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PubMed1993

Fine structure of calcitonin gene-related peptide immunoreactive synaptic contacts in the thalamus of the rat.

Recent studies have shown a prominent calcitonin gene-related peptide immunoreactive (CGRP-ir) pathway extending from the external medial and external lateral para-brachial nuclei to the area surrounding and including the gustatory nuclei in the thalamus, and the cortex and amygdala. The function of the CGRP-ir pathway is not completely understood, but may be involved with the processing of both nociceptive and gustatory information in the thalamus. The purpose of this study was to characterize the nature of the CGRP-ir synaptic contacts in the gustatory nucleus. Electron microscopic examination of CGRP-ir synaptic contacts revealed two classes of CGRP-ir terminals. One class, which was large, formed asymmetric synaptic contacts on dendritic appendages, had many small, round synaptic vesicles, and heavy patches of reaction product which obscured any underlying organelles. Since similar terminals in unstained tissue contained large numbers of dense-cored vesicles, it was concluded that CGRP-ir was contained predominantly in dense-cored vesicles. A second class of CGRP-ir terminals was smaller and made either asymmetric or symmetric synaptic contacts. Both symmetric and asymmetric small terminals contained small, round synaptic vesicles and fewer patches of dense reaction product. Several of the CGRP-ir terminals making symmetric contacts also contained pleomorphic vesicles. There were very few contacts on cell bodies. There were no contacts on other CGRP-ir elements, somal or dendritic, or on axon terminals. None of the CGRP-ir terminal elements were postsynaptic to unlabeled terminals. Axons containing CGRP-ir were primarily unmyelinated, but a few myelinated axons were also seen.

Animals↗
PubMed1993

Experimentally induced visual projections to the auditory thalamus in ferrets: evidence for a W cell pathway.

We have previously reported that following specific neonatal brain lesions in ferrets, a retinal projection is induced into the auditory thalamus (Sur et al., Science 242:1437, '88). In these "rewired" ferrets, a novel visual pathway is established through auditory thalamus [the medial geniculate nucleus (MGN)] and primary auditory cortex (A1); cells in both MGN and A1 are visually responsive and exhibit properties similar to those of visual cells in the normal visual pathway. In this paper, we use three approaches--physiological, anatomical, and developmental--to examine which of the retinal ganglion cells project to the MGN in these rewired ferrets. We find that: 1) physiological response properties of postsynaptic visual cells in the MGN are W-like; 2) retinal ganglion cells back-filled from the MGN are small and similar to soma sizes of subsets of the normal retinal W cell population; and 3) subpopulations of these small cells can be preferentially rerouted to the MGN in response to different surgical manipulations at birth, consistent with differential W cell projection patterns in normal animals. These data suggest that retinal W cells come to project to the MGN in rewired animals. These findings not only provide a basis on which to interpret functional properties of this novel visual pathway, but also provide important information about the developmental capabilities of specific retinal ganglion cell classes and the regulation of their projections by target structures in the brain during development.

Animals↗
PubMed1993

The organization of projections from the mediodorsal nucleus of the thalamus to orbital and medial prefrontal cortex in macaque monkeys.

The organization of interconnections between the mediodorsal nucleus of the thalamus (MD) and the orbital and medial prefrontal cortex and the agranular insular cortex in the monkey was studied by retrograde and anterograde tracing techniques. In addition to the magnocellular and parvicellular divisions of MD, three other subdivisions can be recognized on the basis of myeloarchitecture, cytoarchitecture, and connections. The first two of these represent a parcellation of the magnocellular division into a lateral, fiber-rich MD pars fibrosa and a medial, poorly myelinated MD pars paramediana adjacent to the midline. The third is a small, poorly myelinated area located at the caudomedial and dorsal edges of MD; it is referred to as MD pars caudodorsalis. MD pars fibrosa is reciprocally interconnected primarily with areas 11, 12 and 13 in the central and lateral part of the orbital cortex. There is a general organization within this projection, with the rostrocaudal axis of the cortex represented from dorsal to ventral in the pars fibrosa, and the mediolateral cortical axis represented from medial to lateral. Cells that project to area 12 also extend laterally into the adjacent pars parvicellularis. MD pars paramediana is more heavily interconnected with the caudal and medial portions of the orbital region, particularly the agranular insular areas and the caudal parts of areas 13 and 14. Cells that project to two caudal areas, 13a and Iad, do not fit with the general organization, in that they are located in the dorsomedial parts of the pars fibrosa and pars paramediana, where they overlap with cells that project to area 14. The pars fibrosa and pars paramediana receive inputs from areas of the ventral forebrain such as the amygdala, piriform (olfactory) cortex, and entorhinal cortex, which project directly to the orbital and agranular insular cortex, as well as from the ventral pallidum. MD pars caudodorsalis is reciprocally interconnected with areas 14, 24, and 32 on the medial surface of the prefrontal cortex. In this part of the nucleus the dorsoventral axis of the medial prefrontal cortex is represented from caudal to rostral in the thalamus. The amygdala and other ventral forebrain structures do not send fibers into the pars caudodorsalis, even though some of these structures project directly to the medial prefrontal cortex. Ventral to MD, and separated from it by the internal medullary lamina, a small region was recognized that appears to be comparable to the anteroventral part of the submedial nucleus previously defined in the rat and cat.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Functional anatomy of the thalamus in the blind mole rat Spalax ehrenbergi: an architectonic and electrophysiologically controlled tracing study.

The occipital cortex of the naturally blind mole rat, Spalax ehrenbergi, is occupied by an area of somatosensory representation. To date, no visual cortex has been identified electrophysiologically. In order to determine whether there are corresponding modifications in the thalamus, thalamocortical connections were studied with neuroanatomical tracing methods. Three different fluorescent tracers were injected under electrophysiological control into distinct cortical areas. Injections into the somatosensory head/face and hindlimb/trunk areas of representation revealed a posteromedial ventral nucleus and a posterolateral ventral nucleus, respectively. Additional somatotopic labeling was found in an area dorsomedial to the two ventral nuclei. This structure may be equivalent to the posterior nuclear complex in the laboratory rat. Injections into the auditory cortex of the mole rat resulted in labeling of the medial geniculate body. In contrast to the situation in the laboratory rat, in which a prominent dorsolateral geniculate body and a ventrolateral geniculate body assume dorsolateral positions, the somatosensory thalamus of the mole rat almost reaches the dorsolateral surface. This finding is corroborated by the results of the architectonic study, which failed to reveal a differentiated lateral geniculate body. Our observations suggest that the thalamocortical visual system in the mole rat is minute, whereas the somatosensory system is expanded. This situation fits the mode of life of this subterranean animal, for which touch is more important than vision.

Animals↗
PubMed2002

Reaction time is not impaired by stimulation of the ventral-intermediate nucleus of the thalamus (Vim) in patients with tremor.

We studied the effect of high-frequency electrical stimulation of the ventral-intermediate nucleus of the thalamus (Vim) in four patients implanted with chronic stimulators to determine whether this procedure adversely affects reaction time to a proprioceptive stimulus. Two patients had undergone this surgery for treatment of tremor resulting from Parkinson's disease insufficiently responsive to levodopa therapy and two patients for treatment of essential tremor. Reaction times to auditory, visual, cutaneous, and proprioceptive stimuli were tested in a simple motor task requiring flexion of the elbow joint to a visual target in response to each stimulus. Reaction times were tested postoperatively with and without the stimulator turned on. We found that reaction time for all stimulus modalities was not increased when the stimulator was turned on; in fact, reaction times were, on average, slightly shorter during stimulation, but this difference was not statistically significant. We conclude that transmission of somatosensory inputs, necessary for initiating voluntary movement, from the periphery to the cortex is not significantly impaired by stimulation of the ventral-intermediate nucleus of the thalamus in patients with pathological tremor.

Aged↗
PubMed2006

The paraventricular nucleus of the thalamus as an interface between the orexin and CART peptides and the shell of the nucleus accumbens.

The paraventricular nucleus of the thalamus (PVT) receives afferents from the brainstem and has been thought to relay arousal related information to specific limbic forebrain areas, including the nucleus accumbens. More recent anatomical observations suggest that the PVT also receives afferents from various hypothalamic nuclei. The present anatomical experiments investigated the innervation of the PVT by fibers immunoreactive for orexin and cocaine and amphetamine related transcript (CART), two feeding-related peptides highly concentrated in the hypothalamus. Emphasis was placed on identifying the relationship between these neuropeptides and PVT neurons projecting to the shell of the nucleus accumbens (NacSh). Infusion of a retrograde tracer into the NacSh labeled numerous cells of the midline and intralaminar thalamus, most of which were restricted to the PVT. The retrograde tracer, orexin fibers, and CART fibers were immunopositive throughout the entire PVT whereas no overlap between signals was evident within adjacent thalamic regions. High-magnification light and confocal microscopy showed that both orexin and CART fibers made frequent contact with retrogradely labeled neurons throughout the anteroposterior PVT. Furthermore, single PVT cells retrogradely labeled from the NacSh were apposed by both orexin and CART fibers. The present experiments provide the first evidence suggesting a role for the PVT as a relay of hypothalamic activity to the nucleus accumbens. The PVT may function to link visceral arousal signals with limbic regions involved in behavioral responses.

Animals↗
PubMed1994

Rostral reticular nucleus of the thalamus sends a patchy projection to the pulvinar lateralis-posterior complex of the cat.

The pulvinar lateralis posterior complex (Pul-LP) and the reticular nucleus of the thalamus (RE) are thought to be involved in visual and attention-related tasks. This report provides data on the anatomical connections between these two nuclei following the analysis of injections of horseradish peroxidase (HRP) + [3H]leucine into the Pul-LP and RE of the cat. Following the retrograde transport of HRP from the Pul-LP, labeled cells were distributed in regions of the RE ventral to the caudate nucleus and adjacent to the stria terminalis between Horsley-Clarke anterior-posterior (AP) coordinates 13.0 and 9.5 and more caudally in areas dorsal and ventral to the lateral geniculate nucleus (LGN) between AP 9.0 and 4.5. The majority of the cell labeling within the RE following injections within the Pul-LP was seen dorsal to the lateral geniculate nucleus around AP 6.5-6.0. Cell labeling was heaviest following injections within the lateral LP in contrast to injections within the Pul which resulted in fewer labeled cells. Autoradiographic analysis of the anterograde transport of leucine showed that the labeled Pul-LP fibers within the RE did not completely coincide with the distribution of HRP-labeled reticular cells from the same injection site. This indicated a lack of strict reciprocity between these two nuclei. In addition, injections of [3H]leucine into dorsomedial areas of the RE near the rostral pole of the LGN resulted in a patchy distribution of label within the Pul-LP which was most prominent as oblique dorsoventral slabs across the thalamus. It was inferred that this distribution was along the borders between different subdivisions within the Pul-LP. The lack of strict reciprocity between the thalamic relay nuclei and the reticular nucleus implies that areas of the Pul-LP may receive inhibition from RE regions which they do not directly influence; this anatomical feature may provide a basis for selective inhibition of thalamic nuclei.

Animals↗
PubMed1985

The distribution and topographical organization in the thalamus of anterogradely-transported horseradish peroxidase after spinal injections in cat and raccoon.

The distribution of anterogradely-transported horseradish peroxidase (HRP) was examined in the rostral mesencephalon and thalamus of cats and raccoons that had received injections of HRP in the cervical and/or lumbosacral enlargements of the spinal cord. Labeling was consistently observed in a large number of loci. All regions previously identified as targets of spinomesencephalic or spinothalamic fibers were included. Evidence of topographical organization was obtained in several regions. Adjacent fields of labeling were often separable on the basis of the distribution, appearance and topographical organization of the labeling. Subject to the methodological constraints imposed by the possibilities of transneuronal and/or collateral labeling, we conclude that a wide variety of loci in the thalamus receive direct spinal input. The organization of these projections suggests that each terminal region may be associated with different aspects of spinal cord function.

Animals↗
PubMed1982

Connections of the hippocampal formation, mamillary bodies, anterior thalamus and cingulate cortex. A retrograde study using horseradish peroxidase in the cat.

The afferent projections to, and the interconnections between, four structures of the so-called limbic system were investigated in the cat. The retrograde horseradish peroxidase (HRP) technique was used to trace the origins of fibers projecting to each of these four loci. Particular emphasis was laid on tracing cortical afferents of these regions. Four injections were performed in the dorsal and two in the ventral subicular regions; six were centered within the mamillary nuclei, four within the anterior thalamic nuclei, and three within the cingulate gyrus. For each region, a number of projections were found which had apparently not been described before, at least not for the cat: For injections into the subicular regions, a hitherto unknown number of cortical afferents was detected, including labeled cells in the prefrontal and premotor fields and from large areas within the posterior parietal, temporal and occipital cortex (i.e., sensory and sensory integration cortex); numerous neurons were labeled in the anterior nuclear group of the thalamus. Injections of HRP into the mamillary nuclei revealed, aside from a strong projection from the subicular regions, frontocortical and cingulate projections to the mamillary nuclei; the mamillary nuclei also received subcortical projections from the septum, the diagonal band of Broca and from the periaqueductal gray. Following injections into the anterior thalamic nuclei, labeled cells were found in the prefrontal cortex, and to a lesser extent in lateral parts of the cortical hemisphere; subcortically, the mamillary nuclei received connections from hypothalamic areas, the periaqueductal gray, the diagonal band of Broca and the claustrum. Cingulate injections labeled cells in temporal and parietal cortical areas, in the subicular region, and also in the periaqueductal gray. Our findings reveal that each of the four injected areas receives a large number of afferents from divergent regions of the brain; of these, a considerable number is shared by each of the four injection loci. Furthermore, the present results reveal that the subiculum, the mamillary bodies, and the anterior thalamus are more strongly interconnected than previously assumed.

Afferent Pathways↗
PubMed1986

Neural correlates of isometric force in the "motor" thalamus.

The relationship between single cell activity in the "motor" thalamus and the generation of isometric force between the fingers has been investigated in 2 monkeys. Neurons related to the task were found in the thalamic motor regions VLo, VPLo, and VA where microstimulation occasionally elicited motor reactions in hand and fingers. 58% of these 55 neurons, designated "typical", showed modulation of their discharge patterns with force similar to neurons in precentral cortex and could be assigned to one of 5 discharge patterns described for the motor cortex. Only a small percentage of the thalamic neurons were found to have phasic activity. The other "atypical" neurons (42%) had discharge patterns with complex sequences of phasic and tonic activation with respect to force. For 18 typical and atypical neurons with tonic and phasic-tonic modulation of their firing rate with force significant regression coefficients between firing rate and static force were observed. The mean index of force sensitivity (rate-force slope) was 54.5 Hz/N for the neurons increasing their discharge rate with force, i.e. approximately that of precentral cells. Neurons tested for their sensory properties had receptive fields located on hand and/or fingers and were activated mainly by stimulation of muscle and joint receptors. The characteristics of these thalamic neurons are compared to those of precentral cells recorded under identical experimental conditions and are discussed in relation to the known input-output relationships of the motor thalamic nuclei. The data strongly support the hypothesis that parameters of movement, in particular force are represented by the activity of neurons in the "motor" thalamus.

Animals↗
PubMed1986

Projection of tooth pulp afferents to the thalamus of the cat. I. Focal potentials and thalamocortical connections.

Electrical stimulation of tooth pulp afferents in cats evoked short latency focal potentials in the basal ventromedial nucleus of thalamus (VMB), in the border zone between this nucleus and the arcuate nucleus of the ventrobasal complex (VBA), and in the marginal zone of VBA and the external nucleus of the ventrobasal complex (VBX). No responses were found in the centre of VBA and VBX. Very few responses were found in the intralaminar region. The projection from the tooth pulps was bilateral, but the best responses following stimulation of the ipsi- and the contralateral tooth pulps could be evoked at slightly different locations within VMB. The mean latency of the responses was shorter following stimulation of the contralateral tooth pulp than following stimulation of the ipsilateral one. Electrical stimulation in VMB, VBA, and VBX evoked focal potentials in thalamocortical projection fibres, which were recorded from in the white matter below areas SI and SII after decortication by suction. Conditioning stimulation of the tooth pulps suppressed these responses within 200 ms if the stimulating electrode was placed at the border between VBA and VMB, suggesting that tooth pulp stimulation activates a thalamocortical projection with a postexcitatory inhibition. Finally, lesions were made in the thalamus and their effects were checked on the cortical responses to tooth pulp stimulation. If the lesion included the region of VMB bordering to VBA the cortical responses decreased in amplitude. It is concluded that VMB and the borderzone between VMB and VBA are important relays between the nociceptors of the tooth pulp and the sensory cortex.

Animals↗
PubMed1982

Pallidofugal projections to thalamus and midbrain: a quantitative antidromic activation study in monkeys and cats.

The projections of monkey medial globus pallidus (and of cat entopeduncular nucleus) to thalamus and midbrain were studied with antidromic activation in order to determine the number of pallidal neurons sending axonal branches to the two sites. The animals were anesthetized with pentobarbital and several movable electrodes were used to stimulate the thalamic nuclear complex ventralis anterior - ventralis lateralis (VA-VL), the nucleus "centre médian" (CM), and the midbrain nucleus tegmenti pedunculopontinus (TPP). The responses of pallidal neurons were recorded with extracellular microelectrodes. In 3 monkeys 99% and 87% of 145 medial pallidal neurons responded antidromically to stimulation of VA-VL and TPP respectively. Reciprocal collision tests demonstrated that 86% of the 145 neurons sent axonal branches to the two sites. By comparison in 2 cats the tests demonstrated that 72% of 46 entopeduncular neurons branched to VA-VL and TPP. In 2 monkeys 68% of 53 medial pallidal neurons were shown to branch to VA-VL and CM thalamic nuclei. In the monkeys, the latencies of responses indicate that all pallidofugal fibers have the same mean conduction rate: 6 m/s. The fibers appear to branch profusely in VA-VL where less current was required to activate neurons antidromically than in TPP. The location of neurons in the medial pallidum is weakly correlated with the location of stimulation points in VA-VL activating the neurons antidromically at low threshold, suggesting some topography in the pallidothalamic projection. However there is no particular localization of medial pallidal neurons with and without branching projections. Apart from one exception, the 162 neurons recorded in the lateral pallidum failed to respond antidromically to the stimulation sites. We conclude that the great majority of medial pallidal neurons can send signals to both the thalamus and the midbrain in the cat and in the monkey.

Animals↗
PubMed1989

Function of non-NMDA receptors and NMDA receptors in synaptic responses to natural somatosensory stimulation in the ventrobasal thalamus.

Sensory synaptic responses of rat ventrobasal thalamus neurones were challenged with iontophoretic applications of the excitatory amino acid antagonists CNQX and CPP. CNQX, applied with currents which were selective for non-NMDA receptors, antagonised responses of VB neurones to both 10 ms and 2000 ms air jet stimulation of the peripheral receptive field. In contrast, CPP only antagonised the latter type of response. These results suggest a differential involvement of excitatory amino acid receptors in sensory synaptic transmission to the ventrobasal thalamus, with an initial synaptic component being mediated by non-NMDA receptors (including kainate receptors), and a further NMDA receptor-mediated component being manifested upon maintained sensory stimulation. The expression of this latter component appears to be largely dependent upon the integrity of the non-NMDA receptor-mediated component.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1989

Motor learning in monkeys (Macaca fascicularis) with lesions in motor thalamus.

The study examines the nature of the influence that the basal ganglia exert on frontal cortex via the motor nuclei of the thalamus. Twelve monkeys were trained to pull a handle given one colour cue and to turn it given another. Bilateral lesions were then placed in the ventral thalamus. Four monkeys with large anterior lesions including the VA nucleus and the anterior part of VLo were severely impaired at relearning the task. Monkeys with small lesions in VAmc or with lesions centred on VLo were not impaired. The analysis of the histology suggests that the impairment in the four monkeys did not result from involvement of the cerebellar relay through nucleus X. It is argued that the animals are not impaired because of faulty execution. This suggests that the basal ganglia have an influence on motor learning.

Animals↗
PubMed1991

Alzheimer's disease affects limbic nuclei of the thalamus.

Sensitive silver techniques for amyloid and neurofibrillary changes were applied to examine the pathological changes revealed by limbic nuclei of the thalamus in Alzheimer's disease. Large numbers of extracellular amyloid deposits occurred in almost all thalamic nuclei. The antero-ventral nucleus harbored numerous large globular patches, other areas contained more densely packed and smaller deposits, while narrow zones of gray matter subjacent to the ependymal lining of the third ventricle remained virtually devoid of amyloid. Intraneuronal neurofibrillary changes were encountered in the form of distended argyrophilic processes covering the medial convexity of the antero-ventral nucleus. Similar structures, although in considerably lesser density, occurred in the laterally adjoining reticular nucleus. The anterior nuclear complex, the latero-dorsal nucleus, portions of the intralaminar complex, the paraventricular and reuniens nucleus contained numerous neurofibrillary tangles and neuropil threads. The antero-dorsal nucleus showed the most severe involvement. At first glance, the thalamus appeared to be only mildly affected by Alzheimer's disease. Closer inspection revealed that severe changes were confined to only a few limbic nuclei. These changes were virtually identical in amount, type and location in all cases of severe Alzheimer's disease studied. It is assumed that these changes considerably hamper the transport of information through limbic circuits.

Aged↗
PubMedDate not supplied

Long-term ongoing reorganizations of the processes of analysis of kinesthetic afferentation at the level of cat motor cortex neurons after damage to the ventrolateral nucleus of the thalamus.

The changes in the functional characteristics of neurons of field 4 of the motor cortex (MC) of cats before and at various times (from a week up to five months) following an ipsilateral lesion of the ventrolateral nucleus of the thalamus were investigated in semichronic experiments. The reactions of the cells to tactile stimulation of the forelimb and its passive movement at the wrist at an average speed of 170 degrees/sec were studied. It was demonstrated that a correlation between the impulse activity at speed maxima and the acceleration of monoarticular movement is characteristic for a number of cells of the MC of the intact brain. Experimental confirmation was obtained of the hypothesis, formulated on the basis of the results of preceding investigations, regarding a disturbance of the mechanism of detection by MC neurons of the kinematic indicators of movement following damage to the thalamus. It was established that compensation of this disturbance is associated with the facilitation of conduction to MC neurons of somatosensory afferentation. It is concluded that a morphofunctional reorganization of particular intracortical components of sensorimotor coupling underlies the mechanisms of the compensatory plasticity of the MC.

Acceleration↗
PubMed1998

MRI of germinomas arising from the basal ganglia and thalamus.

We reviewed the MRI findings of germinomas originating from the basal ganglia, thalamus or deep white matter in 13 patients with 14 germinomas, excluding those in the suprasellar or pineal regions. Ten cases were confirmed as germinomas by stereotaxic biopsy, three by partial and one by total removal of the tumour. Analysis was focussed on the location and the signal characteristic of the tumour, haemorrhage, cysts within the tumour and any other associated findings. Thirteen of the tumours were in the basal ganglia and one in the thalamus. Haemorrhage was observed in seven patients, while twelve showed multiple cysts. Associated ipsilateral cerebral hemiatrophy was seen in three patients. The signal intensity of the parenchymal germinomas was heterogeneous on T1- and T2-weighted images due to haemorrhage, cysts and solid portions. We also report the MRI findings of germinomas in an early stage in two patients.

Adolescent↗
PubMed2006

Neuronal organization of the reticular nucleus of the thalamus in adult humans.

The neuronal composition of the thalamic reticular nucleus was studied in serial sections of the sagittal and frontal projections impregnated with silver nitrate by the Golgi method. The neuronal composition of the reticular nucleus of the human thalamus was wider than has previously been described in animals and humans. This nucleus, apart from two types of large, sparsely branched, long-dendrite, reticular, aspiny, neurons, i.e., types R1 and R2, contained cells with spines. Intermediate and small, sparsely-branched, short-dendrite neurons and densely-branched cells with spines were demonstrated. The principles of the organization of the reticular nucleus of the human thalamus are described.

Aged↗