Browsing by Author "BRAVO, H"
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- ItemAUTORADIOGRAPHIC STUDY OF THE DEVELOPMENT OF THE NEOSTRIATUM IN THE RABBIT(1979) FERNANDEZ, V; BRAVO, H; KULJIS, R; FUENTES, IAutoradiographic labeling was used to analyze the morphogenesis of the neostriatum. Pregnant rabbits received a single i.p. injection of 3H-thymidine at different stages of gestation. Careful microscopical observation of the autoradiographs shows that cellular components of the neostriatum originate between days 15-18 of intrauterine life, from a layer of proliferating matrix cells that lies on the floor of the anterior part of the lateral ventricle (ganglionic eminence). From this proliferating layer, precursor cells migrate outwards to reach the developing neostriatum in a sequential fashion according to 2 gradients of histogenesis. Neurons formed at early stages occupy a ventromedial position in the neostriatum, while those formed at latter stages occupy a dorsolateral position (ventromedial to dorsolateral gradient). The rostral regions of the neostriatum arise somewhat later than the caudal ones, demonstrating the existence of a caudo-cephalic gradient of cytogenesis.
- ItemCOMPARATIVE-STUDY OF VISUAL INTER AND INTRAHEMISPHERIC CORTICO-CORTICAL CONNECTIONS IN 5 NATIVE CHILEAN RODENTS(1990) BRAVO, H; OLAVARRIA, J; TORREALBA, FPrevious studies of the visual cortical organization in the rat and other rodent species have raised the possibility that the visual cortical plan in the rat is common to a large number of species within the order. We have tested this idea by comparing the visual plan in the rat to cortical subdivision schemes obtained from five native Chilean rodent species, including members of the Cricetidae family within the Miomorph group, as well as from the Octodontidae family within the Caviomorph group. Cortical subdivision schemes were inferred from the analysis of the patterns of callosal connections revealed following multiple injections of HRP contralaterally, as well as from ipsilateral cortico-cortical connections observed after small injections of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) into striate cortex. As in the rat, callosal connections in the native rodents concentrate at the border between cytoarchitectonic areas 17 and 18a, and along the borders of discrete, sparsely callosal islands of cortex in lateral peristriate cortex. Furthermore, single injections of WGA-HRP into striate cortex produce multiple, separate fields of labelled cells and terminations in cortex surrounding are 17. Together, our data supports the idea of a common plan of visual cortical organization among rodents by providing evidence that the visual cortex in the native species is subdivided into multiple visual areas in a manner that resembles the rat cortical plan.
- ItemFOVEAL TOPOGRAPHY IN THE OPTIC-NERVE AND PRIMARY VISUAL CENTERS IN FALCONIFORMS(WILEY-LISS, 1993) INZUNZA, O; BRAVO, HThe topography of the retinal nasal and temporal foveal projections upon the optic nerve and primary visual centers was studied in diurnal bifoveate birds of prey by means of restricted tritiated proline intraocular injection.
- ItemPATTERNS OF INTERHEMISPHERIC AND STRIATE-PERISTRIATE CONNECTIONS IN VISUAL-CORTEX OF THE SOUTH-AMERICAN MARSUPIAL MARMOSA-ELEGANS (MOUSE OPOSSUM)(1990) BRAVO, H; OLAVARRIA, J; MARTINICH, SWe have analyzed the distributions of interhemispheric and striate-peristriate connections in the South American marsupial, Marmosa elegans (mouse opossum). Following multiple injections of horseradish peroxidase (HRP) into one hemisphere, we found that anterogradely labeled terminations and retrogradely labeled perikarya are distributed unevenly in the contralateral hemisphere, forming a distinct tangential pattern in striate and peristriate cortex. This pattern delineates as many as eight peristriate areas relatively poor in commissural connections in lateral peristriate cortex, and in lateral and anterolateral portions of peristriate cortex. Single injections of HRP conjugated with wheat germ agglutinin into anterior or posterior regions of striate cortex produced as many as nine discrete ipsilateral fields of labeled perikarya, and terminations distributed over a broad cortical area in lateral and anterolateral peristriate cortex. Our observations of multiple areas with little or no HRP labeling in the interhemisferic pattern, and of multiple ipsilateral striate projection fields, indicate that the topography of visual cortex in Marmosa is highly elaborate, and suggest that extrastriate cortex is subdivided into several visual areas. Furthermore, by showing that the organization of visual cortex in this marsupial is as complex as in many placental mammals, our data support the view that a basic cortical plan, consisting of multiple visual areas, appeared early in mammalian evolution.
- ItemPYRAMIDAL NEURONS OF THE RAT CEREBRAL-CORTEX, IMMUNOREACTIVE TO NICOTINIC ACETYLCHOLINE-RECEPTORS, PROJECT MAINLY TO SUBCORTICAL TARGETS(1992) BRAVO, H; KARTEN, HJCortical neurons immunoreactive to nicotinic acetylcholine receptors (nAChR) of the rat brain were characterized with monoclonal antibodies directed to ACh-binding subunits (alpha 4) or to ACh-structural subunits (beta2). A heterogeneous population of nAChR-LI neurons was found in all cortical regions. The most prominent immunoreactive neurons were pyramids of layers V and II-III. The nonpyramidal positive neurons were fusiform horizontally oriented neurons of layer VIb, small cells of layer I and round or ovoid neurons of layers II-V.
- ItemTOPOGRAPHY AND MORPHOLOGY OF RETINAL GANGLION-CELLS IN FALCONIFORMS - A STUDY ON PREDATORY AND CARRION-EATING BIRDS(WILEY-LISS, 1991) INZUNZA, O; BRAVO, H; SMITH, RL; ANGEL, MThe topographic distribution of retinal ganglion cells and their cell body size have been studied in five Falconiform species, including predatory (chilean eagle Buteo fuscenses australis, and sparrow hawk Falco sparverius) and carrion-eating (chimango caracara Milvago chimango; condor Vultur gryphus, and black vulture Coragyps atratus) birds. All these species had a well defined nasal fovea and a horizontal streak. Instead of a temporal fovea as in eagles and hawks, an afoveate temporal area is present in chimango, condor, and vulture. The highest ganglion cell density was found in the nasal fovea of Falco and Buteo with 65,000 and 62,000 cells/mm2, respectively.
- ItemVIBRISSAL ROUGHNESS DISCRIMINATION IS BARRELCORTEX-DEPENDENT(1992) GUICROBLES, E; JENKINS, WM; BRAVO, HWe have investigated the contribution of the neocortical vibrissal representation within the posterior medial barrel subfield (PMBSF) to the high performance levels obtained by rats in a complex roughness discrimination task mediated by vibrissal inputs. Nine binocularly occluded rats were trained in a two-choice roughness discrimination until they obtained the 85% correct response criteria. Subsequently, the PMBSF was localized by electrophysiological recordings and bilaterally ablated. The locus and extent of the cortical lesions were confirmed by histological analysis after additional training and testing. There was no evidence of task retention after the cortical lesion and barrelless rats were unable to obtain prelesion discriminative performance levels when stimulation was restricted solely to vibrissal cues. After extensive postlesion training, four of these rats were allowed to palpate the discriminanda with their forepaws. Under these conditions rats rapidly reached the 85%. correct criterion once again. The present results indicate that the PMBSF is essential for complex tactile discrimination when sensory information is obtained through the vibrissae by active palpation. This deficit is specific for the vibrissal system, the PMBSF is not essential to solve the same tactile discrimination task when the source of the somatosensory information is provided by other non-vibrissal cutaneous sensory receptors.