Dynamical modeling of multi-scale variability in neuronal competition.

Variability is observed at multiple-scales in the brain and ubiquitous in perception. However, the nature of perceptual variability is an open question. We focus on variability during perceptual rivalry, a form of neuronal competition. Rivalry provides a window into neural processing since activity in many brain areas is correlated to the alternating perception rather than a constant ambiguous stimulus. It exhibits robust properties at multiple scales including conscious awareness and neuron dynamics. The prevalent theory for spiking variability is called the balanced state; whereas, the source of perceptual variability is unknown. Here we show that a single biophysical circuit model, satisfying certain mutual inhibition architectures, can explain spiking and perceptual variability during rivalry. These models adhere to a broad set of strict experimental constraints at multiple scales. As we show, the models predict how spiking and perceptual variability changes with stimulus conditions.

Tissue engineering the human auricle by auricular chondrocyte-mesenchymal stem cell co-implantation.

Children suffering from microtia have few options for auricular reconstruction. Tissue engineering approaches attempt to replicate the complex anatomy and structure of the ear with autologous cartilage but have been limited by access to clinically accessible cell sources. Here we present a full-scale, patient-based human ear generated by implantation of human auricular chondrocytes and human mesenchymal stem cells in a 1:1 ratio. Additional disc construct surrogates were generated with 1:0, 1:1, and 0:1 combinations of auricular chondrocytes and mesenchymal stem cells. After 3 months in vivo, monocellular auricular chondrocyte discs and 1:1 disc and ear constructs displayed bundled collagen fibers in a perichondrial layer, rich proteoglycan deposition, and elastin fiber network formation similar to native human auricular cartilage, with the protein composition and mechanical stiffness of native tissue. Full ear constructs with a 1:1 cell combination maintained gross ear structure and developed a cartilaginous appearance following implantation. These studies demonstrate the successful engineering of a patient-specific human auricle using exclusively human cell sources without extensive in vitro tissue culture prior to implantation, a critical step towards the clinical application of tissue engineering for auricular reconstruction.

Tissue Engineering Auricular Cartilage Using Late Passage Human Auricular Chondrocytes.

PURPOSE: The significant shortcomings associated with current autologous reconstructive options for auricular deformities have inspired great interest in a tissue engineering solution. A major obstacle in the engineering of human auricular cartilage is the availability of sufficient autologous human chondrocytes. A clinically obtainable amount of auricular cartilage tissue (ie, 1 g) only yields approximately 10 million cells, where 25 times this amount is needed for the fabrication of a full-scale pediatric ear. It is thought that repeated passaging of chondrocytes leads to dedifferentiation and loss of the chondrogenic potential. However, little to no data exist regarding the ideal number of times that human auricular chondrocytes (HAuCs) can be passaged in a manner that maximizes the cellular expansion while minimizing dedifferentiation. METHODS: Human auricular chondrocytes were isolated from discarded otoplasty specimens. The HAuCs were then expanded, and cells from passages 3, 4, and 5 were encapsulated into discs 8 mm in diameter made from type I collagen hydrogels with a cell density of 25 million cells/mL. The constructs were implanted subcutaneously in the dorsa of nude mice and harvested after 1 and 3 months for analysis. RESULTS: Constructs containing passages 3, 4, and 5 chondrocytes all maintained their original cylindrical geometry. After 3 months in vivo, the diameters of the P3, P4, and P5 discs were 69 ± 9%, 67 ± 10%, and 73 ± 15% of their initial diameter, respectively. Regardless of the passage number, all constructs developed a glossy white cartilaginous appearance, similar to native auricular cartilage. Histologic analysis demonstrated development of an organized perichondrium composed of collagen, a rich proteoglycan matrix, cellular lacunae, and a dense elastin fibrin network by Safranin-O and Verhoeff stain. Biochemical analysis confirmed similar amounts of proteoglycan and hydroxyproline content in late passage constructs when compared with native auricular cartilage. CONCLUSIONS: These data indicate that late passage HAuCs (up to passage 5) form elastic cartilage that is histologically, biochemically, and biomechanically similar to native human elastic cartilage and have the potential to be used for auricular cartilage engineering.

Optimizing cell sourcing for clinical translation of tissue engineered ears.

Background . Currently, the major impediment to clinical translation of our previously described platform for the fabrication of high fidelity, patient-specific tissue engineered ears is the development of a clinically optimal cell sourcing strategy. A limited autologous auricular chondrocyte (AuC) supply in conjunction with rapid chondrocyte de-differentiation during in vitro expansion currently makes clinical translation more challenging. Mesenchymal stem cells (MSCs) offer significant promise due to their inherent chondrogenic potential, and large availability through minimally invasive procedures. Herein, we demonstrate the promise of AuC/MSC co-culture to fabricate elastic cartilage using 50% fewer AuC than standard approaches. METHODS: Bovine auricular chondrocytes (bAuC) and bovine MSC (bMSC) were encapsulated within 10 mg ml-1 type I collagen hydrogels in ratios of bAuC:bMSC 100:0, 50:50, and 0:100 at a density of 25 million cells ml-1 hydrogel. One mm thick collagen sheet gels were fabricated, and thereafter, 8 mm diameter discs were extracted using a biopsy punch. Discs were implanted subcutaneously in the dorsa of nude mice (NU/NU) and harvested after 1 and 3 months. RESULTS: Gross analysis of explanted discs revealed bAuC:bMSC co-culture discs maintained their size and shape, and exhibited native auricular cartilage-like elasticity after 1 and 3 months of implantation. Co-culture discs developed into auricular cartilage, with viable chondrocytes within lacunae, copious proteoglycan and elastic fiber deposition, and a distinct perichondrial layer. Biochemical analysis confirmed that co-culture discs deposited critical cartilage molecular components more readily than did both bAuC and bMSC discs after 1 and 3 months, and proteoglycan content significantly increased between 1 and 3 months. CONCLUSION: We have successfully demonstrated an innovative cell sourcing strategy that facilitates our efforts to achieve clinical translation of our high fidelity, patient-specific ears for auricular reconstruction utilizing only half of the requisite auricular chondrocytes to fabricate mature elastic cartilage.