Optogenetic Stimulation of the Auditory Nerve

Direct electrical stimulation of spiral ganglion neurons (SGNs) by cochlear implants (CIs) enables open speech comprehension in the majority of implanted ...

Label-Free Non-Linear Optics for the Study of Tubulin-Dependent Defects in Central Myelin

The satisfactory visualization of cytoskeletal components in the brain is challenging. The ubiquitous distribution of the networks of microtubules, ...

University Medical Center Goettingen

University of Goettingen

University of Guanajuato

Universidad de Guanajuato

The X-linked form of Charcot-Marie-Tooth disease (CMTX) is caused by mutations in connexin32 (Cx32), a gap junction protein expressed by Schwann cells where it forms reflexive channels that allow the passage of ions and signaling molecules across the myelin sheath. Although most mutations result in loss of function, several studies have reported that some retain the ability to form homotypic intercellular channels. To gain insight into the molecular defect of three functional CMTX variants, S26L, Delta111-116 and R220stop, we have used several fluorescent tracers of different size and ionic charge to compare their permeation properties to those of wild-type Cx32. Although all mutations allowed the passage of the dye with the smallest molecular mass, they exhibited a clear reduction in the permeability of either one or all of the probes with respect to wild-type channels, as assessed by the percentage of injections showing dye coupling. These data reveal that a lower size cutoff distinguishes these functional CMTX variants from wild-type channels and suggest that this defect may be of pathophysiological relevance.

Selective defects in channel permeability associated with Cx32 mutations causing X-linked Charcot-Marie-Tooth disease.

Postdischarge costs associated with primary arthroplasty surgeries have received limited attention in the literature. Our objective was to identify the costs incurred after discharge in primary arthroplasty and to estimate annual postdischarge expenditures in the United States. A cohort of 136 patients who underwent primary arthroplasty was studied. Comprehensive rehabilitation unit (CRU) and home care (HC) costs were obtained. The National Hospital Discharge Survey 2003 data were used to model the national discharge cost estimates. Local patient-oriented outcome was also compared in the patients discharged to CRU vs HC. Total costs were significantly lower in patients discharged directly to home vs those sent to the CRU and who subsequently received HC ($2405 vs $13435, P < .001); both patient groups experienced similar quality of life improvements. An estimated $3.2 billion is spent annually on postsurgical rehabilitation after arthroplasty. Postdischarge costs are significantly higher for patients going to a CRU vs those discharged home; yet, both groups had comparable short-term outcomes.

Postdischarge costs in arthroplasty surgery.

Gap junction channels assembled from connexin protein subunits mediate intercellular transfer of ions and metabolites. Impaired channel function is implicated in several hereditary human diseases. In particular, defective permeation of cAMP or inositol-1,4,5-trisphosphate (InsP(3)) through connexin channels is associated with peripheral neuropathies and deafness, respectively. Here we present a method to estimate the permeability of single gap junction channels to second messengers. Using HeLa cells that overexpressed wild-type human connexin 26 (HCx26wt) as a model system, we combined measurements of junctional conductance and fluorescence resonance energy transfer (FRET) emission ratio of biosensors selective for cAMP and InsP(3). The unitary permeabilities to cAMP (47 x 10(-3) +/- 15 x 10(-3) microm(3)/s) and InsP(3) (60 x 10(-3) +/- 12 x 10(-3) microm(3)/s) were similar, but substantially larger than the unitary permeability to lucifer yellow (LY; 7 +/- 3 x 10(-3) microm(3)/s), an exogenous tracer. This method permits quantification of defects of metabolic coupling and can be used to investigate interdependence of intercellular diffusion and cross-talk between diverse signaling pathways.

Unitary permeability of gap junction channels to second messengers measured by FRET microscopy.

Twenty-four clinically successful, autopsy retrieved porous-coated anatomic total knee arthroplasty (TKA) specimens were evaluated to determine the structure and function of the patellar meniscus. Mean implant duration was 76 months (range: 11-135 months). Histological examination showed the patellar meniscus to be composed of dense fibrous tissue with scattered regions of chronic granulomatous response to polyethylene debris. Patellar wear and polyethylene exposed patellar surface area were correlated with implant duration (r = 0.47, P = .03; r = 0.52, P = .06). Postoperative patellar tilt was also associated with patellar component wear (r = 0.64, P = .03). No other clinical measures were significantly associated with patellar wear or exposed surface area. Additional research is needed to determine what role, if any, the patellar meniscus plays in TKA outcomes.

Patellar meniscus in total knee arthroplasty.

Extracellular ATP controls various signaling systems including propagation of intercellular Ca(2+) signals (ICS). Connexin hemichannels, P2x7 receptors (P2x7Rs), pannexin channels, anion channels, vesicles, and transporters are putative conduits for ATP release, but their involvement in ICS remains controversial. We investigated ICS in cochlear organotypic cultures, in which ATP acts as an IP(3)-generating agonist and evokes Ca(2+) responses that have been linked to noise-induced hearing loss and development of hair cell-afferent synapses. Focal delivery of ATP or photostimulation with caged IP(3) elicited Ca(2+) responses that spread radially to several orders of unstimulated cells. Furthermore, we recorded robust Ca(2+) signals from an ATP biosensor apposed to supporting cells outside the photostimulated area in WT cultures. ICS propagated normally in cultures lacking either P2x7R or pannexin-1 (Px1), as well as in WT cultures exposed to blockers of anion channels. By contrast, Ca(2+) responses failed to propagate in cultures with defective expression of connexin 26 (Cx26) or Cx30. A companion paper demonstrates that, if expression of either Cx26 or Cx30 is blocked, expression of the other is markedly down-regulated in the outer sulcus. Lanthanum, a connexin hemichannel blocker that does not affect gap junction (GJ) channels when applied extracellularly, limited the propagation of Ca(2+) responses to cells adjacent to the photostimulated area. Our results demonstrate that these connexins play a dual crucial role in inner ear Ca(2+) signaling: as hemichannels, they promote ATP release, sustaining long-range ICS propagation; as GJ channels, they allow diffusion of Ca(2+)-mobilizing second messengers across coupled cells.

ATP release through connexin hemichannels and gap junction transfer of second messengers propagate Ca2+ signals across the inner ear.

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Our goal was to assess the integrity of the repaired rotator cuff in patients with partial-thickness rotator cuff tears who underwent a technique of tear completion followed by surgical repair, using post-repair magnetic resonance imaging (MRI) at a minimum of 2 years' follow-up.

Magnetic resonance imaging tendon integrity assessment after arthroscopic partial-thickness rotator cuff repair.

Notre objectif &eacute;tait d&#39;&eacute;valuer l&#39;int&eacute;grit&eacute; de la coiffe des rotateurs r&eacute;par&eacute;e chez les patients avec &eacute;paisseur partielle rotateurs qui ont subi une technique d&#39;ach&egrave;vement larme suivie d&#39;une r&eacute;paration chirurgicale, &agrave; l&#39;aide de l&#39;imagerie par r&eacute;sonance magn&eacute;tique (MRI) apr&egrave;s r&eacute;paration &agrave; un minimum de suivi de 2 ans.

R&eacute;sonance magn&eacute;tique imagerie d&#39;&eacute;valuation de l&#39;int&eacute;grit&eacute; du tendon apr&egrave;s r&eacute;paration de la coiffe des rotateurs sous arthroscopie &eacute;paisseur partielle.

Unser Ziel war, die Integrit&auml;t der reparierten Rotatorenmanschette bei Patienten mit partiellen Dicke Rotatorenmanschette Tr&auml;nen, die eine Technik der Tr&auml;ne Fertigstellung gefolgt von chirurgischen Reparatur unterzogen mit post-repair Magnetresonanz-Bildgebung (MRI) auf ein Minimum von 2 Jahren Follow-up.

Magnetresonanztomographie der Sehne Integrit&auml;t Bewertung nach Arthroskopische partielle-Dicke Rotatorenmanschette Reparatur.

Il nostro obiettivo era di valutare l&#39;integrit&agrave; della cuffia dei rotatori riparati in pazienti con spessore parziale della cuffia dei rotatori lacrime che hanno subito una tecnica di completamento strappo seguito da riparazione chirurgica, utilizzando post-repair risonanza magnetica (MRI) a un minimo di follow-up di 2 anni.

Valutazione dell&#39;integrit&agrave; del tendine dopo riparazione artroscopica della cuffia dei rotatori di spessore parziale di imaging a risonanza magnetica.

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Nuestro objetivo fue evaluar la integridad del manguito de los rotadores reparado en pacientes con profundidad parcial del manguito rotador que experiment&oacute; una t&eacute;cnica de terminaci&oacute;n de la l&aacute;grima seguido de reparaci&oacute;n quir&uacute;rgica, con autos de resonancia magn&eacute;tica (MRI) en un m&iacute;nimo de seguimiento 2 a&ntilde;os.

Resonancia magn&eacute;tica evaluaci&oacute;n de integridad de tend&oacute;n despu&eacute;s de la reparaci&oacute;n artrosc&oacute;pica del manguito rotador de espesor parcial.

Auditory prostheses can partially restore speech comprehension when hearing fails. Sound coding with current prostheses is based on electrical stimulation of auditory neurons and has limited frequency resolution due to broad current spread within the cochlea. In contrast, optical stimulation can be spatially confined, which may improve frequency resolution. Here, we used animal models to characterize optogenetic stimulation, which is the optical stimulation of neurons genetically engineered to express the light-gated ion channel channelrhodopsin-2 (ChR2). Optogenetic stimulation of spiral ganglion neurons (SGNs) activated the auditory pathway, as demonstrated by recordings of single neuron and neuronal population responses. Furthermore, optogenetic stimulation of SGNs restored auditory activity in deaf mice. Approximation of the spatial spread of cochlear excitation by recording local field potentials (LFPs) in the inferior colliculus in response to suprathreshold optical, acoustic, and electrical stimuli indicated that optogenetic stimulation achieves better frequency resolution than monopolar electrical stimulation. Virus-mediated expression of a ChR2 variant with greater light sensitivity in SGNs reduced the amount of light required for responses and allowed neuronal spiking following stimulation up to 60 Hz. Our study demonstrates a strategy for optogenetic stimulation of the auditory pathway in rodents and lays the groundwork for future applications of cochlear optogenetics in auditory research and prosthetics.

Optogenetic stimulation of the auditory pathway.

Hypomyelination with atrophy of the basal ganglia and cerebellum is a recently described tubulinopathy caused by a mutation in the tubulin beta 4a isoform, expressed in oligodendrocytes. The taiep rat is the only spontaneous tubulin beta 4a mutant available for the study of this pathology. We aimed to identify the effects of the tubulin mutation on freshly collected, unstained samples of the central white matter of taiep rats using second harmonic generation microscopy. Cytoskeletal differences between the central white matter of taiep rats and control animals were found. Nonlinear emissions from the processes and somata of oligodendrocytes in tubulin beta 4a mutant rats were consistently detected, in the shape of elongated structures and cell-like bodies, which were never detected in the controls. This signal represents the second harmonic trademark of the disease. The tissue was also fluorescently labeled and analyzed to corroborate the origin of the nonlinear signal. Besides enabling the description of structural and molecular aspects of H-ABC, our data open the door to the diagnostic use of nonlinear optics in the study of neurodegenerative diseases, with the additional advantage of a label-free approach that preserves tissue morphology and vitality.

Victor H. Hernandez

InnerEarLab,
Department of Otolaryngology,
InnerEarLab, Department of Otolaryngology

University Medical Center Goettingen

Optogenetic Stimulation of the Auditory Nerve

Label-Free Non-Linear Optics for the Study of Tubulin-Dependent Defects in Central Myelin

Victor H. Hernandez

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}InnerEarLab,Department of Otolaryngology,InnerEarLab, Department of Otolaryngology

University Medical Center Goettingen

Optogenetic Stimulation of the Auditory Nerve

Label-Free Non-Linear Optics for the Study of Tubulin-Dependent Defects in Central Myelin

InnerEarLab,
Department of Otolaryngology,
InnerEarLab, Department of Otolaryngology