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PubMed1992

Projections from the laterodorsal nucleus of the thalamus to the limbic and visual cortices in the rat.

The laterodorsal nucleus (LD) of the thalamus is an important source of thalamic afferents to the limbic cortex, but the topography and lamination of these projections has not been investigated in detail. Using the anterograde transport of Phaseolus vulgaris leucoagglutinin and Fluoro-Ruby, the present study demonstrates that in the rat, LD projects to infraradiata, precentral agranular, retrosplenial, visual (area 18b), subicular, and entorhinal cortices. Each subregion of LD has a distinct pattern of terminals within these cortical areas. The rostral part and the dorsalmost part of LD project densely to retrosplenial granular a (Rga) cortex, presubiculum and parasubiculum. Slightly more caudal parts of dorsal LD project primarily to the postsubiculum. More ventral parts of LD project primarily to retrosplenial dysgranular (Rdg) and retrosplenial granular b (Rgb) cortices. The projection of LD to area 18b originates from cells in the caudalmost part of LD. In each cortical region, LD terminals display distinct laminar patterns. In area 18b and the adjacent Rdg cortex, the LD terminal field is in layers I, III, and IV, but in both the Rgb and Rga cortices the terminal field is located predominantly in layer I. In the postsubiculum the LD terminals are distributed to layers I and III/IV and extend into superficial layer V; in the presubiculum and the parasubiculum the LD terminals are only in the deep layers (i.e., layers IV-VI). A small number of LD axons terminate in the deep layers (i.e., layers IV-VI) of the medial entorhinal cortex. These results indicate that each area of LD has a distinct projection to limbic and adjacent neocortex.

Afferent Pathways↗

PubMed1994

Parvalbumin immunoreactivity in the thalamus of guinea pig: light and electron microscopic correlation with gamma-aminobutyric acid immunoreactivity.

The relationship of the calcium binding protein parvalbumin (PV) with gamma-aminobutyric acidergic (GABAergic) neurons differs within different thalamic nuclei and animal species. In this study, the distribution of PV and GABA throughout the thalamus of the guinea pig was investigated at the light microscopic level by using immunoperoxidase methods. Intense PV labelling was found in all the GABAergic neurons of the reticular nucleus and in scattered GABAergic neurons in the anteroventral nucleus, whereas GABAergic interneurons in the ventrobasal and lateral geniculate nuclei were not PV labelled. At the electron microscopic level, preembedding immunoperoxidase for PV was combined with postembedding immunogold for GABA. In the ventrobasal nucleus, four types of profiles were recognized: 1) terminals with flattened vesicles and forming symmetric synapses, which were labelled with both PV and GABA and could therefore be identified as afferents from the reticular nucleus; 2) boutons morphologically similar to presynaptic dendrites of interneurons, labelled only with GABA; 3) large terminals with round vesicles and asymmetric synapses, labelled only with PV, which contacted GABAergic presynaptic dendrites in glomerular arrangements and resembled ascending excitatory afferents; and 4) terminals unlabelled by either antiserum. In the ventrobasal nucleus of the guinea pig a double immunocytochemical labelling permits therefore the differentiation of two populations of GABAergic vesicle-containing profiles, i.e., the terminals originating from reticular nucleus (that are double labelled) and the presynaptic dendrites originating from interneurons (that are GABA-labelled only). The possibility to differentiate GABAergic inputs from the reticular nucleus and from interneurons can shed light to the functional interpretation of synaptic circuits in thalamic sensory nuclei.

Animals↗

PubMed1995

Synaptic distribution of afferents from reticular nucleus in ventroposterior nucleus of cat thalamus.

This study was aimed at determining the synaptic circuitry that contributes to the alterations in thalamic function that accompany changes in behavioral states. The somatosensory sector of the thalamic reticular nucleus (RTN) was identified by microelectrode recording in cats and injected with Phaseolus vulgaris-leucoagglutinin (PHA-L). The axons of labeled RTN cells gave rise to collaterals within the RTN and continued into the dorsal thalamus where they terminated predominately in the ventral posterior lateral nucleus (VPL). After small injections in the upper limb representation of RTN, most labeled terminations in VPL were confined to its medial part, suggesting the presence of a topographic organization in the projection. Terminations were concentrated in localized, focal aggregations of boutons. Combined electron microscopic immunocytochemistry, using immunogold labeling for gamma-aminobutyric acid (GABA), showed that the PHA-L labeled boutons were GABA-positive terminals that ended in symmetrical synapses. Eighty-two percent of these synapses were on dendrites of relay neurons, 8.5% on dendrites of interneurons, and 9.3% on somata. The terminals of RTN axons form the majority of axon terminals ending in symmetrical synapses in VPL. Their concentration on relay neurons probably underlies the capacity of the RTN projection to reduce background activity of VPL relay neurons in the awake state and to maintain oscillatory behavior of these neurons in drowsiness and early phases of sleep.

Animals↗

PubMed1995

Connections between the reticular nucleus of the thalamus and pulvinar-lateralis posterior complex: a WGA-HRP study.

The present study utilises the capacity of wheat germ agglutinin-conjugated horseradish peroxidase to label both afferent and efferent projections from selected regions of the thalamic reticular nucleus (TRN) to the pulvinar lateralis-posterior complex (Pul-LP) of the cat. Fourteen injections into the TRN located between anterior-posterior levels 8.5 and 4.5 were analysed. The projection of the TRN to the Pul-LP complex is roughly organised in a topographic manner and is not widespread within the thalamus. Anterograde labelling in the Pul-LP extended rostrocaudally with a slight oblique dorsoventral orientation. Projections to the medial LP were predominantly but not exclusively from rostral areas of TRN, while projections to the lateral LP were largely from caudal areas of the TRN. Projections to other areas of the Pul-LP were sparse. The connections between TRN and Pul-LP were reciprocal, although the distribution of labelled cells and anterograde labelling was not completely overlapping. Reciprocal connections with the dorsal lateral geniculate nucleus were largely with the C-laminae and the medial interlaminar nucleus. The results are discussed with reference to the corticothalamic projections and the visuotopy of the Pul-LP.

Animals↗

PubMed1992

Isomorphic activation of astrocytes in the somatosensory thalamus.

Structural recovery in the rat somatosensory thalamus after the loss of one of its major inputs provided a model for studying the changes in astrocytes associated with reactive synaptogenesis. The temporal separation of the initiation of Wallerian degeneration and reactive synaptogenesis permitted astrocytic changes to be correlated either with the removal of degeneration, early in the recovery sequence, or with synaptogenesis, later in recovery. Over a period of post-lesion times ranging from 3 days to 13.5 months, GFAP-positive astrocytic fibers were quantified and the population density of S-100-positive astrocytic cell bodies was determined in the ventral posterolateral nucleus (VPL). The relative area of astrocytic cell bodies was measured at an early peak of the increased GFAP immunoreactivity (4-5 days post-lesion). The normal side of VPL (c-VPL) was compared to the deafferented side of VPL (d-VPL) and the ratio d-VPL/c-VPL was determined. Astrocytes in d-VPL underwent a minimal isomorphic activation with little or no hypertrophy or proliferation but with a large increase in GFAP immunoreactivity. Prior to the initiation of synaptogenesis, there was a decrease both in GFAP immunoreactivity and in the population density of VPL astrocytes. The decreases in the recovery curves suggested that a suppression of the influence of astrocytes may have been important for sprouting and/or synaptogenesis. In other systems, where synaptogenesis was initiated early in the recovery sequence, the suppression of astrocytes that was related to synaptogenesis may have been masked by astrocytic changes related to the removal of degeneration.

Afferent Pathways↗

PubMed1987

Collateral projections from trigeminal sensory nuclei to ventrobasal thalamus and cerebellar cortex in rats.

The retrograde fluorescent labeling technique reveals that trigeminal projections to the ventroposteromedial nucleus of the thalamus (VPM) of the rat originate from the main sensory nucleus (MSN) of the trigeminal and subnuclei interpolaris (V1) and caudalis (Vc) of the spinal trigeminal nucleus. These projections are predominantly contralateral; however, the presence of a few ipsilateral labeled cells in MSN suggests an uncrossed trigeminothalamic pathway. Trigeminocerebellar fibers projecting to the paramedian lobule (PML) of the cerebellar cortex are located in Vi and caudal subnucleus oralis (Vo). This is principally an ipsilateral pathway, but several bisbenzimide-labeled cells are present in contralateral Vi. The most notable finding occurred after paired injections of Evans Blue into VPM and bisbenzimide into PML, demonstrating neurons in Vi with divergent projections to both structures. The presence of this type of projection was not found in mice (Steindler: J. Comp. Neurol. 237:155-175, 1985) and has not been reported in other species.

Afferent Pathways↗

PubMed1980

Characterization of unit activity recorded from septum, thalamus, and caudate following incremental opiate treatment.

The effects of a wide range of morphine doses and of its antagonist, naloxone, on spontaneous multiunit discharges in freely moving rats were recorded simultaneously from the septum (Spt), medial thalamus (CM-PF complex), and caudate nucleus (CN). A high percentage of neurons in these three areas are affected by morphine. Neurons in the CM-PF complex exhibited a greater number of morphine-induced changes (104/145) than did those in the caudate nucleus (79/160), or in the septum (67/150). The morphine-induced changes exhibited dose-related patterns: the three structures examined in the present study exhibited four response patterns to incremental doses of morphine: either a monophasic effect, an increase or decrease in firing rate, or a biphasic effect; ie, lower morphine doses induced a decrease in activity, whereas higher doses induced an increase in firing rate. There was no observed correlation between the response patterns in the three regions. The technique provides a tool with which to identify and classify the specific response patterns induced by morphine in specific brain regions, and the results may indicate that each region plays a different physiological role in the effects induced by morphine.

Animals↗

PubMed2002

Intracortical inhibition is reduced in a patient with a lesion in the posterolateral thalamus.

We describe a patient who developed a complex movement disorder following an ischemic lesion in the right posterolateral thalamus. Transcranial magnetic stimulation showed a shortening of the cortical silent period and deficient cortico-cortical inhibition using paired magnetic pulses on the affected side, indicating reduced effectiveness of intracortical inhibitory mechanisms.

Adult↗

PubMed1996

Effect of stimulation in the ventral intermediate nucleus of the thalamus on limb control in Parkinson's disease: a case study.

This study focuses on upper extremity strength and movement control in a patient with Parkinson's disease who had stimulating electrodes surgically implanted in the ventral intermediate nucleus (VIM) of the left thalamus. We examined torque generation and control of movement distance in single degree-of-freedom elbow movements under three different stimulation conditions: (a) no stimulation, (b) high stimulation, in which tremor was minimized but there was also tingling and perceived weakness, and (c) moderate stimulation, in which tremor was partially reduced, but there was also a subjective sense of increased strength compared with the high-stimulation condition. The patient's ability to generate both steady torque and rapid movements was poorest with no stimulation. The patient generated the largest torques with moderate stimulation and performed the fastest movements with high stimulation. However, even with tremor minimized, the patient's electromyogram (EMG) burst patterns were not typical of those of neurologically healthy subjects, although the movements were clearly improved.

Elbow↗

PubMed2005

Macroscopic orientation component analysis of brain white matter and thalamus based on diffusion tensor imaging.

Diffusion tensor imaging (DTI) can delineate white matter architecture based on fiber orientation. The purpose of this paper is to use the orientation information contained in DTI to study axonal organization of the brain both macroscopically and quantitatively. After performing gray/white matter segmentation using a fractional anisotropy threshold, the white matter can be further decomposed into components composed of tracts oriented along three orthogonal anatomic axes (right-left, superior-inferior, and anterior-posterior). For each component, the volume and MR parameters were quantified. To characterize the axonal architecture of the brain, this technique was applied to the entire brain using a Talairach-based brain parcellation method and to the thalamus by manual segmentation. Reproducibility of this analysis tool was examined by repeating the measurements in the same subject, and individual differences were appreciated from the data acquired in 11 healthy volunteers. Based on the results from these preliminary data sets, this new analysis technique is expected to be an effective tool for macroscopic white matter characterization.

Adult↗

PubMed1993

Temporal patterning of song production: participation of nucleus uvaeformis of the thalamus.

Birdsong is a learned vocal behavior used in intraspecific communication. The motor pathway serving learned vocalizations includes the forebrain nuclei NIf, HVC, and RA; RA projects to midbrain and brain stem areas that control the temporal and acoustic features of song. Nucleus Uvaeformis of the thalamus (Uva) sends input to two of these forebrain nuclei (NIf and HVC) but has not been thought to be important for song production. We used three experimental approaches to reexamine Uva's function in adult male zebra finches. (1) Electrical stimulation applied to Uva activated HVC and the vocal motor pathway, including tracheosyringeal motor neurons that innervate the bird's vocal organ. (2) Bilateral lesions of Uva including the dorso-medial portion of the nucleus affected the normal temporal organization of song. (3) Chronic multiunit recordings from Uva during normal song and calls show bursts of premotor activity that lead the onset of some song components, and also larger bursts that mark the end of complete song motifs. These results implicate Uva in the production of learned vocalizations, and further suggest that Uva contributes more to the temporal structure than to the acoustic characteristics of song.

Animals↗

PubMed1995

Acoustic response properties of single neurons in the central posterior nucleus of the thalamus of the goldfish, Carassius auratus.

Acoustic responses were recorded extracellularly from single neurons in the thalamic central posterior nucleus (CP). Spontaneous activity, best sensitivity, and sharpness of tuning (Q10dB) of CP neurons ranged from 0 to 36 spikes/s, -40 to 5 dB re: 1 dyne/cm2, and 0.18 to 1.80, respectively. The distribution of characteristic frequency (CF) was nonuniform with a mode at 195 Hz. Temporal response patterns of CP neurons (N = 60) were categorized into three groups: phasic (25%), tonic chopper-like (22%), and tonic nonchopper-like (53%) on the basis of peri-stimulus time and inter-spike interval histograms. Most CP neurons (90%) did not phase-lock to tones, and none phase-locked strongly. The properties of CP neurons are similar to those of the midbrain torus semicircularis neurons in spontaneous rates, best sensitivities, nonuniform CF distributions, and in exhibiting level-independent best frequencies. Both CP and toral neurons show a diversity of response patterns resembling those found in the mammalian central auditory system. However, CP neurons have broader tuning and less phase-locking than toral neurons, suggesting different roles in auditory processing. While peripheral frequency analysis is enhanced at the midbrain level, the integration of frequency-selective channels in the thalamus may function in the processing of wideband spectra characteristic of natural sound sources.

Acoustic Stimulation↗

PubMed1991

Response properties of periodontal mechanosensitive units in the cat's thalamus.

1) The response characteristics of periodontal mechanosensitive neurons in the thalamic nucleus were studied by using 15 adult cats anesthetized with alpha-chloralose (40 mg/kg, i.v.). 2) 468 periodontal mechanosensitive units (PM units) responsive to light mechanical stimulation of the teeth were recorded from a medioventral aspect of the nucleus ventralis posteromedialis (VPM). Of these neurons, 213 units (45.5%) were slowly adapting, and 255 units (54.5%) were rapidly adapting. 3) The receptive field of the PM units was represented by the number of receptive quadrants on the dental arches of both jaws. About half of the PM units (279, 59.6%) were one-quadrant units. Of these neurons, 69 (14.7%) were single tooth units. Two-quadrant, three-quadrant and four-quadrant units numbered 123 (26.3%), 3 (0.6%) and 63 (13.5%) respectively. Of the PM units detected, 246 units (52.6%), 124 units (26.4%) and 98 units (20.9%) responded to mechanical stimulation of the teeth on only the contralateral side, on only the ipsilateral side and on both sides, respectively. 4) One-quadrant units were distributed mainly in the rostral part of the PM area, and four-quadrant units were found in the caudal part of the PM area. A somatotopic organization for each tooth was not found. 5) The incidence of single tooth units in the thalamus was extremely low, compared with those in the primary afferents and in the trigeminal nuclear complex. Most of the thalamic neurons had larger receptive fields than both the primary afferents and the trigeminal nuclear complex neurons. 6) The high incidence of four-quadrant units at the caudal part of the PM area suggests that many PM fibers converge there. However, it is still unclear whether these fibers come through the intrathalamic neurons or directly from the trigeminal nuclear complex.

Animals↗

PubMed1989

Tachykinin immunoreactivity in terminals of trigeminal afferent fibers in adult and fetal monkey thalamus.

Immunocytochemistry of fetal and adult monkey thalamus reveals a dense concentration of tachykinin immunoreactive fibers and terminals in the dorsolateral part of the VPM nucleus in which the contralateral side of the head, face and mouth is represented. The immunoreactive fibers enter the VPM nucleus from the thalamic fasciculus and electron microscopy reveals that they form large terminals resembling those of lemniscal axons and terminating in VPM on dendrites of relay neurons and on presynaptic dendrites of interneurons. Double labeling strategies involving immunostaining for tachykinins after retrograde labeling of brainstem neurons projecting to the VPM failed to reveal the origin of the fibers. The brainstem trigeminal nuclei, however, are regarded as the most likely sources of the VPM-projecting, tachykinin positive fibers.

Amidines↗

PubMed1984

Perioral biting reflex and turning after intranigral injection of a GABA- or metenkephalin-agonist: role of the thalamus and superior colliculus.

Unilateral destruction of the ventromedial thalamus (VMT) with a radiofrequency lesion attenuated turning induced by injection of muscimol (40 ng/0.4 microliter) but not of a metenkephalin-analogue (DAME; 2.5 micrograms/0.4 microliter) into the substantia nigra, pars reticulata (SNR). Unilateral lesions in the deep layers of the superior colliculus (DLSC) attenuated both muscimol- and DAME-induced turning. Lesions in the DLSC but not in the VMT blocked the sensitization of the perioral biting reflex by injection of muscimol or DAME into the SNR on the same side of the lesion. When injected with apomorphine (0.5 mg/kg) all rats with lesions turned ipsiversive to the lesion side and reacted to tactile stimulation of the perioral area on both sides with orienting towards and then biting into the stimulus probe.

Animals↗

PubMed1985

Combined lesions of septum, amygdala, hippocampus, anterior thalamus, mamillary bodies and cingulate and subicular cortex fail to impair the acquisition of complex learning tasks.

Previous investigations (Irle and Markowitsch 1982a, 1983, 1984) demonstrated that triple or fourfold lesions within the cat's limbic system fail to produce learning impairments, as opposed to lesions of single or double loci, when tasks of visual reversal, delayed alternation, and active two-way avoidance were used. On the basis of these results, limbic regions of the cat's brain might be considered unessential for intact learning and mnemonic functions. Therefore, in order to obtain indisputable information on the importance of the limbic system for learning and memory, lesions of nearly all limbic core regions of the cat were performed. Ten cats received lesions of seven limbic core regions: the septum, amygdala, anterior thalamus, mamillary bodies, cingulate cortex, subicular cortex, and the hippocampus proper. Nine of these animals were tested postoperatively in the acquisition of a visual reversal task, a spatial alternation and delayed alternation task, and an active two-way avoidance task, and were then compared to the performance levels of ten control animals. The experimental animals turned out to be unimpaired in all tasks tested; the performance scores in the visual reversal and delayed alternation task and - for some experimental animals - in the active two-way avoidance task even indicate a slight, though statistically insignificant, facilitation in the learning behavior of these animals. It is assumed that the learning functions underlying the tasks used were taken over by other brain regions, which, prior to massive limbic lesions, may be suppressed or otherwise inhibited. Alternatively, utilization of spared tissue in the damaged limbic regions must be considered as the possible explanation.

Amygdala↗

PubMed1984

The distribution of the projection from the parataenial nucleus of the thalamus to the nucleus accumbens in the rat: an autoradiographic study.

In this study the intrastriatal distribution of afferents arising from the parataenial nucleus of the thalamus was investigated. Tritiated leucine and proline injected into the parataenial nucleus was found to densely label the entire anterior-posterior extent of the medial nucleus accumbens. The projection was for the most part limited to this striatal subregion, although some moderate labelling was found along the medial wall of the anterior caudateputamen . The terminal labelling within accumbens was characterized by a distinct patchiness . Other efferent connections of the parataenial nucleus observed in this study include the thalamic reticular nucleus, the basolateral and central nuclei of the amygdala, the septum, the medial frontal cortex, the entorhinal cortex and subiculum. This projection is distributed to the "limbic afferented " sector of striatum, and there is a nearly complete overlap between the parataenial afferents and those coming from hippocampus. The present findings suggest that the parataenial nucleus is an important thalamic link between limbic and striatal processing.

Afferent Pathways↗

PubMed1978

The mole of pallido-thalamic transmission investigated with intracellular recording from cat thalamus.

Pallido-thalamic transmission was studied by intracellular recording from neurons in the ventrolateral (VL) and ventroanterior (VA) nuclei of the thalamus in cats anesthetized with pentobarbital. Stimulation of the entopeduncular nucleus (ENT) produced short latency, inhibitory postsynaptic potentials in the VL-VA neurons (1.60 ms on average). When stimuli were applied closer to the VL-VA region along the pallido-thalamic pathway, i.e., to the rostral Forel's field, the IPSP latency was significantly reduced. Linear regression analysis of the IPSP latency against conduction distance between different stimulating the recording positions indicated that the IPSP was produced through a monosynaptic pathway at a conduction velocity of 5 to 11 m/s. The neurons which received IPSPs from the ENT distributed in the rostromedial VL and in the rostral VA, whereas relay cells responding only to the contralateral brachium conjunctivum were found in the caudal VL and in the dorsolateral portion of the rostral VL-VA complex. Reciprocal convergence of pallidal and cerebellar impulses were observed in only a small number of cells, which were located in the border between the two neuron groups. Recording of extracellular field potentials and focal stimulation within and around the rostral VL also indicated that the fiber potentials arose from the ENT nucleus and propagated along a bundle of fibers which terminated within the rostromedial VL-VA complex. These results are all explicable by assuming that the entopeduncular neurons are inhibitory in nature and so inhibit thalamic neurons monosynaptically.

Animals↗