Repetitive and Retinotopically Restricted Activation of the Dorsal Lateral Geniculate Nucleus with Optogenetics

Optogenetics allows the control of cellular activity using focused delivery of light pulses. In neuroscience, optogenetic protocols have been shown to efficiently inhibit or stimulate neuronal activity with a high temporal resolution. Among the technical challenges associated with the use of optogenetics, one is the ability to target a spatially specific population of neurons in a given brain structure. To address this issue, we developed a side-illuminating optical fiber capable of delivering light to specific sites in a target nucleus with added flexibility through rotation and translation of the fiber and by varying the output light power. The designed optical fiber was tested in vivo in visual structures of ChR2-expressing transgenic mice. To assess the spatial extent of neuronal activity modulation, we took advantage of the hallmark of the visual system: its retinotopic organization. Indeed, the relative position of ganglion cells in the retina is transposed in the cellular topography of both the dorsal lateral geniculate nucleus (LGN) in the thalamus and the primary visual cortex (V1). The optical fiber was inserted in the LGN and by rotating it with a motor, it was possible to sequentially activate different neuronal populations within this structure. The activation of V1 neurons by LGN projections was recorded using intrinsic optical imaging. Increasing light intensity (from 1.4 to 8.9 mW/mm(2)) led to increasing activation surfaces in V1. Optogenetic stimulation of the LGN at different translational and rotational positions was associated with different activation maps in V1. The position and/or orientation of the fiber inevitably varied across experiments, thus limiting the capacity to pool data. With the optogenetic design presented here, we demonstrate for the first time a transitory and spatially-concise activation of a deep neuronal structure. The optogenetic design presented here thus opens a promising avenue for studying the function of deep brain structures

Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of PeriLaurentian Microcontinents and Taconic – Grampian Orogenesis

The Birchy Complex of the Baie Verte Peninsula, northwestern Newfoundland, comprises an assemblage of mafic schist, ultramafic rocks, and metasedimentary rocks that are structurally sandwiched between overlying ca. 490 Ma ophiolite massifs of the Baie Verte oceanic tract and underlying metasedimentary rocks of the Fleur de Lys Supergroup of the Appalachian Humber margin. Birchy Complex gabbro yielded a Late Ediacaran U–Pb zircon ID–TIMS age of 558.3 ± 0.7 Ma, whereas gabbro and an intermediate tuffaceous schist yielded LA–ICPMS concordia zircon ages of 564 ± 7.5 Ma and 556 ± 4 Ma, respectively. These ages overlap the last phase of rift-related magmatism observed along the Humber margin of the northern Appalachians (565–550 Ma). The associated ultramafic rocks were exhumed by the Late Ediacaran and shed detritus into the interleaved sedimentary rocks. Psammite in the overlying Flat Point Formation yielded a detrital zircon population typical of the Laurentian Humber margin in the northern Appalachians. Age relationships and characteristics of the Birchy Complex and adjacent Rattling Brook Group suggest that the ultramafic rocks represent slices of continental lithospheric mantle exhumed onto the seafloor shortly before or coeval with magmatic accretion of mid-ocean ridge basalt-like mafic rocks. Hence, they represent the remnants of an ocean – continent transition zone formed during hyperextension of the Humber margin prior to establishment of a mid-ocean ridge farther outboard in the Iapetus Ocean. We propose that microcontinents such as Dashwoods and the Rattling Brook Group formed as a hanging wall block and an extensional crustal allochthon, respectively, analogous to the isolation of the Briançonnais block during the opening of the Alpine Ligurian–Piemonte and Valais oceanic seaways.Le complexe de Birchy de la péninsule de Baie Verte, dans le nord-ouest de Terre-Neuve, est constitué d’un assemblage de schistes mafiques, de roches ultramafiques et de métasédiments qui sont coincés entre des massifs ophiolitiques d’ascendance océanique de la Baie Verte au-dessus, et des métasédiments du Supergroupe de Fleur de Lys de la marge de Humber des Appalaches en-dessous. Le complexe de gabbro de Birchy a donné une datation U-Pb sur zircon ID-TIMS correspondant à la fin de l’Édiacarien, soit 558,3 ± 0,7 Ma, alors qu’un gabbro et un schiste tufacé intermédiaire montrent une datation LA-ICP-MS Concordia sur zircon de 564 ± 7,5 Ma et 556 ± 4 Ma, respectivement. Ces datations chevauchent la dernière phase de magmatisme de rift observée le long de la marge Humber des Appalaches du Nord (565-550 Ma). Les roches ultramafiques associées ont été exhumées vers la fin de l’Édiacarien et leurs débris ont été imbriqués dans des roches sédimentaires. Les psammites de la Formation de Flat Point susjacente ont donné une population de zircons détritiques typique de la marge laurentienne de Humber des Appalaches du Nord. Les relations chronologiques et les caractéristiques du complexe de Birchy et du groupe de Rattling Brook adjacent, permettent de penser que ces roches ultramafiques pourraient être des écailles de manteau lithosphérique continental qui auraient été exhumées sur le plancher océanique peu avant ou en même temps que l’accrétion magmatique de roches mafiques basaltiques de type dorsale médio-océanique. Par conséquent, elles seraient des vestiges d’une zone de transition océan-continent formée au cours de l’hyper-extension de la marge de Humber avant l’apparition d’une dorsale médio-océanique plus loin au large dans l’océan Iapétus. Nous proposons que des microcontinents comme de Dashwoods et du groupe de Rattling Brook ont constitués respectivement un bloc de toit et un allochtone crustal d’extension, de la même manière que le bloc Briançonnais a été isolé lors de l’ouverture des bras océaniques alpins de Ligurie-Piémont et de Valais.Fil: Van Staal, Cees R.. Geological Survey of Canada; CanadáFil: Chew, Dave M.. Trinity College Dublin; IrlandaFil: Zagorevski, Alexandre. Geological Survey of Canada; CanadáFil: Mcnicoll, Vicki. Geological Survey of Canada; CanadáFil: Hibbard, James. North Carolina State University; Estados UnidosFil: Skulski, Tom. Geological Survey of Canada; CanadáFil: Castonguay, Sébastien. Geological Survey of Canada; CanadáFil: Escayola, Monica Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; ArgentinaFil: Sylvester, Paul J.. Memorial University Of Newfoundland; Canad

Effect of light power output on cortical activation in V1.

<p><b>A</b>. Anatomical image reference taken under a 545 nm illumination. Overlaid on the reference image are the activation maps obtained with different light intensities (green: 3.2 mW/mm², red: 2.2 mW/mm², blue: 1.4 mW/mm²). Maps were obtained by applying a <i>t</i>-stat threshold of p<0.01 (p<0.1 for 1.4 mW/mm² due to lower signal to noise). Blue dots represent V1 delineation according to (Franklin and Paxinos, 2008). Scale bar: 1 mm <b>B</b>. Average time course of cortical reflectance from pixels included in the blue region illustrated in A, using the same light intensities as in A. <b>C</b>. Activated cortical area as a function of light intensity. Determination coefficient of the linear fit: 0.72, p<0.01, F-test, n = 3. <b>D</b>. Peak cortical reflectance as a function of light intensity. Determination coefficient of the logarithmic fit: 0.95, n = 3. <b>E</b>. Monte Carlo simulation of photon transport in the mouse thalamus for a 200 µm fiber with a numerical aperture of 0.37, using the same three light intensities. Concentric black ovals represent boundaries where neurons are illuminated by a fluence >0.5 mW/mm², value at which ChR2 expressing neurons are at half-maximum firing rate (Wang, H., 2007). From smallest to largest: 1.4 mW/mm², 2.2 mW/mm² and 3.2 mW/mm². White bar indicates diameter of the fiber, from which photons are emitted. <b>F</b>. Activated cortical area as a function of estimated LGN volumes excited. Determination coefficient of the linear fit: 0.71, p<0.01 F-test, n = 3. Note the similar distribution with <b>C</b>.</p

Design of side-illuminating optical fiber.

<p><b>A</b>. Close-up diagram of the designed fiber. The tip of an optic fiber was beveled and polished at an angle of 45°. A thin layer of chrome (∼100 nm) was applied by electron beam deposition (gray arrows) on one side of the fiber in order to reflect light (blue arrows) off the tip of the fiber at an angle of 90°. <b>B</b>. Resulting illumination pattern with a 593 nm solid state laser. The white bar and arrows indicate the optic fiber's position.</p

Validation of the LGN localization.

<p>Extracellular multi-unit recording from the LGN of ChR2 expressing mice. Manually triggered flashes of light (red arrows) elicited neuronal activity in the LGN.</p

ChR2 expression profile and optic fiber position verification.

<p>Immunofluorescence image of ChR2 expression from coronal brain sections taken at the level of the LGN of three different animals (A–C). The optical fiber insertion path can be easily detected (thin dashed lines) as well as the LGN, with its distinctive fluorescence intensity (thick dashed line). In B, the arrowhead indicates a lesion caused by the optical fiber. Antero-posterior coordinates, with reference to the Paxinos atlas, are indicated in the top right corner. Dorso-ventral (D–V) and medio-lateral (M–L) axes are presented. Scale bar: 1 mm.</p

Effects of optical fiber rotation in the LGN.

<p><b>A–B</b>. Activation maps obtained with small rotation increments of the optical fiber in the LGN. Red: 0°, orange: 45°, yellow: 90°, green: 135°, blue: 180°, magenta: 270°. <b>A</b>. Maps obtained with rotation increments of 90°. Segregated activation maps in V1 were obtained. <b>B</b>. In a different experiment, increments of 45° were used. Blue dots represent V1 delineation. Threshold for activation maps: p<0.01. Scale bar: 1 mm. Light intensity at fiber tip: 2.2 mW/mm². <b>C</b>. Monte Carlo simulations. Black ovals represent boundaries where neurons are illuminated by a fluence >0.5 mW/mm², for different radial positions of the optical fiber. Rotation increments: 45°.</p

PS Resource Assessment of Oil and Gas Plays in Paleozoic Basins of Eastern Canada*

There are three major Paleozoic basins in eastern Canada: � Cambrian-Ordovician St. Lawrence shallow marine platform and coeval deep water facies � Silurian-Devonian shallow to deep marine Gaspé Belt � Devonian-Permian terrestrial to shallow marine Maritimes Basin The sedimentary successions are bounded by tectonically-generated unconformities- the Taconian unconformity separating Cambrian-Ordovician from Silurian-Devonian strata and the Acadian unconformity at the base of the late Devonian-Permian strata. Each basin contains unique source rock and reservoir units and specific trap types. All of the basins contain producing or discovered hydrocarbon fields but there has been no independent evaluation of their oil and gas resource potential. Over the past five years the Geological Survey of Canada and its partners have acquired new hydrocarbon systems data, in preparation for a first regional hydrocarbon play assessment of Paleozoic strata in eastern Canada. A total of 16 conventional and 2 unconventional plays have been identified. Seven conventional plays are recognized in Cambrian-Ordovician strata: � Cambrian rift sandstones � Lower Ordovician hydrothermal dolomite (HTD) � carbonate thrust slices at the Appalachian structural fron