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PubMed1989

Distribution of terminals of thalamocortical fibers originating from the ventrolateral nucleus of the cat thalamus.

Anterograde labelling following focal injections of Phaseolus vulgaris leucoagglutinin was used to identify the threedimensional cortical distribution of thalamocortical (TC) fibers from the ventrolateral nucleus of the thalamus of the cat. The labelled TC fibers were distributed usually in layers I and III of the motor cortex and the terminals in layer III tended to aggregate into patches about 1-1.5 mm wide in a mediolateral direction. These patches were arranged in longitudinal strips about 2-5 mm long in a rostrocaudal direction and were separated by gaps of terminal free area.

Animals↗

PubMed1989

Prefrontal projections to the medial nuclei of the dorsal thalamus in the rabbit.

Retrograde transport of horseradish peroxidase (HRP) from the mediodorsal (MD), ventromedial (VM), ventroposterior (VP) and intralaminar (IL) nuclei of the dorsal thalamus revealed a topographical pattern of efferents from the frontal cortex. MD injections labeled the midline and insular regions of the prefrontal cortex (Pfc), including the anterior limbic, and most ventral part of the precentral agranular Pfc, as well as the agranular insular cortex. VM injections labeled only the most dorsomedial part of the granular insular cortex, whereas IL and VP injections labeled the dorsal precentral agranular Pfc and a strip of cortex that extended laterally across the superior aspect of the forceps minor. The IL injections also labeled cells that extended ventrally into the granular and agranular insular areas.

Animals↗

PubMed1990

Vibrissa-responsive neurons of the superior colliculus that project to the intralaminar thalamus of the rat.

Responses to deflection of vibrissae were studied in neurons of the superior colliculus projecting to the intralaminar thalamus. Forty-two percent were activated by deflection of several vibrissae. Some units showed habituation and directional sensitivity but no other feature extraction was noted. All responsive units were located in the intermediate and deep layers in a roughly somatotopic distribution and intermingled with other projecting and non-projecting units.

Action Potentials↗

PubMed1990

Postsynaptic potentials evoked in ventrobasal thalamus neurones by natural sensory stimuli.

Intracellular recordings were made in the ventrobasal thalamus of rats anaesthetised with urethane. Postsynaptic responses were evoked by stimulation of the peripheral receptive field with an air jet of 10 ms duration. The postsynaptic response typically consisted of an excitatory postsynaptic potential (EPSP)/inhibitory postsynaptic potential (IPSP) sequence with one or more evoked action potentials. Injection of hyperpolarizing current pulses appeared to increase the EPSP amplitude, whereas depolarising current pulses caused a reduction in EPSP amplitude. These changes in EPSP amplitude were however obscured by the presence of IPSPs and a slow potential similar to a low-threshold Ca2+ spike (LTS).

Animals↗

PubMed1990

Modulation of afferent transmission to single neurons in the ventroposterior thalamus during movement in rats.

Single units (n = 135) were recorded in the ventroposterolateral nucleus of the thalamus in awake rats. The responsiveness of neurons to sensory activation during rest and treadmill locomotion was tested by stimulation through electrodes implanted under the skin of the forepaw. The averaged evoked unit response was suppressed by a mean 31% during movement as compared with rest. This is to be compared with the mean 71% sensory suppression observed previously in the somatosensory cortex. These findings are consistent with the hypothesis that sensory information ascending to, and within the SI cortex is successively modulated at several levels during movement.

Action Potentials↗

PubMed1993

GABAA-receptor immunoreactivity in the rat dorsal thalamus: an ultrastructural investigation.

The ultrastructural localization of GABAA-receptor (GABAA-R) immunoreactivity (ir) in representative nuclei of the rat dorsal thalamus was investigated using the monoclonal antibody 62-3G1 to the beta 2 and beta 3 subunits of the GABAA-R [8]. The pattern of distribution and the subcellular localization of ir were similar in all the thalamic nuclei examined, with the exception of the reticular nucleus that was unlabeled. The reaction product was present along somatic and dendritic plasma membranes of thalamic neurons and on their intracellular membranes. No labelling was observed in glial cells. The ir was present in areas of plasma membranes related and non related to terminals containing flat vesicles, and also on invaginated plasma membranes suggesting a recycling process of the receptor complex. The distribution and mismatches between GABA neurotransmitter and its receptor localization are discussed.

Animals↗

PubMed1994

The sensation of angina can be evoked by stimulation of the human thalamus.

We have performed single-neuron recording and microstimulation in the region of the thalamic principal sensory nucleus (ventrocaudal nucleus, Vc) prior to implantation of a deep brain-stimulating electrode in a patient with pain secondary to arachnoiditis and with a past history of unstable angina. Cells located in the 16 mm lateral plane had cutaneous receptive fields on the chest wall. At and posterior to the location of these cells stimulation coincided precisely with the sensation of angina (stimulation-associated angina). The description of stimulation-associated angina was measured using a questionnaire and was identical to the patient's usual angina except that it began and terminated suddenly. Stimulation-associated angina was coincident with a tingling sensation in the leg. Clinical, hemodynamic, electrophysiologic and biochemical measures of cardiac function showed no evidence of myocardial strain or injury related to stimulation-associated angina. Since cells in the region of the principle sensory nucleus of thalamus respond to cardiac injury in animals, the present results suggest that this region mediates the sensation of angina.

Aged↗

PubMed1982

Anterograde tracer and field potential analysis of the neocortical layer I projection from nucleus ventralis medialis of the thalamus in cat.

The projection of the ventromedial nucleus of the thalamus to the neocortex was studied in cat by means of anterograde and retrograde transport of horseradish peroxidase, by the depth profile of evoked thalamocortical field potentials, and by superfusion of the cortex with manganese to block transmitter release. Horseradish peroxidase injected into the ventromedial nucleus was anterogradely transported to the outer third of layer I in the neocortex, extending from the depth of the cruciate sulcus anterior to the olfactory bulb and tract. The region of projection from the ventromedial nucleus extended mediolaterally from the medial wall of the proreus gyrus to the ventral tip of the coronal gyrus. Horseradish peroxidase injections or applications in these areas of the neocortex resulted in the retrograde labeling of neurons in the ventromedial nucleus. Injections in many other cortical areas did not result in labeled neurons in this nucleus. Stimulation of the ventromedial nucleus with single pulses elicited surface-negative waves in the medial part of the precruciate region that had superficial isoelectric points. Superfusion of the precruciate area with manganese resulted in the suppression of the ventromedial-evoked wave, whereas control extracellular waves in deeper layers were unaffected. An additional additional finding was that horseradish peroxidase injections in the ventromedial nucleus led to a dense reciprocal retrograde labeling of neurons in layer VI of that part of the cortex to which the ventromedial nucleus projects. We conclude that, in cat, (1) the ventromedial nucleus projects to layer I of the cerebral cortex anterior to the cruciate sulcus and receives a dense reciprocal projection from layer VI; (2) stimulation of neurons in the ventromedial nucleus causes depolarization of structures in layer I and these neurons are responsible for recruiting responses in the anterior cortex.

Action Potentials↗

PubMed1982

The distribution and some morphological features of substantia nigra neurons that project to the thalamus, superior colliculus and pedunculopontine nucleus in the monkey.

Neurons of the substantia nigra's pars reticulata that send axons to the thalamus, superior colliculus and midbrain reticular formation (including the pedunculopontine nucleus) have been revealed in monkeys by the technique of retrograde transport of horseradish peroxidase. The populations of nigrothalamic, nigrotectal and nigroreticular neurons differ from one another in their number, intranigral distribution and somatodendritic size and shape. Nigrothalamic cells are the most abundant and, although scattered throughout the mediolateral expanse of the pars reticulata, their numbers progressively diminish from rostral to caudal levels. Nigrotectal cells are least numerous and are restricted almost exclusively to the lateral margin of the rostral one-half of the pars reticulata. Nigroreticular cells, like nigrothalamic, are scattered throughout the mediolateral dimension of the nucleus, but are more commonly located at middle to caudal levels. In addition to their restricted intranigral location, the nigrotectal cells are larger, polygonal and have more major dendritic processes than the smaller nigrothalamic and nigroreticular cells which are usually triangular or fusiform. A small proportion of cells of all three types appears to project contralaterally. These findings indicate that the efferent organization of the primate pars reticulata differs markedly from that of the rodent and the monkey's nigrotectal cells constitute a spatially and morphologically distinct subpopulation within the pars reticulata. These data should be useful in understanding the functional organization of topographic inputs to the pars reticulata such as that from the neostriatum.

Animals↗

PubMed1988

Fine structure of the dorsal part of the nucleus submedius of the rat thalamus: an anatomical study with reference to possible pain pathways.

The dorsal portion of the nucleus submedius of the rat thalamus receives spinal and trigeminal projections which may convey noxious inputs. The present study was undertaken to analyse the fine structure of the nucleus with particular reference to a possible trigemino-thalamo-prefrontal cortical pathway relaying in nucleus submedius. Presynaptic terminals in the dorsal portion of the nucleus submedius were classified into three broad categories usually observed in thalamic nuclei: "small round", "flat" and "large round" types. Axonal tracing using either anterograde transport of horseradish peroxidase or degeneration methods indicated that some "small round" terminals originate from the pre-frontal cortex. Some "large round" terminals were labelled from the trigeminal subnucleus caudalis. These "large round" terminals exhibited distinct morphological features when compared with trigeminal terminals in other thalamic nuclei. In particular they made synaptic contacts predominantly with dendritic protrusions and were surrounded by multilamellate astrocytic processes. Double-labelling experiments were performed by means of the combined retrograde transport of horseradish peroxidase and Wallerian degradation techniques. Terminals degrading after lesion of the trigeminal subnucleus caudalis contacted submedius neurons labelled retrogradely from the prefrontal cortex. These observations demonstrate the existence of a direct monosynaptically relayed pathway from subnucleus caudalis to prefrontal cortex which relays in the dorsal part of nucleus submedius.

Afferent Pathways↗

PubMed1993

Cholinergic responsiveness of neurons in the ventroposterior thalamus of the anesthetized rat.

Acetylcholine has been implicated as an important neurotransmitter in the mechanisms of thalamic activation. Cholinergic mechanisms are thought to directly underlie the high level of excitability observed in thalamic relay neurons during waking and rapid eye movement sleep. We sought to determine if the cholinergic responsiveness of neurons in the ventroposterior nuclei of the thalamus in rat is consistent with this view. Neurons in the chloral hydrate-anesthetized rat were studied with extracellular recording and microiontophoretic application of cholinergic agents. In most cases (63% of 63 cells), the ejection of the agonist, carbachol, had no observable effect on spontaneous activity. Facilitation (25%), inhibition (8%) and inhibition followed by facilitation (3%) were also observed. Carbachol ejections that by themselves were ineffective in altering spontaneous activity proved capable, in 93% of 28 cells, of antagonizing the uniformly facilitatory responses produced by glutamate ejection. The putative M1-selective, cholinergic agonist, McN-A-343, was also ineffective alone in altering spontaneous activity in the majority of cases (74% of 27 cells) and produced only inhibitory responses in the remaining seven neurons studied. Interacting applications of McN-A-343 and glutamate resulted, in all cases, in antagonism of glutamate facilitation (N = 12). The various responses to applied cholinergic agonists were all capable of being antagonized by muscarinic receptor-blocking agents. Both the high proportion of inhibitory responses and the antagonism of glutamate facilitatory responses suggest that ventroposterior neurons in the rat differ from other thalamocortical relay neurons in the rat and cat with regard to cholinergic responsiveness. Additionally, the lack of predominantly facilitatory responding renders it unlikely that cholinergic mechanisms directly underlie increases in excitability of ventroposterior neurons observed during waking and rapid eye movement sleep.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗

PubMed1994

GABAergic interneurons in the somatosensory thalamus of the guinea-pig: a light and ultrastructural immunocytochemical investigation.

This work was performed to confirm previous data reporting the presence of GABAergic interneurons in the ventrobasal complex of guinea-pig, and to investigate the intrinsic organization of this nucleus compared to that of thalamic nuclei lacking interneurons. Immunocytochemical experiments were performed on the thalamus of adult guinea-pigs perfused with mixed aldehydes using an anti-GABA serum. At light microscopy, the immunoreaction on floating Vibratome sections showed that GABAergic neurons are present only in the reticular and lateral geniculate nuclei and in the ventrobasal complex. Quantitative evaluation of their number indicated that they are 20 and 15% of the total neuronal population in lateral geniculate nucleus and ventrobasal complex, respectively, while they are less than 1% in ventrolateral nucleus. At the ultrastructural level, the postembedding immunogold procedure showed the presence, in the ventrobasal complex, of GABA-labeled profiles involved in complex synaptic arrangements similar to those found in carnivores and primates. Conversely, GABA-labeled terminals in thalamic nuclei devoid of interneurons formed exclusively axo-dendritic or axo-somatic contacts, like in rats and mice. The present data suggest that GABAergic neurons in the ventrobasal complex of guinea-pigs give rise to functionally important rearrangements of its intrinsic synaptic organization and that they represent the morphological basis for an intrinsic modulatory mechanism that is absent in other thalamic nuclei lacking inhibitory interneurons. The phylogenetic implications of these findings are also discussed in comparison to other animal species.

Animals↗

PubMedDate not supplied

Intracellular analysis of synaptic potentials in rat neostriatum following stimulation of the cerebral cortex, thalamus, and substantia nigra.

Intracellular recordings were obtained from neostriatal neurons of unparalyzed male hooded rats anesthetized with urethane. Electrical stimulation of the cerebral cortex (Cx), centromedian-parafascicular area of the thalamus (CMP), and the substantia nigra (SN) elicited monosynaptic excitatory postsynaptic potentials (EPSPs) in neostriatal neurons. Response latencies were, on the average, 3.7 msec, 3.3 msec, and 3.8 msec, for Cx, CMP and SN stimulation, respectively. Over 85% of recorded neurons showed convergence of inputs from all three stimulation sites. The SN induced EPSP sometimes had two components, with the second component beginning 10-15 msec after the first. EPSPs from all three stimulation sites were often followed by inhibitory postsynaptic potentials (IPSPs) lasting from 50-250 msec. Double shock experiments indicated that SN induced EPSPs could be reduced in amplitude by 20-80% when preceded by conditioning stimulation to Cx, CMP or SN. In contrast, the EPSP elicited by Cx stimulation were unaffected by conditioning stimulation. Some recorded neurons were morphologically identified by means of intracellular injection of horseradish peroxidase. All were "medium spiny" neurons. The results of the present study agree well with those of previous studies of cat caudate neurons, and extend them to rat neostriatal neurons.

Afferent Pathways↗

PubMed1983

Putative amino acid neurotransmitters and the nucleus dorsomedialis thalamus-prefrontal cortex pathway in the rat.

Endogenous levels of putative amino acid neurotransmitters (glycine, glutamic acid, aspartic acid, and GABA) in medial and sulcal prefrontal cortex of the rat were analyzed using gas liquid chromatography. No changes were found in the levels of these amino acids in medial and sulcal prefrontal cortex after lesion of the nucleus dorsomedialis of the thalamus suggesting, therefore, that the NDMT-prefrontal cortex pathway is not mediated by these amino acids.

Amino Acids↗

PubMed1986

Localization of responses in the somatosensory thalamus of the rat.

In the monkey and cat electrophysiological studies have indicated that unit response characteristics can be correlated with anatomical divisions in the somatosensory thalamus. In the rat, however, one study has suggested that the ventrobasal (VB) and posterior (PO) complexes are not functionally distinct [7]. In the present study, therefore, an attempt was made to correlate anatomical localization and unit response characteristics in the rat. We found that in the VB complex, units responding to light touch (LT) were more common than in the PO complex (45% vs. 9%), while in the PO complex, nociceptive units were more numerous than in the VB complex (55% vs. 38%). In the VB complex LT units had a somatotopic organization; in the PO complex they did not. Within the VB complex all LT units in the ventral posteromedial nucleus had receptive fields on the head; most ventral posterolateral nucleus LT units had receptive fields on the body. These results indicate that a correlation between unit response characteristics and localization does exist in the rat.

Afferent Pathways↗

PubMed1987

3H-2-deoxyglucose uptake after electrical stimulation of cardioactive sites in insular cortex and mediodorsal nucleus of the thalamus in rabbits.

The uptake of 3H-2-deoxyglucose (3H-2-DG) in selected brain structures was determined subsequent to electrical stimulation of insular cortex (Ins) and the mediodorsal (MD) nucleus of the thalamus in rabbits. Stimulation of Ins elicited parasympathetic-like responding (i.e., bradycardia and depressor responses); whereas MD stimulation produced sympathetic-like responses (bradycardia and pressor responses). Stimulation of Ins also resulted in increased 3H-2-DG activity in ipsilateral MD and the ventromedial/ventroposterior complex as well as the contralateral Ins compared to nonstimulated control subjects. The central nucleus of the amygdala also showed increased activity after Ins stimulation. In 2 animals stimulation of Ins resulted in increased 3H-2-DG activity in the caudate/putamen complex. Stimulation of MD resulted in ipsilateral increases in 3H-2-DG activity in the midline, agranular prefrontal cortex, as well as the ipsilateral Ins, and the caudate nucleus and putamen/globus pallidus complex. Two animals also showed increases in 3H-2-DG activity in ipsilateral substantia nigra. However, no increased activity was observed in the lateral hypothalamus, the parabrachial nuclei, the nucleus tractus solitarius, or the dorsal motor nucleus of the vagus, although it has been shown that efferents from Ins reach these areas. A more significant finding however, was that the reciprocal connections of MD and Ins appear to be activated by stimulation of either structure, even though their relationship to autonomic function appears to be quite different.

Animals↗

PubMed1991

Noradrenaline-like terminals in the cat nucleus ventralis posterior of the thalamus.

Noradrenaline-like immunoreactivity in the cat nucleus ventralis posterior of the thalamus was investigated using an indirect immunocytochemical technique. Specific antinoradrenaline antibodies, raised in rabbits, were used. It was first verified that these antibodies recognize noradrenaline cells bodies of the locus coeruleus and their ascending axons in the ascending noradrenergic tract. In the nucleus ventralis posterior itself, noradrenaline-like fibers were observed. They were either randomly distributed or grouped around nonlabeled cell bodies. These neurons were generally oblong and measured 60-80 microns. With electron microscopy, preliminary results showed immunoreactive fibers in close apposition to unlabeled cell bodies or dendrites. The precise nature of these profiles was sometimes difficult to ascertain, since experiments were done in presence of detergent. In some cases symmetric synapses might be observed between immunoreactive axon terminals and unlabeled dendrites. The specificity of the reaction is discussed in the light of several control experiments.

Animals↗

PubMed1996

The midbrain creates and the thalamus sharpens echo-delay tuning for the cortical representation of target-distance information in the mustached bat.

Mustached bats emit complex biosonar 'pulses' for echolocation. A delay of an echo from the emitted pulse carries target-distance information. At the auditory periphery, distance information is expressed by a time interval between the responses of neurons to the emitted pulse and its echo. In the auditory cortex (AC), however, it is mapped by 'FM-FM' neurons which are tuned to particular echo delays. FM-FM neurons have been found not only in the AC but also in the inferior colliculus (IC) of the midbrain and the medial geniculate body (MGB) of the thalamus. In the present study, we found that the IC has a precursor of the cortical echo-delay axis for the systematic representation of target-distance information and that the MGB shows the improved neural representation of target-distance information.

Animals↗