Pulvinar slits: Cellulose-deficient and de-methyl-esterified pectin-rich structures in a legume motor cell.

The cortical motor cells (CMCs) in a legume pulvinus execute the reversible deformation in leaf movement that is driven by changes in turgor pressure. In contrast to the underlying osmotic regulation property, the cell wall structure of CMCs that contributes to the movement has yet to be characterized in detail. Here, we report that the cell wall of CMCs has circumferential slits with low levels of cellulose deposition, which are widely conserved among legume species. This structure is unique and distinct from that of any other primary cell walls reported so far; thus, we named them "pulvinar slits." Notably, we predominantly detected de-methyl-esterified homogalacturonan inside pulvinar slits, with a low deposition of highly methyl-esterified homogalacturonan, as with cellulose. In addition, Fourier transform infrared spectroscopy analysis indicated that the cell wall composition of pulvini is different from that of other axial organs, such as petioles or stems. Moreover, monosaccharide analysis showed that pulvini are pectin-rich organs like developing stems and that the amount of galacturonic acid in pulvini is greater than in developing stems. Computer modeling suggested that pulvinar slits facilitate anisotropic extension in the direction perpendicular to the slits in the presence of turgor pressure. When tissue slices of CMCs were transferred to different extracellular osmotic conditions, pulvinar slits altered their opening width, indicating their deformability. In this study, we thus characterized a distinctive cell wall structure of CMCs, adding to our knowledge of repetitive and reversible organ deformation as well as the structural diversity and function of the plant cell wall.

Molecular changes in the absence of severe pathology in the pulvinar in dementia with Lewy bodies.

BACKGROUND: Dementia with Lewy bodies is characterized by transient clinical features, including fluctuating cognition and visual hallucinations, implicating dysfunction of cerebral hub regions, such as the pulvinar nuclei of the thalamus. However, the pulvinar is typically only mildly affected by Lewy body pathology in dementia with Lewy bodies, suggesting additional factors may account for its proposed dysfunction. METHODS: We conducted a comprehensive analysis of postmortem pulvinar tissue using whole-transcriptome RNA sequencing, protein expression analysis, and histological evaluation. RESULTS: We identified 321 transcripts as significantly different between dementia with Lewy bodies cases and neurologically normal controls, with gene ontology pathway analysis suggesting the enrichment of transcripts related to synapses and positive regulation of immune functioning. At the protein level, proteins related to synaptic efficiency were decreased, and general synaptic markers remained intact. Analysis of glial subpopulations revealed astrogliosis without activated microglia, which was associated with synaptic changes but not neurodegenerative pathology. DISCUSSION: These results indicate that the pulvinar, a region with relatively low Lewy body pathological burden, manifests changes at the molecular level that differ from previous reports in a more severely affected region. We speculate that these alterations result from neurodegenerative changes in regions connected to the pulvinar and likely contribute to a variety of cognitive changes resulting from decreased cortical synchrony in dementia with Lewy bodies. © 2018 International Parkinson and Movement Disorder Society.

Spatiotemporal Profile of Voltage-Sensitive Dye Responses in the Visual Cortex of Tree Shrews Evoked by Electric Microstimulation of the Dorsal Lateral Geniculate and Pulvinar Nuclei.

The primary visual cortex (V1) receives its main thalamic drive from the dorsal lateral geniculate nucleus (dLGN) through synaptic contacts terminating primarily in cortical layer IV. In contrast, the projections from the pulvinar nucleus to the cortex are less clearly defined. The pulvinar projects predominantly to layer I in V1, and layer IV in extrastriate areas. These projection patterns suggest that the pulvinar nucleus most strongly influences (drives) activity in cortical areas beyond V1. Should this hypothesis be true, one would expect the spatiotemporal responses evoked by pulvinar activation to be different in V1 and extrastriate areas, reflecting the different connectivity patterns. We investigated this issue by analyzing the spatiotemporal dynamics of cortical visual areas' activity following thalamic electrical microstimulation in tree shrews, using optical imaging and voltage-sensitive dyes. As expected, electrical stimulation of the dLGN induced fast and local responses in V1, as well as in extrastriate and contralateral cortical areas. In contrast, electrical stimulation of the pulvinar induced fast and local responses in extrastriate areas, followed by weak and diffuse activation in V1 and contralateral cortical areas. This study highlights spatiotemporal cortical activation characteristics induced by stimulation of first (dLGN) and high-order (pulvinar) thalamic nuclei. SIGNIFICANCE STATEMENT: The pulvinar nucleus represents the main extrageniculate thalamic visual structure in higher-order mammals, but its exact role remains enigmatic. The pulvinar receive prominent inputs from virtually all visual cortical areas. Cortico-thalamo-cortical pathways through the pulvinar nuclei may then provide a complementary route for corticocortical information flow. One step toward the understanding of the role of transthalamic corticocortical pathways is to determine the nature of the signals transmitted between the cortex and the thalamus. By performing, for the first time, high spatiotemporal mesoscopic imaging on tree shrews (the primate's closest relative) through the combination of voltage-sensitive dye recordings and brain stimulation, we revealed clear evidence of distinct thalamocortical functional connectivity pattern originating from the geniculate nucleus and the pulvinar nuclei.

Age and sex related differences in subcortical brain iron concentrations among healthy adults.

Age and sex can influence brain iron levels. We studied the influence of these variables on deep gray matter magnetic susceptibilities. In 183 healthy volunteers (44.7 ± 14.2 years, range 20-69, ♀ 49%), in vivo quantitative susceptibility mapping (QSM) at 1.5T was performed to estimate brain iron accumulation in the following regions of interest (ROIs): caudate nucleus (Cd), putamen (Pt), globus pallidus (Gp), thalamus (Th), pulvinar (Pul), red nucleus (Rn), substantia nigra (Sn) and the cerebellar dentate nuclei (Dn). We gauged the influence of age and sex on magnetic susceptibility by specifying a series of structural equation models. The distributions of susceptibility varied in degree across the structures, conforming to histologic findings (Hallgren and Sourander, 1958), with the highest degree of susceptibility in the Gp and the lowest in the Th. Iron increase correlated across several ROIs, which may reflect an underlying age-related process. Advanced age was associated with a particularly strong linear rise of susceptibility in the striatum. Nonlinear age trends were found in the Rn, where they were the most pronounced, followed by the Pul and Sn, while minimal nonlinear trends were observed for the Pt, Th, and Dn. Moreover, sex related variations were observed, so that women showed lower levels of susceptibility in the Sn after accounting for age. Regional susceptibility of the Pul increased linearly with age in men but exhibited a nonlinear association with age in women with a leveling off starting from midlife. Women expected to be post menopause (+51 years) showed lower total magnetic susceptibility in the subcortical gray matter. The current report not only is consistent with previous reports of age related variations of brain iron, but also adds to the current knowledge by reporting age-related changes in less studied, smaller subcortical nuclei. This is the first in-vivo report to show lower total subcortical brain iron levels selectively in women from midlife, compared to men and younger women. These results encourage further assessment of sex differences in brain iron. We anticipate that age and sex are important co-factors to take into account when establishing a baseline level for differentiating pathologic neurodegeneration from healthy aging. The variations in regional susceptibility reported herein should be evaluated further using a longitudinal study design to determine within-person changes in aging.

Comparative anatomy of marmoset and mouse cortex from genomic expression.

Advances in mouse neural circuit genetics, brain atlases, and behavioral assays provide a powerful system for modeling the genetic basis of cognition and psychiatric disease. However, a critical limitation of this approach is how to achieve concordance of mouse neurobiology with the ultimate goal of understanding the human brain. Previously, the common marmoset has shown promise as a genetic model system toward the linking of mouse and human studies. However, the advent of marmoset transgenic approaches will require an understanding of developmental principles in marmoset compared to mouse. In this study, we used gene expression analysis in marmoset brain to pose a series of fundamental questions on cortical development and evolution for direct comparison to existing mouse brain atlas expression data. Most genes showed reliable conservation of expression between marmoset and mouse. However, certain markers had strikingly divergent expression patterns. The lateral geniculate nucleus and pulvinar in the thalamus showed diversification of genetic organization between marmoset and mouse, suggesting they share some similarity. In contrast, gene expression patterns in early visual cortical areas showed marmoset-specific expression. In prefrontal cortex, some markers labeled architectonic areas and layers distinct between mouse and marmoset. Core hippocampus was conserved, while afferent areas showed divergence. Together, these results indicate that existing cortical areas are genetically conserved between marmoset and mouse, while differences in areal parcellation, afferent diversification, and layer complexity are associated with specific genes. Collectively, we propose that gene expression patterns in marmoset brain reveal important clues to the principles underlying the molecular evolution of cortical and cognitive expansion.

Iron content of the pulvinar nucleus of the thalamus is increased in adolescent multiple sclerosis.

OBJECTIVE: The objective of this paper is to assess abnormal phase values, indicative of increased iron content, using susceptibility-weighted imaging (SWI)-filtered phase of the subcortical deep gray matter (SDGM) in adolescent multiple sclerosis (MS) and other neurological disorders (OND) patients, and in healthy controls (HC). METHODS: Twenty adolescent MS and eight adolescent OND patients and 21 age- and sex-matched HC were scanned on a 3T GE scanner. Mean phase of abnormal phase tissue (MP-APT), MP-APT volume, normal phase tissue volume (NPTV) and normalized volume measurements were obtained for total SDGM, as well as specific structures separately. RESULTS: Significantly increased MP-APT (28.2%, p<.001) and MP-APT volume (82.7%, p<.001), and decreased NPTV (-23.3%, p<.001) and normalized volume (-15.5%, p<.001) in the pulvinar nucleus of the thalamus was found in MS patients compared to HC. MP-APT in MS patients was also increased in total SDGM (p=.012) and thalamus (p=.044). Compared to OND patients, MS patients had increased MP-APT volume in the pulvinar nucleus of the thalamus (p=.044) and caudate (p=.045). Increased MP-APT of the SDGM structures were associated with increased T2 and T1 lesion burden and brain atrophy in MS patients. CONCLUSION: Adolescent MS patients showed increased iron content in the SDGM compared to OND patients and HC.

Ultrastructure of ipsilateral and contralateral tectopulvinar projections in the mouse.

Visual pathways of the brain are organized into parallel channels that code different features of the external environment. In the current study, we investigated the anatomical organization of parallel pathways from the superior colliculus (SC) to the pulvinar nucleus in the mouse. Virus injections placed in the ipsilateral and contralateral SC to induce the expression of different fluorescent proteins define two pulvinar zones. The lateral pulvinar (Pl) receives ipsilateral SC input and the caudal medial pulvinar (Pcm) receives bilateral SC input. To examine the ultrastructure of these projections using transmission electron microscopy, we injected the SC with viruses to induce peroxidase expression within synaptic vesicles or mitochondria. We quantitatively compared the sizes of ipsilateral and contralateral tectopulvinar terminals and their postsynaptic dendrites, as well as the sizes of the overall population of synaptic terminals and their postsynaptic dendrites in the Pl and Pcm. Our ultrastructural analysis revealed that ipsilateral tectopulvinar terminals are significantly larger than contralateral tectopulvinar terminals. In particular, the ipsilateral tectopulvinar projection includes a subset of large terminals (≥ 1 µm2 ) that envelop dendritic protrusions of postsynaptic dendrites. We also found that both ipsilateral and contralateral tectopulvinar terminals are significantly larger than the overall population of synaptic terminals in both the Pl and Pcm. Thus, the ipsilateral tectopulvinar projection is structurally distinct from the bilateral tectopulvinar pathway, but both tectopulvinar channels may be considered the primary or "driving" input to the Pl and Pcm.

Synaptic organization of connections between the temporal cortex and pulvinar nucleus of the tree shrew.

We examined the synaptic organization of reciprocal connections between the temporal cortex and the dorsal (Pd) and central (Pc) subdivisions of the tree shrew pulvinar nucleus, regions innervated by the medial and lateral superior colliculus, respectively. Both Pd and Pc subdivisions project topographically to 2 separate regions of the temporal cortex; small injections of anterograde tracers placed in either Pd or Pc labeled 2 foci of terminals in the temporal cortex. Pulvinocortical pathways innervated layers I-IV, with beaded axons oriented perpendicular to the cortical surface, where they synapsed with spines that did not contain gamma amino butyric acid (GABA), likely located on the apical dendrites of pyramidal cells. Projections from the temporal cortex to the Pd and Pc originate from layer VI cells, and form small terminals that contact small caliber non-GABAergic dendrites. These results suggest that cortical terminals are located distal to tectopulvinar terminals on the dendritic arbors of Pd and Pc projection cells, which subsequently contact pyramidal cells in the temporal cortex. This circuitry could provide a mechanism for the pulvinar nucleus to activate subcortical visuomotor circuits and modulate the activity of other visual cortical areas. The potential relation to primate tecto-pulvino-cortical pathways is discussed.

Differentiating attention-deficit/hyperactivity disorder inattentive and combined types: a (1)H-magnetic resonance spectroscopy study of fronto-striato-thalamic regions.

Despite the implication of fronto-striatal circuits in attention-deficit/hyperactivity disorder (ADHD), there is a lack of information on the role of these regions, especially the thalamus, in the heterogeneity of ADHD. We assessed the (1)H-magnetic resonance spectroscopy profile in ventromedial prefrontal cortex (VMPFC)-thalamic-striatal regions bilaterally in three groups of subjects (age range 18-24 years old): ADHD inattentive type (ADHD-I; n = 9), ADHD combined type (ADHD-C; n = 10) and non-ADHD controls (n = 12). The peaks of N-acetylaspartate, Choline (Cho), myo-inositol (mI), creatine (Cr) and glutamate-glutamine-GABA (Glx) to Cr were calculated. Subjects with ADHD-C showed lower mI/Cr ratio in the right VMPFC than controls, higher Cho/Cr ratio in the left thalamus-pulvinar than the ADHD-I group and higher Glx/Cr ratio in left putamen than individuals with ADHD-I and controls. This metabolic profile suggests a disruption of fronto-striato-thalamic structures in the ADHD-C as a result of lower neuronal energetic metabolism.

The nucleus pretectalis principalis: A pretectal structure hidden in the mammalian thalamus.

A defining feature of the amniote tecto-fugal visual pathway is a massive bilateral projection to the thalamus originating from a distinct neuronal population, tectal ganglion cells (TGCs), of the optic tectum/superior colliculus (TeO/SC). In sauropsids, the thalamic target of the tecto-fugal pathway is the nucleus rotundus thalami (Rt). TGCs axons collateralize en route to Rt to target the nucleus pretectalis principalis (PT), which in turn gives rise to bilateral projection to the TeO. In rodents, the thalamic target of these TGCs afferents is the caudal division of the pulvinar complex (PulC). No pretectal structures in receipt of TGC collaterals have been described in this group. However, Baldwin et al. (Journal of Comparative Neurology, 2011;519(6):1071-1094) reported in the squirrel a feedback projection from the PulC to the SC. Pulvino-tectal (Pul-T) cells lie at the caudal pole of the PulC, intermingled with the axonal terminals of TGCs. Here, by performing a combination of neuronal tracing, immunohistochemistry, immunofluorescence, and in situ hybridization, we characterized the pattern of projections, neurochemical profile, and genoarchitecture of Pul-T cells in the diurnal Chilean rodent Octodon degus. We found that Pul-T neurons exhibit pretectal, but not thalamic, genoarchitectonical markers, as well as hodological and neurochemical properties that match specifically those of the avian nucleus PT. Thus, we propose that Pul-T cells constitute a pretectal cell population hidden within the dorsal thalamus of mammals. Our results solve the oddity entailed by the apparent existence of a noncanonic descending sensory thalamic projection and further stress the conservative character of the tectofugal pathway.

Thalamic and prefrontal FDG uptake in never medicated patients with schizophrenia.

OBJECTIVE: Because neuroleptic treatment may cause long-lasting changes in brain structure and function, a group of patients with schizophrenia who had never been medicated was recruited to examine regional glucose metabolic rates in the frontal-striato-thalamic circuit. METHOD: Twelve never medicated patients with schizophrenia (seven men, five women; mean age=29 years) and 13 normal volunteers (eight men and five women; mean age=28.5 years) underwent (18)F-fluorodeoxyglucose (FDG) positron emission tomography, and coregistered anatomical magnetic resonance imaging scans were also obtained. During FDG uptake, subjects performed a spatial attention task previously shown to activate the pulvinar region of the thalamus. RESULTS: Diminished regional glucose metabolism was found in the medial dorsal nucleus, posterior thalamus, and prefrontal cortex of patients with schizophrenia relative to normal volunteers, extending earlier results from studies of medicated and previously medicated patients. CONCLUSIONS: The finding of lower relative metabolic rates in the frontothalamic circuits of patients with schizophrenia is consistent with extended circuit deficits involving interactions of frontal executive areas with thalamic sensory and association processes.

Neurochemical organization of chimpanzee inferior pulvinar complex.

The pulvinar of primates, which connects with all visual areas, has been implicated in visual attention and in control of eye movements. Recently, five separate neurochemical subdivisions of a region termed the inferior pulvinar complex have been identified in monkeys (Gray et al. [1999] J Comp Neurol 409:452-468; Gutierrez et al. [1995] J Comp Neurol 363:545-562), and comparable subdivisions have been mapped in humans (Cola et al. [1999] NeuroReport 10:3733-3738). In the present study, we investigated the inferior pulvinar of the chimpanzee (Pan troglodytes), the closest evolutionary relative of humans, using cytochrome oxidase (CO) and acetylcholinesterase (AChE) histochemistry, and immunocytochemistry for calbindin. Each staining method demarcated five histochemical zones corresponding, from medial to lateral, to the posterior (PI(P)), medial (PI(M)), central PI(C)), lateral (PI(L)), and the lateral-shell (PI(L-S)) divisions in monkeys. The PI(P) division stained darkly for calbindin and lightly for CO and AChE. The PI(M) division was characterized by less neuropil staining for calbindin, and by distinct, intensely stained patches of CO and AChE. PI(C) appeared lighter than adjacent divisions with CO and AChE histochemistry and was moderately stained with calbindin. PI(L) was moderately to darkly stained with each method and was adjoined by a lighter staining shell, PI(L-S). Thus, in the aspects of organization we examined, the inferior pulvinar of chimpanzees closely resembles that of humans and monkeys. This investigation provides a foundation for more detailed studies of the thalamic relationships of extrastriate cortex in apes and humans.

Ultrastructural analysis of projections to the pulvinar nucleus of the cat. II: Pretectum.

The pretectum (PT) can supply the pulvinar nucleus (PUL), and concomitantly the cortex, with visual motion information through its dense projections to the PUL. We examined the morphology and synaptic targets of pretecto-pulvinar (PT-PUL) terminals labeled by anterograde transport in the cat. By using postembedding immunocytochemical staining for gamma-aminobutyric acid (GABA), we additionally determined whether PT-PUL terminals or their postsynaptic targets were GABAergic. We found that the main projection from the PT to the PUL is an ipsilateral, non-GABAergic projection (72.4%) that primarily contacts thalamocortical cell dendrites (87.6%), and also the dendritic terminals of interneurons (F2 profiles; 12.4%). The PT additionally provides GABAergic innervation to the PUL (27.6% of the ipsilateral projection), which chiefly contacts relay cell dendrites (84.6%) but also GABAergic profiles (15.4%). These GABAergic pretectal terminals are smaller, beaded fibers that likely branch to bilaterally innervate the PUL and dLGN, and possibly other targets. We also examined the neurochemical nature of PT-PUL cells labeled by retrograde transport and found that most are non-GABAergic cells (79%) and devoid of calbindin. Taking existing physiological and our present morphological data into account, we suggest that, in addition to the parietal cortex, the non-GABAergic PT-PUL projection may also strongly influence PUL activity. The GABAergic pretectal fibers, however, may provide a more widespread influence on thalamic activity.

Ultrastructural analysis of projections to the pulvinar nucleus of the cat. I: Middle suprasylvian gyrus (areas 5 and 7).

The mammalian pulvinar nucleus (PUL) establishes heavy interconnections with the parietal lobe, but the precise nature of these connections is only partially understood. To examine the distribution of corticopulvinar cells in the cat, we injected the PUL with retrograde tracers. Corticopulvinar cells were located in layers V and VI of a wide variety of cortical areas, with a major concentration of cells in area 7. To examine the morphology and distribution of corticopulvinar terminals, we injected cortical areas 5 or 7 with anterograde tracers. The majority of corticopulvinar axons were thin fibers (type I) with numerous diffuse small boutons. Thicker (type II) axons with fewer, larger boutons were also present. Boutons of type II axons formed clusters within restricted regions of the PUL. We examined corticopulvinar terminals labeled from area 7 at the ultrastructural level in tissue stained for gamma-aminobutyric acid (GABA). By correlating the size of the presynaptic and postsynaptic profiles, we were able to quantitatively divide the labeled terminals into two categories: small and large (RS and RL, respectively). The RS terminals predominantly innervated small-caliber non-GABAergic (thalamocortical cell) dendrites, whereas the RL terminals established complex synaptic arrangements with dendrites of both GABAergic interneurons and non-GABAergic cells. Interpretation of these results using Sherman and Guillery's recent theories of thalamic organization (Sherman and Guillery [1998] Proc Natl Acad Sci U S A 95:7121-7126) suggests that area 7 may both drive and modulate PUL activity.

Effects of diet on brain iron levels among healthy individuals: an MRI pilot study.

Increased brain iron levels may be a risk factor for age-related neurologic disorders. Little is known about factors other than age and sex potentially affecting brain iron concentration. We investigated dietary habits (iron and calcium supplements, dairy products, vegetables, and red meat) as a potential modifiable predictor of brain iron levels using 3-T susceptibility-weighted magnetic resonance imaging. One hundred ninety volunteers were scanned, and mean phase and mean phase of low-phase voxels were determined for deep gray-matter (DGM) structures, including the caudate, putamen, thalamus, pulvinar, hippocampus, amygdala, red nucleus, and substantia nigra. There was a trend for lower mean phase (suggestive of high iron levels) in individuals taking iron supplements (p = 0.075). Among men, both increased dairy and vegetable intakes were significantly associated with lower DGM mean phase (p < 0.05) and mean phase of low-phase voxels (p < 0.05) in the thalamus, pulvinar, and red nucleus. In contrast, among women, iron levels were not associated with dairy consumption (p > 0.05) in the DGM but were inversely associated with vegetable intake in the thalamus (p = 0.006). Brain iron levels appear to be modulated by diet, with effects being highly dependent on gender.

Neurotensin immunolabeling relates to sexually-motivated song and other social behaviors in male European starlings (Sturnus vulgaris).

The brain regions involved in vocal communication are well described for some species, including songbirds, but less is known about the neural mechanisms underlying motivational aspects of communication. Mesolimbic dopaminergic projections from the ventral tegmental area (VTA) are central to mediating motivated behaviors. In songbirds, VTA provides dopaminergic innervation to brain regions associated with motivation and social behavior that are also involved in sexually-motivated song production. Neurotensin (NT) is a neuropeptide that strongly modulates dopamine activity, co-localizes with dopamine in VTA, and is found in regions where dopaminergic cells project from VTA. Yet, little is known about how NT contributes to vocal communication or other motivated behaviors. We examined the relationships between sexually-motivated song produced by male European starlings (Sturnus vulgaris) and NT immunolabeling in brain regions involved in social behavior and motivation. Additionally, we observed relationships between NT labeling, non-vocal courtship behaviors (another measure of sexual motivation), and agonistic behavior to begin to understand NT's role in socially-motivated behaviors. NT labeling in VTA, lateral septum, and bed nucleus of the stria terminalis correlated with sexually-motivated singing and non-vocal courtship behaviors. NT labeling in VTA, lateral septum, medial preoptic nucleus, and periaqueductal gray was associated with agonistic behavior. This study is the first to suggest NT's involvement in song, and one of the few to implicate NT in social behaviors more generally. Additionally, our results are consistent with the idea that distinct patterns of neuropeptide activity in brain areas involved in social behavior and motivation underlie differentially motivated behaviors.

Visual cortical projections and chemoarchitecture of macaque monkey pulvinar.

We investigated the patterns of projections from the pulvinar to visual areas V1, V2, V4, and MT, and their relationships to pulvinar subdivisions based on patterns of calbindin (CB) immunostaining and estimates of visual field maps (P(1), P(2) and P(3)). Multiple retrograde tracers were placed into V1, V2, V4, and/or MT in 11 adult macaque monkeys. The inferior pulvinar (PI) was subdivided into medial (PI(M)), posterior (PI(P)), central medial (PI(CM)), and central lateral (PI(CL)) regions, confirming earlier CB studies. The P(1) map includes PI(CL) and the ventromedial portion of the lateral pulvinar (PL), P(2) is found in ventrolateral PL, and P(3) includes PI(P), PI(M), and PI(CM). Projections to areas V1 and V2 were found to be overlapping in P(1) and P(2), but those from P(2) to V2 were denser than those to V1. V2 also received light projections from PI(CM) and, less reliably, from PI(M). Neurons projecting to V4 and MT were more abundant than those projecting to V1 and V2. Those projecting to V4 were observed in P(1), densely in P(2), and also in PI(CM) and PI(P) of P(3). Those projecting to MT were found in P(1)- P(3), with the heaviest projection from P(3). Projections from P(3) to MT and V4 were mainly interdigitated, with the densest to MT arising from PI(M) and the densest to V4 arising from PI(P) and PI(CM). Because the calbindin-rich and -poor regions of P(3) corresponded to differential patterns of cortical connectivity, the results suggest that CB may further delineate functional subdivisions in the pulvinar.

The visual pulvinar in tree shrews II. Projections of four nuclei to areas of visual cortex.

Patterns of thalamocortical connections were related to architectonically defined subdivisions of the pulvinar complex and the dorsolateral geniculate nucleus (LGN) in tree shrews (Tupaia belangeri). Tree shrews are of special interest because they are considered close relatives of primates, and they have a highly developed visual system. Several distinguishable tracers were injected within and across cortical visual areas in individual tree shrews in order to reveal retinotopic patterns and cortical targets of subdivisions of the pulvinar. The results indicate that each of the three architectonic regions of the pulvinar has a distinctive pattern of cortical connections and that one of these divisions is further divided into two regions with different patterns of connections. Two of the pulvinar nuclei have similar retinotopic patterns of projections to caudal visual cortex. The large central nucleus of the pulvinar (Pc) projects to the first and second visual areas, V1 and V2, and an adjoining temporal dorsal area (TD) in retinotopic patterns indicating that the upper visual quadrant is represented dorsal to the lower quadrant in Pc. The smaller ventral nucleus (Pv) which stains darkly for the Cat-301 antigen, projects to these same cortical areas, with a retinotopic pattern. Pv also projects to a temporal anterior area, TA. The dorsal nucleus (Pd), which densely expresses AChE, projects to posterior and ventral areas of temporal extrastriate cortex, areas TP and TPI. A posterior nucleus, Pp, projects to anterior areas TAL and TI, of the temporal lobe, as well as TPI. Injections in different cortical areas as much as 6 mm apart labeled overlapping zones in Pp and double-labeled some cells. These results indicate that the visual pulvinar of tree shrews contains at least four functionally distinct subdivisions, or nuclei. In addition, the cortical injections revealed that the LGN projects topographically and densely to V1 and that a significant number of LGN neurons project to V2 and TD.

Distribution and properties of GABA(B) antagonist [3H]CGP 62349 binding in the rhesus monkey thalamus and basal ganglia and the influence of lesions in the reticular thalamic nucleus.

GABA(B) receptors are believed to be associated with the efferents of the nucleus reticularis thalami, which is implicated in the regulation of activity in the thalamocortical-corticothalamic circuit and plays a role in absence seizures. Yet, the distribution of GABA(B) receptors in the thalamus has only been studied in the rat, and there is no comparable information in primates. The potent GABA(B) receptor antagonist [3H]CGP 62349 was used to study the distribution and binding properties of the receptor in control monkeys and those with small ibotenic acid lesions in the anterodorsal segment of the nucleus reticularis thalami. Eight-micrometer-thick cryostat sections of the fresh frozen brains were incubated in the presence of varying concentrations of the ligand. Autoradiographs were analysed using a quantitative image analysis technique, and binding parameters were calculated for select thalamic nuclei as well as basal ganglia structures present in the same sections. The overall number of GABA(B) binding sites in the monkey thalamus and basal ganglia was several-fold higher than previously reported values for the rat. In the thalamus, the receptors were distributed rather uniformly and the binding densities and affinities were high (Bmax range of 245.5-437.9 fmol/ mg of tissue, Kd range of 0.136-0.604 nM). In the basal ganglia, the number of binding sites and the affinities were lower (Bmax range of 51.1-244.2 fmol/mg of tissue; K(d) range of 0.416-1.394 nM), and the differences between nuclei were more pronounced, with striatum and substantia nigra pars compacta displaying the highest binding densities. Seven days post-lesion, a 20-30% decrease in Bmax values (P < 0.05) was found in the nuclei receiving input from the lesioned nucleus reticularis thalami sector (the mediodorsal nucleus and densicellular and magnocellular parts of the ventral anterior nucleus) without changes in affinity. No significant changes were detected in any other structures. The results of the lesioning experiments suggest that a portion of thalamic GABA(B) receptors is in a presynaptic location on the nucleus reticularis thalami efferents. The overall distribution pattern in the thalamus also suggests a partial association of GABA(B) receptors with corticothalamic terminals presynaptically.

The retinal input to calbindin-D28k-defined subdivisions in macaque inferior pulvinar.

Several studies have provided evidence for direct retinal input to the pulvinar of macaques monkeys, but there is no general agreement regarding the extent of this projection. Moreover, it is not known how retinal input correlates with chemoarchitectonic subdivisions recently recognized within the large, classical divisions of the pulvinar. The potential implications of this correlation have become more evident after reports that chemoarchitectonic subdivisions of the inferior pulvinar (PI) have specific patterns of connections with cortical visual areas. We have therefore re-examined the retino-PI projection using intraocular injections of horseradish peroxides, and correlated it with pulvinar subdivisions revealed using an antibody for calbindin-D28k. Retinal projections were found preferentially within the medial subdivision of the PI, with some involvement of the posterior and central calbindin-D28k defined subdivisions.