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Beta-endorphin and substance P were immunolocalized in the articular cartilage, synovial membrane and fibrous joint capsule of dogs. Twelve adult greyhounds were randomly assigned to one of three groups: control, limited exercise, or regimented exercise. On day 0, biopsies of articular cartilage and joint capsule were obtained from the left shoulder joints of dogs receiving limited and regimented exercise. On day 72, biopsies of joint capsule from right and left shoulders and articular cartilage from the right shoulder joint were analysed for the presence of glycosaminoglycans (GAG) and for immunolocalization of substance P and beta-endorphin. Regimented exercise increased the presence of GAGs and immunolocalization of substance P and beta-endorphin in articular cartilage and synovial membrane compared to day 0 biopsies and untreated controls. Localization of beta-endorphin became prominent in and around the chondrocytes. Substance P was increased in chondrocytes and extracellular matrix. Concomitant changes in localization of beta-endorphin and substance P may have a role in the modulation of the microphysiological environment, metabolism, or function of joint tissues in response to low-impact exercise.

The gross morphology of the musculus articularis genus and the location of muscle spindles at its point of insertion were studied in 18 adult dogs. The m. articularis genus was usually small and bipartite. From its originate on the cranial surface of the distal femur, it passed distally to terminate at the femoropatellar-joint capsule surface and extend into the synovial membrane. Although the m. articularis genus was usually composed of two parts, only a medial part was present in some dogs and was entirely absent in one specimen. Innervation to the m. articularis genus was provided by a branch of the femoral nerve. Muscle spindles were abundant in the termination of the muscle. spindles were abundant in the termination of the muscle. Frequently, the spindles were not in contact with muscle fibers (dissociated). Muscle spindles were located in close proximity to the surface of the synovial membrane. Morphological adaptations of the m. articularis genus support its potential function as a monitor of joint movement rather than an extensor of the stifle joint.