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Chemical characterization and bioavailability of phosphorus in water-insoluble fractions of three mono-ammonium phosphate fertilizers.

Elemental impurities in mono-ammonium phosphate (MAP) fertilizers, such as Fe, Al, Ca, Mg, and F, result in compounds other than NH4H2PO4. The phosphorus availability of the impurity compounds was determined in 3 commercial MAP fertilizers produced from North Carolina, Florida, and Idaho phosphate rocks. Soluble compounds, including NH4H2PO4, were washed out of the fertilizers, and the water-insoluble fraction was collected. The North Carolina, Florida, and Idaho MAP fertilizers contained 13, 16, and 17% water-insoluble fractions, respectively. Availability of phosphorus in each MAP fertilizer and water-insoluble fraction was determined in a greenhouse pot study using sorghum-sudangrass (Sorghum bicolor) as the test crop. There were no differences in dry matter weights or phosphorus uptake between reagent grade MAP and each MAP fertilizer. Lower dry matter weights and phosphorus uptake were produced from the water-insoluble North Carolina, Florida, and Idaho fractions (NC greater than FL greater than ID). Chemical analysis and characterization with optical microscopy, infrared spectroscopy, and X-ray diffractometry indicated 77.3, 73.8, and 73.6% NH4H2PO4 in the North Carolina, Florida, and Idaho MAP fertilizers, respectively. MgAl(NH4)2H(PO4)2F2, AlNH4HPO4F2, and FeNH4(HPO4)2 were identified as water-insoluble phosphorus compounds. There was a significant negative correlation between the percent phosphorus present as MgAl(NH4)2H(PO4)2F2 and the phosphorus availability. Increased crystallinity of the various water-insoluble compounds also contributed to reduced phosphorus availability.

Biological Availability↗

Retinofugal pathways in fetal and adult spiny dogfish, Squalus acanthias.

Retinofugal pathways in fetal and adult spiny dogfish were determined by intraocular injection of [3H]proline for autoradiography. Distribution and termination of the primary retinal efferents were identical in pups and adults. The retinal fibers decussate completely, except for a sparse ipsilateral projection to the caudal preoptic area. The decussating optic fibers terminate ventrally in the preoptic area and in two rostral thalamic areas, a lateral neuropil area of the dorsal thalamus and more ventrally in the lateral half of the ventral thalamus. At this same rostral thalamic level, a second optic pathway, the medial optic tract, splits from the lateral marginal optic tract and courses dorsomedially to terminate in the rostral tectum and the central and periventricular pretectal nuclei. The marginal optic tract continues caudally to terminate in a superficial pretectal nucleus and also innervates the superficial zone of the optic tectum. A basal optic tract arises from the ventral edge of the marginal optic tract and courses medially into the central pretectal nucleus, as well as continuing more caudally to terminate in a dorsal neuropil adjacent to nucleus interstitialis and in in a more ventrally and medially located basal optic nucleus. Comparison of the retinofugal projections of Squalus with those of other sharks reveals two grades of neural organization with respect to primary visual projections. Squalomorph sharks possess a rostral dorsal thalamic nucleus whose visual input is primarily, if not soley, axodendritic, and an optic tectum in which the majority of the cell bodies are located deep to the visual terminal zone. In contrast, galeomorph sharks are characterized by an enlarged and migrated rostrodorsal thalamic visual nucleus, and an optic tectum in which the majority of the cell bodies are located within the visual terminal zone. These data suggest that evolution of primary visual pathways in sharks occurs by migration and an increase in neuronal number, rather than by the occurrence of new visual pathways.

Animals↗

Effect of fiber orientation on propagation: electrical mapping of genetically altered mouse hearts.

BACKGROUND: Epicardial potentials reveal the strong effects of fiber anisotropy, rotation, imbrication, and coupling on propagation in the intact heart. From the patterns of the surface potentials, we can obtain information about the local fiber orientation, anisotropy, the transmural fiber rotation, and which direction the wave front is traveling through the wall. In this study, lessons learned from epicardial potential mapping of large hearts were applied to studies conducted in genetically altered mouse hearts. METHODS: An inducible model of the overexpression of a gain-of-function alpha5 integrin (cytoplasmic domain truncation) was created in mouse. After 3 days of administration of doxycycline, the animals exhibited an altered electrical phenotype of markedly reduced amplitude of the QRS complex on the surface electrocardiogram. Epicardial potentials were recorded from Langendorff-perfused mouse hearts with alpha5 integrin gain-of-function mutations and from wild-type (WT) control hearts. A cylindrical electrode array consisting of 184 sites with 1-mm uniform interelectrode spacing was placed around the heart, and unipolar electrograms were recorded during atrial and ventricular stimulation at different basic cycle lengths. RESULTS: The total ventricular activation time for the transgenic animals was greater than that of the WT hearts for atrial and ventricular pacing locations. The isopotential maps from the mutated hearts showed a loss of anisotropy, as revealed by the more rounded and less elliptically shaped wave fronts seen immediately after epicardial point stimulation when compared with WT hearts. The weaker potential maxima in the mutated hearts did not exhibit the normal expansion and rotation associated with an advancing wave front in a normal heart, suggesting abnormalities in myocyte coupling in these hearts. Isopotential maps provided additional information about fiber architecture from the electric field that was not obtained from optical recordings alone. These findings provided a phenotypic characterization and specific insights into the mechanisms of the electrical abnormalities associated with altered integrin signaling in cardiac myocytes.

Action Potentials↗

Axonal conduction velocities of functionally characterized retinal ganglion cells in goldfish.

1. Visual response properties and conduction velocities of retinal ganglion cells were studied by extracellular recordings in the intact goldfish eye. Visually responsive single units were confirmed as ganglion cells by collision testing, and their receptive fields were mapped. 2. From compound action potentials, we identified groups I-V in the optic nerve, with overall conduction velocities of 11.5 +/- 1.17, 7.1 +/- 0.79, 4.4 +/- 0.56, 3.1 +/- 0.31 and 2.3 +/- 0.18 m s-1 (mean +/- S.D.) at 23 degrees C. 3. Ganglion cells were classified by their receptive fields as off-, on-off- or on-centre. Nearly all confirmed ganglion cells had axonal conduction velocities in groups II, III and IV; none fell in the fastest group, I. 4. Off-centre ganglion cells had conduction velocities only in the fast group, II. On-off-centre cells fell mainly in group III, with some in group, II. On-centre cells fell in groups II-V, but mainly in groups III and IV. 5. Receptive field centre diameters were 5-30 deg measured with a photopic background. The mean diameters for off-, on-off- and on-centres were 24, 15 and 18 deg, respectively. The relatively larger diameter and higher rate of spontaneous firing of the off-centre cells were maintained under different adaptation conditions. 6. The off-centre cells can be identified with an anatomical class of large, alpha-like ganglion cells in the goldfish retina.

Action Potentials↗

Human postsynaptic density-95 (PSD95): location of the gene (DLG4) and possible function in nonneural as well as in neural tissues.

We have determined the cDNA sequence, expression pattern, and chromosomal location of the human gene DLG4, encoding the postsynaptic density-95 (PSD95) protein. hPSD95 is a 723-amino-acid protein that is 99% identical to its rodent counterparts. This is the fourth human protein identified as showing significant similarity to the Drosophila tumor suppressor Dlg. These proteins constitute the DLG subfamily of the membrane-associated guanylate kinase protein family. The expression of DLG4 in neural tissue is consistent with the pattern observed for its rat homolog. However, DLG4 is also expressed in a wide range of nonneural tissues, suggesting that the protein may have additional roles in humans. Using radiation-hybrid mapping panels, we mapped the DLG4 locus to 17p13.1, a region associated with several diseases, the phenotypes of which are consistent with loss of PSD95 function.

Adaptor Proteins, Signal Transducing↗

Optical detection of neural function in the chick visual pathway in the early stages of embryogenesis.

We investigated the developmental pattern of functional synaptogenesis in the chick visual pathway using a multiple-site optical recording method. Responses to optic nerve stimulation were recorded from the diencephalon and mesencephalon of the chick embryo. The first excitatory postsynaptic responses to optic nerve stimulation appeared in the contralateral diencephalon at Hamburger-Hamilton stage 27, which corresponds to an incubation day 5.5 (E5.5). At more developed stages, the optical signals evoked by optic nerve stimulation spread to several different regions, including the tectum and extra-tectal visual nuclei. We constructed maps of neural activity in the diencephalon and mesencephalon at different stages to investigate the spatio-temporal patterns of functional development in the chick visual system. The maps revealed that distinct postsynaptic response areas in the extra-tectal regions showed different onsets of activity, suggesting that the corresponding visual nuclei exhibit different time courses of functional synaptogenesis. We also identified the onset and location of the first functional synaptic connection in the optic tectum, which had been a point of controversy in earlier studies. In the tectal region, the action potential and the excitatory postsynaptic potential first appeared at E8, although these signals were recognized in the tecto/tegmental region at E7. The response area expanded with retinotectal fibre elongation, and reached the area centralis at E9. These results show that the onset of synaptic function in the tectum occurs 2-3 days earlier than was previously reported.

Animals↗

Differential central distribution of optic nerve components in the rat.

The distribution of Fink-Heimer positive degeneration and neurofibrillar proliferation has been examined in the dorsal lateral geniculate nucleus (dLGN) and superior colliculus of albino and pigmented rats following enucleation between post-natal days 12 and 30 and as adults. With survival times of 6 h to 5 days following enucleation, the location of maximum degenerative reaction stained by the Fink-Heimer method changes with increasing survival time in both regions. In the dLGN contralateral to the eye removal the earliest degeneration appears in a lamina occupying the medioventral extent of the nucleus and is rapidly removed; later degeneration fills a central lamina of the nucleus with a patch of degeneration extending to the outer surface of the nucleus at the mediodorsal margin. The latest occurring degeneration fills the outermost lamina and is still obvious when degeneration is largely dispersed from the inner and central laminae; this outer lamina shows an early filamentous degenerative reaction in the adult. The uncrossed optic pathway occupies a portion of the central lamina of the nucleus, and in albino animals it shows a rapid degeneration and dispersion similar to the innermost lamina on the crossed side; in the pigmented animals degeneration of the uncrossed projection starts as early as that of the albino but persists as long as the degeneration of the central lamina on the crossed side. The degeneration time of the sprouted, uncrossed pathway resulting from unilateral enucleation at birth is similar in albino and pigmented rats and resembles in timing the normal uncrossed pathway of pigmented rats. These results suggest that there are at least 3 different fiber populations in the rat optic nerve with different distribution in the dLGN. The uncrossed optic pathway of albino and pigmented rats appears to differ in fiber composition; this may relate to aberrations in mapping of uncrossed projections in the albino.

Age Factors↗

Variation of tectal morphology in teleost fishes.

The morphological organization of the optic tectum was analyzed in a number of divergent teleost species. Particular attention was focused on the organization of the periventricular gray zone and of afferent and efferent fiber systems within or adjacent to it. A dorsal part of the periventricular gray zone is recognized which is in register with the distribution of tangentially and radially oriented fascicles. A lateral part of the periventricular gray can be identified as being lateral to the lateral-most of the tangentially and radially oriented fascicles and being in register with a large number of circular fascicles in the deep white zone. Circular fascicles pass between the lateral part of the periventricular gray and a more ventral part. There are few if any circular fascicles in the part of the deep white zone that is in register with the ventral part of the gray. These parts of the periventricular gray are most clearly apparent in clupeomorph fishes, due to an exaggerated separation related to the presence of two tectal lobes within the hemisphere. It is hypothesized that the dorsal part of the gray, as can be recognized cytoarchitectonically, is in register with the projection of the dorsal optic tract and that the lateral and ventral parts of the gray are in register with the projection of the ventral optic tract.

Animals↗

Morphology of basal optic tract terminals in the turtle, Pseudemys scripta elegans.

The morphologies of axon terminals of retinal ganglion cells projecting to the basal optic nucleus (BON) via the basal optic tract (BOT) were studied in the red-eared turtle. The BOT was visualized on the ventral surface of the brainstem in vitro, and either biotinylated dextran amine was injected extracellularly or neurobiotin was injected into physiologically identified axons during intracellular recordings. Up to 16 hours after tracer injection, the brains were fixed, sectioned parasagittally, and stained for biotin and Nissl substance. The diameters and depths of extracellularly filled axons were measured at three BON sites. Fourteen axons were reconstructed from serial sections with the aid of appropriate computer software. Analysis of extracellularly filled retinal axons revealed that about three times more axons were present just inside the rostral border of the BON compared with its caudal border. Thick (2-4 microm) axons were located within 100 microm from the ventral border, whereas thin (<2 microm) axons were found throughout the nucleus. Only the thinnest axons (<1 microm) extended caudally from the nucleus, indicating that some extracellularly labelled fibers passed through the BON. The intracellularly filled axons were more similar to the thick axons filled extracellularly and arborized entirely within the BON. All of the intracellularly filled axons had thick ventral trunks from which many thin branches extended dorsally and obliquely within the BON. The thin branches bifurcated repeatedly to form bead-like varicosities or boutons that often formed clusters within regions of 150 microm3 or less. These clusters may reflect areas of focused synaptic contact on BON cells with specific direction preferences.

Animals↗

Bifunctional action of ephrin-B1 as a repellent and attractant to control bidirectional branch extension in dorsal-ventral retinotopic mapping.

We report that the EphB receptor ligand, ephrin-B1, may act bifunctionally as both a branch repellent and attractant to control the unique mechanisms in mapping the dorsal-ventral (DV) retinal axis along the lateral-medial (LM) axis of the optic tectum. EphB receptors are expressed in a low to high DV gradient by retinal ganglion cells (RGCs), and ephrin-B1 is expressed in a low to high LM gradient in the tectum. RGC axons lack DV ordering along the LM tectal axis, but directionally extend interstitial branches that establish retinotopically ordered arbors. Recent studies show that ephrin-B1 acts as an attractant in DV mapping and in controlling directional branch extension. Modeling indicates that proper DV mapping requires that this attractant activity cooperates with a repellent activity in a gradient that mimics ephrin-B1. We show that ectopic domains of high, graded ephrin-B1 expression created by retroviral transfection repel interstitial branches of RGC axons and redirect their extension along the LM tectal axis, away from their proper termination zones (TZs). In contrast, the primary RGC axons are unaffected and extend through the ectopic domains of ephrin-B1 and arborize at the topographically correct site. However, when the location of a TZ is coincident with ectopic domains of ephrin-B1, the domains appear to inhibit arborization and shape the distribution of arbors. Our findings indicate that ephrin-B1 selectively controls, through either attraction or repulsion, the directional extension and arborization of interstitial branches extended by RGC axons arising from the same DV position: branches that arise from axons positioned lateral to the correct TZ are attracted up the gradient of ephrin-B1 and branches that arise from axons positioned medial to the same TZ are repelled down the ephrin-B1 gradient. Alternatively, EphB receptor signaling may act as a 'ligand-density sensor' and titrate signaling pathways that promote branch extension toward an optimal ephrin-B1 concentration found at the TZ; branches located either medial or lateral to the TZ would encounter a gradient of increasingly favored attachment in the direction of the TZ.

Animals↗

Projection of brain stem neurons to the perigeniculate nucleus and the lateral geniculate nucleus in the cat.

Small horseradish peroxidase injections in the perigeniculate nucleus (PGN) or the lateral geniculate nucleus (LGN) gave retrograde labeling of many cells in the pontomesencephalic reticular formation (RF), the nuclei raphe dorsalis and centralis linearis, locus coeruleus, nucleus of the optic tract and nucleus parabigeminalis. Antidromic stimulation was used to identify neurons in the RF projecting to the PGN-LGN complex. Threshold mapping through the PGN and the LGN shows separate projection from the reticular formation to the PGN and the LGN.

Animals↗

Responses of the optic tectum to telencephalic stimulation in catfish.

In order to test physiologically for cerebrotectal connections in a fish, averaged evoked potentials and unit responses were recorded from the optic tectum following electrical stimulation applied to the telencephalon in the siluroid teleost Ictalurus nebulosus. A single shock applied to the area dorsalis centralis (Dc) of the telencephalon, and only to this area, elicits a sequence of deflections in the ipsilateral optic tectum: an initial negative peak at about 8 ms, (= N8), a larger N25 and a slow P50-N95. The configurations, depth profiles, latencies and susceptibility to repetitive stimulation, together with the known tectal anatomy, suggest that the first wave is due to the afferent fibers from the telencephalon and that N25 is due to deep tectal neurons. Telencephalic input exerts a conditioning effect on the field potentials and unit responses evoked by direct optic nerve shock. Such a shock elicits, in the contralateral tectum, small negative, optic tract axon peaks followed by a large N6, believed to be postsynaptic, and a still later P12. As a first approximation it is argued that the telencephalic input and the retinal input are activating different sets of neuronal elements in the optic tectum, since the configuration and depth profile of the telencephalic and optic nerve shock-elicited potentials are different. A conditioning Dc stimulus has a long-lasting effect on the form of the optic nerve field potential, maximally when the pallial shock precedes the optic by about 90 ms. The effect, observed by subtracting the conditioned from the unconditioned tectal response to optic nerve shock, is a difference wave with N11 and P20. The unit activity from deep tectal laminae is either activated or accelerated following Dc stimulation, while superficially located neurons are not affected. In another group of tectal units, the optic nerve shock-induced response is depressed by a preceding pallial dorsalis centralis stimulus. The evidence is compatible with the assumption of direct projections from Dc to the deep layers of the tectum, but the timing could also permit indirect pathways. In any case, the influence is not simple or identical for different tectal cell classes.

Animals↗

Benefits of electronic vision enhancement systems (EVES) for the visually impaired.

PURPOSE: To examine whether objective performance of near tasks is improved with various electronic vision enhancement systems (EVES) compared with the subject's own optical magnifier. DESIGN: Experimental study, randomized, within-patient design. METHODS: This was a prospective study, conducted in a hospital ophthalmology low-vision clinic. The patient population comprised 70 sequential visually impaired subjects. The magnifying devices examined were: patient's optimum optical magnifier; magnification and field-of-view matched mouse EVES with monitor or head-mounted display (HMD) viewing; and stand EVES with monitor viewing. The tasks performed were: reading speed and acuity; time taken to track from one column of print to the next; follow a route map, and locate a specific feature; and identification of specific information from a medicine label. RESULTS: Mouse EVES with HMD viewing caused lower reading speeds than stand EVES with monitor viewing (F = 38.7, P <.001). Reading with the optical magnifier was slower than with the mouse or stand EVES with monitor viewing at smaller print sizes (P <.05). The column location task was faster with the optical magnifier than with any of the EVES (F = 10.3, P <.001). The map tracking and medicine label identification task was slower with the mouse EVES with HMD viewing than with the other magnifiers (P <.01). Previous EVES experience had no effect on task performance (P >.05), but subjects with previous optical magnifier experience were significantly slower at performing the medicine label identification task with all of the EVES (P <.05). CONCLUSIONS: Although EVES provide objective benefits to the visually impaired in reading speed and acuity, together with some specific near tasks, some can be performed just as fast using optical magnification.

Aged↗

Olfactory maps and odor images.

The understanding of neuronal processing of olfactory stimuli has been furthered by genetic studies and specialized imaging of particular neuronal populations. Selective optical imaging of odor-induced presynaptic and postsynaptic glomerular activity in the olfactory bulb/antennal lobe has visualized odorant-responsive receptor repertoires and shown a more confined odor image at the level of projection neurons compared to their olfactory receptor neuron input. Genetic tracing of projection neurons connected to particular glomeruli has revealed a somewhat dispersed spatial map of termination areas for these neurons both in insects and in vertebrates. Modifications of the glomerular odor map have resulted in altered percepts of the corresponding odors.

Animals↗

The representation of the ipsilateral eye in nucleus isthmi of the leopard frog, Rana pipiens.

The retina of the leopard frog projects topographically to the superficial neuropil of the entire contralateral tectum. In the rostromedial neuropil of the tectum, there is a map of the binocular region of the visual field seen from the ipsilateral eye that is in register with the map of the binocular region of the visual field seen from the contralateral eye. The ipsilateral eye projects indirectly to the tectum through nucleus isthmi (n. isthmi), a midbrain tegmental structure. N. isthmi receives input from the ipsilateral optic tectum and sends projections bilaterally that cover both tectal lobes. Previous workers have not been able to find visual activity from the ipsilateral eye in the caudolateral optic tectum, representing the monocular visual field of the contralateral eye. We show electrophysiologically that across the entire extent of n. isthmi there are two superimposed maps, one map representing the entire visual field of the contralateral eye, the other map representing the binocular visual field of the ipsilateral eye. We also studied the behavioral consequences of localized lesions to n. isthmi and compared them to the behavioral consequences of localized lesions to the optic tectum representing equivalent areas of the visual field. Lesions to the optic tectum produce scotomas in the corresponding portion of the visual field. Lesions to n. isthmi, even medial n. isthmi representing the superior visual field, lead to scotomas in the temporal-most portion of the contralateral ground level visual field. Thus, the representation of visual space in n. isthmi is not a simple copy of the tectal representation of visual space.

Animals↗

Modulation of the pharmacokinetics of macromolecular contrast material by avidin chase: MRI, optical, and inductively coupled plasma mass spectrometry tracking of triply labeled albumin.

The goal of this work was to develop an MRI method for mapping the clearance of interstitial macromolecular plasma proteins after their extravasation from permeable blood vessels. To that end, a well-defined window of exposure to elevated blood levels was generated by inducing rapid clearance of macromolecular contrast material from the blood. Experimental removal of the intravascular component allowed subsequent tracking of clearance from the interstitial compartment in the absence of further contrast extravasation. The contrast material was based on albumin triply labeled with biotin, fluorescent tag, and GdDTPA, allowing optical, inductively coupled plasma mass spectrometry (ICP-MS) and MRI detection. The biotin tag was used here for in vivo chasing of the contrast material from the blood by intravenous administration of avidin. Upon administration of avidin the contrast material disappeared from the blood vessels and was cleared by the liver and spleen as detected by MRI, fluorescence of blood samples and histological sections, and by ICP-MS. Nonbiotinylated fluorescent albumin was not affected by administration of avidin. Contrast material that extravasated from leaky blood vessels in a VEGF overexpressing tumor, prior to administration of avidin, was not cleared by the addition of avidin and showed continued interstitial convection. Thus, avidin-chase provides an effective tool for in vivo manipulation of the arterial input function by providing experimental control over the rate of clearance of the contrast material from the circulation.

Animals↗

Retinal projections in the cat: a cholera toxin B subunit study.

The B fragment of cholera toxin (CTb) is a highly sensitive anterograde tracer for the labelling of retinal axons. It can reveal dense retinofugal projections to well-known retinorecipient nuclei along with sparse but distinct input to target areas that are not commonly recognized. Following a unilateral injection of CTb into the vitreous chamber of seven adult cats, we localized the toxin immunohistochemically in order to identify direct retinal projections in these animals. Consistent with previous findings, the strongest projections were observed in the superficial layers of the superior colliculus, the dorsal and ventral lateral geniculate nuclei, the pretectal nuclei, the accessory optic nuclei, and the suprachiasmatic nucleus of the hypothalamus. However, we also found labelled terminals in several other brain areas, including the zona incerta, the medial geniculate nucleus, the lateral posterior-pulvinar complex, the lateral habenular nucleus, and the anterior and lateral hypothalamic regions. The morphological characteristics of the retinal axon terminals in most of the identified novel target sites are described.

Animals↗

Retinohypothalamic projections and the suprachiasmatic nucleus in birds.

Although many investigators have examined retinal projections in birds, there is uncertainty as to the location and identity of a retinorecipient nucleus in the hypothalamus of Aves. A direct retinohypothalamic projection to the medial hypothalamic suprachiasmatic nucleus in mammals is believed to play a role in the entrainment of circadian rhythms. A direct retinohypothalamic projection could subserve a similar function in birds. In the present experiment, horseradish peroxidase, injected intravitreously or applied to the cut optic nerve, consistently labeled a retinorecipient nucleus in the lateral hypothalamus in ringdoves, budgerigars, quails, starlings, and song sparrows, while a significant retinal input to a medial hypothalamic nucleus was absent in these species. These results are interpreted in the light of reports of two retinorecipient nuclei, one in the medial and the other in the lateral hypothalamus, in several classes of vertebrates.

Animals↗