Stochastic dynamics as a principle of brain function

The relatively random spiking times of individual neurons are a source of noise in the brain. We show that in a finite-sized cortical attractor network, this can be an advantage, for it leads to probabilistic behavior that is advantageous in decision-making, by preventing deadlock, and is important in signal detectability. We show how computations can be performed through stochastic dynamical effects, including the role of noise in enabling probabilistic jumping across barriers in the energy landscape describing the flow of the dynamics in attractor networks. The results obtained in neurophysiological studies of decision-making and signal detectability are modelled by the stochastical neurodynamics of integrate-and-fire networks of neurons with probabilistic neuronal spiking. We describe how these stochastic neurodynamical effects can be analyzed, and their importance in many aspects of brain function, including decision-making, memory recall, short-term memory, and attention.     

Evaluation of the anti-inflammatory and antioxidant activities of the plastoquinone derivatives isolated from Roldana barba-johannis

A phytochemical study of Roldana barba-johannis afforded two triterpenic esters, an eremophilanolide and three compounds structurally related to the antioxidants vitamin E and plastoquinone. Evaluation of the anti-inflammatory and antioxidant activities of sargahydroquinoic acid, sargachromenol, their mixture, and their methyl esters showed that most of them are antioxidant and anti-inflammatory agents.     

Enhanced degradation of proteins of the basal lamina and stroma by matrix metalloproteinases from the salivary glands of Sjögren's syndrome patients: correlation with reduced structural integrity of acini and ducts

OBJECTIVE: To determine the effect of matrix metalloproteinase (MMP) activity from the labial salivary glands (LSGs) of Sj?gren's syndrome (SS) patients on proteins of the extracellular matrix (ECM) that form the basal lamina and stroma, and to compare this effect with the structural integrity of acini and ducts as well as the functionality of the LSGs. METHODS: Gelatinase activity was determined by zymography. The digestion pattern of extracellular matrix (ECM) macromolecules was detected by gel electrophoresis and quantified by densitometry. The structural integrity of acini and ducts was evaluated by light and electron microscopy. Secretory function was evaluated by measuring unstimulated salivary flow and by scintigraphy. RESULTS: LSG extracts showed increased levels of proteolytic activity toward purified proteins of the basal lamina (laminin and type IV collagen) and stroma (types I and III collagen and fibronectin). Enhanced degradation was most evident for fibronectin, laminin, and type IV collagen. Analysis of the ultrastructure of the acinar and ductal basal lamina revealed abnormalities ranging from disorganization to disappearance of this ECM structure. These changes were paralleled by an important loss of microvilli on the apical surface, as well as decreased unstimulated salivary flow. Interestingly, the results were similar in LSGs from all SS patients, regardless of the proximity of infiltrating mononuclear cell foci. CONCLUSION: Our observation that the proteolytic action of MMPs toward ECM macromolecules is increased in SS patients provides a rationale for understanding the dramatic changes in the structural organization observed in the basal lamina and apical surface of acini in these patients. The results provide new evidence that acinar and ductal cells from the LSGs of SS patients display a molecular potential, with increased capacity to markedly disorganize their ECM environment and, thus, damage their architecture and functionality.