Neurochemical organization of chimpanzee inferior pulvinar complex

Cortical projections to the two retinotopic maps of primate pulvinar are distinct

Comprised of at least five distinct nuclei, the pulvinar complex of primates includes two large visually driven nuclei; one in the dorsal (lateral) pulvinar and one in the ventral (inferior) pulvinar, that contain similar retinotopic representations of the contralateral visual hemifield. Both nuclei also appear to have similar connections with areas of visual cortex. Here we determined the cortical connections of these two nuclei in galagos, members of the stepsirrhine primate radiation, to see if the nuclei differed in ways that could support differences in function. Injections of different retrograde tracers in each nucleus produced similar patterns of labeled neurons, predominately in layer 6 of V1, V2, V3, MT, regions of temporal cortex, and other visual areas. More complete labeling of neurons with a modified rabies virus identified these neurons as pyramidal cells with apical dendrites extending into superficial cortical layers. Importantly, the distributions of cortical neurons projecting to each of the two nuclei were highly overlapping, but formed separate populations. Sparse populations of double-labeled neurons were found in both V1 and V2 but were very low in number (<0.1%). Finally, the labeled cortical neurons were predominately in layer 6, and layer 5 neurons were labeled only in extrastriate areas. Terminations of pulvinar projections to area 17 was largely in superficial cortical layers, especially layer 1.

Architectonic characteristics of the visual thalamus and superior colliculus in titi monkeys

Titi monkeys are arboreal, diurnal New World monkeys whose ancestors were the first surviving branch of the New World radiation. In the current study, we use cytoarchitectonic and immunohistochemical characteristics to compare titi monkey subcortical structures associated with visual processing with those of other well-studied primates. Our goal was to appreciate features that are similar across all New World monkeys, and primates in general, versus those features that are unique to titi monkeys and other primate taxa. We examined tissue stained for Nissl substance, cytochrome oxidase (CO), acetylcholinesterase (AChE), calbindin (Cb), parvalbumin (Pv), and vesicular glutamate transporter 2 (VGLUT2) to characterize the superior colliculus, lateral geniculate nucleus, and visual pulvinar. This is the first study to characterize VGLUT2 in multiple subcortical structures of any New World monkey. Our results from tissue processed for VGLUT2, in combination with other histological stains, revealed distinct features of subcortical structures that are similar to other primates, but also some features that are slightly modified compared to other New World monkeys and other primates. These included subdivisions of the inferior pulvinar, sublamina within the stratum griseum superficiale (SGS) of the superior colliculus, and specific koniocellular layers within the lateral geniculate nucleus. Compared to other New World primates, many features of the subcortical structures that we examined in titi monkeys were most similar to those in owl monkeys and marmosets, with the lateral geniculate nucleus consisting of two main parvocellular layers and two magnocellular layers separated by interlaminar zones or koniocellular layers.

Unravelling the subcortical and retinal circuitry of the primate inferior pulvinar

The primate visual brain possesses a myriad of pathways, whereby visual information originating at the retina is transmitted to multiple subcortical areas in parallel, before being relayed onto the visual cortex. The dominant retinogeniculostriate pathway has been an area of extensive study, and Vivien Casagrande's work in examining the once overlooked koniocellular pathway of the lateral geniculate nucleus has generated interest in how alternate subcortical pathways can contribute to visual perception. Another subcortical visual relay center is the inferior pulvinar (PI), which has four subdivisions and numerous connections with other subcortical and cortical areas and is directly recipient of retinal afferents. The complexity of subcortical connections associated with the PI subdivisions has led to differing results from various groups. A particular challenge in determining the exact connectivity pattern has been in accurately targeting the subdivisions of the PI with neural tracers. Therefore, in the present study, we used a magnetic resonance imaging (MRI)-guided stereotaxic injection system to inject bidirectional tracers in the separate subdivisions of the PI, the superior layers of the superior colliculus, the retina, and the lateral geniculate nucleus. Our results have determined for the first time that the medial inferior pulvinar (PIm) is innervated by widefield retinal ganglion cells (RGCs), and this pathway is not a collateral branch of the geniculate and collicular projecting RGCs. Furthermore, our tracing data shows no evidence of collicular terminations in the PIm, which are confined to the centromedial and posterior PI.

The evolution and functions of nuclei of the visual pulvinar in primates

In this review, we outline the history of our current understanding of the organization of the pulvinar complex of mammals. We include more recent evidence from our own studies of both New and Old World monkeys, prosimian galagos, and close relatives of primates, including tree shrews and rodents. Based on cumulative evidence, we provide insights into the possible evolution of the visual pulvinar complex, as well as the possible co-evolution of the inferior pulvinar nuclei and temporal cortical visual areas within the MT complex.

Distribution of calcium-binding proteins in the pigeon visual thalamic centers and related pretectal and mesencephalic nuclei. Phylogenetic and functional determinants

Multichannel processing of environmental information constitutes a fundamental basis of functioning of sensory systems in the vertebrate brain. Two distinct parallel visual systems - the tectofugal and thalamofugal exist in all amniotes. The vertebrate central nervous system contains high concentrations of intracellular calcium-binding proteins (CaBPrs) and each of them has a restricted expression pattern in different brain regions and specific neuronal subpopulations. This study aimed at describing the patterns of distribution of parvalbumin (PV) and calbindin (CB) in the visual thalamic and mesencephalic centers of the pigeon (Columba livia). We used a combination of immunohistochemistry and double labeling immunofluorescent technique. Structures studied included the thalamic relay centers involved in the tectofugal (nucleus rotundus, Rot) and thalamofugal (nucleus geniculatus lateralis, pars dorsalis, GLd) visual pathways as well as pretectal, mesencephalic, isthmic and thalamic structures inducing the driver and/or modulatory action to the visual processing. We showed that neither of these proteins was unique to the Rot or GLd. The Rot contained i) numerous PV-immunoreactive (ir) neurons and a dense neuropil, and ii) a few CB-ir neurons mostly located in the anterior dorsal part and associated with a light neuropil. These latter neurons partially overlapped with the former and some of them colocalized both proteins. The distinct subnuclei of the GLd were also characterized by different patterns of distribution of CaBPrs. Some (nucleus dorsolateralis anterior, pars magnocellularis, DLAmc; pars lateralis, DLL; pars rostrolateralis, DLAlr; nucleus lateralis anterior thalami, LA) contained both CB- and PV-ir neurons in different proportions with a predominance of the former in the DLAmc and DLL. The nucleus lateralis dorsalis of nuclei optici principalis thalami only contained PV-ir neurons and a neuropil similar to the interstitial pretectal/thalamic nuclei of the tectothalamic tract, nucleus pretectalis and thalamic reticular nucleus. The overlapping distribution of PV and CB immunoreactivity was typical for the pretectal nucleus lentiformis mesencephali and the nucleus ectomamillaris as well as for the visual isthmic nuclei. The findings are discussed in the light of the contributive role of the phylogenetic and functional factors determining the circuits׳ specificity of the different CaBPr types.

Enlargement of thalamic nuclei in Tourette syndrome

CONTEXT

The basal ganglia and thalamus together connect in parallel closed-loop circuits with the cortex. Previous imaging studies have shown modifications of the basal ganglia and cortical targets in individuals with Tourette syndrome (TS), but less is known regarding the role of the thalamus in TS pathogenesis.

OBJECTIVE

To study the morphological features of the thalamus in children and adults with TS.

DESIGN

A cross-sectional, case-control study using anatomical magnetic resonance imaging.

SETTING

University research center.

PARTICIPANTS

The 283 participants included 149 with TS and 134 normal control individuals aged 6 to 63 years.

MAIN OUTCOME MEASURES

Conventional volumes and measures of surface morphology of the thalamus.

RESULTS

Analyses of conventional volumes and surface morphology were consistent in demonstrating an enlargement in TS-affected thalami. Overall volumes were 5% larger in the group composed of children and adults with TS. Statistical maps of surface contour demonstrated enlargement over the lateral thalamus. Post hoc testing indicated that differences in IQ, comorbid illnesses, and medication use did not account for these findings.

CONCLUSIONS

Morphological abnormalities in the thalamus, together with the disturbances reported in the sensorimotor cortex, striatum, and globus pallidus, support the hypothesis of a circuitwide disorder within motor pathways in TS. The connectivity and function of the numerous and diverse thalamic nuclei within cortical-subcortical circuits constitute an anatomical crossroad wherein enlargement of motor nuclei may represent activity-dependent hypertrophy within this component of cortical-subcortical motor circuits, or an adaptive response within a larger putative compensatory system that could thereby directly modulate activity in motor circuits to attenuate the severity of tics.

Cortical connections of the visual pulvinar complex in prosimian galagos (Otolemur garnetti)

The pulvinar complex of prosimian primates is not as architectonically differentiated as that of anthropoid primates. Thus, the functional subdivisions of the complex have been more difficult to determine. In the present study, we related patterns of connections of cortical visual areas (primary visual area, V1; secondary visual area, V2; and middle temporal visual area, MT) as well as the superior colliculus of the visual midbrain, with subdivisions of the pulvinar complex of prosimian galagos (Otolemur garnetti) that were revealed in brain sections processed for cell bodies (Nissl), cytochrome oxidase, or myelin. As in other primates, the architectonic methods allowed us to distinguish the lateral pulvinar (PL) and inferior pulvinar (PI) as major divisions of the visual pulvinar. The connection patterns further allowed us to divide PI into a large central nucleus (PIc), a medial nucleus (PIm), and a posterior nucleus (PIp). Both PL and PIc have separate topographic patterns of connections with V1 and V2. A third, posterior division of PI, PIp, does not appear to project to V1 and V2 and is further distinguished by receiving inputs from the superior colliculus. All these subdivisions of PI project to MT. The evidence suggests that PL of galagos contains a single, large nucleus, as in monkeys, and that PI may have only three subdivisions, rather than the four subdivisions of monkeys. In addition, the cortical projections of PI nuclei are more widespread than those in monkeys. Thus, the pulvinar nuclei in prosimian primates and anthropoid primates have evolved along somewhat different paths.

Giant neurons in the macaque pulvinar: a distinct relay subpopulation

Calbindin positive (CB+) giant neurons are known to occur within the pulvinar nucleus in subhuman primates. Here, we demonstrate by combined retrograde tracing and immunocytochemistry that at least some of these are pulvinocortical relay neurons, and further report several distinctive features. First, in contrast with non-giant relay neurons, the giant neurons are often solitary and isolated from a main projection focus. The question thus arises of whether their cortical projections may be non-reciprocal or otherwise distinctive. Second, these neurons are positive for GluR4; but third, they are otherwise neurochemically heterogeneous, in that about one-third are positive for both parvalbumin (PV) and CB. Presumably, these subpopulations are also functionally heterogeneous. These results provide further evidence for the idea of multiple, interleaved organizations within the pulvinar; and they imply that thalamocortical projections are more disparate than has yet been appreciated. Finally, we found that giant CB+ neurons have a distinctive meshwork of large, PV+ terminations, prominent at the first dendritic branch point. In size and location, these resemble inhibitory terminations from the zona incerta or anterior pretectal nucleus (APT), as recently described in higher order thalamic nuclei in rats. One can speculate that giant neurons in the macaque pulvinar participate in a layer 5-APT-thalamus (giant neuron) extrareticular pathway, functionally distinct from the layer 6-reticular nucleus-thalamus network.

Long-range interneurons within the medial pulvinar nucleus of macaque monkeys

Like other thalamic nuclei, the primate pulvinar is considered not to have long-range intrinsic connections, either excitatory or inhibitory. Injections of biotinylated dextran amine (BDA) in the medial pulvinar, however, reveal retrogradely filled neurons up to 2.0 mm from the injection edge. Serial section reconstruction (n = 18) confirmed that retrogradely filled neurons projected to the injection site and showed that they had additional long-range collaterals within the posterior pulvinar. Arrays of small, beaded terminations occurred in multiple foci along the collaterals. Terminal arrays were up to 1.0 mm in length; foci were separated by about 0.7 mm. Somata were large (average area = 220 microm2), and dendritic arbors were radiate and also large (about 1.0 mm in diameter), but without either the appendages of classical interneurons or the hairlike spines characteristic of radiate pulvinocortical projection neurons. Double labeling for BDA and parvalbumin (PV) or BDA and gamma-aminobutyric acid (GABA) indicated that these large neurons were positive for both PV and GABA. Double labeling for PV and GABA, or PV and glutamic acid decarboxylase 67 (GAD67) revealed a small number of similarly large neurons in the posterior pulvinar that were positive for both substances. Thus, we propose that these neurons are a novel class of inhibitory interneuron, longer range than the classic thalamic local circuit interneurons. Future questions include how these neurons relate to other inhibitory systems and specific postsynaptic populations and whether they are located preferentially within the posterior pulvinar, possibly related to the multimodal character of this thalamic region.