Category: Frontiers in Neuroanatomy

Development and characterization of a non-human primate model of disseminated synucleinopathy

Alberto J. Rico Edit "Development and characterization of a non-human primate model of disseminated synucleinopathy"
Introduction

The presence of a widespread cortical synucleinopathy is the main neuropathological hallmark underlying clinical entities such as Parkinson’s disease with dementia (PDD) and dementia with Lewy bodies (DLB). There currently is a pressing need for the development of non-human primate (NHPs) models of PDD and DLB to further overcome existing limitations in drug discovery.

Methods

Here we took advantage of a retrogradely-spreading adeno-associated viral vector serotype 9 coding for the alpha-synuclein A53T mutated gene (AAV9-SynA53T) to induce a widespread synucleinopathy of cortical and subcortical territories innervating the putamen. Four weeks post-AAV deliveries animals were sacrificed and a comprehensive biodistribution study was conducted, comprising the quantification of neurons expressing alpha-synuclein, rostrocaudal distribution and their specific location.

Results

Intraputaminal deliveries of AAV9-SynA53T lead to a disseminated synucleinopathy throughout ipsi- and contralateral cerebral cortices, together with transduced neurons located in the ipsilateral caudal intralaminar nuclei and in the substantia nigra pars compacta (leading to thalamostriatal and nigrostriatal projections, respectively). Cortical afferent systems were found to be the main contributors to putaminal afferents (superior frontal and precentral gyri in particular).

Discussion

Obtained data extends current models of synucleinopathies in NHPs, providing a reproducible platform enabling the adequate implementation of end-stage preclinical screening of new drugs targeting alpha-synuclein.

Differences in vocal brain areas and astrocytes between the house wren and the rufous-tailed hummingbird

Carolina López-Murillo Edit "Differences in vocal brain areas and astrocytes between the house wren and the rufous-tailed hummingbird"

The house wren shows complex song, and the rufous-tailed hummingbird has a simple song. The location of vocal brain areas supports the song’s complexity; however, these still need to be studied. The astrocytic population in songbirds appears to be associated with change in vocal control nuclei; however, astrocytic distribution and morphology have not been described in these species. Consequently, we compared the distribution and volume of the vocal brain areas: HVC, RA, Area X, and LMAN, cell density, and the morphology of astrocytes in the house wren and the rufous-tailed hummingbird. Individuals of the two species were collected, and their brains were analyzed using serial Nissl- NeuN- and MAP2-stained tissue scanner imaging, followed by 3D reconstructions of the vocal areas; and GFAP and S100β astrocytes were analyzed in both species. We found that vocal areas were located close to the cerebral midline in the house wren and a more lateralized position in the rufous-tailed hummingbird. The LMAN occupied a larger volume in the rufous-tailed hummingbird, while the RA and HVC were larger in the house wren. While Area X showed higher cell density in the house wren than the rufous-tailed hummingbird, the LMAN showed a higher density in the rufous-tailed hummingbird. In the house wren, GFAP astrocytes in the same bregma where the vocal areas were located were observed at the laminar edge of the pallium (LEP) and in the vascular region, as well as in vocal motor relay regions in the pallidum and mesencephalon. In contrast, GFAP astrocytes were found in LEP, but not in the pallidum and mesencephalon in hummingbirds. Finally, when comparing GFAP astrocytes in the LEP region of both species, house wren astrocytes exhibited significantly more complex morphology than those of the rufous-tailed hummingbird. These findings suggest a difference in the location and cellular density of vocal circuits, as well as morphology of GFAP astrocytes between the house wren and the rufous-tailed hummingbird.

Exploring an innovative decellularization protocol for porcine nerve grafts: a translational approach to peripheral nerve repair

Luisa Muratori Edit "Exploring an innovative decellularization protocol for porcine nerve grafts: a translational approach to peripheral nerve repair"
Introduction

Peripheral nerves are frequently affected by lesions caused by traumatic or iatrogenic damages, resulting in loss of motor and sensory function, crucial in orthopedic outcomes and with a significant impact on patients’ quality of life. Many strategies have been proposed over years to repair nerve injuries with substance loss, to achieve musculoskeletal reinnervation and functional recovery. Allograft have been tested as an alternative to the gold standard, the autograft technique, but nerves from donors frequently cause immunogenic response. For this reason, several studies are focusing to find the best way to decellularize nerves preserving either the extracellular matrix, either the basal lamina, as the key elements used by Schwann cells and axons during the regenerative process.

Methods

This study focuses on a novel decellularization protocol for porcine nerves, aimed at reducing immunogenicity while preserving essential elements like the extracellular matrix and basal lamina, vital for nerve regeneration. To investigate the efficacy of the decellularization protocol to remove immunogenic cellular components of the nerve tissue and to preserve the basal lamina and extracellular matrix, morphological analysis was performed through Masson’s Trichrome staining, immunofluorescence, high resolution light microscopy and transmission electron microscopy. Decellularized porcine nerve graft were then employed in vivo to repair a rat median nerve lesion. Morphological analysis was also used to study the ability of the porcine decellularized graft to support the nerve regeneration.

Results and Discussion

The decellularization method was effective in preparing porcine superficial peroneal nerves for grafting as evidenced by the removal of immunogenic components and preservation of the ECM. Morphological analysis demonstrated that four weeks after injury, regenerating fibers colonized the graft suggesting a promising use to repair severe nerve lesions. The idea of using a porcine nerve graft arises from a translational perspective. This approach offers a promising direction in the orthopedic field for nerve repair, especially in severe cases where conventional methods are limited.

Localization of hyperpolarization-activated cyclic nucleotide-gated channels in the vertebrate retinas across species and their physiological roles

Daniel Kim Edit "Localization of hyperpolarization-activated cyclic nucleotide-gated channels in the vertebrate retinas across species and their physiological roles"

Transmembrane proteins known as hyperpolarization-activated cyclic nucleotide-gated (HCN) channels control the movement of Na+ and K+ ions across cellular membranes. HCN channels are known to be involved in crucial physiological functions in regulating neuronal excitability and rhythmicity, and pacemaker activity in the heart. Although HCN channels have been relatively well investigated in the brain, their distribution and function in the retina have received less attention, remaining their physiological roles to be comprehensively understood. Also, because recent studies reported HCN channels have been somewhat linked with the dysfunction of photoreceptors which are affected by retinal diseases, investigating HCN channels in the retina may offer valuable insights into disease mechanisms and potentially contribute to identifying novel therapeutic targets for retinal degenerative disorders. This paper endeavors to summarize the existing literature on the distribution and function of HCN channels reported in the vertebrate retinas of various species and discuss the potential implications for the treatment of retinal diseases. Then, we recapitulate current knowledge regarding the function and regulation of HCN channels, as well as their relevance to various neurological disorders.

Phylogenetic reduction of the magnocellular red nucleus in primates and inter-subject variability in humans

Martin Stacho Edit "Phylogenetic reduction of the magnocellular red nucleus in primates and inter-subject variability in humans"
Introduction

The red nucleus is part of the motor system controlling limb movements. While this seems to be a function common in many vertebrates, its organization and circuitry have undergone massive changes during evolution. In primates, it is sub-divided into the magnocellular and parvocellular parts that give rise to rubrospinal and rubro-olivary connection, respectively. These two subdivisions are subject to striking variation within the primates and the size of the magnocellular part is markedly reduced in bipedal primates including humans. The parvocellular part is part of the olivo-cerebellar circuitry that is prominent in humans. Despite the well-described differences between species in the literature, systematic comparative studies of the red nucleus remain rare.

Methods

We therefore mapped the red nucleus in cytoarchitectonic sections of 20 primate species belonging to 5 primate groups including prosimians, new world monkeys, old world monkeys, non-human apes and humans. We used Ornstein-Uhlenbeck modelling, ancestral state estimation and phylogenetic analysis of covariance to scrutinize the phylogenetic relations of the red nucleus volume.

Results

We created openly available high-resolution cytoarchitectonic delineations of the human red nucleus in the microscopic BigBrain model and human probabilistic maps that capture inter-subject variations in quantitative terms. Further, we compared the volume of the nucleus across primates and showed that the parvocellular subdivision scaled proportionally to the brain volume across the groups while the magnocellular part deviated significantly from the scaling in humans and non-human apes. These two groups showed the lowest size of the magnocellular red nucleus relative to the whole brain volume and the largest relative difference between the parvocellular and magnocellular subdivision.

Discussion

That is, the red nucleus has transformed from a magnocellular-dominated to a parvocellular-dominated station. It is reasonable to assume that these changes are intertwined with evolutionary developments in other brain regions, in particular the motor system. We speculate that the interspecies variations might partly reflect the differences in hand dexterity but also the tentative involvement of the red nucleus in sensory and cognitive functions.

Arterial supply and morphological characteristics of sympathetic neurons in the human superior cervical ganglion

Jelena Boljanović Edit "Arterial supply and morphological characteristics of sympathetic neurons in the human superior cervical ganglion"

The aim of this study was the micromorphological analysis of the distribution of microvessels, mast cells and ganglionic neurons in two parts, proximal and distal of the human superior cervical sympathetic ganglions (SCSGs). Statistical analyses were applied to detect the possible metric regional differences in their densities. Five injected human SCSGs with colored India ink and gelatin were microdissected and examined. Second group of five human SCSGs was prepared and serially sliced for CD34 and mast cell tryptase immunostaining. The microscopic fields of two parts of the SCSGs were analyzed for the following quantifications: microvessel density (MVD), mast cell density (MCD), and ganglionic cell count and measurements. The mean number of CD34-positive microvessels in microscopic fields, the MVD, had a value of 83 for the upper parts, and 82.7 for the lower parts of SCSGs. The mean number of tryptase-positive mast cells in microscopic fields, the MCD, was 4.5 in the proximal parts, and 4.7 in the distal parts of SCSGs. The mean number of ganglionic neurons in microscopic fields was 19.5 in the proximal parts, and 19.8 in the distal parts of SCSGs. The density of CD34-positive microvessels, the density of tryptase-positive mast cells, and the density, mean diameters and mean areas of ganglionic neurons were not significantly different in two observed parts, upper and lower of the SCSGs. In conclusion, the distributions of microvessels, mast cells, and neurons in two parts of the SCSGs were uniform with no specific micromorphological variations, there is a homogenous vascular and cellular pattern within the SCSGs.

Developmental patterns of extracellular matrix molecules in the embryonic and postnatal mouse hindbrain

Ildikó Wéber Edit "Developmental patterns of extracellular matrix molecules in the embryonic and postnatal mouse hindbrain"

Normal brain development requires continuous communication between developing neurons and their environment filled by a complex network referred to as extracellular matrix (ECM). The ECM is divided into distinct families of molecules including hyaluronic acid, proteoglycans, glycoproteins such as tenascins, and link proteins. In this study, we characterize the temporal and spatial distribution of the extracellular matrix molecules in the embryonic and postnatal mouse hindbrain by using antibodies and lectin histochemistry. In the embryo, hyaluronan and neurocan were found in high amounts until the time of birth whereas versican and tenascin-R were detected in lower intensities during the whole embryonic period. After birth, both hyaluronic acid and neurocan still produced intense staining in almost all areas of the hindbrain, while tenascin-R labeling showed a continuous increase during postnatal development. The reaction with WFA and aggrecan was revealed first 4th postnatal day (P4) with low staining intensities, while HAPLN was detected two weeks after birth (P14). The perineuronal net appeared first around the facial and vestibular neurons at P4 with hyaluronic acid cytochemistry. One week after birth aggrecan, neurocan, tenascin-R, and WFA were also accumulated around the neurons located in several hindbrain nuclei, but HAPLN1 was detected on the second postnatal week. Our results provide further evidence that many extracellular macromolecules that will be incorporated into the perineuronal net are already expressed at embryonic and early postnatal stages of development to control differentiation, migration, and synaptogenesis of neurons. In late postnatal period, the experience-driven neuronal activity induces formation of perineuronal net to stabilize synaptic connections.

Anterograde trans-neuronal labeling of striatal interneurons in relation to dopamine neurons in the substantia nigra pars compacta

Fuyuki Karube Edit "Anterograde trans-neuronal labeling of striatal interneurons in relation to dopamine neurons in the substantia nigra pars compacta"

Recent advances in neural tracing have unveiled numerous neural circuits characterized by brain region and cell type specificity, illuminating the underpinnings of specific functions and behaviors. Dopaminergic (DA) neurons in the midbrain are highly heterogeneous in terms of gene and protein expression and axonal projections. Different cell types within the substantia nigra pars compacta (SNc) tend to project to the striatum in a cell-type-dependent manner characterized by specific topography. Given the wide and dense distribution of DA axons, coupled with a combination of synaptic and volume transmission, it remains unclear how DA release is spatially and temporally regulated, to appropriately achieve specific behaviors and functions. Our hypothesis posits that hidden rules governing synapse formation between pre-synaptic DA neuron types and striatal neuron types may modulate the effect of DA at a single-cell level. To address this conjecture, we employed adeno-associated virus serotype 1 (AAV1) to visualize the neural circuitry of DA neurons. AAV1 has emerged as a potent anatomical instrument capable of labeling and visualizing pre- and post-synaptic neurons simultaneously through anterograde trans-synaptic labeling. First, AAV1-Cre was injected into the SNc, resulting in Cre expression in both medium spiny neurons and interneurons in the striatum. Due to the potential occurrence of the retrograde transfer of AAV1, only striatal interneurons were considered for trans-synaptic or trans-neuronal labeling. Interneuron types expressing parvalbumin, choline acetyltransferase, somatostatin, or nitrogen oxide synthase exhibited Cre expression. Using a combination of AAV1-Cre and Cre-driven fluorophore expressing AAVs, striatal interneurons and the axons originating from the SNc were visualized in distinct colors. Using immunofluorescence against neurotransmitter transporters, almost all axons in the striatum visualized using this approach were confirmed to be dopaminergic. Moreover, individual DA axons established multiple appositions on the somata and proximal dendrites of interneurons. This finding suggests that irrespective of the extensive and widespread axonal arborization of DA neurons, a particular DA neuron may exert a significant influence on specific interneurons. Thus, AAV1-based labeling of the DA system can be a valuable tool to uncover the concealed rules governing these intricate relationships.