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PubMed2006

Stereotactic approach and electrophysiological characterization of thalamic reticular and dorsolateral nuclei of the juvenile pig.

Few reports exist on complex functions of pig's central nervous system. A direct access to thalamic structures enables a deeper understanding of neuronal networks. Here we present an easy to implement stereotactic approach to reach both reticular and dorsolateral thalamic nuclei (RTN and LD). In thirteen pigs (7 weeks old) the correct electrode position was confirmed for 22 out of 26 thalamic electrodes (RTN: A+2, L9, V24 and LD: A-2, L5, V20, with bregma A 0, L 0). Quantitative effects of isoflurane/nitrous oxide (State 1) and fentanyl sedation (State 2) were determined by brain hemodynamics and metabolism. Neurophysiologic features were performed by spectral power, coherence and SEP analysis. Brain blood flow (by 21 +/- 13%) and oxidative brain metabolism (CMRO, by 26 +/- 12%, CMRGlucose by 26 +/- 22%) were markedly reduced during State 1 (P<0.05). Regional thalamic blood flow exhibited similar alterations, but side-differences did not occur. State 1 induced quite similar brain activity in cortical as well as thalamic regions investigated. During State 2 electrocortical activity of low frequency ranges was markedly reduced, whereas spectral band power of high frequency ranges was additionally decreased in RTN (P<0.05). Thus, we used a convenient approach for targeted deep electrode implementation and characterized electrophysiological features in RTN and LD.

Anesthetics↗
PubMed2005

Transient attenuation of neuropathic manifestations in rats following lesion or reversible block of the lateral thalamic somatosensory nuclei.

BACKGROUND AND AIMS: Nociceptive behavior in animal models for mononeuropathy has been shown to be altered by spinal tract lesions which suggest a possible supraspinal modulation. The thalamus constitutes a chief center for the processing of nociception. We have, therefore, investigated the effects of transient or permanent blocks of the lateral somatosensory thalamic nuclei (the ventrobasal complex) on the neuropathic manifestations in rats. METHODS: Different groups of rats (n = 5-6) were subjected to mononeuropathy, following the spared nerve injury model, known to produce sustained heat hyperalgesia and tactile and cold allodynia which peaked about 2 weeks after nerve injury. This was followed by stereotaxic placement of either electrolytic or chemical lesions or implantation of mini osmotic pump for slow release of lidocaine in the ventrobasal complex. RESULTS: Chronic electrolytic and chemical lesions or reversible block of the lateral somatosensory thalamus produced transient (1-2 weeks) attenuation of neuropathic manifestations along with a persistent decrease of the hot plate latency. The most pronounced effect was observed on heat hyperalgesia, and the least significant and short-lived effect was observed on cold allodynia. CONCLUSION: We conclude that the lateral somatosensory thalamic complex is involved in the processing of neuropathic manifestations but cannot be considered as an obligatory or exclusive relay center for the neuropathic syndromes.

Anesthetics, Local↗
PubMed1984

Spatio-temporal organization of a branched tecto-spinal/tecto-diencephalic neuronal system.

The aim of the present study was to identify in the rat the diencephalic nuclei addressed by ascending collaterals of tecto-spinal neurons. For this purpose we made use of anterograde axonal transport method to determine the pattern of diencephalic projections arising from the lateral portion of the superior colliculus where most of tecto-spinal neurons are lying. Next, we used the antidromic activation method to analyse whether some of these colliculo-diencephalic projections were provided through collaterals of tecto-spinal neurons. Following injections of wheatgerm agglutinin, conjugated with horseradish peroxidase, in the lateral part of the superior colliculus, anterograde labelling was observed in: the contralateral superior colliculus, the ipsilateral pretectal nuclei, subthalamic area (zona incerta and Forel field) and thalamic structures namely: dorsal and ventral lateral geniculate, parafascicular, posterior nuclear group, reuniens nuclei and lateral portion of medio-dorsal nucleus. Moreover, bilateral projections were revealed in the following thalamic nuclei: lateral posterior, ventro-medial, paracentral and central-lateral. In the electrophysiological study we established that the thalamic nuclei medio-dorsal/central-lateral, paracentral, ventral-medial and the zona incerta receive ascending collaterals of the tecto-spinal neurons. In addition, an axonal branch to the contralateral superior colliculus was also revealed. The various ascending and descending collaterals of each branched neuron exhibited a similar conduction time for action potentials. It is thus likely that the tecto-spinal/tecto-diencephalic neurons provide a synchronized influence on their targets. The functional implication of such a branched collicular efferent pathway is discussed. Considering that tecto-spinal neurons are one of the collicular neuronal populations on which the substantia nigra exerts its influence, new perspectives in the analysis of basal ganglia collicular relationships are given.

Animals↗
PubMed1996

Organization of the visual reticular thalamic nucleus of the rat.

The visual sector of the reticular thalamic nucleus has come under some intense scrutiny over recent years, principally because of the key role that the nucleus plays in the processing of visual information. Despite this scrutiny, we know very little of how the connections between the reticular nucleus and the different areas of visual cortex and the different visual dorsal thalamic nuclei are organized. This study examines the patterns of reticular connections with the visual cortex and the dorsal thalamus in the rat, a species where the visual pathways have been well documented. Biotinylated dextran, an anterograde and retrograde tracer, was injected into different visual cortical areas [17; rostral 18a: presumed area AL: (anterolateral); caudal 18a: presumed area LM (lateromedial); rostral 18b: presumed area AM (anteromedial); caudal 18b: presumed area PM (posteromedial)] and into different visual dorsal thalamic nuclei (posterior thalamic, lateral geniculate nuclei), and the patterns of anterograde and retrograde labelling in the reticular nucleus were examined. From the cortical injections, we find that the visual sector of the reticular nucleus is divided into subsectors that each receive an input from a distinct visual cortical area, with little or no overlap. Further, the resulting pattern of cortical terminations in the reticular nucleus reflects largely the patterns of termination in the dorsal thalamus. That is, each cortical area projects to a largely distinct subsector of the reticular nucleus, as it does to a largely distinct dorsal thalamic nucleus. As with each of the visual cortical areas, each of the visual dorsal thalamic (lateral geniculate, lateral posterior, posterior thalamic) nuclei relate to a separate territory of the reticular nucleus, with little or no overlap. Each of these dorsal thalamic territories within the reticular nucleus receives inputs from one or more of the visual cortical areas. For instance, the region to the reticular nucleus that is labelled after an injection into the lateral geniculate nucleus encompasses the reticular regions which receive afferents from cortical areas 17, rostral 18b and caudal 18b. These results suggest that individual cortical areas may influence the activity of different dorsal thalamic nuclei through their reticular connections.

Animals↗
PubMed1987

Effects of the GABA receptor agonist, progabide, upon local cerebral glucose utilization.

The effects of a specific GABA receptor agonist, progabide, have been examined on local cerebral glucose utilization through the use of the autoradiographic [14C]2-deoxyglucose technique in conscious rats. The intraperitoneal administration of progabide (80-320 mg.kg-1) resulted in a heterogeneous pattern of significantly reduced glucose utilization throughout the 50 discrete regions of the brain that were studied. Insignificant decreases in local cerebral glucose use were noted following the low dose of progabide (80 mg.kg-1). Following progabide (160 mg.kg-1), reductions of approximately 20% in glucose utilization were observed in most of the extrapyramidal system (substantia nigra, pars compacta and reticulata; globus pallidus; caudate nucleus), some thalamic nuclei (lateral geniculate body, anterior and ventrolateral thalamic nuclei), a number of areas related to the limbic system (cingulate cortex; amygdala; hypothalamus; lateral habenula; nucleus accumbens; dorsal hippocampus as well as the CA3 field) and the raphé nuclei. In contrast, layer IV of the neocortex, the cerebellum and cerebellar nuclei, displayed only minimal (10-15%) reductions in glucose utilization. At the highest dose (320 mg.kg-1) examined, progabide effected widespread though heterogeneously distributed decreases in glucose use. The overall pattern of decreased glucose use seen with progabide was different from that noted with previously studied GABA-mimetic drugs, such as muscimol, except for those changes observed in the extrapyramidal and sensory-motor areas for which similar dose-response relationships occurred. A significant correlation was observed between progabide-induced decreases in glucose utilization and in serotonin synthesis in a number of brain areas. The pattern of progabide-induced changes in integrated functional activity is compatible with its neurochemical spectrum and could indicate the loci at which its anticonvulsant, antidepressant and extrapyramidal activities are initiated.

Animals↗
PubMed2001

Superior colliculus projections to midline and intralaminar thalamic nuclei of the rat.

The superior colliculus (SC) projections to the midline and intralaminar thalamic nuclei were examined in the rat. The retrograde tracer cholera toxin beta (CTb) was injected into one of the midline thalamic nuclei-paraventricular, intermediodorsal, rhomboid, reuniens, submedius, mediodorsal, paratenial, anteroventral, caudal ventromedial, or parvicellular part of the ventral posteriomedial nucleus-or into one of the intralaminar thalamic nuclei-medial parafascicular, lateral parafascicular, central medial, paracentral, oval paracentral, or central lateral nucleus. After 10-14 days, the brains from these animals were processed histochemically, and the retrogradely labeled neurons in the SC were mapped. The lateral sector of the intermediate gray and white layers of the SC send axonal projections to the medial and lateral parafascicular, central lateral, paracentral, central medial, rhomboid, reuniens, and submedius nuclei. The medial sector of the intermediate and deep SC layers project to the parafascicular and central lateral thalamic nuclei. The paraventricular thalamic nucleus is innervated almost exclusively by the medial sectors of the deep SC layers. The superficial gray and optic layers of the SC do not project to any of these thalamic areas. The discussion focuses on the role these SC-thalamic inputs may have on forebrain circuits controlling orienting and defense (i.e., fight-or-flight) reactions.

Animals↗
PubMed1996

TRK and p75 neurotrophin receptor systems in the developing human brain.

The prenatal development of the neurons immunoreactive for high-affinity tropomycin-related kinase (trk) receptor (pan trk which recognizes trkA, trkB, and trkC) and low-affinity p75 neurotrophin receptor (p75NTR) was examined in the human brain from embryonic weeks 10 to 34 of gestation. In the embryonic week 10 specimen in which only brainstem regions were available for evaluation, trk immunoreactivity (trk-ir) was observed in the ventral cochlear, solitary, raphe, spinal trigeminal, and hypoglossal nuclei, as well as the vestibular complex and medullary reticular formation. At this time point of gestation, p75ntr-immunoreactive (p75NTR-ir) staining was observed within these same regions plus the inferior olivary and ambiguus nuclei. At embryonic week 14, trk-ir neurons were seen within the subplate zone of the entorhinal cortex, basal forebrain, caudate nucleus, putamen, external segment of the globus pallidus, specific thalamic nuclei, lateral mammillary nucleus, habenula nucleus, select brainstem nuclei, and the dentate nucleus of cerebellum. At this gestational time point, p75NTR-ir neurons were observed in each of these structures, with the exception of the caudate nucleus, specific thalamic nuclei, lateral mammillary nucleus, and habenula nucleus. Additionally, p75NTR-ir neurons were observed within the corpus callosum. The staining pattern for both trk and p75NTR remained unchanged at embryonic weeks 15 to 16 except for the addition of trk-ir and p75NTR-ir within the cortical subplate zone, hippocampus, and subthalamic nucleus. By embryonic week 18, trk-ir neurons were widely expressed within mostly all thalamic nuclei. In contrast, trk-ir was no longer seen within the hypoglossal, cuneate, and gracile nuclei at this time point. This staining pattern for trk and p75NTR remained virtually unchanged from embryonic weeks 19 to 20 and embryonic weeks 16 to 20, respectively. From embryonic weeks 22 to 34, the distribution of both trk-ir and p75NTR-ir neurons changed gradually. During this period, neurons in most thalamic and some brainstem nuclei became progressively immunonegative for trk, whereas neurons in the neocortical subplate zone, corpus callosum, and hilar region of dentate gyrus gradually lost immunoreactivity for p75NTR. These data demonstrate an important and complex role for both the high-(trk) and low- (p75) affinity neurotrophin receptors during the development of multiple neuronal systems in the human brain.

Antibody Specificity↗
PubMed1967

Some factors involved in the thalamic control of spontaneous barbiturate spindles.

1. The origin of thalamic and cortical spontaneous spindles was studied in cats anaesthetized with sodium pentobarbital.2. Complete removal of all cortical grey matter left the thalamic rhythmic spindle activity unchanged.3. Removal of the entire thalamus or pronounced oedema in the thalamus abolished completely the spindle activity in the corresponding hemisphere.4. In a neuronally isolated cortical area, a fast, low voltage background activity appeared, interrupted by occasional irregular rapid potential changes (sharp waves) of high voltage. Regular spindle rhythms were seldom observed unless excited by a depolarizing drug. Spontaneous spindles did not invade the isolated cortex via a bridge of intact cortical tissue.5. With increasingly larger destruction of the thalamus in a rostro-caudal direction, the activity in the post-cruciate cortex did not change until the anterior third of the thalamus was encroached upon. A transverse section in front of the thalamus nearly eliminated the cortical spindles.6. Complete removal of the mid line and intralaminar nuclei left the spontaneous rhythmic activity of the lateral thalamic nuclei and of the frontal cortex principally unchanged.7. Removal of the laterally located thalamic nuclei, including the n. ventralis posterolateralis (VPL), abolished virtually all spontaneous spindle activity of the frontal cortex, including the post-cruciate area.8. Local cortical cooling reduced the amplitude but not the frequency of the cortical spindles.9. Cooling of the whole brain reduced both the amplitude and the frequency of the spindles. At low temperatures, all spindle activity in the cortex disappeared, and occasional sharp waves occurred, as with de-afferentation.10. It is concluded that the rhythm of the cortical spontaneous barbiturate spindles is generated exclusively by thalamic neurones. The electromotive force of the corticographic waves, however, has a cortical origin.

Animals↗
PubMed1980

[Pallido-thalamic projections of cats].

Projections of the globus pallidus and the entopeduncular nucleus on the thalamic nuclei have been studied in cats by methods of axonal-preterminal degeneration and retrograde cellular degeneration. Together with the known projections of the pallidum on the medial center, ventral anterior and ventral lateral thalamic nuclei, direct projections of the pallidum on the medial dorsal, central lateral and lateral posterior thalamic nuclei have been revealed. In cats not only the entopeduncular nucleus is the source of the fibres projecting on the thalamic nuclei, but also the globus pallidus has direct connections with the thalamic nuclei

Animals↗
PubMed1993

Ischemia-induced changes in alpha-tubulin and beta-actin mRNA in the gerbil brain and effects of bifemelane hydrochloride.

Using in situ hybridization histochemistry, we examined changes in the cytoskeletal protein alpha-tubulin and beta-actin mRNAs in the gerbil brain 14 days after transient ischemia. In an attempt to identify the changes induced in the synthesis of cytoskeletal protein by ischemia, we also evaluated the effects of post-ischemia administration of bifemelane on these cytoskeletal proteins. alpha-Tubulin and beta-actin mRNAs were decreased in the CA1 region 14 days after transient ischemia. These decreases coincided with the loss of CA1 pyramidal cells, suggesting that they may have been related to delayed neuronal death. The beta-actin mRNA level in ischemic controls was significantly increased in the dentate gyrus, habenular nucleus, and medial and lateral thalamic nuclei, where some afferent nerves project into the hippocampal pyramidal cells. The increased beta-actin mRNA suggests that there may be a compensatory enhancement of actin synthesis in the afferent neurons that restores loosened synaptic connections with the ischemic cells in the CA1-4 fields. Administration of bifemelane just after recirculation prevented most of the ischemia-induced mRNA reductions in the CA1 field. Bifemelane's effect may be related to inhibition of Ca2+ influx and its radical scavenging activity. When bifemelane was administered to the ischemic group, alpha-tubulin mRNA levels significantly increased in the dentate gyrus and amygdaloid nucleus, and beta-actin mRNAs showed a tendency to increase in the CA3 and CA4 fields, dentate gyrus, and medial and lateral thalamic nuclei. These findings suggest that bifemelane may enhance synthesis of cytoskeletal protein, especially in the ischemic brain, inducing axon outgrowth or synapse formation.

Actins↗
PubMed2004

Presence and connections of auditory neurons in the rostrodorsal and rostrolateral parts of the thalamic reticular nucleus.

OBJECTIVE: Auditory neurons have been identified in the caudoventral part of the thalamic reticular nucleus (TRN). We examined the acoustic input to single cells in the rostrodorsal part of the TRN. MATERIAL AND METHODS: In alpha-chloralose-anesthetized cats, we extracellularly recorded the responses of single neurons in the rostral TRN to acoustic and light stimuli. Next, to examine efferent projections of auditory neurons in the rostral TRN, we injected wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into other thalamic nuclei where auditory neurons were detected, including the lateral posterior nucleus (LP), the lateral medial and suprageniculate nuclei and the centromedian nucleus. Finally, intracortical microstimulation of the LP was performed to demonstrate antidromic activation of the auditory neurons in the rostral TRN. RESULTS: In the rostral TRN, 2 types of response to auditory stimuli were observed: brief, short-latency bursts (13-20 ms; mean 16.5 ms) and longer bursts with a long latency (38.8-50 ms; mean 44.8 ms). Injection of WGA-HRP into the medial LP labeled cells only in the rostrodorsal TRN, while extending the injection to the other nuclei labeled cells in the rostrodorsal and rostrolateral parts of the nucleus. Auditory neurons in the rostral TRN were activated antidromically by microstimulation of auditory neurons in the LP, with a latency of 1.2 ms. CONCLUSIONS: These results strongly suggest that auditory neurons in the rostrodorsal TRN project to auditory neurons in the LP. The rostral auditory TRN may be involved in transmission of auditory information via the non-specific association system of the thalamus.

Acoustic Stimulation↗
PubMed1981

Alterations in local cerebral glucose utilisation in specific thalamic nuclei following apomorphine.

The alterations in local cerebral glucose utilisation in eight discrete nuclei in the thalamus following the administration of apomorphine (0.5 mg kg-1) have been investigated with the autoradiographic 2-deoxyglucose technique in 11 conscious rats. In two thalamic nuclei (parafascicular and ventrolateral nuclei), glucose utilisation was significantly elevated following apomorphine; in two thalamic nuclei (the anterior medial and anterior ventral nuclei), glucose utilisation was significantly reduced following apomorphine; and in four nuclei (lateral geniculate, medial geniculate, mediodorsal, and lateral thalamic nuclei), glucose use was unchanged.

Animals↗
PubMed1979

Neurochemical and histochemical studies of the effect of a lesion of the nucleus cuneiformis on the cholinergic innervation of discrete areas of the rat brain.

The innervation sites of the dorsal tegmental acetylcholinesterase (AChE)-containing pathway were examined in rats by combining histochemical and biochemical techniques. A lesion was placed in the nucleus cuneiformis (midbrain reticular formation) and brains were examined after 4 days survival for changes in AChE staining and choline acetyltransferase (ChAT) activity in discrete brain areas. An ipsilateral projection appears to exist to the anterior thalamic nuclei, lateral portion of the medial thalamic nucleus, parafascicular nucleus, pretectal nucleus, posterior thalamic nucleus, and deep layers of the superior colliculus. A possible bilateral innervation to the reticular nucleus of the thalamus and the dorsal and ventral lateral geniculates was found. The parallel use of AChE histochemistry and measurements of ChAT activity in discrete nuclei will be useful for future evaluation of cholinergic pathways.

Acetylcholine↗
PubMed2005

Mapping by laser photostimulation of connections between the thalamic reticular and ventral posterior lateral nuclei in the rat.

We used laser scanning photostimulation through a focused UV laser of caged glutamate in an in vitro slice preparation through the rat's somatosensory thalamus to study topography and connectivity between the thalamic reticular nucleus and ventral posterior lateral nucleus. This enabled us to focally stimulate the soma or dendrites of reticular neurons. We were thus able to confirm and extend previous observations based mainly on neuroanatomical pathway tracing techniques: the projections from the thalamic reticular nucleus to the ventral posterior lateral nucleus have precise topography. The reticular zone, which we refer to as a "footprint," within which photostimulation evoked inhibitory postsynaptic currents (IPSCs) in relay cells, was relatively small and oval, with the long axis being parallel to the border between the thalamic reticular nucleus and ventral posterior lateral nucleus. These evoked IPSCs were large, and by using appropriate GABA antagonists, we were able to show both GABA(A) and GABA(B) components. This suggests that photostimulation strongly activated reticular neurons. Finally, we were able to activate a disynaptic relay cell-to-reticular-to- relay cell pathway by evoking IPSCs in relay cells from photostimulation of the region surrounding a recorded relay cell. This, too, suggests strong responses of relay cells, responses strong enough to evoke spiking in their postsynaptic reticular targets. The regions of photostimulation for these disynaptic responses were much larger than the above-mentioned reticular footprints, and this suggests that reticulothalamic axon arbors are less widespread than thalamoreticular arbors, that there is more convergence in thalamoreticular connections than in reticulothalamic connections, or both.

Animals↗
PubMed1996

Noxious colorectal distention induced-c-Fos protein in limbic brain structures in the rat.

Colorectal distention is a non-invasive stimulus used to study visceral pain processing in the nervous system. In this study, immunocytochemical labeling for the immediate-early gene, c-Fos, was used to map limbic brain structures involved in processing visceral pain. Rats received noxious colorectal distention while loosely restrained or loose restraint without distention (control). The brains were immunostained and the density of Fos-labeled nuclei within areas of the brain associated with limbic function were examined. Many cortical (cingulate; retrosplenial; insular; perirhinal, entorhinal) and subcortical (periaqueductal gray; locus coeruleus; lateral parabrachial area; paraventricular, anterodorsal and centromedian thalamic nuclei; lateral septal area; dorsomedial hypothalamus; cortical amygdala; subiculum) areas were labeled in the control rats, but significantly more Fos was observed in these areas following noxious colorectal distention (CRD). Additional areas were labeled following CRD but not restraint (e.g. infralimbic and prelimbic cortices; mediodorsal thalamic nucleus; central amygdaloid nucleus). The results show that noxious visceral stimuli result in Fos expression in limbic structures that exceeds that induced by restraint stress, suggesting that different pathways and circuits are recruited by stimuli which can produce similar emotional responses.

Animals↗
PubMed1978

The cingulate bridge between allocortex, isocortex and thalamus.

The Fink-Heimer silver impregnation and the autoradiographic methods were used to study the fiber projections of the cingulate cortex in the squirrel monkey. It was found that this cortex provides inputs to the straitum, thalamus and several areas of isocortex. Evidence was found for a number of fiber projections (1) Fibers from the anterior limbic area were traced to the central part of the head of the caudate nucleus, putamen, septum, dorsomedial nucleus of the thalamus, anterior hypothalamus and lateral basal nucleus of the amygdala. (2) Projections from the cingulate area were traced to the lateral part of the head of the caudate nucleus, putamen, and to the centromedian, anterior, lateral dorsal, and lateral ventral thalamic nuclei and to medial nuclei of the base of the pons. (3) There were porjections from the retrosplenial area of the anterior, lateral dorsal, dorsomedial, and posterior thalamic nuclei and lateral nuclei of the pons. These results indicate that most of the cingulate gyrus is an intermediate structure between the thalamus and overlying cortex. The anterior limbic area forms a bridge between the thalamus and other areas of the cingulate gyrus and the frontal cortex. (4) the retrosplenial area and the posterior part of the cingulate area bridge the adjacent visual snesory association cortex and pelvic areas of the snesory motor cortex, respectively. These areas of the cingulate gyrus project directly to the striatum as well as to the thalamus, structurally providing limbic system input to subcortical motor structures.

Animals↗