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Feng Luo

Publications and source records attributed to Feng Luo.

38 records · Page 3Linked to original sources
PubMed2002

Transient relationships among BOLD, CBV, and CBF changes in rat brain as detected by functional MRI.

The transient relationship between arterial cerebral blood flow (CBF(A)) and total cerebral blood volume (CBV(T)) was determined in the rat brain. Five rats anesthetized with urethane (1.2 g/kg) were examined under graded hypercapnia conditions (7.5% and 10% CO(2) ventilation). The blood oxygenation level-dependent (BOLD) contrast was determined by a gradient-echo echo-planar imaging (GE-EPI) pulse sequence, and CBV(T) changes were determined after injection of a monocrystalline iron oxide nanocolloid (MION) contrast agent using an iron dose of 12 mg/kg. The relationship between CBV(T) and CBF(A) under transient conditions is similar to the power law under steady-state conditions. In addition, the transient relationship between CBV(T) and CBF(A) is region-specific. Voxels with > or =15% BOLD signal changes from hypercapnia (7.5% CO(2) ventilation) have a larger power index (alpha = 3.26), a larger maximum possible BOLD response (M = 0.85), and shorter T(*)(2) (32 ms) caused by deoxyhemoglobin, compared to voxels with <15% BOLD signal changes (alpha = 1.82, M = 0.16, and T(*)(2) = 169 ms). It is suggested that the biophysical model of the BOLD signal can be extended under the transient state, with a caution that alpha and M values are region-specific. To avoid overestimation of the cerebral metabolic rate of oxygen changes seen using fMRI, caution should be taken to not include voxels with large veins and a large BOLD signal.

Animals↗
PubMed2002

Roles of the plasminogen activator streptokinase and the plasminogen-associated M protein in an experimental model for streptococcal impetigo.

Primary infection by group A streptococci (GAS) takes place at either the throat or skin of the human host, often leading to pharyngitis or impetigo, respectively. Many GAS strains differ in their preference for throat and skin tissue sites. Previous epidemiological findings show that many of the strains displaying strong tropism for the skin have a high-affinity binding site for plasminogen, located within M protein (PAM), a prominent surface fibril. Plasminogen bound by PAM interacts with streptokinase, a plasminogen activator secreted by GAS, to yield bacterial-bound plasmin activity. In this study, PAM and streptokinase were tested for their roles in infection using an experimental model that closely mimics human impetigo. Inactivation of genes encoding either PAM or streptokinase led to a partial, but significant, loss of virulence in vivo, as measured by net growth of the bacteria and pathological alterations. The relative loss in virulence in vivo was greater for the streptokinase mutant than for the PAM mutant. However, the PAM mutant, but not the streptokinase mutant, displayed a partial loss in resistance to phagocytosis in vitro. The combined experimental and epidemiological data provide evidence that PAM and streptokinase play a key role in mediating skin-specific infection by GAS. In addition, secreted cysteine proteinase activity due to SpeB leads to degradation of streptokinase in stationary phase broth cultures. Since SpeB is also a determinant of tissue-specific GAS infection at the skin, direct interactions between these two proteolytic pathways may constitute an important pathogenic mechanism. An integrated model for superficial infection at the skin is presented.

Animals↗