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PubMed1991

Restricted cortical termination fields of the midline and intralaminar thalamic nuclei in the rat.

The projections from the midline and intralaminar thalamic nuclei to the cerebral cortex were studied in the rat by means of anterograde tracing with Phaseolus vulgaris-leucoagglutinin. The midline and intralaminar nuclear complex taken as a whole projects to widespread, predominantly frontal, cortical areas. Each of the constituent thalamic nuclei has a restricted cortical projection field that overlaps only slightly with the projection fields of adjacent midline and intralaminar nuclei. The projections of the intralaminar nuclei cover a larger cortical area than those of the midline nuclei. The laminar distributions of fibres from individual midline and intralaminar thalamic nuclei are different and include both deep and superficial cortical layers. The parataenial, paraventricular and intermediodorsal midline nuclei each project to circumscribed parts of the prefrontal cortex and the hippocampal and parahippocampal regions. In the prefrontal cortex, the projections are restricted to the medial orbital, infralimbic, ventral prelimbic and agranular insular fields, and the rostral part of the ventral anterior cingular cortex. In contrast to the other midline nuclei, the rhomboid nucleus projects to widespread cortical areas. The rostral intralaminar nuclei innervate dorsal parts of the prefrontal cortex, i.e. the dorsal parts of the prelimbic, anterior cingular and dorsal agranular insular cortical fields, the lateral and ventrolateral orbital areas, and the caudal part of the ventral anterior cingular cortex. Additional projections are aimed at the agranular fields of the motor cortex and the caudal part of the parietal cortex. The lateral part of the parafascicular nucleus sends fibres predominantly to the lateral agranular field of the motor cortex and the rostral part of the parietal cortex. The medial part of the parafascicular nucleus projects rather sparsely to the dorsal part of the prelimbic cortex, the anterior cingular cortex and the medial agranular field of the motor cortex. Individual midline and intralaminar thalamic nuclei are thus in a position to directly influence circumscribed areas of the cerebral cortex. In combination with previously reported data on the organization of the midline and intralaminar thalamostriatal projections and the prefrontal corticostriatal projections the present results suggest a high degree of differentiation in the convergence of thalamic and cortical afferent fibres in the striatum. Each of the recently described parallel basal ganglia-thalamocortical circuits can thus be expanded to include projections at both the cortical and striatal levels from a specific part of the midline and intralaminar nuclear complex. The distinctive laminar distributions of the fibres originating from the different nuclei emphasize the specificity of the midline and intralaminar thalamocortical projections.

Animals↗

PubMed2005

Organization of anterior cingulate and frontal cortical projections to the anterior and laterodorsal thalamic nuclei in the rat.

The anterior and laterodorsal thalamic nuclei provide massive projections to the anterior cingulate and frontal cortices in the rat. However, the organization of reciprocal corticothalamic projections has not yet been studied comprehensively. In the present study, we clarified the organization of anterior cingulate and frontal cortical projections to the anterior and laterodorsal thalamic nuclei, using retrograde and anterograde axonal transport methods. The anteromedial nucleus (AM) receives mainly ipsilateral projections from the prelimbic and medial orbital cortices and bilateral projections from the anterior cingulate and secondary motor cortices. The projections from the anterior cingulate cortex are organized such that the rostrocaudal axis of the AM corresponds to the rostrocaudal axis of the cortex, whereas those from the secondary motor cortex are organized such that the rostrocaudal axis of the AM corresponds to the caudorostral axis of the cortex. The ventromedial part of the anteroventral nucleus receives ipsilateral projections from the anterior cingulate cortex and bilateral projections from the secondary motor cortex, in a topographic manner similar to the projections to the AM. The ventromedial part of the laterodorsal nucleus (LD) receives ipsilateral projections from the anterior cingulate and secondary motor cortices. The projections are roughly organized such that more dorsal and ventral regions within the ventromedial LD receive projections preferentially from the anterior cingulate cortex. The difference in anterior cingulate and frontal cortical projections to the anterior and laterodorsal nuclei may suggest that each thalamic nucleus plays a different functional role in spatial memory processing.

Animals↗

PubMed1983

Effects of unilateral electrical stimulation of various thalamic nuclei on the release of dopamine from dendrites and nerve terminals of neurons of the two nigrostriatal dopaminergic pathways.

The role of several motor and intralaminar thalamic nuclei in the regulation of dopamine release from terminals and dendrites of the nigrostriatal dopaminergic neurons was investigated in halothane-anaesthetized cats. For this purpose, the effects of the unilateral electrical stimulation of various thalamic nuclei on the release of newly synthesized [3H]dopamine were simultaneously determined in both substantiae nigrae and caudate nuclei using the push-pull cannula method. The electrical stimulation of the motor nuclei was the only one to induce asymmetric changes in the four structures since [3H]dopamine release was enhanced in the ipsilateral caudate nucleus and reduced in the contralateral structure while opposite responses were observed in the corresponding substantiae nigrae. A reduction of [3H]dopamine release occurred in the four structures or only in the contralateral substantia nigra and caudate nucleus following the stimulation of the parafascicularis nucleus and the adjacent posterior part of the nucleus centrum medianum or of the nucleus centralis lateralis and the adjacent paralaminar part of the nucleus medialis dorsalis, respectively. The stimulation of the anterior part of the nucleus centrum medianum, which in contrast to other thalamic nuclei examined, receives few nigral inputs, selectively enhanced [3H]dopamine release in the contralateral substantia nigra. No significant changes in [3H]dopamine release were seen either in the substantiae nigrae or in the caudate nuclei following the stimulation of midline thalamic nuclei. These results indicate that the motor and intralaminar thalamic nuclei exert multiple and selective influences on the release of dopamine from terminals and/or dendrites of the dopaminergic neurons. They also further support a role of thalamic nuclei in the transfer of information from one substantia nigra to the contralateral dopaminergic neurons. The possible involvement of connections between paired thalamic nuclei was underlined by the observations of evoked potentials in contralateral homologous nuclei following unilateral stimulation of motor, or some intralaminar, nuclei. The present report provides new insights on the mechanisms contributing to the reciprocal and/or bilateral regulations of nigrostriatal dopaminergic pathways.

Animals↗

PubMed1993

Branching projections from mesopontine nuclei to the nucleus reticularis and related thalamic nuclei: a double labelling study in the rat.

Branching projections from pedunculopontine and laterodorsal tegmental nuclei to different thalamic targets were studied by means of a double retrograde tracing technique. The results show a topographic distribution of mesopontine neurons projecting to different thalamic targets. In addition, the present data demonstrate that a small percentage (< or = 5%) of mesopontine neurons projecting to the intralaminar nuclei or to the rostral pole of the reticular nucleus innervate both these areas by means of branching axons. By contrast, a large number of mesopontine neurons projecting to the sensorimotor thalamic nuclei send axon collaterals to the caudal part of the reticular nucleus. The present findings support the hypothesis of an inhomogeneity of different sectors of the thalamic reticular nucleus. Thus, this nucleus can be differentiated into two functional areas, in accordance with their connections with functionally different cortical fields and thalamic districts. The possibility that these two areas of the thalamic reticular nucleus subserve different mechanisms during sleep phenomena is discussed.

Animals↗

PubMed2006

Reversible attenuation of neuropathic-like manifestations in rats by lesions or local blocks of the intralaminar or the medial thalamic nuclei.

BACKGROUND AND AIM: Thalamic somatosensory nuclei have been classified into medial and lateral systems based on their role in nociception. An imbalance between these two systems may result in abnormal somatic sensations and spontaneous pain. This study aims to investigate the effects of transient or permanent block of the medial and intralaminar nuclear groups on the neuropathic-like behavior in a rat model for mononeuropathy. METHODS: Neuropathy was induced on one hind paw in different groups of rats following the spared nerve injury model. When the resulting hyperalgesia and allodynia (tactile and cold) reached a maximum plateau, the rats received either chemical or electrolytic lesion or lidocaine (2%) microperfusion, placed in the various thalamic nuclear groups. RESULTS: All procedures produced transient but significant decrease of neuropathic manifestations. The magnitude and duration of decrease depended on the type and the site of the block. These effects can be ranked in increasing order as follows, electrolytic<chemical<lidocaine micro-perfusion according to the procedure, and as rostro-medial<ventro-median<parafascicular nuclei, according to the site of the block. Thermal hyperalgesia was the most affected while cold allodynia showed the least attenuation. Neuropathic manifestations returned to their pre-lesion levels after 2-3 weeks, along with frequently observed delayed hyper-responsiveness to the hotplate test. CONCLUSION: The observed results demonstrate the involvement of the medial and intralaminar thalamic nuclei in the processing of neuropathic-like manifestations, and the reversibility of the effects suggests the flexibility of the neural network involved in supraspinal processing of nociceptive information.

Animals↗

PubMed1976

Inhibition of gonadotropin secretion induced by stimulation of thalamic nuclei.

The effect of electrochemical stimulation (anodic current, 100 micronA/30 sec) of thalamic nuclei was studied in nonanesthetized freely-behaving rats bearing chronic implanted electrodes and plastic cannulae inserted into the jugular vein for blood sampling. Stimulation of the anterior thalamic nuclei, the nucleus (n.) mediodorsalis thalami (MD) and the n. posteromedianus thalami at 2 p.m. on the day of proestrus prevented spontaneous ovulation and the release of LH which takes place on that day. No effect on ovulation or LH release was observed after stimulation of the n. lateralis thalami, the n. ventralis thalami or other thalamic nuclei or after passing a cathodic current through the n. MD. Stimulation of the n. MD resulted also in a significant decrease of the elevated serum LH levels found after an injection of progesterone into ovariectomyzed estrogen-primed rats. These results indicate that nuclei of the medial thalamic region are capable of inhibiting LH secretion. No stimulatory influence of LH release was observed after thalamic stimulation in ovariectomized estrogen-treated rats.

Animals↗

PubMed1984

[Neuronal populations in the posterior group of thalamic nuclei projecting into the amygdaloid complex and auditory cortex in the cat].

Location of neurons in posterior thalamic nuclei and neighbouring structures of the midbrain regions projecting to the amygdaloid complex and auditory cortex of cat was studied by the method of horseradish peroxidase. The main sources of these brain region projections to amygdaloid complex are peripeduncular , subparafascicular and suprageniculate nuclei and caudal division of the medial geniculate body. The cells of origin of projections to the auditory cortex are located in all medial geniculate nuclei and wide regions of the posterior thalamic group. Neuron pools projecting to the auditory cortex and amygdala exist in medial parts of the posterior thalamic nuclei. The role of posterior thalamic nuclei in transmission of auditory signals to amygdala is discussed.

Amygdala↗

PubMed2005

The differential distribution of the growth-associated protein-43 in first and higher order thalamic nuclei of the adult rat.

Corticothalamic axons from layer 5 of primary and secondary auditory and visual areas have large terminals that make multiple synaptic contacts on proximal dendrites of relay cells in higher order thalamic nuclei and have been termed "driver" inputs. The corticothalamic cells express mRNA for the presynaptic growth-associated protein-43, in the adult rat [Feig SL (2004) Corticothalamic cells in layers 5 and 6 of primary and secondary sensory cortex express GAP-43 mRNA in the adult rat. J Comp Neurol 468:96-111]. In contrast, ascending driver afferents to first order nuclei (e.g. retinal, inferior collicular, and lemniscal) lose growth-associated protein-43 as mature synaptic terminals are established. Levels of immunoreactivity for growth-associated protein-43 are compared for first and higher order visual (lateral geniculate and lateral posterior), auditory (ventral and dorsal divisions of the medial geniculate), and somatosensory (ventral posterior and posterior) thalamic nuclei. At one week postnatal, staining for growth-associated protein-43 is uniform throughout first and higher order thalamic nuclei. By three weeks and thereafter, staining is denser in the higher order than first order thalamic nuclei. Electron microscopy shows growth-associated protein-43 in profiles with characteristics of afferents from layer 5 in LP and medial geniculate nucleus and no such label in retinal afferents in lateral geniculate nucleus. In these nuclei, approximately 25% of the profiles with characteristics of cortical afferents from layer 6 have label for growth-associated protein-43. The superficial layers of the superior colliculus also show growth-associated protein-43 positive profiles with characteristics of terminals from cortical layer 5. Some growth-associated protein-43 positive terminals were also positive for GABA in the thalamic nuclei studied and in the superior colliculus. The data suggest that sensory afferents to first order thalamocortical relays become stabilized once mature synaptic patterns are established, but the higher stages of information processing involving higher order thalamic relays, via cells in cortical layer 5, retain plasticity related to growth-associated protein-43 in the adult.

Animals↗

PubMed1993

The contribution of the anterior thalamic nuclei to anterograde amnesia.

This paper first reviews the anatomical, pathological, and neuropsychological evidence implicating the anterior thalamic nuclei in memory processes. It is concluded that there is much indirect evidence indicating that anterior thalamic dysfunction is an important factor in anterograde amnesia. More direct evidence for the involvement of the anterior thalamic nuclei in memory processes emerges from two experiments with rats that examined performance of a spatial test of working memory, delayed nonmatching-to-position. The first study revealed that neurotoxic lesions of the anterior thalamic nuclei and radiofrequency lesions of the fornix both produce equivalent performance deficits. In contrast, lesions of the mamillary bodies were without effect. A second study showed that lesions of the fornix and removal of the hippocampus produced very similar deficits. These data indicate that while the involvement of the anterior thalamic nuclei in certain memory functions depends on inputs from the hippocampus, this involvement need not depend on indirect afferents via the mamillary bodies.

Amnesia↗

PubMedDate not supplied

[Memory and aging: changes in the mammillary body and anterior thalamic nuclei due to age].

Karyometric changes and variation of neuron number in mammillary body and anterior thalamic nuclei, dependent of the age, have been studied in humans and rats. The behaviour of the neurons number is very similar in all studied nuclei of both species: there is a constant and gradual loss of neurons from the first until the last period of the life. The intensity of the neuronal loss, however, is different according the nuclei and is more pronounced in rats than in humans. The evolution of the nuclear area of the human mammillary body is similar to that of the anterior thalamic nuclei: there is a significant decrease until the age of 60-70 years and then begins an increase up to the end of the life. This increase is more intense in the mammillary nuclei than in the thalamic ones. In rats, the behaviour of the mammillary nuclei is different to that of the anterior thalamic nuclei. In the mammillary body there is an increase of the nuclear are until 18 months of age, followed by a decrease until the end of the life. The anterior thalamic nuclei show a double inflexion: first, it appears a marked decrease of the nuclear area during the first 6 months, then the area remains unchanged until the age of 15 months, but from this period up to the end of the 2nd year undergoes an increase and, finally, during the 3 year shows a significant decrease. There is not a complete correlation between neuronal loss and nuclear area increase. Although the neuronal loss is constant during the entire life, the nuclear are increase only in a certain period: in rats during the second year and in humans in the final period of life. The signification of this partial correlation is discussed.

Adolescent↗

PubMed2000

Differential projection of the posterior paralaminar thalamic nuclei to the amygdaloid complex in the rat.

The thalamic paralaminar nuclei that border the medial and ventral edges of the medial geniculate body, viz. the suprageniculate nucleus (SG), the posterior intralaminar nucleus (PIN), the medial division of the medial geniculate nucleus (MGm), and the peripeduncular nucleus (PP), are regarded as important extralemniscal relay nuclei for sensory stimuli and as an important link for the direct transmission of sensory stimuli to the amygdala. Each of these thalamic nuclei receives a unique pattern of afferent input but an unresolved question is, how each of these thalamic nuclei project to the amygdala and whether there are zones of convergence and/or non-overlapping regions within amygdaloid target nuclei. Small injections of PHA-L or Miniruby, which were made into single thalamic nuclei at different rostrocaudal levels, revealed a non-uniform distribution of anterogradely labeled axons within the amygdaloid complex. Injections into the SG, MGm, and rostral PIN predominantly labeled axons in the laterodorsal and lateroventral portions of the lateral nucleus of the amygdala (LA). Axons from the MGm were located rather in the dorsal part of the LA, whereas SG-derived axons were concentrated in the ventrolateral part of the LA. Injections into the PP labeled axons predominantly in the medial part of the LA, whereas after injections into the caudal PIN axons were seen in the entire LA. In addition, the PIN projects heavily to the anterior basomedial nucleus and medial division of the central nucleus, whereas this projection is virtually absent from the other thalamic nuclei. The lateral part of the central nucleus and the basal nucleus of the amygdala are spared by axons from the thalamic paralaminar nuclei. The present results suggest that, despite a considerable degree of convergence of the thalamoamygdaloid projection in the lateral nucleus, each thalamic nucleus plays a unique role in the transmission of sensory stimuli to the amygdala and in the modulation of intraamygdaloid circuits.

Amygdala↗

PubMed1997

Assessing the magnitude of the allocentric spatial deficit associated with complete loss of the anterior thalamic nuclei in rats.

The behavioural effects of complete lesions of the anterior thalamic nuclei (ANT), the anterior thalamic nuclei plus the lateral dorsal nucleus (ANT + LD), and fornix (FX) were compared using a series of tests of spatial memory. ALl three lesion groups were found to have an equally severe and long-lasting impairment in the acquisition of a T-maze alternation task when compared with the control animals (COMB SHAM). In Experiment 2, the control animals were able to perform the alternation task when the test trial was started from a different location to the sample trial, so demonstrating that they were able to use allocentric cues in order to differentiate the most recently visited arm. In contrast, all the lesion groups performed close to chance level. In fact, for this condition the ANT / LD group was significantly worse than the FX group. In contrast, none of the lesion groups was impaired on an egocentric discrimination and subsequent reversal task (Experiment 3). The control animals came from two different control procedures, a surgical control sub-group (SHAM) and a group of animals that received injections of N-methyl-D-aspartic (NMDA) into the fornix (NMDA SHAM). There were no differences in the performance levels of the NMDA SHAM group compared with the surgical control group in any of the experiments conducted, so showing that the anterior thalamic lesion effects were not due to non-specific damage to the fornix by NMDA. This series of experiments demonstrated that complete lesions of the anterior thalamic region impair the ability to process allocentric information, and provide evidence for a contribution from the lateral dorsal thalamic nucleus.

Animals↗

PubMed2003

Distribution and binding parameters of GABAA receptors in the thalamic nuclei of Macaca mulatta and changes caused by lesioning in the globus pallidus and reticular thalamic nucleus.

Ascending output from the basal ganglia to the primate motor thalamus is carried by GABAergic nigro- and pallido-thalamic pathways, which interact with intrinsic thalamic GABAergic systems represented in primates by local circuit neurons and axons of the reticular thalamic nucleus. Disease-triggered pathological processes in the basal ganglia can compromise any of these pathways either directly or indirectly, yet the effects of basal ganglia lesioning on its thalamic afferent-receiving territories has not been studied in primates. Two GABA(A) receptor ligands, [(3)H]muscimol and [(3)H]flunitrazepam, were used to study the distribution and binding properties of the receptor in intact monkeys, those with kainic acid lesions in the globus pallidus, and those with ibotenic acid lesions in the reticular nucleus using quantitative autoradiographic technique on cryostat sections of fresh frozen brain tissue. In control monkeys the binding affinities for [(3)H]muscimol averaged 50 nM in the thalamic nuclei and 86 nM in the basal ganglia while the binding densities varied (maximum density of binding sites [Bmax] range of 99.4-1000.1 fmol/mg of tissue). Binding affinities and Bmax values for [(3)H]flunitrazepam averaged 2.02 nM and 81-113 fmol/mg of tissue, respectively. Addition of 100-microM GABA increased average affinity to 1.35 nM whereas Bmax values increased anywhere from 1-50% in different nuclei. Zolpidem (100 nM) decreased binding by 68-80%. Bmax values for both ligands were decreased at the two survival times in both medial and lateral globus pallidus implying involvement of both nuclei in the lesion. Statistically significant, 40% decrease (P=0.055) of Bmax for [(3)H]muscimol was observed in the ventral anterior nucleus pars densicellularis (VAdc, the main pallidal projection territory in the thalamus) 1 week after globus pallidus lesioning and a 36% decrease (P=0.017) 4 months post-lesioning. In contrast, [(3)H]flunitrazepam Bmax values in the VAdc of the same animals were increased by 23% (P=0.021) at 1 week and 28% (P=0.005) 4 months postlesion, respectively. One week after the reticular nucleus lesioning, the binding densities of [(3)H]muscimol and [(3)H]flunitrazepam were decreased in the thalamic nuclei receiving projections from the lesioned reticular nucleus sector by approximately 50% (P<0.05) and 10-33% (P<0.05), respectively. The results suggest that different GABA(A) receptor subtypes are associated with different GABAergic systems in the thalamus which react differently to deafferentation.

Animals↗

PubMed2006

[Primary structural moduli of the dorsal thalamic nuclei and motor cortex in man].

The aim of this work was to study the primary structural modular organization of neurons in dorsal thalamic nuclei (ventral anterior, ventral lateral, anterior medial, anterior ventral, anterior dorsal, medial, nucleus reticularis) and motor cortex (areas 4 and 6) in man using the methods of Nissl, Kluver-Barrera and Golgi silver nitrate impregnation. It was shown that in both dorsal thalamic nuclei and motor cortex neurons had regular organization--they were forming small groups or short chains and meet specific criteria. These neuronal associations, formed single structural units, that were called primary structural moduli. Comparison of primary structural moduli found in dorsal thalamic nuclei and motor cortex has demonstrated the identity of their organizational principle. The differences were only in the cells, that formed primary structural moduli. Thus, in human dorsal thalamic nuclei and motor cortex two principles of neuronal organization into primary structural moduli were detected--group and chain.

Humans↗

PubMed2002

Brainstem projections to midline and intralaminar thalamic nuclei of the rat.

The projections from the brainstem to the midline and intralaminar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin beta -subunit (CTb) were made in each of the intralaminar nuclei of the dorsal thalamus: the lateral parafascicular, medial parafascicular, central lateral, paracentral, oval paracentral, and central medial nuclei; in the midline thalamic nuclei-the paraventricular, intermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, and submedius nuclei; and, in the anteroventral, parvicellular part of the ventral posterior, and caudal ventral medial nuclei. The retrograde cell body labeling pattern within the brainstem nuclei was then analyzed. Nearly every thalamic site received a projection from the deep mesencephalic reticular, pedunculopontine tegmental, dorsal raphe, median raphe, laterodorsal tegmental, and locus coeruleus nuclei. Most intralaminar thalamic sites were also innervated by unique combinations of medullary and pontine reticular formation nuclei such as the subnucleus reticularis dorsalis, gigantocellular, dorsal paragigantocellular, lateral, parvicellular, caudal pontine, ventral pontine, and oral pontine reticular nuclei; the dorsomedial tegmental, subpeduncular tegmental, and ventral tegmental areas; and, the central tegmental field. In addition, most intralaminar injections resulted in retrograde cell body labeling in the substantia nigra, nucleus Darkschewitsch, interstitial nucleus of Cajal, and cuneiform nucleus. Details concerning the pathways from the spinal trigeminal, nucleus tractus solitarius, raphe magnus, raphe pallidus, and the rostral and caudal linear raphe nuclei to subsets of midline and intralaminar thalamic sites are discussed in the text. The discussion focuses on brainstem-thalamic pathways that are likely involved in arousal, somatosensory, and visceral functions.

Animals↗

PubMed1985

Absence of spindle oscillations in the cat anterior thalamic nuclei.

Intracellular recordings were performed in cat anterior thalamic nuclei (anterior ventral, medial and dorsal) which, according to a recent anatomical study, do not receive afferents from the reticularis thalami nucleus. Neurons of anterior nuclei did not display spontaneous membrane potential oscillations of the spindle type and such oscillations could neither be evoked in these cells by cortical stimulation. The absence of spontaneous and evoked spindling activity was observed despite that anterior thalamic cells displayed intrinsic membrane properties similar to those of thalamocortical cells in other nuclei. Electrographic recordings from cortical areas connected to anterior thalamic nuclei were also free of spindle activity. Taken together with the evidence that thalamic relay neurons deprived from their reticularis input by sections or kainic acid lesions lose their spindling activity, our results point to the essential role of the reticularis complex in the genesis of thalamic spindle waves.

Animals↗

PubMed2001

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

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

Animals↗

PubMed2000

Periaqueductal gray matter projections to midline and intralaminar thalamic nuclei of the rat.

The periaqueductal gray matter (PAG) projections to the intralaminar and midline thalamic nuclei were examined in rats. Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected in discrete regions of the PAG, and axonal labeling was examined in the thalamus. PHA-L was also placed into the dorsal raphe nuclei or nucleus of Darkschewitsch and interstitial nucleus of Cajal as controls. In a separate group of rats, the retrograde tracer cholera toxin beta-subunit (CTb) was injected into one of the intralaminar thalamic nuclei-lateral parafascicular, medial parafascicular, central lateral (CL), paracentral (PC), or central medial nucleus-or one of the midline thalamic nuclei-paraventricular (PVT), intermediodorsal (IMD), mediodorsal, paratenial, rhomboid (Rh), reuniens (Re), or caudal ventral medial (VMc) nucleus. The distribution of CTb labeled neurons in the PAG was then mapped. All PAG regions (the four columns of the caudal two-thirds of the PAG plus rostral PAG) and the precommissural nucleus projected to the rostral PVT, IMD, and CL. The ventrolateral, lateral, and rostral PAG provided additional inputs to most of the other intralaminar and midline thalamic nuclei. PAG inputs to the VMc originated from the rostral and ventrolateral PAG areas. In addition, the lateral and rostral PAG projected to the zona incerta. No evidence was found for a PAG input to the ventroposterior lateral parvicellular, ventroposterior medial parvicellular, caudal PC, oval paracentral, and reticular thalamic nuclei. PAG --> thalamic circuits may modulate autonomic-, nociceptive-, and behavior-related forebrain circuits associated with defense and emotional responses.

Animals↗