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At least 703 records · Page 39Linked to original sources
PubMed1998

A critical period for reduced brain vulnerability to developmental injury. II. Volumetric study of the neocortex and thalamus in cats.

Groups of young adult cats with a left hemineodecortication at postnatal (P) ages (in days) 5-15 (P10), 30 (P30) 60 (P60), 90 (P90), 120 (P120) and in adulthood, were used to measure the volume of the thalamus, bilaterally, and of the remaining neocortex (right hemisphere). The same subjects were employed for the behavioral studies reported in the preceding paper. There was a bilateral, age-dependent, thalamic volume decrease. Ipsilateral to the resection, the thalamic shrinkage was the largest for the adult-lesioned cats (by 56.7%) and it was the smallest for the P30 group (43.4%), with a tendency towards a greater atrophy as the age at lesion increased. A similar pattern of atrophy was seen for the contralateral thalamus but the volume reduction was much less pronounced such that it was significant only for the four older age-at-lesion groups (ranging from 18.2% to 11.2% for the P120 and P90 groups respectively). Once again, the shrinkage was the smallest for the P30 group (5.3%). The remaining neocortex also shrunk in these animals, but the volume decrease was significant only for the adult-lesioned (17.8%) and the P120 group (15.4%), while the P30 group had practically no shrinkage (2.4%). The frontal cortex had no atrophy or it was minimal but the shrinkage gradually increased caudally such that all lesioned groups had some size reduction of the occipital cortex. The present results, together with the main conclusion of the preceding paper, indicate that there is a critical maturation period (CMP) of reduced forebrain vulnerability to neocortical injury which, in cats, tends to end between 30 to 60 days postnatally. The implications for developmental brain damage in other higher mammal species as well as the possible morphological ontogenetical underpinnings of this period are discussed.

Aging↗
PubMed1998

Postnatal expression pattern of calcium-binding proteins in organotypic thalamic cultures and in the dorsal thalamus in vivo.

The present study describes the postnatal expression of calbindin, calretinin and parvalbumin and glutamic acid decarboxylase (GAD) and microtubule-associated protein 2 (MAP2) in organotypic monocultures of rat dorsal thalamus compared to the thalamus in vivo. Cultures were maintained for up to 7 weeks. Cortex-conditioned medium improved the survival of thalamic cultures. MAP2-immunoreactive material was present in somata and dendrites of small and large-sized neurons throughout the cultures. Parvalbumin immunoreactivity was present in larger multipolar or bitufted neurons along the edge of a culture. These neurons also displayed strong parvalbumin mRNA and GAD mRNA expression, and GABA immunoreactivity. They likely corresponded to cells of the nucleus reticularis thalami. Parvalbumin mRNA, but neither parvalbumin protein nor GAD mRNA, was expressed in neurons with large somata within the explant. They likely represented relay cells. GAD mRNA, but not parvalbumin mRNA, was expressed in small neurons within the explants. Small neurons also displayed calbindin- and calretinin-immunoreactivity. The small neurons likely represented local circuit neurons. The time course of expression of the calcium-binding proteins revealed that all were present at birth with the predicted molecular weights. A low, but constant parvalbumin expression was observed in vitro without the developmental increase seen in vivo, which most likely represented parvalbumin from afferent sources. In contrast, the explantation transiently downregulated the calretinin and calbindin expression, but the neurons recovered the expression after 14 and 21 days, respectively. In conclusion, thalamic monocultures older than three weeks represent a stable neuronal network containing well differentiated neurons of the nucleus reticularis thalami, relay cells and local circuit neurons.

Aging↗
PubMed1998

Calretinin gene expression in the human thalamus.

The localization and levels of expression of the calcium-binding protein calretinin (CR) in the human thalamus was studied with an in situ hybridization method applied to formalin-fixed postmortem material from normal individuals. The riboprobe used was generated from a specific fragment of human CR cDNA. As visualized on X-ray film autoradiographs, high levels of CR gene transcript occurred in several thalamic nuclei, including the reticular nucleus, mediodorsal nucleus, rostral intralaminar nuclei (paracentral, central medial and central lateral) and several midline nuclei (paraventricular, reuniens and medioventral nuclei). In the reticular nucleus, neurons expressing CR mRNA were few in number but formed dense and widely distributed clusters. In contrast, virtually all neurons in the rostral intralaminar and midline nuclei expressed very high levels of CR mRNA and formed a prominent rim around the mediodorsal nucleus, which contained scattered clusters of labeled neurons. The caudal intralaminar nuclei, principally the centromedian nucleus, displayed very few neurons expressing CR mRNA. Only the medial part of the parafascicular nucleus expressed moderate levels of CR mRNA. The nuclei of the ventral group (ventral anterior, lateral and posterior nuclei) were virtually devoid of CR gene transcript. This highly heterogeneous pattern of mRNA expression suggests that CR may be heavily involved in the function of the so-called non-specific nuclei, but not in that of the specific relay nuclei of the human thalamus. The data also demonstrate that the presence of CR gene transcript can easily be detected on formalin-fixed sections of the human brain.

Adult↗
PubMed2003

Diurnal changes in corticotropin-releasing hormone messenger RNA in the rat thalamus.

Corticotropin-releasing hormone (CRH) is critical for mediating the stress response. CRH messenger RNA (mRNA) is present in a variety of brain regions including the thalamus and thalamic CRH mRNA concentrations increase in response to stress exposure. The present study assessed changes in basal CRH mRNA concentrations in the rat thalamus during different times of the day. Using in situ hybridization, we demonstrated that thalamic CRH mRNA levels exhibited more than two-fold increases during the dark phase between 20:00 and 02:00 h, followed by a decrease at 08:00 and 14:00 h during the light phase. Dramatic changes in thalamic CRH mRNA levels may have important implications for the possible role of thalamic CRH systems in waking, arousal, and the stress response.

Animals↗
PubMed1997

Collateral projections from single neurons in the dorsal column nuclei to the inferior colliculus and the ventrobasal thalamus: a retrograde double-labeling study in the rat.

A number of single neurons in the dorsal column nuclei (DCN) and the sensory trigeminal nuclear complex were found to project to the thalamus and the inferior colliculus (IC). In the rats which were injected unilaterally with tetramethylrhodamine-dextran amine (TMR-DA) and Fluoro-Gold (FG) respectively into the posterolateral ventral thalamic nucleus and the external nucleus of IC, a number of neuronal cell bodies labeled retrogradely with both TMR-DA and FG were found throughout DCN contralateral to the injections. A few double-labeled neurons were also seen in the caudomedial part of the gracile nucleus ipsilateral to the injections. The double-labeled DCN neurons had relatively small cell bodies which are oval or fusiform in shape. When the injection sites in the thalamus extend into the posteromedial ventral thalamic nucleus, a few double-labeled neuronal cell bodies were seen contralaterally in the trigeminal sensory nuclear complex, mainly in the caudal part of the interpolar spinal trigeminal nucleus.

Animals↗
PubMed1997

Histamine H1 receptors and inositol phosphate formation in rat thalamus.

In membranes of rat thalamus the density of histamine H1 receptors, as estimated from saturation curves with [3H]mepyramine, was 66 +/- 5 fmol.mg protein-1 (Kd 1.3 +/- 0.1 nM). Specific [3H]mepyramine binding was inhibited by mepyramine (best fit to one-site model, Kd 2.2 +/- 0.2 nM) and by histamine (best fit to a two-site model, Ki high 0.35 +/- 0.04 microM and 54 +/- 7% of binding sites; Ki low 7.0 +/- 1.1 microM). In the presence of 300 microM GppNHp (5'-guanylylimidodiphosphate) the inhibition curve for histamine best-fit to a one-site model (Ki 3.1 +/- 0.3 microM). In cross-chopped slices and in the presence of 10 mM LiCl, histamine stimulated the accumulation of total [3H]inositol phosphates ([3H]IPs) with a maximum effect of 163 +/- 3% of basal accumulation, EC50 of 8 +/- 2 microM and Hill coefficient (nH) of 0.8 +/- 0.1. [3H]IPs accumulation induced by 100 microM histamine was inhibited by the selective H1 antagonist mepyramine (1 microM, 90 +/- 8% inhibition; Ki 2.1 +/- 0.4 nM) but not by 10 microM ranitidine (a selective H2 antagonist) or 1 microM thioperamide (a selective H3 antagonist). These results show the presence in rat thalamus of functional H1 receptors coupled in inositol phosphate accumulation.

Animals↗
PubMed1998

Transient expression of the vesicular monoamine transporter during development in the rat thalamus and cortex.

The postnatal developmental pattern of the central vesicular monoamine transporter-2 (VMAT2) was analyzed in the rat brain by means of quantitative autoradiography with a specific and high affinity ligand [3H]dihydrotetrabenazine ([3H]TBZOH). We show a dense expression of VMAT2 in the cortex (especially area 17) and thalamus (particularly the dorsal lateral geniculate nucleus) at postnatal days 1 and 8. This pattern of VMAT2 distribution was transient since it was no longer observed at day 20 or in the adult rat brain where VMAT2 density was weak and uniform in these regions. These data suggest that monoamine vesicular storage participates in the early postnatal maturation of thalamus and cortex.

Animals↗
PubMed1999

Metabotropic glutamate receptors 2 and 3 expressed by astrocytes in rat ventrobasal thalamus.

It has been reported that pharmacologic activation of metabotropic receptors mGluR2/3 may produce inhibition of GABAergic transmission in rat ventrobasal thalamus. We use double immunolabeling to show that: (i) mGluR2/3 is expressed in glial processes surrounding GABAergic terminals, rather than in the terminals themselves, and (ii) mR2/3 positive glial lamellae more frequently surround GABAergic terminals and ascending terminals, than cortical terminals. This suggests involvement of glia in glutamate/GABA interactions in the sensory thalamus.

Afferent Pathways↗
PubMed1997

Expression of cholecystokinin messenger RNA in reciprocally-connected auditory thalamus and cortex in the rat.

Cholecystokinin exerts a potent antiepileptic action in mammalian auditory system and undergoes seizure-mediated up-regulation. The present study investigated cholecystokinin messenger RNA expression in the reciprocally-connected auditory thalamus and cortex in the rat. Immunofluorescence in situ hybridization was performed using a 24-base cholecystokinin-messenger RNA oligonucleotide probe. Corticothalamic projection neurons were identified by means of the retrograde fluorescent tracer rhodamine latex microspheres injected into the medial geniculate body. In our experiments, cholecystokinin messenger RNA transcripts were found in about 80% of neurons located within the reciprocally-connected regions of the medial geniculate body and the auditory cortices. These observations provide evidence of cholecystokinin production in the reciprocally-connected regions of the auditory thalamus and cortex, the structures which jointly create the thalamo-corticothalamic circuit which has been implicated in seizure genesis.

Animals↗
PubMed1997

Preproenkephalin messenger RNA-expressing neurons in the rat parabrachial nucleus: subnuclear organization and projections to the intralaminar thalamus.

The pontine parabrachial nucleus, which is a key structure in the central processing of autonomic, nociceptive and gustatory information, is rich in a variety of neuropeptides. In this study we have analysed the distribution of parabrachial neurons that express preproenkephalin messenger RNA, which encodes for the precursor protein for enkephalin opioids. Using an in situ hybridization method, we found that preproenkephalin messenger RNA-expressing neurons were present in large numbers in four major areas of the parabrachial nucleus: the Kölliker-Fuse nucleus, the external lateral subnucleus, the ventral lateral subnucleus, and in and near the internal lateral subnucleus. Many preproenkephalin messenger RNA-expressing neurons were also seen in the central lateral subnucleus, and in the medial and external medial subnuclei. Few labeled neurons were found in the dorsal and superior lateral subnuclei. Injection of the retrograde tracer substance cholera toxin subunit B into the midline and intralaminar thalamus demonstrated that the enkephalinergic neurons in and near the internal lateral subnucleus were thalamic-projecting neurons. Taken together with the results of previous tract-tracing studies, the present findings show that many of the enkephalinergic cell groups in the parabrachial nucleus are located within the terminal zones of the ascending projections that originate from nociresponsive neurons in the medullary dorsal horn and spinal cord, as well as from viscerosensory neurons within the nucleus of the solitary tract. The enkephalinergic neurons in the parabrachial nucleus may thus transmit noci- and visceroceptive-related information to their efferent targets. On the basis of the present and previous observations, we conclude that these targets include the intralaminar and midline thalamus, the ventrolateral medulla and the spinal cord. Through these connections, nociceptive and visceroceptive stimuli may influence several functions, such as arousal, respiration and antinociception.

Animals↗
PubMed1999

Patterns of spontaneous activity and morphology of interneuron types in organotypic cortex and thalamus-cortex cultures.

The physiological and morphological properties of interneurons in infragranular layers of rat visual cortex have been studied in organotypic cortex monocultures and thalamus-cortex co-cultures using intracellular recordings and biocytin injections. Cultures were prepared at the day of birth and maintained for up to 20 weeks. Twenty-nine interneurons of different types were characterized, in addition to 170 pyramidal neurons. The cultures developed a considerable degree of synaptically driven "spontaneous" bioelectric activity without epileptiform activity. Interneurons in cortex monocultures and thalamus-cortex co-cultures had the same physiological and morphological properties, and also pyramidal cell properties were not different in the two culture conditions. All interneurons and the majority of pyramidal cells displayed synaptically driven action potentials. The physiological group of fast-spiking interneurons included large basket cells, columnar basket cells (two cells with an arcade axon) and horizontally bitufted cells. The physiological group of slow-spiking interneurons included Martinotti cells and a "long-axon" cell. Analyses of the temporal patterns of activity revealed that fast-spiking interneurons have higher rates of spontaneous activity than slow-spiking interneurons and pyramidal cells. Furthermore, fast-spiking interneurons fired spontaneous bursts of action potentials in the gamma frequency range. We conclude from these findings that physiological and morphological properties of interneurons in organotypic mono- and co-cultures match those of interneurons characterized in vivo or in acute slice preparations, and they maintain in long-term cultures a well-balanced state of excitation and inhibition. This suggests that cortex-intrinsic or cell-autonomous mechanisms are sufficient for the expression of cell type-specific electrophysiological properties in the absence of afferents or sensory input.

Animals↗
PubMed1997

GABAergic neurons in mammalian thalamus: a marker of thalamic complexity?

The present study evaluated the occurrence, distribution, and number of GABAergic neurons in the thalamus of different mammalian species (bat, mouse, rat, guinea pig, rabbit, cat, monkey, humans), by means of light microscopical immunoenzymatic localization of GABA or of its biosynthetic enzyme glutamic acid decarboxylase and by ultrastructural immunogold detection of GABA. Our data demonstrated that: 1) GABAergic local circuit neurons were detected in the thalamic visual domain in all the species analyzed, whereas in other thalamic nuclei their presence and number varied among species; 2) the number of GABAergic local circuit neurons progressively increased in the dorsal thalamus of species with more complex behavior; 3) the presence of local circuit neurons conferred a similar intrinsic organization to the dorsal thalamic nuclei, characterized by complex synaptic arrangements; 4) in the reticular thalamic nucleus, whose neurons were GABA-immunoreactive in all the examined species, the cellular density decreased from the bat to humans. These findings strongly suggest that thalamic GABAergic local circuit neurons are not directly related to the ability to perform specific sensorimotor tasks, but they are likely to reflect an increasing complexity of the local information processing that occurs at thalamic level.

Animals↗
PubMed2004

Local gating of information processing through the thalamus.

Inhibitory sculpting of afferent signals in the thalamus is exerted by two types of neurons using gamma-amino butyric acid (GABA) as neurotransmitter. Of them, local-circuit neurons exert their functions via two outputs: axons and presynaptic dendrites. In this issue of Neuron, Govindaiah and Cox reveal that synaptic activation of metabotropic glutamate receptors selectively increases the output of presynaptic dendrites of local interneurons in rat visual thalamus, without affecting the axonal output.

Afferent Pathways↗
PubMed2000

Proton magnetic resonance spectroscopy (1H-MRS) of the thalamus in schizophrenia.

This study applied (1)H-MRS in the thalamus of schizophrenic patients and healthy subjects. There were no differences in the metabolite ratios (NAA/Cr, Cho/Cr or mI/Cr) between the two groups. Relationships were noted between NAA/Cr and age in patients with a trend toward this correlation in controls, suggesting an effect of age on the metabolism of the thalamus.

Adult↗
PubMed2001

Event-related potentials, CNV, readiness potential, and movement accompanying potential recorded from posterior thalamus in human subjects. A SEEG study.

Intracranial recordings were obtained from three patients with intractable chronic pain who underwent analgesic electrical stimulation of the contralateral thalamus. Multilead electrode made it possible to record from several thalamic nuclei. The electrode was targeted into the ventroposterolateral (VPL) nucleus of the thalamus. During separate recording sessions, the following tests were performed: somatosensory evoked potentials (SEP) of the median or posterior tibial nerve, event-related cognitive potentials (auditory oddball P3 wave), readiness potential (RP) and contingent negative variation (CNV) using auditory warning (S1) and visual imperative (S2) stimuli. The movement accompanying potential (MAP), which was present in the VPL in all but one of the recordings, behaved as a far-field potential. Recordings obtained from the VPL confirmed its established role as a relay nucleus, processing somatosensory information to the primary somatosensory cortex. The VPL generated the 'thalamic' SEP, which was the only potential regularly recorded in this nucleus. In the recordings from one patient (No. 3), auditory and visual evoked potentials of the CNV protocol, peaking at approximately 300 ms, were obtained from the VPL and appeared to be generated in situ. Neither RP, CNV nor 'oddball' ERPs appeared in the VPL. From the pulvinar, only a visually evoked potential was recorded. Oddball P3, RP, CNV, and middle and long latency auditory and visual potentials (evoked in the CNV paradigm) appeared to be generated 'dorsally' to the VPL, probably in the nucleus posterolateralis (PL). This structure may therefore be involved in both the processing of afferent information and in cognitive operations.

Aged↗
PubMed1993

Microdialysis calibration using retrodialysis and zero-net flux: application to a study of the distribution of zidovudine to rabbit cerebrospinal fluid and thalamus.

A retrodialysis (RD) method for the real-time calibration of on-line microdialysis (MD) procedures was investigated in vitro and in vivo. Calibration by retrodialysis was simultaneously validated through the use of a zero-net flux (ZNF) method, which assumes directional independence of diffusion of the solute. In RD, a calibrator with dialysance (PeA; effective permeability-surface area product) similar to that of the compound of interest is introduced into the perfusate. If the calibrator is suitable, its loss from the perfusate during RD is identical to the recovery of the solute of interest determined simultaneously by normal MD. Two antiviral nucleosides (AZT and AZdU) which differ structurally by only a methylene group were utilized as solute and calibrator, respectively. Both nucleosides exhibited similar recovery and loss at flow rates of 0.5 to 5 microL/min in vitro, indicating a similar PeA product in this flow domain. Furthermore, both compounds showed similar loss into the lateral ventricle or thalamus of rabbits (n = 4) during RD at a flow rate of 1 microL/min for 6 hr. The relative loss decreased rapidly within the first hour, reaching a relatively stable value after 2 hr. The significant reduction in the loss of AZdU and AZT in vivo compared with that in vitro likely results from a lower diffusion coefficient in tissue. The distribution of AZT between plasma and cerebrospinal fluid (CSF) in the ventricle and extracellular fluid (ECF) in thalamus was determined at steady state using calibration by RD and ZNF simultaneously.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed2003

Ischemic infarct involving all arterial territories of the thalamus.

Ischemic infarcts of the thalamus involve one or two of its four arterial territories that are usually supplied by the posterior cerebral (PCA) and the posterior communicating (PCoA) arteries. We report a patient who suffered ischemic infarcts in all arterial territories of the right thalamus. Magnetic resonance (MR) angiography showed an occlusion of the right PCA and failed to visualize a PCoA. We assume that the absence of a relevant thalamic blood supply deriving from the PCoA enabled PCA occlusion to cause infarcts in all thalamic territories.

Arteries↗
PubMed1992

Delayed-nonmatching-to-sample performance is impaired by extensive, but not by limited, lesions of the thalamus in the rat.

Two experiments were conducted to determine whether lesions affecting limited areas of the thalamus can impair the performance of rats on a spatial delayed-nonmatching-to-sample (DNMTS) task trained before surgery. In Experiment 1, DNMTS was not affected by lesions produced by injecting 5 microliters of 1 mM N-methyl-D-aspartate into either the midline thalamus (n = 16) or bilaterally 1.0 mm from the midline (n = 16). In experiment 2, radio-frequency lesions were made 1.0 mm lateral to the midline at 3 anterior-posterior locations that destroyed the full rostral-caudal extent of the lateral internal medullary lamina (L-IML; n = 8), or at single anterior-posterior locations that destroyed either the anterior (n = 8) or posterior (n = 8) portions of the L-IML site. Although complete L-IML lesions disrupted DNMTS performance to an extent comparable to that of another study (Mair & Lacourse, 1992), lesions that were restricted to either the anterior or posterior portion of the L-IML site had no significant effect on this task.

Animals↗