Entire Midbrain Research Articles

A Topographic Atlas of the Human Brainstem in the Ponto-Mesencephalic Junction Plane.

The human brainstem harbors neuronal aggregates that ensure the maintenance of several vital functions. It also acts as a major relay structure for the neuronal information that travels between the cerebral cortex, the cerebellum and the spinal cord. As such, this relatively small portion of the human brain houses a multitude of ascending and descending fibers that course among numerous nuclei whose exact boundaries are still uncertain. Such a large number of nuclei and fiber tracts confined to a relatively small and compact brain region imposes upon the brainstem a highly complex cytoarchitectonic organization that still needs to be deciphered. The present work provides a topographic atlas of the human brainstem composed of 45 anatomical plates, each containing a pair of adjacent sections stained with Cresyl Violet and Luxol Fast Blue to help delineating brainstem nuclei and fiber tracts, respectively. The plates, which cover the entire midbrain, pons and medulla oblongata, are composed of equally-spaced sections referenced and aligned parallel to the ponto-mesencephalic junction rather than the fastigium or the obex. This topographic landmark is particularly suitable for neurosurgical interventions aiming at specific nuclei of the mesencephalic tegmentum. In complement, we provide 8 anatomical plates containing adjacent sections stained for choline acetyltransferase and Luxol Fast Blue, taken through the midbrain and the pons. This open access atlas of the human brainstem is intended to assist neuroanatomists, neurosurgeons and neuropathologists in their work.

Impact of region of interest size on transcranial sonography based computer-aided diagnosis for Parkinson's disease.

Transcranial sonography (TCS) has gained increasing application for diagnosis of Parkinson's disease (PD) in clinical practice in recent years, because most PD patients, even in the early stage of PD, have abnormal hyperechogenicity of the substantia nigra (SN) in brainstem shown in TCS images. Therefore, the region of interest (ROI) for feature extraction should cover the SN region in a computer-aided diagnosis (CAD) system. The ROI size naturally affects the feature representation. However, there currently exist no unified standard for determining the size of ROI. In this work, we quantitatively compare the performance of TCS-based CAD with three sizes of ROIs, namely the entire midbrain (EM) region, the half of midbrain (HoM) region and the SN region. The experimental results on the original extracted features and the features by dimensionality reduction show that ROI covering the EM region achieves the overall best diagnosis performance. The results indicates that the neighboring regions around SN might also have abnormal symptoms, which cannot be clearly observed with naked eyes. It suggests that the large ROI includes more information for feature representation to improve the diagnosis performance of TCS-based CAD for PD.

Immunoreactivity of a G protein-coupled l-DOPA receptor GPR143, in Lewy bodies

l-3,4-Dihydroxyphenylalanine (l-DOPA) has been believed to be an inert amino acid precursor of dopamine, and is the most effective therapeutic agent in Parkinson’s disease (PD). We proposed l-DOPA as a neurotransmitter in the central nervous system. Recently, the ocular albinism 1 gene product, OA1/GPR143 (GPR143), was identified as a receptor for l-DOPA. In this study, we examined by generating anti-human GPR143 antibody, the localization of GPR143-immunoreactive signals in the brains from control and PD subjects. GPR143-immunoreactive signals were detected throughout the entire midbrain including substantia nigra pars compacta. In the PD brains, we found that GPR143-immunoreactive signals were detected in Lewy bodies and were colocalized with immunoreactive signals with anti-human Ser129 phosphorylated α-synuclein antibody. Although the significance of its occurrence in the inclusion bodies is unknown, our finding suggests possible implications of GPR143 in PD.

Using an Optical Clearing Technique for Visualizing the Midbrain Cholinergic System in Mice

The 3D visualization of the midbrain cholinergic system is key for understanding its function and its relationship with other brain areas. In preliminary experiments, our lab used an optical clearing technique, CLARITY, along with confocal microscopy, to image cholinergic cells and projections in up to 4 mm thick brain slices. Brains from transgenic mice expressing YFP under the choline aceteyltransferase 1 (CHaT1) promotor were harvested and sliced into coronal sections of different thicknesses. The samples were then embedded into a hydrogel monomer solution for 3 hours and left to incubate at 37°C. Afterwards, the tissue samples were left in a clearing solution for lipid membrane removal and left to incubate at 37 °C between 19 to 44 days.When qualitatively studied, passive CLARITY was found to effectively clear coronal sections of 1, 2, 3 and 4 mm thick after 19, 26, 35 and 44 days of incubation, respectively. Confocal microscopy confirmed sufficient expression of YFP to visualize thin axons and single axon terminals of cholinergic neurons within the rostral regions of the mouse brain. Based on our preliminary results, our ultimate goal is to construct a 3D visualization of the entire midbrain cholinergic system and its projections in the mouse brain.

A new assessment tool for Parkinson disease: the nigral lesion load obtained by transcranial sonography.

A sonographic method that provides for the measurement of a single frozen image and ignores the remaining portions of the midbrain has been used recently as a biological marker of Parkinson disease. We propose a new approach to evaluating the midbrain: obtaining the nigral lesion load, with which it is possible to acquire an estimate of the real damage to the substantia nigra. We studied 60 patients with Parkinson disease and classified them according to the Hoehn and Yahr scale (Neurology 1967; 17:427-442). Magnetic resonance imaging of the brain, ioflupane-labeled single-photon emission computed tomography, and technetium Tc 99m-labeled single-photon emission computed tomography were performed. Assessment of the midbrain parenchyma was performed with transcranial sonography to quantify the extent of hyperechoic signals on 2 different scans (upper and lower substantia nigra). In 90% of patients (54), we found pathologic hyperechoic substantia nigra signals (>0.25 cm(2)). These data were similar to those described previously by other authors. However, the sum of the values obtained from each measurement (total of 4 per patient) showed that patients with severe disease had larger nigral lesion loads. In most cases, the study showed impairment of the nigrostriatal dopaminergic system when the hyperechoic pattern was more pronounced. Transcranial sonography is a useful tool for Parkinson disease workup. A single measurement of substantia nigra echogenicity may be insufficient for an optimal definition of the stage of the disease. A study of the entire midbrain may deliver more information than a single measurement.

Gbx2 and Fgf8 are sequentially required for formation of the midbrain-hindbrain compartment boundary

In vertebrates, the common expression border of two homeobox genes, Otx2 and Gbx2, demarcates the prospective midbrain-hindbrain border (MHB) in the neural plate at the end of gastrulation. The presence of a compartment boundary at the MHB has been demonstrated, but the mechanism and timing of its formation remain unclear. We show by genetic inducible fate mapping using a Gbx2(CreER) knock-in mouse line that descendants of Gbx2(+) cells as early as embryonic day (E) 7.5 do not cross the MHB. Without Gbx2, hindbrain-born cells abnormally populate the entire midbrain, demonstrating that Gbx2 is essential for specifying hindbrain fate. Gbx2(+) and Otx2(+) cells segregate from each other, suggesting that mutually exclusive expression of Otx2 and Gbx2 in midbrain and hindbrain progenitors is responsible for cell sorting in establishing the MHB. The MHB organizer gene Fgf8, which is expressed as a sharp transverse band immediately posterior to the lineage boundary at the MHB, is crucial in maintaining the lineage-restricted boundary after E7.5. Partial deletion of Fgf8 disrupts MHB lineage separation. Activation of FGF pathways has a cell-autonomous effect on cell sorting in midbrain progenitors. Therefore, Fgf8 from the MHB may signal the nearby mesencephalic cells to impart distinct cell surface characteristics or induce local cell-cell signaling, which consequently prevents cell movements across the MHB. Our findings reveal the distinct function of Gbx2 and Fgf8 in a stepwise process in the development of the compartment boundary at the MHB and that Fgf8, in addition to its organizer function, plays a crucial role in maintaining the lineage boundary at the MHB by restricting cell movement.

Connections of the Superior Paraolivary Nucleus of the Rat: II. Reciprocal Connections with the Tectal Longitudinal Column

The superior paraolivary nucleus (SPON), a prominent GABAergic center of the mammalian auditory brainstem, projects to the ipsilateral inferior colliculus (IC) and sends axons through the commissure of the IC (CoIC). Herein we demonstrate that the SPON is reciprocally connected with the recently discovered tectal longitudinal column (TLC). The TLC is a long and narrow structure that spans nearly the entire midbrain tectum longitudinally, immediately above the periaqueductal gray matter (PAG) and very close to the midline. Unilateral injections of biotinylated dextran into the SPON of the rat label abundant terminal fibers in the TLC of both sides, with an ipsilateral predominance. The SPON provides a dense innervation of the entire rostrocaudal extent of the ipsilateral TLC, and a relatively sparser innervation of the caudal and rostral portions of the contralateral TLC. SPON fibers reach the TLC by two routes: as collaterals of axons of the CoIC, and as axons that circumvent the ipsilateral IC before traveling in the deep layers of the superior colliculus (SC). The density of these projections identifies SPON as a significant source of input to the TLC. Other targets of the SPON discovered in this study include the deep layers of the SC and the PAG. The same experiments reveal numerous labeled cell bodies in the TLC, interspersed among the labeled SPON fibers. This observation suggests that the SPON is a significant target of TLC projections. The discovery of novel reciprocal connections between the SPON and the TLC opens unexpected avenues for investigation of sound processing in mammalian brainstem circuits.

Graded Levels of FGF Protein Span the Midbrain and Can Instruct Graded Induction and Repression of Neural Mapping Labels

Graded guidance labels are widely used in neural map formation, but it is not well understood which potential strategy leads to their graded expression. In midbrain tectal map development, FGFs can induce an entire midbrain, but their protein distribution is unclear, nor is it known whether they may act instructively to produce graded gene expression. Using a receptor-alkaline phosphatase fusion probe, we find a long-range posterior > anterior FGF protein gradient spanning the midbrain. Heparan sulfate proteoglycan (HSPG) is required for this gradient. To test whether graded FGF concentrations can instruct graded gene expression, a quantitative tectal explant assay was developed. Engrailed-2 and ephrin-As, normally in posterior > anterior tectal gradients, showed graded upregulation. Moreover, EphAs, normally in anterior > posterior countergradients, showed coordinately graded downregulation. These results provide a mechanism to establish graded mapping labels and more generally provide a developmental strategy to coordinately induce a structure and pattern its cell properties in gradients.

Recombinant AAV Viral Vectors Pseudotyped with Viral Capsids from Serotypes 1, 2, and 5 Display Differential Efficiency and Cell Tropism after Delivery to Different Regions of the Central Nervous System

Recombinant adeno-associated virus 2 (rAAV2) has been shown to deliver genes to neurons effectively in the brain, retina, and spinal cord. The characterization of new AAV serotypes has revealed that they have different patterns of transduction in diverse tissues. We have investigated the tropism and transduction frequency in the central nervous system (CNS) of three different rAAV vector serotypes. The vectors contained AAV2 terminal repeats flanking a green fluorescent protein expression cassette under the control of the synthetic CBA promoter, in AAV1, AAV2, or AAV5 capsids, producing the pseudotypes rAAV2/1, rAAV2/2, and rAAV2/5. Rats were injected with rAAV2/1, rAAV2/2, or rAAV2/5 into selected regions of the CNS, including the hippocampus (HPC), substantia nigra (SN), striatum, globus pallidus, and spinal cord. In all regions injected, the three vectors transduced neurons almost exclusively. All three vectors transduced the SN pars compacta with high efficiency, but rAAV2/1 and rAAV2/5 also transduced the pars reticulata. Moreover, rAAV2/1 showed widespread distribution throughout the entire midbrain. In the HPC, rAAV2/1 and rAAV2/5 targeted the pyramidal cell layers in the CA1–CA3 regions, whereas AAV2/2 primarily transduced the hilar region of the dentate gyrus. In general, rAAV2/1 and rAAV2/5 exhibited higher transduction frequencies than rAAV2/2 in all regions injected, although the differences were marginal in some regions. Retrograde transport of rAAV1 and rAAV5 was also observed in particular CNS areas. These results suggest that vectors based on distinct AAV serotypes can be chosen for specific applications in the nervous system.

Temperature acclimation in the central nervous system of rainbow trout ( Salmo gairdnerii)

1. 1. The midbrain response to direct electrical stimulation of the retina was measured in rainbow trout acclimated to 10°C and following transfer and acclimation to 4 and 16°C. The evoked midbrain potential consisted first of a positive deflection upon which was superimposed two negative spikes of supposed pre-synaptic origin, and secondly of a slow negative potential, interpreted as post-synaptic in origin. 2. 2. Transfer of 10° acclimated trout to 4° caused an average 39 per cent protraction of the entire midbrain response pattern. After 21 days' acclimation to 4°, the negative spike latencies had decreased to 18 and 19 per cent above the 10° controls and the duration of the slow potential had decreased to 16 per cent above the 10° controls. 3. 3. Transfer of 10° acclimated trout to 16° caused an initial shortening of the negative spike latencies and slow potential duration. These values lengthened somewhat during acclimation to 16° but, since a similar lengthening occurred int he 10° controls, the change was judged noncompensatory. 4. 4. Thus, significant compensation occurred in response to low temperature acclimation (4°) but not to high temperature acclimation (16°). These results contrast with brain tissue respiration measurements that show that metabolic compensation is much more complete between 10 and 16° than between 4 and 10°.