Ultrabithorax Confers Spatial Identity in a Context-Specific Manner in the Drosophila Postembryonic Ventral Nervous System

In holometabolous insects such as Drosophila melanogaster, neuroblasts produce an initial population of diverse neurons during embryogenesis and a much larger set of adult-specific neurons during larval life. In the ventral CNS, many of these secondary neuronal lineages differ significantly from one body segment to another, suggesting a role for anteroposterior patterning genes. Here we systematically characterize the expression pattern and function of the Hox gene Ultrabithorax (Ubx) in all 25 postembryonic lineages. We find that Ubx is expressed in a segment-, lineage-, and hemilineage-specific manner in the thoracic and anterior abdominal segments. When Ubx is removed from neuroblasts via mitotic recombination, neurons in these segments exhibit the morphologies and survival patterns of their anterior thoracic counterparts. Conversely, when Ubx is ectopically expressed in anterior thoracic segments, neurons exhibit complementary posterior transformation phenotypes. Our findings demonstrate that Ubx plays a critical role in conferring segment-appropriate morphology and survival on individual neurons in the adult-specific ventral CNS. Moreover, while always conferring spatial identity in some sense, Ubx has been co-opted during evolution for distinct and even opposite functions in different neuronal hemilineages.

Synaptic regulation of spike firing in interneurons of the striatum in vivo

The striatum, the major input nucleus of the basal ganglia, is numerically dominated by a single class of principal neurons, the GABAergic spiny projection neuron (SPN) that has been extensively studied both in vitro and in vivo. Much less is known about the sparsely distributed interneurons, principally the cholinergic interneuron (CIN) and the GABAergic fast-spiking interneuron (FSI). Here, we summarize results from two recent studies on these interneurons where we used in vivo intracellular recording techniques in urethane-anaesthetized rats (Schulz et al., J Neurosci 31[31], 2011; J Physiol, in press). Interneurons were identified by their characteristic responses to intracellular current steps and spike waveforms. Spontaneous spiking contained a high proportion (~45%) of short inter-spike intervals (ISI) of <30 ms in FSIs, but virtually none in CINs. Spiking patterns in CINs covered a broad spectrum ranging from regular tonic spiking to phasic activity despite very similar unimodal membrane potential distributions across neurons. In general, phasic spiking activity occurred in phase with the slow ECoG waves, whereas CINs exhibiting tonic regular spiking were little affected by afferent network activity. In contrast, FSIs exhibited transitions between Down and Up states very similar to SPNs. Compared to SPNs, the FSI Up state membrane potential was noisier and power spectra exhibited significantly larger power at frequencies in the gamma range (55-95 Hz). Cortical-evoked inputs had faster dynamics in FSIs than SPNs and the membrane potential preceding spontaneous spike discharge exhibited short and steep trajectories, suggesting that fast input components controlled spike output in FSIs. Intrinsic resonance mechanisms may have further enhanced the sensitivity of FSIs to fast oscillatory inputs. Induction of an activated ECoG state by local ejection of bicuculline into the superior colliculus, resulted in increased spike frequency in both interneuron classes without changing the overall distribution of ISIs. This manipulation also made CINs responsive to a light flashed into the contralateral eye. Typically, the response consisted of an excitation at short latency followed by a pause in spike firing, via an underlying depolarization-hyperpolarization membrane sequence. These results highlight the differential sensitivity of striatal interneurons to afferent synaptic signals and support a model where CINs modulate the striatal network in response to salient sensory bottom-up signals, while FSIs serve gating of top-down signals from the cortex during action selection and reward-related learning.

Enhanced proliferation and dopaminergic differentiation of ventral mesencephalic precursor cells by synergistic effect of FGF2 and reduced oxygen tension

Effective numerical expansion of dopaminergic precursors might overcome the limited availability of transplantable cells in replacement strategies for Parkinson's disease. Here we investigated the effect of fibroblast growth factor-2 (FGF2) and FGF8 on expansion and dopaminergic differentiation of rat embryonic ventral mesencephalic neuroblasts cultured at high (20%) and low (3%) oxygen tension. More cells incorporated bromodeoxyuridine in cultures expanded at low as compared to high oxygen tension, and after 6 days of differentiation there were significantly more neuronal cells in low than in high oxygen cultures. Low oxygen during FGF2-mediated expansion resulted also in a significant increase in tyrosine hydroxylase-immunoreactive (TH-ir) dopaminergic neurons as compared to high oxygen tension, but no corresponding effect was observed for dopamine release into the culture medium. However, switching FGF2-expanded cultures from low to high oxygen tension during the last two days of differentiation significantly enhanced dopamine release and intracellular dopamine levels as compared to all other treatment groups. In addition, the short-term exposure to high oxygen enhanced in situ assessed TH enzyme activity, which may explain the elevated dopamine levels. Our findings demonstrate that modulation of oxygen tension is a recognizable factor for in vitro expansion and dopaminergic differentiation of rat embryonic midbrain precursor cells.

Dorsal rather than ventral visual pathways discriminate freezing status in Parkinson's disease

BACKGROUND: Although visuospatial deficits have been linked with freezing of gait (FOG) in Parkinson's disease (PD), the specific effects of dorsal and ventral visual pathway dysfunction on FOG is not well understood. METHOD: We assessed visuospatial function in FOG using an angle discrimination test (dorsal visual pathway bias) and overlapping figure test (ventral visual pathway bias), and recorded overall response time, mean fixation duration and dwell time. Covariate analysis was conducted controlling for disease duration, motor severity, contrast sensitivity and attention with Bonferroni adjustments for multiple comparisons. RESULTS: Twenty seven people with FOG, 27 people without FOG and 24 controls were assessed. Average fixation duration during angle discrimination distinguished freezing status: [F (1, 43) = 4.77 p < 0.05] (1-way ANCOVA). CONCLUSION: Results indicate a preferential dysfunction of dorsal occipito-parietal pathways in FOG, independent of disease severity, attentional deficit, and contrast sensitivity.

The overexpression of homeotic complex gene Ultrabithorax in the post-embryonic neuronal lineages of the ventral nervous system in Drosophila melanogaster

This study uses a molecular technique called MARCM (Mosaic Analysis with a Repressible Cell Marker) to label neuronal lineages that overexpress the Hox gene Ultrabithorax (Ubx) in an unlabeled, wild type background. The results indicate that the overexpression of Ubx is sufficient to transform more anterior neuronal lineages to themorphology of their more posterior counterparts. The data presented here begin to elucidate the role that the Hox genes have in shaping segment-specific neural connections in the post-embryonic ventral nervous system.

The Role of Antennapedia in Anteroposterior Patterning of the Drosophila Melanogaster Ventral Nervous System

A major unresolved question in developmental neurobiology is how the nervous system is adapted to the specific needs of the organism at different life stages. In the holometabolous insect Drosophila melanogaster, the larval ventral nervous system (VNS) is comprised of similar repeating segments, as opposed to the adult VNS, which varies greatly from segment to segment both in number and types of neurons. The adult-specific neurons of each segment are generated by 25 distinct types of neuronal progenitor cells called neuroblasts (NBs) that appear in a stereotyped array (Truman et al., 2004). Each NB divides repeatedly to produce a distinct set of daughter cells termed a lineage, which is bilaterally symmetric but present to varying degrees in each segment. These daughter cells can be distinguished by their position within the nervous system as well as by their axonal projections. Each of the 25 NBs produces neurons; if both daughter cells are present in a lineage then both sibling populations survived, whereas if only one projection is seen cell death occurred, leaving a hemilineage (half lineage). In some lineages, the same sibling type survives in all segments in which the lineage appears, but in others, the surviving sibling type varies across segments, resulting in a different morphology for the same lineage in different segments. How are these differences in survival and morphology controlled? The Hox genes provide positional information for developing structures along the anterior-posterior (AP) axis of animals. They encode transcription factors, thereby controlling the activity of genes down stream. In the postembryonic VNS, each NB lineage features its own characteristic expression pattern of Hox genes Antp and Ubx, which can vary from segment-to-segment, and can thereby cause variation in the number of neural cells and axonal projections that survive. This study defines the wild-type expression pattern of Antp and elucidates the role of Antp in gain of function studies. These studies are possible due to the MARCM (Mosaic Analysis with a Repressible Cell Marker) method, which allows the genetically manipulated cells to be specifically labeled in an otherwise normal, unlabeled organism. The results indicate that Antp is expressed in a segment-, lineage-, and hemilineage-specific manner. Antp is sufficient for both anterior and posterior transformations of particular lineages, including promotion of cell death and/or survival as well as axon guidance.

GDNF family ligands display distinct action profiles on cultured GABAergic and serotonergic neurons of rat ventral mesencephalon

Glial-cell-line-derived neurotrophic factor (GDNF), neurturin (NRTN), artemin (ARTN) and persephin (PSPN), known as the GDNF family ligands (GFLs), influence the development, survival and differentiation of cultured dopaminergic neurons from ventral mesencephalon (VM). Detailed knowledge about the effects of GFLs on other neuronal populations in the VM is essential for their potential application as therapeutic molecules for Parkinson's disease. Hence, in a comparative study, we investigated the effects of GFLs on cell densities and morphological differentiation of gamma-aminobutyric acid-immunoreactive (GABA-ir) and serotonin-ir (5-HT-ir) neurons in primary cultures of E14 rat VM. We observed that all GFLs [10 ng/ml] significantly increased GABA-ir cell densities (1.6-fold) as well as neurite length/neuron. However, only GDNF significantly increased the number of primary neurites/neuron, and none of the GFLs affected soma size of GABA-ir neurons. In contrast, only NRTN treatment significantly increased 5-HT-ir cells densities at 10 ng/ml (1.3-fold), while an augmentation was seen for GDNF and PSPN at 100 ng/ml (2.4-fold and 1.7-fold, respectively). ARTN had no effect on 5-HT-ir cell densities. Morphological analysis of 5-HT-ir neurons revealed a significant increase of soma size, number of primary neurites/neuron and neurite length/neuron after GDNF exposure, while PSPN only affected soma size, and NRTN and ARTN failed to exert any effect. In conclusion, we identified GFLs as effective neurotrophic factors for VM GABAergic and serotonergic neurons, demonstrating characteristic individual action profiles emphasizing their important and distinct roles during brain development.

Laparoscopic ventral hernia repair is safe and cost effective

BACKGROUND: Ventral hernia repair is increasingly performed by laparoscopic means since the introduction of dual-layer meshes. This study aimed to compare the early complications and cost effectiveness of open hernia repair with those associated with laparoscopic repair. METHODS: Open ventral hernia repair was performed for 92 consecutive patients using a Vypro mesh, followed by laparoscopic repair for 49 consecutive patients using a Parietene composite mesh. RESULTS: The rate of surgical-site infections was significantly higher with open ventral hernia repair (13 vs 1; p = 0.03). The median length of hospital stay was significantly shorter with laparoscopic surgery (7 vs 6 days; p = 0.02). For laparoscopic repair, the direct operative costs were higher (2,314 vs 2,853 euros; p = 0.03), and the overall hospital costs were lower (9,787 vs 7,654 euros; p = 0.02). CONCLUSIONS: Laparoscopic ventral hernia repair leads to fewer surgical-site infections and a shorter hospital stay than open repair. Despite increased operative costs, overall hospital costs are lowered by laparoscopic ventral hernia repair.

Computer-assisted, fluoroscopy-based ventral spondylodesis of thoracolumbar fractures

OBJECTIVE: To design and evaluate a novel computer-assisted, fluoroscopy-based planning and navigation system for minimally invasive ventral spondylodesis of thoracolumbar fractures. MATERIALS AND METHODS: Instruments and an image intensifier are tracked with the SurgiGATE navigation system (Praxim-Medivision). Two fluoroscopic images, one acquired from anterior-posterior (AP) direction and the other from lateral-medial (LM) direction, are used for the complete procedure of planning and navigation. Both of them are calibrated with a custom-made software to recover their projection geometry and to co-register them to a common patient reference coordinate system, which is established by attaching an opto-electronically trackable dynamic reference base (DRB) on the operated vertebra. A bi-planar landmark reconstruction method is used to acquire deep-seated anatomical landmarks such that an intraoperative planning of graft bed can be interactively done. Finally, surgical actions such as the placement of the stabilization devices and the formation of the graft bed using a custom-made chisel are visualized to the surgeon by superimposing virtual instrument representations onto the acquired images. The distance between the instrument tip and each wall of the planned graft bed are calculated on the fly and presented to the surgeon so that the surgeon could formalize the graft bed exactly according to his/her plan. RESULTS: Laboratory studies on phantom and on 27 plastic vertebras demonstrate the high precision of the proposed navigation system. Compared with CT-based measurement, a mean error of 1.0 mm with a standard deviation of 0.1 mm was found. CONCLUSIONS: The proposed computer assisted, fluoroscopy-based planning and navigation system promises to increase the accuracy and reliability of minimally invasive ventral spondylodesis of thoracolumbar fractures.

Toxic effects of lipid-mediated gene transfer in ventral mesencephalic explant cultures

Adverse effects of cDNA and oligonucleotide delivery methods have not yet been systematically analyzed. We introduce a protocol to monitor toxic effects of two non-viral lipid-based gene delivery protocols using CNS primary tissue. Cell membrane damage was monitored by quantifying cellular uptake of propidium iodide and release of cytosolic lactate dehydrogenase to the culture medium. Using a liposomal transfection reagent, cell membrane damage was already seen 24 hr after transfection. Nestin-positive target cells, which were used as morphological correlate, were severely diminished in some areas of the cultures after liposomal transfection. In contrast, the non-liposomal transfection reagent revealed no signs of toxicity. This approach provides easily accessible information of transfection-associated toxicity and appears suitable for prescreening of transfection reagents.

Ventral intraspinal cysts associated with the intervertebral disc: magnetic resonance imaging observations in seven dogs

OBJECTIVE: To report clinical and diagnostic imaging features, and outcome after surgical treatment of ventral intraspinal cysts in dogs. STUDY DESIGN: Retrospective study. ANIMALS: Dogs (n=7) with ventral intraspinal cysts. METHODS: Clinical signs, magnetic resonance imaging (MRI) findings and surgical findings of 7 dogs and histologic findings (1 dog) with intraspinal cysts associated with the intervertebral disc were reviewed. RESULTS: Ventral intraspinal cyst is characterized by: (1) clinical signs indistinguishable from those of typical disc herniation; (2) an extradural, round to oval, mass lesion with low T1 and high T2 signal intensity on MRI, compatible with a liquid-containing cyst; (3) cyst is in close proximity to the intervertebral disc; and (4) MRI signs of disc degeneration. Although the exact cause is unknown, underlying minor disc injury may predispose to cyst formation. CONCLUSION: Intraspinal cysts have clinical signs identical to those of disc herniation. Given the close proximity of the cyst to the corresponding disc and the similarity of MRI findings to discal cysts in humans, we propose the term "canine discal cyst" to describe this observation. CLINICAL RELEVANCE: Discal cysts should be considered in the differential choices for cystic extradural compressing lesions.

Role of calcium-independent phospholipase A2 in cortex striatum thalamus cortex circuitry-enzyme inhibition causes vacuous chewing movements in rats

RATIONALE: High levels of calcium independent phospholipase A2 (iPLA2) are present in certain regions of the brain, including the cerebral cortex, striatum, and cerebellum (Ong et al. 2005). OBJECTIVES: The present study was carried out to elucidate a possible role of the enzyme in the motor system. METHODS: The selective iPLA2 inhibitor bromoenol lactone (BEL), the nonselective PLA2 inhibitor methyl arachidonyl fluorophosphonate (MAFP), and an antisense oligonucleotide were used to interfere with iPLA2 activity in various components of the motor system. Control animals received injections of carrier (phosphate buffered saline, PBS) at the same locations. The number of vacuous chewing movements (VCM) was counted from 1 to 14 days after injection. RESULTS: Rats that received BEL and high-dose MAFP injections in the striatum, thalamus, and motor cortex, but not the cerebellum, showed significant increase in VCM, compared to those injected with PBS at these locations. BEL-induced VCM were blocked by intramuscular injections of the anticholinergic drug, benztropine. Increased VCM was also observed after intrastriatal injection of antisense oligonucleotide to iPLA2. The latter caused a decrease in striatal iPLA2 levels, confirming a role of decreased enzyme activity in the appearance of VCM. CONCLUSIONS: These results suggest an important role for iPLA2 in the cortex-striatum-thalamus-cortex circuitry. It is postulated that VCM induced by iPLA2 inhibition may be a model of human parkinsonian tremor.