Anatomical observations on the dorsal column nuclei, their thalamic projection and the cytoarchitecture of some somatosensory thalamic nuclei in the monkey.
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Daily and photoperiodic melatonin binding changes in the suprachiasmatic nuclei, paraventricular thalamic nuclei, and pars tuberalis of the female Siberian hamster (Phodopus sungorus).
Using quantitative autoradiography, 2-(125)I-melatonin binding was investigated throughout the light:dark cycle in the suprachiasmatic nuclei (SCN), paraventricular nuclei (PVT), and pars tuberalis (PT) of adult female Siberian hamsters kept for 10 weeks in either long or short photoperiods (LP or SP, respectively). Plasma melatonin concentrations were measured by radioimmunoassay, and the sexual status of the animals was established by visual inspection of vaginal smears and by weighing uteri after sacrifice. The SCN displayed neither daily nor photoperiod-dependent variations in specific binding. Melatonin receptors in these nuclei would be regulated neither by plasma melatonin nor by the light:dark cycle or sexual steroids. By contrast, melatonin receptor density in the PT displayed both strong daily (maximal values during the first half of the light period and minimal values during the night) and photoperiod-dependent (maximal values in LP) variations. These variations dependent on changes in the maximal binding (Bmax) without differences in the dissociation constant (Kd). Daily melatonin receptor densities in the PT of LP- and SP-exposed animals might be regulated by the dark:light transition but not by melatonin. Daily profiles of 2-(125)I-melatonin-specific binding in the PT were independent of photoperiod. Factors underlying the photoperiod-related variations presently are unknown. Concerning the PVT, weak variations in specific binding were detected in SP only when time points were grouped according to the light or dark periods. It is not yet possible to conclude whether they have any physiological relevance. These results show clearly that the regulation of melatonin receptors varies among structures (SCN, PVT, and PT) in the Siberian hamster and is also totally different from that found in the rat.
Analysis of Variance↗
Immunohistochemical studies of localization and co-localization of glutamate, aspartate and GABA in the anterior thalamic nuclei, retrosplenial granular cortex, thalamic reticular nucleus and mammillary nuclei of the rat.
Localization and possible co-localization of glutamate, aspartate and GABA immunoreactivities was examined in the anterior thalamic nuclei, retrosplenial granular cortex, thalamic reticular nucleus and mammillary nuclei of the rat by double antigen immunohistochemistry using diaminobenzidine and benzidine dihydrochloride in one series and double immunofluorescence labelling with rhodamine and fluorescein in a second series of animals. In three of these regions, retrosplenial granular cortex, anterior thalamic nuclei, and mammillary nuclei, glutamate immunoreactivity was co-localized with aspartate immunoreactivity in a majority of the projection neurons (pyramidal neurons, predominantly in layers V and VI in retrosplenial granular cortex; rounded polygonal multipolar neurons throughout the rostrocaudal extent of the anterior thalamic and mammillary nuclei). None of the cells showing glutamate and/or aspartate immunoreactivity in these regions also displayed GABA immunoreactivity, which was present in non-pyramidal cells in the retrosplenial granular cortex (chiefly in layers I-III) and in small numbers of cells within the anterior thalamic nuclei. In the thalamic reticular nucleus, in contrast, most neurons were immunoreactive for GABA and in the majority of these neurons glutamate (and/or aspartate) immunoreactivity was co-localized with GABA.
Animals↗
Organization of serotoninergic projections from the raphé nuclei to the anterior thalamic nuclei in the rat: a combined retrograde tracing and 5-HT immunohistochemical study.
We combined retrograde transport of horseradish peroxidase (HRP) with 5-hydroxytryptamine (5-HT) immunohistochemistry to study serotoninergic projections to the anterior thalamic nuclei (ATN) of the rat. Small iontophoretic injections of HRP into the anterodorsal thalamic nucleus resulted in double-labelled neurons predominantly in the ventromedial and also in the ventrolateral part of the ipsilateral dorsal raphé (DR). A smaller number of double-labelled neurons was also found in the dorsomedial part of the nucleus, predominantly ipsilaterally, and in the median raphé nucleus (MnR), close to the midline. After injection into the medial subdivision of the anteroventral thalamic nucleus, the pattern of labelling in DR and MnR was similar to that detected following injections into the anterodorsal thalamic nucleus. However, injection into the posterior subdivision of the anteroventral thalamic nucleus resulted in bilateral retrograde labelling of a few 5-HT-containing neurons in the dorsolateral part of the DR. Labelling in the ventromedial, ventrolateral and dorsomedial regions of DR and MnR was similar to that detected after injections into the medial subdivision of the anteroventral thalamic nucleus. After all injections into the ATN, double-labelled cells were found throughout the rostrocaudal extent of MnR and throughout the rostral two-thirds of DR. The caudal extension of DR was devoid of double-labelled cells. Although double-labelled cells were observed bilaterally in the dorsolateral part of the DR, the projection from DR to ATN was predominantly ipsilateral. These results show that there is an internal organization within DR such that subnuclei of the DR can be defined on the basis of their efferent projections to specific subdivisions of the ATN.
Afferent Pathways↗
Connectivity patterns of thalamic nuclei implicated in dyskinesia.
Thalamic nuclei implicated in the neural mechanisms of dyskinesia (1) have projections to components of the basal ganglia; (2) receive efferents from the corpus striatum, and/or (3) project fibers to regions of the cerebral cortex that generate signals which produce or modulate motor phenomenon. The neostriatum receives a major input from the intralaminar thalamic nuclei (ITN). Thalamostriate fibers projecting to the caudate nucleus (CN) and the putamen (Put) originate from different neuronal populations; clusters of cells in the rostral ITN and in the parafascicular nucleus (PF) project to the CN, while cells in the centromedian nucleus (CM) project to the Put. Smaller numbers of cells in the medial, dorsal and ventral nuclear subdivisions of the thalamus also project to the striatum. The amygdaloid nuclear complex receives afferents from the midline thalamic nuclei. Ventromedial and rostral parts of the subthalamic nucleus receive a small input from the centromedian-parafascicular nuclear complex. Segments of the globus pallidus (GP) and the substantia nigra (SN) do not receive afferents from either the cerebral cortex or the thalamus. Thalamic afferents originate ipsilaterally from the medial segment of the globus pallidus (MPS), and the pars reticulata of the substantia nigra (SNR), and contralaterally from the deep cerebellar nuclei (DCN). Each of these projections to nuclear subdivisions of the thalamus is distinctive without overlap. Projections from the MPS are to the ventral anterior pars principalis (VApc) and ventral lateralis, pars oralis (VLo) thalamic nuclei with collaterals to CM. The SNR provides projections to the ventral anterior, pars magnocellularis, the ventral lateral, pars medialis and the mediodorsal, pars paralaminaris thalamic nuclei. Output from the subthalamic nucleus (STN) projects to both the MPS and the SNR and could modulate influences upon thalamic nuclei. In the monkey the projection of STN to the GP is four times greater than to the SNR. The most massive input to the thalamus arises from the contralateral DCN and terminates in the so-called cell-sparse zone, which consists of the ventral posterolateral nucleus, pars oralis, the ventral lateral nucleus pars caudalis, and pars postrema and area x of Olszewski. Nuclear subdivisions of the thalamus receiving afferents from the MPS and the SNR have gamma-aminobutyric acid (GABA) as their major neurotransmitter; fiber systems originating from the DCN appear to have glutamate as their neurotransmitter.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Convergent and complementary projections of the caudal paralaminar thalamic nuclei to rat temporal and insular cortex.
Thalamic nuclei adjacent to the medial geniculate body play a pivotal role in processing of sensory stimuli during emotional situations. These nuclei, which include the suprageniculate nucleus (SG), the posterior intralaminar nucleus (PIN), the peripeduncular nucleus (PP) and the medial division of the medial geniculate body (MGm), project to both cortex and amygdala, but target areas and the extent of the projection of individual nuclei are not known yet. The aim of the present study was to analyze the contribution of individual nuclei to the cortical projection with modern sensitive tracing techniques. Small injections of Miniruby or PHA-L were made into single thalamic nuclei. All thalamic nuclei have in common a projection into the upper portion of layer I of the temporal aspect of the cortical mantle. Furthermore, SG, PIN, MGm and PP each demonstrated a convergent projection to lower layer III and to layer IV of the ectorhinal and visceral cortex. Only MGm projects to layer VI of primary auditory and temporal association cortices. Within the perirhinal cortex zones of convergence and divergence exist. The present results demonstrate a differential thalamocortical projection of single thalamic nuclei to those cortical areas which are involved in the transmission of sensory signals to the amygdala via the thalamocortico-cortical pathway and to the hippocampus via the entorhinal cortex. The thalamic nuclei are thus in a position to activate the amygdala and to modulate the information flow of the thalamocortico-cortical pathway to both amygdala and hippocampus.
Animals↗
Physiological characteristics of anterior thalamic nuclei, a group devoid of inputs from reticular thalamic nucleus.
This study tested the hypothesis that neurons of thalamic nuclei, which are normally devoid of inputs from the reticular thalamic nucleus, do not display spindle oscillations and related rhythmic spike bursts. This proposal derived from our recent studies indicating that the reticular nucleus is the generator of spindling rhythmicity. We used retrograde tracing methods, intracellular recordings in barbiturized cats, and extracellular recordings of single neurons and field potentials in anteroventral (AV), anteromedial (AM), ventroanterior (VA), ventrolateral (VL), and central lateral (CL) thalamic nuclei in cats with rostral brain stem transections (cerveau isolé preparations), before and after administration of barbiturates. The observation that AV and AM nuclei do not receive inputs from the reticular nucleus was confirmed by using injections of horseradish peroxidase conjugated to wheat germ agglutinin confined within the limits of anterior nuclei. Such injections led to massive retrograde labeling in mammillary nuclei and layer VI of the retrosplenial cortex but left free of labeling the neurons of the reticular thalamic nucleus. Intracellular recordings showed that AV-AM neurons discharge tonically in response to a depolarizing current applied at rest, whereas they give rise to a slow spike that underlies a burst of fast action potentials when the membrane is hyperpolarized by 5-12 mV. Despite the fact that they share similar properties with other thalamic neurons, intracellularly recorded AV-AM neurons do not exhibit spindle waves under barbiturate anesthesia, whereas VA-VL, CL, and other thalamocortical neurons that receive afferents from the reticular nucleus commonly display such oscillations. With extracellular recordings performed simultaneously in CL and AV or AM nuclei of the unanesthetized cerveau isolé preparation, focal spindle oscillations and related rhythmic high-frequency spike bursts of single CL cells contrasted with absence of spindles and spike bursts in AV or AM neurons. Spindling could be induced in AV-AM nuclei only after administration of barbiturates at doses exceeding 3 mg/kg, and it appeared approximately 35-40 s after the barbiturate effect was detected in the simultaneously recorded CL nucleus. Moreover, the spike bursts that were elicited in AV-AM neurons after barbiturate administration were not temporally related with focal spindles. Since spindle oscillations did not appear intracellularly in AV-AM neurons, the possibility was envisaged that barbiturate-induced spindles were the passive reflection of field potentials actively generated in neighboring thalamic nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Reciprocal interactions between intralaminar and lateral thalamic nuclei in rats.
Reciprocal interactions between intralaminar thalamic nuclei (ncl. centralis lateralis, CL, and ncl. parafascicularis, Pf), the pretectal area (Pt) and lateral thalamic nuclei (ventrobasal complex, VB, ncl. anterior ventralis, AV, and ncl. ventralis anterior, VA) have been observed in ketamine-anaesthetized rats. Extracellular single unit activity has been recorded after single electrical stimuli. Electrical stimulation of the VB evoked a short latency orthodromic response followed by a pause in spontaneous activity in neurones of medial thalamic nuclei. Lateral thalamic neurones responded to electrical stimulation of the intralaminar nuclei or the pretectal area with the same pattern of response. Striatal, sensorimotor cortical or peripheral electrical stimulation also evoked similar responses. The pauses in spontaneous activity were shown to be the result of inhibition since the responsiveness of the intralaminar nuclei or the lateral thalamic neurones to all inputs was abolished or reduced after a conditioning electrical single-shock stimulation in the VB or in the intralaminar nuclei, respectively. The two components of the response were of a different origin, since most of the short latency responses disappeared after medullary, upper cervical sections or large decortications, while the inhibitions persisted. These inhibitions were shown to be of thalamic origin since their duration was decreased after extensive decortications increased after medullary section. It is concluded that the neuroneal properties studied in this report are probably broadly represented throughout the thalamus and that thalamic neurones are under inhibitory control elicited by afferent volleys. This inhibitory control includes a relay in the nucleus reticularis thalami (nRT). The mechanisms of sensory interaction can be purely thalamic, but they can be modulated by suprathalamic and/or mesencephalic loops.
Animals↗
Neuronal and synaptic structure of the specific thalamic nuclei.
1. Neuronal organization of the specific thalamic nuclei is rather uniform. The ratio of thalamocortical relay neuron and Golgi II type interneuron is 2:1, as well as 3:1. 2. Interneurons show GABA-immunoreactivity. The presynaptic dendrites (F2-profiles) modify the intrathalamic transmission of the specific afferent impulses. 3. The two principal types of synaptic arrangements were observed in the specific thalamic nuclei: the synaptic glomeruli and the general neuropil. 4. Three different types of axon-terminals could be distinguished in the neuropil of all specific thalamic nuclei: the large RL-boutons are terminals of the specific afferents, the small RS-boutons are mainly the terminals of cortical afferents and the F1-boutons are probably axon-terminals of the Golgi II type interneurons, as well as axon-endings originating from the reticular nucleus of thalamus. 5. Synaptic contacts of the specific afferent fibers have basic importance in the relay nuclei. 6. In associative and anterior thalamic nuclei the RS- and F1-boutons have a significant modification effect on the interneurons (inhibition-disinhibition).
Animals↗
Topographic organization of subcortical projections to the anterior thalamic nuclei in the rat.
Subcortical projections to the anterior thalamic nuclei were studied in the rat, with special reference to projections from the mammillary nuclei, by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. The medial mammillary nucleus (MM) projects predominantly ipsilaterally to the entire anterior thalamic nuclei, whereas the lateral mammillary nucleus projects bilaterally to the anterodorsal nucleus (AD) of the anterior thalamic nuclei. A topographic relationship was recognized between the MM and the anterior thalamic nuclei. The dorsal region of the pars mediana of the MM projects to the interanteromedial nucleus (IAM), whereas the ventral region projects to the rostral part of the anteromedial nucleus (AM). The dorsal and the ventral regions of the pars medialis project to the dorsomedial part of the AM at its caudal and rostral levels, respectively. The dorsomedial region of the pars lateralis projects to the ventral AM. The ventrolateral region of the pars lateralis projects to the ventral part of the anteroventral nucleus (AV) in such a manner that rostral cells project rostrally and caudal cells project caudally. The pars basalis projects predominantly ipsilaterally to the dorsolateral AV and bilaterally to the AD. The rostrolateral region of the pars posterior projects to the lateral AV, whereas the medial and the caudal regions of the pars posterior project to the dorsomedial AV. The rostrodorsal part of the nucleus reticularis thalami was found to project to the anterior thalamic nuclei; cells located rostrally in this part project to the IAM and AM, whereas cells located caudodorsally project to the AV and AD. The laterodorsal tegmental nucleus projects predominantly ipsilaterally to the AV, especially to its dorsolateral part. The present study demonstrates that subdivisions of the subcortical structures are connected to the subnuclei of the anterior thalamic nuclei, with a clear-cut topography arranged in the dorsoventral and the rostrocaudal dimensions.
Animals↗
The specificity of the 'nonspecific' midline and intralaminar thalamic nuclei.
The midline and intralaminar thalamic nuclei have long been considered to be a 'nonspecific' nuclear complex that relays the activity of the brain-stem reticular formation to widespread cerebral-cortical areas. Over the past decade, it has become clear that individual midline and intralaminar nuclei each receive specific sets of afferents and project to specific parts of the cerebral cortex and striatum. Moreover, the targets of the thalamocortical and thalamostriatal projections of a given nucleus are interconnected through corticostriatal projections. Therefore, the midline and intralaminar nuclei might have a dual role in corticosubcortical interactions in the forebrain. Through distinct sets of inputs to individual midline or intralaminar thalamic nuclei, these nuclei are in a position to interact selectively with particular, functionally segregated basal-ganglia-thalamocortical circuits. By way of nonselective inputs, in particular from cholinergic brain-stem nuclei, the midline and intralaminar nuclei might act in concert to modify the level of activity of the entire basal-ganglia-thalamocortical system.
Animals↗
Parabrachial nucleus projections to midline and intralaminar thalamic nuclei of the rat.
The projections from the parabrachial nucleus to the midline and intralaminar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin-beta (CTb) were made in each of the intralaminar nuclei of the dorsal thalamus (the lateral parafascicular, medial parafascicular, oval paracentral, central lateral, paracentral, and central medial nuclei), as well as the midline thalamic nuclei (the paraventricular, intermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, parvicellular part of the ventral posterior, and caudal ventral medial nuclei). The retrograde cell body labeling pattern within the parabrachial subnuclei was then analyzed. The paracentral thalamic nucleus received an input only from the internal lateral parabrachial subnucleus. However, this subnucleus also projected to all the other intralaminar thalamic nuclei, except for the central lateral thalamic nucleus, which received no parabrachial afferent inputs. The external lateral parabrachial subnucleus projected to the lateral parafascicular, reuniens, central medial, parvicellular part of the ventral posterior, and caudal ventromedial thalamic nuclei. Following CTb injections in the paraventricular thalamic nucleus, retrogradely labeled cells were found in the central lateral, dorsal lateral, and external lateral parabrachial subnuclei. The medial and ventral lateral parabrachial subnuclei projected to the oval paracentral, parafascicular, and rhomboid thalamic nuclei. Finally, the waist area of the parabrachial nucleus was densely labeled after CTb injections in the parvicellular part of the ventral posterior thalamic nucleus. Nociceptive, visceral, and gustatory signals may reach specific cortical and other forebrain sites via this parabrachial-thalamic pathway.
Animals↗
Degeneration of anterior thalamic nuclei differentiates alcoholics with amnesia.
The specific neural substrate underlying the amnesia in alcoholic Korsakoff's psychosis is poorly defined because of the considerable brain damage found in many non-amnesic alcoholics, particularly those with Wernicke's encephalopathy. Using operational criteria to identify alcoholics with and without Korsakoff's psychosis, we have shown that many of the cortical and subcortical regions involved in the encoding and retrieval of episodic memory are either unaffected (hippocampus) or damaged to the same extent (prefrontal cortex and the cholinergic basal forebrain) in both amnesic and non-amnesic alcoholics. In the present study we analysed the diencephalic regions involved in episodic memory to determine the neural substrate for the amnesia observed in alcoholic Korsakoff's psychosis. The number of neurons in spaced serial sections containing the hypothalamic mamillary nuclei and the anterior and mediodorsal thalamic nuclei was estimated using unbiased stereological techniques. Neurodegeneration of the hypothalamic mamillary nuclei and the mediodorsal thalamic nuclei was substantial in both non-amnesic and amnesic alcoholics with Wernicke's encephalopathy. However, neuronal loss in the anterior thalamic nuclei was found consistently only in alcoholic Korsakoff's psychosis. This is the first demonstration of a differentiating lesion in alcoholic Korsakoff's psychosis and supports previous evidence that degeneration of thalamic relays are important in this memory disorder.
Aged↗
Medullo adrenal response to lesion of anterodorsal thalamic nuclei in rats.
Anterodorsal thalamic nuclei (ADTN) exert an inhibitory influence on hypophyso-adrenal system (HAS) in rats. With the purpose of evaluating if ADTN are also involved in the control of medullo adrenal activity, experiments were conducted on female rats with bilateral lesion of these nuclei. Thirty days after lesion, plasma epinephrine (E) concentration in lesioned rats was higher than that in sham-lesioned control group (P < 0.02). Meanwhile, adrenal E content was significantly lower in lesioned animals than that found in the control group (P < 0.005). Plasma norepinephrine (NE) values in lesioned rats were not significantly different from those in the control ones, however, there was a significant decrease in adrenal NE when compared to the control one (P < 0.02). Basal values of plasma ACTH and plasma and adrenal corticosterone (C) were signicantly higher than those in sham lesioned rats (P < 0.05; P < 0. 001; P < 0.001 respectively). These findings demonstrate that the ADTN in rats are involved in the regulation of both cortico and medullo adrenal activity.
Adrenal Medulla↗
Glutamic acid decarboxylase immunoreactivity in some dorsal thalamic nuclei in Crocodilia.
Glutamic acid decarboxylase (GAD) immunocytochemical properties of thalamic nuclei known to project to the telencephalon were investigated in reptiles, Caiman crocodilus and Alligator mississippiensis, by monoclonal antibodies to GAD epitopes designated as GAD-1, GAD-2 and GAD-5. GAD-immunoreactive puncta were observed with all three monoclonal antibodies in the following dorsal thalamic nuclei by avidin-biotin complex methodology: dorsolateralis anterior, dorsomedialis anterior, diagonalis, rotundus, reuniens pars centralis and pars diffusa, and the medialis complex. In general, immunoreactivity to GAD was more robust in Alligator than in Caiman. GAD-2 immunoreactivity was more intense than immunoreactivity to GAD-1 or GAD-5 at similar antibody concentrations in both species. Thalamic nuclei varied in the pattern and intensity of GAD (+)puncta staining in Caiman and Alligator. No GAD-immunoreactive neurons were observed in any of these seven thalamic nuclei with any GAD antibody in either species.
Alligators and Crocodiles↗
Projections from visual areas of the middle suprasylvian sulcus onto the lateral posterior complex and adjacent thalamic nuclei in cat.
The distribution of corticothalamic projections from lateral suprasylvian areas AMLS, PMLS, ALLS, and PLLS was investigated with the autoradiographic method. Areas AMLS and PMLS were both found to project retinotopically upon the medial interlaminar nucleus and the lateral and pulvinar zones of the lateral posterior complex, as well as to the ventral lateral geniculate nucleus, intralaminar nuclei, and thalamic reticular complex. Retinotopic projections to the dorsal lateral geniculate nucleus were demonstrated from PMLS but not AMLS, and projections to zona incerta were demonstrated from AMLS but not PMLS. Areas PLLS and ALLS were both found to project retinotopically upon the interjacent zone of the lateral posterior complex, as well as to the intermediate and suprageniculate divisions of the posterior nuclear group, the magnocellular division of the medial geniculate complex, the thalamic reticular complex, and central lateral nucleus. Area ALLS was also found to project onto the dorsal division of the medial geniculate complex and lateral division of the posterior nuclear group. Differences between the four cortical areas in the pattern and density of their thalamic projections supports the parcellation of these areas as proposed by Palmer et al. ('78). The projection patterns of areas PMLS, AMLS, PLLS, and ALLS were found to respect the boundaries of the zones of the lateral posterior complex, which had been identified and defined previously (Updyke, '77), and the results thus support the hypothesis that these zones are the functional units of organization of visual traffic between the cat's extrastriate visual areas.
Animals↗
[Thalamic somatosensory potentials after peripheral stimulation and cortical somatosensory potentials after electric stimulation of thalamic nuclei VOa and VOp (preliminary report)].
In patients with extrapyramidal syndromes thalamic action potentials were recorded during operations with a five-point brain electrode and in the same cases somatosensory evoked potentials were recorded from the skull. Thalamic potentials were recorded after peripheral stimulation, and evoked potentials from the skull were recorded after electrostimulation of thalamic nuclei VOa and VOp. At the thalamic level a short-latency positive-negative potential had a maximal amplitude in one only lead, which confirmed sharp projection of body surface into various thalamic nuclei. Somatosensory evoked potentials recorded from the skull in response to stimulation of thalamic nuclei were usually biphasic and stimulation of VOa and VOp nuclei gave potentials with similar configuration of phases. This confirms the divergence of the projection fibres from the thalamus to the cortex.
Adult↗
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↗