We examined how variation in working memory (WM) capacity due to aging or individual differences among young adults is associated with intrinsic or resting-state anticorrelations, particularly between (1) the medial prefrontal cortex (MPFC), a component of the default-mode network (DMN) that typically decreases in activation during external, attention-demanding tasks, and (2) the dorsolateral prefrontal cortex (DLPFC), a component of the fronto-parietal control network that supports executive functions and WM and typically increases in activation during attention-demanding tasks. We compared the magnitudes of MPFC-DLPFC anticorrelations between healthy younger and older participants (Experiment 1) and related the magnitudes of these anticorrelations to individual differences on two behavioral measures of working memory capacity in two independent groups of young adults (Experiments 1 and 2). Relative to younger adults, older adults exhibited reductions in working memory capacity and in MPFC-DLPFC anticorrelations. Within younger adults, greater MPFC-DLPFC anticorrelation at rest correlated with greater working memory capacity. These findings show that variation in MPFC-DLPFC anticorrelations, whether related to aging or to individual differences, may reflect an intrinsic functional brain architecture supportive of working memory capacity.

Groundbreaking research in animals has demonstrated that the hippocampus contains neurons that distinguish between overlapping navigational trajectories. These hippocampal neurons respond selectively to the context of specific episodes despite interference from overlapping memory representations. The present study used functional magnetic resonance imaging in humans to examine the role of the hippocampus and related structures when participants need to retrieve contextual information to navigate well learned spatial sequences that share common elements. Participants were trained outside the scanner to navigate through 12 virtual mazes from a ground-level first-person perspective. Six of the 12 mazes shared overlapping components. Overlapping mazes began and ended at distinct locations, but converged in the middle to share some hallways with another maze. Non-overlapping mazes did not share any hallways with any other maze. Successful navigation through the overlapping hallways required the retrieval of contextual information relevant to the current navigational episode. Results revealed greater activation during the successful navigation of the overlapping mazes compared with the non-overlapping mazes in regions typically associated with spatial and episodic memory, including the hippocampus, parahippocampal cortex, and orbitofrontal cortex. When combined with previous research, the current findings suggest that an anatomically integrated system including the hippocampus, parahippocampal cortex, and orbitofrontal cortex is critical for the contextually dependent retrieval of well learned overlapping navigational routes.

Swiss mouse 3T3 cells, when grown in the presence of 5 mM chlorate, an inhibitor of PAPS synthesis, produce heparan sulfate glycosaminoglycan chains containing only about 8% of the sulfate normally present and which have lost the ability to bind to fibronectin. These undersulfated chains are sensitive to nitrous acid at pH 4.5, indicating that many glucosaminyl residues have unsubstituted amino groups. The iduronic acid content of the heparan sulfate produced in the presence of chlorate is reduced to less than 7% as compared to the 36% in that from untreated cells. The chlorate-treated cells do not demonstrate any alterations in their growth control. However, the spreading behavior of these cells is altered to a flat rounded morphology compared to the more typical fibroblastic appearance of the untreated cell. The sulfation of chondroitin chains is also inhibited, but at a lower chlorate concentration which does not alter growth control or the spreading ability of the cells. These data indicate that (a) 3T3 cell surface heparan sulfate proteoglycan is not involved in growth control but may be involved in cell spreading, (b) the use of chlorate should be a valuable method for the study of the biosynthesis and structure/function relationships of sulfated glycosaminoglycans, and (c) the temporal sequence of the heparan sulfate chain modification reactions predicted from results of studies with cell-free extracts also operates in the cell.

Abstract. We examined the electrophoretic properties of the proteins and glycoproteins in the smooth membranes and virions purified from cells infected with herpes simplex virus strains differing with respect to their effects on the interaction of cells among themselves. The data show the following: (1) The glycoproteins in virions and binding to membranes share common features but vary quantitatively and qualitatively depending on the virus strain. (2) The binding to smooth membranes is ordered and not random. (3) Differences in the glycosylation of membrane proteins in African green monkey (VERO) and human (HEp-2) cells indicate that glycosylation is at least in part determined by the host.

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A difference in the extent of sulfation between the heparan sulfate isolated from Swiss 3T3 mouse cells and that from Swiss 3T3 cells transformed by the DNA virus SV40 has been reported previously. This variance is manifested by different chromatographic and electrophoretic properties. Heparan sulfates from the two cell types were treated with nitrous acid under conditions that gave selective deaminative cleavage of glucosaminyl residues with sulfated amino groups in order to define the nature of the difference in sulfation further. The O-sulfate containing fragments from the heparan sulfates were compared by gel filtration and ion-exchange chromatography. The results showed that the 3T3 heparan sulfate contains 8% more O-sulfate than does the SV3T3 heparan sulfate. Analysis of uronic acids revealed that both types of heparan sulfates contain 45% L-iduronic acid and 55% D-glucuronic acid. These and other observations indicate that the primary difference in sulfation between the 3T3 and SV3T3 heparan sulfates lies in the extent of O-sulfation.