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PubMed2001

Delayed increase in neuronal nitric oxide synthase immunoreactivity in thalamus and other brain regions after hypoxic-ischemic injury in neonatal rats.

We examined the response of neuronal nitric oxide synthase (nNOS)-containing CNS neurons in rats exposed to a unilateral hypoxic-ischemic insult at 7 days of age. Animals were sacrificed at several time points after the injury, up to and including 7 days (Postnatal Day 14). Brain regions ipsilateral to the injury (including cerebral cortex, caudate-putamen, and thalamus) exhibited delayed, focal increases in nNOS immunoreactivity. The increase in nNOS immunoreactive fiber staining was prominent in areas adjacent to severe neuronal damage, especially in the cortex and the thalamus, regions that are also heavily and focally injured in term human neonates with hypoxic-ischemic encephalopathy. In cerebral cortex, these increases occurred despite modest declines in nNOS catalytic activity and protein levels. Proliferation of surviving nNOS immunoreactive fibers highlights regions of selective vulnerability to hypoxic-ischemic insult in the neonatal brain and may also contribute to plasticity of neuronal circuitry during recovery.

Animals↗
PubMed2000

The Morel stereotactic atlas of the human thalamus: atlas-to-MR registration of internally consistent canonical model.

In 1997, Morel, Magnin, and Jeanmonod presented a microscopic stereotactic atlas of the human thalamus. Parcellations of thalamic nuclei did not only use cyto- and myeloarchitectonic criteria, but were additionally corroborated by staining for calcium-binding proteins, which bears functional significance. The atlas complies with the Anglosaxon nomenclature elaborated by Jones and the data were sampled in three orthogonal planes in the AC-PC reference space. We report on the generation of three-dimensional digital models of the thalamus based on the three sets of sections (sagittal, horizontal, and frontal). Spatial differences between the three anatomical specimens were evaluated using the centers of gravity of 13 selected nuclei as landmarks. Subsequent linear regression analysis yielded equations, which were used to normalize the frontal and horizontal digital models to the sagittal one. The outcome is an internally consistent Canonical Model of Morel's atlas, which minimizes the linear component of the variability between the three sectioned anatomical specimens. In addition, we demonstrate the feasibility of the atlas-to-MRI registration in conjunction with on-line visualization of the trajectory in the digital models.

Brain Mapping↗
PubMed1987

Short latency somatosensory-evoked potentials--direct recording from the human midbrain and thalamus.

Short latency somatosensory-evoked potentials were recorded from the human thalamus and the midbrain during stereotactic operations. Several subcomponents were recognized on the peak of N18. These were recorded with maximal amplitude at the border between the caudal portion of the thalamus and the rostral midbrain. Two positive-negative responses, not previously shown, were observed between P14 and N18. These responses were prominent in the rostral midbrain. These findings indicate that the ascending phase of N18, and the N18 itself, are the compound potential generated in the mesodiencephalic junction.

Brain Mapping↗
PubMed1990

Demonstration of a reciprocal connection between the periaqueductal gray matter and the reticular nucleus of the thalamus.

Lectin-conjugated horseradish peroxidase was either injected or implanted in crystalline form in various parts of the periaqueductal gray substance in the cat. After survival times ranging between 24 and 48 h the animals were fixed, and the mesencephalon and thalamus were sectioned and processed for peroxidase histochemistry, using tetramethylbenzidine as the chromogen. Light microscopic examination of the sections revealed that there exists a prominent reciprocal connection between the ventral and lateral parts of the periaqueductal gray matter on one hand, and the reticular nucleus of the thalamus on the other. The connections are mainly ipsilateral, and involve the entire rostrocaudal extent of the thalamic reticular nucleus, but mainly the ventrolateral sector of its caudal two thirds. There is a differential labelling within the thalamic reticular nucleus.

Animals↗
PubMed1994

Corticothalamic influences on transmission of tactile information in the ventroposterolateral thalamus of the cat: effect of reversible inactivation of somatosensory cortical areas I and II.

The influence of the corticothalamic projections from somatosensory areas I and II (SI and SII) on the transmission of tactile information through the ventroposterolateral (VPL) thalamus was investigated by examining the effects of cooling-induced, reversible inactivation of SI and/or SII on the responsiveness of 32 VPL neurons to controlled tactile stimulation of the distal forelimb in anaesthetized cats. Both the response levels and spontaneous activity were unaffected in 21 (66%) of the VPL neurons as a result of inactivation of SI or SII singly, or both SI and SII simultaneously. In the remaining 11 neurons, 10 displayed a reduction in response level, an effect observed over the whole of the stimulus-response relations for the neurons studied at different stimulus amplitudes, and one neuron displayed an increase in response level in association with cortical inactivation. When responses in VPL neurons were affected by inactivation of one cortical somatosensory area, they were not necessarily affected by inactivation of the other. Of 14 neurons studied for the effects of the separate inactivation of SI alone and of SII alone, 7 were affected, one from both areas, but the remaining 6 were affected by inactivation of only one of these areas. Phaselocking, and therefore the precision of impulse patterning in the responses of VPL neurons to skin vibration, was unchanged by the cortical inactivation irrespective of whether the response level was affected. The results suggest that SI and SII may exert a facilitatory influence on at least a third of VPL neurons and in this way may modulate the gain of transmission of tactile signalling through the thalamus.

Animals↗
PubMed1992

The medullary relay from neck receptors to somatosensory thalamus in the rat: a neuroanatomical study.

Experiments were performed on rats to determine the location of thalamic projecting neurones in the medulla which receive direct contacts from neck primary afferents. The medullary terminations of primary afferents from the cervical region were identified by silver staining their degenerating terminals, diffusely filling their axons with horseradish peroxidase (HRP), or reacting for transganglionically transported HRP applied to muscle or cutaneous nerves. Neurones projecting to the ventrobasal thalamus were identified in the same experimental animals by using retrograde transport of HRP or Fluoro-Gold. En passant swellings or terminals of neck primary afferents were found in the vicinity of neurones projecting to the thalamus in the dorsolateral part of the rostral cuneate nucleus, the ventral aspect of the external cuneate nucleus, and the border zone between the two. Terminals of neck afferents and retrogradely labelled cells also coincided in nucleus x. Putative synaptic contacts were found in the region between the dorsolateral part of the rostral cuneate nucleus and ventromedial external cuneate nucleus. Cutaneous afferents from the neck were associated with thalamic projecting cells located along the dorsolateral border of the rostral cuneate nucleus, and afferents from neck muscles were associated with thalamic projecting cells in the caudal third of the external cuneate nucleus and in nucleus x.

Afferent Pathways↗
PubMed1992

Direct retinal projections of the "non-image forming" system to the hypothalamus, anterodorsal thalamus and basal telencephalon of mink (Mustela vison) brain.

The retinal projections of the "non-image forming" system to the hypothalamus, anterodorsal thalamus and basal telencephalon were visualized in adult mink using the anterograde transport of cholera toxin conjugated to horseradish peroxidase injected intraocularly. A major and nearly symmetrical bilateral input of labeled retinal fibers to the suprachiasmatic nuclei was observed. A dense innervation was also evident in both paraventricular nuclei, and in the anterior, lateral and mediobasal hypothalamus on the side contralateral to the injection. Two projections leaving the optic tract at the level of the lateral hypothalamus or after crossing the geniculate body entered the anterior thalamus and ran in a ventro-dorsal or a caudorostral direction before terminating in the stria terminalis. Fibers were also observed in the horizontal limb of the diagonal band of Broca. These observations are compared to those in other mammalian species and discussed according to their possible implication in photoperiodic signal processing.

Animals↗
PubMed1994

Response properties of single units in areas of rat auditory thalamus that project to the amygdala. I. Acoustic discharge patterns and frequency receptive fields.

Projections from the auditory thalamus to the amygdala have been implicated in the processing of the emotional significance of auditory stimuli. In order to further our understanding of the contribution of thalamoamygdala projections to auditory emotional processing, acoustic response properties of single neurons were examined in the auditory thalamus of chloral hydrate-anesthetized rats. The emphasis was on the medial division of the medial geniculate body (MGm), the suprageniculate nucleus (SG), and the posterior intralaminar nucleus (PIN), thalamic areas that receive inputs from the inferior colliculus and project to the lateral nucleus of the amygdala (AL). For comparison, recordings were also made from the specific thalamocortical relay nucleus, the ventral division of the medial geniculate body (MGv). Responses latencies were not statistically different in MGv, MGm, PIN, and SG, but were longer in the posterior thalamic region (PO). Overall, frequency tuning functions were narrower in MGv than in the other areas but many cells in MGm were as narrowly tuned as cells in MGv. There was some organization of MGv, with low frequencies represented dorsally and high frequencies ventrally. A similar but considerably weaker organization was observed in MGm. While the full range of frequencies tested (1-30 kHz) was represented in MGv, cells in MGm, PIN, and SG tended to respond best to higher frequencies (16-30 kHz). Thresholds were higher in PIN than in MGv (other areas did not differ from MGv). Nevertheless, across the various areas, the breadth of tuning was inversely related to threshold, such that more narrowly tuned cells tended to have lower thresholds. Many of the response properties observed in MGm, PIN, and SG correspond with properties found in AL neurons and thus add support to the notion that auditory responses in AL reflect thalamoamygdala transmission.

Acoustic Stimulation↗
PubMed1991

GABAergic interneurons and neuropil of the intralaminar thalamus: an immunohistochemical study in the rat and the cat, with notes in the monkey.

Immunohistochemistry using antibodies to glutamic acid decarboxylase (GAD) was used to investigate the intralaminar nuclei of the thalamus in rat, cat and monkey. Antibodies to gamma aminobutyric acid (GABA) were also used in the cat. Intralaminar immunoreactive cell bodies were not detected in the rat, but were clearly present in cat and monkey. In the latter species, GABA- or GAD-immunopositive perikarya were distributed throughout the anterior intralaminar nuclei, whereas in the posterior intralaminar complex they prevailed in the lateral part of the centre median nucleus and around the fasciculus retroflexus. Measurements of the area of immunostained intralaminar cell bodies in cat and monkey indicated that they are represented by small neurons. Experiments in the cat, based on retrograde tracers injections involving large sectors of the frontal and parietal cortices and the head of the caudate nucleus, revealed that the GABA- or GAD-immunoreactive cells and the retrogradely labeled projection neurons represented two separate intralaminar cell populations, although the latter also included small cells. Considerable differences were observed in the immunoreactive GABAergic neuropil of the anterior and posterior intralaminar nuclei. Clusters of densely packed bouton-like immunoreactive elements were detected in the former structures in the rat, cat and monkey, and were especially evident in the central lateral nucleus; immunopositive varicose fibers and puncta were diffusely distributed in the posterior intralaminar structures. Taken together with data from the literature, the present findings indicate that in cat and monkey local circuit inhibitory cells regulate not only the activity of principal thalamic nuclei which project densely upon restricted cortical fields, but also of the intralaminar structures which are widely connected with the cerebral cortex and the striatum. Regional variations in the distribution of GABAergic fibers and terminals suggest major differences in the organization of inhibitory circuits and synaptic arrangements of the anterior and posterior intralaminar thalamus.

Animals↗
PubMed1981

Divergent collaterals from deep cerebellar neurons to thalamus and tectum, and to medulla oblongata and spinal cord: retrograde fluorescent and electrophysiological studies.

In cat the existence of collaterals from deep cerebellar neurons, which project to mesencephalon and thalamus has been investigated anatomically by means of the multiple retrograde fluorescent tracer technique as well as electrophysiologically by means of conventional antidromic techniques. Both sets of data indicate that several neurons in the medial nucleus, which project to mesencephalon and thalamus, also distribute collaterals to medulla oblongata and spinal cord. These branching neurons were principally located in the caudal and intermediate portions of the medial nucleus. The electrophysiological data in addition indicate that the branching point of the neurons in the medial nucleus is located relatively close to the cell soma. The anatomical findings show a further group of branching neurons in the lateral nucleus at the border with the interpositus nuclei. The majority of these latter neurons distribute collaterals to medulla oblongata but some distribute collaterals to spinal cord. However, it could not be decided as yet whether the collaterals to the medulla oblongata terminate either in medullary medial reticular formation or in inferior olive or in both.

Animals↗
PubMed1987

Neuronal response thresholds to and encoding of thermal stimuli during carrageenin-hyperalgesic-inflammation in the ventro-basal thalamus of the rat.

This study analyzed neuronal encoding and response thresholds to thermal stimuli at the ventro-basal (V.B.) thalamus level during a hyperalgesic inflammation induced by intra-plantar injection of carrageenin in the rat. The threshold and the encoding capacity of the cells were studied during two phases of the inflammatory process, namely the "acute" phase (the first two hours following the injection), and "sub-acute" phase 24 h after). In this second phase the hyperalgesia was verified using a behavioral nociceptive test, just prior to the recording session. Only VB neurones with a receptive field that included the injected paw were considered. In the acute phase, neurones exclusively driven by noxious stimuli were studied before and during the first two hours following the induction of the inflammatory oedema. In the sub-acute phase two groups of neurones which, on the basis of our previous studies, were presumably involved in the transmission of messages giving rise to the hyperalgesia could be separated: a group of neurones which were driven by intense mechanical stimuli and another group driven by moderate mechanical stimulation applied to the inflamed joints and/or the surrounding cutaneous areas. In the "acute" phase there was a dramatic lowering (by about 4 degrees C) of the response threshold of the neurones when the thermal stimulus was applied to the injected paw, although their threshold to the mechanical stimulus was still high. A linear encoding of the bath temperature used as a stimulus was observed for both the injected and the non-injected paws. For a few neurones, a leftward shift of the stimulus-response curve was found for the inflamed limb. In the "sub-acute" phase, neurones with high thresholds to the mechanical indentations still exhibited a low response threshold to the thermal stimulation, not only from the injected but also from the non-injected paw. The other group of neurones responded with relatively low thresholds to the both stimulus modalities. By contrast to the acute phase, the two groups of neurones exhibited only a weak ability to encode the stimulus intensity especially when the stimulus was applied to the inflamed paw. Both peripheral and central mechanisms are likely to be involved in the modifications of response threshold and encoding capacity at the VB thalamus level seen in these conditions of hyperalgesic inflammation. The differential time course of the responses to a liminal or to a supra-liminal temperature during the inflammation, are discussed in reference to some of the mismatches occurring in clinical situations of hyperalgesia.

Action Potentials↗
PubMed1981

System degeneration of the thalamus. A clinico-neuropathological study.

A case of essential degeneration of the thalamus is reported. The patient was a 43-year-old Japanese male, who, a few weeks after mild head trauma, suffered from forgetfulness, psychomotor slowing, and Korsakoff's syndrome. Four to five months later, there were optical hallucinations and delirium and he died 19 months after the onset of symptoms. Neuropathological examination revealed symmetrical thalamic degeneration, whose distribution corresponded to phylogenetically younger subunits of the thalamus. In addition, there was olivovermian degeneration. These findings are identical to those of eleven cases hitherto reported. Five of these were Japanese, including the present one. The syndrome thalamic degeneration may now be classified as a special type of "system degeneration".

Adult↗
PubMed1980

Noradrenaline release from slices of the thalamus of normal and morphine-dependent rats.

The effect of morphine on potassium-induced stimulation of (3H)-noradrenaline release from slices of the rat thalamus was investigated. The in vitro addition of morphine (10(-6)M) significantly depressed potassium-induced tritium overflow by 42% and this was prevented by the prior addition of naloxone (3 x 10(-6)M) to the medium. The stimulation-evoked overflow of tritium from slices of the thalamus of morphine-dependent rats was not significantly different from normal controls. Addition of naloxone (10(-5)M) 10 min before exposure of the tissues to 20 mM K+ significantly enhanced noradrenaline release from 'dependent' slices. The results suggest that the basic release mechanism may have adapted to the continuous presynaptic inhibition of release by morphine.

Animals↗
PubMed1994

Changes in the basal ganglia and thalamus following reperfusion after complete cerebral ischaemia.

We report specific changes bilaterally in the basal ganglia and thalamus following reperfusion after complete cerebral ischaemia. A 69-year-old man, resuscitated after cardiac arrest, showed symmetrical low-density lesions in the head of the caudate nucleus and lentiform nucleus on CT. MRI revealed methaemoglobin derived from minor haemorrhage in the basal ganglia and thalamus, not evident on CT. We suggest that this haemorrhage results from diapedesis of red blood cells through the damaged capillary endothelium following reperfusion.

Aged↗
PubMed1988

The nature and timing of excitotoxic neuronal necrosis in the cerebral cortex, hippocampus and thalamus due to flurothyl-induced status epilepticus.

Flurothyl-induced status epilepticus was studied by light and electron microscopy (LM, EM) to determine the time course and structural features of neuronal necrosis in the vulnerable brain regions in epilepsy. The cerebral cortex, hippocampus and thalamus were examined after closely spaced recovery periods of up to 1 week. The results showed that acidophilic neurons appeared simultaneously in neurons of the neocortex, hippocampus and thalamus, and that this occurred within 1 h following the end of the epilepsy. The corresponding features of acidophilic neurons by EM were mitochondrial flocculent densities and large discontinuities in cell and nuclear membranes. Dark neurons were ubiquitous during the epilepsy, but recovered almost universally. A few dark neuronal forms persisted and underwent cytorrhexis after 12-h recovery or longer. Axon-sparing dendritic lesions characteristic of excitotoxic neuronal death were found in the neuropil of the neocortex, and in both vulnerable CA1 and resistant CA3 neurons of the hippocampus. Other than acute edema, glial changes were absent. The findings support an excitotoxic mechanism in epilepsy-induced selective neuronal necrosis also in brain regions outside the hippocampus, and contrast with previous reports in ischemia and hypoglycemia in that neuronal necrosis occurs virtually immediately after an epileptic insult. No "maturation" of cell damage, as described in ischemia, was seen. Furthermore, even exceedingly dark neuronal forms and massive dendritic swelling must be considered sub-lethal or prelethal cellular changes. Lethal cellular changes include acidophilia by LM, cell membrane breaks, and mitochondrial flocculent densities by EM.

Animals↗
PubMed1977

Multiple system degeneration and involving thalamus, reticular formation, pallido-nigral, pallido-luysian and dentato-rubral systems. A case report.

An autopsy case of multiple system degeneration is characterized by the following; (1) progressive dementia and abnormal sleep patterns, followed by Parkinsonian symptoms with terminal akinetic mutism; (2) severe symmetrical degeneration in the thalamus, particularly nucl. medialis thalami, the reticular formation of the brain stem, also the pallidonigral, pallido-Luysian and dentato-rubral systems. As far as we known, there is no case in the literature, of combined system degeneration, which shows such a wide anatomical range of lesions as the present one. Clinico-pathological correlation between dementia and degeneration of the thalamus, and between abnormal sleep-consciousness mechanism and degeneration of the reticular formation are discussed. The extrapyramidal symptoms are discussed from the clinico-pathological aspect. In addition, peculiar eosinophilic bodies are described, which were most frequently found in the putamen.

Adult↗
PubMedDate not supplied

Local blood flow in the thalamus and frontal cortex in alert and narcotized dogs.

The magnitude of the local blood flow in the thalamus and cerebral cortex is studied on 22 sexually mature nonpedigree dogs. Mean values of local blood flow are obtained in alert animals, and the effect of narcosis (nitrous oxide) on the local cerebral blood flow is studied. The mean local blood flow in alert dogs is found to be 84.8 +/- 2.9 ml/100 g/min in the cerebral cortex and 68.7 +/- 1.6 ml/100 g/min in the thalamus. Insignificant fluctuations are found during a dynamic recording of the local blood flow during 7 days. Under narcosis (70% nitrous oxide) the local blood flow decreases 3-12%. According to the findings, nitrous oxide narcosis does not significantly affect the brain circulation, so that it is suitable for an experimental study of the latter.

Animals↗