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S Borges

Publications and source records attributed to S Borges.

24 records · Page 2Linked to original sources
PubMedDate not supplied

Neurotensin induces calcium oscillations in cultured amacrine cells.

The peptide, neurotensin, is found in a class of amacrine cells synapsing chiefly with other amacrine cells in the chicken retina (Li & Lam, 1990; Watt et al., 1991). To investigate the possible effects of neurotensin, we have used Ca2+ imaging to measure cytosolic Ca2+ concentrations in cultured chick amacrine cells. Following a delay of about 2 min, neurotensin (300 nM) induced oscillations in Ca2+ concentration that typically had a period of 2 min and peak values of about 300 nM when averaged over the cell body. The phospholipase C inhibitors U-73, 112 and 4'-bromophenacyl bromide terminated oscillations induced by neurotensin but the protein kinase inhibitors H7 and staurosporine did not inhibit oscillations, increasing their frequency instead. In the absence of external Ca2+, neurotensin induced only a single Ca2+ transient, much briefer than when external Ca2+ was present. Together these results suggest that neurotensin activates phospholipase C, thereby producing IP3 that triggers Ca2+ release from an internal store. Although this released Ca2+ contributes to periodic Ca2+ peaks, the majority of cytosolic Ca2+, even in the first peak, comes from Ca2+ influx across the plasmalemma.

Amino Acid Sequence↗
PubMedDate not supplied

Signal clipping by the rod output synapse.

The properties of synapses between retinal neurons make an essential contribution to early visual processing. Light produces a graded hyperpolarization in photoreceptors, up to 25 mV in amplitude, and it is conventionally assumed that all of this response range is available for coding visual information. We report here, however, that the rod output synapse rectifies strongly, so that only potential changes within 5 mV of the rod dark potential are transmitted effectively to postsynaptic horizontal cells. This finding is consistent with the voltage-dependence of the calcium current presumed to control neurotransmitter release from rods. It suggests functional roles for the strong electrical coupling of adjacent rods and the weak electrical coupling of adjacent rods and cones. The existence of photoreceptor coupling resolves the apparent paradox that rods have a 25 mV response range, while signals greater than 5 mV in amplitude are clipped during synaptic transmission. We predict that the strengths of rod-rod and rod-cone coupling are quantitatively linked to the relationship between the rod response range and the synapse operating range.

Animals↗
PubMedDate not supplied

The effect of ethanol on the cellular composition of the cerebellum.

Pregnant Wistar rats were fed on a diet of food pellets and a 10% (v/v) solution of ethanol in water during pregnancy and up to 21 days postnatally. Control groups were given food pellets and water ad libitum. Areal analysis of the cerebellum of neonates showed a significant reduction of 9.7% to 12.4% in three selected lobules of the mid-sagittal vermis. Although there were no significant decreases in the linear frequency and absolute number of Purkinje cells, all three lobules showed a small percentage decrease in the length of Purkinje cell layer. The total number of granule cells was significantly reduced in all three lobules, and the ratio of granule cells to Purkinje cells was reduced by between 8.6% and 13.6%, although not significantly. The pyknotic index in the external granular layer (but not in the internal granular layer) and significantly increased at 21 days, while mitotic activity was unchanged. The extent of the diminution in the cell number of the internal granular layer suggests that besides increased cell death there may be a disturbance of cell proliferation kinetics in the precursor pool of the external granular layer. Although it is known that high blood levels can cause death of Purkinje cells, the moderate alcohol blood levels attained in this study were insufficient to do so.

Alcohol Drinking↗