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PubMed2000

Neurotrophin receptor (p75) in the trigeminal thalamus of the rat: development, response to injury, transient vibrissa-related patterning, and retrograde transport.

We report on the transient, patterned expression of p75 in the ventrobasal (VB) thalamus, the major thalamic relay for somatosensation. We immunostained the brains of developing rats ranging in age from embryonic day (E) 14.5 to postnatal day (PD) 15 with an antibody against p75. To compare p75 expression with the developing synaptic organization within VB, we also immunolocalized the synaptic-vesicle-associated protein, synaptophysin (SYN), on alternate sections. p75-immunoreactivity (IR) was dense and uniform in the ventroposterior medial nucleus (VPM) in the late embryonic and early postnatal periods (E 16.5 to PD 3). In contrast, from PD 4-10, p75-IR in the VPM was patterned, reminiscent of cytochrome-oxidase-stained barreloids, a characteristic feature of the VB in rodents. By PD 14, p75-IR in the VPM was no longer detectable. The ventroposterior lateral nucleus (VPL), in contrast, exhibited no p75-IR. No p75-IR was detected in the ventroposterior lateral nucleus (VPL) at any developmental stage in which VPM could be distinguished from VPL. Light, but clearly patterned SYN-IR, first detectable on PD 2-3, increased in intensity in both VPL and VPM through PD 15. Sectioning the infraorbital nerve on PD 0 resulted in blurred patterns of p75- and SYN-IR within VPM in PD 7-9 rat pups. Removing large portions of the somatosensory cortex on PD 0 resulted in subsequent greatly reduced p75- and SYN-IR within VB. To specify the source of the p75-IR terminals, we stereotaxically injected into the VPM of PD 4-5 rats a monoclonal antibody to p75. One to 2 days later, IR of retrogradely transported p75 antibodies could be traced within axons and cell bodies of neurons associated with the trigeminothalamic pathway through the caudal diencephalon and mesencephalon; labelling was confined to the contralateral trigeminal principal sensory nucleus. The observed, transiently patterned p75-IR in VPM the early postpartum period suggests a role for p75 in synaptogenesis and pattern formation.

Age Factors↗

PubMed2001

Reorganization of somatic sensory function in the human thalamus after stroke.

A patient with thalamic stroke underwent microelectrode-guided stereotactic thalamic exploration during surgery for control of tremor. The results of somatic sensory mapping in this patient were compared with explorations carried out during stereotactic surgery for the control of essential tremor (70 patients). There was evidence both of somatotopic reorganization and of anatomic reorganization of the representation of deep structures in the principal somatic sensory nucleus of the thalamus and the nuclei located anterior to it. This case demonstrates that thalamic reorganization can occur after a thalamic stroke and may play a role in recovery from such a stroke.

Brain Ischemia↗

PubMed1985

Amnesia in monkeys after lesions of the mediodorsal nucleus of the thalamus.

Recent successes in developing an animal model of human amnesia in the monkey have made it feasible to try to identify with certainty the specific structures in the diencephalon and medial temporal region that cause amnesia when damaged. Monkeys with small lesions restricted largely to the posterior portion of the mediodorsal nucleus of the thalamus were given a test of memory sensitive to human amnesia and a second test that is analogous to the skill-based tasks performed normally by amnesic patients. The monkeys exhibited a marked impairment on the first test and performed normally on the second. The results show that circumscribed lesions of the mediodorsal nucleus can cause substantial amnesia.

Amnesia↗

PubMed2003

Dendritic orientation and laminar architecture in the rabbit auditory thalamus.

A laminar organization composed of the dendritic fields of principal neurons and afferent axonal arbors has been proposed as the anatomical substrate for the frequency map at several levels of the mammalian central auditory system, including the inferior colliculus and medial geniculate body (MGB). In contrast to the auditory thalamus in most mammals, the ventral division of the rabbit medial geniculate body (MGV) has cellular laminae visible in routine Nissl stains, allowing a direct comparison of the laminar organization with the dendritic architecture and frequency organization. In total 30 presumptive relay neurons in the MGV were labeled with the juxtacellular recording method, and their dendritic arbors were fully reconstructed from serial sections with the aid of a computer microscope. The spatial organization of MGV dendritic fields was analyzed using the dendritic prism, dendritic stick, and fan-in projection methods. Quantitative spatial analyses revealed that, for MGV neurons in the central pars lateralis subdivision, the major axis of the dendritic fields (approximately 29 degrees relative to the horizontal plane) was closely aligned with that of the Nissl laminae (approximately 25 degrees). Both were oriented orthogonally to the tonotopic axis. In contrast, cells in the pars ovoidea had their major axis of orientation parallel to the anteroposterior axis of the brain. Although a bitufted dendritic field was the norm, it was not uncommon for MGV neurons to have pronounced spatial asymmetries in their dendritic fields. A model is presented that incorporates cellular laminae and oriented dendritic growth to form frequency-related slabs within the MGV.

Animals↗

PubMed2003

Projections from the paraventricular nucleus of the thalamus to the rat prefrontal cortex and nucleus accumbens shell: ultrastructural characteristics and spatial relationships with dopamine afferents.

The paraventricular nucleus of the thalamus (PVT) participates in the functional integration of limbic cortical and striatal circuitry. In the rat, the PVT projects to the deep layers of the medial prefrontal cortex (PFC) and to the shell of the nucleus accumbens (NAc). However, the synaptic organization of PVT afferents within these regions remains undescribed. Furthermore, although dopamine (DA) modulates excitatory glutamate transmission in both areas, possible anatomic substrates for specific DA modulation of PVT inputs have not yet been investigated. To address these issues, immunoperoxidase labeling for tyrosine hydroxylase (TH) in DA axons was combined with anterograde tract-tracing, either by biotinylated dextran amine (BDA) labeled with immunogold-silver or by degeneration after lesions of the PVT. In both regions, and with either tracing method, PVT terminals formed primarily asymmetric axospinous synapses; in the NAc, a proportion of PVT terminals also synapsed onto dendrites. PVT profiles in both regions were often seen in direct apposition to TH-immunoreactive axons; this association was more evident in the NAc where the DA innervation is denser. Within the PFC, PVT profiles and TH-labeled axons were occasionally apposed to the same dendrites, but synaptic specializations were not typically seen at these seeming points of convergence. Within the NAc, PVT profiles occasionally made synapses onto spines and distal dendrites that received convergent synapses from TH-immunoreactive varicosities. These findings represent the first demonstration of postsynaptic convergence between DA and thalamic afferents to a striatal region and are consistent with direct synaptic modulation of PVT transmission by DA in the NAc but not the PFC.

Afferent Pathways↗

PubMed2006

GABA(B) receptors in the centromedian/parafascicular thalamic nuclear complex: an ultrastructural analysis of GABA(B)R1 and GABA(B)R2 in the monkey thalamus.

Strong gamma-aminobutyric acid type B (GABA(B)) receptor binding has been shown throughout the thalamus, but the distribution of the two GABA(B) receptor subunits, GABA(B) receptor subunit 1 (GABA(B)R1) and GABA(B) receptor subunit 2 (GABA(B)R2), remains poorly characterized. In primates, the caudal intralaminar nuclei, centromedian and parafascicular (CM/PF), are an integral part of basal ganglia circuits and a main source of inputs to the striatum. In this study, we analyzed the subcellular and subsynaptic distribution of GABA(B) receptor subunits by using light and electron microscopic immunocytochemical techniques. Quantitative immunoperoxidase and immunogold analysis showed that both subunits display a similar pattern of distribution in CM/PF, being expressed largely at extrasynaptic and perisynaptic sites in neuronal cell bodies, dendrites, and axon-like processes and less abundantly in axon terminals. Postsynaptic GABA(B)R1 labeling was found mostly on the plasma membrane (70-80%), whereas GABA(B)R2 was more evenly distributed between the plasma membrane and intracellular compartments of CM/PF neurons. A few axon terminals forming symmetric and asymmetric synapses were also labeled for GABA(B)R1 and GABA(B)R2, but the bulk of presynaptic labeling was expressed in small axon-like processes. About 20% of presynaptic vesicle-containing dendrites of local circuit neurons displayed GABA(B)R1/R2 immunoreactivity. Vesicular glutamate transporters (vGluT1)-containing terminals forming asymmetric synapses expressed GABA(B)R1 and/or displayed postsynaptic GABA(B)R1 at the edges of their asymmetric specialization. Overall, these findings provide evidence for multiple sites where GABA(B) receptors could modulate GABAergic and glutamatergic transmission in the primate CM/PF complex.

Animals↗

PubMed2007

Functional and anatomical connection between the paraventricular nucleus of the thalamus and dopamine fibers of the nucleus accumbens.

The shell of the nucleus accumbens (NacSh) receives a dense innervation from dopamine (DA) neurons in the ventral tegmental area (VTA) and from glutamate neurons in the paraventricular nucleus of the thalamus (PVT). The present study examined in urethane-anesthetized rats the effects of electrical stimulation of the PVT on DA levels in the NacSh as measured with amperometry and chronoamperometry. Stimulation of the PVT (40 Hz, 1.0 ms, 400 microA, 5 seconds) resulted in a brief increase in electrochemical currents detected in the NacSh. Inhibition of DA neurons in the VTA using lidocaine (4%, 500 nL) or intravenous apomorphine (0.15 mg/kg) decreased the resting voltammetric signal but had no effect on PVT-evoked responses. Blocking of ionotropic glutamate receptors in the NacSh with local administration of kynurenic acid attenuated the PVT-evoked responses. Anterograde tracing with biotinylated dextran amine demonstrated that PVT targets regions of very dense tyrosine hydroxylase fiber staining in the NacSh. Consistent with the projection pattern of the PVT to the NacSh, stimulation of the PVT evoked the largest oxidation current changes in the NacSh, whereas small or no changes were elicited in other areas of the striatum. This study suggests that glutamate release from PVT terminals can act on ionotropic glutamate receptors in the NacSh to induce DA efflux. Modulation of DA levels in the NacSh by the PVT may be linked to arousal-induced increases in DA tone and could be involved in the facilitation of specific behavioral patterns associated with arousal or stressful situations.

Animals↗

PubMed1980

The nucleus of the solitary tract in the monkey: projections to the thalamus and brain stem nuclei.

The projections of the nucleus of the solitary tract (NST) were studied by autoradiographic anterograde fiber-tracing and horseradish peroxidase (HRP) retrograde cell-labeling. Tritiated proline and leucine were deposited in electrophysiologically identified regions of NST. Injections of NST at levels caudal to where the vagus enters the nucleus, from which responses were evoked by stimulation of cranial nerves IX and X, revealed topographically organized bilateral projections to, most prominently, the ventrolateral medullary reticular formation which contains neurons of the ambiguus complex, and to the lateral and medial parabrachial nuclei, including a small portion of the medially adjacent central gray substance. Labeled fibers in the ventrolateral reticular formation were present from the nucleus retroambigualis rostralward to the retrofacial nucleus, with the densest concentration located over the nucleus ambiguus proper. The parabrachial projection was confirmed using HRP and shown to originate from cells in the medial subdivision of NST. Due to the problem of fibers en passant, it was not possible to interpret conclusively the cell-labeling seen around the solitary tract after HRP injections made in the region of the nucleus ambiguus. Labeled fibers were also traced from caudal NST to the dorsal motor nucleus of the vagus, but their origin could not be determined with certainty. Other labeled axons, traced to circumscribed parts of the inferior olivary complex and via the contralateral medial lemniscus to VPL of the thalamus, were shown in HRP experiments to originate from the dorsal column nuclei rather than NST. No labeled fibers were traced into the spinal cord, nor were any cells labeled in NST after large HRP deposits in upper cervical segments. Isotope deposits at levels of NST rostral to the entrance of the vagus, from which responses were evoked by rapid stimulation of the tongue, revealed an ipsilateral projection which ascends as a component of the central tegmental tract to the parvicellular part of the ventral posteromedial thalamic nucleus (VPMpc). After small HRP deposits in VPMpc, labeled cells in NST were restricted to the rostral part of the lateral subdivision. No labeled axons were traced from rostral NST to the ambiguus complex or parabrachial area. Injections of 3H-amino acids at intermediate levels of NST resulted in fiber-labeling in VPMpc, the parabrachial area, and the ambiguus complex.

Animals↗

PubMed1980

Somatosensory thalamus of a prosimian primate (Galago senegalensis). I. Configuration of nuclei and termination of spinothalamic fibers.

The configuration of somatosensory relay nuclei and termination of spinothalamic fibers were studied in the dorsal thalamus of a prosimian primate(Galago senegalensis) using Nissl, Klüver and Barrera ('53), Weil ('45), and Fink and Heimer ('67) methods. The ventral posterolateral nucleus (VPL) is divided into medial and lateral parts (VPLm and VPLl, respectively) by a sheet-like lamina of fibers. Spinothalamic input to Galago VPL is somatopically arranged; input from the forelimb terminates in VPLm and that from hindlimb in VPLl. In addition, preterminal debris in caudal VPL is dense and organized into "parcellated bursts" (terminology of Mehler, '69). Consequently, the nature of the spinothalamic debris in VPL of Galago is similar to that reported for higher primates (Mehler et al., '60). Located dorsomedial to the rostral extension of VPL is a zone of large, deeply staining cells designated as the ventral intermediate nucleus (Vim). Following hemisection at either cervical or lumbar spinal cord levels, preterminal debris, independent of that coursing into VPL, enters the Vim. This substantiates the presence of an intermediate nucleus (i.e., Vim) between VPL and the more rostral ventral lateral nucleus. In the medial thalamic region, axonal degeneration is located in the central lateral nucleus (CL) and in the densocellular and the multiform portions of the dorsomedial nucleus. Only fibers of passage are identified in the centre median, the paracentral and the subparacentral nuclei. The posterior nuclear group (PO) in Galago is divided into medial and lateral parts designated as POm and POl, respectively. In addition, PO contains three distinct nuclei: 1) the magnocellular (MC) portion of the medial geniculate nucleus; 2) the nucleus limitans (Lim); and 3) the suprageniculate nucleus (SG). Following spinal cord hemisection, preterminal debris is located throughout the POm and around cells of the MC. Lim and SG contain no discernible degeneration. Preterminals are also found in a group of cells designated as the caudal part of the central lateral nucleus (CLC).

Animals↗

PubMed1980

Somatosensory thalamus of a prosimian primate (Galago senegalensis). II. An HRP and Golgi study of the ventral posterolateral nucleus (VPL).

The topographic arrangement and cytoarchitecture of cells in the ventral posterolateral nucleus (VPL) of a prosimian primate (Galago senegalensis) were studied using horseradish peroxidase (HRP) and Golgi impregnation techniques. Following cortical implants of HRP, reactive neurons in VPL are organized into medially concave lamellae which extend through the dorsoventral and rostrocaudal dimensions of the nucleus. After implant in forelimb and hindlimb areas of motor-sensory cortex, labeled cells are confined to the medial (VPLm) and lateral (VPLl) portions of VPL, respectively. HRP-positive cells in the ventral part of each lamella are organized into clusters which correspond to the clusters of cells and "parcellated-bursts" of preterminal debris previously described in bushbaby VPL (Pearson and Haines, this volume). HRP-reactive cells in the ventral intermediate nucleus (Vim) are evenly distributed as contrasted to the tightly clustered groups of somata in the adjacent VPL. This evidence argues in favor of the presence of Vim in dorsal thalamus of this prosimian. Golgi impregnations reveal two main types of relay cells in Galago VPL. Type I cells have multiangular somata, straight distal dendrites, and primary dendritic branch points which are free of appendages. Tye II cells have rounded somata, sinuous distal dendrites, and clusters of appendages located at primary branch points. Intermediate cells (i.e., cells with morphological features in between types I and II) are also present in VPL. Comparison of tufted Golgi impregnated cells with neurons labeled with HRP shows definite similarities in somata size and shape, and in the orientation of proximal dendrites. This evidence corroborates the relay nature of the tufted neurons in VPL. Relay cells in Galago VPL have morphological features which are similar to those of relay cells in lateral and medial geniculate nuclei of cat and primate. Type III cells have small round somata, radiate dendrites with elaborate appendages, and axons which appear to be intrinsic to VPL. Consequently, these cells are considered to be interneurons in the VPL of Galago. Glial-like neurons (type IV cells) were also observed. These have beaded dendritic processes similar to those which presumably represent presynaptic boutons in other species. Consequently, these cells are also assumed to function intrinsically within VPL.

Animals↗

PubMed1982

Brainstem afferents to the thalamus in a lizard, Varanus exanthematicus.

HRP was injected into various thalamic nuclei in order to investigate the brainstem projections to the thalamus in the lizard Varanus exanthematicus. Nucleus dorsomedialis receives afferents from the septal area, nucleus entopeduncularis anterior, nucleus periventricularis hypothalami, area triangularis, nucleus raphes superior, nucleus reticularis inferior, and locus coeruleus. Nucleus dorsolateralis receives afferents from septal area, nucleus dorsomedialis, nucleus entopeduncularis anterior, nucleus periventricularis hypothalami, and the torus semicircularis. Nucleus rotundus receives an input from the tectum mesencephali, the pretectal area, and from the mesencephalic reticular formation. Nucleus intermedius dorsalis receives afferents from the dorsal column nuclei and nucleus periventricularis hypothalami. Nucleus ventrolateralis receives afferents from the dorsal column nuclei, the trigeminal complex, locus coeruleus, and the reticular formation. Nucleus ventromedialis also receives afferents from the trigeminal complex and the reticular formation. Afferents to the habenula have been demonstrated from the septal area, nucleus entopeduncularis anterior, triangular area, nucleus periventricularis hypothalami, nucleus interpeduncularis, nucleus raphes superior, locus coeruleus, nucleus isthmi, nucleus dorsalis motorius nervi vagi, and the mesencephalic tegmentum. The laminar part of the torus semicicularis projects to nucleus medialis.

Afferent Pathways↗

PubMed1984

An immunocytochemical study of the serotonergic innervation of the thalamus of the rat.

The serotonergic innervation of the rat thalamus was studied with an indirect immunocytochemical technique using an antiserum raised against a serotonin-hemocyanin conjugate in animals pretreated with L-tryptophan and a monoamine oxidase (MAO) inhibitor. When pretreatment was not used there was a decrease in the number of immunoreactive fibers observed in the thalamic region. Innervation was greatest in nucleus ventralis corporis geniculati lateralis, and in the following midline nuclei: nucleus periventricularis, nucleus rhomboideus, and nucleus reuniens. Also well labeled were nucleus anterior ventralis, the intralaminar nuclei, and nucleus lateralis dorsalis. Moderate innervation was found in nucleus reticularis, nucleus anterior dorsalis, nucleus ventralis medialis, nucleus lateralis pars posterior, the posterior complex, and in nucleus dorsalis corporis geniculati lateralis. Very few serotonergic fibers were observed in nucleus paratenialis, nucleus gelatinosus, nucleus anterior medialis, nucleus medialis dorsalis, nucleus ventralis, nucleus ventralis pars dorsomedialis, or in nucleus corporis geniculati medialis. Serotonin immunoreactivity was also noted in a number of fiber bundles in the thalamic region. These include the fasciculus retroflexus, the fasciculus mamillothalamicus, the stria medullaris, and the stria terminalis. These results differ from those of previous descriptions of the serotonergic innervation of thalamic nuclei most notably in the midline nuclei and in the posterior complex. In this study the midline nuclei, nucleus rhomboideus, and nucleus reuniens were more densely innervated than had been described, and in the posterior complex a moderate, rather than sparse, innervation was observed. The more densely innervated nuclei of the anterior and lateral nuclear groups, nucleus lateralis dorsalis and nucleus anterior ventralis, also contained a greater number of labeled fibers than had been indicated.

Animals↗

PubMed1986

The overlap of spinothalamic and dorsal column nuclei projections in the ventrobasal complex of the rat thalamus: a double anterograde labeling study using light microscopy analysis.

Projections from the spinal cord and the dorsal column nuclei (DCN) to the ventrobasal complex of the thalamus (VB) were studied in the rat by using double anterograde labeling strategy. This strategy was based on the injection of 3H-leucine into the DCN and of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the spinal cord and their subsequent transport. Adjacent 30-micron-thick sections were then processed differentially for autoradiography or for HRP by using tetramethyl benzidine (TMB) as a chromogen. Similar areas of the ventrobasal complex were labeled, in adjacent sections, after a large injection of 3H-leucine into the DCN and when wheat germ agglutinin-HRP had been injected in any part of the spinal cord. If, however, a small injection of the radioactive tracer was centered in the gracile nucleus and compared with an injection of WGA-HRP placed in the lumbar enlargement of the cord, the rostral and dorsal portions of the lateral VB were labeled from both sources. On the other hand, if tritiated leucine was injected into the cuneate nucleus, and WGA-HRP placed in the cervical enlargement, then the caudal and ventral portions of the lateral VB demonstrated overlap of both labels. The present results show that, in the rat, areas of termination of both the spinothalamic tract and the lemniscal pathway originating from the DCN overlap in the lateral VB. This overlap is somatotopically organized, thus indicating that the same area of the VB receives somatic inputs from one particular part of the body through both pathways. These results are discussed in comparison to those of comparable studies performed in the cat and in the monkey and with reference to the electrophysiological data that have demonstrated that, in the rat VB, neurons responding to noxious stimulation are intermingled with neurons exclusively responding to non-noxious stimulation.

Afferent Pathways↗

PubMed1987

Time course of the reaction of glial fibers in the somatosensory thalamus after lesions in the dorsal column nuclei.

These experiments were designed to examine the relationship of glial hypertrophy to the time course of reactive synaptogenesis in the ventral posterolateral nucleus of the rat thalamus after lesions in the dorsal column nuclei. Because synaptogenesis is delayed for 30 days following lesions of the dorsal column nuclei, the initial hypertrophy of the glial processes in response to degeneration can be separated temporally from synaptogenesis. Glial hypertrophy was determined by measuring the relative area of neuropil occupied by profiles of glial processes on electron micrographs. The initial glial hypertrophy reached its peak 2 days after the lesion. However, at the time when synaptogenesis began, the area of neuropil occupied by glial processes was less than normal. When synaptogenesis was complete, the area of glial profiles also returned to normal. The role of glia in synaptogenesis was clearly different from its role in response to degeneration. In those systems such as the hippocampus, in which reactive synaptogenesis starts early in the recovery sequence, the relationship of glia to synaptogenesis may be masked by the glial response to degeneration. Hypertrophy of glial processes after lesions of other afferent pathways to the ventral posterolateral nucleus was compared to the hypertrophy following lesions of the dorsal column nuclei in order to see if there was a special relationship between glia and the lemniscal afferents to the ventral posterolateral nucleus. Lesions were placed in the medial lemniscus, somatosensory cortex, and the mesencephalon in addition to the dorsal column nuclei. The area of neuropil occupied by the glial processes expanded markedly after each of the lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1987

Afferent connections of anterior thalamus in rats: sources and association with muscarinic acetylcholine receptors.

Afferent connections of the anterior thalamic nuclei (ATN) are classically thought to originate in the mammillary body and limbic cortex. This study explores nonlimbic sources of ATN afferents by using retrograde transport of horseradish peroxidase (HRP) to ascertain the relative contribution of these connections. Spread of HRP into adjacent regions was prevented either by removing the overlying cortex or by injecting through permanently implanted cannulas. The main sources of nonlimbic ATN afferents are the pretectum and central gray. Pretectal neurons were HRP-labeled primarily in the contralateral medial pretectal nucleus with a smaller number in the ipsilateral posterior pretectal nucleus. In the central gray, labeled cells were concentrated ipsilaterally in the laterodorsal tegmental nucleus. Additional projections to ATN originate in the reticular and ventral lateral geniculate nuclei of the thalamus, raphe nuclei, peripontine tegmental nucleus, and locus coeruleus. The association of ATN afferents with muscarinic receptors was also explored by means of in vitro receptor autoradiography with the muscarinic ligands propylbenzilylcholine mustard (PrBCM) and pirenzepine (PZ) in normal rats and rats with ablations. Ibotenic acid injections into ATN were used to destroy intrinsic neurons while leaving afferent fibers intact. Whereas such ablations produced statistically significant decreases in PrBCM binding in the anterior dorsal (AD, -45%) and anterior ventral, magnocellular part (AVm, -51%) nuclei, binding in the anterior ventral, parvicellular part (AVp) and anterior medial (AM) nuclei was not significantly decreased. Furthermore, PZ binding in normal rat ATN was significantly less (-72%) than PrBCM binding. These results suggest that a major proportion of muscarinic binding is associated with presynaptic elements. Ibotenic acid ablations of the mammillary body reduced PrBCM binding in ATN whereas lesions in cingulate cortex and laterodorsal tegmental nucleus had no effect. Compared to sham lesion controls, mammillary body lesions resulted in statistically significant decreases in binding bilaterally in AD (-15%), AVm (-19%), and AM (-20%). In conclusion, ATN receive afferents from several nonlimbic regions. Of these inputs, the pretectum may be the primary route through which sensory information reaches ATN. In addition, cholinergic input may modulate activity in projections from the mammillary body to ATN through presynaptic muscarinic receptors.

Afferent Pathways↗

PubMed1989

Light and electron microscopic study of galanin-immunoreactive nerve fibers in the rat posterior thalamus.

Light and electron microscopic immunocytochemistry was used to study certain cell groups in the posteromedial thalamus which contain galanin-immunoreactive (GAL-IR) fibers. The nuclei subparafascicularis pars parvicellularis (SPFpc) and parafascicularis (PF) contain a dense network of GAL-IR fibers which form basketlike structures around unstained cells. The periventricular area also contains numerous GAL-IR fibers and these also occasionally form basketlike structures. The GAL-IR terminal fields continue caudally in the mesodiencephalic junction and merge with other GAL-IR fibers in the dorsal aspects of the substantia nigra and around the dorsolateral tip of the medial lemniscus. Ultrastructural analysis of the GAL-IR basketlike structures revealed that GAL-IR terminals make numerous synapses with the cell bodies and proximal dendrites of SPFpc neurones. These results suggest that the activity of cells in the SPFpc and PF nuclei may be strongly influenced by galanin-containing nerve fibers probably originating in the spinal cord.

Animals↗

PubMed1989

Development of the rat thalamus: VI. The posterior lobule of the thalamic neuroepithelium and the time and site of origin and settling pattern of neurons of the lateral geniculate and lateral posterior nuclei.

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to determine the time of origin, site of origin, migratory route, and settling pattern of neurons of the dorsal lateral geniculate (LGD), ventral lateral geniculate (LGV), and lateral posterior (LP) nuclei of the thalamus. Quantitative examination of long-survival radiograms established that the neurons of the LGD are produced on days E14 and E15. Within the LGD there is an external-to-internal neurogenetic gradient; the majority (77%) of neurons of the external half are generated on day E14, while in the internal half the majority (64%) of neurons originate on day E15. The late-generated LGD neurons are located in the termination field of the uncrossed fibers of the optic tract. Examination of short-survival radiograms indicated that the neurons of the LGD originate in a discrete neuroepithelial eversion situated ventral to the pineal rudiment and dorsal to the putative neuroepithelium of the ventral nuclear complex. In sequential radiograms from rats injected with 3H-thymidine on day E15 and killed on days E16 and E17, the migration of young LGD neurons was followed in a posterolateral direction to the formative lateral geniculate body. By day E17, the day when the optic tract fibers begin to disperse over the lateral surface of the posterior diencephalon, the distribution of early and late-generated neurons of the LGD resembles that seen in young pups. As a whole, the neurons of the LGV are produced earlier than the neurons of the LGD. The bulk of LGV neurons are generated on days E14 and E15 in a caudal-to-rostral intranuclear neurogenetic gradient. Caudal LGV neurons are generated mainly on day E14 (82%), while a substantial proportion of rostral neurons (32%) are generated on day E15. Examination of short-survival and sequential radiograms suggest that the LGV neurons originate in an inverted sublobule situated beneath the putative neuroepithelium of the LGD. At anterior levels the putative inverted sublobule of the LGV merges imperceptibly with the neuroepithelium that produces the neurons of the lateral habenular nucleus. Like the neurons of the LGD and LGV, so also those of the LP are generated on days E14 and E15, but the neurogenetic gradients are different. There is a lateral-to-medial gradient within the LP as a whole. Peak production of neurons is on day E14 laterally (58%) and on day E15 medially (59%).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Trigeminal projections to the nucleus submedius of the thalamus in the rat.

Methods involving the anterograde and retrograde transport of wheat-germ agglutinin conjugated horseradish peroxidase and the retrograde transport of Fluoro-Gold were used in rats to examine the distribution within the spinal trigeminal nucleus of trigeminal neurons projecting to the nucleus submedius (Sm) of the thalamus, as well as the distribution of axon terminals within the Sm. Following injections into the trigeminal nucleus, axon terminals were seen in the dorsal part of the anterior Sm; the terminals occurred bilaterally but had an obvious contralateral dominance. To help determine the precise location of the Sm-petal neurons, the border between trigeminal subnuclei interpolaris and caudalis was examined by the use of immunohistochemical procedures for calcitonin gene-related peptide (CGRP). The Sm-petal neurons that were labeled retrogradely occurred only at the caudal interpolaris and rostral caudalis levels; the number of labeled neurons on the contralateral side was approximately six times that on the ipsilateral side. Most of these neurons were located in the ventral part of the caudal interpolaris and rostral caudalis and spinal trigeminal tract; in caudalis, the neurons were almost exclusively localized to its superficial layers. There were approximately three times more labeled neurons in interpolaris than in caudalis. In the experiments combined with immunohistochemistry for CGRP, many neurons (34%) were seen in proximity to CGRP-like immunopositive fibers. These results suggest that the Sm of the rat receives its orofacial afferent inputs from brainstem neurons that are localized to the caudal interpolaris and rostral caudalis. In view of previous studies that have implicated these three structures in somatosensory function, and in particular nociception, our data point to a role for this direct projection from interpolaris and caudalis to Sm in the central processing of pain.

Animals↗