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At least 1,171 records · Page 65Linked to original sources
PubMed2006

Always returning: feedback and sensory processing in visual cortex and thalamus.

Feedback projections are an integral part of the mammalian visual system. Although it is tempting to relegate them to a subsidiary role in visual processing, because their supposed latency and lag might appear to be unfavourable for an involvement in fast processing, this is a dangerous simplification. Certainly for the world in motion, feedback from higher motion areas can influence the transfer of ascending input when, or even before, the input arrives. Here, we consider the circuit formed by layer 6 feedback cells in the visual cortex and how this straddles the retinothalamic and thalamocortical transfer of visual input. We discuss its links to feedback from the cortical motion area MT (V5), and suggest that motion perception involves a dynamic interplay between MT, V1 and the thalamus. This review is part of the TINS special issue on The Neural Substrates of Cognition.

Animals↗
PubMed2000

Abnormalities in the thalamus and prefrontal cortex during episodic object recognition in schizophrenia.

BACKGROUND: Many patients with schizophrenia demonstrate memory deficits. We studied patterns of brain activity during episodic recognition of new and previously seen three-dimensional objects. METHODS: We used (15)O positron emission tomography to study regional cerebral blood flow in eight normal subjects and nine patients with schizophrenia during a visual object recognition task. RESULTS: In comparison with control subjects, patients with schizophrenia showed less regional cerebral blood flow increases in the pulvinar region of the right thalamus and the right prefrontal cortex during the recognition of new objects and significantly greater left prefrontal cortex regional cerebral blood flow increases during the recognition of previously seen objects. Patients with schizophrenia exhibited alarm rates to new objects similar to those of control subjects, but significantly lower recognition rates for previously seen objects. CONCLUSIONS: Schizophrenia is associated with attenuated right thalamic and right prefrontal activation during the recognition of novel visual stimuli and with increased left prefrontal cortical activation during impaired episodic recognition of previously seen visual stimuli. This study provides further evidence for abnormal thalamic and prefrontal cortex function in schizophrenia.

Adult↗
PubMed2003

Effects of a mediodorsal thalamus lesion on prefrontal inhibitory circuitry: implications for schizophrenia.

BACKGROUND: Schizophrenia is associated with both reductions in prefrontal cortical (PFC) inhibitory markers and in neuron number in the mediodorsal thalamus (MDTN), which provides excitatory input to the PFC. To investigate the potential pathophysiologic relationship between these observations, we sought to provide experimental evidence that a reduction in MDTN neurons can produce decreased PFC glutamate decarboxylase (GAD(67)) mRNA expression. METHODS: Ibotenic acid was injected bilaterally into MDTN in rats. Four weeks later, thalamic lesion volumes were assessed stereologically, and PFC GAD(67) mRNA expression was measured using in situ hybridization. RESULTS: Selective MDTN lesions produced no changes in PFC GAD(67) mRNA expression, either overall or by cortical layer, and lesion volumes and GAD(67) mRNA expression were not correlated. CONCLUSIONS: In rats, a substantial lesion of MDTN neurons does not decrease PFC GAD(67) mRNA expression. These results do not support the hypothesis that decreased PFC GAD(67) mRNA expression in schizophrenia is attributable to a reduction in MDTN neuron number.

Animals↗
PubMed1999

The thalamus and the schizophrenia phenotype: failure to replicate reduced volume.

BACKGROUND: Thalamic abnormalities resulting in impaired attention and information processing may form a foundation for cognitive and perceptual disturbances in schizophrenia. Measurements of the thalamus in patients with schizophrenia have shown reductions relative to normal comparison subjects. METHODS: In the current project, magnetic resonance images of the brain were obtained in 10 male and 11 female subjects with paranoid-type schizophrenia, and 15 male and 12 female normal comparison subjects. Total brain and bilateral thalamic volumes were calculated. RESULTS: There were no significant diagnosis, hemisphere, or gender differences in thalamic volumes. CONCLUSIONS: Structural thalamic abnormalities are not likely to universally and parsimoniously explain the schizophrenia phenotype. Abnormal thalamic size in patients with schizophrenia should be understood as reflecting one of several possible structural abnormalities contributing to production of the schizophrenia phenotype, but must be regarded with caution unless paired with functional studies.

Adult↗
PubMed2001

PET neuroimaging of clomipramine challenge in humans: focus on the thalamus.

PET neuroimaging of serotonin responsivity relied previously mainly on fenfluramine, but that drug has been withdrawn from the market. Therefore, we determined whether clomipramine, which stimulates serotonergic mechanisms by inhibiting serotonin reuptake, has reliable effects in the healthy human brain as measured by [15O]H2O PET. The clomipramine challenge markedly reduced the relative rate of blood flow in the selected region of interest, namely the dorsomedial nucleus of the thalamus, a limbic region rich in serotonin uptake sites. These findings show similarities between effects of fenfluramine and clomipramine in the healthy human brain, and support the use of the clomipramine challenge in conjunction with PET for studying cerebral serotonergic mechanisms.

Aged↗
PubMed1997

Modulatory role of catecholamines in the transsynaptic expression of c-fos in the rat medial prefrontal cortex induced by disinhibition of the mediodorsal thalamus: a study employing microdialysis and immunohistochemistry.

We studied the interaction of catecholaminergic and thalamic afferents of the medial prefrontal cortex (PFC) by analyzing the effects of catecholamine depletion on thalamus-induced c-fos expression in the PFC of freely moving rats. Thalamic projections to the PFC were pharmacologically activated by perfusing the GABA-A receptor antagonist bicuculline (0.03 mM or 0.1 mM) through a dialysis probe implanted into the mediodorsal thalamic nucleus. Bicuculline perfusion induced Fos-like immunoreactivity in the thalamic projection areas, including the PFC, and in the thalamic nuclei surrounding the dialysis probe. 6-Hydroxydopamine lesions of the ventral tegmental area causing a 70-80% depletion of catecholamines in the PFC did not influence the increase in the number of Fos-like immunoreactive nuclei in the prefrontal cortex in response to thalamic stimulation. However, densitometric image analysis revealed that the intensity of Fos-like immunoreactivity in the PFC of lesioned rats perfused with 0.1 mM bicuculline was higher than in correspondingly treated controls. The behavioral activity to bicuculline perfusion, an increase of non-ambulatory activity (0.03 mM) followed by locomotion and rearing (0.1 mM), was not changed in 6-hydroxydopamine-lesioned rats. It is suggested that the thalamically induced c-fos response is directly mediated by excitatory, presumably glutamatergic, transmission and not indirectly by an activation of catecholaminergic afferents of the PFC. The increase in the intensity of Fos-like immunostaining in strongly stimulated, catecholamine-depleted rats suggests that catecholamines modulate the degree to which thalamic activity can activate the PFC of awake animals.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1997

Three-dimensional morphology and distribution of pallidal axons projecting to both the lateral region of the thalamus and the central complex in primates.

This study presents a three-dimensional analysis of pallido-thalamic axons and axonal endings in the monkey (Macaca mulatta and M. irus). Injections of the anterograde tracer biocytin were made in the dorsal, associative region of the medial pallidum. Numerous axonal endings were observed within the pallidal territory of the lateral region of the thalamus and the central complex. Individual axons were reconstructed from serial sections and traced in three dimensions. Two axons made a collateral branch in the ventral part of the lateral region and ended in the central complex. In the pallidal territory of the lateral region, axons divided several times before ending in different parts of the territory in a 'bunch', a characteristic dense terminal arborization. Axonal endings in the central complex were differently organized. Our data show that associative medial pallidal information is distributed throughout the pallidal territory of the lateral region and the pars media of the central complex by means of individual axons with numerous branches and axonal endings specific to each of the two targets.

Animals↗
PubMed1997

Projections from the renal nerve to the cat's lateral somatosensory thalamus.

The representation of the kidney in the lateral somatosensory thalamus was mapped using electrical stimulation of the renal nerve in pentobarbitone-anesthetized cats. Ninety-five of 197 thalamic neurons studied responded to renal nerve stimulation. The responsive neurons were located in the periphery of the ventral posterolateral nucleus (42%; VPLp) and the neighboring dorsal and lateral aspects of the posterior complex (58%; POd and POl). No visceroceptive neurons were found within VPL proper. The mean response latency of the thalamic neurons to electrical nerve stimulation was 9.5 +/- 2.6 ms (mean +/- S.D.), suggesting an involvement of A delta, and possibly A beta fibers in the primary afferent pathway. The visceroceptive neurons were further characterized with innocuous mechanical stimulation of the body surface, and for 94 of the 95 neurons a somatic receptive field could be determined. Of these, 35% were located on the lower back and belly, i.e., the dermatomes of the lower thoracic and upper lumbar spinal projection areas of the renal nerve. 52% of the somatic receptive fields were located on the contralateral foot, thigh, tail, or hind leg (lower lumbar, sacral and coccygeal dermatomes) and 13% covered the arm and upper body (upper thoracic and lower cervical dermatomes). Comparison between the thalamic representations of the renal and pelvic nerves showed that both covered comparable areas adjacent and around, but not within VPL proper. It is concluded that VPLp, POd and POl play a role in processing visceral, possibly including nociceptive, information from the kidney of the cat.

Animals↗
PubMed1997

Differential effects of nipecotic acid and 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol on extracellular gamma-aminobutyrate levels in rat thalamus.

Using the microdialysis technique and HPLC (high-performance liquid chromatography) determination of amino acids, the extracellular concentrations of gamma-aminobutyrate (GABA), glutamate, aspartate and a number of other amino acids were determined in rat thalamus during infusion through the microdialysis tubing of the GABA transport inhibitors 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) and nipecotic acid. Administration of 5.0 mM THPO led to a 200% increase in the extracellular GABA concentration. Simultaneous infusion of THPO and GABA (50 microM) increased the extracellular GABA concentration to 1200% of the basal level whereas GABA alone was found to increase the GABA level to 500%. If nipecotic acid (0.5 mM) was administered together with GABA (50 microM) the extracellular concentration of GABA was not increased further. While administration of GABA alone or GABA together with nipecotic acid had no effect on the extracellular levels of glutamate and aspartate it was found that GABA plus THPO increased the extracellular concentration of these amino acids. GABA administered alone or together with nipecotic acid or THPO led to relatively small but significant increases in the extracellular concentrations of the amino acids glycine, glutamine, serine and threonine. The results demonstrate that THPO, which preferentially inhibits glial GABA uptake and which is not a substrate for the GABA carriers, was more efficient increasing the extracellular concentration of GABA than nipocotic acid which is a substrate and an inhibitor of both neuronal and glial GABA uptake. This indicates that GABA uptake inhibitors that are not substrates for the carrier and which preferentially inhibit glial GABA uptake may constitute a group of drugs by which the efficacy of GABAergic neurotransmission may be enhanced.

Animals↗
PubMed1999

Tiagabine antinociception in rodents depends on GABA(B) receptor activation: parallel antinociception testing and medial thalamus GABA microdialysis.

The effects of a new antiepileptic drug, tiagabine, (R)-N-[4,4-di-(3-methylthien-2-yl)but-3-enyl] nipecotic acid hydrochloride, were studied in mice and rats in antinociceptive tests, using three kinds of noxious stimuli: mechanical (paw pressure), chemical (abdominal constriction) and thermal (hot plate). In vivo microdialysis was performed in parallel in awake, freely moving rats in order to evaluate possible alterations in extracellular gamma-aminobutyric acid (GABA) levels in a pain-modulating region, the medial thalamus. Systemic administration of tiagabine, 30 mg kg(-1) i.p., increased nearly twofold the extracellular GABA levels in rats and increased significantly the rat paw pressure nociceptive threshold in a time-correlated manner. Dose-related significant tiagabine-induced antinociception was also observed at the doses of 1 and 3 mg kg(-1) i.p. in the mouse hot plate and abdominal constriction tests. The tiagabine antinociception was completely antagonised by pretreatment with the selective GABA(B) receptor antagonist, CGP 35348, (3-aminopropyl-diethoxy-methyl-phosphinic acid) (2.5 microg/mouse or 25 microg/rat i.c.v.), but not by naloxone (1 mg kg(-1) s.c.), both administered 15 min before tiagabine. Thus, it is suggested that tiagabine causes antinociception due to raised endogenous GABA levels which in turn activate GABA(B) receptors.

Abdomen↗
PubMed1995

Eosinophilic neuronal inclusions in the thalamus of ageing B6C3F1 mice.

The age-related incidence of thalamic neuronal inclusions in the brains of aged B6C3F1 mice and their histopathological and ultrastructural features were studied. Round to oval or rod-shaped eosinophilic inclusions, which were frequently observed in the neurons of the thalamic area, were stained positively with phosphotungstic acid haematoxylin. The inclusions were detected first at 32 weeks of age and the incidence and severity were higher in older animals, all of the mice being affected after 58 weeks of age. Ultrastructurally, the inclusions appeared as sheaves of parallel osmiophilic filaments in the perikaryon of the neurons in the thalamus. Thus thalamic neuronal inclusions in mice seem to be age-related, but their significance remains unclear.

Aging↗
PubMed1997

Gustatory thalamus lesions in the rat: III. Simultaneous contrast and autoshaping.

The performance of rats with electrophysiologically guided electrolytic lesions of the gustatory thalamus (GT) was compared to that of control subjects in two experiments. In Experiment 1, the lesioned rats showed normal simultaneous contrast effects (both positive and negative) during brief, alternating access to 0.15% saccharin and 1.0 M sucrose. There was, however, a substantial lesion-induced impairment in the level of conditioned stimulus-directed maintenance responding on the autoshaping procedure of Experiment 2. These findings are discussed with respect to the anticipatory contrast deficit recently reported in GT-lesioned rats.

Animals↗
PubMed1990

The anatomical relationship of the prefrontal cortex with the striatopallidal system, the thalamus and the amygdala: evidence for a parallel organization.

Recent findings in primates indicate that the connections of the frontal lobe, the basal ganglia, and the thalamus are organized in a number of parallel, functionally segregated circuits. In the present account, we have focused on the organization of the connections between the prefrontal cortex, the basal ganglia and the mediodorsal thalamic nucleus in the rat. It is concluded that in this species, in analogy with the situation in primates, a number of parallel basal ganglia-thalamocortical circuits exist. Furthermore, data are presented indicating that the projections from particular parts of the amygdala and from individual nuclei of the midline and intralaminar thalamic complex to the prefrontal cortex and the striatum are in register with the arrangements in the parallel circuits. These findings emphasize that the functions of the different subregions of the prefrontal cortex cannot be considered separately but must be viewed as components of the integrative functions of the circuits in which they are involved.

Amygdala↗
PubMed1991

Actions of norepinephrine in the cerebral cortex and thalamus: implications for function of the central noradrenergic system.

Norepinephrine (NE) has potent and long-lasting ionic effects on cortical and thalamic neurons. In cortical pyramidal cells, activation of beta-adrenergic receptors results in an enhanced excitability and responsiveness to depolarizing inputs. This enhanced excitability is expressed as a reduction in spike frequency adaptation and is mediated by a marked suppression of a slow Ca(++)-activated potassium current known as IAHP. In the thalamus, application of NE results in the suppression of ongoing rhythmic burst activity and a switch to the single spike firing mode of action potential generation. This effect is mediated through an alpha 1-adrenergic suppression of a resting leak potassium current, IKL, and through a beta-adrenoceptor-mediated enhancement of the hyperpolarization activated cation current Ih. Together with the actions of other neuromodulatory neurotransmitters (i.e., acetylcholine, histamine, serotonin) these effects facilitate the switch of these neurons from a state of rhythmic oscillation and low excitability during drowsiness and slow-wave sleep to a state of increased excitability and responsiveness during periods of waking, attentiveness and cognition.

Action Potentials↗
PubMed2000

Absence of neurodegeneration in the thalamus and caudate of elderly patients with schizophrenia.

The cognitive and functional deterioration observed in many 'poor-outcome' patients with schizophrenia suggests an ongoing neurodegenerative process. Diagnostic neuropathologic studies have excluded known neurodegenerative diseases as the cause of this dementia, and in a previous quantitative investigation of neurodegeneration and neural injury in this population we found no abnormalities in the cerebral cortex. However, it is possible that the deterioration observed in these patients could be due to subcortical neurodegenerative processes. Neurodegeneration and neural injury in the caudate nucleus and mediodorsal nucleus of the thalamus were investigated in a postmortem study of 11 prospectively accrued, clinically well-characterized elderly people with schizophrenia, 11 elderly control subjects with no neuropsychiatric illness, and 12 subjects with Alzheimer's disease. Traditional and immunohistochemical staining and unbiased computerized counting methods were used to quantify common markers of neurodegeneration and neural injury (neuron loss, neurofibrillary tangles, astrocytosis, microgliosis). No statistically significant differences were found between schizophrenia and control subjects for the densities of any markers. There is no evidence that abnormal neurodegeneration occurs in these two important subcortical structures.

Age Factors↗
PubMed2003

Behavioral effects of neonatal and adult excitotoxic lesions of the mediodorsal thalamus in the adult rat.

We examined in the rat, the effects of neonatal (postnatal Day 7) and adult excitotoxic lesions of the mediodorsal thalamus (MDT), a brain area innervating the prefrontal cortex and implicated as a site of neuropathology in schizophrenia. Previous studies showed that rats with neonatal excitotoxic damage of the ventral hippocampus (VH), used as an animal model of this disorder, display in young adulthood a variety of abnormalities reminiscent of schizophrenia, including hyperactivity to stressful stimuli and amphetamine. It has been speculated that behavioral abnormalities of the neonatally VH lesioned animals are mediated through MDT projections to the prefrontal cortex. We tested if rats with ibotenic acid (1.5 microg per hemisphere in neonates, 2 microg in adults) lesions of MDT exhibited motor hyperactivity in the same experimental conditions (i.e. in response to novelty, saline injections and amphetamine administration) as rats with the VH lesions. We found that, in contrast to rats with VH lesions, neonatally lesioned MDT rats showed reduced vertical activity in response to amphetamine and no changes in locomotor activity to novelty, saline or amphetamine injections 7 weeks postlesion. Adult lesioned MDT rats exhibited no changes in motor activity as compared to controls at 7 weeks postlesion. These results indicate that neonatal or adult excitotoxic lesions of MDT do not produce behavioral changes analogous to those seen after neonatal VH lesions and do not appear to reproduce animal model-like features of schizophrenia.

Aging↗
PubMed2000

Sustained depolarisation induces changes in the extracellular concentrations of purine and pyrimidine nucleosides in the rat thalamus.

ATP and adenosine are well-known neuroactive compounds. Other nucleotides and nucleosides may also be involved in different brain functions. This paper reports on extracellular concentrations of nucleobases and nucleosides (uracil, hypoxanthine, xanthine, uridine, 2'-deoxycytidine, 2'-deoxyuridine, inosine, guanosine, thymidine, adenosine) in response to sustained depolarisation, using in vivo brain microdialysis technique in the rat thalamus. High-potassium solution, the glutamate agonist kainate, and the Na(+)/K(+) ATPase blocker ouabain were applied in the perfusate of microdialysis probes and induced release of various purine and pyrimidine nucleosides. All three types of depolarisation increased the level of hypoxanthine, uridine, inosine, guanosine and adenosine. The levels of measured deoxynucleosides (2'-deoxycytidine, 2'-deoxyuridine and thymidine) decreased or did not change, depending on the type of depolarisation. Kainate-induced changes were TTX insensitive, and ouabain-induced changes for inosine, guanosine, 2'-deoxycytidine and 2'-deoxyuridine were TTX sensitive. In contrast, TTX application without depolarisation decreased the extracellular concentrations of hypoxanthine, uridine, inosine, guanosine and adenosine. Our data suggest that various nucleosides may be released from cells exposed to excessive activity and, thus, support several different lines of research concerning the regulatory roles of nucleosides.

Animals↗
PubMed2000

Electroencephalogram alpha (8-15 Hz) responses to visual stimuli in cat cortex, thalamus, and hippocampus: a distributed alpha network?

To investigate possible functional correlates of alpha (8-15 Hz) oscillations in the electroencephalogram (EEG) intracranial recordings in cats (from thalamus, occipital cortex, and hippocampus) were performed. In response to visual stimuli, event-related alpha oscillations were observed. Such alpha responses were found not only in a specific sensory (visual) pathway but also in the hippocampus, hinting at a possible distributed alpha response system.

Alpha Rhythm↗