only four CTs formed synapses with two TCN dendrites. These CTs also synapsed on dendrites containing pleomorphic synaptic vesicles (presynaptic dendrites). Single CTs synapsed on 0-6 presynaptic dendrites (2.2 +/- 1.5, N = 43) through their whole extents, and about 40% of these presynaptic dendrites that were contacted by CTs established synaptic contacts with the same TCN dendrites on which the CTs synapsed. Thus, a CT, a presynaptic dendrite, and a TCN dendrite formed a triadic arrangement. Triadic arrangements were identified in approximately 60% of these 43 CTs. However, they rarely had a glomerulus-like appearance, as described previously in the ventral lateral nucleus and other main thalamic relay nuclei. In another series of 83 and 43 serial sections along dendrites of TCNs, observations were focused on the triadic arrangement. Triadic arrangements were located evenly on the primary and secondary dendrites of TCNs. Computer-assisted three-dimensional reconstructions were made on one WGA-HRP-labeled CT and two intra-axonally labeled CTs (a bouton en passant and a bouton terminal) with their surrounding neuronal elements, and complex spatial arrangement of neuronal processes became obvious. These results provide the quantitative assessment of synaptic arrangements among CTs, presynaptic dendrites, and TCN dendrites and reveal their spatial interrelations in the cat ventral lateral nucleus.

Animals↗
PubMed2000

Ultrastructural organization of transmitters in the cat lateralis medialis-suprageniculate nucleus of the thalamus: an immunohistochemical study.

The lateralis medialis-suprageniculate nuclear (LM-Sg) complex of the cat's posterior thalamus receives a rather wide variety of inputs from diverse cortical and subcortical areas. Previous ultrastructural studies of this nucleus demonstrated the presence of four types of vesicle-containing profiles and characterized some of these as gamma-aminobutyric acid (GABA)-containing terminals (Norita and Katoh [1987] J. Comp. Neurol. 263:54-67; Norita and Katoh [1988] Prog. Brain Res. 75:109-118). The present study has extended these observations by examining the immunoreactivity (ir) of LM-Sg, with antibodies raised against aspartate (Asp), glutamate (Glu), GABA, the acetylcholine (ACh) marker, choline acetyltransferase (ChAT), and substance P (SP), by using light and electron microscopy. Neuronal somata immunopositive for the excitatory amino acids (EAAs) Asp and Glu, were of medium size. EAA-ir terminals also were of medium size and contained round synaptic vesicles; they made asymmetrical synaptic contacts with dendritic profiles. Neuronal somata immunopositive for GABA were small. GABA-positive terminals also were small and contained pleomorphic synaptic vesicles; they formed symmetrical synaptic contacts with dendritic profiles. No neurons immunolabeled for ChAT were found. Terminals immunopositive for ChAT were small and contained round synaptic vesicles; these made symmetrical synaptic contacts, asymmetrical synaptic contacts, or both, of the en passant type with dendritic profiles. SP-immunolabeled neuronal somata were not found. Immunolabeled terminals were small, contained round synaptic vesicles, and made asymmetrical synaptic contacts with dendritic profiles. ChAT-ir and SP-ir axon terminals were not expressed evenly within LM-Sg. This difference in distribution suggests that within the LM-Sg, there may be a difference in specific sensory processing functions which correlate with transmitter type.

Animals↗