Targeted ischemic stroke induction and mesoscopic imaging assessment of blood flow and ischemic depolarization in awake mice

Despite advances in experimental stroke models, confounding factors such as anesthetics used during stroke induction remain. Furthermore, imaging of blood flow during stroke is not routinely done. We take advantage of in vivo bihemispheric transcranial windows for longitudinal mesoscopic imaging of cortical function to establish a protocol for focal ischemic stroke induction in target brain regions using photothrombosis in awake head-fixed mice. Our protocol does not require any surgical steps at the time of stroke induction or anesthetics during either head fixation or photoactivation. In addition, we performed laser speckle contrast imaging and wide-field calcium imaging to reveal the effect of cortical spreading ischemic depolarization after stroke in both anesthetized and awake animals over a spatial scale encompassing both hemispheres. With our combined approach, we observed ischemic depolarizing waves (3 to [Formula: see text]) propagating across the cortex 1 to 5 min after stroke induction in genetically encoded calcium indicator mice. Measures of blood flow by laser speckle were correlated with neurological impairment and lesion volume, suggesting a metric for reducing experimental variability. The ability to follow brain dynamics immediately after stroke as well as during recovery may provide a valuable guide to develop activity-dependent therapeutic interventions to be performed shortly after stroke induction.

Effects of Boron on Rhizobium-Legume Cell-Surface Interactions and Nodule Development

Boron (B) is an essential micronutrient for the development of nitrogen-fixing root nodules in pea (Pisum sativum). By using monoclonal antibodies that recognize specific glycoconjugate components implicated in legume root-nodule development, we investigated the effects of low B on the formation of infection threads and the colonization of pea nodules by Rhizobium leguminosarum bv viciae. In B-deficient nodules the proportion of infected host cells was much lower than in nodules from plants supplied with normal quantities of B. Moreover, the host cells often developed enlarged and abnormally shaped infection threads that frequently burst, releasing bacteria into damaged host cells. There was also an over-production of plant matrix material in which the rhizobial cells were embedded during their progression through the infection thread. Furthermore, in a series of in vitro binding studies, we demonstrated that the presence of B can change the affinity with which the bacterial cell surface interacts with the peribacteroid membrane glycocalyx relative to its interaction with intercellular plant matrix glycoprotein. From these observations we suggest that B plays an important role in mediating cell-surface interactions that lead to endocytosis of rhizobia by host cells and hence to the correct establishment of the symbiosis between pea and Rhizobium.

Ionic Stress and Osmotic Pressure Induce Different Alterations in the Lipopolysaccharide of a Rhizobium meliloti Strain

A halotolerant strain of Rhizobium meliloti was isolated from nodules of a Melilotus plant growing in a salt marsh in Donana National Park (southwest Spain). This strain, EFB1, is able to grow at NaCl concentrations of up to 500 mM, and no effect on growth is produced by 300 mM NaCl. EFB1 showed alterations on its lipopolysaccharide (LPS) structure that can be related to salt stress: (i) silver-stained electrophoretic profiles showed a different mobility that was dependent on ionic stress but not on osmotic pressure, and (ii) a monoclonal antibody, JIM 40, recognized changes in LPS that were dependent on osmotic stress. Both modifications on LPS may form part of the adaptive mechanism of this bacterium for saline environments.

Essentiality of Boron for Symbiotic Dinitrogen Fixation in Pea (Pisum sativum) Rhizobium Nodules

The effect of boron deficiency on symbiotic nitrogen fixation in pea (Pisum sativum) was examined. The absence of boron in the culture medium resulted in a decrease of the number of nodules and an alteration of nodule development leading to an inhibition of nitrogenase activity. Examination of boron-deficient nodules showed dramatic changes in cell walls and in both peribacteroid and infection thread membranes, suggesting a role for boron in the stability of these structures. These results indicate that boron is a requirement for normal nodule development and functionality.