Calcitonin gene-related peptide-like immunoreactivity marks putative visceral sensory pathways in human brain

Calcitonin gene-related peptide serves as a neuromodulator in several ascending visceral sensory pathways from the parabrachial nucleus to the thalamus, amygdala and the visceral sensory cortex in rats, but these pathways have not been studied in primates. We have examined the distribution of calcitonin gene-related peptide-like immunoreactive innervation of the corresponding areas of the human brain, including the cortex, diencephalon and brainstem. We report the finding of three populations of calcitonin gene-related peptide-like immunoreactive cells that are homologous to those that have been characterized in the rat: the external lateral and external medial parabrachial subnuclei and the posterior intralaminar thalamic complex, including the subparafascicular, lateral subparafascicular and peripeduncular nuclei. In addition, scattered calcitonin gene-related peptide-like immunoreactive cells were found in the periventricular hypothalamus. Calcitonin gene-related peptide-like immunoreactive terminals were found in regions homologous to the projection areas of the external medial and external lateral parabrachial subnuclei in the rat, including the ventroposterior parvicellular nucleus of the thalamus, the central nucleus of the amygdala, the bed nucleus of the stria terminalis and the insular cortex; and in the terminal field of the posterior intralaminar thalamic complex, including the amygdalo-striatal transition region and the insular cortex.These results suggest that, similarly to other species, calcitonin gene-related peptide may also serve as a marker for ascending visceral sensory pathways in the human brain.     

大鼠间脑和皮质下端脑到前额叶皮质的传入投射——WGA-HRP法研究

本研究将 WGA-HRP 注射于25只大鼠前额叶皮质的前扣带回背部、前边缘区及岛叶无颗粒皮质背部,观察其间脑和皮质下端脑的传入联系。间脑的传入主要来自丘脑背内侧核,并有一定的局部定位。此外,丘脑的板内核群(中央外侧核、旁中央核、中央内侧核及束旁核)、腹侧核群(腹外侧核、腹内侧核、腹前核及腹后核)、中线核群(菱形核、连合核、带旁核及室旁核)、前内侧核、外侧缰核、后核及外侧核亦有到前额叶皮质的传入投射,且投射到前额叶皮质不同部位的数量不同。丘脑下部的传入主要来自外侧区、外侧视前区、尾侧大细胞核及乳头体上核,少量传入也可见于丘脑下部后区、背内侧核、腹内侧核及未定带。皮质下端脑的传入主要来自苍白球,其次为斜角带核、隔核、杏仁核及屏状核。在隔核中,除内侧隔核外还观察到外侧隔核,繖隔核及三角隔核亦投射到前额叶皮质。杏仁核中除杏仁外侧核、杏仁基底核外侧部及内侧部外,还观察到杏仁内侧核及杏仁皮质核亦有少量到前额叶皮质的传入。     

Monoclonal antibody Cat-301 selectively identifies a subset of nuclei in the cat''s somatosensory thalamus

Summary Recently it has been demonstrated that the monoclonal antibody Cat-301 is capable of identifying functionally related neurons in the mammalian visual thalamus. We have examined the possibility that this antibody might display a similar capacity in nonvisual thalamic areas. We demonstrate that in the cat's somatosensory thalamus the distribution of Cat-301-positive cells and neuropil is restricted to a subset of nuclei. These include the ventroposterior medial, ventroposterior lateral, and ventroposterior inferior nuclei. Staining with Cat-301 provides a clear visualisation of the entire somatotopic map within these nuclei. The somatosensory sector of the thalamic reticular nucleus and the perireticular nucleus, which may have a somatosensory sector, are also Cat-301-positive. In contrast, cells that do not express the Cat-301 antigen are located in the ventroposterior oralis nucleus, the ventroposterior shell region, the medial and lateral divisions of the posterior nuclear group, and the inner small cell region adjacent to the thalamic reticular nucleus. In comparison with previous physiological studies, cells that express the Cat-301 antigen most likely represent subpopulations in only a few of the somatic submodality-specific groups. These include cells in the small-field and Pacinian cutaneous-responsive groups, excluding cells in the wide-field cutaneous-, muscle-, joint-, and noxious-responsive groups. Taken together these findings indicate that monoclonal antibody Cat-301 is capable of selectively identifying neurons with distinct functional properties in the mammalian somatosensory thalamus.     

Connections to the lateral posterior-pulvinar thalamic complex from the reticular and ventral lateral geniculate thalamic nuclei: a topographical study in the cat

The projections from the reticular thalamic nucleus and the ventral lateral geniculate nucleus to the lateral posterior-pulvinar thalamic complex were studied in the adult cat using the retrograde transport of horseradish peroxidase. Small, stereotaxically guided injections of the enzyme were placed in the various nuclei of this complex, including the pulvinar, lateralis intermedius oralis, lateralis intermedius caudalis, lateralis posterior lateralis, lateralis posterior medialis and lateralis medialis nuclei. The distribution of labeled neurons indicates that these nuclei receive topographically organized projections from the reticular and ventral lateral geniculate nuclei. The pulvinar nucleus receives only very scarce projections from the reticular thalamic nucleus originating in its posterodorsal and posteroventral sectors. The reticular projection to the nucleus lateralis intermedius oralis is even sparser. The nuclei lateralis intermedius caudalis, lateralis posterior lateralis and lateralis posterior medialis receive substantial projections from the suprageniculate sector of the reticular thalamic nucleus. The nucleus lateralis medialis receives an abundant projection from the three sectors (suprageniculate, pregeniculate and infrageniculate) of the reticular thalamic nucleus. Except for the lateralis intermedius caudalis, all nuclei of the lateral posterior-pulvinar complex receive consistent projections from the ventral lateral geniculate nucleus, the nucleus lateralis medialis receiving the densest one. Our findings suggest that visual, auditory, somatosensory, motor and limbic impulses from thalamic nuclei and from primary sensory and association cortical areas modulate the activity of the nucleus lateralis medialis via the reticular thalamic nucleus. The remaining nuclei of the lateral posterior-pulvinar complex are mainly modulated by sectors of the reticular thalamic nucleus that receive afferent connections from visual structures. The intrathalamic projections arising from the ventral lateral geniculate nucleus may be the way through which visuomotor inputs reach the different components of the lateral posterior-pulvinar thalamic complex.     

Efferent connections of an auditory area in the caudal insular cortex of the rat: anatomical nodes for cortical streams of auditory processing and cross-modal sensory interactions

In the rat cortex, the two non-primary auditory areas, posterodorsal and ventral auditory areas, may constitute the two streams of auditory processing in their distinct projections to the posterior parietal and insular cortices. The posterior parietal cortex is considered crucial for auditory spatial processing and directed attention, while possible auditory function of the insular cortex is largely unclear. In this study, we electrophysiologically delineated an auditory area in the caudal part of the granular insular cortex (insular auditory area, IA) and examined efferent connections of IA with anterograde tracer biocytin to deduce the functional significance of IA. IA projected to the rostral agranular insular cortex, a component of the lateral prefrontal cortex. IA also projected to the adjacent dysgranular insular cortex and the caudal agranular insular cortex and sent feedback projections to cortical layer I of the primary and secondary somatosensory areas. Corticofugal projections terminated in auditory, somatosensory and visceral thalamic nuclei, and the bottom of the thalamic reticular nucleus that could overlap the visceral sector. The ventral part of the caudate putamen, the external cortex of the inferior colliculus and the central amygdaloid nucleus were also the main targets. IA exhibited neural response to transcutaneous electrical stimulation of the forepaw in addition to acoustic stimulation (noise bursts and pure tones). The results suggest that IA subserves diverse functions associated with somatosensory, nociceptive and visceral processing that may underlie sound-driven emotional and autonomic responses. IA, being potentially involved in such extensive cross-modal sensory interactions, could also be an important anatomical node of auditory processing linked to higher neural processing in the prefrontal cortex.     

Somatosensory systems and the milk-ejection reflex in the rat. II. The effects of lesions in the ventroposterior thalamic complex, dorsal columns and lateral cervical nucleus-dorsolateral funiculus

Bilateral electrolytic lesions of some somatosensory structures in the thalamus and spinal cord were made in order to assess their participation in the afferent limb of the milk-ejection reflex in the rat. Lesions involving the lateral cervical nucleus and a part of the dorsolateral funiculus region blocked the milk-ejection reflex, whereas animals with lesions in the dorsal column of the spinal cord or in the ventroposterior complex of the thalamus displayed milk-ejection reflexes similar to those of control animals. Unilateral injections of horseradish peroxidase coupled to wheat germ agglutinin were made after lesioning the lateral cervical nucleus and part of the dorsolateral funiculus. Anterograde labelling was seen mainly contralateral to the injection site: in the external nucleus of the inferior colliculus, the intercollicular zone, the brachium of the inferior colliculus, the lateral reticular nucleus of the thalamus and in the thalamic ventroposterior complex. Sparse projections ipsilateral to the injection site were also observed. These results, combined with our previous observations, suggest that the projection of the lateral cervical nucleus on the mesencephalon is part of the pathway which conveys the sensory information from the suckling stimulus.     

The organization of lateral ventromedial thalamic connections in the rat: a link for the distribution of nociceptive signals to widespread cortical regions

We have used several anatomical tracing techniques to study the organization of the lateral ventromedial thalamic nucleus in the rat, a region that is selectively activated by cutaneous nociceptive inputs from any part of the body. The lateral ventromedial thalamic projections are organized as a widespread dense band covering mainly layer I of the dorsolateral anterior-most aspect of the cortex. This band diminishes progressively as one moves caudally, disappearing completely at 1mm caudal to bregma level. These widespread projections contrast with the circumscribed projections to the deep layers of the primary somatosensory and insular cortices from the adjacent ventral posteromedial and ventroposterior parvicellular thalamic regions, respectively. Injections into the lateral part of the ventromedial thalamic nucleus of an anterograde/retrograde tracer showed that the cortical layer I areas showing the densest projections from this thalamic region also contain the greatest number of retrogradely labeled cells in cortical layers V and VI. The same injections retrogradely labeled numerous cells which were confined to the dorsal subnucleus reticularis dorsalis in an area that contains a concentration of neurons with widespread nociceptive convergence. Finally, the lateral part of the ventromedial thalamic nucleus was also differentially labeled following a topical application of tetramethylrhodamine-labeled dextran on the dorsolateral anterior cortex. These findings suggest that lateral ventromedial thalamic neurons could be part of a spino-reticulo-thalamo-cortical network that allows signals of pain from any part of the body surface to spread across widespread cortical areas.     

Corticothalamic and thalamocortical pathfinding in the mouse: dependence on intermediate targets and guidance axis

Recently, increasing attention has been paid to the study of intermediate targets and their relay guidance role in long-range pathfinding. In the present study, mechanisms of corticothalamic and thalamocortical pathfinding were investigated in C57BL/6 mice using in vitro DiI labeling and in vivo cholera toxin labeling. Specifically, three important intermediate targets, the subplate, ganglionic eminence, and reticular thalamic nucleus, were studied for their role in corticothalamic and thalamocortical pathfinding. The results show that the neuroepithelium of the ganglionic eminence is a source of pioneer neurons and pioneer fibers. Through radial and tangential migration, these pioneer neurons and fibers can approach the differentiating field of the ganglionic eminence, the subplate and thalamic reticular nucleus to participate in the formation of these three intermediate targets. Furthermore, the subplate, ganglionic eminence and thalamic reticular nucleus are linked by pioneer neurons and fibers to form a guidance axis. The guidance axis and the three important intermediate targets provide an ideal environment of contact guidance and chemical guidance for the corticothalamic and thalamocortical pathfinding. The concept of a "waiting time" in the subplate and the thalamic reticular nucleus is likely due to the expression of a guidance effect, so that the thalamocortical and corticothalamic projections can be deployed spatially and temporally to the subplate and thalamic reticular nucleus before these projections enter their final destinations, the neocortex and thalamus.Abbreviations CLSM confocal laser scanning microscope - CP cortical plate - DF differentiating field - E embryonic day - GE ganglionic eminence - IC internal capsule - IZ intermediate zone - MZ marginal zone - NP neuroepithelium - P postnatal day - PB phosphate buffer - PBS phosphate-buffered saline - Po posterior group nucleus - Pr5 principle sensory trigeminal nucleus - SI somatosensory cortex - SP subplate - SZ subventricular zone - RT reticular thalamic nucleus - V ventricle - VPM ventral posterior medial nucleus - VZ ventricular zone - WGA wheat germ agglutinin - WM white matter     

Cortical projections from the suprasylvian gyrus to the reticular thalamic nucleus in the cat

The cat's suprasylvian gyrus was injected iontophoretically with either 4% wheat germ agglutinin-horseradish peroxidase, 4% dextran-fluororuby or 4% dextran-biotin. The locations of labelled fibres, presumed terminals and cell bodies were determined with the aid of a camera lucida attachment and computer aided stereometry. Cells from the crown of the suprasylvian gyrus project to the dorsal-most portion of the rostral half of the reticular nucleus. The region or 'sector' is distinct, albeit with some overlap, from the visual sector of the reticular nucleus defined by projections from adjacent extrastriate visual cortices. The projection from the suprasylvian gyrus to the reticular nucleus has a rough topography such that the caudal areas project to the more caudal aspects of the sector and rostral areas project to the more rostral areas of the reticular nucleus. There is a large degree of overlap of rostrocaudal projections from the suprasylvian gyrus within the sector, however, the projections originating from rostral sites are situated in a more ventral location compared to the projection originating from the caudal suprasylvian gyrus. Analysis of the distribution of biotin labelled presumptive terminals did not support the notion of 'slabs' or regional variation in terminal density across the mediolateral thickness of the reticular nucleus. In addition, a number of presumptive terminals were found within the internal capsule which coincided with the position of retrogradely labelled cells in the internal capsule following thalamic injections and appears to be part of the perireticular nucleus.The results suggest that the reticular nucleus may be segregated into sectors connected with modality specific cortical areas (e.g. striate and extrastriate visual areas) and nonspecific sectors connected with polymodal (e.g. area 7) cortical regions. The reticular nucleus and its connections with the suprasylvian gyrus may form an important link in binding eye movements to sensory integrative process through visuomotor and auditory thalamic connections.     

Projections to the rostral reticular thalamic nucleus in the rat

Summary Afferent pathways to the rostral reticular thalamic nucleus (Rt) in the rat were studied using anterograde and retrograde lectin tracing techniques, with sensitive immunocytochemical methods. The analysis was carried out to further investigate previously described subregions of the reticular thalamic nucleus, which are related to subdivisions of the dorsal thalamus, in the paraventricular and midline nuclei and three segments of the mediodorsal thalamic nucleus. Cortical inputs to the rostral reticular nucleus were found from lamina VI of cingulate, orbital and infralimbic cortex. These projected with a clear topography to lateral, intermediate and medial reticular nucleus respectively. Thalamic inputs were found from lateral and central segments of the mediodorsal nucleus to the lateral and intermediate rostral reticular nucleus respectively and heavy paraventricular thalamic inputs were found to the medial reticular nucleus. In the basal forebrain, afferents were found from the vertical and horizontal limbs of the diagonal band, substantia innominata, ventral pallidum and medial globus pallidus. Brainstem projections were identified from ventrolateral periaqueductal grey and adjacent sites in the mesencephalic reticular formation, laterodorsal tegmental nucleus, pedunculopontine nucleus, medial pretectum and ventral tegmental area. The results suggest a general similarity in the organisation of some brainstem Rt afferents in rat and cat, but also show previously unsuspected inputs. Furthermore, there appear to be at least two functional subdivisions of rostral Rt which is reflected by their connections with cortex and thalamus. The studies also extend recent findings that the ventral striatum, via inputs from the paraventricular thalamic nucleus, is included in the circuitry of the rostral Rt, providing further evidence that basal ganglia may function in concert with Rt. Evidence is also outlined with regard to the possibility that rostral Rt plays a significant role in visuomotor functions.Abbreviations ac anterior commissure - aca anterior commissure, anterior - Acb accumbens nucleus - AI agranular insular cortex - AM anteromedial thalamic nucleus - AV anteroventral thalamic nucleus - BST bed nucleus of stria terminalis - Cg cingulate cortex - CG central gray - CL centrolateral thalamic nucleus - CM central medial thalamic nucleus - CPu caudate putamen - DR dorsal raphe nucleus - DTg dorsal tegmental nucleus - EP entopeduncular nucleus - f fornix - Fr2 Frontal cortex, area 2 - G gelatinosus thalamic nucleus - GP globus pallidus - Hb habenula - HDB horizontal limb of diagonal band - IAM interanterodorsal thalamic nucleus - ic internal capsule - INC interstitial nucleus of Cajal - IF interfascicular nucleus - IL infralimbic cortex - IP interpeduncular nucleus - LC locus coeruleus - LDTg laterodorsal tegmental nucleus - LH lateral hypothalamus - LHb lateral habenular nucleus - ll lateral lemniscus - LO lateral orbital cortex - LPB lateral parabrachial nucleus - MD mediodorsal thalamic nucleus - MDL mediodorsal thalamic nucleus, lateral segment - Me5 mesencephalic trigeminal nucleus - MHb medial habenular nucleus - mlf medial longitudinal fasciculus - MnR median raphe nucleus - MO medial orbital cortex - mt mammillothalamic tract - OPT olivary pretectal nucleus - pc posterior commissure - PC paracentral thalamic nucleus - PF parafascicular thalamic nucleus - PPTg pedunculopontine tegmental nucleus - PrC precommissural nucleus - PT paratenial thalamic nucleus - PV paraventricular thalamic nucleus - PVA paraventricular thalamic nucleus, anterior - R red nucleus - Re reuniens thalamic nucleus - RRF retrorubral field - Rt reticular thalamic nucleus - Scp superior cerebellar peduncle - SI substantia innominata - sm stria medullaris - SNR substantia nigra, reticular - st stria terminalis - TT tenia tecta - VL ventrolateral thalamic nucleus - VO ventral orbital cortex - VP ventral pallidum - VPL ventral posterolateral thalamic nucleus - VTA ventral tegmental area - 3 oculomotor nucleus - 3V 3rd ventricle - 4 trochlear nucleus     

大鼠间脑到前额叶皮质的传入投射——FG逆行追踪法

目的:探讨间脑中神经核向前额叶中央外侧区的投射.方法:用荧光金(FG)逆行追踪法对15只Wistar大鼠进行研究.结果:大鼠前额叶中央外侧区接受同侧丘脑前内侧核,丘脑前腹核;丘脑腹内侧核,丘脑腹外侧核,丘脑腹后内侧核,丘脑腹后外侧核;丘脑内侧背核中间部、外侧部、内侧部,丘脑外侧背核;丘脑后核,丘脑外侧后核;丘脑板内核的中央内侧核,中央旁核,中央外侧核,丘脑束旁核;丘脑中线核的丘脑带旁核,丘脑菱形核,丘脑连结核,丘脑室旁核;丘脑网状核,膝上核;下丘脑的室旁核,室周核,下丘脑后区,下丘脑外侧区,乳头体上核,乳头体内侧核.下丘脑外侧大细胞核,外侧视前区,内侧视前区及丘脑底部中的未定带,Forel区,丘脑底核的投射纤维.结论:前额叶中央外侧区接受广泛的间脑核团的投射,并存在着局部定位的关系.     

The pathways connecting the hippocampal formation, the thalamic reuniens nucleus and the thalamic reticular nucleus in the rat

Most dorsal thalamic nuclei send axons to specific areas of the neocortex and to specific sectors of the thalamic reticular nucleus; the neocortex then sends reciprocal connections back to the same thalamic nucleus, directly as well indirectly through a relay in the thalamic reticular nucleus. This can be regarded as a 'canonical' circuit of the sensory thalamus. For the pathways that link the thalamus and the hippocampal formation, only a few comparable connections have been described. The reuniens nucleus of the thalamus sends some of its major cortical efferents to the hippocampal formation. The present study shows that cells of the hippocampal formation as well as cells in the reuniens nucleus are retrogradely labelled following injections of horseradish peroxidase or fluoro-gold into the rostral part of the thalamic reticular nucleus in the rat. Within the hippocampal formation, labelled neurons were localized in the subiculum, predominantly on the ipsilateral side, with fewer neurons labelled contralaterally. Labelled neurons were seen in the hippocampal formation and nucleus reuniens only after injections made in the rostral thalamic reticular nucleus (1.6-1.8 mm caudal to bregma). In addition, the present study confirmed the presence of afferent connections to the rostral thalamic reticular nucleus from cortical (cingulate, orbital and infralimbic, retrosplenial and frontal), midline thalamic (paraventricular, anteromedial, centromedial and mediodorsal thalamic nuclei) and brainstem structures (substantia nigra pars reticularis, ventral tegmental area, periaqueductal grey, superior vestibular and pontine reticular nuclei). These results demonstrate a potential for the thalamo-hippocampal circuitry to influence the functional roles of the thalamic reticular nucleus, and show that thalamo-hippocampal connections resemble the circuitry that links the sensory thalamus and neocortex.     

大白鼠扣带回3区向杏仁体及其他核群的纤维投射——菜豆白细胞凝集素顺行示踪研究

本文用菜豆自细胞凝集素免疫组织化学顺行示踪技术,观察大白鼠扣带回3区(Cg3)向皮质下核团的纤维投射。其投射区自前向后主要有:伏核、尾壳核内侧1/3、终纹床核、外侧视前区、带旁核、丘脑前内侧核、背内侧核、前室旁核、网状核、外侧缰核、后室旁核、束旁核及丘脑筛状核等。在丘脑下方,标记纤维密集于未定带、内囊的内侧边缘区和乳头丘脑束的周围。自这些区域,有纤维投射至下丘脑外侧区。本文着重分析了标记纤维在杏仁体的分布情况,标记纤维密集于基底外侧前核和外侧核的腹内侧亚核。从而证实Cg3皮质的纤维投射参与基底外侧核一边缘系环路,即所谓记忆环路。而杏仁体中央核仅偶见极稀疏的标记纤维。所以我们认为,Cg3皮质未参与“内脏环路”。标记纤维自注射侧经胼胝体膝至对侧半球,其投射区与注射侧的投射区一致,但标记纤维比较稀疏。     

猫丘脑中央外侧核的皮质下传入联系

本实验用HRP逆行性轴浆运输技术,对猫丘脑中央外侧核的传入纤维联系及其局部定位关系进行了观察。投射至丘脑中央外侧核尾侧区的主要核团包括:外侧膝状体腹核背侧带、丘脑网状核特别是它的背侧部、上丘深层,以同侧为主。板内核、丘脑下部外侧区和黑质网状部神经元的轴突终止在同侧丘脑中央外侧核吻侧区。丘脑中央外侧核全长的传入起自脑干网状结构和前庭神经核,呈双侧投射。前者以同侧为主,后者以对侧占优势。同侧未定带,顶盖前区、动眼神经核周围的细胞群、对侧三叉神经感觉主核、楔束核、薄束核以及小脑齿状核内也含有少量标记细胞。我们还观察到HRP注射中心区位于中央外侧核并扩散至丘脑腹前核者,同侧脚内核含大量HRP阳性细胞,而Gudden被盖腹侧核内充满密集的标记终末。这些结果表明,丘脑中央外侧核可能涉及多种感觉和运动功能。     

Acetylcholinesterase histochemistry in the macaque thalamus reveals territories selectively connected to frontal, parietal and temporal association cortices

The patterns of histochemical staining for acetylcholinesterase (AChE) activity in the macaque thalamus were analyzed and compared with the distribution of cells and terminals labeled from injections of axonal tracers in the dorsolateral and orbital prefrontal cortex, in area 7a of the posterior parietal cortex and in the polysensory cortex of the superior temporal sulcus. AChE histochemistry is very useful in delineating the thalamic nuclei connected with the association cortex and in uncovering thalamic subdivisions that are barely evident on cytoarchitectonic grounds. Moreover, AChE activity reveals previously unrecognized heterogeneities within several thalamic nuclei, like the ventral anterior (VA), where a new ventromedial subdivision (VAvm) is described, the medial pulvinar (PuIM) or the mediodorsal nucleus (MD). In this nucleus three distinct chemical domains are present: the medial, ventral and lateral sectors characterized by low, moderate and high AChE activities, respectively. The staining pattern of the lateral sector is markedly heterogeneous with patches of intense AChE activity surrounded by a moderately stained matrix. The MD medial sector is connected with the orbitofrontal cortex, whereas the AChE-rich patches in the lateral sector are selectively connected with the dorsolateral prefrontal, parietal and temporal association cortices. In the PulM, a dorsomedial AChE-rich patch is selectively connected with the orbitofrontal cortex, whereas the surrounding territory, which shows moderate AChE activity, is preferentially connected with the parietal and temporal cortices. Chemically specific domains in the anterior, ventral anterior, midline, and intralaminar thalamic nuclei are also connected with the examined association cortices. These findings indicate that the topographic patterns of the thalamo-cortical connections of primate association areas conform to the chemical architecture of the thalamus. This implies that because each cortical area is connected to a particular set of thalamic regions, the influence of the thalamus on cortical function is exclusive for each area, highly diverse among the various association areas, and subject to a wide range of modulation at the thalamic level.     

Modulation of inhibitory activity by nitric oxide in the thalamus

The dorsal lateral geniculate nucleus (dLGN) is essential for the transfer of visual information from the retina to visual cortex, and inhibitory mechanisms can play a critical in regulating such information transfer. Nitric oxide (NO) is an atypical neuromodulator that is released in gaseous form and can alter neural activity without direct synaptic connections. Nitric oxide synthase (NOS), an essential enzyme for NO production, is localized in thalamic inhibitory neurons and cholinergic brain stem neurons that innervate the thalamus, although NO-mediated effects on thalamic inhibitory activity remain unknown. We investigated NO effects on inhibitory activity in dLGN using an in vitro slice preparation. The NO donor, SNAP, selectively potentiated the frequency, but not amplitude, of spontaneous inhibitory postsynaptic currents (sIPSCs) in thalamocortical relay neurons. This increase also persisted in tetrodotoxin (TTX), consistent with an increase in GABA release from presynaptic terminals. The SNAP-mediated actions were attenuated not only by the NO scavenger carboxy-PTIO but also by the guanylyl cyclase inhibitor ODQ. The endogenous NO precursor L-arginine produced actions similar to those of SNAP on sIPSC activity and these L-arginine-mediated actions were attenuated by the NOS inhibitor L-NMMA acetate. The SNAP-mediated increase in sIPSC activity was observed in both dLGN and ventrobasal thalamic nucleus (VB) neurons. Considering the lack of interneurons in rodent VB, the NO-mediated actions likely involve an increase in the output of axon terminals of thalamic reticular nucleus neurons. Our results indicate that NO upregulates thalamic inhibitory activity and thus these actions likely influence sensory information transfer through thalamocortical circuits.     

An analysis of potentially converging inputs to the rostral ventral thalamic nuclei of the cat

Summary Potentially convergent inputs to cerebellar-receiving and basal ganglia-receiving areas of the thalamus were identified using horseradish peroxidase (HRP) retrograde tracing techniques. HRP was deposited iontophoretically into the ventroanterior (VA), ventromedial (VM), and ventrolateral (VL) thalamic nuclei in the cat. The relative numbers of labeled neurons in the basal ganglia and the cerebellar nuclei were used to assess the extent to which the injection was in cerebellar-receiving or basal ganglia-receiving portions of thalamus. The rostral pole of VA showed reciprocal connections with prefrontal portions of the cerebral cortex. Only the basal ganglia and the hypothalamus provided non-thalamic input to modulate these cortico-thalamo-cortical loops. In VM, there were reciprocal connections with prefrontal, premotor, and insular areas of the cerebral cortex. The basal ganglia (especially the substantia nigra), and to a lesser extent, the posterior and ventral portions of the deep cerebellar nuclei, provided input to VM and may modulate these corticothalamo-cortical loops. The premotor cortical areas connected to VM include those associated with eye movements, and afferents from the superior colliculus, a region of documented importance in oculomotor control, also were labeled by injections into VM. The dorsolateral portion of the VA-VL complex primarily showed reciprocal connections with the medial premotor (area 6) cortex. Basal ganglia and cerebellar afferents both may modulate this cortico-thalamo-cortical loop, although they do not necessarily converge on the same thalamic neurons. The cerebellar input to dorsolateral VA-VL was from posterior and ventral portions of the cerebellar nuclei, and the major potential brainstem afferents to this region of thalamus were from the pretectum. Mid- and caudo-lateral portions of VL had reciprocal connections with primary motor cortex (area 4). The dorsal and anterior portions of the cerebellar nuclei had a dominant input to this corticothalamo-cortical loop. Potentially converging brainstem afferents to this portion of VL were from the pretectum, especially pretectal areas to which somatosensory afferents project.List of Abbreviations AC central amygdaloid nucleus - AL lateral amygdaloid nucleus - AM anteromedial thalamic nucleus - AV anteroventral thalamic nucleus - BC brachium conjunctivum - BIC brachium of the inferior colliculus - Cd caudate nucleus - CL centrolateral thalamic nucleus - CM centre median nucleus - CP cerebral peduncle - CUN cuneate nucleus - DBC decussation of the brachium conjunctivum - DR dorsal raphe nuclei - EC external cuneate nucleus - ENTO entopeduncular nucleus - FN fastigial nucleus - FX fornix - GP globus pallidus - GR gracile nucleus - IC internal capsule - ICP inferior cerebellar peduncle - IP interpeduncular nucleus - IVN inferior vestibular nucleus - LD lateral dorsal thalamic nucleus - LGN lateral geniculate nucleus - LH lateral hypothalamus - LP lateral posterior thalamic complex - LRN lateral reticular nucleus - LVN lateral vestibular nucleus - MB mammillary body - MD mediodorsal thalamic nucleus - MG medial geniculate nucleus - ML medial lemniscus - MLF medial lengitudinal fasciculus - MT mammillothalamic tract - MVN medial vestibular nucleus - NDBB nucleus of the diagonal band of Broca - NIA anterior nucleus interpositus - NIP posterior nucleus interpositus - OD optic decussation - OT optic tract - PAC paracentral thalamic nucleus - PPN pedunculopontine region - PRO gyrus proreus - PRT pretectal region - PT pyramidal tract - PTA anterior pretectal region - PTM medial pretectal region - PTO olivary pretectal nucleus - PTP poterior pretectal region - Pul pulvinar nucleus - Put putamen - RF reticular formation - RN red nucleus - Rt reticular complex of the thalamus - S solitary tract - SCi superior colliculus, intermediate gray - SN substantia nigra - ST subthalamic nucleus - VA ventroanterior thalamic nucleus - VB ventrobasal complex - VL ventrolateral thalamic nucleus - VM ventromedial thalamic nucleus - III oculomotor nucleus - IIIn oculomotor nerve - 5S spinal trigeminal nucleus - 5T spinal trigeminal tract - VII facial nucleus     

Efferent connections of the medial prefrontal cortex in the rabbit

The different cytoarchitectonic regions of the medial prefrontal cortex (mPFC) have recently been shown to play divergent roles in associative learning in rabbits. To determine if these subareas of the mPFC, including areas 24 (anterior cingulate cortex), 25 (infralimbic cortex), and 32 (prelimbic cortex) have differential efferent connections with other cortical and subcortical areas in the rabbit, anterograde and retrograde tracing experiments were performed using the Phaseolus vulgaris leukoagglutinin (PHA-L), and horseradish peroxidase (HRP) techniques. All three areas showed local dorsal-ventral projections into each of the other areas, and a contralateral projection to the homologous area on the other side of the brain. All three also revealed a trajectory through the striatum, resulting in heavy innervation of the caudate nucleus, the claustrum, and a lighter projection to the agranular insular cortex. The thalamic projections of areas 24 and 32 were similar, but not identical, with projections to the mediodorsal nucleus (MD) and all of the midline nuclei. However, the primary thalamic projections from area 25 were to the intralaminar and midline nuclei. All three areas also projected to the ventromedial and to a lesser extent to the ventral posterior thalamic nuclei. Projections were also observed in the lateral hypothalamus, in an area just lateral to the descending limb of the fornix. Amygdala projections from areas 32 and 24 were primarily to the lateral, basolateral and basomedial nuclei, but area 25 also projected to the central nucleus. All three areas also showed projections to the midbrain periaqueductal central gray, median raphe nucleus, ventral tegmental area, substantia nigra, locus coeruleus and pontine nuclei. However, only areas 24 and the more dorsal portions of area 32 projected to the superior colliculus. Area 25 and the ventral portions of area 32 also showed a bilateral projection to the parabrachial nuclei and dorsal and ventral medulla. The dorsal portions of area 32, and all of area 24 were, however, devoid of these projections. It is suggested that these differential projections are responsible for the diverse roles that the cytoarchitectonic subfields of the mPFC have been demonstrated to play in associative learning.Abbreviations ACC anterior cingullate cortex - ACN amygdaloid central nucleus - AD anterodorsal nucleus of thalamus - AIC, Iag agranular insular cortex - AM anteromedial nucleus of thalamus - AMG amygdala - AV anteroventral nucleus of thalamus - BL basolateral nucleus of amygdala - BM basomedial nucleus of amygdala - CdN, CD caudate nucleus - CL claustrum - CN centromedian nucleus of thalamus - D MV, DVM dorsal motor nucleus of vagus - IC internal capsule - L lateral nucleus of amygdala - LC locus coeruleus - LH lateral hypothalamus - MB mammillary bodies - MDN mediodorsal nucleus of thalamus - mPFC medial prefrontal cortex - MRN, R median raphe nucleus - MV medioventral nucleus of thalamus - NA nucleus ambiguus - NTS nucleus of solitary tract - PAG periaqueductal central gray - PAV, PV para ventricular nucleus of thalamus - PC paracentral nucleus of thalamus - PF parafascicular nucleus of thalamus - PN,LP pontine nuclei - PS posterior subiculum - PS CG posterior cingulate cortex - PT paratenial nucleus of thalamus - Put putamen - ReN nucleus reuniens of thalamus - RF reticular formation - RN reticular nucleus of thalamus - RhN rhomboid nucleus of thalamus - RS CX retrosplenial cortex - S septum - SC superior colliculus - SN substantia nigra - tt tenia tecta - VL ventrolateral nucleus of thalamus - VM ventromedial nucleus of thalamus - VP ventroposterior nucleus of thalamus - VTA ventral tegmental area     

Thalamocortical projections activated by phrenic nerve afferents in the cat

This study identified thalamocortical projections activated by respiratory afferents. Cortical evoked potentials were recorded in the right primary somatosensory cortex of the cat following electrical stimulation of the left C5 root of the phrenic nerve. The majority of primary sites were located in the vicinity of the postcruciate dimple, in area 3a near the 3a/3b border, corresponding to the trunk region of the cortical body map. Retrograde fluorescent tracers injected at the sites of primary activation produced labeled cells in the oralis nucleus of the ventroposterior complex [4]. Control injections made in adjacent cortical areas not activated by phrenic stimulation resulted in labeling in the ventroposterior complex which did not overlap that seen with injections of primary activation sites. We conclude that respiratory muscle afferents in the phrenic nerve elicit activity in the trunk region of primary somatosensory cortex via specific thalamocortical projections originating in the oralis portion of the thalamic ventroposterior complex.     

Cyto- and chemoarchitecture of the dorsal thalamus of the monotreme Tachyglossus aculeatus,the short beaked echidna

We have examined the cyto- and chemoarchitecture of the dorsal thalamus of the short beaked echidna (Tachyglossus aculeatus), using Nissl and myelin staining, immunoreactivity for parvalbumin, calbindin, calretinin and non-phosphorylated neurofilament protein (SMI-32 antibody), and histochemistry for acetylcholinesterase and NADPH diaphorase. Immunohistochemical methods revealed many nuclear boundaries, which were difficult to discern with Nissl staining. Parvalbumin immunoreactive somata were concentrated in the ventral posterior, reticular, posterior, lateral and medial geniculate nuclei, while parvalbumin immunoreactivity of the neuropil was present throughout all but the midline nuclei. Large numbers of calbindin immunoreactive somata were also found within the midline thalamic nuclei, and thalamic sensory relay nuclei. Immunoreactivity for calretinin was found in many small somata within the lateral geniculate “a” nucleus, with other labelled somata found in the lateral geniculate “b” nucleus, ventral posterior medial and ventral posterior lateral nuclei. Immunoreactivity with the SMI-32 antibody was largely confined to somata and neuropil within the thalamocortical relay nuclei (ventral posterior medial and lateral nuclei, lateral and medial geniculate nuclei and the posterior thalamic nucleus). In broad terms there were many similarities between the thalamus of this monotreme and that of eutheria (e.g. disposition of somatosensory thalamus, complementarity of parvalbumin and calbindin immunoreactive structures), but there were some unique features of the thalamus of the echidna. These include the relatively small size of the thalamic reticular nucleus and the preponderance of calbindin immunoreactive neurons over parvalbumin immunoreactive neurons in the ventral posterior nucleus.