Hermes Bravo

Tuberomammillary nucleus activation anticipates feeding under a restricted schedule in rats.

We used FOS-immunoreactivity to map changes in the neuronal activity of brain nuclei related to the state of arousal, in rats under a restricted feeding schedule. Our main finding was the outstanding activation of the tuberomammillary nucleus 24h after a meal, and its steep deactivation, which was independent of actually having the meal. The time course of FOS activation and deactivation indicated a burst of tuberomammilary nucleus activity in close temporal relation with the increased locomotor activity shown by rats in anticipation of the next meal.

Comparative study of visual inter and intrahemispheric cortico-cortical connections in five native Chilean rodents.

SummaryPrevious 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 labeled cells and terminations in the cortex surrounding area 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.

The pattern of callosal connections in posterior neocortex of congenitally anophthalmic rats

SummaryIn an effort to assess the innate capacity of the central visual system to specify corticocortical connectivity in the absence of retinal afferents, we examined the tangential distribution of callosal cells and terminations in posterior neocortex of congenitally anophthalmic rats. Although our results indicate that the callosal pattern is clearly anomalous in these rats, all features of the normal visual callosal pattern are recognizable in mutant rats, indicating that central visual pathways can generate many aspects of normal interhemispheric connectivity in the absence of input from the periphery. On the other hand, the presence of anomalies in the pattern indicates that the eyes are necessary to finetune the distribution of callosal connections at some developemental stage. Moreover, the fact that abnormalities in the callosal pattern of mutant rats are the same as those previusly described in rats enucleated at birth suggests that the eyes begin to exert their influence on callosal development after birth.

Patterns of interhemispheric and striate-peristriate connections in visual cortex of the South American marsupial Marmosa elegans (mouse opossum)

SummaryWe have analyzed the distributions of inter-hemispheric 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.

EVALUACIÓN PRÁCTICA DE ANATOMÍA. RENDIMIENTO DE LOS ALUMNOS DE PRIMER AÑO DE MEDICINA ANTE DISTINTAS FORMAS DE PREGUNTAR

Los anatomistas hemos debido hacer innovaciones para mantener una ensenanza de alto nivel, enfrentando factores como la disminucion del horario lectivo, aumento del numero de alumnos, falta de material cadaverico y de docentes. Los cambios incluyen el uso de disecciones preparadas con anticipacion, desarrollo de una pagina Web con fotos animadas y el uso de imagenes clinicas (RX, TAC, RNM). Las pruebas practicas del curso han incluido preguntas en este material, disponible en los pabellones de diseccion y en el sistema computacional. En este trabajo analizamos el rendimiento de los alumnos ante nuevas formas de evaluar el conocimiento practico de Anatomia. Se compararon los puntajes obtenidos por los estudiantes en seis tipos de preguntas de reconocimiento en: 1.- Preparaciones cadavericas que han visto con anterioridad. 2.- Fotos animadas de la pagina Web del curso. 3.- Imagenes de resonancia nuclear. 4.- Preparaciones anatomicas nuevas. 5.-Secciones anatomicas. 6.- Radiografias. El analisis estadistico de los resultados demostro que los alumnos reconocen con facilidad estructuras anatomicas en planos bidimensionales como la pantalla del computador o RX, presentando una complejidad mayor la identificacion de elementos en las preparaciones cadavericas o secciones de segmentos corporales; diferencias que son estadisticamente significativas. La utilizacion de imagenes anatomicas computacionales representan un apoyo importante a las actividades practicas. Sin embargo, subsiste el problema de la concepcion tridimensional de la estructura anatomica, que no alcanza a ser resuelta por el uso de las imagenes; resaltando el valor de las disecciones anatomicas en este tipo de cursos

Autoradiographic Study of the Development of the Neostriatum in the Rabbit

Autoradiographic labelling has been employed to analyze the morphogenesis of the neostriatum. Pregnant rabbits received a single intraperitoneal injection of tritiated thymidine at different stages of gestation. Careful microscopical observation of the autoradiographs shows that cellular components of the neostriatum originate between days 15 and 18 of the intrauterine life from a layer of proliferating matrix cells that lies on the floor of the anterior part of the lateral ventrical (ganglionic eminence). From this proliferating layer, precursor cells migrate outwards to reach the developing neostriatum in a sequential fashion according to two gradients of histogenesis. Thus, it was found that neurons formed at early stages occupy a ventromedial position in the neostriatum, while those formed at later stages occupy a dorsolateral position (ventromedial to dorsolateral gradient). Furthermore, the present study indicates that the rostral regions of the neostriatum arise somewhat later than the caudal ones, demonstrating the existence of a caudocephalic gradient of cytogenesis.

Distribution of NADPH-d positive neurons during postnatal development of the rat somatosensory cortex correlates with gradients of neurogenesis and development.

The expression of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) was studied in the rat somatosensory cortex during postnatal development from day 6 to 120. Distribution of labeled neurons was quantified in dorso-medial and ventro-lateral aspects of the cortex, and correlated with known tridimensional gradients of histogenetic development and maturation of cortical neurons. NADPH positive neurons were non-pyramidal cells that in all developmental periods were more numerous in infragranular than in supragranular layers of the cortex. Additionally, more labeled cells were found in ventro-lateral than dorso-medial infragranular layers and in anterior than posterior aspects of the cerebral cortex. These patterns of distribution correlate well with the gradients of histogenetic development and with the pattern of maturation of cortical neurons.

Anatomía y Neuroanatomía, Disciplinas Perjudicadas por la Reforma Curricular

En los ultimos tiempos, la docencia en Morfologia ha debido enfrentar un escenario cambiante, producto de: a) un cambio curricular que ha llevado a la reduccion de las horas destinadas a los cursos de Anatomia y Neuroanatomia; b) la dificultad creciente de obtener material cadaverico para las actividades practicas de dichos cursos; c) el incremento en el numero de alumnos de los cursos de pregrado; y, d) la reduccion alarmante de los cultores de estas ciencias basicas del curriculo de Medicina. Como resultado de lo anterior, es dable esperar, que esta situacion -que tiene un alcance mundial-, mas temprano que tarde tenga un efecto en el conocimiento morfologico de los medicos recien formados. En este estudio se analiza el rendimiento obtenido en pruebas diagnosticas de reconocimiento de estructuras en Anatomia y Neuroanatomia, aplicadas a medicos residentes de primer ano de la especialidad de Radiologia, formados bajo este nuevo paradigma curricular. Los resultados mostraron que la nota promedio (escala 1 a 7) de la prueba diagnostica fue 3,14 + 0,99. Es interesante notar que para una evaluacion similar, los alumnos de primer ano de la carrera de medicina obtienen una nota promedio de 5,75 +0,55. Luego de aplicar a los mismos residentes del estudio un curso teorico-practico de nivelacion en Anatomia, se aprecia un mejoramiento en el reconocimiento de estructuras anatomicas, con nota promedio de 4,79 + 0,96; detectandose una mejora sustantiva en la identificacion de elementos en secciones anatomicas de tronco. En las evaluaciones de temas neuroanatomicos, las diferencias son aun mas notorias (1,53 v/s 3,97). Estos datos reposicionan a las actividades practicas de Anatomia, en especial el trabajo con material cadaverico , como un quehacer central en el proceso de aprendizaje de estos temas. Esta situacion de olvido y/o desconocimiento observada en los nuevos medicos, ha generado una gran demanda por cursos de apoyo morfologico para las distintas especialidades

Plastinación, una Herramienta Adicional para la Enseñanza de la Anatomía

En nuestro Departamento de Anatomia de la Escuela de Medicina hemos implementado un laboratorio de plastinacion, con el fin de aprovechar eficientemente el material cadaverico disponible. Para tal efecto, utilizamos polimeros de silicona que se trabajan a temperatura ambiente. Esto nos ha permitido maximizar los procesos de produccion de plastinados. De hecho, en los tres anos de funcionamiento de nuestro laboratorio, hemos realizado 300 plastinados en silicona y 85 en resina poliester. Todos ellos han sido incorporados a la docencia de los cursos de pregrado de Anatomia y Neuroanatomia para Medicina, de Anatomia para Enfermeria y a los cursos de postitulo para los Becados de Neurologia - Neurocirugia, de Radiologia, de Anestesiologia y de Otorrinolaringologia. Esto ha significado que ademas, de las disecciones tradicionales, los alumnos puedan contar con un numero significativamente mayor de preparados anatomicos disponibles en los pasos practicos, situacion muy apreciada por ellos, dado que estan concientes de disponer de este material es muy importante en el aprendizaje de la anatomia del cuerpo humano

The oculomotor nucleus, not the abducent, innervates the muscles which advance the nictitating membrane in birds

The topographic distribution of the neurones that innervate the muscles that advance the nictitating membrane in birds was studied using intra-axonal retrograde transport of horseradish peroxidase. The motor neurones are distributed in the oculomotor complex of the ipsilateral and contralateral sides. In the ipsilateral side, the neurones innervating the pyramidalis muscles were located in the dorsolateral, dorsomedial and ventromedial subnuclei, while those neurones innervating the quadratus muscle were found in the dorsomedial and dorsolateral subnuclei. In the contralateral side the neurones innervating both the pyramidalis and quadratus were distributed in the ventromedial and ventrolateral subnuclei. The sensory neurones were found in the trigeminal ganglion and trigeminal mesencephalic nucleus.