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At least 1,081 records · Page 60Linked to original sources
PubMed1990

Somatosensory neurons in human thalamus respond to speech-induced orofacial movements.

As part of stereotactic surgery, microelectrode recordings of somatosensory neurons in thalamus were obtained in 5 patients. Neurons with receptive fields on the lips and tongue were consistently activated when these structures were involved in production of speech sounds. The magnitudes of these responses were similar to those elicited by experimentally applied mechanical stimuli, suggesting that speech-induced somatosensory inputs are not suppressed at the thalamic level.

Action Potentials↗
PubMed1990

Evidence for spatiotemporal firing patterns within the auditory thalamus of the cat.

Multiple spike trains were recorded in the auditory thalamus of cats. Each unit was studied before, during and after cooling of the ipsilateral primary auditory cortex, during spontaneous activity and acoustically evoked activity. The search for spatiotemporal firing patterns provided evidence that excess of patterns does exist and that the acoustical stimulation increased their number. Cortical cooling did not affect the probability of finding the firing pattern.

Acoustic Stimulation↗
PubMed1990

Scopolamine but not haloperidol disrupts training-induced neuronal activity in cingulate cortex and limbic thalamus during learning in rabbits.

Rabbits previously trained to asymptotic performance of discriminative active avoidance behavior (n = 8) received systemic injections of scopolamine hydrobromide (SH: 1.0, 2.0, or 4.0 mg/kg) and scopolamine methylbromide (SM: 4.0 mg/kg). Each rabbit received all of the doses in a counterbalanced order. Single injections were administered 30 min before daily training sessions in which the multi-unit activity in the cingulate cortex and anterior thalamus was recorded. A single session in which saline was administered prior to testing preceded each of the drug sessions, and two days without training followed each drug session to allow dissipation of the drug effects. Additional groups received injections of haloperidol (HA: 0.025, 0.10, or 0.40 mg/kg; n = 7), or both SH/SM and HA (n = 5). The rabbits had been trained to step in an activity wheel in response to a tone CS + to avoid a footshock unconditional stimulus (US), and to ignore a different tone not followed by the US. SH and HA, but not SM, reduced significantly the frequency of conditioned avoidance responses (CRs). All doses of SH significantly attenuated cingulate cortical and AV thalamic training-induced neuronal discharges. HA injections also impaired CR performance but had no effect on the neuronal activity. These results suggest that the loss of the neuronal responses is contributory to the SH-induced CR loss. Absence of an effect of HA on neuronal activity indicates that the HA-induced CR impairment is due to disruption of other neural systems.

Animals↗
PubMed1991

Neonatal whisker removal in rats stabilizes a transient projection from the auditory thalamus to the primary somatosensory cortex.

A normally transient cross-modal thalamocortical projection from the magnocellular subdivision of the medial geniculate nucleus (MGm) to the primary somatosensory (SI) cortex of rats was found to remain unchanged throughout adulthood following unilateral removal of whiskers in newborn animals. The normal MGm projection to the auditory cortex is not lost in these neonatally whisker-deprived adults rats but some of the MGm neurons send collaterals to both primary auditory and SI cortices. Parallel electrophysiological experiments demonstrated the multimodal character of some MGm neurons, since they responded to both auditory and cutaneous stimulation. These results suggest that the areal distribution in the cortex of thalamocortical projections arising from a multimodal thalamic nucleus, such as the MGm, may be determined during early postnatal development by the normal flow of sensory information from the periphery to the thalamus and that an early postnatal somatosensory deprivation may prevent the normal withdrawal of a cross-modal projection from the MGm to the SI.

Aging↗
PubMed1991

Effects of daytime and nighttime stress on Fos-like immunoreactivity in the paraventricular nucleus of the hypothalamus, the habenula, and the posterior paraventricular nucleus of the thalamus.

Circadian effects on basal and stress-induced Fos-like immunoreactivity (IR) in the paraventricular nucleus of the hypothalamus (PVN), the habenula (Hab) and the posterior paraventricular nucleus of the thalamus (PVN-Thal) were examined. Stress induced a significant increase in the number of Fos-like IR cells within all 3 brain regions. In the Hab, expression was localized specifically to the medial region of the lateral Hab. No differences between the effects of daytime vs nighttime stress on numbers of Fos-like IR cells in the PVN and PVP-Thal were observed. Significantly fewer Fos-like IR cells were observed, however, in the lateral habenula of nighttime vs daytime non-stressed controls, resulting in a significantly greater percentage increase in Fos-like IR in the lateral habenula following nighttime vs daytime stress.

Animals↗
PubMed1992

In vivo voltammetric evidence for the detection of norepinephrine release in the thalamus of freely moving rats.

The ventrobasal complex (VB) of the thalamus was monitored in awake rats for the presence of norepinephrine (NE) overflow following pharmacological manipulations and physiological stimulation. Overflow was detected using chronoamperometry with electrochemically pretreated, Nafion-coated carbon fiber microelectrodes. In vivo evaluation of the electrode responses to systemic drug administration showed that alpha-methyl-p-tyrosine (alpha-MPT) and FLA-63 caused decreases in baseline current. Increases in baseline current in the VB were observed in animals treated with pargyline, yohimbine and yohimbine injected 2 h postpargyline. The results suggest that an electrochemical signal primarily due to NE overflow can be monitored in thalamic regions. Vigorous somatosensory stimulation induced small, long-lasting (approximately 30 min), reproducible electrochemical signals in the VB which were suppressed by alpha-MPT or FLA-63. These studies provide in vivo evidence which suggests that stressful somatosensory input to the VB initiates the release of NE.

Animals↗
PubMed1992

Intracellular HRP study of nociceptive neurons within the ventrobasal complex of the cat thalamus.

Locations and morphological characteristics of nociceptive specific (NS) and wide dynamic range (WDR) neurons of the ventrobasal (VB) thalamic complex were studied using an intracellular HRP injection technique in cats anesthetized with urethane and chloralose. Both NS and WDR neurons were found within the marginal zone of the VB complex. Their somata were confined to the VB complex, but dendrites were extended into the structures of the thalamus surrounding the VB complex. NS neurons were found in the caudal part of the VB complex, whereas WDR neurons were found more rostrally. Examinations of their locations within the marginal zone of the VB complex confirmed the somatotopic organization, as found previously. We also confirmed the previous reports that there are 3 different types of low-threshold mechanoreceptive (LTM) neurons within the VB complex. They are type I, type II and type III neurons. Both NS and WDR neurons were either type I or type II neurons. Obvious morphological differences were not found between LTM neurons and two classes of nociceptive VB neurons investigated.

Animals↗
PubMed1992

Identification of nociceptive neurons in the medial thalamus: morphological studies of nociceptive neurons with intracellular injection of horseradish peroxidase.

Somatosensory neurons including nociceptive ones in the medial thalamus have been studied extracellularly, and are classified into three types: nociceptive-specific, wide dynamic range, and tap neurons. However, the morphological characteristics of these three neurons have not yet been clarified. We studied the morphological characteristics of the neurons by iontophoretic injection of HRP into single neurons in 32 cats. Nine wide dynamic range neurons and two tap neurons were electrophysiologically identified and successfully stained with HRP in and around the parafascicular and subparafascicular nuclei, and in the mediodorsal nucleus. All nine wide dynamic range neurons had fewer dendrites which formed scanter tufts, whereas the two tap neurons had many more dendrites which formed denser tufts: i.e. wide dynamic range neurons were of the isodendritic type, and the tap neurons were of the allodendritic type, according to Ramón-Moliner's classification. The axons of the two tap neurons ran antero-laterally whereas those of wide dynamic range neurons ran in many directions. These morphological differences suggest that tap neurons may have more specialized and fixed functions than wide dynamic range neurons.

Animals↗
PubMed1992

Neurons in the dorsal column nuclei of the rat respond to stimulation of neck mechanoreceptors and project to the thalamus.

Electrophysiological recordings were made from neurons in the dorsal column nuclei which were activated by stimulation of muscle and cutaneous receptors in the neck of the rat. 222 units were studied, 158 (71%) of which responded to activation of cutaneous mechanoreceptors while 64 (29%) were activated by muscle receptors. The response patterns of 12 neurons with input from receptors in neck muscles were tested more fully. Their response patterns strongly suggested that 6 were activated by muscle spindle afferents while the other 6 were activated by Golgi tendon organ afferents. 18 (8%) of the neck-responsive neurons in the medulla were shown to project rostrally to the thalamus.

Animals↗
PubMed1995

Thalamic reticular input to the rat visual thalamus: a single fiber study using biocytin as an anterograde tracer.

This study describes the axonal projections of single thalamic reticular (TR) neurons within the visual thalamus in rats. Experiments were performed under urethane anesthesia and reticular cells were labeled by extracellular or juxtacellular microiontophoretic applications of biocytin. The axonal arborizations of 19 TR cells projecting to the dorsal lateral geniculate nucleus (DLG) or to the lateral dorsal/lateral posterior complex (LD/LP) were reconstructed from serial horizontal sections. It was found that single TR cells projected within the limits of a single thalamic nucleus, either the DLG or the LD/LP complex, where their terminal fields formed rostrocaudally oriented rods (length: approximately 800 microns; diameter: approximately 100 microns) densely packed with grape-like boutons and varicosities. In addition, none of the labeled TR cells possessed recurrent axonal collaterals that ramified within the reticular complex itself. The functional implications of these morphological data for the synchronization of thalamic oscillations are discussed.

Animals↗
PubMed1994

Reversible inactivation of the lateral dorsal thalamus disrupts hippocampal place representation and impairs spatial learning.

Place-specific discharge of hippocampal cells was monitored while rats performed daily 15 trials of a spatial memory task. During the intertrial interval between trials 5 and 6, the lateral dorsal nucleus of the thalamus (LDN) was reversibly inactivated. Choice accuracy on the maze became impaired, and many hippocampal place fields became disrupted. These data support the proposition that the LDN passes onto hippocampus important (spatial) information that is used for accurate maze navigation.

Animals↗
PubMed1994

Preserved features of thalamocortical projection neuron dendritic architecture in the somatosensory thalamus of the rat, cat and macaque.

A number of studies have shown that the organization of the mammalian somatosensory thalamus varies between species. As differences in cellular and synaptic thalamic organization would be expected to influence neuronal dendritic architecture, we compared somatosensory thalamocortical projection (TCP) neurons from the rat, cat and macaque. The results show that key features of the dendritic branching pattern remain unchanged despite large differences in the size of TCP neurons between the species. The features examined were: (i) ratio of the length of terminal branches to the length of the entire dendritic tree; (ii) the percentage of branch points that gave rise to two daughter branches as opposed to those that gave rise to three or more daughter branches; (iii) the proportional sum of absolute deviations (a measure of branching symmetry), and (iv) the mean branch order of the terminal segments. The present study provides evidence that somatosensory TCP neurons in these species comprise a homogeneous class and share a common dendritic architecture that is conserved across species despite changes in other aspects of thalamic circuitry. This suggests that TCP neuronal form is based on relatively stable genetic blueprint and that epigenetic factors (e.g. synaptic input) resulting from evolutionary changes in thalamic organization have had less influence on dendritic architecture.

Animals↗
PubMed1995

In vitro thermosensitivity of the midline thalamus.

This study compared the thermosensitivity and spontaneous activity of thalamic midline neurons with those of neurons in areas widely regarded to be involved in thermoregulation (preoptic/anterior hypothalamus and posterior hypothalamus). In vitro single unit recordings were made from neurons within the thalamic midline nuclei, the preoptic/anterior hypothalamus and posterior hypothalamus prior to and during a temperature change 3-7 degrees C above and below 37 degrees C. There were no significant differences in the degree of thermosensitivity or the proportion of thermosensitive neurons in the three areas. In each area examined, the thermosensitive neurons had a spontaneous activity which was significantly greater than that of the temperature-insensitive neurons. The results suggest that structures of the midline thalamus may play a role similar to that of the preoptic/anterior hypothalamus and posterior hypothalamus in the processing of temperature related information.

Action Potentials↗
PubMed1996

Fos-like immunoreactivity in the mamillary body and thalamus following injections of muscimol into the ventral tegmental nucleus of Gudden in the rat.

In many neurons, increased rates of firing are accompanied by expression of the proto-oncoprotein Fos. The current study examined Fos-like immunoreactivity in the mamillary body and the anterior thalamus following unilateral injections of the inhibitory GABA-A agonist muscimol into the ventral tegmental nucleus of Gudden (VTN). These injections resulted in a marked increase in Fos-like immunoreactivity ipsilaterally in both the medial mamillary nucleus and in its principle thalamic projection targets, the anteroventral and anteromedial thalamic nuclei. Since the projection from the VTN to the mamillary body has been shown to contain a substantial GABAergic component, these results are likely to reflect a disinhibition of mamillothalamic circuitry resulting from suppression of tonic inhibitory inputs arising in the VTN.

Animals↗
PubMed1996

Depression by morphine-6-glucuronide of nociceptive activity in rat thalamus neurons: comparison with morphine.

To assess the contribution of the active metabolite of morphine, morphine-6-glucuronide (M6G), to the analgesic effect of systemically administered morphine, experiments were carried out on rats under urethane anesthesia in which nociceptive activity was evoked by electrical stimulation of afferent C fibers in the sural nerve and recorded from single neurons in the ventrobasal complex of the thalamus. Intravenous (i.v.) injections of morphine completely blocked the activity at doses of 500 and 1000 micrograms/kg, the ED50 being 44 micrograms/kg. M6G administered by i.v. injection reduced the evoked nociceptive activity only by about 40% at 80 and 160 micrograms/kg, the ED50 being 6 micrograms/kg. After intrathecal (i.t.) injection, morphine produced maximum depression of 55% of the control activity at 20 micrograms; the ED50 is 18 micrograms. M6G injected i.t. produced maximum depression of 40% at doses ranging from 0.2 to 10 micrograms. The ED50 of M6G i.t. is below 0.2 micrograms. The effects of morphine and M6G were reversed by naloxone (200 micrograms/kg i.v.). The results show that M6G is more potent than morphine, regardless of the route of administration, while morphine is more effective when injected i.v. Due to the low efficacy of M6G, it seems unlikely that this glucuronide contributes substantially to the analgesic effect of morphine when renal function is normal. The results also make evident that the maximum effect of morphine results from an action at spinal and supraspinal sites.

Animals↗
PubMed1979

A peculiar rhythmic EEG activity from ventrobasal thalamus during paradoxical sleep in man.

A peculiar 3/sec rhythmic EEG activity (named Vc rhythm) was consistently found at the ventrobasal thalamus (nucleus ventrocaudalis) during paradoxical sleep of patients with implanted electrodes used as an electrophysiological procedure for identification of the thalamic targets for the surgical treatment of tremor and rigidity. The Vc rhythm was formed by high voltage, sharp biphasic positive negative potentials which were absent during wakefulness, rare and isolated during slow wave sleep, increased in number and organized in trains during paradoxical sleep and blocked during arousal. Significant changes in number of Vc waves were found when patients shifted through these wakefulness-sleep states. Integrated EMG multiple unit activity also showed significant changes during these wakefulness-sleep shifts, which were parallel although inverse to those showed by Vc waves. A significant negative correlation (r = -0.7126) between number of Vc waves and EMG units was found. In contrast, Vc waves showed no correlation with other electrophysiological indicators of thalamic excitability (multiple unit activity and early evoked potentials) and sleep (scalp EEG frequency and ocular movements).

Electric Stimulation↗
PubMed1986

Localization in human thalamus of units triggered during 'verbal commands,' voluntary movements and tremor.

Microelectrode recordings in the rostral (n. reticularis) and lateral (ventralis lateralis) human thalamus were carried out in locally anaesthetized diskinetic patients during stereotaxic operations. Their responses to voluntary motor tasks prompted by imperative verbal stimuli were tested. Spontaneous and evoked unit activities were studied using computer processing techniques. In the n. reticularis thalami and immediately adjacent thalamic zones, not only units reacting during the initiation of voluntary movements (100-200 msec before the movement), but also units responding to the verbal command itself ('triggered verbal command' units) were found. They proved to be concerned directly with the semantic meaning of the command. In the VL anterior area (Voa-Vop in German nomenclature) the majority of the units responded during the phases of initiation and/or realization of the voluntary motor act ('voluntary movement' units of Jasper and Bertrand 1966); when these units were not spontaneously rhythmic they were transiently transformed into rhythmic (5 +/- 1 Hz) ones. This transformation appeared during the preparation and realization of movement but also in some cells as a rebound phenomenon. In patients without tremor (akinetic and rigid forms of parkinsonism, torticollis), the transient rhythmogenic transformation was frequently provoked by the repetition of motor tasks. In the posterior part of VL (Vim), cells were driven by proprioceptive inflow coming from a specific peripheral region. They react also during the voluntary movement of the same region. The majority of these units were rhythmic at 5 +/- 1 Hz, and they presented a close correlation in phase and frequency with the tremor. The anatomical locations of the three main pools of neurons were determined. 'Triggered verbal command' units were placed more anteriorly and laterally. 'Voluntary movements' and 'rhythmic 5 +/- 1 Hz units' had identical spatial localizations. This fact supports the contributions of these two last types to the central mechanisms of both tremor and voluntary movement.

Electromyography↗
PubMed1989

The thalamus participates in the regulation of the sleep-waking cycle. A clinico-pathological study in fatal familial thalamic degeneration.

Loss of slow-wave sleep (SWS) and abnormal REM sleep behaviour were associated with a lack of vegetative and endocrine circadian rhythms in a patient with fatal familial thalamic degeneration. Physiological EEG patterns of SWS (spindles, K complexes, delta activity) were absent. EEG fast rhythms could not be induced by barbiturate or benzodiazepine administration. RO 15-1788, a benzodiazepine antagonist, induced arousal and awakened the patient from coma. Pathological findings were severe neuronal loss restricted to the anterior and dorso-medial thalamic nuclei. The clinical and electrophysiological data, together with the pathological correlates, emphasize the role played by the thalamus in the regulation of the sleep-waking and other circadian cycles.

Circadian Rhythm↗