Posterior Thalamic Region Research Articles

CNS pattern of metabolic activity during tonic pain: evidence for modulation by beta-endorphin.

CNS correlates of acute prolonged pain, and the effects of partial blockade of the central beta-endorphin system, were investigated by the quantitative 2-deoxyglucose technique in unanaesthetized, freely moving rats. Experiments were performed during the second, tonic phase of the behavioural response to a prolonged chemical noxious stimulus (s.c. injection of dilute formalin into a forepaw), or after minor tissue injury (s.c. saline injection). During formalin-induced pain, local glucose utilization rates in the CNS were bilaterally increased in the grey matter of the cervical spinal cord, in spinal white matter tracts and in several supraspinal structures, including portions of the medullary reticular formation, locus coeruleus, lateral parabrachial region, anterior pretectal nucleus, the medial, lateral and posterior thalamic regions, basal ganglia, and the parietal, cingulate, frontal, insular and orbital cortical areas. Pretreatment with anti-beta-endorphin antibodies, injected i.c.v., led to increased metabolism in the tegmental nuclei, locus coeruleus, hypothalamic and thalamic structures, putamen, nucleus accumbens, diagonal band nuclei and dentate gyrus, and in portions of the parietal, cingulate, insular, frontal and orbital cortex. In formalin-injected rats, pretreated with anti-beta-endorphin, behavioural changes indicative of hyperalgesia (increased licking response) were found, which were paralleled by a significant enhancement of functional activity in the anterior pretectal nucleus and in thalamo-cortical systems. A positive correlation was found between the duration of the licking response and metabolic activity of several forebrain regions. These results provide a map of the CNS pattern of metabolic activity during tonic somatic pain, and demonstrate a modulatory role for beta-endorphin in central networks that process somatosensory inputs.

Collateral projections of single neurons in the posterior thalamic region to both the temporal cortex and the amygdala: a fluorescent retrograde double-labeling study in the rat

It has been reported that the acoustic thalamus of the rat sends projection fibers to both the temporal cortical areas and the lateral amygdaloid nucleus to mediate conditioned emotional responses to an acoustic stimulus. In the present study, fluorescent retrograde double labeling with Fast Blue and Diamidino Yellow has been used in the rat to examine whether single neurons in the posterior thalamic region send axon collaterals to both the temporal cortical areas and lateral amygdaloid nucleus. One of the tracers was injected into the lateral amygdaloid nucleus and the other into the temporal cortical areas close to the rhinal sulcus. Neurons double-labeled with both tracers were found mainly in the posterior intralaminar nucleus and suprageniculate nucleus, and to a lesser extent in the subparafascicular nucleus and medial division of the medial geniculate nucleus. No double-labeled neurons were seen in either the dorsal or ventral division of the medial geniculate nucleus. When one of the tracers was injected into the lateral amygdaloid nucleus and the other into either the dorsal portion of the temporal cortex, the dorsal portion of the entorhinal cortex, or the posterior agranular insular cortex, no double-labeled neurons were found in the posterior thalamic region. The present results indicate that a substantial number of single neurons in the acoustic thalamus project to both the limbic cortical areas and lateral amygdaloid nucleus by way of axon collaterals. These neurons may be implicated in affective and autonomic components of responses to multi-sensory stimuli, including acoustic ones.

Collateral projections of single neurons in the posterior thalamic region to both the temporal cortex and the amygdala: a fluorescent retrograde double‐labeling study in the rat

Collateral projections of single neurons in the posterior thalamic region to both the temporal cortex and the amygdala: a fluorescent retrograde double‐labeling study in the rat

Pretecto-tectal influences

(1)From the dorsal surface of the toad (Bufo b. spinosus, B. marinus) optic tectum (OT), field potentials (FP) were recorded at 9 reference sites in response to electrical stimulation of the optic nerve (ON). The FP showed 4 main components, besides an initial deflection attributed to axonal potentials: two negative waves N1, N2 (attributed to postsynaptic excitatory processes) and two positive waves P2, P3 (attributed to postsynaptic inhibitory processes). The responses across the reference sites were rather similar in different individuals. (2) Electrical stimulation of an area in the ipsilateral pretectal lateral posterodorsal and posterior (Lpd/P) thalamic region evoked tectal FPs showing mainly a negative and a positive wave. Regarding wave amplitudes, the FPs displayed disproportionalities across the reference sites. (3) Electrical stimulation of the contralateral Lpd/P evoked mainly a positive wave in the tectal FP whose disproportionality corresponded roughly to the one obtained to ipsilateral Lpd/P stimulation. (4) The inital negative wave of the tectal FP in response to ON stimulation was nearly abolished, if Lpd/P stimulation preceded ON stimulation at a delay of 17–25 ms. (5) Since FPs showed adaptation to repetitive stimulation, various experiments were carried out to distinguish adaptation phenomena from effects of neuronal interactions between Lpd/P and OT. (6) The results provide evidence that ON- and Lpd/P-mediated inputs interact in superficial tectal layers, whereby pretectotectal input suppresses retinotectal excitatory information transfer. Input of Lpd/P to the contralateral superficial OT suggests postsynaptic inhibition. This study provides no information about pretectal inputs to deeper tectal layers, which anatomically are known to exist.

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

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

Substance P innervation of the rat and cat thalamus. I. Distribution and relation to ascending spinal pathways.

An antiserum for substance P (SP) with minimal cross-reactivity for other tachykinins was employed to map the distribution of SP-positive nerve fibers and terminals in the thalamus of cats and rats with special emphasis on the innervation by these fibers of nuclei related to the somatosensory system. In both species SP innervation is predominantly along the midline, in medial and posterior thalamic regions, and sparser in sensory relays for specific modalities. Among the most densely innervated nuclei are the parafascicular, paraventricular, rhomboid, central medial and parts of mediodorsal, lateral posterior, and ventral lateral geniculate. SP innervation of somatosensory-related nuclei is also evident in central lateral nucleus, posterior complex (PO), and in ventroposterolateral (VPL) nucleus of both cats and rats. In VPL of cats SP fibers and terminals are present along its ventral and lateral border, a paralaminar area in which spinothalamic fibers have been shown to terminate and where neurons responsive to noxious stimuli have been reported. Also in rats the SP innervation of VPL is similar to that of spinothalamic tract fibers. The SP innervation of somatosensory thalamic nuclei may be supplied, at least in part, by spinothalamic afferent as suggested by the depletion of SP after anterolateral chordotomy but not after ablation of the dorsal column nuclei. The presence of SP-positive spinothalamic neurons in the spinal cord is reported in the following paper.

Calcitonin gene-related peptide immunoreactivity in the visceral sensory cortex, thalamus, and related pathways in the rat.

It has been proposed that calcitonin gene-related peptide (CGRP) may serve as a major neuromodulator in visceral sensory pathways, but its exact role in the visceral sensory thalamus and cortex has not been determined. We therefore examined the distribution of CGRP-like immunoreactive (CGRPir) innervation of the insular cortex and the parvicellular division of the ventroposterior nucleus of the thalamus (VPpc) in the rat by using immunohistochemistry for CGRP combined with retrograde transport of the fluorescent dye fluoro-gold. Modest numbers of CGRPir fibers were distributed in the dysgranular and agranular insular cortex, but few were observed in the granular insular cortex. The density of CGRPir innervation increased caudally along the rhinal fissue and was considerably greater in the perirhinal cortex. When fluoro-gold was injected into the insular cortex numerous retrogradely labeled neurons were seen in the VPpc, but few of these were CGRPir. Retrogradely labeled CGRPir neurons were, however, seen in the ventral lateral and medial parabrachial (PB) subnuclei. Injection of fluoro-gold into the perirhinal cortex (which is just caudal to the insular cortex along the rhinal fissure) resulted in many retrogradely labeled CGRPir neurons in the posterior thalamic region, including the subparafascicular, the lateral subparafascicular, and the posterior intralaminar nuclei. The VPpc was heavily innervated by CGRPir fibers but contained few CGRPir cell bodies. Injection of fluoro-gold into the VPpc resulted in many retrogradely labeled CGRPir neurons in the external medial PB subnucleus bilaterally, but with a contralateral predominance. Smaller numbers of retrogradely labeled CGRPir neurons were also observed in the ventrolateral PB subnucleus, bilaterally with an ipsilateral predominance. These results suggest that CGRP may be a neuromodulator in the ascending visceral sensory pathways from the PB to the VPpc and the insular cortex, but not between the latter two structures.

Extrahypothalamic projection of luteinizing hormone-releasing hormone fibers in the brain of the toad, Bufo japonicus

Extrahypothalamic projection of luteinizing hormone-releasing hormone (LHRH) fibers in the brain of the toad ( Bufo japonicus) was examined immunohistochemically by the avidin-biotin-peroxidase complex (ABC) method. Immunoreactive LHRH perikarya are localized in the nuclei medialis septi and of the diagonal band of Broca. A part of the LHRH fibers are sent anteriad to the medial and dorsal pallia. Some fibers reach the olfactory bulb. Dorsocaudally, LHRH neurons in the medial septum project their fibers to the deep layers of the optic tectum and the posterior mesencephalon including the nucleus pretrigeminalis, which is considered to be a generator of mate calling behavior, via the habenular and posterior thalamic regions. In addition, LHRH fibers which run caudad through the dorsal infundibular region and then the mesencephalic reticular formation were widely distributed in both the gray and the white matter of the medulla oblongata. These findings suggest that LHRH acts as a neurotransmitter or a neuromodulator in the various neuronal circuitries for reproductive behavior in the central nervous system, because LHRH has been considered to be related to amphibian seasonal breeding, and many regions where the immunoreactive LHRH fibers were observed are the loci concerned with mating behavior.

Diencephalic and mesencephalic afferents of the rat claustrum.

The retrograde fluorescent tracers Fast Blue (FB) and Diamidino Yellow (DY) have been used to study subcortical afferents of the claustrum. DY or FB was injected into the claustrum. The greatest amount of labeled cell bodies were observed in the posterior thalamic nuclear complex. They were especially abundant in its caudal part, lying between the medial geniculate body and the pretectal area. In comparison to the numerous labeled cells near the diencephalic-mesencephalic junction, the number of fluorescing neurons in the brain stem was considerably lower. These neurons were mostly concentrated in the monoaminergic cell groups. The results indicate the presence of a substantial projection from the posterior thalamic and anterior pretectal region to the claustrum.

Topographical projections from the posterior thalamic regions to the striatum in the cat, with reference to possible tecto-thalamo-striatal connections.

Projections from the posterior thalamic regions to the striatum were studied in the cat by the anterograde tracing method after injecting wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) into the caudalmost regions of the lateroposterior thalamic nucleus (caudal LP), suprageniculate nucleus (Sg) and magnocellular division of the medial geniculate nucleus (MGm). The results were further confirmed by the retrograde tracing method after injecting WGA-HRP into the regions of the caudate nucleus (Cd) and putamen (Put) where afferent fibers from the caudal LP, Sg and MGm were distributed. Fibers from the MGm, Sg or caudal LP were distributed mainly in the medial, middle or lateral part of the caudal half of the putamen (caudal Put), respectively. Although there was a considerable overlap, thalamostriatal fibers from the caudal LP terminated more caudally than those from the MGm. On the other hand, thalamocaudate fibers from the MGm, Sg and lateral part of the caudal LP overlapped with each other in the ventrolateral part of the caudal half of the caudate nucleus (caudal Cd). Fibers from the medial part of the caudal LP were distributed in the ventral part of the caudal Cd. In the superior colliculus (SC) of the cats with WGA-HRP injections in the caudal LP, retrogradely labeled neuronal cell bodies were mainly seen ipsilaterally in the superficial SC layer, and simultaneously, anterogradely labeled axon terminals were observed in the striatum. On the other hand, when WGA-HRP was injected into the Sg or MGm, labeled SC neurons were mainly located in the intermediate and deep SC layers. Thus, ascending impulses from the superficial SC layer may possibly be conveyed ipsilaterally via the caudal LP to the ventral and ventrolateral parts of the caudal Cd and the lateral part of the caudal Put, whereas those from the intermediate and deep SC layers may be relayed via the Sg and/or MGm to the ventrolateral part of the caudal Cd and the middle and medial parts of the caudal Put.

Efferent connections of the claustrum to the posterior thalamic and pretectal region in the rat

Injection of the fluorescent retrograde tracers Fast Blue and Diamidino Yellow in the posterior thalamic and anterior pretectal region of rats resulted in significant retrograde neuronal labeling of the ipsilateral claustrum. The labeled cell bodies were especially abundant in the central third of the claustrum, while the rostral and caudal portions of the nucleus contained only few fluorescing cells. Thus, in addition to the major reciprocal connections of the claustrum with the cerebral cortex, a substantial number of claustral neurons project to the posterior thalamic and anterior pretectal region. Unlike the cortico-claustrocortical loop, this connection appears to be only ipsilateral.

Topographical projections from the thalamus to the putamen in the cat

Thalamic projections to the putamen (Put) in the cat were studied by the retrograde horseradish peroxidase method. Major thalamic projections to the Put originate from the midline and intralaminar nuclear regions including the centre médian-parafascicular complex (CM-Pf). The other thalamic projections to the Put arise mainly from the suprageniculate nucleus (Sg), magnocellular division of the medial geniculate nucleus (MGm), caudomedial part of the lateroposterior nucleus (LP) and ventrolateral part of the ventromedial nucleus (VM). The VM projects to the rostral Put, while the posterior thalamic regions (Sg, MGm, LP) project to the caudal Put.

Direct projections from the substantia nigra to the posterior thalamic regions in the cat

The substantia nigra (SN) of the cat was shown, by the anterograde and retrograde horseradish peroxidase methods, to contain neurons which send their axons to the caudomedial portions of the suprageniculate nucleus and/or lateroposterior nucleus of the thalamus; these neurons were located in the restricted region in the lateral part of the SN, which corresponds to the pars lateralis of the SN.

Viscerosomatic convergence and responses to intestinal distension of neurons at the junction of midbrain and posterior thalamus in the cat

In cats anesthetized with sodium pentobarbital, microelectrode recordings were made from single neurons in the posterior thalamic region of termination of the spinothalamic tract (medial magnocellular division of the medial geniculate) and adjoining mesencephalic reticular formation, to determine if they receive input of visceral as well as of somatic origin. Of 309 units encountered, 136 (44%) demonstrated viscerosomatic convergency by responding to electrical stimulation of the greater splanchnic nerve as well as a somatic nerve (superficial radial and/or posterior tibial). Of 125 units tested, 42 (34%) had large somatic receptive fields spanning two or more limbs. Most of these responded best to intense skin stimuli (pressure, pinch, sometimes noxious heating). The remaining 83 had receptive fields restricted to part of one limb, and most of these responded to weak stimuli (e.g., hair movement, light tap) with no increment in responses to stronger stimuli. To determine of neurons in this region respond to intense visceral stimulation, the small intestine was distended by inflation of a balloon catheter which was inserted into a fistulated portion of the jejunum. Of 134 units with splanchnic nerve input, 28 responded to intestinal distension. Nine units responded only during the initial phase of distension. The other 19 units responded for all or part of the stimulus duration. Each of these 19 units tested had large somatic receptive fields, and most responded best to strong stimuli (e.g., pinch). In addition, they typically had thresholds for electrical stimulation of the splanchnic nerve which were well above threshold for the viscerointercostal reflex, suggesting that the input was mediated by Aδ-C fibers.

Connections of the mediodorsal nucleus of the thalamus in the tree shrew. I. Afferent connections

In three specimens of Tupaia belangeri horseradish peroxidase was injected into the mediodorsal nucleus of the thalamus (MD). Labeled cell bodies were found in the deep layers of three cortical areas and in 9 subcortical regions. The cortical areas projecting to MD are: the frontal pole, the anterior cingulate cortex, and the insula. The subcortical afferents to MD originate in the basal nucleus of amygdala, the magnocellular nuclei of the basal forebrain, nucleus reticularis thalami, hypothalamus, the posterior dorsomedial thalamic region, substantia nigra, central gray, the dorsal and central raphe nuclei and locus coeruleus. No direct connections were found from any formation belonging to the classical sensory or motor systems. Addition of adenosine in the injected solution seems to improve labeling.

Differential localization of the influence of lysine vasopressin and of ACTH 4-10 on avoidance behavior: a study in rats bearing lesions in the parafascicular nuclei.

A single subcutaneous injection of either 1.8 or5.4 µg lysine vasopressin (LVP) into parafascicular (pf) lesioned rats induced a dose-dependent preservation of a pole-jump shock avoidance response. The effect of the higher dose of LVP lasted for a minimum of 5 days whereas the effect of the lower dose was present for only 2 days. These results can be contrasted with the effect of 1.8 µg LVP in sham-operated rats in which the avoidance response is maintained for many days after injection. Daily subcutaneous administration of either 1 or 9 µg of the ACTH analogue (ACTH 4–10) to pf rats did not preserve the pole-jump response. However, in sham-operated animals, 1 or 3 µg ACTH 4–10 was effective in preserving the avoidance response in a dose-dependent way. Because ACTH 4–10 does not preserve avoidance behavior in pf-lesioned animals, the results of these experiments support the conclusion that the parafascicular area is essential for the behavioral effects of this peptide. In contrast, the fact that LVP is effective in lesioned animals (even though higher doses are required than are normally used), together with the earlier finding that local application of LVP in the posterior thalamic region results in a preservation of the avoidance response, indicates that LVP may have its site of action in the parafascicular area as well as in other brain structures.

Some Fiber Pathways Related to the Posterior Thalamic Region in the Cat; pp. 379–393

Some afferent and efferent connections of theposterior thalamic region have been studied in the cat by means of anterograde degeneration methods. The organization of these connections is discussed with the aid of a more general framework that interprets each of a variety of ascending sensory channels as comprising <i>lemniscal line system </i>or <i>lemniscal adjunct channels </i>and that distinguishes within the posterior convexity cortex (1) <i>sensory cortex, </i>(2) <i>proximal association cortex </i>and (3) <i>distal association cortex.</i>

Some fiber pathways related to the posterior thalamic region in the cat.

Some afferent and efferent connections of theposterior thalamic region have been studied in the cat by means of anterograde degeneration methods. The organization of these connections is discussed with the aid of a more general framework that interprets each of a variety of ascending sensory channels as comprising lemniscal line system or lemniscal adjunct channels and that distinguishes within the posterior convexity cortex (1) sensory cortex, (2) proximal association cortex and (3) distal association cortex.

Role of limbic and reticular systems in self-stimulation

1. Reinforcement systems are located in the mesencephalic reticular formation, posterior and anterior hypothalamus, and septum pellucidum, and are more compactly arranged in the posterior hypothalamus. 2. The active zones of Olds, located in the various structures of the limbic-reticular complex, constitute a relative hierarchy. 3. The mesencephalic reticular formation, the central gray matter, and the posterior thalamic region facilitate the general functional activity of Olds' diencephalic centers associated with emotional behavior. 4. The hippocampus is able to modulate selectively the function of emotionally positive zones of the posterior hypothalamus, lowering activity of its ventro-lateral and slightly facilitating activity of its ventro-medial regions. 5. The hippocampal-septal complex is responsible mainly for inhibitory mechanisms on the emotional centers of Olds.

The corticothalamic projection from the second somatosensory cortical area in the cat. An experimental study with silver impregnation methods.

The corticothalamic projection from the anterior ectosylvian gyrus in the cat has been studied with the silver impregnation method of Nauta. The second somatosensory cortical area (SII) projects upon the ipsilateral nucleus ventralis posterolateralis (VPL), nucleus ventralis posteromedialis (VPM), the posterior thalamic region (PO) and to a slight extent upon the reticular nucleus of the thalamus (R), the centrum medianum (CM), the parvocellular part of VPM (VPMpc) and the nucleus ventralis posterior inferior (VPI). A somatotopical arrangement in the projection upon the ventro-basal (VB) complex has been demonstrated and a topical arrangement in the corticothalamic fibers from SII to PO is also evident. The transitional area between SII and the second auditory cortex sends fibers mainly to the entire magnocellular part of the medial geniculate body (MGmc) and to a lesser degree to the principal division of this nucleus (MGp). The corticofugal fibers from SII follow various and rather complicated circuitous routes before they end in the different thalamic nuclei. The experimental findings are discussed in the light of recent anatomical and physiological observations. It is shown that zones B and C of SII which have been shown by Carreras and Andersson (1963) to possess a large number of place and modality specific neurons project upon the VB-complex. On the other hand, zone A which contains a majority of place and modality unspecific neurons sends its fibers exclusively to PO. Finally the problem of thalamocortical projections to SII is briefly discussed.