No abstract

The blood-brain barrier (BBB) serves as a critical regulator of brain homeostasis. Following hypoxia (i.e. 6% oxygen/1hr) and reoxygenation (H/R), the BBB tight junctional complex is disrupted, resulting in increased BBB permeability and the development of vasogenic brain edema. In this study, we examined the effect of H/R on the in vivo rat BBB over a 36 hr time course in conjunction with paracellular permeability, grey matter edema, and systemic inflammatory activity. A biphasic increase was observed in the brain uptake of 14 C-sucrose, a paracellular permeability marker; with the first increase at the 10 min reoxygenation time point, and the second increase at the 6−18hr time points. Increased brain water weight gain (edema) also showed a biphasic response with the first increase at the 10 min-1 hr reoxygenation time points; and the second increase at only the 24 hr time point). Analysis of serum derived cytokines (IL-1β, TNFα, IL-6, IL-10, & IFNγ) demonstrated that only IL-1β and IL-6 were at detectable levels, but these levels were similar to controls. White bloodcell counts showed significant decreases in lymphocytes (10 min-3 hr), increases in monocytes (10 min-3 hr & 12 hr), and increases in polymorphonuclear cells (1hr & 3 hr). We have shown that H/R elicits a biphasic increase in paracellular permeability and edema, which parallel to post-stroke sequelae, despite the lack of occlusion or complete depletion of oxygen.

No abstract

Soluble amyloid β-protein (Aβ) oligomers are primary mediators of synaptic dysfunction associated with the progression of Alzheimer’s disease. Such Aβ oligomers exist dependent on their rates of aggregation and metabolism. Use of selective somatostatin receptor-subtype agonists have been identified as a potential means to mitigate Aβ accumulation in the brain, via regulation of the enzyme neprilysin. Herein, we first evaluated the impact of the somatostatin receptor subtype-4 agonist 1-[3-[N-(5-Bromopyridin-2-yl)-N-(3,4-dichlorobenzyl)amino]propyl]-3-[3-(1H-imidazol-4-yl)propyl]thiourea (NNC 26-9100) on learning and memory in 12-month SAMP8 mice (i.c.v. injection). NNC 26-9100 (0.2 μg-dose) was shown to enhance both learning (T-maze) and memory (object recognition) compared to vehicle controls. Cortical and hippocampal tissues were evaluated subsequent to NNC 26-9100 (0.2 μg) or vehicle administration for changes in neprilysin activity, along with protein expression of amyloid-precursor protein (APP), neprilysin, and Aβ1-42 oligomers within respective cellular fractions (extracellular, intracellular and membrane). NNC 26-9100 increased neprilysin activity in cortical tissue, with an associated protein expression increase in the extracellular fraction and decreased in the intracellular fraction. A decrease in intracellular APP expression was found with treatment in both cortical and hippocampal tissues. NNC 26-9100 also significantly decreased expression of Aβ1-42 trimers within both the extracellular and intracellular cortical fractions. No expression changes were found in membrane fractions for any protein. These finding suggest the potential use of selective SSTR4 agonists to mitigate toxic oligomeric forms of Aβ1-42 in critical regions of the brain identified with learning and memory decline.

Selective somatostatin receptor subtype agonists have been proposed as a means to mitigate learning and memory loss associated with Alzheimer's disease. The first aim of this study evaluated blood-to-brain transport and regional brain distribution of NNC 26-9100, a selective somatostatin subtype-4 (sst4) receptor agonist. The entry rate of 131I-NNC 26-9100 was Ki = 0.25 μl/g min, with a ∼93% association with the parenchymal component. The second goal of this study was to evaluate the effect of chronic NNC 26-9100 administration (i.p) on learning and memory, brain Aβx-42 levels, and protein expression of sst4 receptor and amyloid precursor protein (APP) in the senescence-accelerated mouse p8 (SAMP8) model of Alzheimer's disease. Mice chronically treated with NNC 26-9100 showed improved learning (day-21) and memory (day-28) using the T-maze paradigm (20 and 200 μg). Ex vivo tissue analyses showed a decline in Aβx-42 levels at the 20μg dose, while no alterations were observed in sst4 receptor or APP protein expression compared to vehicle controls. These findings indicate NNC 26-9100 is taken up into key brain regions associated with learning and memory. Furthermore, chronic administration of NNC 26-9100 improved learning and memory and decreased Aβx-42 brain levels. These results suggest sst4 receptor agonists may provide a viable therapy in the treatment of Alzheimer's disease and other forms of cognitive impairment.