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PubMed2003

Roles of the auditory midbrain and thalamus in selective phonotaxis in female gray treefrogs (Hyla versicolor).

Diencephalic and midbrain auditory nuclei are involved in the processing of auditory communication signals in anurans [Comparative Hearing: Fish and Amphibians, Springer-Verlag, New York, 1999, p. 218], but their exact roles in acoustically guided behavior, such as female phonotaxis, are unclear. To address this question, behavioral experiments were combined with lesions of dorsal thalamic nuclei and the midbrain torus semicircularis. Females were tested in two-alternative-forced-choice phonotactic experiments before and after a defined brain area was lesioned. During phonotactic tests, females had to choose between a "standard" synthetic call and one of three different variants, each of which had a single acoustic property (pulse rate, pulse rise-time, sound spectrum) that differed from the standard synthetic call. Results showed that dorsomedial thalamus lesions produced little or no effect on phonotaxis. In contrast, superficial and deep thalamus lesions, as well as lesions of the torus semicircularis, significantly decreased the number of phonotactic responses and increased the response time. Superficial thalamus lesions also abolished or reversed preferences for the standard call in the rise-time and sound spectrum tests. This effect is likely to have been caused by an imbalance in the stimulation of the thalamus by the low- and high-frequency pathways because these preferences were not affected in animals with more extensive lesions that included the superficial thalamus. Our data suggest that the torus semicircularis, but not the dorsal thalamus is crucial for phonotaxis in gravid, reproductively active females. Although dorsal thalamic nuclei seem to play a role in spectral sensitivity, they may additionally have motivational or attentional functions that contribute to achieving a state of phonotactic readiness.

Acoustic Stimulation↗

PubMedDate not supplied

Organization of the mouse dorsal thalamus based on topology, calretinin immnunostaining, and gene expression.

To better understand the organization and evolution of the dorsal thalamus, we have made a first approach to analyze the possible histogenetic compartments of the mammalian dorsal thalamus using mouse embryos. For that, we have analyzed the expression of the proneural gene Math4a and the protein calretinin. Our results suggest the existence of rostrodorsal, caudoventral, and ventral compartments in the embryonic dorsal thalamus of the mouse, which partly parallel the dorsoventral histogenetic tiers postulated in the dorsal thalamus of sauropsids. The rostrodorsal compartment of the mouse dorsal thalamus is characterized by expression of Math4a, and it appears to include sensory and motor thalamic nuclei projecting to the dorsal pallium (isocortex). This compartment appears equivalent to the lemnothalamus proposed by Butler in tetrapods based on hodological grounds. The caudoventral and ventral compartments of the mouse dorsal thalamus lack expression of Math4a in the mantle, but they are characterized by several populations of calretinin-immunorective neurons that show projections to the claustroamygdaloid region in the ventrolateral pallium. More studies will be needed to analyze if the compartments proposed in this study represent true histogenetic units, and to find homologous developmental fields in all vertebrates.

Animals↗

PubMed1999

Neuroimaging of serotonin uptake sites and antidepressant binding sites in the thalamus of humans and 'higher' animals.

This review presents the results of in vitro, ex vivo and in vivo studies carried out primarily for identifying serotonin uptake sites and/or antidepressant binding sites in the brain of humans and 'higher' animals, namely nonhuman primates and pigs. Five lines of evidence are considered. First, studies carried out in vitro using synaptosomes or membrane preparations from human, nonhuman primate, and porcine brain have shown that certain thalamic nuclei are major sites of serotonergic neurotransmission in these species. Second, studies carried out in vitro or ex vivo using autoradiography or immunohistochemistry have indicated that the dorsomedial nucleus and some adjacent regions of the thalamus have a particularly high density of binding sites for antidepressant drugs that are selective serotonin reuptake inhibitors (SSRIs). Third, studies carried out in the living brain of nonhuman primates and pigs have found that SSRIs, radiolabeled for use in PET or SPECT, accumulate to a relatively high degree in midline and dorsal nuclei of the thalamus. Fourth, studies carried out using PET or SPECT radioligands in humans have demonstrated that regions in and around the dorsomedial nucleus of the thalamus are principal sites for accumulation of SSRIs. Fifth, studies of behavior of humans suffering from localized tissue damage in the thalamus have reported that symptoms of mania often occur in the patients, in accordance with the notion that an intact thalamus is required for normal regulation of mood. Taken together, the findings are consistent with the hypothesis that serotonergic neurotransmission in the dorsomedial nucleus of the thalamus could be causally involved in the pathophysiology of affective disease as well as in therapeutic actions of SSRIs.

Animals↗

PubMed2002

The histaminergic system in human thalamus: correlation of innervation to receptor expression.

The mRNA expression of three histamine receptors (H1, H2 and H3) and H1 and H3 receptor binding were mapped and quantified in normal human thalamus by in situ hybridization and receptor binding autoradiography, respectively. Immunohistochemistry was applied to study the distribution of histaminergic fibres and terminals in the normal human thalamus. mRNAs for all three histamine receptors were detected mainly in the dorsal thalamus, but the expression intensities were different. Briefly, H1 and H3 receptor mRNAs were relatively enriched in the anterior, medial, and part of the lateral nuclei regions; whereas the expression level was much lower in the ventral and posterior parts of the thalamus, and the reticular nucleus. H2 receptor mRNA displayed in general very low expression intensity with slightly higher expression level in the anterior and lateropolar regions. H1 receptor binding was mainly detected in the mediodorsal, ventroposterolateral nuclei, and the pulvinar. H3 receptor binding was detected mainly in the dorsal thalamus, predominantly the periventricular, mediodorsal, and posterior regions. Very high or high histaminergic fibre densities were observed in the midline nuclear region and other nuclei next to the third ventricle, ventroposterior lateral nucleus and medial geniculate nucleus. In most of the core structures of the thalamus, the fibre density was very low or absent. The results suggest that histamine in human brain regulates tactile and proprioceptory thalamocortical functions through multiple receptors. Also, other, e.g. visual areas and those not making cortical connections expressed histamine receptors and contained histaminergic nerve fibres.

Adult↗

PubMed2003

Tremor-related activity of neurons in the 'motor' thalamus: changes in firing rate and pattern in the MPTP vervet model of parkinsonism.

The pathophysiology of parkinsonian tremor remains a matter of debate with two opposing hypotheses proposing a peripheral and a central origin, respectively. A central origin of tremor could arise either from a rhythmic activity of the internal segment of the globus pallidus (GPi) or from a structure such as the thalamus, outside the basal ganglia. In this study, single-unit recordings were performed in three 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys within the GPi and within three territories of the motor thalamus (delimited by their afferent inputs from the GPi, the substantia nigra and the cerebellum, respectively). For each recorded neuron, we compared the variations in firing rate and pattern in tremor and no tremor periods. Tremor either occurred spontaneously or was induced by external stimulation. When the animals entered into a tremor period we observed: (i) an increase in the mean firing rate in about half of the recorded neurons of the motor thalamus; and (ii), a change from an irregular to a rhythmic discharge within the range of tremor frequency (5-7 Hz) in about 10% of the recorded neurons of the motor thalamus (pallidal and cerebellar territories) and the GPi. Most of the thalamic neurons that exhibited a rhythmic discharge during tremor were found to be sensitive to external stimulation. Because the changes in firing rate occurred predominantly in the motor thalamus and not in the GPi, and because a fast rhythmic discharge of 10-15 Hz was frequently observed in the GPi and not in the motor thalamus, we conclude that thalamic activity is not a simple reproduction of basal ganglia output. Moreover, we suggest that thalamic processing of basal ganglia outputs could participate in the genesis of tremor, and that this thalamic processing could be influenced by sensory inputs and/or changes in attentional level elicited by external stimulation.

Action Potentials↗

PubMed2004

Involvement of human thalamus in the preparation of self-paced movement.

Cortical areas participating in the preparation of voluntary movements have been studied extensively. There is emerging evidence that subcortical structures, particularly the basal ganglia, also contribute to movement preparation. The thalamus is connected to both the basal ganglia and the cerebellar pathways, but its role in movement preparation has not been studied extensively in humans. We studied seven patients who underwent deep brain stimulation (DBS) electrode implantation in the thalamus for treatment of tremor (six patients) and myoclonus-dystonia (one patient). We recorded from the DBS contacts and scalp simultaneously, while patients performed self-paced wrist extension movements. Post-surgical MRI was used for precise localization of the DBS contacts in six patients. Back-averaging of the scalp recordings showed a slow negative movement-related potential (MRP) in all patients (onset 1846 +/- 189 ms prior to electromyography onset), whereas DBS electrode recordings showed pre-movement MRP in five out of seven patients. The thalamic MRP preceded both contralateral and ipsilateral wrist movements. There was no significant difference between the onset time of thalamic MRP (-2116 +/- 607 ms) and cortical MRP. Neither the scalp nor the thalamus showed pre-movement potentials with passive wrist extensions in two patients. In four patients with postoperative MRI who had thalamic MRP, the maximum amplitude or phase reversal occurred at contacts located in the ventral lateral nucleus. Frequency analysis was performed in the five patients with thalamic MRP. The medial frontocentral scalp contacts and the thalamic contacts with maximum MRP amplitude showed two discrete frequency bands in the alpha (mean peak 9 Hz) and beta (mean peak 17 Hz) range. Both frequency bands showed pre-movement event-related desynchronization (ERD). In the grand average, alpha and beta ERD in the scalp and beta ERD in the thalamus began 2.5-2.8 s prior to the onset of movement. However, the thalamic alpha ERD began considerably later, at 1.2 s before EMG onset. The beta band showed cortico-thalamic coherence from the beginning of the baseline period until approximately 0.5 s before the onset of movement. There was no cortico-thalamic coherence in the alpha band. Our findings suggest that the cerebellar thalamus is involved early in the process of movement preparation. Different cortico-subcortical circuits may mediate alpha and beta oscillations. During movement preparation, the motor thalamus and the supplementary motor area predominantly interact in the beta band.

Adult↗

PubMed2000

Microelectrode studies of normal organization and plasticity of human somatosensory thalamus.

Microelectrode studies of single units in the human thalamus during stereotactic surgery offer a unique opportunity to study the organization and plasticity of the sensory thalamus. In this review the authors present results using single-unit microelectrode recording in the mapping of human sensory thalamus in a variety of patients. First they outline the overall organization of the human sensory thalamus, including both somatosensory and pain pathways. They also show that the sensory maps for receptive and projection fields can be altered during pathologic states such as amputation and spinal transection. Additionally, the sensory maps show plasticity during states with abnormal patterns of motor activity, like dystonia. Lastly, they discuss the processing of painful and emotionally laden sensory experiences through the thalamus. The physiologic results of thalamic pain processing are discussed in relation to the sensory-limbic model of pain. The studies reviewed demonstrate the spectrum of stimulus processing and plasticity of both painful and nonpainful signals by the human thalamus.

Brain Mapping↗

PubMed2005

Differences in neuronal firing rates in pallidal and cerebellar receiving areas of thalamus in patients with Parkinson's disease, essential tremor, and pain.

The motor symptoms of Parkinson's disease (PD) are thought to result from increased inhibitory outflow from the basal ganglia to the pallidal receiving areas of thalamus (ventral oral anterior and posterior-Voa,Vop). To test this hypothesis, we examined the firing rates of neurons in pallidal and cerebellar receiving areas of thalamus in five PD patients and compared them to those of neurons in comparable regions of motor thalamus in two other patient groups where hyperactivity of GPi is not believed to occur [essential tremor (ET), pain]. Neuronal recordings were made during microelectrode-guided functional stereotactic neurosurgery. The mean spontaneous firing rate (MSFR) of neurons classified as voluntary neurons and presumed to be in pallidal receiving areas of thalamus in PD patients [7.4 +/- 1.0 (SE) Hz] was significantly lower (P < 0.01) than in the ET (18.1 +/- 3.0 Hz) and pain (19.0 +/- 1.9Hz) groups. In contrast, the MSFR of neurons classified as kinesthetic and presumed to be primarily in the cerebellar receiving area of thalamus (ventral intermediate-Vim), although some are probably in the deep shell region of the ventrocaudal nucleus (VPLa), was significantly greater in ET patients (25.8 +/- 3.5 Hz) than in the PD (14.3 +/- 1.6 Hz; P < 0.01) and pain (16.1 +/- 1.5 Hz; P < 0.05) groups. Similar findings were obtained when the neurons were grouped according to their estimated locations in Voa/Vop and Vim of motor thalamus. These data provide support for the prediction of the classical pathophysiological model of PD and moreover suggest that pathophysiology in the cerebello-thalamo-cortical pathway may be a possible cause of tremor in ET patients.

Action Potentials↗

PubMed2005

Response characterstics of spinothalamic tract neurons that project to the posterior thalamus in rats.

A sizeable number of spinothalamic tract axons terminate in the posterior thalamus. The functional roles and precise areas of termination of these axons have been a subject of recent controversy. The goals of this study were to identify spinothalamic tract neurons (STT) within the cervical enlargement that project to this area, characterize their responses to mechanical and thermal stimulation of their receptive fields, and use microantidromic tracking methods to determine the nuclei in which their axons terminate. Forty-seven neurons were antidromically activated using low-amplitude (< or =30 microA) current pulses in the contralateral posterior thalamus. The 51 points at which antidromic activation thresholds were lowest were surrounded by ineffective tracks indicating that the surrounded axons terminated within the posterior thalamus. The areas of termination were located primarily in the posterior triangular, medial geniculate, posterior and posterior intralaminar, and suprageniculate nuclei. Recording points were located in the superficial and deep dorsal horn. The mean antidromic conduction velocity was 6.4 m/s, a conduction velocity slower than that of other projections to the thalamus or hypothalamus in rats. Cutaneous receptive fields appeared to be smaller than those of neurons projecting to other areas of the thalamus or to the hypothalamus. Each of the examined neurons responded exclusively or preferentially to noxious stimuli. These findings indicate that the STT carries nociceptive information to several target nuclei within the posterior thalamus. We discuss the evidence that this projection provides nociceptive information that plays an important role in fear conditioning.

Action Potentials↗

PubMed2001

High-pass filtering of corticothalamic activity by neuromodulators released in the thalamus during arousal: in vitro and in vivo.

The thalamus is the principal relay station of sensory information to the neocortex. In return, the neocortex sends a massive feedback projection back to the thalamus. The thalamus also receives neuromodulatory inputs from the brain stem reticular formation, which is vigorously activated during arousal. We investigated the effects of two neuromodulators, acetylcholine and norepinephrine, on corticothalamic responses in vitro and in vivo. Results from rodent slices in vitro showed that acetylcholine and norepinephrine depress the efficacy of corticothalamic synapses while enhancing their frequency-dependent facilitation. This produces a stronger depression of low-frequency responses than of high-frequency responses. The effects of acetylcholine and norepinephrine were mimicked by muscarinic and alpha(2)-adrenergic receptor agonists and blocked by muscarinic and alpha-adrenergic antagonists, respectively. Stimulation of the brain stem reticular formation in vivo also strongly depressed corticothalamic responses. The suppression was very strong for low-frequency responses, which do not produce synaptic facilitation, but absent for high-frequency corticothalamic responses. As in vitro, application of muscarinic and alpha-adrenergic antagonists into the thalamus in vivo abolished the suppression of corticothalamic responses induced by stimulating the reticular formation. In conclusion, cholinergic and noradrenergic activation during arousal high-pass filters corticothalamic activity. Thus, during arousal only high-frequency inputs from the neocortex are allowed to reach the thalamus. Neuromodulators acting on corticothalamic synapses gate the flow of cortical activity to the thalamus as dictated by behavioral state.

Acetylcholine↗

PubMed2000

Selenium altered the levels of lipids, lipid peroxidation, and sulfhydryl groups in straitum and thalamus of rat.

The effect of sodium selenite (0.05, 0.1, and 0.2 mg/kg body weight, i.p.) on the lipid levels (total lipids, phospholipids, cholesterol, gangliosides), thiobarbituric acid reactive substance (TBARS), and sulfhydryl group (-SH) in the striatum and thalamus of a male Wistar rat was studied after 7 d of treatment. The level of total lipids and cholesterol was significantly and dose-dependently elevated in the striatum and thalamus with 0.1 and 0.2 mg/kg of sodium selenite. However, the cholesterol level was significantly increased only with 0.2 mg/kg of sodium selenite in the thalamus. The level of phospholipids and gangliosides was more significant with 0.1 mg/kg of sodium selenite as compared to 0.2 mg. No significant alteration on the gangliosides level was observed in the thalamus with various doses of sodium selenite although the elevation with 0.2 mg dose was 25.9%. The content of TBARS was elevated dose dependently in striatum, but its level was depleted significantly with 0.1-mg/kg dose of sodium selenite in the thalamus. The level of the -SH group was significantly depleted in the striatum with 0.1-mg/kg dose of sodium selenite; conversely, this dose has significantly elevated the levels of -SH group in the thalamus.

Animals↗

PubMed2005

The primate thalamus is a key target for brain dopamine.

The thalamus relays information to the cerebral cortex from subcortical centers or other cortices; in addition, it projects to the striatum and amygdala. The thalamic relay function is subject to modulation, so the flow of information to the target regions may change depending on behavioral demands. Modulation of thalamic relay by dopamine is not currently acknowledged, perhaps because dopamine innervation is reportedly scant in the rodent thalamus. We show that dopaminergic axons profusely target the human and macaque monkey thalamus using immunolabeling with three markers of the dopaminergic phenotype (tyrosine hydroxylase, dopamine, and the dopamine transporter). The dopamine innervation is especially prominent in specific association, limbic, and motor thalamic nuclei, where the densities of dopaminergic axons are as high as or higher than in the cortical area with the densest dopamine innervation. We also identified the dopaminergic neurons projecting to the macaque thalamus using retrograde tract-tracing combined with immunohistochemistry. The origin of thalamic dopamine is multiple, and thus more complex, than in any other dopaminergic system defined to date: dopaminergic neurons of the hypothalamus, periaqueductal gray matter, ventral mesencephalon, and the lateral parabrachial nucleus project bilaterally to the monkey thalamus. We propose a novel dopaminergic system that targets the primate thalamus and is independent from the previously defined nigrostriatal, mesocortical, and mesolimbic dopaminergic systems. Investigating this "thalamic dopaminergic system" should further our understanding of higher brain functions and conditions such as Parkinson's disease, schizophrenia, and drug addiction.

Aged↗

PubMed2000

[Reduced signal intensity of T2 weighted MR imaging of thalamus and putamen in multiple sclerosis in Japan].

Although studies using magnetic resonance imaging (MRI) in multiple sclerosis (MS) patients have focused on findings in the white matter because of its demyelination pathogenesis, Drayer et al. have reported a high incidence of low signal intensity on T2 weighted MR imaging (MRI) in gray matter such as the thalamus and putamen. In Japan there has been no investigation of MRI findings of the basal ganglia in MS patients. Therefore, we attempted to examine the incidence and clinical significance of the imaging phenomenon in 34 Japanese patients with MS (12 male, 22 female, ages 18-54 years). As it is well known that the spinal cord and optic nerves are more frequently involved in MS than the brain in Japanese patients, we divided the patients into two subgroups based on their clinical features and the major sites of demyelination on MRI. One group included the 17 patients whose demyelinations occurred in the brain (brain-type), and the other group included the 17 patients whose abnormalities were found in the spinal cord with or without optic nerve involvement (non-brain type). As a control, MRI studies were also performed in age-matched patients with headache without any neurological signs. On T2 weighted MRI, decreased signal intensity in the thalamus was found in only four patients with MS, 11.8% of the total number examined, and in the putamen in three patients with MS, 8.8% of the total examined. All of the patients who showed abnormal decreased signal intensity in the thalamus and/or putamen belonged to the brain-type group, and these incidences were 23.5% in the thalamus and 17.6% in the putamen among the brain-type patients. No patient belonging to the non-brain type showed this imaging sign. This imaging sign was well correlated with the degree of white matter abnormalities in the brain estimated as a score according to modified Callanan et al.'s method. In addition, this sign was also correlated with the expanded disability status scales (EDSS) in the brain-type patients. These observations suggest that the axonal damages due to severe demyelination may induce the impaired transport of iron resulting in an accumulation of ferritin in the thalamus and putamen, and would cause decreased signal intensity on T2 weighted MRI. The relatively low incidence of decreased signal intensity in the thalamus and putamen in this study may be associated with differences in the clinical phenotype of MS between Japan and the USA. In brain-type patients the evaluation of basal ganglia on T2 weighted MRI may be a useful tool for estimating patients' disabilities.

Adolescent↗

PubMed1991

[Effects of cerebral cortical lesions on the ipsilateral thalamus].

An injury to the central nervous system causes a focal logical disturbance, and further may affect the blood flow, metabolism, and function of other brain regions. Recent studies using PET or SPECT have demonstrated that impairment of regional hemodynamics or metabolism in cerebrovascular disease involves not only the site of the lesion itself but also more remote areas. Although depression of the metabolism of the ipsilateral thalamus in patients with cerebral cortical lesions has been shown by PET study, the pathophysiological implications of this remain unclear. The functional and morphological effects of cortical infarcts on the ipsilateral thalamus were studied by assessment of cerebral blood flow using 123I-IMP SPECT and by determining atrophic changes on CT or MRI. Nine out of 17 patients with cortical infarcts showed hypoperfusion of the ipsilateral thalamus, especially patients with larger infarcts involving the frontal or parietal cortex. Thalamic hypoperfusion persisted from early after the insult to several months or even years later. In addition, atrophy of the ipsilateral thalamus was not uncommon following larger cortical infarcts. This tended to be evident about 1 year after the infarct and progressed over several years. Furthermore, atrophic changes in the thalamus was often demonstrated in such patients as hypoperfusion in the later stages. Thus, cortical lesions had functional and morphological effects on the ipsilateral thalamus ranging from early hypoperfusion to later irreversible atrophic changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1982

[Electrophysiological atlas of human thalamus and adjacent structures.--Microcomputer assisted mapping of neurophysiological data and its application to stereotaxic surgery].

During stereotaxic surgery anatomical structures and their extent on trajectories were identified by neural noise (field potential) obtained by semi-microelectrode technique. Locations of anatomical structures (the white mater, caudate nucleus, thalamus, subthalamic field and nuclei in the subthalamic field) were fed into microcomputer (NEC PC-8001) as 3 dimensional correlates and stored in minifloppy disc system (NEC PC-8031). Data with satisfactory recordings from 48 trajectories from 30 patients (18 parkinsonism, 5 central pain, 7 others) entered this study. Microcomputer was so programmed that locations of the trajectories and electrophysiologically identified anatomical structures at that location in various coronal, sagittal and horizontal planes were displayed. Accumulation of this display from various groups of patients automatically created electrophysiological atlas. For comparison of thus created electrophysiological atlas with anatomical atlas display was made on various sections of the Schaltenbrand and Bailey's Atlas which were also stored in the mimifloppy disc system. Electrophysiological topography of the thalamus and adjacent structures was reasonably similar to anatomical topography with minor, but significant individual variations. In most cases the ventral border of the thalamus was located in the close vicinity of CA-CP line, however, in some cases the thalamus was located deep into the subthalamic field. This was thought to be due to the difficulty in identifying the ventral border of the thalamus by this technique and in such occasions other neurophysiological method for identifying the ventral border of the thalamus, i.e., thalamocortical evoked potential and other stimulation technique, were necessary. Medial aspect of the V. im. nucleus emitted neural noise of different characteristics which in current program was recognized as the subthalamic field. This implies that the medial and lateral aspects of the V. im. nucleus are cytoarchitecturally different and that it is possible to differentiate the medial and lateral aspects of the V. im. nucleus by this technique. The lateral thalamic border, i.e., thalamocapsular border, also showed relatively wide range of individual variations. When various parameters including age, sex, diagnosis and width of the 3rd ventricles were examined for possible cause of these variations, a tendency was noted that the thalamocapsular border was medially placed when the width of the 3rd ventricle was small. In this system it is possible to display sequentially electrophysiologically identified structures along any trajectory. This display method, which was called "tract study," was very usefull for comprehensive understanding of location of trajectory in relation to individually varying anatomical structures...

Adolescent↗

PubMed1998

Functional anatomy, vascularisation and pathology of the human thalamus.

The thalamus is a nuclear complex situated in the diencephalon. Besides a neuro-anatomical description of the thalamus, this article reviews the current knowledge on the functional anatomy of the three functional classes of thalamic nuclei: specific, non-specific and association nuclei. As the majority of the pathology affecting the thalamus is of cerebrovascular origin, the vascularisation of the human thalamus will be reviewed as well. Finally, the knowledge of the functional anatomy and the vascularisation of the human thalamus will be integrated in the review of the semeiology of thalamic syndromes. Besides its function as a relay centre in subserving sensory and motor mechanisms, the thalamus participates in various neurocognitive processes such as memory and language. The current knowledge on these topics will be reviewed as well.

Cerebrovascular Disorders↗

PubMed1996

Projections from the cerebellar interposed and dorsal column nuclei to the thalamus in the rat: a double anterograde labelling study.

It is generally agreed that cerebellar and lemniscal pathways project to largely separate areas of the thalamus and influence different functional areas of the cerebral cortex. Cerebellar afferents arise from neurones in the deep cerebellar nuclei and terminate in the ventral lateral group of thalamic nuclei or the "motor thalamus," whereas lemniscal afferents arise from the dorsal column nuclei and terminate in the adjacent ventral posterior group of thalamic nuclei or "sensory thalamus." However, it remains unclear whether or not these pathways converge onto thalamic neurones in the border zone between motor and sensory thalamus. The aim of this study was to compare directly the locations of cerebellar interposed and dorsal column nuclei terminals in the rat thalamus by using a double anterograde labelling technique. Microinjections of dextran-tetramethylrhodamine and dextran-fluorescein were made into the interposed and dorsal column nuclei, and labelled terminals in the thalamus were examined in the same sections. The labelled cerebellar and lemniscal terminals were located in separate areas throughout most of the ventral lateral and ventral posterior lateral nuclei, and there was only a limited region around the rostral border between these nuclei where the two groups of terminals came in close proximity to each other. In this common projection zone, however, cerebellar and lemniscal terminals seldom intermingled, and they mostly occupied separate, discreet areas. The results show that cerebellar and lemniscal fibres do indeed project to the border zone between the sensory and cerebellar thalamic nuclei, but they show practically no overlap in this region and are likely to influence separate thalamic neurones.

Animals↗

PubMed2002

Analysis of projections from the medial prefrontal cortex to the thalamus in the rat, with emphasis on nucleus reuniens.

The medial prefrontal cortex (mPFC) is involved in high-order cognitive processes, including, but not limited to, decision making, goal directed behavior, and working memory. Although previous reports have included descriptions of mPFC projections to the thalamus in overall examinations of mPFC projections throughout the brain, no previous study has comprehensively examined mPFC projections to the thalamus. The present report compares and contrasts projections from the four divisions of the mPFC, i.e., the infralimbic, prelimbic, anterior cingulate and medial agranular cortices, to the thalamus in the rat by using the anterograde anatomic tracer Phaseolus vulgaris-leucoagglutinin. We showed that (1) the infralimbic, prelimbic, anterior cingulate cortices distribute heavily and selectively to midline/medial structures of the thalamus, including the paratenial, paraventricular, interanteromedial, anteromedial, intermediodorsal, mediodorsal, reuniens, and the central medial nuclei; (2) the medial agranular cortex distributes strongly to the rostral intralaminar nuclei (central lateral, paracentral, central medial nuclei) as well as to the ventromedial and ventrolateral nuclei of thalamus; and (3) all four divisions of the mPFC project densely to the nucleus reuniens (RE) of the thalamus. The nucleus reuniens is the major source of thalamic afferents to the hippocampal formation. There are essentially no direct projections from the mPFC to the hippocampus. The present demonstration of pronounced mPFC projections to RE suggests that the nucleus reuniens is a critical relay in the transfer of information from the medial prefrontal cortex to the hippocampus. Our further demonstration of strong mPFC projections to several additional thalamic nuclei, particularly to the mediodorsal nucleus, suggests that these thalamic nuclei, like RE, represent important output stations (or gateways) for the actions of mPFC on diverse subcortical and cortical structures of the brain.

Animals↗