Functional network differences in schizophrenia: a rCBF study of semantic processing

Studies of regional cerebral blood flow in patients with schizophrenia have led to the idea that dysfunctional neurocircuitry may play a role in patients' cognitive deficits. The present PET study was designed to explore this idea by comparing the functional neural networks associated with semantic processing for patients and normal controls through structural equation modeling (path analysis). The patients showed significantly different neural interactions among frontal regions, between the frontal and temporal cortices, and between the frontal lobe and anterior cingulate than controls. These discrepancies were especially striking given there were minimal group differences in task performance. Results suggest that schizophrenia involves a neural abnormality that is evident in functional networks during cognitive performance.     

Proteolysis of factor V by cathepsin G and elastase indicates that cleavage at Arg1545 optimizes cofactor function by facilitating factor Xa binding

The single-chain procofactor factor V is cleaved by thrombin (FVaIIa) at Arg709, Arg1018, and Arg1545 and by a variety of other proteases to generate a cofactor species with various levels of cofactor function. Having demonstrated previously that monocyte-bound forms of cathepsin G and elastase cleave and activate factor V, studies were initiated here using purified proteins to probe factor V structure/function. Electrophoretic, Western blotting, and amino-terminal sequence analyses revealed that cathepsin G cleaves factor V at several sites (Phe1031, Leu1447, Tyr1518, and potentially Tyr696), ultimately generating an amino-terminal 103 kDa heavy chain and a carboxy-terminal 80 kDa light chain (FVaCG). Elastase also cleaves factor V at several sites (Ile708, Ile819, Ile1484, and potentially Thr678), generating a cofactor species, FVaHNE, with an amino-terminal 102 kDa heavy chain and a carboxy-terminal 90 kDa light chain. Incubation of FVaIIa with either cathepsin G or elastase resulted in cleavage within the heavy chain, releasing peptides of approximately 2000 and approximately 3000 Da, respectively, generating FVaIIa/CG and FVaIIa/HNE. The functional activity of each cofactor species was assessed either by clotting assay or by employing a purified prothrombinase assay using saturating amounts of factor Xa. Significant differences in cofactor function were observed between the two assay systems. Whereas FVaIIa, FVaCG, FVaIIa/CG, FVaHNE, and FVaIIa/HNE all had similar cofactor activities in the purified prothrombinase assay, FVaCG and FVaHNE had no cofactor activity in the clotting-based assay, and FVaIIa/CG and FVaIIa/HNE had approximately 30-35% clotting activity relative to FVaIIa. These disparate results led us to examine the binding interactions of these cofactors with the various prothrombinase components. Kinetic analyses indicated that FVaIIa (Kd(app) = 0.096 nM), FVaIIa/CG (Kd(app) = 0.244 nM), and FVaIIa/HNE (Kd(app) = 0.137 nM) bound to membrane-bound factor Xa much more effectively than FVaCG (Kd(app) = 1.46 nM) and FVaHNE (Kd(app) = 0.818 nM). In contrast, studies of the activated protein C (APC)-catalyzed inactivation of each of the factor V(a) species indicated that they were all equivalent substrates for APC with no differences observed in the rate of inactivation or the cleavage mechanism, suggesting that APC interacts with the light chain at a site distinct from factor Xa. The Km values for prothrombin, as well as the kcat values for each of the FV(a) species, were all similar (approximately 0.25 microM and approximately 1900 min-1). In addition, kinetic analyses indicated that whereas FVaCG and FVaHNE exhibited a slightly reduced ability to interact with phospholipid vesicles (approximately 2-3-fold), the remaining FV(a) species assembled equally well on this surface. Collectively, these data indicate that FVaCG and FVaHNE have a diminished capacity to support factor Xa binding; however, cleavage at Arg1545 and removal of the extended B-domain in these cofactors restore near-total factor Xa binding. Thus, cleavage at Arg1545 optimizes cofactor function within prothrombinase by facilitating factor Xa binding to membrane-bound FVa.     

Epidermal growth factor-dependent cell cycle progression is altered in mammary epithelial cells that overexpress c-myc

Amplification and overexpression of the c-myc gene are common in primary human breast cancers and have been correlated with highly proliferative tumors. Components of the epidermal growth factor (EGF) receptor signaling pathway are also often overexpressed and/or activated in human breast tumors, and transgenic mouse models have demonstrated that c-myc and transforming growth factor alpha (a member of the EGF family) strongly synergize to induce mammary tumors. These bitransgenic mammary tumors exhibit a higher proliferation rate than do tumors arising in single transgenics. We, therefore, chose to investigate EGF-dependent cell cycle progression in mouse and human mammary epithelial cells with constitutive c-myc expression. In both species, c-myc overexpression decreased the doubling time of mammary epithelial cells by approximately 6 h, compared to parental lines. The faster growth rate was not due to increased sensitivity to EGF but rather to a shortening of the G1 phase of the cell cycle following EGF-induced proliferation. In cells with exogenous c-myc expression, retinoblastoma (Rb) was constitutively hyperphosphorylated, regardless of whether the cells were growth-arrested by EGF withdrawal or were traversing the cell cycle following EGF stimulation. In contrast, the parental cells exhibited a typical Rb phosphorylation shift during G1 progression in response to EGF. The abnormal phosphorylation status of Rb in c-myc-overexpressing cells was associated with premature activation of cdk2 kinase activity, reduced p27 expression, and early onset of cyclin E expression. These results provide one explanation for the strong tumorigenic synergism between deregulated c-myc expression and EGF receptor signal transduction in the mammary tissue of transgenic mice. In addition, they suggest a possible tumorigenic mechanism for c-myc deregulation in human breast cancer.     

2nd revision consensus on blood transfusion. Central Guidance Organization for Peer Review

Since 1982 several consensus conferences regarding the transfusion practice in hospitals have been organized in the Netherlands. Repeated updating of the consensus text such as described in this article is required to keep abreast of new developments and changes in clinical practice. Guidelines concerning compatibility testing (the result of compatibility testing is valid for three days at most), the organization of responsibilities and the clinical use of red cell concentrates, including a protocol for transfusion in patients with massive bleeding, were changed. No consensus was reached concerning the need to use only red cells that are antigen c, E and K compatible in women younger than 45 years of age and in patients with abnormal erythropoiesis. Although the need of systematic reviews to support guidelines was recognized, literature reviews revealed that only few studies were designed well enough to allow definitive conclusions regarding the benefits and risks of red cell transfusion.     

Properties and regional distribution of nicotinic cholinergic receptors in the rat hypothalamus

The rat hypothalamus has the capacity to bind alpha-bungarotoxin with high affinity to a saturable number of non-interacting receptors with a pharmacologic profile consistent with a nicotinic receptor. Studies of the hypothalamic nuclear distribution of cholinergic receptors showed no specific pattern of enrichment of muscarinic receptors. In contrast, there was a distinct distribution of nicotinic receptors with high concentrations in the suprachiasmatic, dorsomedial and preoptic suprachiasmatic nuclei. Thus, the quantitative distribution of nicotinic receptors in hypothalamic nuclei is in general agreement with the observed autoradiographic distribution of radioactive alpha bungarotoxin. Further, these results confirm the existence of high concentrations of nicotinic receptors in hypothalamic regions of the rat implicated in neuroendocrine function.     

Apparent thermodynamic parameters of ligand binding to the cloned rat mu-opioid receptor

This study examined the involvement of spinal dopamine D2 receptors in the cardiovascular effects induced by intravenous administration of the selective dopamine D2 receptor agonist quinpirole, as has been previously reported for the hypotensive action of systemic bromocriptine. In normotensive pentobartitone-anaesthetised rats, intravenous injection of quinpirole (25 to 1000 microg/kg) decreased mean aortic pressure and heart rate in a dose-related manner. The intravenous (0.5 mg/kg) or intrathecal (40 microg/rat at T9-T10) pretreatment with domperidone, a dopamine D2 receptor antagonist that does not cross the blood-brain barrier, significantly reduced the maximal hypotensive and bradycardic responses to intravenous quinpirole (1000 microg/kg). In contrast, the latter effects were fully abolished either by intravenous metoclopramide (5 mg/kg) or combined pretreatment with intravenous and intrathecal domperidone. In addition, when injected intrathecally at the T9-T10 level of the spinal cord, quinpirole (7.7 to 61.4 microg/rat) also produced dose-dependent depressor and bradycardic effects which could be blocked by intrathecal, but not intravenous, domperidone pretreatment. This suggests that, in anaesthetised normotensive rats, the hypotensive and bradycardic responses to intravenous quinpirole are fully mediated by dopamine D2 receptors, some of which are located in the peripheral circulation and some of which are located within the spinal cord. The latter finding is novel, suggesting that partial spinal mediation may not be peculiar to bromocriptine, as was previously thought. Rather, partial spinal mediation may be common to most dopamine D2 receptor agonists.     

Role of acoustic striae in hearing: discrimination of sound-source elevation

After years of systematic experimentation, we finally uncovered one thing the dorsal system contributes to hearing which the ventral system may not -- the mechanism for orienting to an elevated sound source [Sutherland, D.P., Masterton, R.B., Glendenning, K.K. (1998) Behav. Brain Res. in press]. This paper follows up this one positive result on a historical background of uniformly negative results. The focus of this report is on the fusiform cells of the dorsal cochlear nucleus whose axons course through the dorsal acoustic stria (DAS). Because electrophysiological studies have shown that the cues for sensing the elevation of a sound source would seem to be best analyzed by the dorsal cochlear nucleus, we tested, behaviorally, normal cats and cats deprived of their DAS or intermediate acoustic stria, bilaterally or ipsilaterally (with or without their contralateral ear deafened), for their ability to orient to elevated sources of broad-band noise. For behavioral testing, we made use of a conventional shock-avoidance procedure. The results lead to the conclusion that DCN and DAS may play no role in learned elevation discriminations. This result builds on that of another of our papers which suggests that a deficit in reflexive discrimination of elevation is strictly auditory in nature [Sutherland, D.P., Masterton, R.B., Glendenning, K.K. (1998) Behav. Brain Res. in press].     

Retrograde cerebral perfusion enhances cerebral protection during prolonged hypothermic circulatory arrest: a study in a chronic porcine model

BACKGROUND: This study was undertaken to confirm earlier findings that retrograde cerebral perfusion (RCP) can improve cerebral outcome after prolonged hypothermic circulatory arrest (HCA), and to determine whether RCP with inferior vena caval occlusion, which is more effective in removing particulate emboli, is superior to conventional RCP in enhancing cerebral protection. METHODS: Sixty-two pigs (27 to 30 kg) were randomly assigned to undergo one of the following for 90 minutes at 20 degrees C: antegrade cerebral perfusion (ACP); conventional RCP (RCP); RCP with occlusion of the inferior vena cava (RCP-O), or HCA with the head packed in ice. RCP flow was regulated to a sagittal sinus pressure of 20 mm Hg. Hemodynamic, electrophysiologic, and metabolic monitoring were carried out until 4 hours after rewarming, daily behavioral and neurologic assessments until elective sacrifice on day 7, and histologic analysis of the brain after death. RESULTS: Complete behavioral recovery was seen in all surviving animals by day 5 after ACP or RCP, but in only 83% after RCP-O and 50% after HCA (p = 0.001). A histopathologic score of 2 or more, indicating more than mild injury, was not found in any animal after ACP, in 27% after RCP, in 47% after HCA, and in 68% after RCP-O (p = 0.002). The median oxygen consumption was 6.66 mL/min after ACP, 1.37 mL/min with RCP, and 1.02 mL/min with RCP-O (p < 0.0001). The median amount of fluid sequestered was 2,450 mL after RCP-O, 760 mL after RCP, and -200 mL after ACP (p < 0.0001). CONCLUSIONS: Conventional RCP without inferior vena caval occlusion results in a significantly better outcome than RCP-O after prolonged HCA, despite more efficient cerebral perfusion during RCP-O, and also provides cerebral protection superior to prolonged HCA alone, but care must be taken during its implementation to minimize cerebral edema and other possible causes of retroperfusion-related cerebral injury.