Chemical architecture of the posterior striatum in the human brain

DARPP-32 cells and neuropil define striosomal system and isolated matrix cells in human striatum

The dorsal striatum forms a central node of the basal ganglia interconnecting the neocortex and thalamus with circuits modulating mood and movement. Striatal projection neurons (SPNs) include relatively intermixed populations expressing D1-type or D2-type dopamine receptors (dSPNs and iSPNs) that give rise to the direct (D1) and indirect (D2) output systems of the basal ganglia. Overlaid on this organization is a compartmental organization, in which a labyrinthine system of striosomes made up of sequestered SPNs is embedded within the larger striatal matrix. Striosomal SPNs also include D1-SPNs and D2-SPNs, but they can be distinguished from matrix SPNs by many neurochemical markers. In the rodent striatum the key signaling molecule, DARPP-32, is a exception to these compartmental expression patterns, thought to befit its functions through opposite actions in both D1- and D2-expressing SPNs. We demonstrate here, however, that in the dorsal human striatum, DARPP-32 is concentrated in the neuropil and SPNs of striosomes, especially in the caudate nucleus and dorsomedial putamen, relative to the matrix neuropil in these regions. The generally DARPP-32-poor matrix contains scattered DARPP-32-positive cells. DARPP-32 cell bodies in both compartments proved negative for conventional intraneuronal markers. These findings raise the potential for specialized DARPP-32 expression in the human striosomal system and in a set of DARPP-32-positive neurons in the matrix. If DARPP-32 immunohistochemical positivity predicts differential functional DARPP-32 activity, then the distributions demonstrated here could render striosomes and dispersed matrix cells susceptible to differential signaling through cAMP and other signaling systems in health and disease. DARPP-32 is highly concentrated in cells and neuropil of striosomes in post-mortem human brain tissue, particularly in the dorsal caudate nucleus. Scattered DARPP-32-positive cells are found in the human striatal matrix. Calbindin and DARPP-32 do not colocalize within every spiny projection neuron in the dorsal human caudate nucleus.

Morphological development of the human fetal striatum during the second trimester

The morphological development of the fetal striatum during the second trimester has remained poorly described. We manually segmented the striatum using 7.0-T MR images of the fetal specimens ranging from 14 to 22 gestational weeks. The global development of the striatum was evaluated by volume measurement. The absolute volume (Vabs) of the caudate nucleus (CN) increased linearly with gestational age, while the relative volume (Vrel) showed a quadratic growth. Both Vabs and Vrel of putamen increased linearly. Through shape analysis, the changes of local structure in developing striatum were specifically demonstrated. Except for the CN tail, the lateral and medial parts of the CN grew faster than the middle regions, with a clear rostral-caudal growth gradient as well as a distinct "outside-in" growth gradient. For putamen, the dorsal and ventral regions grew obviously faster than the other regions, with a dorsal-ventral bidirectional developmental pattern. The right CN was larger than the left, whereas there was no significant hemispheric asymmetry in the putamen. By establishing the developmental trajectories, spatial heterochrony, and hemispheric dimorphism of human fetal striatum, these data bring new insight into the fetal striatum development and provide detailed anatomical references for future striatal studies.

Quantitative analysis of spiny neurons in the adult human caudate nucleus: can it confirm the current qualitative cell classification?

The caudate nucleus, as a part of the striatum (neostriatum or dorsal striatum), is involved in the control of cognitive, motor and limbic functions. The majority of the caudate nucleus cells are projection spiny neurons, whose activity is determined by excitatory inputs from the cortex, thalamus, globus pallidus and brainstem. A qualitative analysis of human caudate nucleus neurons involves the description of the structure and features of cells, and accordingly, their classification into an appropriate type. The aim of this study is to determine the justification of the current qualitative classification of spiny neurons in the precommissural head of the human caudate nucleus by quantifying morphological properties of neurons. After the qualitative analysis of microscopic images of the Golgi-impregnated caudate nucleus neurons, five morphological properties of cells were measured/quantified. In terms of the dendritic field area, caudate nucleus neurons were divided into two subgroups: small and large neurons. In our sample of 251 projection nerve cells, 58.17 % (146) were small and 41.83 % (105) were large neurons. These data show that suggested groups of spiny neurons in the human caudate nucleus differ in their morphology. Since the structure and function of cells are closely correlated, it is possible that these morphologically different types of neurons may represent different functional groups.

Distribution of GABAergic interneurons and dopaminergic cells in the functional territories of the human striatum

Background

The afferent projections of the striatum (caudate nucleus and putamen) are segregated in three territories: associative, sensorimotor and limbic. Striatal interneurons are in part responsible for the integration of these different types of information. Among them, GABAergic interneurons are the most abundant, and can be sorted in three populations according to their content in the calcium binding proteins calretinin (CR), parvalbumin (PV) and calbindin (CB). Conversely, striatal dopaminergic cells (whose role as interneurons is still unclear) are scarce. This study aims to analyze the interneuron distribution in the striatal functional territories, as well as their organization regarding to the striosomal compartment.

Methodology/Principal Findings

We used immunohistochemical methods to visualize CR, PV, CB and tyrosine hydroxylase (TH) positive striatal neurons. The interneuronal distribution was assessed by stereological methods applied to every striatal functional territory. Considering the four cell groups altogether, their density was higher in the associative (2120±91 cells/mm³) than in the sensorimotor (959±47 cells/mm³) or limbic (633±119 cells/mm³) territories. CB- and TH-immunoreactive(-ir) cells were distributed rather homogeneously in the three striatal territories. However, the density of CR and PV interneurons were more abundant in the associative and sensorimotor striatum, respectively. Regarding to their compartmental organization, CR-ir interneurons were frequently found in the border between compartments in the associative and sensorimotor territories, and CB-ir interneurons abounded at the striosome/matrix border in the sensorimotor domain.

Conclusions/Significance

The present study demonstrates that the architecture of the human striatum in terms of its interneuron composition varies in its three functional territories. Furthermore, our data highlight the importance of CR-ir striatal interneurons in the integration of associative information, and the selective role of PV-ir interneurons in the motor territory. On the other hand, the low density of dopaminergic cells casts doubts about their role in the normal human striatum.

Neurochemical characterization of the tree shrew dorsal striatum

The striatum is a major component of the basal ganglia and is associated with motor and cognitive functions. Striatal pathologies have been linked to several disorders, including Huntington’s, Tourette’s syndrome, obsessive–compulsive disorders, and schizophrenia. For the study of these striatal pathologies different animal models have been used, including rodents and non-human primates. Rodents lack on morphological complexity (for example, the lack of well defined caudate and putamen nuclei), which makes it difficult to translate data to the human paradigm. Primates, and especially higher primates, are the closest model to humans, but there are ever-increasing restrictions to the use of these animals for research. In our search for a non-primate animal model with a striatum that anatomically (and perhaps functionally) can resemble that of humans, we turned our attention to the tree shrew. Evolutionary genetic studies have provided strong data supporting that the tree shrews (Scadentia) are one of the closest groups to primates, although their brain anatomy has only been studied in detail for specific brain areas. Morphologically, the tree shrew striatum resembles the primate striatum with the presence of an internal capsule separating the caudate and putamen, but little is known about its neurochemical composition. Here we analyzed the expression of calcium-binding proteins, the presence and distribution of the striosome and matrix compartments (by the use of calbindin, tyrosine hydroxylase, and acetylcholinesterase immunohistochemistry), and the GABAergic system by immunohistochemistry against glutamic acid decarboxylase and Golgi impregnation. In summary, our results show that when compared to primates, the tree shrew dorsal striatum presents striking similarities in the distribution of most of the markers studied, while presenting some marked divergences when compared to the rodent striatum.

The nigrostriatal pathway: axonal collateralization and compartmental specificity

This paper reviews two of the major features of the nigrostriatal pathway, its axonal collateralization, and compartmental specificity, as revealed by single-axon labeling experiments in rodents and immunocytological analysis of human postmortem tissue. The dorsal and ventral tiers of the substantia nigra pars compacta harbor various types of neurons the axons of which branch not only within the striatum but also in other major components of the basal ganglia. Furthermore, some nigrostriatal axons send collaterals both to thalamus and to brainstem pedunculopontine tegmental nucleus. In humans, the compartmental specificity of the nigrostriatal pathway is revealed by the fact that the matrix compartment is densely innervated by dopaminergic fibers, whereas the striosomes display different densities of dopaminergic terminals depending on their location within the striatum. The nigral neurons most severely affected in Parkinson's disease are the ventral tier cells that project to the matrix and form deep clusters in the substantia nigra pars reticulata.

Decreased number of parvalbumin and cholinergic interneurons in the striatum of individuals with Tourette syndrome

Corticobasal ganglia neuronal ensembles bring automatic motor skills into voluntary control and integrate them into ongoing motor behavior. A 5% decrease in caudate (Cd) nucleus volume is the most consistent structural finding in the brain of patients with Tourette syndrome (TS), but the cellular abnormalities that underlie this decrease in volume are unclear. In this study the density of different types of interneurons and medium spiny neurons (MSNs) in the striatum was assessed in the postmortem brains of 5 TS subjects as compared with normal controls (NC) by unbiased stereological analyses. TS patients demonstrated a 50%-60% decrease of both parvalbumin (PV)+ and choline acetyltransferase (ChAT)+ cholinergic interneurons in the Cd and the putamen (Pt). Cholinergic interneurons were decreased in TS patients in the associative and sensorimotor regions but not in the limbic regions of the striatum, such that the normal gradient in density of cholinergic cells (highest in associative regions, intermediate in sensorimotor and lowest in limbic regions) was abolished. No significant difference was present in the densities of medium-sized calretinin (CR)+ interneurons, MSNs, and total neurons. The selective deficit of PV+ and cholinergic striatal interneurons in TS subjects may result in an impaired cortico/thalamic control of striatal neuron firing in TS.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Cerebral amyloid angiopathy in Lewy body disease

While Alzheimer and Lewy body pathologies are discussed as major substrates of dementia in Parkinson's disease (PD/Lewy body disease of brainstem type), the incidence and impact of cerebral amyloid angiopathy (CAA) and its association with cognitive decline in PD and dementia with Lewy bodies (DLB) are unknown. The severity of CAA and other Alzheimer lesions were assessed in 68 cases of autopsy-confirmed PD, 32 of them with dementia (PDD), and in 20 cases of DLB. PDD patients were significantly older than those without dementia (mean age 84.5 vs 77.6 years; p < 0.01), the age of DLB patients was in between both groups (mean 80.0 years), while duration of disease was DLB < PDD < PD (mean 6.5 vs 8.5 and 14.3 years). PDD patients had a significantly higher neuritic Braak stage (mean 4.2 vs 2.4, p < 0.01), significantly higher cortical amyloid beta (Abeta) load, capillary cerebral amyloid angiopathy (CapCAA) and generalized CAA than those without dementia (mild CapCAA in 22% vs moderate to severe CapCAA in 87%; mild generalized CAA in 5.5% vs moderate to severe generalized CAA in 82%). Mean PD stage was higher in both DLB and PDD than in PD (mean 5.2 vs 4.5 and 4.0, respectively): Mean neuritic Braak stage in DLB was 3.4, severe Abeta plaque load was seen in 95%, moderate to severe CapCAA in 90% and mild to severe generalized CAA in 70%. This and other recent studies imply an association of CAA with cognitive decline in both PD/PDD and DLB, particularly in cases with concomitant AD-type pathology.

Cholinergic interneurons are differentially distributed in the human striatum

Background

The striatum (caudate nucleus, CN, and putamen, Put) is a group of subcortical nuclei involved in planning and executing voluntary movements as well as in cognitive processes. Its neuronal composition includes projection neurons, which connect the striatum with other structures, and interneurons, whose main roles are maintaining the striatal organization and the regulation of the projection neurons. The unique electrophysiological and functional properties of the cholinergic interneurons give them a crucial modulating function on the overall striatal response.

Methodology/Principle Findings

This study was carried out using stereological methods to examine the volume and density (cells/mm³) of these interneurons, as visualized by choline acetyltransferase (ChAT) immunoreactivity, in the following territories of the CN and Put of nine normal human brains: 1) precommissural head; 2) postcommissural head; 3) body; 4) gyrus and 5) tail of the CN; 6) precommissural and 7) postcommissural Put. The distribution of ChAT interneurons was analyzed with respect to the topographical, functional and chemical territories of the dorsal striatum. The CN was more densely populated by cholinergic neurons than the Put, and their density increased along the anteroposterior axis of the striatum with the CN body having the highest neuronal density. The associative territory of the dorsal striatum was by far the most densely populated. The striosomes of the CN precommissural head and the postcommissural Put contained the greatest number of ChAT-ir interneurons. The intrastriosomal ChAT-ir neurons were abundant on the periphery of the striosomes throughout the striatum.

Conclusions/Significance

All these data reveal that cholinergic interneurons are differentially distributed in the distinct topographical and functional territories of the human dorsal striatum, as well as in its chemical compartments. This heterogeneity may indicate that the posterior aspects of the CN require a special integration of information by interneurons. Interestingly, these striatal regions have been very much left out in functional studies.