Effects of Selective Deafferentation on the Discharge Characteristics of Medial Rectus Motoneurons

Medial rectus motoneurons receive two main pontine inputs: abducens internuclear neurons, whose axons course through the medial longitudinal fasciculus (MLF), and neurons in the lateral vestibular nucleus, whose axons project through the ascending tract of Deiters (ATD). Abducens internuclear neurons are responsible for conjugate gaze in the horizontal plane, whereas ATD neurons provide medial rectus motoneurons with a vestibular input comprising mainly head velocity. To reveal the relative contribution of each input to the oculomotor physiology, single-unit recordings from medial rectus motoneurons were obtained in the control situation and after selective deafferentation from cats with unilateral transection of either the MLF or the ATD. Both MLF and ATD transection produced similar short-term alterations in medial rectus motoneuron firing pattern, which were more drastic in MLF of animals. However, long-term recordings revealed important differences between the two types of lesion. Thus, while the effects of the MLF section were permanent, 2 months after ATD lesioning all motoneuronal firing parameters were similar to the control. These findings indicated a more relevant role of the MLF pathway in driving motoneuronal firing and evidenced compensatory mechanisms following the ATD lesion. Confocal immunocytochemistry revealed that MLF transection produced also a higher loss of synaptic boutons, mainly at the dendritic level. Moreover, 2 months after ATD transection, we observed an increase in synaptic coverage around motoneuron cell bodies compared with short-term data, which is indicative of a synaptogenic compensatory mechanism of the abducens internuclear pathway that could lead to the observed firing and morphological recovery. SIGNIFICANCE STATEMENT Eye movements rely on multiple neuronal circuits for appropriate performance. The abducens internuclear pathway through the medial longitudinal fascicle (MLF) and the vestibular neurons through the ascending tract of Deiters (ATD) are a dual system that supports the firing of medial rectus motoneurons. We report the effect of sectioning the MLF or the ATD pathway on the firing of medial rectus motoneurons, as well as the plastic mechanisms by which one input compensates for the lack of the other. This work shows that while the effects of MLF transection are permanent, the ATD section produces transitory effects. A mechanism based on axonal sprouting and occupancy of the vacant synaptic space due to deafferentation is the base for the mechanism of compensation on the medial rectus motoneuron

Análisis Comparativo del Posicionamiento Preciso Utilizando el Receptor de Bajo Costo GNSS ZED-F9P en Conjunto con la Antena BEIBT300 y Diferentes Modelos de Antena de Orden Geodésico

Con el avance de la Geodesia y la mejora de las especificaciones técnicas de los receptores de bajo costo, los GNSS abren nuevas alternativas para investigar las capacidades técnicas y rendimiento real que proveen este tipo de receptores para diferentes propósitos geodésicos. En este contexto, la precisión alcanzable fue analizada usando el receptor de bajo costo GNSS ZED-F9P en conjunto con dos antenas de orden geodésico (ASH701975.01B y LEIAS10 NONE) y una antena de bajo costo (BEIBT300 NONE). Las observaciones GNSS fueron llevadas a cabo en un periodo de dos días para cada modelo de antena. El análisis fue realizado en tiempos de observación de 12, 6 y 1 h, respectivamente. Estas observaciones fueron procesadas usando el método relativo estático mediante la inclusión de una estación de referencia continua del Instituto Nacional de Estadística y Geografía, la cual está localizada a una distancia aproximada de 4 km. Los resultados demuestran que la mayor precisión es lograda en un periodo de 12 h, con diferencias mínimas de 3 cm para la componente Norte y 33 cm para la vertical. En este sentido, la solución menos precisa es obtenida en el periodo de 1 h resultando diferencias de 70 cm, 46 cm y 2.3 m para la componente Norte, Este y vertical respectivamente.   With advancements in geodesy and enhancements in the technical specifications of low-cost receivers, GNSS opens up new avenues for investigating the capabilities and performance provided by these receivers for various geodetic purposes. In this context, the precision achievable using the low-cost GNSS receiver ZED-F9P in conjunction with two geodetic antennas (ASH701975.01B and LEIAS10 NONE) and a low-cost antenna (BEIBT300 NONE) was analyzed. GNSS observations were conducted over a 2-day period for each antenna model. The analysis involved observation durations of 12, 6, and 1 h. These observations were processed using the static relative method alongside a continuously operating GNSS station from the Active National Geodetic Network of the National Institute of Statistics and Geography, situated at ~4 km. The results demonstrate that the highest precision was achieved over a 12 h period, with minimal differences of 3 cm for the North component and 33 cm for the vertical component. Conversely, the least accurate solution was obtained within a 1 h observation period, resulting in differences of up to 70 cm, 46 cm, and 2.3 m for the North, East, and vertical components, respectively

6β,22-Dihydroxyhopane, a new triterpene from the fern Cheilanthes marantae

2 pages, 1 scheme.In addition to saccharose, diplopterol, femenol, sitosterol and sitosterol-o-β-D-glucoside, the new natural triperpene 6β,22-dihydroxyhopane (1a), characterized by its IR, PMR and MS spectra, was isolated from the stems and leaves of Cheilanthes marantae. The hopane framework of (1a) was deduced from its MS which showed the same fragmentation pattern as that of zeorin (1d) and related compounds [I]. The large downfield shifts of the methyl groups at C-4β, C-8β and C-10β observed in the PMR spectrum (ca 0.35 ppm) compared with 22-hydroxyhopane are compatible only with the presence of a C-6β hydroxyl group [2]. These assumptions were chemically confirmed by partial synthesis of (1a) from zeorin

Reduction of aliphatic nitramines. Approach to the synthesis of nitrosamines and amines

4 pages, 2 tables, 2 schemes.Deoxygenation of several aliphatic nitramines with tributyltin hydride in the presence of AIBN led to the formation of the corresponding nitrosamines. The nitrosamines underwent denitrosation when submitted to further treatment with tributyltin hydride. The 19-methyl steroid (9) was synthesized by α-alkylation of the nitrosamine (2).This work was supported by the Investigation Programme of the Comisión Asesora de Investigación Científica y Técnica. P.A.G. expresses his gratitude to the Excmo. Cabildo Insular de Tenerife for a fellowship

Seven-membered cyclic transition state in the alkoxy-radical induced intramolecular hydrogen abstraction of 26-hydroxy-furostans

4 pages, 2 schemes.-- Available online 6 April 2001.The photolysis of 26-hydroxy-furostan (5) and (8) in the presence of Pb(OAc)4/I2 afforded spirostan sapogenins (4) and (7) respectively in 80% yield. This cyclization takes place by an uncommon 1,6-hydrogen shift involving a 7-membered transition state as demonstrated by using specifically deuterium labeled compounds.Part of this work has been supported by the Investigation Programme of the Comisión Asesora de Investigación Científica y Técnica

Ring expansion reactions of 1,3-dithiolans and 1,3-dithians. A new synthesis of dihydro-1,4-dithiins and dihydro-1,4-dithiepins

4 pages, 1 table, 2 schemes.A mild and convenient method for ring expansion of 1,3-dithiolans and 1,3-dithians to dihydro-1,4-dithiins and dihydro-1,4-dithiepins, respectively, using phenyl selenenyl chloride in methylene chloride is described. A mechanism involving sulphenyl chloride derivatives as intermediates is proposed.Part of this work was supported by the Investigation Programme of the Comisión Asesora de Investigación Científica y Técnica

Labdane diterpenes from Cistus symphytifolius

4 pages.The investigation of the aerial part of Cistus symphytifolius afforded, in addition to sitosterol, trimethoxykaempferol, cativic acid, labdenic acid, labdanolic acid and labdan-8α,15-diol, three new bicyclic diterpenes: cistadienic acid, cistenolic acid and labd-13(E)- ene-8α,15-diol. The structures of these were determined by spectral studies and correlations. CD spectral studies showed that cistenolic acid and salvic acid are enantiomeric compounds, so the stereochemistry of salvic acid (7α-hydroxy-labd-8(17)-ene-15-oic acid) should be changed to 7β-hydroxy-eperu-8(17)-ene-15-oic acid (7β-hydroxy-ent-labd-8(17)-ene-15-oic acid).Part of this work was subsidized by the Comisión Asesora de Investigación Científica y Técnica. M.C. wishes to thank the Centro Iberoamericano de Cooperación of Spain for a fellowship

Nuevas fuentes naturales de sapogeninas esteroidales XII. Gloriogenina y 12 β-hidroxi-esmilagenina, dos nuevas sapogeninas esteroidales de la Yuca gloriosa Linn.

9 páginas, 1 tabla, 3 esquemas.-- Para la parte XI de la serie "Nuevas fuentes naturales de sapogeninas esteroidales" véase http://digital.csic.es/handle/10261/16971From the leaves of the Yuca gloriosa Linn. a spirostan monohydroxy-ketosapogenin is isolated, the physical data of which coincide with those of gloriogenin obtained from the same plant by Dávila and Panizo (2). We established its structure as (25R)-5β-spirostan-3β-ol-12-one. Furthermore, the structure of a second compound, not yet described in the literature, is found to be (25R)-5β-spirostan-3β 12β-diol. β-sitosterol, smilagenin, tigogenin, hecogenin, rockogenin and gitogenin are also obtained and identified by direct comparison with authentic samples.Tres de nosotros (R.F.B., R.H.G. y J.A.S.R.) agradecen al Ministerio de Educación y Ciencia las ayudas recibidas para "Formación de Personal Investigador"

25S-Dihydrodracogenin: A new spirostan sapogenin from Semele androgyna

3 pages, 1 scheme.-- Part XX in the series "New Sources of Steroid Sapogenins". For Part XIX see González, A. G., Freire, R., Francisco, C. G., Salazar, J. A. and Suárez, E. (1973) Tetrahedron 29, 1731.From stems and leaves of Semele androgyna L. the new steroid sapogenin 25S-dihydrodracogenin (Ia) has been isolated and its structure confirmed by conversion into the acetates of 25R-dihydrosansevierigenin (Id) and ruscogenin (If) and by partial hydrogenation of dracogenin.One of us (R.H.) thanks the Ministerio de Educación y Ciencia for a fellowship 'Formación de Personal Investigador'. This work was realized within the Programme 1971 conceded by the 'Juan March' Foundation

A 3,4-seco-triterpene from Caralluma buchardii

3 pages, 2 schemes.From Carulluma buchardii N. E. Brown, endemic to Fuerteventura, Canary Islands, squalene, sitosterol acetate, lupeol acetate, guimarenol [1], lupenone, lupeol sitosterol and the new natural triterpene 3,4-seco-lup-20(29)-en-3-oic acid methyl ester (1) were isolated [2]. The structure of the latter was established from its spectral data and transformation to the product 3,4-seco-lupan-3-oic acid methyl ester (2), which could be synthesized from lupeol (3).Part of this work was financed by a subsidy from the Spanish Government to foster the industrial and cultural development of the Canary Islands