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PubMed2002

Reduced basal release of serotonin from the ventrobasal thalamus of the rat in a model of neuropathic pain.

Drugs that inhibit reuptake of monoamines are frequently used to treat pain syndromes, e.g. neuropathy or fibromyalgia, where mechanical allodynia is present. Several lines of evidence suggest the involvement of supraspinal sites of action of these drugs. However, a direct study of supraspinal serotonin (5-HT) or norepinephrine (NE) release in an animal model in which allodynia is expressed, e.g. neuropathy, has not been done. The ventrobasal (VB) thalamus and the hypothalamus are major supraspinal projection regions for spinal neurons that transmit nociceptive information and are innervated by monoaminergic fibers. This study determined if peripheral neuropathy would induce changes in extracellular monoamines in VB thalamus and hypothalamus. Male Sprague-Dawley rats had spinal nerve roots L5 and L6 tightly ligated (neuropathic rats; NP) or sham (SHAM) surgery; contralateral and ipsilateral VB thalamus and contralateral hypothalamus were dialyzed with modified artificial cerebral spinal fluid (aCSF), with and without fluoxetine. NP rats had significantly decreased 5-HT content in dialysates of the contralateral VB thalamus compared with SHAM rats with (82% decrease) or without (63% decrease) fluoxetine in the perfusion medium over the 180 min of the study. There were no differences in the ipsilateral VB thalamus. In contrast, release of 5-HT was unchanged in the hypothalamic dialysates of SHAM vs. NP rats. NE release was not different in dialysates of either the VB thalamus or hypothalamus of SHAM vs. NP rats. Synthesis of 5-HT, as assessed by accumulation of 5-hydroxytrytophan after treatment with an L-amino acid decarboxylase inhibitor, was not different between NP and SHAM rats in VB thalamic and hypothalamic brain tissue. This study is the first to demonstrate changes in monoamine release supraspinally in NP rats. The differential effect between VB thalamus and hypothalamus suggests that a terminal field change may be involved. Putative mechanisms for mediating this change include alterations of GABA-ergic systems and/or plasticity related to alterations in N-methyl-D-aspartate receptor activation and nitric oxide release related to afferent hyperactivity induced by neuropathic pain.

Animals↗
PubMed1989

A cyto-architectonic description of the thalamus of the tammar wallaby, Macropus eugenii.

Very few studies are available on the cyto-architectural features of the thalamus of metatherian mammals. Most of these studies describe the thalamus of a polyprotodont metatherian, the North American opossum, Didelphis virginiana. Studies on diprotodont metatherians are fewer still. There are two descriptions of the thalamus of the Australian possum Trichosurus vulpecula. The only part of the thalamus that has been described in the wallabies is the lateral geniculate nucleus. Hence, there was a need for a description of the thalamus in a wallaby. This study describes the organisation and the cyto-architectonics of the thalamus of the tammar, Macropus eugenii. Except for the midline nuclei, the boundaries of all other nuclei are well demarcated due to their well-differentiated nuclear components. Within the lateral posterior complex, a pulvinar nucleus was identified, and the pre-tectal nuclei show extensive differentiation, as do the medial geniculate nuclei. Also, a small centre-median nucleus was identified. The anteroventral nucleus retains its dorsal position for its entire rostrocaudal extent. The nucleus of the optic tract is located in a dorsal position in the tammar, as it is in cats. The general conclusion from this study is that the nuclear organisation of the thalamus in the tammar, a metatherian mammal, is complex and comparable in most respects to that in cats, eutherian mammals.

Animals↗
PubMed1999

Connections between cells of the internal capsule, thalamus, and cerebral cortex in embryonic rat.

The aim of our study is to understand the development of the earliest connections in the mammalian pallium by documenting the distribution of cells and fibres labelled from the dorsal and ventral thalamus, internal capsule, perirhinal, and dorsal cortex during the period between embryonic day (E) 14 and 17 by using carbocyanine dye tracing in fixed embryonic rat brains. Dye placed in the thalamus of E14 brains backlabels cells in the thalamic reticular nucleus and within the primitive internal capsule. Both anterograde and retrograde tracing confirmed that the first corticofugal projections reach the internal capsule by E14. At E15-E16, after the first cortical plate cells have migrated into the lateral cortex, some cells of the cortical plate and subplate and marginal zone, are backlabelled from the internal capsule, but still not from the dorsal thalamus, even with very long incubation periods. Crystal placement into the perirhinal cortex at E14-E15 labels numerous cells within the internal capsule, whereas no such cells are revealed from dorsal cerebral cortex until E17, suggesting that internal capsule cells establish early connections with the perirhinal and ventral but not dorsal cortex. We propose that the growth of axons from cortex to dorsal thalamus is delayed in two regions: first from E14-E15 at the lateral entrance of the internal capsule and then, from E16, closer to the thalamus, probably within the thalamic reticular nucleus. Subplate projections reach the proximity of the diencephalon at an early stage, but they might never enter the dorsal thalamus.

Animals↗
PubMed1994

Movement disorders following lesions of the thalamus or subthalamic region.

Reports of 62 cases with a movement disorder associated with a focal lesion in the thalamus and/or subthalamic region were analyzed. Thirty-three cases had a lesion confined to the thalamus. Sixteen cases had a thalamic lesion extending into the subthalamic region and/or midbrain. Thirteen cases had a lesion in the subthalamic region or a subthalamic lesion extending into the midbrain. Nineteen cases with dystonia, 18 with asterixis, 17 with ballism-chorea, three with paroxysmal dystonia, and five with clonic or myorhythmic movements have been described. No case with isolated tremor has been described. In 53 cases with unilateral thalamic or subthalamic lesions, all but one with bilateral blepharospasm (associated with right posterior thalamic, pontomesencephalic, and bilateral cerebellar lesions) had dyskinesias in the limbs contralateral to the lesion. The other nine cases had bilateral paramedian thalamic lesions; seven developed bilateral dyskinesias, and the remaining two had unilateral dyskinesias. Regarding the 19 patients with dystonia, the two with bilateral blepharospasm had thalamic and upper brainstem lesions, and one with hemidystonia and torticollis had a subthalamic lesion. The other 16 patients all had a unilateral thalamic lesion with contralateral dystonia (10 hemidystonia, five focal dystonia affecting a hand and/or and one segmental dystonia involving face, arm, and hand). The exact location of the thalamic lesion was mentioned in 10 cases; the posterior or posterolateral thalamus was involved in six and the paramedian thalamus in four. These areas are more posterior or medial to the ventrolateral and ventroanterior thalamic nuclei, which receive pallido-thalamic and nigro-thalamic afferents. Two cases developed dystonia immediately after thalamotomy, and one case developed it 4 days after head trauma. The others initially had a hemiplegia and developed dystonia 1-9 months after the acute insult. Fifteen of the 17 patients with chorea had a unilateral lesion in the subthalamic nucleus or subthalamic region (eight due to infarcts, one to hemorrhage, five to mass lesions, and one to multiple sclerosis). All had contralateral hemichorea or hemiballism. One other case had bilateral chorea of the hands and tongue due to paramedian thalamic infarction. Another case with generalized chorea and thalamic atrophy was complicated by stereotaxic surgery. Thirteen of the 18 cases with asterixis had lesions confined to the thalamus. Eight were associated with thalamotomy, and five others had a stroke (four infarction and one hemorrhage) affecting the contralateral thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Dominance, Cerebral↗
PubMed1988

Transient asymmetry in the projections of the rostral thalamus to the visual hyperstriatum of the chicken, and reversal of its direction by light exposure.

Asymmetry in the visual pathways from the rostral thalamus to the hyperstriatum of the chicken has been found after injecting the retrograde tracer, True Blue (TB), into either the left or right hyperstriatum on day 2 or 12, post-hatching. There are ipsilateral connections from the ventromedial region of the left dorsolateral thalamus, lateral part (DLL) to the left hyperstriatum, and contralateral connections from the left dorsolateral thalamus, rostrolateral part (DLAlr) and the dorsolateral thalamus, dorsal part (DLLd) to the right hyperstriatum. On the right side of the thalamus, the ipsilateral connections from DLL to the right hyperstriatum are present, but there are only very few contralateral connections to the left hyperstriatum. No asymmetry in these pathways is seen in animals injected with TB on day 21. By this age the contralateral connections from the right thalamus to the left hyperstriatum have developed. Thus, the structural asymmetry in these visual pathways is transient, a finding which explains a controversy between two papers published recently in this journal, and which adds considerably to our understanding of the behavioural asymmetries known to occur in the chicken's response to stimuli presented to either the left or right eye. The direction of the asymmetry in visual pathways depends on asymmetrical light input to the eyes of the embryo. Normally the head of the embryo is oriented such that the left eye is occluded. If the head is withdrawn from the egg so that the right eye can be occluded and the left eye exposed to light, the direction of asymmetry in the thalamo-hyperstriatal pathways is reversed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Evidence for a projection from the perireticular thalamic nucleus to the dorsal thalamus in the adult rat and ferret.

During early development, the perireticular thalamic nucleus is very large (i.e. has many cells) and has a strong projection to the dorsal thalamus and to the cerebral neocortex. By adulthood, the nucleus has much reduced in size and only a few cells remain. It is not clear whether these perireticular cells that remain into adulthood maintain their connections with the dorsal thalamus and with the neocortex. This study examines this issue by injecting neuronal tracers into various nuclei of the dorsal thalamus (dorsal lateral geniculate nucleus, medial geniculate complex, ventroposteromedial nucleus, lateral posterior nucleus, posterior thalamic nucleus) and into different areas of the neocortex (somatosensory, visual, auditory). After injections of tracer into the individual nuclei of the rat and ferret dorsal thalamus, retrogradely-labelled perireticular cells are seen. In general, after each injection, the retrogradely-labelled perireticular cells lie immediately adjacent to a group of retrogradely-labelled reticular cells. For instance, after injections into the medial geniculate complex, perireticular cells adjacent to the auditory reticular sector are retrogradely-labelled, whilst after an injection into the dorsal lateral geniculate nucleus, retrogradely-labelled perireticular cells adjacent to the visual reticular sector are seen. By contrast, injections of tracer into various areas of the rat and ferret neocortex result in no retrogradely-labelled cells in the perireticular nucleus. Thus, unlike during perinatal development when perireticular cells project to both neocortex and dorsal thalamus, perireticular cells in the adult seem to project to the dorsal thalamus only: the perireticular projection to the neocortex appears to be entirely transient.

Animals↗
PubMed1998

Neuronal activity in the monkey ventrolateral thalamus following perturbations of voluntary wrist movements.

Extracellular single-cell recordings were made from the cerebellar thalamus (89 neurones) and the VPLc (53 neurones) of three conscious monkeys. The animals were trained to perform wrist movement paradigms including: (a) visually triggered skilled, voluntary movements; (b) 100-ms duration torque pulse perturbations applied during a hold period (termed Pa perturbations); (c) 100-ms perturbations that commenced 100 ms after the visual trigger but during preparation before a skilled, voluntary movement (termed Pb perturbations); and (d) 100-ms perturbations during the skilled, voluntary movement (termed Pm perturbations). These Pb and Pm perturbations were used to identify central and peripheral influences on patterns of neuronal discharge in the ventrolateral thalamus. There was no systematic difference between the responses to Pb and Pm perturbations of neurones in the cerebellar thalamus and those in VPLc. The responses of VPLc and cerebellar thalamic neurones to Pa perturbations were considered to represent transduction of peripheral afferent input, and these responses were compared with the responses to the other types of perturbations. Up to 40% of neurones in cerebellar thalamus and VPLc responded to Pb and Pm perturbations in a similar pattern to that which followed Pa perturbations, and therefore most likely represented faithful transduction of peripheral input. However, the response of over half the neurones in VPLc and cerebellar thalamus to Pb or Pm perturbations differed from Pa perturbations in a manner suggesting that central influences had gated the peripheral input. The short-latency response in cerebellar thalamus which was modified by central influences is appropriately timed to contribute to the "intended" response to perturbations of motor cortical neurones.

Afferent Pathways↗
PubMed1987

Importance of bilateral sympathetic innervation on cerebral blood flow autoregulation in the thalamus.

Effects of bilateral sympathetic innervation on the regulation of cerebral blood flow to the thalamus were examined in spontaneously hypertensive rats (SHR). The superior cervical ganglion was removed on one side or bilaterally, and blood flow in the thalamus was repeatedly measured with a hydrogen clearance technique during a stepwise increase in arterial pressure. Regional blood flow in the thalamus was unchanged following acute ganglionectomy: 55 +/- 6 ml/100 g/min in the intact rats and 56 +/- 4 in the denervated rats. Sympathectomy on one side neither had effects on the pressure-flow relationship nor on the blood pressure levels of upper limits of autoregulation in the ipsilateral thalamus. In contrast, bilateral sympathetic denervation impaired the autoregulatory function in the thalamus and the upper limits were significantly lower than those in intact rats: 206 +/- 8 vs 226 +/- 10 mm Hg, respectively (P less than 0.02). It is concluded that overlapping innervation of sympathetic nerves has an important role in regulation of blood flow to the thalamus during an acute rise in arterial pressure in SHR.

Adrenergic Fibers↗
PubMed2026

Large-Scale Neuroimaging and Genetic Analyses of the Human Thalamus in Loneliness.

BACKGROUND: Although loneliness is prevalent and significantly impacts society globally, its neural and genetic bases remain poorly understood. The thalamus, which receives sensory information from the environment, may have a more significant role in social interactions than previously recognized. Here, we integrate neuroimaging and genetic approaches to characterize structural differences within the thalamus associated with loneliness. METHODS: We obtained thalamic nuclei volumes on brain scans from 45,834 individuals (age range: 45-82 years) in the UK Biobank and grouped them into 6 anatomical groups. We investigated effects of loneliness and social isolation using self-reported data. Then, we performed a genome-wide association study (GWAS) analysis on the genetic overlap between thalamic volumes and loneliness. RESULTS: The volumes of the whole thalamus and its medial, lateral, and posterior nuclei are significantly reduced in individuals with loneliness compared with those who do not feel lonely. Loneliness with frequent social contact is associated with smaller volumes, whereas social isolation without loneliness shows no such reduction in thalamus volumes. Leveraging data from GWASs on thalamic volumes (n = 30,114) and loneliness (n = 370,342) in the UK Biobank, we identified shared loci between thalamus structure and loneliness. CONCLUSIONS: Our findings support the emerging view that the thalamus plays important roles in social interactions and in the experience of loneliness.

Genetic architecture↗
PubMed2000

Proton spectroscopic imaging of the thalamus in treatment-naive pediatric obsessive-compulsive disorder.

BACKGROUND: Neurobiological abnormalities in the thalamus, particularly the dorsomedial nucleus of the thalamus, are believed to be involved in the pathophysiology of obsessive-compulsive disorder. Although obsessive-compulsive disorder commonly arises in childhood and adolescence, no prior study has examined the thalamus in pediatric obsessive-compulsive disorder patients. METHODS: In this study, N-acetyl-aspartate, a putative marker of neuronal viability, creatine/phosphocreatine, and choline levels were measured in the lateral and medical subregions of the left and right thalami using a multislice proton magnetic resonance spectroscopic imaging sequence in 11 treatment-naive, nondepressed obsessive-compulsive disorder outpatients, 8-15 years old, and 11 case-matched control subjects. RESULTS: A significant reduction in N-acetyl-aspartate/choline and N-acetyl-aspartate/(creatine/phosphocreatine + choline) was observed in both the right and left medial thalami in obsessive-compulsive disorder patients compared with control subjects. The N-acetyl-aspartate/choline and N-acetyl-aspartate/(creatine/phosphocreatine + choline) levels did not differ significantly between case-control pairs in either the left or the right lateral thalamus. Reduction in N-acetyl-aspartate levels in the left medial thalamus was inversely correlated with increased obsessive-compulsive disorder symptom severity. CONCLUSIONS: These findings provide new evidence of localized functional neurochemical marker abnormalities in the thalamus in pediatric obsessive-compulsive disorder. Our results must be considered preliminary, however, given the small sample size.

Adolescent↗
PubMed1998

Destruction of the auditory thalamus disrupts the production of fear but not the inhibition of fear conditioned to an auditory stimulus.

The auditory thalamus is part of a neural circuit that mediates the expression of fear to auditory stimuli. Bilateral lesions of the auditory thalamus prevent the expression of fear to an auditory stimulus paired with shock. The present study assessed whether bilateral lesions of the auditory thalamus would also disrupt the inhibition of fear to an auditory stimulus paired with the absence of shock. Rats were given bilateral lesions of the auditory thalamus followed by Pavlovian conditioned inhibition training in which a light was paired with shock and a noise and light compound was presented in the absence of shock. Fear and the inhibition of fear were measured with the fear-potentiated startle effect. Lesions of the auditory thalamus did not disrupt the ability of the noise to inhibit the expression of fear to the light. However, these lesions did disrupt the ability of the noise to produce fear-potentiated startle after it had been subsequently paired with shock. These results suggest that although the auditory thalamus is an essential part of a neural circuit that mediates the expression of fear to auditory stimuli, it is not an essential part of the circuit that mediates the inhibition of fear to auditory stimuli.

Acoustic Stimulation↗
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↗
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↗
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↗