Orientation selectivity in the primary visual cortex: Simulation of three models

S16 (TBI), made it applicable to mouse and studied it in vivo. T1-, T2-, T2*, and Diffusion-weighted MR images, at 8.4 T, were acquired during the first 2 h, at 24 h, 3 days , and 14 days following trauma. Cerebral edema, which is one of the most serious complications following TBI, was also assessed in separate groups, using the wet weight/dry weight tissue punch technique for measurement of water content. Both MRI and water content measurements failed to detect significant amount of edema in the first 2 h following contusion. At this time point, only small areas of hyperintensity were observed on the diffusion-weighted images indicating the formation of cytotoxic edema. At 24 h large areas of hyperintensity were observed in all cases on the T2-weighted MR images indicating the formation of vasogenic edema. Finally, at 2 weeks following contusion areas of hyper- and hypo-intensity were observed on the T2- and diffusion-weighted images, respectively which may indicate tissue gliosis. The establishment of the model in mice will enable us to conduct future studies on the role of TBI and pharmacological treatments in mice with specific genetic alteration. A PLAUSIBLE RAT MODEL OF OBSESSIVE-COMPULSIVE DISORDER: COMPULSIVE CHECKING BEHAVIOR IS INDUCED IN RATS CHRONICALLY INJECTED WITH QUINPIROLE D. Eilam and H. Szechtman Dept. of Zoology, Tel-Aviv University, Tel Aviv, Israel and Dept. of Biomedical Sci., McMaster University, Canada Compulsive checking is the common form Obsessive-Compulsive Disorder (OCD). We found that after 10 repeated injections of the D2/D3 agonist, quinpirole, rats were excessively engaged in compulsive checking behavior. The behavior of these rats met 5 criteria which are the characteristics of compulsive checking in human sufferers of OCD: (a) there were a few particular places/objects to which they returned excessively more often than to others; (b) the time to return to these preferred places/objects was excessively shorter than to others; (c) excessively few places were visited in between returns to the preferred place/object; (d) a characteristic set of acts was performed at each place/object, which differed from the acts performed at other locations/objects; and, (e) activity was altered when the environmental properties of the place/object were changed. The behavior induced by quinpirole was attenuated, but not extinguished, by co-administration of the anti-compulsive drug clomipramine. The preferred locations in quinpirole-treated rats also met the criterion of home base in normal rats. Therefore, compulsive checking behavior in rats may be related to normal checking to home site in rats. The similarity between the forms of activity in rats under chronic injections of quinpirole and compulsive checking in OCD suggests that this quinpirole preparation provides an animal model of OCD with strong face validity. ORIENTATION SELECTIVITY IN THE PRIMARY VISUAL CORTEX: SIMULATION OF THREE MODELS G. Elran, Y. Baharav, R. Gutman and Moshe Gur Dept. of Biomedical Engineering, Technion, Haifa,Israel Orientation selectivity is one of the basic organizational features of the primary visual cortex (V1). More than 30 years after its discovery, the mechanisms generating orientation selectivity are still under intense debate. The simplest model, suggested by Hubel and Wiesel, is one whereby orientation selectivity is generated by appropriately aligned rows of ‘on’ and ‘off’ center LGN cells converging on a cortical cell to create a spatially oriented ‘simple’ cell. Another, more recent model, is a variant of the above one whereby orientation bias generated by LGN cells is greatly enhanced by excitatory connections between simple cortical cells of alike orientations. In these two models orientation selectivity is generated by excitatory mechanisms. We are suggesting a third model whereby LGN orientation bias is enhanced by excitatory mechanisms but sharp orientation tuning and lack of response to extended stimuli is generated by intra-cortical inhibition. All three models

have been simulated with large scale (> 5000 cells) neural nets and tested with a host of spatial and temporal stimuli. Results were compared with those of actual physiological experiments. Simulation data show that only the third model is compatible with all physiological data. We conclude that intra-cortical inhibition is essential to generating orientation selectivity in V1 cells. MODELING THE COCKROACH ESCAPE SYSTEM DISCRIMINATION BETWEEN RIGHT AND LEFT E.A. Ezrachi and H. Parnas Dept. of Neurobiology and the Center for Neural Computation, The Hebrew University of Jerusalem, Jerusalem, Israel A minimal model of the neural network underlying a cockroach evasive behavior is shown. Using computer simulation, we demonstrate how a comparatively simple network is able to discriminate between inputs, and evoke directional response. The cockroach Periplaneta Americana is an optimal preparation to study fast directional escape responses. The cockroach responds to a wind puff by a quick pivotal turn, followed by a run. The movement is to the side opposite to the wind source; i.e. a wind from the left evokes a movement to the right and vice versa. The angle of the turn varies gradually from a wide turn for a front wind to only a slight turn for wind from the back. Therefore the sharpest discrimination of the direction of wind is between front, left and right winds. Here we concentrate on these directional discrimination of right vs. left, for wind from ether side in front of the cockroach. Using SONN – Simulator Of Neural Networks, we developed a theoretical model, where the model cells represent biological cells known to govern the directional escape system. The model is based as much as possible on experimental data, and the input - output relations are compared to electrophysiological and behavioral data. We show that for a wide range of inputs, representing different wind directions, the model was able to create an output pattern that resembles the pattern found experimentally. Furthermore, we show that synapses with facilitatory characteristics are operating as a sharpening device, enabling sharp discrimination of the direction of the wind, important for creating a distinct choice of escape turn.

F-SPONDIN AND A NOVEL HOMOLOGOUS GENE - MINDIN, ARE EXPRESSED IN CAJAL-RETIUS CELLS Y. Feinstein, T. Cohen and A. Klar Dept. of Anatomy and Cell Biology, The Hebrew University - Hadassah Medical School, Jerusalem, Israel During development of the nervous system, specific recognition molecules provide the cues necessary for the formation of neural connections. The floor plate and the cortical Cajal-Retius (CR) cells are two regions that exist only transiently during development. These regions provide cues for axonal pathfinding and for cell migration. In the cortex CR cells are the earliest-generated neurons and the first to mature. They lie in a characteristic subpial location in layer I. Several evidences point out that the CR cells may act as ‘pathfinder’ neurons and are involved in the primordial organization of the cortex. We found that F-spondin, previously described as a floor plate gene, is expressed in CR cells, by in situ hybridization and immunohistochemistry. In addition a new member of this family – mindin was found to be expressed in CR cells. We cloned mindin by using PCR with degenerate primers based on evolutionary conservation between C. elegans Fspondin and the vertebrate F-spondin genes. F-spondin and mindin share homology in two regions: the N-terminal half, and one of the thrombospondin type I repeats. F-Spondin shows also a limited homology to reelin- an extracellular protein that is secreted from CR cells. Mutation in the reelin gene yields morphological abnormalities in cortical structures. The possibility that F-spondin and/or mindin have a role in cortical laminar formation either directly or indirectly by interactions with reelin is being studied.