Browsing by Author "Avendano, C."

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    Infrared variability of young solar analogues in the Lagoon Nebula
    (2022) Ordenes-Huanca, C.; Zoccali, M.; Bayo, A.; Cuadra, J.; Ramos, R. Contreras; Hillenbrand, L. A.; Lacerna, I; Abarzua, S.; Avendano, C.; Diaz, P.; Fernandez, I; Lara, G.
    T Tauri stars are low-mass pre-main sequence stars that are intrinsically variable. Due to the intense magnetic fields they possess, they develop dark spots on their surface that, because of rotation, introduce a periodic variation of brightness. In addition, the presence of surrounding discs could generate flux variations by variable extinction or accretion. Both can lead to a brightness decrease or increase, respectively. Here, we have compiled a catalogue of light curves for 379 T Tauri stars in the Lagoon Nebula (M8) region, using VVVX survey data in the K-s-band. All these stars were already classified as pre-MS stars based on other indicators. The data presented here are spread over a period of about eight years, which gives us a unique follow-up time for these sources at this wavelength. The light curves were classified according to their degree of periodicity and asymmetry, to constrain the physical processes responsible for their variation. Periods were compared with the ones found in literature, on a much shorter baseline. This allowed us to prove that for 126 stars, the magnetically active regions remain stable for several years. Besides, our near-IR data were compared with the optical Kepler/K2 light curves, when available, giving us a better understanding of the mechanisms responsible for the brightness variations observed and how they manifest at different bands. We found that the periodicity in both bands is in fairly good agreement, but the asymmetry will depend on the amplitude of the bursts or dips events and the observation cadence.
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    The nigrostriatal system in the presymptomatic and symptomatic stages in the MPTP monkey model: A PET, histological and biochemical study
    (2012) Blesa, J.; Pifl, C.; Sanchez-Gonzalez, M. A.; Juri, C.; Garcia-Cabezas, M. A.; Adanez, R.; Iglesias, E.; Collantes, M.; Penuelas, I.; Sanchez-Hernandez, J. J.; Rodriguez-Oroz, M. C.; Avendano, C.; Hornykiewicz, O.; Cavada, C.; Obeso, J. A.
    Parkinson's disease (PD) is diagnosed when striatal dopamine (DA) loss exceeds a certain threshold and the cardinal motor features become apparent. The presymptomatic compensatory mechanisms underlying the lack of motor manifestations despite progressive striatal depletion are not well understood. Most animal models of PD involve the induction of a severe dopaminergic deficit in an acute manner, which departs from the typical, chronic evolution of PD in humans. We have used 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine (MPTP) administered to monkeys via a slow intoxication protocol to produce a more gradual development of nigral lesion. Twelve control and 38 MPTP-intoxicated monkeys were divided into four groups. The latter included monkeys who were always asymptomatic, monkeys who recovered after showing mild parkinsonian signs, and monkeys with stable, moderate and severe parkinsonism. We found a close correlation between cell loss in the substantia nigra pars compacta (SNc) and striatal dopaminergic depletion and the four motor states. There was an overall negative correlation between the degree of parkinsonism (Kurlan scale) and in vivo PET (F-18-DOPA K-i and C-11-DTBZ binding potential), as well as with TH-immunoreactive cell counts in SNc, striatal dopaminergic markers (TH, DAT and VMAT2) and striatal DA concentration. This intoxication protocol permits to establish a critical threshold of SNc cell loss and dopaminergic innervation distinguishing between the asymptomatic and symptomatic parkinsonian stages. Compensatory changes in nigrostriatal dopaminergic activity occurred in the recovered and parkinsonian monkeys when DA depletion was at least 88% of control, and accordingly may be considered too late to explain compensatory mechanisms in the early asymptomatic period. Our findings suggest the need for further exploration of the role of non-striatal mechanisms in PD prior to the development of motor features. (C) 2012 Elsevier Inc. All rights reserved.