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PubMed2004

[Acute onset of somnolence and amnesia due to cerebral infarction of bilateral thalamus accompanied with tuberculous meningitis: a case report].

A 55-year-old man was admitted to our hospital because of somnolence and aspontaneity. He was hospitalized in the psychopathic ward under the initial diagnosis of depression. Chest X-ray showed infiltration in both upper lobe. Twelve days later, Mycobacterium tuberculosis was detected from his sputum and was confirmed by RT-PCR. Cerebrospinal fluid findings showed elevated ADA and mononuclear cells, suggesting the presence of tuberculous meningitis. However, the brain CT revealed no abnormal findings. By applying antituberculous treatment the pulmonary lesion improved but psychological symptoms remained. Three months later follow-up brain MRI was examined. Contrast enhanced granuloma was detected in the ambiens, suprasellar and quadrigeminal cisterns. A strong signal was seen in the left frontal thalamus and a weak enhanced lesion was detected in the right frontal thalamus on a T2 enhanced image. These lesions showed low intensity on a T1 enhanced image, suggesting cerebral infarction affecting the bilateral thalamus. Somnolence and memory disorder was due to cerebral infarction of the bilateral thalamus and tuberculous meningitis contributed to form the intracranial lesion. From the experience of this case, it is needed to consider cerebral infarction (especially the thalamus) due to tuberculous meningitis when we examine the patients with acute onset of psychological symptoms.

Amnesia↗
PubMed1991

Patterns of activity coding discrimination of auditory stimuli differ between mid- and posterolateral thalamus of cats.

The auditory function of units in the mid- (lateralis dorsalis and centrolateral nuclei) and posterolateral (lateralis posterior-pulvinar complex) thalamus of cats was assessed during performance of conditioned eye blink responses (CRs) elicited discriminatively by a forward-paired, 70 dB click conditioned stimulus (CS) as opposed to a backward-paired, 70 dB hiss discriminative stimulus (DS). Discharges in response to the CS or DS were found in over 40% of units tested in each area, with onset latencies as short as 28-32 msec in mid-thalamus and 14 msec in posterolateral thalamus. The results provide evidence that both mid- and posterolateral thalamic regions of cats contain sufficient numbers of auditory responsive neurons to be considered part of the auditory system functionally. Patterns of activity changed after conditioning discriminative responses to the click CS. In mid-thalamus, the ratio of CS-evoked activity to baseline activity increased relative to levels found before conditioning. This increase was attributable to an increase in the magnitude of response to the CS. In posterolateral thalamus, an increase in the signal: noise ratio of activity in response to the CS was also found after conditioning, but this increase depended in large part on a decrease in the rate of baseline firing. Posterolateral thalamic units had substantially higher mean rates of baseline firing than mid-thalamic units before any conditioning sessions were begun.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1988

Neuronal populations stained with the monoclonal antibody Cat-301 in the mammalian cerebral cortex and thalamus.

The monoclonal antibody Cat-301 was used to examine neurons in the cerebral cortex and dorsal thalamus of several mammalian species, including Old World monkeys, cats, bush babies, guinea pigs, and rats. In each species, subpopulations of cortical and thalamic neurons are stained along the surfaces of their somata and proximal dendrites. Cat-301-positive cortical neurons include specific groups of pyramidal cells (e.g., corticospinal but not corticobulbar or callosal neurons in the monkey sensory-motor areas) and certain GABA-immunoreactive nonpyramidal cells. In the thalamus, the relay neurons projecting to the cortex and not the intrinsic neurons are stained. The Cat-301-positive neurons are nonhomogeneously distributed in the cat and monkey cortex and thalamus. In the cortex, they are densely packed in 2 bands that in most areas include layers III and V, but that in primary sensory areas include layers IV and VI. Because the density of stained neurons, their distribution, and the intensity of their staining vary among cortical areas, the borders between neighboring areas can often be detected by the differences in Cat-301 staining. Broader, regional differences are also readily apparent, for areas in the parietal and occipital lobes contain large numbers of intensely stained cells, but most areas in the frontal and temporal lobes contain fewer, more lightly stained neurons. The same broad differences are seen within the thalamus: only those nuclei reciprocally connected with intensely stained cortical areas contain large numbers of Cat-301-positive neurons. Differences among species include variations in cell density and distribution when a given cortical area or thalamic nucleus is compared between cats and monkeys. Greater differences are seen among the other species. Immunoreactive neurons in the cerebral cortex are sparse and lightly stained in guinea pigs, are restricted to the hippocampal formation in rats, and are very rare and isolated in bush babies. Similarly, Cat-301-positive thalamic neurons are restricted to only one or 2 nuclei in the guinea pig and rat and are extremely rare in the bush baby. Cat-301 stains organized groups of neurons in the cat and monkey cortex and thalamus. In addition to the laminar organization of stained cells in all cortical areas (see above), the Cat-301-positive neurons of monkey areas 17 and 18 are grouped into radial arrays. In area 17, clusters of stained cells are present in layers above and below layer IVC. These clusters lie at the centers of ocular dominance columns, within patches stained for cytochrome oxidase (CO). Most of these cells are also GABA-immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Effect of verapamil and diltiazem on the rCBF and the rCBF autoregulation in cortex and thalamus of cats.

The effects of Verapamil and Diltiazem, administered at a dose of 0.3 mg/kg i.v., on the autoregulation of the regional cerebral blood flow (rCBF) in the cortex and the thalamus were studied on 28 cats. The animals were anesthetized with ether and alfa-chloralose. The rCBF was registered by the hydrogen clearance method with locally generated hydrogen. The mean arterial blood pressure (MABP) elevation was performed by an i.v. infusion of angiotensin (0.2 microgram/min). The mean initial values of the cortical rCBF were 71.15 ml/100g/min and of the thalamic rCBF -46.85 ml/100 g/min. The mean limits of the cortical rCBF autoregulation were: 137.5 mm Hg for the absolute limit (La) and 31.25 mm Hg for the relative limit (Lr). The mean limits of the thalamic rCBF autoregulation were: 157.75 mm Hg for the (La) and 46.5 mm Hg for the (Lr). Verapamil increased the cortical rCBF by 40% and the thalamic rCBF by 24%. The absolute limits of rCBF autoregulation were decreased by 22% in the cortex, and by 15% in the thalamus. The relative limits were decreased by 31% in the cortex and by 35% in the thalamus. Diltiazem increased the cortical rCBF by 42% and the thalamic rCBF by 6%. The absolute limits of rCBF autoregulation were decreased by 21% in the cortex and the thalamus. The relative limits were decreased by 52% in the cortex, and by 38% in the thalamus.

Animals↗
PubMed1979

Development of the diencephalon in the rat. VI. Re-evaluation of the embryonic development of the thalamus on the basis of thymidine-radiographic datings.

The development of the thalamus was examined in normal and X-irradiated embryos from day 13 (E13) to the day before birth (E22). The differentiating, radioresistant neurons of the lateral habenular nucleus, derived from a portion of the superior neuroepithelial lobule (SL1), were settling by day E15 and by this time the habenulopeduncular tract was forming. The neurons of the reticular nucleus, derived from the middle neuroepithelial lobe, began to settle on day E15 but a massive migration was still evident on day E16. Adjacent to the reticular nucleus the internal capsule appeared on day E16; this fiber bundle seemed to be continuous with fibers embedded in the first transitory zone of cells issuing from the dorsal neuroepithelial lobe. Because of the immaturity of the neocortex at this time, it was postulated that thalamocortical fibers of the dorsal thalamus are the earliest components of the internal capsule. By day E17 all the sensory relay nuclei of the thalamus were recognizable and it was assumed that the second transitory zone issuing from the receding dorsal neuroepithelial lobe contained the neurons of the later forming intralaminar nuclei. Suggestive evidence was obtained that the late arising neurons of the medial thalamus (the anterior nuclei, the mediodorsal nucleus, and some or all of the midline nuclei) originate in a portion of the superior neuroepithelial lobule designated as SL2. Our present and previous studies showed that the major divisions of the hypothalamus and thalamus are derived embryonically from distinguishable parts of the third ventricle neuroepithelium. This implies the te third ventricle neuroepithelium has a "mosaic" organization and suggests that the fate of hypothalamic and thalamic neurons may be determined to some extent while their precursors are still proliferating.

Animals↗
PubMed1981

Connections of the ventroposterior nucleus of the thalamus with the body surface representations in cortical areas 3b and 1 of the cynomolgus macaque, (Macaca fascicularis).

The somatotopic pattern of the connections of the ventroposterior nucleus of the thalamus with the representations of the body surface in somatic cortical Areas 3b and 1 were investigated in macaque monkeys using the anatomical tracers horseradish peroxidase (HRP), and 3H-proline. These tracers, in combination or separately, were injected into one or more cortical sites, after the skin surface capable of activating neurons at each site had been defined with microelectrode mapping methods. These injection sites were later related to the overall organizations of the two cutaneous representations as determined in more extensive mapping experiments (Nelson et al, '80). Finally, zones of anterograde and retrograde label in the thalamus were located with reference to architectonically defined subnuclei in the ventroposterior nucleus (VP). The results led to the following conclusions. (1) Zones of cells in VP projecting to a given location in either Area 3b or 1 also receive reciprocal projections from the cortical target. (2) A given cortical location typically relates to a disc-shaped or lamellar region in VP with the disc extending rostrocaudally and dorsoventrally, being most narrow in the mediolateral dimension. (3) The representations of the same body surface in Area 1 and Area 3b relate to the same region of VP. However, since fewer cells were generally labeled after Area 1 injections, less dense terminations are suggested from VP to Area 1 than to Area 3b. (4) VP is the major or exclusive relay of somatosensory information to the two cutaneous representations from the thalamus. Labeled neurons or zones of terminations were found outside VP in other parts of the somatosensory thalamus only when injection sites extended into cortex outside Areas 3b and 1. (5) The face, hand, limbs, and foot are represented in a mediolateral sequence of subnuclei within VP. A dorsal capping subnucleus is apparently largely devoted to the axial trunk and perhaps other hairy skin surfaces such as some parts of the proximal surfaces of the limbs. (6) While anterior and posterior surfaces of the hind limb are widely separated by the glabrous foot in the cortical representations, they appear to be represented in adjacent zones in the thalamus.

Animals↗
PubMed1987

Evidence for a viscerotopic sensory representation in the cortex and thalamus in the rat.

The functional organization of the insular cortex was studied by recording neuronal responses to visceral sensory stimuli. Horseradish peroxidase (HRP) was then iontophoresed at the recording sites to identify afferents from the ventrobasal thalamus to specific visceroceptive sites in the insular cortex. The relationship of the ventrobasal thalamus to the insular cortex and to brainstem relay nuclei for the ascending visceral projections was then examined by using the axonal transport of HRP, wheat germ agglutinin conjugated to HRP (WGA-HRP), and fluorescent dyes. Of a total of 55 neurons that were tested for responses to visceral sensory stimuli, 33 units responded to at least one visceral sensory modality: 6 received gastric mechanoreceptor input, 8 responded to taste inputs, 13 were activated by arterial chemoreceptors and/or showed respiratory related activity, and 6 responded to cardiovascular baroreceptor stimulation. On the basis of its cytoarchitecture and connections with the thalamus, the insular cortex was divided into a dorsal granular area, an intermediate dysgranular region, and a ventral agranular strip. Taste-responsive neurons were located anteriorly, primarily in the dysgranular region, whereas unit responses to general visceral modalities were distributed dorsally and posteriorly in the granular insular cortex. Gastric mechanoreceptor-responsive units were situated more dorsally and anteriorly in the granular insular cortex, while cardiopulmonary inputs were located more ventrally and posteriorly. Injections of HRP into the gustatory insular cortex resulted in retrograde labeling of neurons in the parvicellular part of the ventroposterior medial thalamic nucleus (VPMpc). Injections into the general visceral insular cortex retrogradely labeled neurons lateral to VPMpc in the ventroposterior lateral parvicellular thalamic nucleus (VPLpc). Injections of HRP, WGA-HRP, and fluorescent dyes into VPMpc and VPLpc verified that their projection to the insular cortex is topographically organized. In the same experiments, retrogradely labeled neurons in the parabrachial nucleus identified the likely subnuclei within this nucleus for relay of visceral sensory information to the thalamus. Injections of WGA-HRP into the parabrachial nucleus demonstrated that its projection to the ventrobasal thalamus is also topographically organized. These results demonstrate the relationship of general visceral and special visceral (taste) representations in the insular cortex. The ascending pathway for visceral sensory information appears to be viscerotopically organized at all levels of the neuraxis, including the insular cortex.

Action Potentials↗
PubMed2006

Excitatory actions of the ventral midline thalamus (rhomboid/reuniens) on the medial prefrontal cortex in the rat.

The medial prefrontal cortex (mPFC) has been associated with diverse functions including attentional processes, visceromotor activity, decision making, goal directed behavior, and working memory. The present report examined the effects of stimulation of the midline thalamus, concentrating on ventral nuclei of the midline thalamus, on evoked activity at the mPFC. The nucleus reuniens (RE) of the ventral midline thalamus is a major source of projections to the hippocampus and to the mPFC, and has been shown to exert pronounced excitatory effects on the hippocampus. No previous study has systematically examined the actions of the ventral midline thalamus on the mPFC. We showed that stimulation of the dorsal and ventral midline thalamus, but not of an intermediate region lying between them (null zone), produced short latency, large amplitude evoked potentials throughout the dorsoventral extent of the medial PFC. The largest effects were elicited with ventral midline stimulation (rhomboid/reuniens nuclei) at the ventral mPFC--the prelimbic (PL) and infralimbic (IL) cortices. Specifically, stimulation of RE produced evoked potentials (early negative component, N2) at the PL cortex at a mean latency of 22.6 msec and mean amplitude of 0.85 mV, indicative of monosynaptic effects. In addition, we showed that paired pulse stimulation of RH/RE produced strong facilitatory actions (paired pulse facilitation) at IL (83%) and PL (75%). These findings indicate that RE exerts strong direct excitatory effects on the mPFC, and coupled with the demonstration that RE produces similar actions on the hippocampus, indicates that RE is in a position to influence and possibly coordinate the activity of these two forebrain structures subserving memory.

Animals↗
PubMed1985

Efferent fibers from the motor cortex terminate bilaterally in the thalamus of rats and cats.

The anterograde transport of lectin-conjugated horseradish peroxidase (WGA-HRP) was here employed in order to visualize crossed corticothalamic efferents of the motor cortex in rats and cats. After WGA-HRP cortical injections in the rat retrogradely labeled cells were observed in the ipsilateral thalamus, and heavy anterograde labeling was observed both in the ipsi- and contralateral thalamus. The contralateral anterograde labeling was less intense than the ipsilateral one and it was distributed in the anterior intralaminar structures, in the parafascicular nucleus, in the ventromedial, ventrolateral and ventrobasal nuclei and in the posterior complex, symmetrically to the labeling observed on the ipsilateral side. Further experiments were made in the rat in order to ascertain that the bilateral anterograde labeling in the thalamus derived unilaterally from the cortex. To this purpose, kainic acid was injected unilaterally either into the frontal cortex or into the thalamus, and WGA-HRP was later injected on the same side in the frontal cortex. Moreover, WGA-HRP was injected into the frontal cortex after splitting of the corpus callosum. The results obtained in these experiments confirmed that cortical neurons projected bilaterally upon the thalamus. Further, these experiments indicated that at least the majority of the contralateral fronto-thalamic fibers crossed the midline in the thalamic massa intermedia. WGA-HRP injections into the pericruciate cortex in the cat confirmed the presence of anterogradely labeled terminals in the contralateral anterior and posterior intralaminar, ventral anterior, ventromedial and ventrolateral nuclei. The labeling was in all cases heavier in the intralaminar nuclei than in the other structures, but it was less intense than that observed in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Cholinergic projections from the midbrain and pons to the thalamus in the rat, identified by combined retrograde tracing and choline acetyltransferase immunohistochemistry.

The distribution of cholinergic neurons in the midbrain and pons which project directly to the thalamus was investigated in the rat using a procedure which allows the simultaneous detection of retrogradely transported horseradish peroxidase (HRP) and immunohistochemical demonstration of choline acetyltransferase (ChAT) in the same neurons. HRP injections were placed in the dorsal half of the anterior third of the thalamus on one side which included the anteroventral nucleus as well as portions of the rostral intralaminar and reticular nuclei. These thalamic nuclei showed the highest density of immunohistochemically detectable cholinergic fibers. Neurons containing both HRP and ChAT, which represented cholinergic neurons projecting directly to the thalamus, were found in the midbrain and pons in the lateral tegmental reticular formation, parabrachial region and lateral dorsal tegmental nucleus. Ipsilateral to the injection site over 91% of the HRP labeled neurons in all of these regions were cholinergic, while an average of 60% of the cholinergic neurons had transported HRP. Contralateral to the injection site 5-6% of the cholinergic neurons in these regions were also retrogradely labeled. These findings demonstrate direct cholinergic projections to the thalamus from neurons in several regions in the tegmentum and suggest that tegmental projections to the thalamus are predominantly cholinergic.

Animals↗
PubMed1984

Nuclear distribution of glutamate, gamma-aminobutyrate and aspartate within the normal human thalamus.

Detailed mapping of amino acid neurotransmitter candidates, glutamate, gamma-aminobutyrate and aspartate within the human thalamus, was performed with a grid microdissection method using two horizontal slices of the right thalamus from four neurologically normal cases. Although the fine distribution of these amino acids varied considerably from case to case, characteristic patterns of distribution for each amino acid could be demonstrated by superimposing maps of each case. Glutamate was high around a caudal part of nucleus medialis and a rostral part of nucleus pulvinaris. Interestingly enough, gamma-aminobutyrate distributed in a similar manner to glutamate, suggesting the possible interaction between glutamate and gamma-aminobutyrate in these areas of the thalamus. The distribution of aspartate was different from the former two amino acids and highly concentrated areas were patchy and scattered in the middle part of the thalamus. The results were discussed in relation to the recently accumulated evidence obtained from animal brains for neurotransmitter roles of these amino acids in the thalamus.

Aged↗
PubMed2005

Reduced sensorimotor inhibition in the ipsilesional motor cortex in a patient with chronic stroke of the paramedian thalamus.

OBJECTIVE: Unilateral or bilateral paramedian infarction in the region of the thalamus and upper midbrain may lead to hypersomnia. To determine whether unilateral infarction of the paramedian thalamus leads to changes in excitability of ipsilesional primary motor hand area (M1). METHODS: We describe a patient with chronic stroke of the right dorsomedian and intralaminar thalamic nuclei, who suffered from mild persistent hypersomnia. We studied the excitability of the right and left M1 with transcranial magnetic stimulation (TMS) in the patient, and in 10 healthy controls. RESULTS: In contrast to healthy controls, contralateral electrical stimulation of the median nerve failed to induce short-latency afferent inhibition (SAI) in the ipsilesional M1. Other measures of corticomotor excitability and somatosensory evoked potentials were normal. CONCLUSIONS: The selective loss of ipsilateral SAI in a patient with paramedian thalamic stroke suggests that during wakefulness, the intact paramedian thalamus facilitates the excitability of intracortical inhibitory circuits, which process thalamocortical sensory inputs in the ipsilateral M1. This preliminary finding suggests that measurements of SAI may provide a means of probing the integrity of some neural pathways, which are involved in the control of wakefulness and arousal. SIGNIFICANCE: In addition to the established role of the paramedian thalamus in arousal and memory, our observation suggests that thalamocortical projections from the paramedian thalamus contribute to the integration of sensory input at the cortical level during wakefulness.

Adult↗
PubMed1998

Correlation between potentiation of AP1 DNA binding and expression of c-Fos in association with phosphorylation of CREB at serine133 in thalamus of gerbils with ischemia.

Protein biosynthesis is mainly under the control at the level of gene transcription in eukaryotes. Transcription factors are nuclear proteins with abilities to modulate the activity of RNA polymerase II which is responsible for the formation of messenger RNA from double stranded DNA in the cell nuclei. Binding of a radiolabeled oligonucleotide probe for the transcription factor activator protein-1 (AP1) was transiently potentiated 1 to 6 h after the recirculation of blood supply in the thalamus and striatum, but not in the entorhinal cortex, olfactory bulb, frontal cortex, cerebellar cortex and medulla-pons, in gerbils with transient global forebrain ischemia for 5 min, in addition to the hippocampal subregions. The ischemic insult not only increased the immunoreactivity with an antibody against cyclic AMP response element binding protein (CREB) phosphorylated at serine133, but also induced the expression of both c-Jun and c-Fos family proteins 3 h after the recirculation in the thalamus. Limited proteolysis by Staphylococcus aureus (S. aureus) V8 protease revealed the expression of different partner proteins of AP1 in response to ischemic signals in the thalamus. Moreover, ischemia for 2 min led to more prolonged elevation of AP1 binding in the thalamus at least up to 12 h after the reperfusion than that seen with ischemia for 5 min. These results suggest that potentiation of AP1 DNA binding may at least in part involve mechanisms associated with the expression of c-Fos protein through phosphorylation of CREB at serine133 in the thalamus of gerbils with ischemia.

Amino Acid Sequence↗
PubMed2001

Theta-rhythmically firing neurons in the anterior thalamus: implications for mnemonic functions of Papez's circuit.

In 1937 Papez described an anatomical circuit (or loop) beginning and ending in the hippocampal formation that he proposed subserved emotional experience (Papez, 1937). Specifically, the projections of the circuit were as follows: hippocampal formation--> mammillary bodies--> anterior thalamus--> cingulate cortex--> parahippocampal gyrus--> hippocampal formation. Although the circuit has been refined based on subsequent anatomical findings (Amaral and Witter, 1995; Shibata, 1992; Van Groen and Wyss, 1995), the major links of the circuit unquestionably represent a prominent system of connections in the mammalian brain. Hence, the enduring nature of 'Papez's circuit'. Unlike, however, its persistence as anatomical entity, the proposed functional role for the circuit has been less resilient. The early notion that Papez's circuit subserves emotional experience/expression has been abandoned (LeDoux, 1993) and replaced by the proposal that it is primarily involved in mnemonic functions (Aggleton and Brown, 1999). Lesions of each of the major components of the circuit have been shown to disrupt memory (Aggleton and Brown, 1999; Sutherland et al., 1988; Sziklas and Petrides, 1993). The mammillary bodies represent a major output from the hippocampus in Papez's circuit (Amaral and Witter, 1995). It has recently been shown that cells of mammillary body fire rhythmically in bursts synchronous with the theta rhythm of the hippocampus (Bland et al., 1995; Kirk et al., 1996; Kocsis and Vertes, 1994, 1997) and that this rhythmical activity is dependent upon the action of the hippocampus on the mammillary bodies (Bland et al., 1995; Kirk et al., 1996). It is well established that the mammillary bodies project massively to the anterior thalamus (Shibata, 1992), which taken together with the demonstration that mammillary body cells fire synchronously with theta, suggests that the mammillary bodies may act on the anterior thalamus, possibly in the manner that the hippocampus acts on the mammillary bodies, to rhythmically activate cells of the anterior thalamus at theta frequency. We demonstrated that approximately 75% of cells of the anterior ventral nucleus of the thalamus fire rhythmically synchronous with the hippocampal theta rhythm and the activity of 46% of these anterior ventral neurons was highly correlated with theta. These findings, together with demonstration of theta-rhythmically firing cells in other structures of Papez's circuit, indicate that a theta-rhythmic signal may resonate throughout Papez's circuit, possibly involved in the control of mnemonic functions of the circuit.

Action Potentials↗
PubMed2003

Integrated contributions of basal forebrain and thalamus to neocortical activation elicited by pedunculopontine tegmental stimulation in urethane-anesthetized rats.

Efferents from the pedunculopontine tegmentum (PPTg) exert widespread control over neocortical electrocorticographic (ECoG) activity and aid in maintaining high-frequency ECoG activation during waking and rapid eye movement sleep. The mechanisms and subcortical routes that allow the PPTg to influence cortical activity remain controversial. We examined the relative contributions of the thalamus and basal forebrain in ECoG activation elicited by PPTg stimulation in urethane-anesthetized rats. Stimulation (100 Hz, 2 s) of the PPTg suppressed large-amplitude, low-frequency oscillations, replacing them with high-frequency beta-gamma activity. Systemic administration of the anti-muscarinic drug scopolamine (1 mg/kg, i.p.) abolished activation elicited by PPTg stimulation, suggestive of an essential role of acetylcholine in this effect. Local infusions of lidocaine (1 microl, 1%) into the region of the cholinergic basal forebrain complex produced a strong reduction in activation elicited by PPTg stimulation. Lidocaine infusions into the reticular thalamic nucleus had no effect, but infusions into central thalamus produced a small attenuation of PPTg-evoked cortical activation. Combined basal forebrain-central thalamic infusions (1 microl/site) produced roughly additive effects, leading to a greater loss of activation than single-site infusions. These results indicate that, under the present experimental conditions, high-frequency cortical ECoG activation elicited by the PPTg involves relays in both the basal forebrain and central thalamus, with a predominant role of the basal forebrain. After concurrent central thalamic-basal forebrain inactivation, the forebrain can maintain only limited, short-lasting activation in response to PPTg stimulation. The additivity of infusion effects suggests that, rather than participating in one serial system, basal forebrain and central thalamus constitute parallel activating pathways. These findings aid in resolving previous controversies regarding the role of thalamus and basal forebrain in activation by emphasizing the importance of multiple, large-scale networks between brainstem and cortex in regulating the activation state of the mammalian neocortex.

Acetylcholine↗
PubMed2003

Increased c-Fos expression in the centromedial nucleus of the thalamus in metabotropic glutamate 8 receptor knockout mice following the elevated plus maze test.

Ligands for metabotropic glutamate 8 (mGlu8) receptors, such as (S)-2-amino-4-phosphonobutanoic acid and (S)-3,4-dicarboxyphenylglycine suppress CNS excitability via presynaptic regulation of glutamate release and are anticonvulsant in mice. These observations suggest that mGlu8 receptors play a role in the regulation of neuronal excitability. To further characterize the role of mGlu8 receptors in vivo, the mGlu8 receptor knockout mouse was generated. Recently, we reported that mGlu8 receptor knockout mice showed increased anxiety in the elevated plus maze (EPM). Here, the pattern of c-Fos expression was studied in mGlu8 receptor knockout and wild-type mice after exposure to the EPM test for 5 min. The present study shows that the increased anxiety-related behavior of mGlu8 receptor knockout mice in the EPM was associated with a 2.3-fold higher (P<0.05) number of c-Fos positive cells in the centromedial nucleus of the thalamus compared with wild-type mice (when prehandled mice were used). The increased neuronal activity in the centromedial nucleus of the thalamus in the mGlu8 receptor knockout mouse was also observed in a separate experiment with naive mice (no prehandling). In these naive mGlu8 receptor knockouts, c-Fos expression was significantly induced by the EPM in the centrolateral nucleus of the thalamus, paraventricular nucleus of the hypothalamus, and granular cell layer of the dentate gyrus, but in naive wild-type mice c-Fos was significantly increased only in the piriform cortex. Basal c-Fos expression in the absence of EPM exposure did not differ between wild-type and mGlu8 receptor knockout mice in any brain region we examined. As the centromedial nucleus of the thalamus is important in regulating sensory information to higher brain regions, these results support the hypothesis that mGlu8 receptors are involved in the response to certain novel, aversive environments. In particular, the deletion of the mGlu8 receptor reduced the threshold of neuronal activation in stress-related brain regions such as the centromedial nucleus of the thalamus.

Animals↗
PubMed1999

Calcium-binding protein immunoreactivity delineates the intralaminar nuclei of the thalamus in the human brain.

Immunohistochemical studies have shown that the three calcium-binding proteins (calbindin-D28k, calretinin and parvalbumin) are heterogeneously distributed in the mammalian brain and are useful for delineating nuclear boundaries. We have investigated the distribution of the three calcium-binding proteins in the human thalamus in order to assist in the delineation of the equivocal nuclear boundaries of the intralaminar nuclei of the thalamus. The results show that each of the "functional" nuclear complexes in the human thalamus demonstrates a characteristic pattern of calcium-binding protein immunoreactivity. In particular, the intralaminar nuclei are characterized by a unique combination of calcium-binding protein staining which clearly delineates the component nuclei in this complex from the other nuclei of the human thalamus. The anterior group of intralaminar nuclei (central lateral nucleus, paracentral nucleus and central medial nucleus) showed intense staining for both calbindin-D28k and calretinin. By contrast, the posterior group of intralaminar nuclei (centre median nucleus and parafascicular nucleus) showed a complementary pattern of staining; the centre median nucleus showed immunoreactivity only for one calcium-binding protein, parvalbumin, while the parafascicular nucleus showed immunoreactivity for both calbindin-D28k and calretinin. No other nucleus in the human thalamus showed these particular combinations of calcium-binding protein staining. Since the intralaminar nuclei also have unique topographically organized connectional affiliations with both the cerebral cortex and the basal ganglia, these results suggest that the calcium-binding proteins may play an important role in the influence of the intralaminar nuclei on interactions between the cerebral cortex and the basal ganglia.

Adult↗
PubMed2000

Bilateral blockade of NMDA receptors in anterior thalamus by dizocilpine (MK-801) injures pyramidal neurons in rat retrosplenial cortex.

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, ketamine, phencyclidine (PCP) and dizocilpine (MK-801), produce psychosis in people. In rodents they produce cytoplasmic vacuoles in injured retrosplenial cortical neurons that express HSP70 heat shock protein. This study examined possible circuits and receptors that mediate this neuronal injury. Bilateral, but not unilateral, injection of dizocilpine (5, 10, 15, 20 microg/microL per side) into the anterior thalamus induced HSP70 protein in pyramidal neurons in deep layer III of rat retrosplenial cortex 24 h later. In contrast, bilateral dizocilpine injections (5, 10, 15, 20 microg/microL per side) into the retrosplenial cortex or into the diagonal band of Broca did not induce HSP70. Bilateral injections of muscimol (0.1, 1, 10 microg/microL per side), a GABAA (gamma-aminobutyric acid) agonist, into the anterior thalamus blocked HSP70 induction in the retrosplenial cortex produced by systemic dizocilpine (1 mg/kg). Bilateral thalamic injections of baclofen (0.1, 1, 10 microg/microL per side), a GABAB agonist, were ineffective. Anterograde tracer studies confirmed that neurons in the anterior thalamus project to superficial layer III of the retrosplenial cortex where the dendrites of HSP70-immunostained neurons in deep layer III reside. Bilateral blockade of NMDA receptors on GABA neurons in the reticular nuclei of the thalamus is proposed to decrease GABA neuronal firing, decrease GABA release and decrease activation of GABAA receptors. This activates thalamic projection neurons that damage retrosplenial cortical neurons presumably via unblocked cortical glutamate alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) and kainate receptors. The increases of blood flow that occur in the thalamus and retrosplenial cortex of people that have psychosis produced by NMDA antagonists could be related to thalamic excitation of the retrosplenial cortex produced by these drugs.

Animals↗