219 research outputs found
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Localization and contribution of voltage-gated calcium channels in retinal ganglion cells and their unmyelinated axons
Get PDFABSTRACT OF DISSERTATIONLocalization and contribution of voltage-gated calcium channels in retinal ganglion cells and their unmyelinated axonsbyAllison Michelle SargoyDoctor of Philosophy in NeurobiologyUniversity of California, Los AngelesDr. Nicholas C. Brecha, ChairRetinal ganglion cell (RGC) death has been attributed to aberrant calcium signaling in injury and disease. Calcium has a dual nature in mediating both homeostatic and apoptotic signaling pathways that modulate cell survival and cell death, respectively. The regulation of excessive calcium signaling through the inhibition of voltage-gated calcium channels (VGCCs) provides a potential strategy to reduce the loss of RGCs in injury and disease. My dissertation outlines the identification and contribution of the VGCCs, their modulation through the use of pharmacological blockers and the identification of an injury-resistant subtype of RGCs to provide a platform for future studies to investigate the expression and functional properties of VGCCs that may contribute to the superior ability to withstand injury. Calcium channel expression studies that utilized immunohistochemical techniques localized the L-, P/Q- and N-type VGCCs to the RGCs and the L-type VGCCs to the RGC axons. Weak immunostaining of the N-type VGCC was detected in the RGC axons. Likewise, calcium imaging studies investigating the functional contributions of the VGCCs provided evidence for the L-, P/Q-, N- and T-type VGCCs to the RGCs and the L-type VGCCs to the RGC axons. Patch clamp analysis further confirmed the presence of T-type VGCCs in RGCs. Lastly, the survival of RGCs and their axons that underwent optic nerve transection was investigated to identify a RGC type that is more resistant to injury than any other RGC type in the retina. Immunohistochemical analysis further confirmed the M1 RGC as the most resistant RGC type in the retina to injury
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Neuropeptide releasing amacrine cells modulate microcircuits in the inner retina
Get PDFAmacrine cells form the most diverse group of interneurons in the retina. There are at least 30 identified types, which are differentiated based on their stratification patterns, neurotransmitter content, and soma and dendritic field sizes. Despite knowing the morphology of each amacrine cell type, our understanding of the connectivity, intrinsic, and functional properties of a majority of the amacrine cell types remain unclear. This study aims to investigate the intrinsic properties of neuropeptide-expressing amacrine cells, as well as their role in modulating inner retinal microcircuits. These studies will focus on two neuropeptide-expressing amacrine cells examined are the somatostatin-expressing (SRIF) and vasoactive intestinal polypeptide-expressing (VIP) amacrine cells. Previous studies have shown SRIF and VIP amacrine cells play a role in regulating dopamine levels or modulating GABA signaling in the inner retina. In this study we tested how SRIF amacrine cells can modulate the cells that comprise the light adaptation network: dopamine-expressing (DA) amacrine cells and melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). In addition, we used a novel transgenic mouse line to map the intrinsic electrophysiological properties and synaptic partners of VIP amacrine cells.In order to address these questions about SRIF- and VIP-amacrine cells in the network of cells in the inner retina, I employed a combination of anatomical, pharmacological, and electrophysiological manipulations in multiple transgenic mouse lines. The 3D modeling generated from antibody-labeled whole mount retinas showed the relationship of the processes of SRIF- and DA-amacrine cells, as well as the processes between SRIF amacrine cells and melanopsin ipRGCs. Using pharmacology and whole patch clamp protocols I showed SRIF, acting through specific SRIF receptor subtypes (sst2A and sst4), effectively increases K+ currents, decreases Ca2+ currents, as well as regulate the spontaneous firing rate of both cell types. In addition, SRIF can directly inhibit the intrinsic light response of melanopsin ipRGCs.Using the VIP-tdTomato transgenic mouse line we detail the ion channel composition of VIP- amacrine cells, which include delayed inward rectifying K+ channels, verapamil-sensitive L-type Ca2+ channels, a hyperpolarizing activated K= channel (Ih), and TTX-sensitive Na+ channel currents. The recorded VIP amacrine cells showed varying combination of these ion channels, suggesting there may be multiple subtypes of VIP amacrine cells. Finally, using a puff protocol, we showed VIP amacrine cells receive inhibitory inputs mediated by GABA and glycine. In addition, they receive excitatory input from type 2 OFF- and type 6 ON-cone bipolar cells, likely through activation of an ionotropic glutamate receptor subtype, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor
Heterogeneous functional organization of somatostatin- and dopamine-containing wide-field amacrine cells in mouse retina
Get PDFIn the retina, somatostatin (SRIF) is an inhibitory neuropeptide that influences multiple cell types, including bipolar, amacrine and ganglion cells. SRIF is reported to have multiple cellular actions including modulation of the release of dopamine (DA) from tyrosine hydroxylase (TH)-containing amacrine cells; however, the cellular basis of this interaction is unknown. Using immunohistochemistry I showed SRIF- and TH-containing wide-field amacrine cells co-stratify in the OFF sublamina of the inner plexiform layer (IPL) adjacent to the inner nuclear layer (INL). These processes form a dense network, which co-ramify and make numerous contacts along their processes and at varicosities. SRIF- and TH-immunoreactive (IR) cell bodies and processes also contain GABA and vesicular GABA transporter (VGAT) immunoreactivity, and express the GABAA α3 receptor subunit. TH-IR cells also express the SRIF receptor subtype 2A (sst2A) and SRIF-IR cells express the D1 receptor. Calcium imaging recordings of Fluo-4 labeled TH-red fluorescent protein (TH-RFP) processes exhibited a ~40% decrease in fluorescent intensity following 60 mM [K+] depolarization in the presence of SRIF (100nM-100 μM) and L054264 (1-10μM), a selective sst2A agonist. These findings suggest a reciprocal relationship between these two amacrine cell types mediated by both feedback and feed forward actions. SRIF amacrine cells act at TH-containing amacrine cells by a paracrine mechanism at sst2A, as well as directly at GABAA receptors. TH amacrine cells likely act at SRIF-containing amacrine cells at D1 and GABAA receptors. This retinal microcircuit defines a novel modulatory relationship for SRIF and demonstrates its broad influence on multiple visual processes
Development of the Tyrosine Hydroxylase Immunoreactive Cell Population in the Rabbit Retina
No full textImmunocytochemical evidence for SNARE protein-dependent transmitter release from guinea pig horizontal cells
No full textExpression of GAT‐1, a high‐affinity gamma‐aminobutyric acid plasma membrane transporter in the rat retina
No full textPostnatal development of tyrosine hydroxylase immunoreactive amacrine cells in the rabbit retina: II. Quantiative analysis
No full textPostnatal development of tyrosine hydroxylase immunoreactive amacrine cells in the rabbit retina: I. Morphological characterization
No full textLearning from biophysical heterogeneity: inductive use of case studies for maize cropping systems in Central America
No full textGlobal society has become conscious that efforts towards securing food production will only be successful if agricultural production increases are obtained through mechanisms that ensure active regeneration of the natural resource base. Production options should be targeted in the sense of that their suitability to improve agricultural production and maintain natural resources is evaluated prior to their introduction. Biophysical targeting evaluates production options as a function of the spatial and temporal variability of climate conditions, in interaction with soil, crop characteristics and agronomic management strategies. This thesis contributes to the development of a system-based methodology for biophysical targeting. Cropping system simulation and weather generator tools are interfaced to geographical information systems. Inductive use of two case studies - a green manure cover crop and reduced tillage with residue management - helped to develop the methodology. Insight is gained into the regional potential for and the soil and climate conditions under which successful introduction of these production options may be achieved. The resulting information supports regional stakeholders involved in agriculture in their analysis and discussion, negotiation and decision-making concerning where to implement production systems. This process can improve the supply of appropriate agricultural production practices that enhance production and conserve soil and water resources
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