1. Receptive-field (RF) properties of 212 single cells in the superior colliculus of paralyzed macaque monkeys were studied with microelectrodes. Units were divided into superficial (0-1 mm) and deep (1-2.5 mm) layers. Orthodromic action potentials were evoked in these cells by shocking optic chiasm. 2. The vast majority of superficial cells responded to stationary or moving stimuli with transient bursts of activity and were nondirectionally selective. Moving stimuli were most effective and three main cell groups, based on response patterns to leading and trailing stimulus edges, were identified. 3. All cells had chromatically nomopponent RFs, as judged by their spectral response functions in the presence of neutral and chromatic backgrounds and on their lack of response to moving, equal-luminance chromatic borders. 4. With the exception of some very short and very long values, orthodromic latencies were unimodally distributed with a mean of 7.8 ms. The prime determinant of a cell's latency was its depth below the collicular surface rather than a specific RF feature. 5. Cells with shorter latencies (located in superficial layers) were able to reliably signal high-velocity stimulus movement; those with longer latencies (located in deeper layers) reliably signaled low-velocity motion only. 6. Results support the hypothesis that response latency is related to differences in RF organization between layers.
This study evaluated the ability of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in an injectable calcium phosphate carrier (a-BSM) to accelerate healing in a rabbit ulna osteotomy model compared to untreated surgical controls. Healing was assessed by radiography, histology and biomechanics. Bilateral mid-ulnar osteotomies were created in 16 skeletally mature rabbits. One limb in each animal was injected with either 0.1 mg rhBMP-Z/a-BSM (BMP) ( N = 8) or bufferla-BSM (BSM) ( N = 8). Contralateral osteotomies served as untreated surgical controls (SXCT). Gamma scintigrdphy showed 75%, 45% and 5% of the initial '251-rhBMP-2 dose was retained at the osteotomy site at 3 h, 1 week and 3 weeks. The biological activity of rhBMP-2 (alkaline phosphatase activity from bioassay) extracted from a-BSM incubated in vitro up to 30 days at 37 "C was unchanged. Radiographs demonstrated complete bridging of the BMP limbs at 4 weeks whereas none of the BSM or SXCT limbs were bridged. Post-mortem peripheral quantitative computed tomography determined mineralized callus area was 62% greater in BMP limbs compared to SXCT limbs. Torsional stiffness and strength were 63% and 103% greater in BMP limbs compared to SXCT limbs. There was no difference in torsional properties between BSM and SXCT limbs. Failure occurred outside the osteotomy in four out of seven of the BMP limbs. All BSM and SXCT limbs failed through the osteotomy. Histology showed bony bridging of the osteotomy and no residual carrier in the BMP limbs. BSM and SXCT groups showed less mature calluses composed of primarily fibrocartilaginous tissue and immature bone in the osteotomy gap. These data indicate rhBMP-2 delivered in a-BSM accelerated healing in a rabbit ulna osteotomy model compared to BSM and SXCT groups.
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