Biomedical subjects

R E Blanco

Publications and source records attributed to R E Blanco.

15 recordsLinked to original sources

PubMed2001

Measuring the CP violating phase gamma using B+/- --> pi(+/-)pi(+)pi(-) and B+/- --> K+/-pi(+)pi(-) decays.

A new and simple procedure to measure the angle gamma from B+/--->pi(+/-)pi(+)pi(-) and B+/--->K+/-pi(+)pi(-) decays using SU(3) symmetry is presented. It is based on a full Dalitz plot analysis of these decays. All diagrams, including strong and electroweak penguins, are considered in the procedure. The method is also free from final state interaction problems. The theoretical error in the extraction of gamma within the method should be of the order of 10(0) or even less. Taking into account the B-meson production in the first generation of B factories and recent measurements from CLEO, this method could bring the best measurement of gamma in the next years.

Journal Article↗

PubMed2000

Basic fibroblast growth factor applied to the optic nerve after injury increases long-term cell survival in the frog retina.

The neuroprotective effects of basic fibroblast growth factor (bFGF) on the long-term survival of axotomized retinal ganglion cells (RGCs) were studied in the frog Rana pipiens. Cell loss was quantified in different regions of the ganglion cell layer using Nissl staining and tetramethylrhodamine dextran amine backfilling. All regions of the retina showed a significant decrease (32-66%) in RGC numbers between 4 and 16 weeks after axotomy. Some cells showed morphological and biochemical signs of apoptosis. A single application of bFGF to the optic nerve stump at the time of axotomy protected many of the cells 6 weeks after the injury, but this effect was lost by 12 weeks. A second application of bFGF, 6 weeks after the injury, rescued many RGCs at 12 weeks. In contrast, single or double injections of bFGF into the eyeball had no effect on RGC survival. Axotomized RGCs were significantly enlarged and elongated after axotomy, and these morphological changes were increased by bFGF treatment. In the normal retina and optic nerve, immunocytochemical staining showed bFGF-like immunoreactivity (-LI) in the pigment epithelial layer, in the outer segments of photoreceptors, and in occasional RGCs. Strong bFGF-LI was present in Müller cells and in optic nerve astrocytes and oligodendrocytes. FGF receptor-LI was present in photoreceptors, outer plexiform layer, retinal ganglion cell axons, and Müller cells. FGF receptor-LI was also observed in optic nerve glia.

Animals↗

PubMed1997

Somatostatin-like immunoreactive cells in the ground squirrel retina.

Immunocytochemical techniques were employed to locate somatostatin (SS)-containing cells in the retina of the 13-lined ground squirrel (Spermophilus tridecemlineatus). In normal retinas immunostain was limited to neuronal processes, yet distinctly labeled somata were detected in retinas of animals pretreated with colchicine. Labeled cell bodies were located in the outermost and innermost portions of the inner nuclear layer (INL) and in the ganglion cell layer (GCL). The largest population of SS-like immunoreactive neurons was found in the innermost INL. These cells were identified as small and medium sized amacrine cells whose soma diameters ranged from 4 to 14 microns. A smaller population of immunoreactive cells was observed in the outermost region of the INL. These cells, presumptive horizontal cells, were found mainly in peripheral regions of the retina. Immunoreactive cells in the GCL were of two types: displaced amacrines, and retinal ganglion cells. SS-positive axons in the optic fiber layer suggest that some of the immunoreactive GCL neurons were ganglion cells, and it is our opinion that these cells belong to a class of associational ganglion cells previously identified in other species.

Animals↗

PubMed1996

Megatherium, the stabber.

The traditional point of view that fossil ground sloths (Xenarthra) were a relatively uniform, ecologically little diverse group has been recently challenged. Marine habits have been ascribed to Thalassocnus natans of the Pliocene of Peru. Also, a more diverse diet has been proposed by one of us (R.A.F.) for some Lujanian (late Pleistocene-early Holocene of South America genera of ground sloths. In this paper, an aspect of this latter hypothesis is tested, i.e. that Megatherium americanum had morphological features that are better explained by its having had carnivorous habits rather than by solely herbivorous ones. Specifically, the question of its forearms having been designed for optimizing speed rather than strength of extension is addressed. Such a trait might have been associated with a potentially aggressive use of the animal large claws, whereas a strong extension would be more proper for tearing branches out. On the other hand the high mechanical advantage of the biceps might have made it possible for the animal to have lifted and carried heavy weights. This in turn, suggests the possibility that the animal could have manipulated large prey (for instance, turning dorsally armoured preys or carcasses upside down to expose softer parts and cached large food pieces in a safer place. By this view, Megatherium americanum would be the largest land mammal hunter to have existed.

Animals↗

PubMed1996

Specificity of identified central synapses in the embryonic cockroach: appropriate connections form before the onset of spontaneous afferent activity.

The mechanisms by which neurons recognize the appropriate postsynaptic cells remain largely unknown. A useful approach to this problem is to use a system with a few identifiable neurons that form highly specific synaptic connections. We studied the development of synapses between two identified cercal sensory afferents and two giant interneurons (GIs) in the embryonic cockroach Periplaneta americana. By 46% of embryonic development, the axons of the filiform hair sensory neurons have entered the terminal ganglionic neuropil and grow alongside the GI primary dendrites, although they do not form synapses. From 50% of development, the GI dendrites grow outward from the center of the neuropil to contact the presynaptic axons and their branches. The sensory neurons begin to spike at 52% of development, and, from 55% of development, these action potentials evoked excitatory postsynaptic potentials in the GIs. Synaptic contacts were first seen at this time. The pattern of synaptic connections was highly specific from the outset. G12 had strong input from the medial (M) afferent and had almost negligible input from the lateral (L) afferent, whereas G13 had input from both. This specificity was present before bursts of spontaneous activity began in the sensory neurons at 59% of development. G12 filopodia selectively formed synaptic contacts with the M axon rather than the L axon. The few contacts made by G12 with the L axon had a normal morphology but fewer presynaptic densities. Filopodial insertions were not involved in selective synapse formation. In this system, highly specific synaptic recognition appears to be activity independent.

Animals↗

PubMed1996

Astrocytes and regenerating axons at the proximal stump of the severed frog optic nerve.

We have studied the growing tip of the severed frog optic nerve, a central nervous system pathway that successfully regenerates. Since reconnection with the distal stump was prevented, guidance of the growing axons along anterogradely degenerating axons and their debris was precluded. One week after nerve section, there was vigorous mononuclear macrophage activity at the cut end, which quickly subsided. Phagocytosis of the remaining debris of retrograde degeneration in the proximal stump was carried out by astrocytes. Regenerating axons appeared at the tip of the stump 3 weeks after the cut. They were preferentially located near the periphery of the stump, in close proximity to astrocytes of the glia limitans. Eight weeks after the cut, regenerating axons formed a region of outgrowth protruding from the tip of the proximal stump. They were always accompanied by astrocytes, and no myelin-producing oligodendrocytes were seen in the outgrowth.

Animals↗

PubMed1995

Localization of the heptapeptide GFSKLYFamide in the sea cucumber Holothuria glaberrima (Echinodermata): a light and electron microscopic study.

Two peptides, Gly-Phe-Ser-Lys-Leu-Tyr-Phe-NH2 (GFSKLYFamide) and Ser-Gly-Tyr-Ser-Val-Leu-Tyr-Phe-NH2 (SGYSVLYFamide), recently isolated from the sea cucumber Holothuria glaberrima [Díaz-Miranda et al. (1992) Biol. Bull. 182:241-247] represent the first neuropeptides isolated from holothurians. Using an antibody against GFSKLYFa, we describe here the localization and distribution pattern of GFSKLYFa-like immunoreactivity in H. glaberrima, where immunoreactive fibers form a prominent and extensive peptidergic nervous system component. Neuron-like cells and nerve fibers expressing GFSKLYFa-like immunoreactivity are found in the ectoneural and hyponeural divisions of the radial nerve cords as well as in the digestive, haemal, respiratory, and reproductive systems; in the tentacles; and in tube feet. Neuroendocrine-like cells are found in the mucosal layer of the intestine. Ultrastructure immunocytochemical analysis revealed that, in nerve cells and fibers in the serosal layer of the intestine, the immunoreactivity is concentrated in vesicles. The immunoreactive nerve fibers are found mainly within a dense nerve plexus overlying and in close contact with smooth muscle cells of the intestine. The exclusive expression of GFSKLYFa-like immunoreactivity in neuronal or neuroendocrine tissue together with the close apposition of some fibers to muscle cells suggests that GFSKLYFa acts as a neuromuscular transmitter or neuromodulator in H. glaberrima. The wide occurrence of GFSKLYFa-like immunoreactivity throughout the nervous system of the sea cucumber suggests that GFSKLYFa plays an important role in the control of multiple action systems, including digestion, respiration, circulation, reproduction, and locomotion.

Animals↗

PubMed1993

Changes in ultrastructure and voltage-dependent currents at the glia limitans of the frog optic nerve following retinal ablation.

The surface of the frog optic nerve consists of astrocytic processes separated by narrow extracellular clefts underlying a pial sheath of loose connective tissue. Macroscopic voltage dependent currents can be recorded from this surface using the loose patch-clamp technique. In this study the changes in ultrastructure and voltage dependent Na currents have been studied for up to 1 year following removal of the retina. During the first 1-4 weeks, many of the myelinated and unmyelinated axons of the retinal ganglion cells degenerate, and the debris is phagocytosed by macrophages and glial cells. However, some morphologically intact axons remain even 12 weeks after surgery. Finally, after 16 weeks all the axons have disappeared, leaving a nerve consisting only of glial cells, some of which contain phagosomes. At 40-52 weeks after enucleation, the nerve persists, at 20-40% of the normal diameter, consisting mostly of normal looking astrocytes. The amplitude of the voltage dependent Na currents recorded from nerves during the first 1-4 weeks after enucleation, with the pial sheath intact, decreases by about 50%. After 8 weeks, the Na current recorded from the surface is about 30% of control. At 16-52 weeks after removal of the retina, when there are no intact axons, the Na current is reduced by 90%. If, however, the pial sheath is stripped away, the Na currents recorded from the glial surface are 40-50% of control during this same 16- to 52-week period, suggesting that in the all-glia nerve, the currents are shunted by the relatively thicker pial sheath.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1993

Dopaminergic neurons in the cone-dominated ground squirrel retina: a light and electron microscopy study.

Tyrosine hydroxylase (TH), the rate limiting enzyme in the conversion of tyrosine to DOPA, is a reliable marker for catecholaminergic (dopaminergic) neurons. To investigate the distribution of dopamine in the cone-dominated retina of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), retinal sections and wholemounts were incubated with an antiserum directed against TH and then processed using immunofluorescence and the avidin-biotin immunohistochemical method. TH-like immunoreactivity was exhibited by amacrine and interplexiform-like cells in the innermost portion of the inner nuclear layer (INL) and by cells we presume to be displaced amacrines in the ganglion cell layer (GCL). Their somata were 12 to 28 microns in diameter, with the majority measuring approximately 18 microns. In transverse sections the processes of the three types of neurons were seen to extend into lamina 1 of the inner plexiform layer (IPL). In horizontal sections 2-3 primary dendrites were seen to ramify and the branches extended for considerable distances, with overlap between the dendritic fields of neighboring TH-cells. A distance to the nearest neighbor analysis suggested the TH-neurons in the INL are distributed in a non-random fashion. The mean overall density of labeled amacrines is 15 cells/mm2, low when compared to the mean density reported in other species. EM results indicate that TH-labeled amacrines make synaptic contacts with unlabeled amacrines, although the possibility that they may contact ganglion cells can not be ruled out.

Animals↗

PubMed1993

Morphology and distribution of dopaminergic neurons in the ground squirrel retina.

Tyrosine hydroxylase (TH), the rate limiting enzyme in the conversion of tyrosine to DOPA, is a reliable marker for catecholaminergic (dopaminergic) neurons. To investigate the distribution of dopamine in the retina of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), retinal sections and wholemounts were incubated with an antiserum directed against TH and then processed using the avidin-biotin immunohistochemical method. TH-like immunoreactivity was exhibited by amacrine and interplexiform-like cells in the innermost portion of the inner nuclear layer (INL) and by cells we presume to be displaced amacrines in the ganglion cell layer (GCL). Their somata were 12 to 20 microns in diameter, with the majority measuring approximately 18 microns. In transverse sections the processes of the three types of neurons were seen to extend into lamina 1 of the inner plexiform layer (IPL). In horizontal sections 2-3 primary dendrites were seen to ramify and the branches extended for considerable distances, with overlap between the dendritic fields of neighboring TH cells. A distance to the nearest neighbor analysis suggests the TH-neurons in the INL are distributed in a non-random fashion.

Animals↗

PubMed1991

Localization of GAD- and GABA-like immunoreactivity in ground squirrel retina: retrograde labeling demonstrates GAD-positive ganglion cells.

Glutamic acid decarboxylase (GAD)- and gamma-aminobutyric acid (GABA)-like immunoreactivity was examined in the retina of the 13-lined ground squirrel (Spermophilus tridecemlineatus). Labeling was observed in the inner nuclear layer (INL), inner plexiform layer (IPL) and ganglion cell layer (GCL). The immunoreactive cell bodies in the inner third of the INL were 6-13 microns in diameter and, because of their size and location it was considered that these were amacrine cells. Labeling in the IPL was concentrated in 5 bands corresponding to laminae 1a, 1c, 2, 4 and 5. In the GCL a heterogeneous population of neurons exhibited GAD- and GABA-like immunoreactivity. The soma diameters of the GCL cells ranged from 5 to 17 microns. These may represent displaced amacrines and/or ganglion cells. To determine if any of the immunoreactive cells in the GCL were ganglion cells, double labeling experiments were performed using rhodamine latex microspheres ('beads') as retrograde neuronal tracers. Rhodamine beads were injected into the superior colliculus, and retinas with retrogradely labeled ganglion cells were subsequently incubated with the anti-GAD antiserum. These experiments revealed a small population of GAD-positive ganglion cells, setting a lower limit for the total number of GABAergic ganglion cells.

Animals↗

PubMed1991

Positional information determines the anatomy and synaptic specificity of cockroach filiform hair afferents using independent mechanisms.

Mutant first instar cockroaches (Periplaneta americana) with supernumerary filiform hair sensilla on their cerci were used to study the effects of cell body position on axonal morphology and synaptic connections. The wild-type cercus has two hairs, one lateral (L) and the other medial (M), each with an underlying sensory neuron. Silver-intensified cobalt fills show that the supernumerary lateral neuron (SIN) in the mutant has the same shape of arborization as L, and electrophysiological recording shows that it forms synaptic connections with the same subset of giant interneurons (GIs) as L in the terminal ganglion: GI3 and GI6. The supernumerary medial neuron (SuM) has the same axonal morphology as M and synapses with the same GIs as does M: ipsilateral GIs 1 and 2 and contralateral GIs 1, 2, 3, 5 and 6. In 0.1% of approximately 8000 animals screened, a supernumerary hair arose on the cercal midline (C hair). The C neuron sends its axon to the CNS in the same branch of the cercal nerve as the L and SIN, and has a similar arborization. However, the C neuron forms synapses with the same GIs as do M and SuM. Electron microscopy of horseradish peroxidase-injected neurons was used to confirm that the C afferent forms a monosynaptic connection to GI2. It was concluded that the position of the sensory neuron cell body does control its axonal morphology and synaptic connectivity, but that these characteristics are produced by independent mechanisms.

Animals↗

PubMed1990

Ultrastructural changes in glial cells during regeneration of cockroach peripheral nerve.

After peripheral nerve 5 in the cockroach Periplaneta americana was cut, changes occurring in the glial cells in the proximal stump were studied immediately after damage and during the process of nerve regeneration. During the first week haemocytes accumulated outside the nerve and morphologically similar granule-containing cells appeared inside the nerve. These cells were involved in phagocytic activity. Between the second and the fourth week, signs of regeneration were distinguishable; many small axonal sprouts were formed which were surrounded by glial processes, and the nerve stump increased in length. During this period the glial cells produced large amounts of extracellular material in which the bundles of axons and glia were embedded. The structural differences between glial and perineurial cells were lost during these stages of regeneration and there was no restriction to the penetration of the extracellular tracer lanthanum. After 8 weeks, reinnervation of the muscles had taken place, perineurial and glial cells were again distinguishable, and the perineurial cells were able to exclude lanthanum.

Animals↗

PubMed1990

Changes in intercellular junctions during peripheral nerve regeneration in insects.

Peripheral nerves of the adult cockroach have been cut and the changes in glial cells followed during the subsequent process of regeneration. After three to four weeks of regrowth, the severed tips of nerves were examined by freeze-fracture to assess the state of intercellular junctions between the perineurial sheath cells as well as the underlying glial cells. Both pleated septate and gap junctions were found in the immature state; their intramembranous particle (IMP) distribution was characteristic of junctions in the process of assembly, since the IMPs were irregularly and loosely arrayed in contrast with the parallel septate junctional IMP rows and gap junctional plaques found in the fully regenerated or control tissues. These junctional stages resembled those occurring in developing embryonic or metamorphosing insect tissues.

Animals↗

PubMedDate not supplied

Ultrastructural studies of dorsal root axons regenerating through adult frog optic and sciatic nerves.

Optic nerves of adult fish and amphibia can successfully regenerate, in part because their glial cells, unlike those of mammals, provide an environment permissive to regrowth. We altered the environment of regenerating dorsal root axons in the frog, Rana pipiens, by grafting segments of optic nerve to test the permissiveness of CNS glial cells to other sensory neurons. We compared these preparations to grafts of segments of sciatic nerve. After allowing various times for survival, light and electron microscopy were used to evaluate the grafts. An agglomeration of astrocytes, tightly joined by desmosomes, initially formed in the center of the optic nerve grafts. Around this grew regenerating dorsal root axons, accompanied by Schwann cells. At early stages, some axons formed dilated terminal structures, which were not seen in peripheral nerve grafts. The appearance of blood vessels within the graft and the dispersion of cells allowed larger numbers of axons to grow through the graft. By eight weeks, 48% of dorsal root sensory axons had grown through optic nerve grafts, compared to 84% for sciatic nerve. These results suggest that astrocytes from optic nerve are not inhibitory to, and provide a suitable substrate for, regrowing sensory neurons.

Animals↗