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Biomedical subjects

M T Herrera

Publications and source records attributed to M T Herrera.

7 recordsLinked to original sources
PubMed2000

GluR5 and GluR6 kainate receptor subunits coexist in hippocampal neurons and coassemble to form functional receptors.

We have performed nonradioactive double in situ hybridization to study the expression of glutamic acid decarboxylase and GluR6 or GluR5 subunits in hippocampal slices. Our results indicate that although GluR6 is primarily expressed by pyramidal cells and dentate granule neurons and GluR5 is prominently expressed in nonpyramidal cells, there is a significant population of GABAergic interneurons that coexpress the two glutamate receptor subunits. To assess whether the two subunits could coassemble to form heteromeric receptors, we studied the electrophysiological responses when both subunits were coexpressed in HEK293 cells. Responses evoked by rapid application of either glutamate, (RS)-alpha-amino-3-hydroxy-5-tert-butyl-4-isoxazolepropionic acid (ATPA) the selective agonist of GluR5 receptors), and AMPA in cells cotransfected with GluR6(R) and GluR5(Q) presented a similar degree of outward rectification. This can only be attributed to the fact that all receptors have at least one GluR6(R) subunit in their structure, conferring outward rectification, and at least one GluR5(Q) subunit to confer sensitivity to ATPA and AMPA. More than 80% of the receptors expressed by a single cell were found to be GluR5/R6 heteromers, presenting different desensitization and gating properties to homomeric R6 receptors. These results lead us to believe that a population of interneurons in the hippocampus express receptors made up of both GluR5 and GluR6 subunits and provide evidence for a greater diversity of kainate receptors in the brain than previously thought, that may account for a higher functional complexity.

Animals↗
PubMed1998

The expression and regulation of chick EphA7 suggests roles in limb patterning and innervation.

Eph receptors and their ligands, the ephrins, have been implicated in early patterning and axon guidance in vertebrate embryos. Members of these families play pivotal roles in the formation of topographic maps in the central nervous system, the formation of brain commissures, and in the guidance of neural crest cells and motor axons through the anterior half of the somites. Here, we report a highly dynamic expression pattern of the chick EphA7 gene in the developing limb. Expression is detected in discrete domains of the dorsal mesenchyme from 3 days of incubation. The expressing cells are adjacent to the routes where axons grow to innervate the limb at several key points: the region of plexus formation, the bifurcation between dorsal and ventral fascicles, and the pathway followed by axons innervating the dorsal muscle mass. These results suggested a role for EphA7 in cell-cell contact-mediated signalling in dorsal limb patterning and/or axon guidance. We carried out experimental manipulations in the chick embryo wing bud to alter the dorsoventral patterning of the limb. The analyses of EphA7 expression and innervation in the operated wings indicate that a signal emanating from the dorsal ectoderm regulates EphA7 in such a way that, in its absence, the wing bud lacks EphA7 expression and shows innervation defects at the regions where the gene was downregulated. EphA7 downregulation in the dorsal mesenchyme after dorsal ectoderm removal is more rapid than that of Lmx-1, the gene known to mediate dorsalisation in response to the ectodermal signal. These results add a new gene to the dorsalisation signalling pathway in the limb. Moreover, they implicate the Eph receptor family in the patterning and innervation of the developing limb, extending its role in axon pathfinding to the distal periphery.

Animals↗
PubMed1984

[Not Available].

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History, Ancient↗
PubMed1981

Effects of fasting and refeeding on insulin binding to liver plasma membranes and hepatocytes from normal rats.

The effect of acute and chronic starvation on insulin binding to liver cells and liver cell membranes was studied in normal rats. A short-term (1 day) fasting period did not induce significant changes in insulin binding to liver plasma membranes in spite of the hypoinsulinemia present in the rats, as compared with normo-insulinemic fed controls. Longer periods of fasting (2 and 4 days) elicited an increase in insulin binding to liver membranes that was due to an increase in the number of insulin receptors rather than to changes in affinity. All groups of membranes were similar with respect to the rates of association and dissociation of hormone, degree of negative cooperativity and extents of both hormone and receptor inactivation. The fasting-induced increase of insulin binding was not a consequence of the methodological procedure for membrane isolation since the same conclusions were obtained when intact hepatocytes were used. Refeeding of fasted animals resulted in a decrease of insulin binding together with an increase of insulinemia towards the fed control values. These results suggest that the number of insulin receptors is inversely related to the circulating levels of the hormone and support the hypothesis of insulin regulating its own receptor.

Animals↗
PubMed1981

[Not Available].

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Gynecology↗
PubMed1978

Effect of prolonged fasting upon insulin and glucagon secretion from isolated rat pancreatic islets.

To study insulin-glucagon interrelationships in the regulation of pancreatic islet functions, glucose-mediated insulin and glucagon secretion have been studied in isolated pancreatic islets from fed and from 4 and 8-day fasted rats. At low glucose levels (50 mg %) a continuous decrease of insulin and increase of glucagon secretion were observed during prolonged fasting. High glucose concentrations 300 mg %) stimulated insulin and inhibited glucagon secretion until 4 days, but did not cause any effect after 8 days fasting. These results suggest that the secretory mechanisms of the two hormones may have a common basis.

Animals↗