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PubMed1986

Reciprocal connections between the claustrum and visual thalamus in the tree shrew (Tupaia glis).

We previously described the existence of reciprocal connections between the dorsal claustrum and striate cortex in the tree shrew, Tupaia glis. These projections were found to originate and terminate in a distinct topographic manner within the mid region of the upper portion of the dorsal claustrum. In this investigation, we examined the afferent and efferent projections between the claustrum and the lateral intermediate nucleus (Li) of the visual thalamus using small electrophoretic injections of anterograde and/or retrograde tracers (horseradish peroxidase, wheat germ agglutinin/horseradish peroxidase, or tritiated amino acids) into the claustrum, as well as the Li. Following tracer injections in the dorsal claustrum, labeled cells and/or terminal grains were found throughout the Li, except at the more caudal levels where the activity was confined to the lateral and medial borders. Tracer injections within the same nuclear region of the dorsal thalamus confirmed the existence of reciprocal projections between the Li and the claustrum. Following anterograde tracer injections, labeled terminals were found only within the most ventral zone of the dorsal claustrum--the 'hilum'; while retrograde tracer injections, produced labeled cells principally along the outer margins of the claustrum, including the hilum and tended to encapsulate the nucleus at all levels. Both sets of labeled activity were found to extend in this specific fashion over the majority of the dorsal claustrum, but appeared not to overlap with regions interconnected with striate cortex. These results thus suggest that the claustrum is capable of exerting a neural influence on cortex directly as well as indirectly via the visual thalamus. However, since the thalamic projection terminates in a claustral region not known to project to visual cortex, it is uncertain what function such projections have within the claustrum. It is possible that since Li receives ascending projections from the pretectum and superior colliculus, that it provides a multisensory input to the claustrum for relay onto areas outside of primary visual cortex.

Animals↗
PubMed1991

Neurons of the acoustic thalamus that project to the amygdala contain glutamate.

Injection of WGA-HRP into the lateral nucleus of the amygdala produced retrograde axonal transport to cell bodies in areas of the acoustic thalamus: the medial division of the medial geniculate body, the suprageniculate nucleus, and the posterior intralaminar nucleus. Glutamate-immunoreactive neurons were present throughout the acoustic thalamus, including the regions containing the retrogradely labeled neurons. Many of the retrogradely labeled cells were also immunoreactive for glutamate. Thus, glutamate is present in those neurons of the acoustic thalamus that project to the amygdala and may contribute to neurotransmission and synaptic plasticity in this pathway.

Amygdala↗
PubMed1992

The primate dorsal spinothalamic tract: evidence for a specific termination in the posterior nuclei (Po/SG) of the thalamus.

The spinothalamic tract in primates and other mammals arises primarily from cells in lamina I of the dorsal horn, from lamina V cells and to a lesser extent from other laminae. Most of the neurons of lamina I respond only to noxious mechanical or thermal stimuli. Spinothalamic tract (STT) cells of lamina V tend to respond to both innocuous and noxious stimuli. Recent studies have suggested that the classical STT in the anterolateral quadrant (ALQ) contains primarily the axons of lamina V cells and that the axons of lamina I cells travel more dorsally in the dorsolateral quadrant (DLQ) to constitute the dorsal spinothalamic tract (DSTT). Using the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) injected into the spinal cord in conjunction with a contralateral anterolateral cordotomy, we have found there is a substantial projection of the DSTT to the posterior nuclei of the caudal-ventral thalamus, designated Po/SG. This projection is almost entirely abolished when the lesion includes the area of spinal cord white matter at the level of the denticulate ligament. Larger lesions that destroy the ALQ and much of the lateral column white matter, but that spare the dorsolateral column white matter in the region of the corticospinal tract, abolish all transport of WGA-HRP to the thalamus. We conclude that the spinothalamic pathway in the non-human primate encompasses a continuous fiber bundle that extends dorsally to include the region of lateral column white matter opposite the denticulate ligament and that the more dorsal aspect of this pathway projects primarily to Po/SG of thalamus.

Animals↗
PubMed1982

The cells of origin of the incertofugal projections to the tectum, thalamus, tegmentum and spinal cord in the rat: a study using the autoradiographic and horseradish peroxidase methods.

Efferent projections of the zona incerta were examined in the rat using the autoradiographic and horseradish peroxidase methods, with special reference to the cytoarchitectonic structure of the zona incerta. Autoradiographic experiments showed that the incertofugal fiber systems reach ipsilaterally to the thalamus (lateral dorsal, central lateral, ventral lateral geniculate, parafascicular, subparafascicular and reuniens nuclei, and posterior nuclear complex), to the hypothalamus (dorsal, lateral and posterior hypothalamic areas), to the tectum (medial pretectal area, deep pretectal and pretectal nuclei, superior colliculus and periaqueductal gray) and to the midbrain tegmentum, pons and medulla oblongata (subcuneiform, cuneiform and red nuclei, nuclei of the posterior commissure and Darkschewitsch, interstitial nucleus of Cajal, pedunculopontine tegmental nucleus, oral and caudal pontine reticular nuclei, nucleus raphe magnus, gigantocellular reticular nucleus, pontine gray and inferior olivary complex). Contralaterally, incertal efferent fibers reach to the zona incerta. Cells of origin of the incertofugal fiber systems to the tectum, thalamus, tegmentum and spinal cord were examined using the retrograde horseradish peroxidase method. Cells of origin of the incertotectal pathway are located mainly in the ventral and causal parts of the zona incerta and partly in the antero-polar, dorsal and postero-polar parts. Cells projecting to the thalamus (at least to the lateral dorsal and central lateral nuclei) are situated in the ventral and caudal parts of the zona incerta, but they are rare in the other incertal structures. Cells of origin of the incertotegmental system are located mainly in the dorsal, magnocellular and caudal parts and partly in the antero- and postero-polar parts, but they are not situated in the ventral part. Cells of the magnocellular part project more caudally to the medulla oblongata and spinal cord than those of the other parts of the zona incerta. Forel's field contains many cells projecting to the tegmentum. The results provide good evidence that the cells of origin of efferent projections are topographically organized and are related to cytoarchitectonic areas within the zona incerta.

Animals↗
PubMed1989

Dorsal raphe stimulation, 5-HT and morphine microiontophoresis effects on noxious and nonnoxious identified neurons in the medial thalamus of the rat.

In single cell experiments, the characterization of the responses of medial thalamic neurons to noxious and nonnoxious stimulation was made to examine the effects of two substances involved in pain, morphine and 5-HT, and the action of one pain suppressor mechanism, dorsal raphe stimulation. Single cell activity was recorded in urethane anesthetized rats. Tail pinch and tail immersion in hot water were used as nociceptive stimuli. Skin strokes, air puffs and hair brushing were used as nonnociceptive stimuli. Morphine, 5-HT microiontophoresis and dorsal raphe stimulation were performed in all the recorded units. Fifty-eight percent from 61 medial thalamic recorded units responded both to noxious and nonnoxious stimulation; whereas only 18% and 24.6% of the units responded exclusively to noxious and nonnoxious stimulation, respectively. The noxious responding units were located in the most posterior portions of the medial thalamus. Dorsal raphe stimulation and 5-HT ejection prevented the excitation elicited by noxious input. Morphine ejection prevented both the noxious and nonnoxious input in medial thalamus, in a different population as compared to dorsal raphe stimulation or 5-HT ejection. These findings support the existence of a pain ascending mechanism mediated by an opioid-serotonergic interaction in the medial thalamus of the rat.

Action Potentials↗
PubMed2004

Neonatal neurosteroid administration alters parvalbumin expression and neuron number in medial dorsal thalamus of adult rats.

The neuroactive steroid 3alpha-hydroxy-5alpha-pregnane-20-one (allopregnanolone) is a potent endogenous modulator of GABAA receptor function. A single neonatal allopregnanolone administration (10 mg/kg, i.p.) was previously shown to alter the localization of parvalbumin-positive neurons in the prefrontal cortex at maturity. Cells in the prefrontal cortex receive the majority of their inputs from the medial dorsal nucleus of the thalamus. We investigated whether neonatal allopregnanolone administration alters the neuronal population of the medial dorsal nucleus of the thalamus. We show that the number of parvalbumin-expressing neurons is increased while the total neuron number is decreased in the medial dorsal nucleus after allopregnanolone administration. EAAT3 (excitatory amino acid transporter type 3, the neuron-specific glutamate reuptake transporter) immunoreactivity was unchanged in adjacent sections. These findings suggest that neonatal allopregnanolone administration disrupts the normal development of the prefrontal cortex and medial dorsal thalamus, indicating that neurosteroid levels are important for proper development of thalamocortical systems and may play a role in neurodevelopmental disorders such as schizophrenia.

Amino Acid Transport System X-AG↗
PubMed2007

Gender and age differences in expression of GABAA receptor subunits in rat somatosensory thalamus and cortex in an absence epilepsy model.

Absence epilepsy is more prevalent in females, but reasons for this gender asymmetry are unknown. We reported previously that perinatal treatment of Long-Evans Hooded rats with the cholesterol synthesis inhibitor (CSI) AY9944 causes a life-long increase in EEG spike-wave discharges (SWDs), correlated with decreased expression of GABA(A) receptor subunit gamma2 protein levels in thalamic reticular and ventrobasal nuclei (SS thalamus) [Li, H., Kraus, A., Wu, J., Huguenard, J.R., Fisher, R.S., 2006. Selective changes in thalamic and cortical GABA(A) receptor subunits in a model of acquired absence epilepsy in the rat. Neuropharmacology 51, 121-128]. In this study, we explored time course and gender different effects of perinatal AY9944 treatment on expression of GABA(A) receptor alpha1 and gamma2 subunits in SS thalamus and SS cortex. Perinatal AY9944 treatment-induced decreases in GABA(A) gamma2 receptor subunits in rat SS thalamus and increases in SS cortex are gender and age specific. The findings suggest a mechanism for the higher prevalence of absence epilepsy in female patients.

Age Factors↗
PubMed2001

Response properties of periodontal mechanosensitive neurones in the rat trigeminal sensory complex projecting to the posteromedial ventral nucleus of the thalamus.

Unitary discharges from periodontal mechanosensitive (PM) neurones responding to mechanical stimulation of the tooth were recorded from the trigeminal sensory complex in the rat brainstem. Of the PM units recorded, 22% were activated by antidromic stimulation of the contralateral (20%) or ipsilateral (2%) posteromedial ventral nucleus of the thalamus. Although thalamic-projecting neurones were recorded extensively throughout the trigeminal sensory complex, they originated most often in the region from the caudal main sensory nucleus to the rostral subnucleus oralis of the trigeminal spinal tract nucleus. The response latencies of the rostral nucleus units to orthodromic stimulation of peripheral receptive fields and antidromic stimulation of the thalamus were significantly shorter than those of the caudal nucleus units. More than half were single-tooth units originating from incisor teeth. They responded continuously when pressure was applied to the tooth. The magnitude of the response varied with the direction of the stimulus. Maximal responses were obtained when the stimulus was applied labiolingually or vice versa. The threshold for mechanical stimulation of the tooth was less than 0.05 N. The rostrocaudal distribution and response properties of thalamic-projecting PM neurones were very similar to those of non-thalamic-projecting PM units that were not activated by antidromic stimulation of the thalamus.

Animals↗
PubMed2000

Metabotropic glutamate receptor mRNA expression in the schizophrenic thalamus.

BACKGROUND: The central role that the thalamus plays in information processing and sensory integration suggests that its dysfunction may be a factor in the pathophysiology of schizophrenia. Glutamate is a key neurotransmitter in thalamic function, and although all aspects of thalamic glutamate neurotransmission have not been elucidated, transcripts encoding members of each family of the glutamate receptors have been identified in the thalamus. Recently, activation of group II metabotropic glutamate receptors (mGluRs) was demonstrated in rats to ameliorate the behavioral effects associated with exposure to phencyclidine, an uncompetitive NMDA receptor antagonist that can induce psychotic symptoms, suggesting the possibility of mGluR abnormalities in schizophrenia. We investigated whether expression of thalamic mGluR mRNA is altered in this illness. METHODS: We examined the expression of the transcripts encoding the mGluR1, 2, 3, 4, 5, 7, and 8 receptors in postmortem thalamic tissue samples from elderly schizophrenic and control subjects, using in situ hybridization. We identified six thalamic nuclei in each section (anterior, dorsomedial, lateral dorsal, central medial, reticular, and nuclei of the ventral tier). RESULTS: There were no differences between elderly schizophrenic and control subjects in the expression of mGluR1, 2, 3, 4, 5, 7, or 8 transcript levels in any of these six thalamic nuclei. CONCLUSIONS: mGluR mRNA expression is not abnormal in the thalamus of patients with schizophrenia. The modulatory roles proposed for mGluRs, and the potentially important relationship between mGluRs and NMDA receptors, suggest that mGluRs may be involved in the pathophysiology of schizophrenia, but this is not detectable at this level of gene expression.

Aged↗
PubMed1991

The role of different nuclei of the thalamus in processing episodic information.

Male rats received either electrolytic or sham lesions bilaterally into the dorsomedial nucleus or the anterior nuclei of the thalamus or were assigned to an unoperated control group. After the postoperative recovery period all lesioned and control animals were tested for the ability to master a delayed alternation task. It was characterized by the alternation of Go and No Go trials, which were separated by intervals ranging between 0 and 80 s. Its successful performance required, firstly, the learning of the general principle that Go and No Go trials alternate with each other and secondly, in every trial, recalling the specific consequences of the responses in the previous trial after a short or long delay. Bilateral damage of the thalamus including the dorsomedial nucleus or anterior nuclei severely disrupted the performance of a delayed alternation task. A detailed analysis of the performance throughout the training suggests that the impairment associated with both thalamic lesions could be interpreted as a deficit in recalling specific information. This analysis also reveals a failure in the early stages of learning. Further research concerning the role of the dorsomedial nucleus and the anterior nuclei of the thalamus in learning and memory is proposed as necessary.

Animals↗
PubMed1998

Facilitation of responses to AMPA but not kainate by cyclothiazide in primate somatosensory thalamus.

This study examines the possibility of multiple ionotropic non-N-methyl-D-aspartate (NMDA) receptors in the chief sensory nuclei of the primate thalamus. Cyclothiazide, an antagonist of rapid desensitization of non-NMDA receptors, is shown to produce a facilitation of responses to the synthetic agonist (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) but not kainate or NMDA in cells of the ventral posterior lateral and medial thalamic nuclei in the anesthetized monkey. These differential effects suggest the presence of multiple ionotropic non-NMDA excitatory amino acid receptors in the primate ventral posterior (VP) thalamus. Cyclothiazide-sensitive excitatory amino acid receptors have important roles in mechanisms of plasticity and excitotoxicity in other neural systems and so may mediate similar mechanisms in the somatosensory thalamus.

Animals↗
PubMed2000

Single-unit analysis of the pallidum, thalamus and subthalamic nucleus in parkinsonian patients.

Microelectrode-guided stereotactic operations performed in 29 parkinsonian patients allowed the recording of 86 cells located in the globus pallidus and 563 in thalamic nuclei. In the globus pallidus, the average firing rate was significantly higher in the internal (91+/-52 Hz) than in the external (60+/-21 Hz) subdivision. This difference was further accentuated when the average firing rate in the external subdivision was compared with that of the internal part of the internal subdivision (114+/-30 Hz). A rhythmic modulation in globus pallidus activities was observed in 19.7% of the cells, and this only during rest tremor episodes. In these cases, modulation frequency of unit activities was not statistically different from the rest tremor frequency (average: 4.6+/-0.5 vs 4. 4+/-0.4 Hz, respectively). In the medial thalamus, four types of unit activities could be defined. A sporadic type was mainly found in the parvocellular division of the mediodorsal nucleus (96.8% of the cells recorded) and in the centre median-parafascicular complex (74.2%). Two other types of activities characterized by random or rhythmic bursts fulfilling the extracellular criteria of low-threshold calcium spike bursts were concentrated in the central lateral nucleus (62.3%) and the paralamellar division of the mediodorsal nucleus (34.1%). These activities could be recorded independently of the presence of a rest tremor. When a tremor episode occurred, the rhythmic low-threshold calcium spike bursts had an interburst frequency similar to rest tremor frequency, although they were not synchronized with it. The fourth type, the so-called tremor locked, was also characterized by rhythmic bursts which, however, did not display low-threshold calcium spike burst properties. These bursts occurred only when a rest tremor was present and was in-phase with the electromyographic bursts. All tremor-locked cells were located in the centre median-parafascicular complex. In the lateral thalamus, cells exhibiting random or rhythmic low-threshold calcium spike bursts were found preponderantly in the ventral anterior nucleus (53.4%) and in the ventral lateral anterior nucleus (52.7%). Tremor-locked units were confined to the ventral division of the ventral lateral posterior nucleus (35.4%). None of the random or rhythmic low-threshold calcium spike bursting units responded to somatosensory stimuli or voluntary movements, either in the medial or in the lateral thalamus. The presence of low-threshold calcium spike bursts at the thalamic level, together with the paucity (8%) of responses to voluntary movements compared to what is found in normal non-human primates, demonstrate a pathological state of inhibition due to the overactivity of the internal subdivision of the globus pallidus units. Activities of the thalamic cells producing low-threshold calcium spike bursts are not synchronized with each other or with the tremor. However, this does not exclude a causal role of these activities in the generation of tremor. Indeed, it has been demonstrated that even random electrical stimulations of the rolandic cortex in parkinsonian patients induce tremor episodes, probably due to the triggering of rhythmic, low-threshold calcium spike-dependent, thalamocortical activities. Similarly, low-threshold calcium spike bursts could be at the origin of rigidity and dystonia through an activation of the supplementary motor area and of akinesia when reaching the pre-supplementary motor area. We conclude that the intrinsic oscillatory properties of individual neurons, combined with the dynamic properties of the thalamocortical circuitry, are responsible for the three cardinal parkinsonian symptoms.

Action Potentials↗
PubMed2004

Electrical stimulation of the anterior nucleus of the thalamus for the treatment of intractable epilepsy.

PURPOSE: Animal studies and sporadic case reports in human subjects have suggested that intermittent electrical stimulation of the anterior nucleus of the thalamus reduces seizure activity. We embarked on an open-label pilot study to determine initial safety and tolerability of bilateral stimulation of the anterior nucleus of the thalamus (ANT), to determine a range of appropriate stimulation parameters, and to begin to gather pilot efficacy data. METHODS: We report an open-label pilot study of intermittent electrical stimulation of the anterior nucleus of the thalamus in five patients (three men, two women; age range, 24-47 years), with follow-up between 6 and 36 months. All patients had intractable partial epilepsy. Four of the five patients also had secondarily generalized seizures. Stimulation was delivered by bilateral implantable, programmable devices by using an intermittent, relatively high-frequency protocol. Stimulation parameters were 100 cycles per second with charge-balanced alternating current; pulse width, 90 ms; and voltages ranging between 1.0 and 10.0 V. Seizure counts were monitored and compared with preimplantation baseline. RESULTS: Four of the five patients showed clinically and statistically significant improvement with respect to the severity of their seizures, specifically with respect to the frequency of secondarily generalized tonic-clonic seizures and complex partial seizures associated with falls. One patient showed a statistically significant reduction in total seizure frequency. No adverse events could clearly be attributed to stimulation. None of the patients could determine whether the stimulator was on or off at these parameters. CONCLUSIONS: Electrical stimulation of the ANT appears to be well tolerated. Preliminary evidence suggests clinical improvement in seizure control in this small group of intractable patients. Further controlled study of deep brain stimulation of the anterior nucleus is warranted.

Adult↗
PubMed2006

Developmental remodelling of the lemniscal synapse in the ventral basal thalamus of the mouse.

Synapse elimination occurs throughout the nervous system during development, and is essential for the formation of neural circuits. The mechanisms underlying synapse elimination in the brain, however, remain largely unknown. Using whole-cell patch-clamp recording in a slice preparation, we examined synaptic refinement at the somatosensory relay synapse (lemniscal synapse) in the ventral basal thalamus of the mouse during postnatal development. At 1 week old, each neuron in the ventral basal thalamus is innervated by multiple lemniscal fibres, as revealed by multiple increments of the synaptic response. By 16 days after birth (P16), the majority of neurons showed an all-or-none response, suggesting a single fibre innervation. In addition to synapse elimination, extensive modifications in synaptic properties occur during the second week after birth. The ratio of AMPA to NMDA component of the synaptic current tripled between P7 and P17. The decay constant of the NMDA component decreased by about 70% between P7 and P17; ifenprodil (3 microm) reduced the NMDA component by about 40% in neurons at P7-9, but was much less effective at P20-24. On the other hand, there was little change in the inward rectification of AMPA component between P11 and P24. Paired-pulse ratios, measured at -70 and +40 mV, were stable between P7 and P24. Whisker deprivation from P5 through P19 had no effect on the elimination or the maturation of the lemniscal synapse. These results suggest that the lemniscal synapse in the ventral basal thalamus undergoes extensive refinement during the second week, and that sensory experience has a rather limited role in this process.

Age Factors↗
PubMed2004

Effects of lesions of the human posterior thalamus on ocular fixation during voluntary and visually triggered saccades.

OBJECTIVE: To investigate the role of the posterior thalamus in controlling voluntary and visually triggered eye movements and ocular fixation. METHODS: The latency to initiate saccades to peripheral targets (visually triggered) and in response to verbal commands (voluntary) was measured in three patients with unilateral lesions of the posterior thalamus, in normal controls, and in neurological controls with Parkinson's disease. On half the trials a fixation point offset simultaneously with target onset, and on half it remained visible. RESULTS: Offset of the fixation point simultaneous with target onset decreased saccade latency for both voluntary and visually triggered eye movements in controls, but only for voluntary saccades in patients with thalamic lesions. CONCLUSIONS: These findings suggest that separate neural systems control fixation when making voluntary and visually triggered eye movements, and that the thalamus is involved in the control of fixation for visually triggered but not for voluntary saccades.

Aged↗
PubMed2004

Comparison of oculomotor neuronal activity in paralaminar and mediodorsal thalamus in the rhesus monkey.

We previously reported that neurons in the mediodorsal thalamic nucleus (MD) are topographically organized and express spatial and nonspatial coding properties similar to those of the prefrontal areas with which they are connected. In the course of mapping the dorsal thalamus, we also studied neurons in a subset of thalamic nuclei (the caudal part of the ventral lateral nucleus (VLc), the oral part of the ventral posterior lateral nucleus (VPLo), the parvocellular part of the ventral anterior nucleus (VApc)) lateral to the MD and just across the internal medullary lamina. We compared these "paralaminar" neurons to MD neurons by having monkeys perform the same spatial and nonspatial cognitive tasks as those used to investigate the MD; these included two saccadic tasks-one requiring delayed and the other immediate responses-and one picture fixation task. Of the paralaminar thalamic neurons modulated by the saccadic tasks, a majority had saccade-related activity, and this was nearly always spatially tuned. Also, for about half of these neurons, the saccade-related activity occurred exclusively during the delayed-response task. No neurons with event-related activity in the saccadic tasks were preferentially modulated by specific picture stimuli, although other neurons were. All of these results were similar to what we had found for MD neurons. However, in contrast to the high proportion of presaccadic responses observed in the MD, the majority of saccade-related neurons in paralaminar thalamus exhibited mid- or postsaccadic activity, i.e., that started during or after the saccade. Our findings suggest that neurons in the paralaminar thalamus may be possible conduits of oculomotor feedback signals, especially during memory-guided saccades.

Animals↗
PubMed1986

Periventricular gray inhibition of thoracic spinothalamic cells projecting to medial and lateral thalamus.

Effects of electrical stimulation of the periventricular gray (PVG) on spinothalamic tract (STT) cell activity were determined in 19 anesthetized monkeys (Macaca fascicularis). Twenty-two STT cells projected to the ventral posterior lateral nucleus (L-STT cells), 11 to the medial thalamus (M-STT cells), and 9 to both thalamic regions (LM-STT cells). All cells had somatic receptive fields and responded to electrical stimulation of cardiopulmonary sympathetic afferent fibers. PVG stimulation inhibited activity of 41 of 42 STT cells. Degree of inhibition of background activity was related to intensity and frequency. Stimulus currents of 300 microA or less completely silenced background activity of most cells. Thresholds for stimulus current averaged 100 +/- 20 microA and were unrelated to cell projection site, laminar location, or type of somatic or visceral input. However, lowest thresholds were found when the PVG electrodes were located within 0.5 mm of the third ventricle in the dorsomedial hypothalamus or nucleus reuniens of the thalamus. PVG stimulation inhibited responses of 22 of 22 cells to intracardiac injections of bradykinin. Bradykinin (2 micrograms/kg) increased cell activity from 15 +/- 3 to 31 +/- 5 spikes/s (P less than 0.01), and PVG stimulation (380 +/- 40 microA) reduced activity to 9 +/- 3 spikes/s (P less than 0.001). PVG stimulation inhibited responses of 33 of 33 STT cells to noxious pinch of skin or skin and muscle and responses of 8 of 8 cells to hair movement. Degree of inhibition of cell responses to noxious pinch was not significantly different from inhibition of responses to bradykinin. Effects of PVG stimulation on activity of six STT cells were studied before and after bilateral lesions were made in the dorsolateral funiculus (DLF). In no case did the lesions abolish or attenuate inhibitory effects of PVG stimulation. These results suggest that PVG may participate in descending inhibition of STT cells including cells mediating cardiac pain. The descending pathways are not located in the DLF. Further, descending inhibitory systems modulate STT cells projecting to both medial and lateral thalamus.

Afferent Pathways↗
PubMed1986

The ventroposterior inferior nucleus in the thalamus of cats: a relay nucleus in the Pacinian pathway to somatosensory cortex.

The ventroposterior region of the thalamus of mongrel cats was searched to locate zones activated by somatic stimuli. By using stimuli that selectively excited Pacinian corpuscles, areas activated by this class of afferent fibers were differentiated from regions activated by other classes of cutaneous mechanoreceptors. The results showed that Pacinian inputs excite neurons in the ventroposterior inferior nucleus (VPI) of the thalamus, whereas other more dorsal zones within the ventroposterior thalamus receive inputs from other mechanoreceptor classes. This definition of the VPI tended to be larger and to extend further lateral than some published descriptions. Horseradish peroxidase (HRP) was injected into ventroposterior zones shown by electrophysiological recordings to receive inputs from Pacinian afferents. Subsequently, labeled cell bodies were observed in the caudal poles of the dorsal column nuclei, a region previously shown to be activated by Pacinian afferents. Very few labeled cells were found in the central region of these nuclei, a region previously shown to be activated by other classes of cutaneous mechanoreceptors. Electrophysiological recordings were used to locate a small portion of the second somatosensory cortex driven by Pacinian stimuli. When HRP was injected into this region cell bodies in the VPI and the lateral part of the posterior group were labeled, but few or no labeled cells were found in ventroposterior lateral nucleus. We hypothesize that the VPI receives Pacinian information from a cytoarchitecturally distinct region in the caudal poles of the dorsal column nuclei. Further, we suggest that a major cortical target for the VPI is a subdivision of the second somatosensory cortex. These studies do not exclude the possibility that Pacinian inputs have other thalamic and cortical targets.

Afferent Pathways↗