bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ontogeny of preproenkephalin mRNA expression in the rat retina
Authors: Isayama Tomoki , McLaughlin Patricia J. , Zagon Ian S. 
Published: June 2009

AbstractEndogenous opioid systems (i.e. opioid peptides and opioid receptors) modulate developmental events in the neonatal mammalian retina. In the present study, the mRNA encoding preproenkephalin A (PPE), the prohormone for the opioid growth factor (OGF), [Met5]-enkephalin, was studied in the developing and the adult retinas of rats. Northern analysis indicated the presence of a 1.4-kb message in the developing and adult retinas corresponding to rat PPE mRNA. Quantitation showed that PPE message was present on postnatal day 1 at 5% of the adult level, and increased during development until the adult quantity was reached by postnatal day 27.In situhybridization experiments first detected the presence of PPE mRNA in retinal tissues during late gestation. In late prenatal and neonatal retinas, PPE message was associated with areas of the developing retina containing proliferating neuroblasts and postmitotic cells. Later in development, message appeared to be located primarily within the inner retina, with abundant PPE mRNA associated with putative horizontal cells of the inner nuclear layer (INL). The adult retina showed a similar pattern of PPE gene expression in the cells of the INL. These findings document that the gene expression in the retina for PPE begins in the fetus, continues during retinal development, and coincides with the presence of a PPE mRNA derivative ([Met5]-enkephalin) that regulates DNA synthesis during retinal ontogeny. Our results are also the first to show the presence of PPE message in the adult mammalian retina, suggesting transcription of an opioid gene in the mature visual system.
Factors controlling the dendritic arborization of retinal ganglion cells
Authors: Troilo David , Xiong Meijuan , Crowley Justin C. , Finlay Barbara L. 
Published: June 2009

AbstractThe effects of changing retinal ganglion cell (RGC) density and availability of presynaptic sites on the development of RGC dendritic arbor in the developing chick retina were contrasted. Visual form deprivation was used to induce ocular enlargement and expanded retinal area resulting in a 20–30% decrease in RGC density. In these retinas, RGC dendritic arbors increased in a compensatory manner to maintain the inner nuclear layer to RGC convergence ratio in a way that is consistent with simple stretching; RGC dendritic arbors become larger with increased branch lengths, but without change in the total number of branches. In the second manipulation, partial optic nerve section was used to produce areas of RGC depletion of approximately 60% in the central retina. This reduction in density is comparable to the density of locations in the normal peripheral retina. In RGC-depleted retinas, dendritic arbor areas of RGCs in the central retina grow to match the size of normal peripheral arbors. In contrast to the expanded case, two measures of intrinsic arbor structure are changed in RGC-depleted retinas; the branch density of RGC dendrites is greater, and the relative areas of the two arbors of bistratified cells are altered. We discuss the potential roles of retinal growth, local RGC density, and availability of presynaptic terminals in the developmental control of RGC dendritic arbor.
Pattern of ocular dominance columns in human striate cortex in strabismic amblyopia
Authors: Horton Jonathan C. , Hocking Davina R. 
Published: June 2009

AbstractPrevious experiments in animals have shown that early unilateral eyelid suture, a model of amblyopia induced by cataract, causes shrinkage of ocular dominance columns serving the deprived eye in the striate cortex. It is unknown whether the ocular dominance columns are affected in amblyopia produced by strabismus. We examined specimens of striate cortex obtained postmortem from a 79-year-old woman with a history of amblyopia in her left eye (20/800) since age 2 from accommodative esotropia. Four years prior to her death, she suffered an ischemic infarct of the left optic disc. This injury to the left optic disc made it possible to label the ocular dominance columns using cytochrome oxidase histochemistry. The pattern of ocular dominance columns was reconstructed throughout most of the right striate cortex. No shrinkage of columns was found. In the left cortex only half the column mosaic was labelled, because the patient had some residual vision in the temporal retina of her left eye. The columns within the labelled portion of the overall mosaic appeared normal. These findings indicate that shrinkage of ocular dominance columns does not occur in humans with amblyopia caused by accommodative esotropia. The ocular dominance columns are probably no longer susceptible to shrinkage at the age when most children with this condition begin to develop amblyopia.
Neural responses to velocity gradients in macaque cortical area MT
Authors: Treue Stefan , Andersen Richard A. 
Published: June 2009

AbstractVisual motion, i.e. the pattern of changes on the retinae caused by the motion of objects or the observer through the environment, contains important cues for the accurate perception of the three-dimensional layout of the visual scene. In this study, we investigate if neurons in the visual system, specifically in area MT of the macaque monkey, are able to differentiate between various velocity gradients. Our stimuli were random dot patterns designed to eliminate stimulus variables other than the orientation of a velocity gradient. We develop a stimulus space (“deformation space”) that allows us to easily parameterize our stimuli. We demonstrate that a substantial proportion of MT cells show tuned responses to our various velocity gradients, often exceeding the response evoked by an optimized flat velocity profile. This suggests that MT cells are able to represent complex aspects of the visual environment and that their properties make them well suited as building blocks for the complex receptive-field properties encountered in higher areas, such as area MST to which many cells in area MT project.
Rapid AMPA receptor desensitization in catfish cone horizontal cells
Authors: Eliasof Scott , Jahr Craig E. 
Published: June 2009

AbstractAMPA and NMDA type glutamate receptors were studied in isolated catfish cone horizontal cells using the whole-cell and outside-out patch-recording techniques. In whole-cell recordings, cyclothiazide (CTZ) enhanced the peak current in response to glutamate (in the presence of NMDA receptor antagonists). In patch recordings, currents evoked by rapid and maintained applications of glutamate desensitized with a time constant of one millisecond. CTZ blocked this rapid desensitization. Recovery from desensitization of the AMPA receptors was rapid, having a time constant of 8.65 ms. In contrast, the whole-cell and patch responses to applications of NMDA were much smaller than the AMPA receptor responses and did not desensitize. The relative contribution of these two receptor subtypes depends critically on the condition of the synapse: if glutamate levels are tonically present, the NMDA receptors contribute significantly to the postsynaptic response. If glutamate levels fall rapidly following the release of a single quantum of glutamate, then AMPA receptor currents will dominate the postsynaptic response.
Are there ionotropic glutamate receptors on the rod bipolar cell of the mouse retina?
Authors: Hughes Thomas E. 
Published: June 2009

AbstractThere is some evidence that the mammalian rod bipolar cell expresses ionotropic glutamate receptors. This is surprising in light of the strong evidence that the glutamate released by the rod photoreceptor acts upon a metabotropic glutamate receptor-mGluRo-present in the dendrites of the rod bipolar cell. To reexamine the issue of which glutamate receptor subunits may be present on the rod bipolar cell, an immunohistochemical study of acutely dissociated retinal cells was undertaken. Two monoclonal antibodies provided some evidence that GluR2 and/or GluR4, as well as NMDAR1 subunit, are present on the rod bipolar cell. A monoclonal antibody directed against the N-terminus of GluR2 labeled the rod bipolar cells, but two antisera directed against the C-terminus of the same subunit did not. One possible explanation for this discrepancy could be that the rare splice variant GluR2-long, which is endowed with a different C-terminus, could be expressed by the rod bipolar cell. To explore this possibility, RT-PCR was used to amplify the transcripts encoding GluR2 in the neural retina. This revealed that GluR2-long transcripts, with the flop exon, are present.
Postnatal development of functional properties of visual cortical cells in rats with excitotoxic lesions of basal forebrain cholinergic neurons
Authors: Siciliano Rosita , Fontanesi Gigliola , Casamenti Fiorella , Berardi Nicoletta , Bagnoli Paola , Domenici Luciano 
Published: June 2009

AbstractIn the rat, visual cortical cells develop their functional properties during a period termed as critical period, which is included between eye opening, i.e.˘postnatal day (PD) 15, and PD40. The present investigation was aimed at studying the influence of cortical cholinergic afferents from the basal forebrain (BF) on the development of functional properties of visual cortical neurons. At PD15, rats were unilaterally deprived of the cholinergic input to the visual cortex by stereotaxic injections of quisqualic acid in BF cholinergic nuclei projecting to the visual cortex. Cortical cell functional properties, such as ocular dominance, orientation selectivity, receptive-field size, and cell responsiveness were then assessed by extracellular recordings in the visual cortex ipsilateral to the lesioned BF both during the critical period (PD30) and after its end (PD45). After the recording session, the rats were sacrificed and the extent of both cholinergic lesion in BF and cholinergic depletion in the visual cortex was determined. Our results show that lesion of BF cholinergic nuclei transiently alters the ocular dominance of visual cortical cells while it does not affect the other functional properties tested. In particular, in lesioned animals recorded during the critical period, a higher percentage of visual cortical cells was driven by the contralateral eye with respect to normal animals. After the end of the critical period, the ocular dominance distribution of animals with cholinergic deafferentation was not significantly different from that of controls. Our results suggest the possibility that lesions of BF cholinergic neurons performed during postnatal development only transiently interfere with cortical competitive processes.
Activity correlates of cytochrome oxidase-defined compartments in granular and supragranular layers of primary visual cortex of the macaque monkey
Authors: Deyoe Edgar A. , Trusk Thomas C. , Wong-Riley Margaret T.T. 
Published: June 2009

AbstractTo determine if changes in metabolic capacity revealed by cytochrome oxidase (CO) histochemistry are related to sustained changes in energy-utilizing neuronal activity, we assayed CO levels and recorded multiunit firing rates along nearly tangential penetrations of V1 in seven adult macaque monkeys before and after single, monocular injections of TTX. Within as little as 14 h, TTX blockade began to reduce CO staining in zones of layer 4C that received dominant input from the injected eye. Since simple monocular occlusion has only minor effects on cortical CO levels (Trusk et al., 1990), the changes in activity that were specifically associated with CO depletion were isolated by comparing spike rates during monocular TTX blockade and during monocular occlusion. Five second samples of multiunit spike rate were obtained after 2-min adaptation to each of four adapting fields: black, gray, white, and textured. Results were similar for these four conditions. In layer 4C, ocular dominance zones with input from the TTX eye had ongoing spike rates that were 48% of the rates in zones with input from a normal but occluded eye. In six animals, it was possible to record activity at a single site before, during, and after the onset of TTX blockade. Background activity at these interpuff sites decreased as much as 3-fold in less than 1 h but stabilized within 3–4 h to an average of 53% of pre-TTX rates. These data support the interpretation that energy utilization linked to sustained spike rates partially regulates CO levels under normal conditions, at least in layer 4. Furthermore, changes in neuronal activity induced by retinal TTX preceded the detectable reduction in CO activity in V1 suggesting that the adjustment of CO levels was in response to the altered activity.
Functional role of GABA in cat retina: I. Effects of GABAA agonists
Authors: Frumkes Thomas E. , Nelson Ralph 
Published: June 2009

AbstractPutative GABAergic mechanisms were studied in perfused cat retina by means of intracellular recording and application of GABA and the GABAA agonists δ-amino valeric acid (dAVA), muscimol, and THIP. In contrast to results reported previously for cold-blooded vertebrates, introduction of 20 mM GABA into the superfusate had no influence upon the response properties of cat retinal horizontal cells (HCs). In common with results reported in cold-blooded vertebrates, introduction of the GABAA agonists dAVA (2–12 mM) and THIP or muscimol (0.2–1 mM) had four consistent reversible influences upon the response properties of cat retinal HCs: (1) they reduced photic-response amplitude, (2) slowed response onset, (3) slowed response offset, and (4) depolarized the dark membrane potential. Both rod and cone signal components were affected. GABAA agonists had similar influences upon both the time course and amplitude of responses recorded from amacrine and ganglion cells. In all cell types examined, the influence upon response kinetics was made particularly apparent with rapidly flickering stimuli. Flicker responses were reduced in amplitude much more than sustained responses. These results suggest that, in addition to other influences, GABAergic action serves to modify the time course of photic responses in both the inner and outer plexiform layer of mammalian retina making responses slower and less phasic.
Functional role of GABA in cat retina: II. Effects of GABAAantagonists
Authors: Frumkes Thomas E. , Nelson Ralph , Pflug Renate 
Published: June 2009

AbstractPutative GABAergic mechanisms were studied in the cat retina by exogenous application of the GABAAantagonists picrotoxin (PTX), native bicuculline (BCC), and bicuculline methyl bromide (BCC MeBr). When recording intracellular responses from horizontal cells (HCs) and amacrine cells as well as electroretinograms (ERGs), drugs were added to the perfusate used to maintain the isolated eyecup; when recording extracellular spikes from ganglion cells of anesthetized cats, drugs were introduced by iontophoretic injection. Both PTX and BCC MeBr had relatively little influence upon the response properties of HCs. In contrast, native BCC tended to decrease the amplitude of and to slow the photic response to light onset and both to quicken and to increase the amplitude of response to light offset; in the presence of native BCC, HC responses were dominated by a prominent spike-like “Off-overshoot.” The influence of GABAAagonists upon HC responses was not blocked by GABAAantagonists. ERGb−wave amplitude was reduced both by PTX and by native BCC, but was not influenced by BCC MeBr. Latency (time to half-peak) was increased by low doses of native BCC, and to a lesser extent PTX but not BCC MeBr. Rod-amacrine On-transient responses were increased in amplitude by PTX. Extracellular recordings from On- and Off- X and Y ganglion cell types became considerably more transient with application of either PTX, native BCC, or BCC MeBr; this tendency was greater in Off-type ganglion cells. Collectively, these results strengthen conclusions from the previous paper suggesting that GABA serves to slow onset and offset kinetics of retinal neurons, making them more sustained and less phasic. They also suggest that in mammalian retina heterogeneous types of GABAAreceptors exist, segregated into different zones: a distal zone, sensitive only to native BCC, a central zone sensitive to both native BCC and PTX, and a proximal zone sensitive to native BCC, BCC methyl halides (BCC MeH), and PTX. Only the proximal zone obeys conventional GABAApharmacology.
Tryptophan hydroxylase is expressed by photoreceptors inXenopus laevisretina
Authors: Green Carla B. , Cahill Gregory M. , Besharse Joseph C. 
Published: June 2009

AbstractSerotonin has important roles, both as a neurotransmitter and as a precursor for melatonin synthesis. In the vertebrate retina, the role and the localization of serotonin have been controversial. Studies examining serotonin immunoreactivity and uptake of radiolabeled serotonin have localized serotonin to inner retinal neurons, particularly populations of amacrine cells, and have proposed that these cells are the sites of serotonin synthesis. However, other reports identify other cells, such as bipolars and photoreceptors, as serotonergic neurons. Tryptophan hydroxylase (TPH), the rate-limiting enzyme in the serotonin synthetic pathway, was recently cloned fromXenopus laevisretina, providing a specific probe for localization of serotonin synthesis. Here we demonstrate that the majority of retinal mRNA encoding TPH is present in photoreceptor cells inXenopus laevisretina. These cells also contain TPH enzyme activity. Therefore, in addition to being the site of melatonin synthesis, the photoreceptor cells also synthesize serotonin, providing a supply of the substrate needed for the production of melatonin.
Receiver operating characteristic (ROC) analysis of neurons in the cat's lateral geniculate nucleus during tonic and burst response mode
Authors: Guido W. , Lu S.-M. , Vaughan J.W. , Godwin Dwayne W. , Sherman S. Murray 
Published: June 2009

AbstractRelay cells of the lateral geniculate nucleus respond to visual stimuli in one of two modes: burst and tonic. The burst mode depends on the activation of a voltage-dependent, Ca2+ conductance underlying the low threshold spike. This conductance is inactivated at depolarized membrane potentials, but when activated from hyperpolarized levels, it leads to a large, triangular, nearly all-or-none depolarization. Typically, riding its crest is a high-frequency barrage of action potentials. Low threshold spikes thus provide a nonlinear amplification allowing hyperpolarized relay neurons to respond to depolarizing inputs, including retinal EPSPs. In contrast, the tonic mode is characterized by a steady stream of unitary action potentials that more linearly reflects the visual stimulus. In this study, we tested possible differences in detection between response modes of 103 geniculate neurons by constructing receiver operating characteristic (ROC) curves for responses to visual stimuli (drifting sine-wave gratings and flashing spots). Detectability was determined from the ROC curves by computing the area under each curve, known as the ROC area. Most cells switched between modes during recording, evidently due to small shifts in membrane potential that affected the activation state of the low threshold spike. We found that the more often a cell responded in burst mode, the larger its ROC area. This was true for responses to optimal and nonoptimal visual stimuli, the latter including nonoptimal spatial frequencies and low stimulus contrasts. The larger ROC areas associated with burst mode were due to a reduced spontaneous activity and roughly equivalent level of visually evoked response when compared to tonic mode. We performed a within-cell analysis on a subset of 22 cells that switched modes during recording. Every cell, whether tested with a low contrast or high contrast visual stimulus exhibited a larger ROC area during its burst response mode than during its tonic mode. We conclude that burst responses better support signal detection than do tonic responses. Thus, burst responses, while less linear and perhaps less useful in providing a detailed analysis of visual stimuli, improve target detection. The tonic mode, with its more linear response, seems better suited for signal analysis rather than signal detection.
Neonatal administration of the neurotoxin 5,7-dihydroxytryptamine results in synaptic reorganization in the superficial gray layer of the hamster's superior colliculus
Authors: Arce Erick A. , Rhoades Robert W. , Mooney Richard D. 
Published: June 2009

AbstractNeonatal subcutaneous administration of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) to hamsters results in a marked depletion of serotonin (5-HT) in cortex and an increase in the concentration of this amine in the superior colliculus (SC). To determine whether this increase was associated with an alteration in the synaptic organization of 5-HT-containing axons in the superficial gray layer of the SC, immunocytochemistry was combined with electron microscopy. In normal adult hamsters, only 4.0% of 500 5-HT-immunoreactive profiles make synaptic contacts in the superficial gray layer of the hamster's SC. In 5,7-DHT-treated animals, examination of 400 individual profiles indicated that 25.5% of 5-HT-positive profiles made synaptic contacts (P < 0.05). Given the recently demonstrated effect of 5-HT on retinotectal transmission in this species, the present results suggest that the functional organization of the SC may also be markedly altered in animals that sustain neonatal 5,7-DHT administration.
Age dependent modification of cytochrome oxidase activity in the cat dorsal lateral geniculate nucleus following removal of primary visual cortex
Authors: Payne Bertram R. , Lomber Stephen G. 
Published: June 2009

AbstractThe purpose of the present study was to assess changes in the levels of cytochrome oxidase (CO) activity in the dorsal lateral geniculate nucleus (dLGN) of the adult cat following removal of primary visual cortical areas 17 and 18 on the day of birth (P1), P28, or in adulthood (≫6 months). Cytochrome oxidase activity was measured in histological sections 9 or more months after the cortical ablation. Control measures obtained from intact cats show that CO activity is normally highest in the A-laminae of dLGN, and slightly lower in the C-complex. Following visual cortex ablations incurred at any age, CO activity levels are reduced in the A-laminae. This reduction is most profound following ablations incurred on P28 or in adulthood. In contrast, CO activity in the C-complex of dLGN is at nearly normal levels following ablations on P1 or P28, but not in adulthood. These findings contribute to our understanding of the role played by the dLGN in the transfer of visual signals along retino-geniculo-extrastriate pathways that expand following early removal of areas 17 and 18. Moreover, they have implications for our understanding of spared behavioral functions attributed to the extrastriate cortex in cats which incurred early damage of areas 17 and 18.