Human brainstem catecholamine neuronal anatomy as indicated by immunocytochemistry with antibodies to tyrosine hydroxylase

Multimodal MRI reveals brainstem connections that sustain wakefulness in human consciousness

Consciousness is composed of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that underlie awareness in the human brain, but knowledge about the subcortical networks that sustain arousal in humans is incomplete. Here, we aimed to map the connectivity of a proposed subcortical arousal network that sustains wakefulness in the human brain, analogous to the cortical default mode network (DMN) that has been shown to contribute to awareness. We integrated data from ex vivo diffusion magnetic resonance imaging (MRI) of three human brains, obtained at autopsy from neurologically normal individuals, with immunohistochemical staining of subcortical brain sections. We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain. Deterministic and probabilistic tractography analyses of the ex vivo diffusion MRI data revealed projection, association, and commissural pathways linking dAAN nodes with one another and with DMN nodes. Complementary analyses of in vivo 7-tesla resting-state functional MRI data from the Human Connectome Project identified the dopaminergic ventral tegmental area in the midbrain as a widely connected hub node at the nexus of the subcortical arousal and cortical awareness networks. Our network-based autopsy methods and connectivity data provide a putative neuroanatomic architecture for the integration of arousal and awareness in human consciousness.

Corticotropin-releasing factor-dopamine interactions in male and female macaque: Beyond the classic VTA

Dopamine (DA) is involved in stress and stress-related illnesses, including many psychiatric disorders. Corticotropin-releasing factor (CRF) plays a role in stress responses and targets the ventral midbrain DA system, which is composed of DA and non-DA cells, and divided into specific subregions. Although CRF inputs to the midline A10 nuclei ("classic VTA") are known, in monkeys, CRF-containing terminals are also highly enriched in the expanded A10 parabrachial pigmented nucleus (PBP) and in the A8 retrorubral field subregions. We characterized CRF-labeled synaptic terminals on DA (tyrosine hydroxylase, TH+) and non-DA (TH-) cell types in the PBP and A8 regions using immunoreactive electron microscopy (EM) in male and female macaques. CRF labeling was present mostly in axon terminals, which mainly contacted TH-negative dendrites in both subregions. Most CRF-positive terminals had symmetric profiles. In both PBP and A8, CRF symmetric (putative inhibitory) synapses onto TH-negative dendrites were significantly greater than asymmetric (putative excitatory) profiles. This overall pattern was similar in males and females, despite shifts in the size of these effects between regions depending on sex. Because stress and gonadal hormone shifts can influence CRF expression, we also did hormonal assays over a 6-month time period and found little variability in basal cortisol across similarly housed animals at the same age. Together our findings suggest that at baseline, CRF-positive synaptic terminals in the primate PBP and A8 are poised to regulate DA indirectly through synaptic contacts onto non-DA neurons.

Dephosphorylation of Six2Y129 protects tyrosine hydroxylase-positive cells in SNpc by regulating TEA domain 1 expression

Parkinson's disease (PD) is a neurodegenerative disease characterized by selective loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). We recently reported that Six2 could reverse the degeneration of DA neurons in a dephosphorylation state. Here we further identified that Eya1 was the phosphatase of Six2 that could dephosphorylate the tyrosine 129 (Y129) site by forming a complex with Six2 in damaged DA cells. Dephosphorylated Six2 then translocates from the cytoplasm to the nucleus. Using ChIP-qPCR and dual luciferase assay, we found that dephosphorylated Six2 down-regulates TEA domain1 (Tead1) expression, thus inhibiting 6-hydroxydopamine (6-OHDA)-induced apoptosis in DA cells. Furthermore, we showed Six2Y129F/Tead1 signaling could protect against the loss of SNpc tyrosine hydroxylase-positive (TH+) cells and improve motor function in PD model rats. Our results demonstrate a dephosphorylation-dependent mechanism of Six2 that restores the degeneration of DA neurons, which could represent a potential therapeutic target for PD.

Sustaining wakefulness: Brainstem connectivity in human consciousness

Consciousness is comprised of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that modulate awareness in the human brain, but knowledge about the subcortical networks that sustain arousal is lacking. We integrated data from ex vivo diffusion MRI, immunohistochemistry, and in vivo 7 Tesla functional MRI to map the connectivity of a subcortical arousal network that we postulate sustains wakefulness in the resting, conscious human brain, analogous to the cortical default mode network (DMN) that is believed to sustain self-awareness. We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain by correlating ex vivo diffusion MRI with immunohistochemistry in three human brain specimens from neurologically normal individuals scanned at 600-750 μm resolution. We performed deterministic and probabilistic tractography analyses of the diffusion MRI data to map dAAN intra-network connections and dAAN-DMN internetwork connections. Using a newly developed network-based autopsy of the human brain that integrates ex vivo MRI and histopathology, we identified projection, association, and commissural pathways linking dAAN nodes with one another and with cortical DMN nodes, providing a structural architecture for the integration of arousal and awareness in human consciousness. We release the ex vivo diffusion MRI data, corresponding immunohistochemistry data, network-based autopsy methods, and a new brainstem dAAN atlas to support efforts to map the connectivity of human consciousness.

Human Brainstem and Cerebellum Atlas: Chemoarchitecture and Cytoarchitecture Paired to MRI

Lesion localization is the basis for understanding neurologic disease, which is predicated on neuroanatomical knowledge carefully cataloged from histology and imaging atlases. However, it is often difficult to correlate clinical images of brainstem injury obtained by MRI scans with the details of human brainstem neuroanatomy represented in atlases, which are mostly based on cytoarchitecture using Nissl stain or a single histochemical stain, and usually do not include the cerebellum. Here, we report a high-resolution (200 μm) 7T MRI of a cadaveric male human brainstem and cerebellum paired with detailed, coregistered histology (at 2 μm single-cell resolution) of the immunohistochemically stained cholinergic, serotonergic, and catecholaminergic (dopaminergic, noradrenergic, and adrenergic) neurons, in relationship to each other and to the cerebellum. These immunohistochemical findings provide novel insights into the spatial relationships of brainstem cell types and nuclei, including subpopulations of melanin and TH⁺ neurons, and allows for more informed structural annotation of cell groups. Moreover, the coregistered MRI-paired histology helps validate imaging findings. This is useful for interpreting both scans and histology, and to understand the cell types affected by lesions. Our detailed chemoarchitecture and cytoarchitecture with corresponding high-resolution MRI builds on previous atlases of the human brainstem and cerebellum, and makes precise identification of brainstem and cerebellar cell groups involved in clinical lesions accessible for both laboratory scientists and clinicians alike.SIGNIFICANCE STATEMENT Clinicians and neuroscientists frequently use cross-sectional anatomy of the human brainstem from MRI scans for both clinical and laboratory investigations, but they must rely on brain atlases to neuroanatomical structures. Such atlases generally lack both detail of brainstem chemical cell types, and the cerebellum, which provides an important spatial reference. Our current atlas maps the distribution of key brainstem cell types (cholinergic, serotonergic, and catecholaminergic neurons) in relationship to each other and the cerebellum, and pairs this histology with 7T MR images from the identical brain. This atlas allows correlation of the chemoarchitecture with corresponding MRI, and makes the identification of cell groups that are often discussed, but rarely identifiable on MRI scan, accessible to clinicians and clinical researchers.

Brainstem noradrenergic neurons: Identifying a hub at the intersection of cognition, motility, and skeletal muscle regulation

Brainstem noradrenergic neuron clusters form a node integrating efferents projecting to distinct areas such as those regulating cognition and skeletal muscle structure and function, and receive dissimilar afferents through established circuits to coordinate organismal responses to internal and environmental challenges. Genetic lineage tracing shows the remarkable heterogeneity of brainstem noradrenergic neurons, which may explain their varied functions. They project to the locus coeruleus, the primary source of noradrenaline in the brain, which supports learning and cognition. They also project to pre-ganglionic neurons, which lie within the spinal cord and form synapses onto post-ganglionic neurons. The synapse between descending brainstem noradrenergic neurons and pre-ganglionic spinal neurons, and these in turn with post-ganglionic noradrenergic neurons located at the paravertebral sympathetic ganglia, support an anatomical hierarchy that regulates skeletal muscle innervation, neuromuscular transmission, and muscle trophism. Whether any noradrenergic neuron subpopulation is more susceptible to damaged protein deposit and death with ageing and neurodegeneration is a relevant question that answer will help us to detect neurodegeneration at an early stage, establish prognosis, and anticipate disease progression. Loss of muscle mass and strength with ageing, termed sarcopenia, may predict impaired cognition with ageing and neurodegeneration and establish an early time to start interventions aimed at reducing central noradrenergic neurons hyperactivity. Complex multidisciplinary approaches, including genetic tracing, specific circuit labelling, optogenetics and chemogenetics, electrophysiology, and single-cell transcriptomics and proteomics, are required to test this hypothesis pre-clinical.

Unbiased Stereological Estimates of Dopaminergic and GABAergic Neurons in the A10, A9, and A8 Subregions in the Young Male Macaque

The ventral midbrain is the primary source of dopamine- (DA) expressing neurons in most species. GABA-ergic and glutamatergic cell populations are intermixed among DA-expressing cells and purported to regulate both local and long-range dopamine neuron activity. Most work has been conducted in rodent models, however due to evolutionary expansion of the ventral midbrain in primates, the increased size and complexity of DA subpopulations warrants further investigation. Here, we quantified the number of DA neurons, and their GABA-ergic complement in classic DA cell groups A10 (midline ventral tegmental area nuclei [VTA] and parabrachial pigmented nucleus [PBP]), A9 (substantia nigra, pars compacta [SNc]) and A8 (retrorubral field [RRF]) in the macaque. Because the PBP is a disproportionately expanded feature of the A10 group, and has unique connectional features in monkeys, we analyzed A10 data by dividing it into 'classic' midline nuclei and the PBP. Unbiased stereology revealed total putative DA neuron counts to be 210,238 ± 17,127 (A10 = 110,319 ± 9649, A9 = 87,399 ± 7751 and A8 = 12,520 ± 827). Putative GABAergic neurons were fewer overall, and evenly dispersed across the DA subpopulations (GAD67 = 71,215 ± 5663; A10 = 16,836 ± 2743; A9 = 24,855 ± 3144 and A8 = 12,633 ± 3557). Calculating the GAD67/TH ratio for each subregion revealed differential balances of these two cell types across the DA subregions. The A8 subregion had the highest complement of GAD67-positive neurons compared to TH-positive neurons (1:1), suggesting a potentially high capacity for GABAergic inhibition of DA output in this region.

Spatiotemporal characterization of cellular tau pathology in the human locus coeruleus-pericoerulear complex by three-dimensional imaging

Tau pathology of the noradrenergic locus coeruleus (LC) is a hallmark of several age-related neurodegenerative disorders, including Alzheimer's disease. However, a comprehensive neuropathological examination of the LC is difficult due to its small size and rod-like shape. To investigate the LC cytoarchitecture and tau cytoskeletal pathology in relation to possible propagation patterns of disease-associated tau in an unprecedented large-scale three-dimensional view, we utilized volume immunostaining and optical clearing technology combined with light sheet fluorescence microscopy. We examined AT8⁺ pathological tau in the LC/pericoerulear region of 20 brains from Braak neurofibrillary tangle (NFT) stage 0-6. We demonstrate an intriguing morphological complexity and heterogeneity of AT8⁺ cellular structures in the LC, representing various intracellular stages of NFT maturation and their diverse transition forms. We describe novel morphologies of neuronal tau pathology such as AT8⁺ cells with fine filamentous somatic protrusions or with disintegrating soma. We show that gradual dendritic atrophy is the first morphological sign of the degeneration of tangle-bearing neurons, even preceding axonal lesions. Interestingly, irrespective of the Braak NFT stage, tau pathology is more advanced in the dorsal LC that preferentially projects to vulnerable forebrain regions in Alzheimer's disease, like the hippocampus or neocortical areas, compared to the ventral LC projecting to the cerebellum and medulla. Moreover, already in the precortical Braak 0 stage, 3D analysis reveals clustering tendency and dendro-dendritic close appositions of AT8⁺ LC neurons, AT8⁺ long axons of NFT-bearing cells that join the ascending dorsal noradrenergic bundle after leaving the LC, as well as AT8⁺ processes of NFT-bearing LC neurons that target the 4th ventricle wall. Our study suggests that the unique cytoarchitecture, comprised of a densely packed and dendritically extensively interconnected neuronal network with long projections, makes the human LC to be an ideal anatomical template for early accumulation and trans-neuronal spreading of hyperphosphorylated tau.

The Mammalian Locus Coeruleus Complex-Consistencies and Variances in Nuclear Organization

Descriptions of the nuclear parcellation of the locus coeruleus complex have been provided in approximately 80 mammal species spanning the phylogenetic breadth of this class. Within the mammalian rostral hindbrain, noradrenergic neurons (revealed with tyrosine hydroxylase and dopamine-ß-hydroxylase immunohistochemistry) have been observed within the periventricular grey matter (A4 and A6 nuclei) and parvicellular reticular nucleus (A5 and A7 nuclei), with the one exception to date being the tree pangolin, where no A4/A6 neurons are observed. The alphanumeric nomenclature system, developed in laboratory rodent brains, has been adapted to cover the variation observed across species. Cross-species homology is observed regarding the nuclear organization of noradrenergic neurons located in the parvicellular reticular nucleus (A5 and A7). In contrast, significant variations are observed in the organization of the A6 neurons of the locus coeruleus proper. In most mammals, the A6 is comprised of a moderate density of neurons, but in Murid rodents, primates, and megachiropteran bats, the A6 exhibits a very high density of neurons. In primates and megachiropterans, there is an additional moderate density of A6 neurons located rostromedial to the high-density portion. These variations are of importance in understanding the translation of findings in laboratory rodents to humans.

Nuclear organization of catecholaminergic neurons in the brains of a lar gibbon and a chimpanzee

Using tyrosine hydroxylase immunohistochemistry, we describe the nuclear parcellation of the catecholaminergic system in the brains of a lar gibbon (Hylobates lar) and a chimpanzee (Pan troglodytes). The parcellation of catecholaminergic nuclei in the brains of both apes is virtually identical to that observed in humans and shows very strong similarities to that observed in mammals more generally, particularly other primates. Specific variations of this system in the apes studied include an unusual high-density cluster of A10dc neurons, an enlarged retrorubral nucleus (A8), and an expanded distribution of the neurons forming the dorsolateral division of the locus coeruleus (A4). The additional A10dc neurons may improve dopaminergic modulation of the extended amygdala, the enlarged A8 nucleus may be related to the increased use of communicative facial expressions in the hominoids compared to other primates, while the expansion of the A4 nucleus appears to be related to accelerated evolution of the cerebellum in the hominoids compared to other primates. In addition, we report the presence of a compact division of the locus coeruleus proper (A6c), as seen in other primates, that is not present in other mammals apart from megachiropteran bats. The presence of this nucleus in primates and megachiropteran bats may reflect homology or homoplasy, depending on the evolutionary scenario adopted. The fact that the complement of homologous catecholaminergic nuclei is mostly consistent across mammals, including primates, is advantageous for the selection of model animals for the study of specific dysfunctions of the catecholaminergic system in humans.

Calbindin-D28K, parvalbumin, and calretinin in young and aged human locus coeruleus

Certain neuronal populations, including basal forebrain cholinergic neurons (BFCN) and noradrenergic neurons of the locus coeruleus (LC), are selectively vulnerable to pathology and loss early in the course of aging and Alzheimer's disease (AD). Human BFCN show substantial loss of the calcium-binding protein (CBP), calbindin-D28K (CB), during normal aging, which is associated with formation of neurofibrillary tangles and BFCN loss in AD. Here we determined if, similar to the BFCN, LC neurons contain CB or the other 2 ubiquitous CBPs parvalbumin and calretinin, and whether these proteins display an age-related loss from LC neurons. Immunostaining for CBP and tyrosine hydroxylase, a marker of catecholaminergic neurons, was used in sections from the LC of young and aged human brains. Parvalbumin and calretinin immunoreactivities were completely absent from human LC neurons. A subpopulation of LC neurons (~10%) contained CB immunoreactivity. Quantitative analysis revealed no age-related loss of CB from LC neurons. Thus, unlike the BFCN, age-related loss of CB does not figure prominently in the selective vulnerability of LC neurons to degeneration in AD.

Next generation histology methods for three-dimensional imaging of fresh and archival human brain tissues

Modern clearing techniques for the three-dimensional (3D) visualisation of neural tissue microstructure have been very effective when used on rodent brain but very few studies have utilised them on human brain material, mainly due to the inherent difficulties in processing post-mortem tissue. Here we develop a tissue clearing solution, OPTIClear, optimised for fresh and archival human brain tissue, including formalin-fixed paraffin-embedded material. In light of practical challenges with immunostaining in tissue clearing, we adapt the use of cresyl violet for visualisation of neurons in cleared tissue, with the potential for 3D quantification in regions of interest. Furthermore, we use lipophilic tracers for tracing of neuronal processes in post-mortem tissue, enabling the study of the morphology of human dendritic spines in 3D. The development of these different strategies for human tissue clearing has wide applicability and, we hope, will provide a baseline for further technique development.

Systematic Morphometry of Catecholamine Nuclei in the Brainstem

Catecholamine nuclei within the brainstem reticular formation (RF) play a pivotal role in a variety of brain functions. However, a systematic characterization of these nuclei in the very same experimental conditions is missing so far. Tyrosine hydroxylase (TH) immune-positive cells of the brainstem correspond to dopamine (DA)-, norepinephrine (NE)-, and epinephrine (E)-containing cells. Here, we report a systematic count of TH-positive neurons in the RF of the mouse brainstem by using stereological morphometry. All these nuclei were analyzed for anatomical localization, rostro-caudal extension, volume, neuron number, neuron density, and mean neuronal area for each nucleus. The present data apart from inherent informative value wish to represent a reference for neuronal mapping in those studies investigating the functional anatomy of the brainstem RF. These include: the sleep-wake cycle, movement control, muscle tone modulation, mood control, novelty orienting stimuli, attention, archaic responses to internal and external stressful stimuli, anxiety, breathing, blood pressure, and innumerable activities modulated by the archaic iso-dendritic hard core of the brainstem RF. Most TH-immune-positive cells fill the lateral part of the RF, which indeed possesses a high catecholamine content. A few nuclei are medial, although conventional nosography considers all these nuclei as part of the lateral column of the RF. Despite the key role of these nuclei in psychiatric and neurological disorders, only a few of them aspired a great attention in biomedical investigation, while most of them remain largely obscure although intense research is currently in progress. A simultaneous description of all these nuclei is not simply key to comprehend the variety of brainstem catecholamine reticular neurons, but probably represents an intrinsically key base for understanding brain physiology and physiopathology.

Beyond the Classic VTA: Extended Amygdala Projections to DA-Striatal Paths in the Primate

The central extended amygdala (CEA) has been conceptualized as a 'macrosystem' that regulates various stress-induced behaviors. Consistent with this, the CEA highly expresses corticotropin-releasing factor (CRF), an important modulator of stress responses. Stress alters goal-directed responses associated with striatal paths, including maladaptive responses such as drug seeking, social withdrawal, and compulsive behavior. CEA inputs to the midbrain dopamine (DA) system are positioned to influence striatal functions through mesolimbic DA-striatal pathways. However, the structure of this amygdala-CEA-DA neuron path to the striatum has been poorly characterized in primates. In primates, we combined neuronal tracer injections into various arms of the circuit through specific DA subpopulations to assess: (1) whether the circuit connecting amygdala, CEA, and DA cells follows CEA intrinsic organization, or a more direct topography involving bed nucleus vs central nucleus divisions; (2) CRF content of the CEA-DA path; and (3) striatal subregions specifically involved in CEA-DA-striatal loops. We found that the amygdala-CEA-DA path follows macrostructural subdivisions, with the majority of input/outputs converging in the medial central nucleus, the sublenticular extended amygdala, and the posterior lateral bed nucleus of the stria terminalis. The proportion of CRF+ outputs is >50%, and mainly targets the A10 parabrachial pigmented nucleus (PBP) and A8 (retrorubal field, RRF) neuronal subpopulations, with additional inputs to the dorsal A9 neurons. CRF-enriched CEA-DA projections are positioned to influence outputs to the 'limbic-associative' striatum, which is distinct from striatal regions targeted by DA cells lacking CEA input. We conclude that the concept of the CEA is supported on connectional grounds, and that CEA termination over the PBP and RRF neuronal populations can influence striatal circuits involved in associative learning.

Turning on the Light Within: Subcortical Nuclei of the Isodentritic Core and their Role in Alzheimer's Disease Pathogenesis

Pharmacological interventions in Alzheimer's disease (AD) are likely to be more efficacious if administered early in the course of the disease, foregoing the spread of irreversible changes in the brain. Research findings underline an early vulnerability of the isodendritic core (IC) network to AD neurofibrillary lesions. The IC constitutes a phylogenetically conserved subcortical system including the locus coeruleus in pons, dorsal raphe nucleus, and substantia nigra in the midbrain, and nucleus basalis of Meynert in basal forebrain. Through their ascending projections to the cortex, the IC neurons regulate homeostasis and behavior by synthesizing aminergic and cholinergic neurotransmitters. Here we reviewed the evidence demonstrating that neurons of the IC system show neurofibrillary tangles in the earliest stages of AD, prior to cortical pathology, and how this involvement may explain pre-amnestic symptoms, including depression, agitation, and sleep disturbances in AD patients. In fact, clinical and animal studies show a significant reduction of AD cognitive and behavioral symptoms following replenishment of neurotransmitters associated with the IC network. Therefore, the IC network represents a unique candidate for viable therapeutic intervention and should become a high priority for research in AD.

Differential involvement of brainstem noradrenergic and midbrain dopaminergic nuclei in cognitive control

Several lines of evidence suggest that the lateral prefrontal cortex (PFC), the dorsal anterior cingulate cortex (dACC), the parietal cortex, and the thalamus are central cortical nodes in a network underlying cognitive control. However, the role of catecholamine producing midbrain and brainstem structures has rarely been addressed by functional magnetic resonance imaging (fMRI). We hypothesized differential activation patterns in the ventral tegmental area (VTA)/substantia nigra (SN) and locus coeruleus (LC) with respect to the degree of cognitive control during a Stroop task in healthy subjects. Forty-five healthy subjects were investigated by the manual version of the Stroop task in an event-related fMRI design. We observed significant BOLD activation of both the SN/VTA and LC during the Stroop interference condition (incongruent vs. congruent condition). LC, but not SN/VTA activation significantly correlated with the Stroop interference. Interestingly, a significant linear decrease in BOLD activation during the incongruent condition during the experiment was mainly observed in the fronto-cingulo-striatal network, but not in SN/VTA and LC. Using psychophysiological (PPI) analyses, a significant functional connectivity during cognitive control was observed between SN/VTA and the nigrostriatal/mesolimbic dopaminergic system. For the LC, distinct functional connectivity pattern was observed mainly to the dorsolateral and ventrolateral PFC. Both regions revealed significant functional connectivity to the dACC, parietal and occipital regions. Thus, we demonstrate for the first time that functional activation patterns in the SN/VTA and the LC are modulated by different demands of cognitive control. In addition, these nuclei exhibit distinguishable functional connectivity patterns to cortical brain networks. Hum Brain Mapp 37:2305-2318, 2016. © 2016 Wiley Periodicals, Inc.

The Effect of Perinatal Hypoxic/Ischemic Injury on Tyrosine Hydroxylase Expression in the Locus Coeruleus of the Human Neonate

We have previously shown that perinatal hypoxic/ischemic injury (HII) may cause selective vulnerability of the mesencephalic dopaminergic neurons of human neonate. In the present study, we investigated the effect of perinatal HII on the noradrenergic neurons of the locus coeruleus (LC) of the same sample. We studied immunohistochemically the expression of tyrosine hydroxylase (TH, first limiting enzyme for catecholamine synthesis) in LC neurons of 15 autopsied infants (brains collected from the Greek Brain Bank) in relation to the neuropathological changes of acute or chronic HII of the neonatal brain. Our results showed that perinatal HII appears to affect the expression of TH and the size of LC neurons of the human neonate. In subjects with neuropathological lesions consistent with abrupt/severe HII, intense TH immunoreactivity was found in almost all neurons of the LC. In most of the neonates with neuropathological changes of prolonged or older injury, however, reduction in cell size and a decrease or absence of TH staining were observed in the LC. Intense TH immunoreactivity was found in the LC of 3 infants of the latter group, who interestingly had a longer survival time and had been treated with anticonvulsant drugs. Based on our observations and in view of experimental evidence indicating that the reduction of TH-immunoreactive neurons occurring in the LC after perinatal hypoxic insults persists into adulthood, we suggest that a dysregulation of monoaminergic neurotransmission in critical periods of brain development in humans is likely to predispose the survivors of perinatal HII, in combination with genetic susceptibility, to psychiatric and/or neurological disorders later in life.

Sex differences and effects of prenatal exposure to excess testosterone on ventral tegmental area dopamine neurons in adult sheep

Prenatal testosterone (T) excess in sheep results in a wide array of reproductive neuroendocrine deficits and alterations in motivated behavior. The ventral tegmental area (VTA) plays a critical role in reward and motivated behaviors and is hypothesised to be targeted by prenatal T. Here we report a sex difference in the number VTA dopamine cells in the adult sheep, with higher numbers of tyrosine hydroxylase (TH)-immunoreactive (-ir) cells in males than females. Moreover, prenatal exposure to excess T during either gestational days 30-90 or 60-90 resulted in increased numbers of VTA TH-ir cells in adult ewes compared to control females. Stereological analysis confirmed significantly greater numbers of neurons in the VTA of males and prenatal T-treated ewes, which was primarily accounted for by greater numbers of TH-ir cells. In addition, immunoreactivity for TH in the cells was denser in males and prenatal T-treated females, suggesting that sex differences and prenatal exposure to excess T affects both numbers of cells expressing TH and the protein levels within dopamine cells. Sex differences were also noted in numbers of TH-ir cells in the substantia nigra, with more cells in males than females. However, prenatal exposure to excess T did not affect numbers of TH-ir cells in the substantia nigra, suggesting that this sex difference is organised independently of prenatal actions of T. Together, these results demonstrate sex differences in the sheep VTA dopamine system which are mimicked by prenatal treatment with excess T.

NPY and VGF immunoreactivity increased in the arcuate nucleus, but decreased in the nucleus of the Tractus Solitarius, of type-II diabetic patients

Ample animal studies demonstrate that neuropeptides NPY and α-MSH expressed in Arcuate Nucleus and Nucleus of the Tractus Solitarius, modulate glucose homeostasis and food intake. In contrast is the absence of data validating these observations for human disease. Here we compare the post mortem immunoreactivity of the metabolic neuropeptides NPY, αMSH and VGF in the infundibular nucleus, and brainstem of 11 type-2 diabetic and 11 non-diabetic individuals. α-MSH, NPY and tyrosine hydroxylase in human brain are localized in the same areas as in rodent brain. The similar distribution of NPY, α-MSH and VGF indicated that these neurons in the human brain may share similar functionality as in the rodent brain. The number of NPY and VGF immuno positive cells was increased in the infundibular nucleus of diabetic subjects in comparison to non-diabetic controls. In contrast, NPY and VGF were down regulated in the Nucleus of the Tractus Solitarius of diabetic patients. These results suggest an activation of NPY producing neurons in the arcuate nucleus, which, according to animal experimental studies, is related to a catabolic state and might be the basis for increased hepatic glucose production in type-2 diabetes.

Stages of the pathologic process in Alzheimer disease: age categories from 1 to 100 years

Two thousand three hundred and thirty two nonselected brains from 1- to 100-year-old individuals were examined using immunocytochemistry (AT8) and Gallyas silver staining for abnormal tau; immunocytochemistry (4G8) and Campbell-Switzer staining were used for the detection ofβ-amyloid. A total of 342 cases was negative in the Gallyas stain but when restaged for AT8 only 10 were immunonegative. Fifty-eight cases had subcortical tau predominantly in the locus coeruleus, but there was no abnormal cortical tau (subcortical Stages a-c). Cortical involvement (abnormal tau in neurites) was identified first in the transentorhinal region (Stage 1a, 38 cases). Transentorhinal pyramidal cells displayed pretangle material (Stage 1b, 236 cases). Pretangles gradually became argyrophilic neurofibrillary tangles (NFTs) that progressed in parallel with NFT Stages I to VI. Pretangles restricted to subcortical sites were seen chiefly at younger ages. Of the total cases, 1,031 (44.2%) had β-amyloid plaques. The first plaques occurred in the neocortex after the onset of tauopathy in the brainstem. Plaques generally developed in the 40s in 4% of all cases, culminating in their tenth decade (75%). β-amyloid plaques and NFTs were significantly correlated (p < 0.0001). These data suggest that tauopathy associated with sporadic Alzheimer disease may begin earlier than previously thought and possibly in the lower brainstem rather than in the transentorhinal region.

The pathological process underlying Alzheimer's disease in individuals under thirty

Brains of 42 individuals between the ages of 4 and 29 were examined with antibodies (AT8, 4G8) and silver stains for the presence of intraneuronal and extracellular protein aggregates associated with Alzheimer's disease. Thirty-eight of 42 (38/42) cases displayed abnormally phosphorylated tau protein (pretangle material) in nerve cells or in portions of their cellular processes, and 41/42 individuals showed no extracellular amyloid-β protein deposition or neuritic plaques-an individual with Down syndrome was the only exception. In 16/42 cases abnormal tau was found in the transentorhinal region, and in 3/42 cases this site was Gallyas-positive for isolated NFTs (NFT stage I). Of 26 cases that lacked abnormal tau in the transentorhinal region, 4 did not show pretangle material at subcortical sites. The remaining 22 of these same 26 cases, however, had subcortical lesions confined to non-thalamic nuclei with diffuse projections to the cerebral cortex, and, remarkably, in 19/22 individuals the pretangle material was confined to the noradrenergic coeruleus/subcoeruleus complex. Assuming the pretangle alterations are not transient and do not regress, these findings may indicate that the Alzheimer's disease-related pathological process leading to neurofibrillary tangle formation does not begin in the cerebral cortex but, rather, in select subcortical nuclei, and it may start quite early, i.e., before puberty or in early young adulthood.

Aromatic L-amino acid decarboxylase-immunoreactive structures in human midbrain, pons, and medulla

The objective of the present study was to determine with precision the localization of neurons and fibers immunoreactive (ir) for aromatic L-amino acid decarboxylase (AADC), the second-step enzyme responsible for conversion of L-dihydroxyphenylalanine (L-DOPA) to dopamine (DA) and 5-hydroxytryptophan (5-HTP) to serotonin (5-hydroxytryptamine: 5-HT) in the midbrain, pons, and medulla oblongata of the adult human brain. Intense AADC immunoreactivity was observed in a large number of presumptive 5-HT neuronal cell bodies distributed in all of the raphe nuclei, as well as in regions outside the raphe nuclei such as the ventral portions of the pons and medulla. Moderate to strong immunoreaction was observable in presumptive DA cells in the mesencephalic reticular formation, substantia nigra, and ventral tegmental area of Tsai, as well as in presumptive noradrenergic (NA) cells, which were aggregated in the locus coeruleus and dispersed in the subcoeruleus nuclei. In the medulla oblongata, immunoreaction of moderate intensity was distributed in the mid and ventrolateral portions of the intermediate reticular nucleus, which constitutes the oblique plate of A1/C1 presumptive adrenergic and/or NA neurons. The dorsal vagal AADC-ir neurons were fewer in number and stained more weakly than cells immunoreactive for tyrosine hydroxylase (TH). AADC immunoreactivity was not identified in an aggregate of TH-ir neurons lying in the gelatinous subnucleus of the solitary nucleus, a restricted region just rostroventral to the area postrema. Nonaminergic AADC-positive neurons (D neurons), which are abundant in the rat and cat midbrain, pons, and medulla, were hardly detectable in homologous regions in the human brain, although they were clearly distinguishable in the forebrain.

Labetalol facilitates GABAergic transmission to rat periaqueductal gray neurons via antagonizing beta1-adrenergic receptors--a possible mechanism underlying labetalol-induced analgesia

Labetalol, a combined alpha1, beta1, and beta2 adrenoceptor-blocking drug, has been shown to have analgesic properties in vivo. To determine the underlying mechanisms, we examined its effects on GABAA receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) and spontaneous firings of rat ventrolateral periaqueductal gray (PAG) neurons, either mechanically dissociated, or in acute brain slices. These PAG neurons mediate opioid-mediated analgesia and pain transmission and are under tonic control of GABAergic interneurons. An increase in GABAergic transmission to these neurons yields an inhibitory hyperpolarized state and may interrupt pain signal transmission. Using patch clamp techniques, we found that labetalol reversibly increases the frequency of sIPSCs without changing their mean amplitude. This indicates that labetalol enhances GABAergic synaptic transmission by a presynaptic mechanism. Metoprolol, a specific beta1-adrenoceptor antagonist, also reversibly enhanced sIPSC frequency. In the presence of metoprolol, labetalol-induced increase in sIPSC frequency was significantly attenuated or even abolished. These results suggest that labetalol shares the same pathway as metoprolol in enhancing GABAergic transmission via an inhibition of presynaptic beta1-adrenoceptors. We further showed that labetalol reversibly reduced the firing rate of PAG neurons. This reduction was significantly attenuated in the presence of bicuculline, a selective antagonist of GABAA receptors. These data indicate that labetalol-induced inhibition of PAG cell firing is attributable to its potentiation of GABAergic transmission. Based on these data, we postulate that labetalol-induced analgesia is at least in part ascribed to its antagonistic effects on presynaptic beta1-adrenoceptors.

Distribution and morphology of putative catecholaminergic and serotonergic neurons in the medulla oblongata of a sub-adult giraffe, Giraffa camelopardalis

The current study details the nuclear parcellation and appearance of putative catecholaminergic and serotonergic neurons within the medulla oblongata of a sub-adult giraffe, using immunohistochemistry for tyrosine hydroxylase and serotonin. We hypothesized that the unusual phenotype of the giraffe, this being the long neck and potential axonal lengthening of these neurons, may pose specific problems in terms of the efficient functioning of these systems, as several groups of catecholaminergic and serotonergic neurons, especially of the medulla, are known to project to the entire spinal cord. This specific challenge may lead to observable differences in the nuclear parcellation and morphology of these systems in the giraffe. Our personal observations in the giraffe reveal that, as with other Artiodactyls, the spinal cord extends to the caudal end of the sacral vertebrae. Within the giraffe medulla we found evidence for five putative catecholaminergic (neurons containing tyrosine hydroxylase) and five serotonergic nuclei. In terms of both morphological appearance of the neurons and nuclear parcellation we did not find any evidence for features that may be considered affected by the phenotype of the giraffe. The nuclear parcellation and appearance of both the putative catecholaminergic and serotonergic systems in the medulla of the giraffe studied are strikingly similar to that seen in previous studies of other Artiodactyls. We interpret these findings in terms of a growing literature detailing order specific phylogenetic constraints in the evolution of these neuromodulatory systems.

Distribution and morphology of cholinergic, putative catecholaminergic and serotonergic neurons in the brain of the Egyptian rousette flying fox, Rousettus aegyptiacus

Over the past decade much controversy has surrounded the hypothesis that the megachiroptera, or megabats, share unique neural characteristics with the primates. These observations, which include similarities in visual pathways, have suggested that the megabats are more closely related to the primates than to the other group of the Chiropteran order, the microbats, and suggests a diphyletic origin of the Chiroptera. To contribute data relevant to this debate, we used immunohistochemical techniques to reveal the architecture of the neuromodulatory systems of the Egyptian rousette (Rousettus aegypticus), an echolocating megabat. Our findings revealed many similarities in the nuclear parcellation of the cholinergic, putative catecholaminergic and serotonergic systems with that seen in other mammals including the microbat. However, there were 11 discrete nuclei forming part of these systems in the brain of the megabat studied that were not evident in an earlier study of a microbat. The occurrence of these nuclei align the megabat studied more closely with primates than any other mammalian group and clearly distinguishes them from the microbat, which aligns with the insectivores. The neural systems investigated are not related to such Chiropteran specializations as echolocation, flight, vision or olfaction. If neural characteristics are considered strong indicators of phylogenetic relationships, then the data of the current study strongly supports the diphyletic origin of Chiroptera and aligns the megabat most closely with primates in agreement with studies of other neural characters.

Nuclear factor kappa-B p50 and p65 subunits expression in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia after Alzheimer's disease (AD). Parkinsonism in DLB is mainly caused by neuronal loss with Lewy bodies (LBs) in the substantia nigra, thereby inducing degeneration of the nigrostriatal dopaminergic pathway similar to that in Parkinson's disease (PD). To clarify the pathogenesis of DLB, it is important to investigate the mechanisms involved in the degenerative process of LB-bearing neurones. Several reports suggest a role for nuclear factor kappa-B (NFkappaB) in the manifestation of neurodegenerative conditions such as AD and PD. The aim of the present study was to investigate whether NFkappaB subunits are involved in the pathogenesis of neurodegeneration in DLB by measuring tyrosine hydroxylase (TH), NFkappaB p65 and p50 protein expression in frontal cortex and substantia nigra pars compacta of DLB and control human brains. An increase, although not statistically significant, in nigral TH expression in DLB cases was observed. There were no differences in the cortical and nigral expression levels of NFkappaB p65 subunit between control and DLB cases. Western blots of the frontal cortex showed no differences in the expression levels of NFkappaB p50 subunit. However, NFkappaB p50 levels were significantly decreased (P < 0.05) in the pars compacta of the substantia nigra in the DLB cases in comparison with controls. The decrease in the expression of the p50 subunit in the substantia nigra of DLB cases achieved in the present study may increase the vulnerability of the dopaminergic neurones to a possible neurotoxic effect of p65 subunit. Thus, normal levels of NFkappaB p65 might be toxic in neurones with a low expression of the NFkappaB p50 subunit.

Development of A9/A10 dopamine neurons during the second and third trimesters in the African green monkey

Disruption in the development of dopamine-containing neurons has been postulated to underlie several CNS disorders. However, there have been no quantitative studies on the normal development of primate dopamine neurons. Thus, the fetal maturation of primate midbrain dopamine neurons was examined to establish changes that occur in the A9/A10 groups during the second and third trimesters. Eleven fetal African green monkey midbrains were immunostained for tyrosine hydroxylase (TH-ir) as a marker for dopamine neurons and quantified using stereological techniques (nucleator method). The number and size of defined dopamine neurons and the volume occupied by A9/A10 neurons increased in near linear fashion throughout the term. The estimated number of defined dopamine neurons in each hemisphere rose from approximately 50,000 at embryonic day (E) 70 to 225,000 at birth (E165), similar to the adult population. The size and the area occupied by them at birth were, however, well below the estimated adult levels. Additionally, the younger fetal midbrains had far less diversity in dopamine cell volumes compared with older fetuses and adult brains. Until midway through gestation (E81), clusters of apparently immature midbrain TH-ir cells were observed, but could not be counted. Even though the majority of cells destined to become dopamine neurons are generated in the first trimester, phenotypical maturation of A9 and A10 cell bodies continues steadily throughout gestation and extends well into the postnatal period. These data have relevance to transplantation studies that employ fetal dopaminergic grafts, and to disorders hypothesized to result from damage to developing midbrain dopamine neurons.

Tyrosine hydroxylase and acetylcholinesterase in the domestic pig mesencephalon: An immunocytochemical and histochemical study

The mesencephalon of the young domestic pig was studied by tyrosine hydroxylase (TH) immunocytochemistry and acetylcholinesterase (AChE) histochemistry with focus on the substantia nigra (SN), the ventral tegmental area (VTA), and related areas. The purpose was to obtain information on the organization of the mesencephalic, TH immunoreactive (TH-i), and dopaminergic areas of the pig, in order to provide the necessary background for the possible use of the pig as an alternative large animal experimental model for research on Parkinson's disease, including the use of encapsulated pig dopaminergic neurons for intracerebral xenotransplantation. Significant findings in the pig, compared to observations in other species, included the presence of prominent bundles of TH-i dendrites passing in a dorsoventral direction from pars compacta into pars reticulata at middle and caudal levels of the SN, and the presence of a distinct TH-i substantia nigra pars lateralis (SNL). Caudally in the pig mesencephalon, the retrorubral field (RRF) was found to be very extensive. The view of the RRF, SN, and VTA as parts of the same integrated system was indicated by the crisscrossing of TH-i dendrites at the transitions between these areas. Estimation of the number of TH-i neurons in the SN and the VTA showed that these nuclei were of equal size in the pig. Further, it was found that TH-i nerve cells were present in the midline between the VTA in the interfascicular and rostral linear groups. TH-i nerve cells were also present in the otherwise serotoninergic dorsal raphe nuclei, just as other TH-i cells formed a perirubral cell group. AChE-positive neurons were present in both SN and VTA, and appeared to have the same size and morphology as the TH-i neurons in these areas. Within both nuclei, there were local differences in the AChE staining density, but perhaps more significantly were some marked differences in the structure of the AChE-positive neuropil of the two areas. We anticipate that the present description of the cellular organization of the TH-i dopaminergic areas in the domestic pig ventral mesencephalon will be useful for the development of a nonprimate, large animal, experimental model of Parkinson's disease.

Noradrenaline storage function of species-specific protein bodies, markers of monoamine neurons in human locus coeruleus demonstrated by dopamine-beta-hydroxylase immunogold localization

Our histochemical and ultrastructural studies have identified, in human catecholamine locus coeruleus (LC) neurons, abundant and large spherical protein bodies (PB), containing histone-like, arginine-rich proteins, which originate as dense bodies in mitochondria. This species-specific phenotype in the neurons of man is highly intriguing. In the electron microscope PB are disrupted in LC neurons in depressed individuals, where noradrenaline is known to be reduced. This coincidence of ultrastructure and neurochemistry raises the question whether these bodies could qualify as noradrenaline-storing organelles in the human LC. Our rationale was to examine, in known model tissues that contain catecholamines--sympathetic ganglia and tumors of the autonomic nervous system--if vesicles show the same fine structure and histochemistry as the PB of the human LC. Hence, we selected biopsy tissues of five ganglioneuromas and postmortem tissues of LC from 25 control subjects. Since dopamine-beta-hydroxylase (DBH) is a hallmark of noradrenaline identity and present in dense core vesicles, the investigation of DBH localization with the immunogold method constituted the experiment of choice for this study. Histochemical determinations of arginine with Carmoisine L, and of lipids with Rhodamine B complemented the study of similarities between the PB of the human LC and ganglioneuromas. Our results showed, with the colloidal gold method, that DBH immunogold labeling was localized in the core and in the double membranes of the PB, and also in the adjacent mitochondria. These results indicate that protein bodies (a) are unequivocal storage vesicles of noradrenaline, and (b) derive from regular mitochondria and represent a new phenotype in man, which is probably an evolutionary adaptation of amine-storing organelles.

Phenotypic expression of monoamines and GABA in the early development of human telencephalon, transient or not transient

We review the phenotypic expression of molecules involved in monoamine and GABA neurotransmission in the developing human brain. Recent experimental reports have analyzed neurotransmitter signaling before the onset of synaptogenesis, which could act to influence early developmental events such as proliferation, migration, and differentiation of animal brain development. Such signaling may also occur in human development. The expression of molecules involved in neurotransmission in precocious human brain may reflect either the differentiation of a permanent neurotransmitter system of the adult brain or transient expression to serve specific developmental functions different from those in the adult brain. We review the changes observed in the expression of various catecholamine markers such as tyrosine-hydroxylase (TH) immunoreactivity in various neuronal populations of the developing human telencephalon. The specific transporter for serotonin, serotonin transporter (SERT) has been detected in fibers of the internal capsule (IC) during the restricted time period of 12-14 gestational weeks in humans. These serotonin-containing fibers do not correspond to serotoninergic ascending axons from the raphe nuclei. They may be the human counterpart of the thalamo-cortical axons that have been shown to uptake serotonin during the critical period of development of the sensory systems in rodents. GABA phenotypes are expressed in numerous cells of the human ganglionic eminence (GE) and cerebral wall at the end of the embryonic period proper. These results are similar to that described at comparable developmental stages in the mouse and support the hypothesis of an early migration from ganglionic progenitors in humans. But one cannot exclude a transient expression of GABA within the post-mitotic neurons, which could influence early developmental events. In conclusion, data showing the phenotypic expression of molecules in discrete areas of the brain at various points in the protracted human development require careful interpretation.

Catecholaminergic neurons in the brain-stem and sleep apnea in SIDS victims

BACKGROUND

Tyrosine hydroxylase (TH) is a specific marker for catecholaminergic neurones. Some reports have demonstrated a decrease of TH in the Sudden Infant Death Syndrome (SIDS) compared with controls. To further investigate this, the correlation between TH and sleep apnea was investigated here.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age. They included 26 cases of SIDS. All the infants had been recorded during one night in a pediatric sleep laboratory some 3 to 12 weeks before death. The frequency and the duration of sleep apnea were analyzed. The brain stem material was collected and subjected to immunohistochemical studies for TH. The density of TH-immunoreactive neurons was measured in the nucleus hypoglossus, nervus vagus dorsalis, solitary and ambiguous and the ventrolateral medulla (VLM) in the medulla oblongata. Correlation analyses were carried out between the density of TH-immunoreactive neurons and the data from the sleep apnea studies.

RESULTS

There was no SIDS specific correlation between TH-immunoreactive neurons in the nucleus hypoglossus, nervus vagus dorsalis, solitary and ambiguous and the ventrolateral medulla (VLM) in the medulla oblongata and the frequency and duration of sleep apnea.

CONCLUSIONS

No significant association between the pathological data and the physiological data refers to TH positive neurons in the medulla oblongata in SIDS victims.

Development of catecholaminergic neurons in the human medulla oblongata

Distribution and maturation of catecholaminergic (CA) neurons have been studied by tyrosine hydroxylase immunohistochemistry in the medulla oblongata of human fetuses aged 14.5-25 weeks of gestation. Already at 14.5 weeks, CA neurons were observed in two longitudinally oriented cell clusters, one located ventrolaterally in the area of the lateral reticular and ambiguous nuclei, the other one dorsomedially forming 4 groups related to the dorsal vagal nucleus, the commissural nucleus of the vagus, the nucleus of the tractus solitarius and the area postrema. CA neurons in the area postrema were often found close to blood vessels. Scattered intermediate CA neurons were seen between these two larger clusters. CA neurons still appeared immature exhibiting bipolar morphology with only one or two short stout processes, which hardly branched. At 21 weeks, CA neurons occupied essentially the same location, but had a more mature morphology. Though still bipolar in shape, they had thinner and much longer processes which frequently branched. Both in the ventrolateral and the dorsomedial cell clusters, these processes were frequently lying close to blood vessels. At 25 weeks, CA cells had matured into multipolar neurons with long thin processes forming fine fiber networks in the ventrolateral medulla as well as around and within the dorsal vagal and solitarius nuclei. Only at this stage, a distinct CA fiber tract was seen located in the region of the tractus solitarius. Our results indicate that CA neurons in the human medulla, which are presumably involved in the control of ventilation and blood pressure, though generated rather early during development, mature relatively late.

Degeneration of tyrosine hydroxylase-immunoreactive neurons in the cerebral cortex and hippocampus of patients with dementia with Lewy bodies

We immunohistochemically investigated the degeneration of tyrosine hydroxylase (TH)-positive neurons in the cerebral cortex and hippocampus of dementia with Lewy bodies (DLB) brains. TH-positive neurons in the cerebral cortex and hippocampus were decreased in number, and were rarely associated with Lewy bodies (LB) or neurofibrillary tangles (NFT). A mild to moderate loss of TH-positive neurons was observed in both the cerebral cortex and substantia nigra. In addition, most brains showing low NFT stages and lacking amyloid deposits (AM), corresponding to pure-form DLB brains, demonstrated a moderate to severe loss of TH-positive neurons. These findings suggest that TH-positive neurons in the cerebral cortex degenerate by a pathomechanism similar to that in the substantia nigra, and that the degeneration of these neurons is partly related to LB or NFT formation in either the substantia nigra or cerebral cortex.

Clinical and neuropathological correlates of Lewy body disease

We investigated distribution of neuronal and glial inclusions in 30 brains obtained at autopsy from patients with Lewy bodies (LBs) disease, which was clinically diagnosed as Parkinson's disease (PD), dementia with Lewy bodies (DLB), or pure autonomic failure (PAF). The cases were classified, according to the guidelines for the pathological diagnosis of DLB, into three types: the neocortical type, the limbic type, and the brain stem-predominant type. All postmortem brains had coil-like glial inclusions as well as LBs, and the distribution pattern and density of glial inclusions and LBs varied. The distribution of glial inclusions was strikingly similar to that of LBs. In the cerebral cortex in particular, the number of glial inclusions was fairly well correlated with the number of LBs, irrespective of the three pathological types. In the brain stem, distribution was similar between glial inclusions and LBs, and there was no distinct pathological difference among the three types. Glial inclusions and LBs were immunohistopathologically similar with respect to ubiquitin, alpha-synuclein, and Gallyas-Braak staining. The clinical features of the three types of LB disease were also similar; i.e., parkinsonism, some dementia, and/or autonomic failure. The inclusions in neurons and glial cells occurred in parallel with respect to tissue distribution and immunohistochemical features, suggesting that accumulation of neuronal and glial inclusions in the LB diseases have a common pathological feature. Our findings suggest that DLB, PD with and without dementia, and PAF share one clinicopathological entity.

Localization of sepiapterin reductase in the human brain

Sepiapterin reductase (SPR) is the enzyme that catalyzes the final step of the synthesis of tetrahydrobiopterin (BH4), the cofactor for phenylalanine hydroxylase, tyrosine hydroxylase (TH), tryptophan hydroxylase, and nitric oxide synthase (NOS). Although SPR is essential for synthesizing BH4, the distribution of SPR in the human brain has not yet been clarified. In the present study, we purified recombinant human SPR from cDNA, raised an antibody against human SPR (hSPR), and examined the localization of SPR protein and SPR activity. Human brain homogenates from the substantia nigra (SN), caudate nucleus (CN), gray and white matters of the cerebral cortex (CTX), and dorsal and ventral parts of the medulla oblongata (MO) were subjected to Western blot analysis with anti-hSPR antibody or with anti-TH antibody. Whereas TH protein showed a restricted localization, being mainly detected in the SN and CN, SPR protein was detected in all brain regions examined. SPR activity was relatively high compared with the activity of GTP cyclohydrolase I (GCH), the rate-limiting biosynthetic enzyme of BH4, and was more widely distributed than GCH activity. Immunohistochemistry revealed SPR immunoreactivity in pyramidal neurons in the cerebral CTX, in a small number of striatal neurons, and in neurons of the hypothalamic and brain stem monoaminergic fields and olivary nucleus. Double-staining immunohistochemistry showed that TH and SPR were colocalized in the SN dopamine neurons. Localization of SPR immunoreactive neurons corresponded to monoamine or NOS neuronal fields, and also to the areas where no monoamine or NOS neurons were located. The results indicate that there might be a BH4 biosynthetic pathway where GCH is not involved and that SPR might have some yet unidentified function(s) in addition to BH4 biosynthesis.

Developmental neurotransmitter pathology in the brainstem of sudden infant death syndrome: a review and sleep position

Developmental studies on neurotransmitters and their receptors in sudden infant death syndrome (SIDS) infants and controls are reviewed, including comparison between the prone and supine positions at death. In SIDS infants, there are an increase of glial fibrillary acidic protein (GFAP)-positive astrocytes in the brainstem, an increase of substance P (SP) in the medulla and pons, a decrease of tyrosine hydroxylase (TH)-positive catecholaminergic neurons in the ventrolateral medulla (VLM), and vagal nuclei in the medulla oblongata and basal ganglia, a decrease of tryptophan hydroxylase (TrH)-positive serotonergic neurons in the periaqueductal gray matter (PAG), and decreases of 5-hydroxytryptamine 1A (5-HT1A) and 5-HT2A receptor immunoreactivities in the VLM and vagal nuclei in the medulla oblongata. These findings may be the result of chronic or repeated hypoxia and at the same time suggest hypofunction or immaturity of cardiorespiratory regulation. In contrast, 5-HT1A and 5-HT2A receptor immunoreactivities are increased in the PAG of SIDS infants. These increased immunoreactivities may reflect delayed neuronal maturation or a developmental abnormality of the nocicetive reaction of cardiorespiratory and arousal control in SIDS. Also, there are no differences of brainstem gliosis and catecholaminergic neuron changes between the prone and supine positions. Therefore, these changes may be predisposing factors for SIDS.

Distribution of alpha 2-adrenergic receptor binding in the developing human brain stem

Rapid and dramatic changes occur in cardiorespiratory function during early human life. Catecholamines within select brain stem nuclei are implicated in the control of autonomic and respiratory function, including in the nucleus of the solitary tract and the dorsal motor nucleus of X. Animal and adult human studies have shown high binding to alpha 2-adrenergic receptors in these regions. To determine the developmental profile of brainstem alpha 2-adrenergic binding across early human life, we studied brain stems from five fetuses at midgestation, three newborns (37-38 postconceptional weeks), and six infants (44-61 postconceptional weeks). We used quantitative tissue receptor autoradiography with [3H]para-aminoclonidine as the radioligand and phentolamine as the displacer. In the fetal group, binding was high (63-93 fmol/mg tissue) in the nucleus of the solitary tract, dorsal motor nucleus of X, locus coeruleus, and reticular formation; it was low (< 32 fmol/mg tissue) in the principal inferior olive and basis pontis. Binding decreased in all regions with age: in infancy, the highest binding was in the intermediate range (32-62 fmol/mg tissue) and was localized to the nucleus of the solitary tract and dorsal motor nucleus of X. The most substantial decrease in binding (75%-85%) between the fetal and infant periods occurred in the pontine and medullary reticular formation and hypoglossal nucleus. Binding remained low in the principal inferior olive and basis pontis. The decreases in binding with age remained significant after quench correction. These data suggest that rapid and dramatic changes occur in early human life in the brain stem catecholaminergic system in regions related to cardiorespiratory control.

Noradrenergic dysfunction in the prefrontal cortex in depression: an [15O] H2O PET study of the neuromodulatory effects of clonidine

BACKGROUND

Noradrenergic dysfunction has been consistently implicated in depression. Much of the evidence, though, has been indirect, such as an attenuated growth hormone response to the alpha2-adrenoceptor agonist clonidine. To more directly examine central functioning of the noradrenergic system in depression, we have used [15O] H2O positron emission tomography (PET) to measure cerebral blood flow (rCBF) in combination with clonidine as a neuromodulatory probe.

METHODS

Subjects were six depressed and six healthy women, medication free and matched for age and phase of menstrual cycle. Two PET scans were acquired at baseline and two scans at 20 and 35 min following an intravenous clonidine infusion of 1.4 microg/kg while subjects performed a sustained attention task.

RESULTS

The growth hormone response did not show a significant difference between groups. However, PET results revealed a difference in the right superior prefrontal cortex that was resolved as an interaction from decreased rCBF in healthy control subjects but increased rCBF in the depressed group, which was not accounted for by differences in task performance.

CONCLUSIONS

This differential effect of clonidine in the right prefrontal cortex provides in vivo evidence of noradrenergic dysfunction in depression, which we postulate arises from functionally impaired presynaptic alpha2-adrenoceptors as well as regionally "supersensitive" postsynaptic cortical alpha2-adrenoceptors.

Expression of calbindin D28K in the dopaminergic mesotelencephalic system in embryonic and fetal human brain

A subset of tyrosine-hydroxylase (TH) neurons of the substantia nigra (A9) containing calbindin D28K (CaBP) appeared to be less vulnerable to cell death induced by Parkinson's disease than the subset containing dopamine (DA) alone. Because grafting procedures of fetal human neurons are increasingly used in the therapy of Parkinson's disease, it is important to study the development of DA neurons coexpressing CaBP. In humans, the genesis of TH immunoreactivity of A9, of the ventral tegmental area (A10), and of the retrorubral area (A8) occurred during a 2-week period from the 4. 5th gestational week (g.w.) in the ventricular zone of the floor plate and the contiguous basal plate of the mesencephalon and diencephalon, i.e., the prosomeres p1-p3. Double-immunolabeled TH-CaBP neurons were detected from 5.5 g.w. on, in the first wave of DA neuron's migration, and were observed in their final residence in the dorsal A9 by 10.5 g.w. Calretinin immunoreactivity was expressed in TH-immunoreactive (IR) neurons from 10.5 g.w. on. Ascending TH-CaBP-IR axons were observed toward the telencephalon from 6-7 g.w. , reaching the anlage of the nucleus accumbens and amygdaloid complex at 10.5 g.w., but were not detected in the ganglionic eminence at this latter stage. Dopaminergic patches were detected at 13 g.w. in the anlage of the putamen, but no TH-CaBP-IR fibers were observed in the matrix at this stage. In conclusion, even if CaBP immunoreactivity was detected in TH-IR cell bodies during the embryonic period, the TH-CaBP-IR axonal terminal was observed earlier in some limbic-related areas than in the matrix compartment of the basal ganglia in humans.

Distribution of tyrosine hydroxylase-immunoreactive neurones in the diencephalon and mesencephalon of the coypu (Myocastor coypus)

The aim of the present study was to examine the catecholaminergic neurones located within the midbrain of the coypu, a South American hystricomorph rodent. The neuronal distribution of the catecholaminergic systems and morphological parameters of the immunostained cell bodies and fibres were investigated, using an immunohistochemical method. The brains of five coypu were fixed, immersed in gelatine-glycerol and cut in 40-micron slices using a freezing microtome. Samples were processed with ultrasound-based antigen retrieval and stained with labelled antityrosine hydroxylase monoclonal antibody. An image analyser was used to measure the neuronal bodies. The catecholaminergic neurones of the tuberoinfundibular system were mainly observed in the arcuate and periventricular nuclei with their axons projecting towards to the median eminence; they represented 28% of the global population of tyrosine hydroxylase-immunoreactive cells observed. Significant morphological differences were observed in comparison with the other two studied systems. Fifty per cent of total catecholaminergic neurones were detected in the nigrostriatal system distributed in the reticular and compact substance nigra. Most neuronal bodies had a fusiform aspect. The immunoreactive neurones of the mesolimbic system represented 22% of the total population. They were distributed around the interpeduncular nucleus. Two types of morphologically different catecholaminergic systems of the brain were established: hypothalamic neurones located in the periventricular and arcuate nuclei and mesencephalic neurones located in the substance nigra and interpeduncular nuclei. These systems showed morphological and probably physiological-pharmacological differences.

Tyrosine hydroxylase-like immunoreactive synaptic boutons in the inferior colliculus of the cat

The data on the distribution of catecholaminergic cells and fibers in such a significant subcortical relay auditory center as the inferior colliculus (IC) are both few and controversial, and ultrastructural data are lacking. Young adult mongrel cats of both sexes were used. Following routine preparation procedures, the ultrathin sections were prepared for the ultrastructural examination of tyrosine hydroxylase (TH)-like immunoreactivity. TH-positive neuronal perikarya were not detected in the IC. On the other hand, an appreciable number of TH-immunoreactive unmyelinated axons and synaptic boutons were found in all subdivisions of the IC, most often in the nucleus externus, followed by the nucleus pericentralis, and a few were seen in the dorsomedial part of the central nucleus. The boutons measured 0.5-1.8 microns, contained pleomorphic synaptic vesicles, and established symmetrical synaptic contacts almost exclusively with dendrites of small caliber.

Up-regulation of tyrosine hydroxylase mRNA in a sub-population of A10 dopamine neurons in Parkinson's disease

Neuronal injury has been consistently found in A10 midbrain dopamine neurons in Parkinson's disease (PD). To assess changes in neurotransmitter-related gene transcription, in these neurons in PD, tyrosine hydroxylase (TH) mRNA expression was examined in the ventral tegmental area (VTA) of seven PD cases and seven control subjects, using in situ hybridization histochemistry (ISHH). In controls, TH mRNA expression was found in both melanised and non-melanised neurons in the VTA. Neither population expressed dopamine beta-hydroxylase (DBH). Of the melanised neurons, 99% were TH mRNA positive. The level of the TH mRNA signal (expressed as grain density per cell) was similar in the two populations (melanised: 0.129+/-0.004 (mean+/-S.E.M.), n=142 vs. non-melanised: 0.138+/-0.006, n=89, P>0.05, Student's t-Test). In PD cases there was no significant change in TH mRNA expression in melanised neurons (0.138+/-0.003, n=196), and the proportion of positively labeled melanised neurons was 98%. However, non-melanised neurons showed significantly higher TH mRNA (0.163+/-0.006, n=87) than non-melanised neurons in control subjects (P<0.005) and melanised neurons in the PD cases (P<0.0005). This up-regulation of TH mRNA expression in non-melanised neurons may suggest the existence of a compensatory mechanism at presynaptic level.

The connections of the dopaminergic system with the striatum in rats and primates: an analysis with respect to the functional and compartmental organization of the striatum

This Commentary compares the connections of the dopaminergic system with the striatum in rats and primates with respect to two levels of striatal organization: a tripartite functional (motor, associative and limbic) subdivision and a compartmental (patch/striosome-matrix) subdivision. The topography of other basal ganglia projections to the dopaminergic system with respect to their tripartite functional subdivision is also reviewed. This examination indicates that, in rats and primates, the following observations can be made. (1) The limbic striatum reciprocates its dopaminergic input and in addition innervates most of the dopaminergic neurons projecting to the associative and motor striatum, whereas the motor and associative striatum reciprocate only part of their dopaminergic input. Therefore, the connections of the three striatal subregions with the dopaminergic system are asymmetrical, but the direction of asymmetry differs between the limbic versus the motor and associative striatum. (2) The limbic striatum provides the main striatal input to dopamine cell bodies and proximal dendrites, with some contribution from a subset of neurons in the associative and motor striatum (patch neurons in rats; an unspecified group of neurons in primates), while striatal input to the ventrally extending dopamine dendrites arises mainly from a subset of neurons in the associative and motor striatum (matrix neurons in rats; an unspecified group of neurons in primates). (3) Projections from functionally corresponding subdivisions of the striatum, pallidum and subthalamic nucleus to the dopaminergic system overlap, but the specific targets (dopamine cells, dopamine dendrites, GABA cells) of these projections differ. Major differences include the following. (1) In rats, neurons projecting to the motor and associative striatum reside in distinct regions, while in primates they are arranged in interdigitating clusters. (2) In rats, the terminal fields of projections arising from the motor and associative striatum are largely segregated, while in primates they are not. (3) In rats, patch- and matrix-projecting dopamine cells are organized in spatially, morphologically, histochemically and hodologically distinct ventral and dorsal tiers, while in primates there is no (bi)division of the dopaminergic system that results in two areas which have all the characteristics of the two tiers in rats. Based on the anatomical data and known dopamine cell physiology, we forward an hypothesis regarding the influence of the basal ganglia on dopamine cell activity which captures at least part of the complex interplay taking place within the substantia nigra between projections arising from the different basal ganglia nuclei. Finally, we incorporate the striatal connections with the dopaminergic system into an open-interconnected scheme of basal ganglia-thalamocortical circuitry.