Biology subjects

Siddiqui, A. M.

Publications and source records attributed to Siddiqui, A. M..

3 recordsLinked to original sources

bioRxiv2020

Segment-specific orientation of the dorsal and ventral roots for precise therapeutic targeting of human spinal cord

An understanding of spinal cord functional neuroanatomy is essential for diagnosis and treatment of multiple disorders including, chronic pain, movement disorders, and spinal cord injury. Till now, no information is available on segment-specific spinal roots orientation in humans. In this study we collected neuroanatomical measurements of the dorsal and ventral roots from C2-L5, as well as spinal cord and vertebral bone measurements from adult cadavers. Spatial orientation of dorsal and ventral roots were measured and correlated to the anatomical landmarks of the spinal cord and vertebral column. The results show less variability in rostral root angles compared to the caudal angles across all segments. Dorsal and ventral rootlets were oriented mostly perpendicular to the spinal cord at the cervical level and demonstrate more parallel orientation at the thoracic and lumbar segments. The number of rootlets was the highest in dorsal cervical and lumbar segments. Spinal cord transverse diameter and size of the dorsal columns were largest at cervical and lumbar segments. The strongest correlation was found between the length of intervertebral foramen to rostral rootlet and vertebral bone length. These results could be used to locate spinal roots and spinal cord landmarks based on bone marks on CT or X-rays. These results also provide background for future correlations between anatomy of spinal cord and spinal column structures that could improve stereotactic surgical procedures and electrode positioning for spinal cord neuromodulation. One Sentence SummaryThis is the first detailed analysis of the segment-specific dorsal and ventral spinal roots spatial orientation measured and correlated to the anatomical landmarks of the spinal cord and vertebral column for human.

neuroscience↗

bioRxiv2019

Regenerating axons and blood vessels in tissue engineered scaffolds have defined spatial relationships after spinal cord injury.

Positively charged oligo-polyethylene glycol fumarate (OPF+) hydrogel scaffolds, implanted into a complete transection spinal cord injury (SCI), facilitate a permissive regenerative environment and provide a platform for controlled observation of repair mechanisms. Axonal regeneration after SCI is critically dependent upon the availability of nutrients and oxygen from a newly formed blood supply. In this study, the objective was to investigate fundamental characteristics of revascularization in association with the ingrowth of axons into hydrogel scaffolds, and to define the spatial relationships between axons and the neovasculature. A novel combination of stereologic estimates and precision image analysis techniques are described to quantitate neurovascular regeneration in rats. Multichannel hydrogel scaffolds containing Matrigel-only (MG), Schwann cells (SCs), or SCs with rapamycin-eluting poly(lactic co-glycolic acid) (PLGA) microspheres (RAPA) were implanted for 6 weeks following complete spinal cord transection. Image analysis of 72 scaffold channels identified a total of 2,494 myelinated and 4,173 unmyelinated axons at 10 micron circumferential intervals centered around 708 individual blood vessel profiles. Blood vessel number, density, volume, diameter, inter-vessel distances, total vessel surface and cross-sectional areas, and radial diffusion distances in each group were measured. Axon number and density, blood vessel surface area, and vessel cross-sectional areas in the SC group exceeded that in the MG and RAPA groups. Axons were concentrated within a concentric radius of 200-250 microns from the blood vessel wall in Gaussian distributions which identified a peak axonal number (mean peak amplitude) corresponding to defined distances (mean peak distance) from each vessel. Axons were largely excluded from a 25 micron zone immediately adjacent to the vessel. Higher axonal densities correlated with smaller vessel cross-sectional areas. A statistical spatial algorithm was used to generate cumulative distribution F- and G-functions of axonal distribution in the reference channel space. Axons located around blood vessels were definitively organized as clusters and were not randomly distributed. By providing methods to quantify the axonal-vessel relationships, these results may refine spinal cord tissue engineering strategies to optimize the regeneration of complete neurovascular bundles in their relevant spatial relationships after SCI. Impact StatementVascular disruption and impaired neovascularization contribute critically to the poor regenerative capacity of the spinal cord after injury. In this study, hydrogel scaffolds provide a detailed model system to investigate the regeneration of spinal cord axons as they directly associate with individual blood vessels, using novel methods to define their spatial relationships and the physiologic implications of that organization. These results refine future tissue-engineering strategies for spinal cord repair to optimize the re-development of complete neurovascular bundles in their relevant spatial architectures.

neuroscience↗

bioRxiv2019

Promoting neuronal outgrowth using ridged scaffolds coated with extracellular matrix proteins.

Spinal cord injury (SCI) results in cell death, demyelination, and axonal loss. The spinal cord has a limited ability to regenerate and current clinical therapies for SCI are not effective in helping promote neurologic recovery. We have developed a novel scaffold biomaterial that is fabricated from the biodegradable hydrogel oligo[poly(ethylene glycol)fumarate] (OPF). We have previously shown that positively charged OPF scaffolds (OPF+) in an open spaced, multichannel design can be loaded with Schwann cells to support axonal generation and functional recovery following SCI. We have now developed a hybrid OPF+ biomaterial that increases the surface area available for cell attachment and that contains an aligned microarchitecture and extracellular matrix (ECM) proteins to better support axonal regeneration. OPF+ was fabricated as 0.08 mm thick sheets containing 100 m high polymer ridges that self-assembles into a spiral shape when hydrated. Laminin, fibronectin, or collagen I coating promoted neuron attachment and axonal outgrowth on the scaffold surface. In addition, the ridges aligned axons in a longitudinal bipolar orientation. Decreasing the space between the ridges increased the number of cells and neurites aligned in the direction of the ridge. Schwann cells seeded on laminin coated OPF+ sheets aligned along the ridges over a 6-day period and could myelinate dorsal root ganglion neurons over 4 weeks. The OPF+ sheets support axonal regeneration when implanted into the transected spinal cord. This novel scaffold design, with closer spaced ridges and Schwann cells is a novel biomaterial construct to promote regeneration after SCI.\n\nGraphical Abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC=\"FIGDIR/small/788539v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (42K):\norg.highwire.dtl.DTLVardef@1ea0ae3org.highwire.dtl.DTLVardef@70e1f7org.highwire.dtl.DTLVardef@1034b77org.highwire.dtl.DTLVardef@14f784d_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗