Joint-specific changes in locomotor complexity in the absence of muscle atrophy following incomplete spinal cord injury

ackground Following incomplete spinal cord injury (iSCI), descending drive is impaired, possibly leading to a decrease in the complexity of gait. To test the hypothesis that iSCI impairs gait coordination and decreases locomotor complexity, we collected 3D joint angle kinematics and muscle parameters of rats with a sham or an incomplete spinal cord injury. Methods 12 adult, female, Long-Evans rats, 6 sham and 6 mild-moderate T8 iSCI, were tested 4 weeks following injury. The Basso Beattie Bresnahan locomotor score was used to verify injury severity. Animals had reflective markers placed on the bony prominences of their limb joints and were filmed in 3D while walking on a treadmill. Joint angles and segment motion were analyzed quantitatively, and complexity of joint angle trajectory and overall gait were calculated using permutation entropy and principal component analysis, respectively. Following treadmill testing, the animals were euthanized and hindlimb muscles removed. Excised muscles were tested for mass, density, fiber length, pennation angle, and relaxed sarcomere length. Results Muscle parameters were similar between groups with no evidence of muscle atrophy. The animals showed overextension of the ankle, which was compensated for by a decreased range of motion at the knee. Left-right coordination was altered, leading to left and right knee movements that are entirely out of phase, with one joint moving while the other is stationary. Movement patterns remained symmetric. Permutation entropy measures indicated changes in complexity on a joint specific basis, with the largest changes at the ankle. No significant difference was seen using principal component analysis. Rats were able to achieve stable weight bearing locomotion at reasonable speeds on the treadmill despite these deficiencies. Conclusions Decrease in supraspinal control following iSCI causes a loss of complexity of ankle kinematics. This loss can be entirely due to loss of supraspinal control in the absence of muscle atrophy and may be quantified using permutation entropy. Joint-specific differences in kinematic complexity may be attributed to different sources of motor control. This work indicates the importance of the ankle for rehabilitation interventions following spinal cord injury.

Immunophylogenetic aspects of a gorgonian coral

One goal of comparative immunology is to derive inferences about evolutionary pathways in the development of immune-defense systems. Almost 700 million years ago, a major divergence occurred in the phylogeny of animals, spitting all descendants into either the protostome or deuterostome (includes vertebrates) lineages. Genes have evolved independently along these lineages for that amount of time. Cnidarians originated before that divergence event, and can hold clues as to which immune response genes are homologous to both lineages. This work uses the gorgonian coral, Swiftia exserta, for two major reasons: (1) because of their phylogenetic position, corals are an important animal model in studies concerning the phylogeny of immune-response genes, and (2) nothing is known about the genes controlling immunocompetence in corals. The work described here has important implications in both innate and adaptive immunity. ^ The vertebrate complement system is a major component of innate immunity. C3 is a critical component of the three pathways of complement. Because of its opsonic properties, a C3-like protein is expected to have evolved early. However, currently available data suggests that complement-like components are unique to the deuterostome lineage. This work describes the cloning and characterization of a C3-like gene from S. exserta. The deduced polypeptide sequence reveals conservation of multiple, functionally critical, sites while sharing physiochemical and structural properties with the complement components C3/C4/C5. ^ Antigen processing, via intracellular enzymatic proteasomes, is a major requirement of vertebrate adaptive immunity. These organelles have a catalytic core, through which pass intracellular proteins for degradation into peptides presentable to the immune system. LMP 7 is one component of the paralogous “immuno-proteasome”. LMP 7 is a paralog of the ubiquitous LMP X, but is restricted to vertebrates. While LMP 7 is absent in the coral, this work describes a coral LMP X gene. Phylogenetic analyses, along with hydropathy profiling of a critical portion of the invertebrate and vertebrate paralogous genes, suggests that some invertebrates have two diverging LMP X genes. In some cases, one LMP X protein shares characteristics with vertebrate LMP 7. This work presents new evidence for how the LMP X and 7 genes evolved. ^

Navigating racial boundaries: The one-drop rule and mixed-race Jamaicans in South Florida

Like many West Indians, mixed-race Jamaican immigrants enter the United States with fluid notions about race and racial identifications that reflect socio-political events in their home country and that conflict with the more rigid constructions of race they encounter in the U.S. This dissertation explores the experiences of racially mixed Jamaicans in South Florida and the impact of those experiences on their racial self-characterizations through the boundary-work theoretical framework. Specifically, the study examines the impact of participants’ exposure to the one-drop rule in the U.S., by which racial identification has been historically determined by the existence or non-existence of black forebears. Employing qualitative data collected through both focus group and face-to-face semi-structured interviews, the study analyzes mixed-race Jamaicans’ encounters in the U.S. with racial boundaries, and the boundary-work that reinforces them, as well their response to these encounters. Through their stories, the dissertation examines participants’ efforts to navigate racial boundaries through choices of various racial identifications. Further, it discusses the ways in which structural forces and individual agency have interacted in the formation of these identifications. The study finds that in spite of participants’ expressed preference for non-racialism, and despite their objections to rigid racial categories, in seeking to carve out alternative identities, they are participating in the boundary-making of which they are so critical.^