Porous silicon confers bioactivity to polycaprolactone composites in vitro.

Silicon is an essential element for healthy bone development and supplementation with its bioavailable form (silicic acid) leads to enhancement of osteogenesis both in vivo and in vitro. Porous silicon (pSi) is a novel material with emerging applications in opto-electronics and drug delivery which dissolves to yield silicic acid as the sole degradation product, allowing the specific importance of soluble silicates for biomaterials to be investigated in isolation without the elution of other ionic species. Using polycaprolactone as a bioresorbable carrier for porous silicon microparticles, we found that composites containing pSi yielded more than twice the amount of bioavailable silicic acid than composites containing the same mass of 45S5 Bioglass. When incubated in a simulated body fluid, the addition of pSi to polycaprolactone significantly increased the deposition of calcium phosphate. Interestingly, the apatites formed had a Ca:P ratio directly proportional to the silicic acid concentration, indicating that silicon-substituted hydroxyapatites were being spontaneously formed as a first order reaction. Primary human osteoblasts cultured on the surface of the composite exhibited peak alkaline phosphatase activity at day 14, with a proportional relationship between pSi content and both osteoblast proliferation and collagen production over 4 weeks. Culturing the composite with J744A.1 murine macrophages demonstrated that porous silicon does not elicit an immune response and may even inhibit it. Porous silicon may therefore be an important next generation biomaterial with unique properties for applications in orthopaedic tissue engineering.

Etiologic theories of idiopathic scoliosis: autonomic nervous system and the leptin-sympathetic nervous system concept for the pathogenesis of adolescent idiopathic scoliosis.

The autonomic nervous system through its hypothalamic neuroendocrine control of puberty, skeletal growth and menarche contributes importantly to the pathogenesis of adolescent idiopathic scoliosis (AIS). Melatonin dysfunction detected in AIS subjects also involves the autonomic nervous system. The thoracospinal concept for the pathogenesis of right thoracic AIS in girls thought by some to result from dysfunction of the sympathetic nervous system (SNS), is supported by recent vascular and peripheral nerve studies. Lower body mass index (BMI).in girls with AIS is associated with decreased circulating leptin levels. Leptin, secreted by adipocytes, is a master hormone with many regulatory functions for growth and reproduction, including: 1) appetite repression, anorexigenic; 2) initiation of puberty in girls in a permissive action, and 3) in mice, longitudinal bone growth, chondrogenic and angiogenic, and in bone formation, antiosteogenic acting centrally through the SNS and possibly directly. In AIS girls, autonomic nervous system activity was reported to be higher than in controls. We suggest that in AIS susceptible girls, given adequate nutrition and energy stores, circulating leptin talks to the hypothalamus where dysfunction leads to an altered sensitivity to leptin resulting in increased SNS activity contributing with neuroendocrine mechanisms to: 1) earlier age at, and increased peak height velocity, 2) general skeletal overgrowth, 3) earlier skeletal maturation, 4) extra-spinal skeletal length asymmetries, including periapical ribs and ilia, 5) generalized osteopenia, and 6) lower BMI. The SNS-driven effects may also add adventitious changes to the spine including asymmetries complicating the neuroendocrine effects on adolescent spinal growth. In AIS pathogenesis, the leptin-SNS concept is complementary to our NOTOM escalator concept involving the somatic nervous system. Together these two concepts view AIS in girls as being initiated by a hypothalamic dysfunction of energy metabolism (bioenergetics) affecting skeletal growth in the trunk. Where, in susceptible girls, the postural mechanisms of the somatic nervous system fail to control the asymmetric spinal and/or rib growth changes in a rapidly enlarging adolescent spine; this failure becomes evident as mild back-shape shape asymmetry, or scoliosis. The environmentally-enhanced stature of normal subjects in the last 300 years, in girls susceptible to AIS, may have exaggerated any developmental dysharmony between the autonomic and somatic nervous systems being fought out in the spine and trunk of the girl - possibly making mild back-shape asymmetry, or scoliosis more prevalent today than hitherto.

Chronic transcutaneous electrical stimulation of calf muscles improves functional capacity without inducing systemic inflammation in claudicants.

OBJECTIVES: To assess whether electrical stimulation of ischaemic calf muscles in claudicants causes a systemic inflammatory response and to evaluate effects of its chronic application on muscle function and walking ability. DESIGN: Prospective randomised controlled trial of calf muscle stimulation. MATERIALS AND METHODS: Stable claudicants were randomised to receive either active chronic low frequency (6 Hz) motor stimulation (n=15) or, as a control treatment, submotor transcutaneous electrical nerve (TENS) stimulation (n=15) of calf muscles in one leg, 3 x 20 min per day for four weeks. Leucocyte activation was quantified by changes in cell morphology, vascular permeability by urinary albumin:creatinine ratio (ACR), calf muscle function by isometric twitch contractions and walking ability by treadmill performance pre- and post-intervention. RESULTS: Acute active muscle stimulation activated leucocytes less (28% increase) than a standard treadmill test (81% increase) and did not increase ACR. Chronic calf muscle stimulation significantly increased pain-free walking distance by 35 m (95% CI 17, 52, P<0.001) and maximum walking distance by 39 m (95% CI 7, 70, P<0.05) while control treatment had no effect. Active stimulation prevented fatigue of calf muscles during isometric electrically evoked contractions by abolishing the slowing of relaxation that was responsible for loss of force. CONCLUSIONS: Chronic electrical muscle stimulation is an effective treatment for alleviating intermittent claudication which, by targeted activation of a small muscle mass, does not engender a significant systemic inflammatory response.

Appositions between cocaine and amphetamine-related transcript- and gonadotropin releasing hormone-immunoreactive neurons in the hypothalamus of the Siberian hamster.

Recent in vitro studies have provided evidence that cocaine and amphetamine-related transcript (CART) pathways in the hypothalamus mediate the effects of leptin upon gonadotropin releasing hormone (GnRH) secretion. The aim of the current study was to use dual label immunofluorescence to investigate the anatomical basis of such a pathway. CART-ir processes were found extensively in regions where GnRH cell bodies where located. Analysis using confocal microscopy showed that the majority of GnRH neurons (62%) had close appositions from CART-ir processes. The proportion of GnRH-ir perikarya with CART-ir appositions was significantly higher (P<0.05) in neurons located in the diagonal band of Broca (70%) compared to those more caudally located in the preoptic area (53%). This anatomical evidence for close appositions between CART-ir processes and GnRH cell bodies supports the hypothesis that one mechanism by which leptin causes its effect on the GnRH pulse generator is indirectly via CART neurons, thus allowing information about nutritional status and body fat stores to be conveyed to the reproductive system.