Una (aparente) excepción en la filosofía natural aristotélica: antiperístasis como acción en las cualidades contrarias y su interpretación en la tradición del comentario médico y filosófico medieval

This paper explores the scholastic debate about antiperistasis, a mechanism in Aristotle’s dynamics described in the first book of Meteorology as an intensification of a quality caused by the action of the contrary one. After having distinguished this process from a homonymous, but totally different, principle concerning the dynamics of fluids that Aristotle describes in his Physics, I focus on the medieval reception of the former. Scholastic commentators oriented their exegetical effort in elaborating a consistent explanation of an apparently paradoxical process like the intensification of a quality by the opposite one. From the fourteenth century onwards, most of the commentators resorted to the theory of the multiplication of species, according to which each entity acts through the emission of simulacra of the objects (species) that spread spherically in the medium. When these rays encounter an obstacle, such as a contrary quality, they are pushed back towards their source. The reflection of the species determined by the surrounding and opposite quality produces a concentration of the first one, which is therefore intensified. Another distinctive feature of the scholastic interpretation of Aristotle’s antiperistasis is the convergence between the discussions on inorganic and organic matter,physical and medical discourse. This convergence found its most significant expression in the adoptionof the model described in the first book of Aristotle’s Meteorology to the biological context of Hippocrates’s Aphorisms I, 15. Following Galen’s exegesis of this passage, medieval commentators established a link between physics and medicine substantially extraneous to Aristotle’s theory.Este artículo explora los debates escolásticos sobre la antiperístasis, un mecanismo en la dinámica de Aristóteles descrito en el primer libro de la Meteorología como una intensificación de una cualidad provocada por la acción de la cualidad contraria. Después de haber distinguido este proceso de un principio homónimo, relativo a la dinámica de los fluidos que Aristóteles describe en su Física, mi análisis se centra en la recepción medieval del primer proceso. Los comentaristas escolásticos orientaron su esfuerzo exegético hacia la elaboración de una explicación consistente de un proceso aparentemente paradójico como la intensificación de una cualidad por su cualidad contraria. A partir del siglo XIV, la mayoría de los comentaristas recurrió a la teoría de la multiplicación de especies, según la cual cada entidad actúa mediante la emisión de rayos virtuales (species) que se difunden de forma esférica en el medio. Cuando estos rayos encuentran un obstáculo, como una cualidad contraria, son empujados hacia su fuente. El reflejo de los rayos virtuales determinado por la cualidad circundante y contraria produce una concentración de la primera cualidad, que, como consecuencia, se intensifica. Otro rasgo distintivo de la interpretación escolástica de la antiperístasis de Aristóteles es la convergencia entre la reflexión sobre la materia orgánica e inorgánica, el discurso físico y médico. Esta convergencia encontró su expresión más significativa en la adopción del modelo descrito en el primer libro de la Meteorología de Aristóteles al contexto biológico de los Aforismos de Hipócrates I, 15. Siguiendo la exégesis de Galeno, los comentaristas medievales establecieron un vínculo entre la física y la medicina sustancialmente ajeno a la teoría de Aristóteles

The parvocellular vasotocin system of Japanese quail: a developmental and adult model for the study of influences of gonadal hormones on sexually differentiated and behaviorally relevant neural circuits.

Vasotocin (VT; the antidiuretic hormone of birds) is synthesized by diencephalic magnocellular neurons projecting to the neurohypophysis. A sexually dimorphic system of VT-immunoreactive (ir) parvocellular elements has been described within the male medial preoptic nucleus (POM) and the nucleus of the stria terminalis, pars medialis (BSTm). VT-ir fibers are present in many diencephalic and extradiencephalic locations, and quantitative morphometric analyses demonstrated their sexually dimorphic distribution in regions involved in the control of different aspects of reproduction. Moreover, systemic or intracerebroventricular injections of VT markedly inhibit the expression of some aspects of male sexual behavior. In adult animals, circulating levels of testosterone (T) have a profound influence on the VT immunoreactivity within BSTm, POM, and lateral septum. Castration markedly decreases the immunoreaction, whereas T-replacement therapy restores a situation similar to the intact birds. We observed no changes in gonadectomized females treated with T. These changes parallel similar changes in male copulatory behavior (not present in castrated male quail, fully expressed in castrated, T-treated males). The restoration by T of the VT immunoreactivity in castrated male quail could be fully mimicked by a treatment with estradiol (E(2)), suggesting that the aromatization of T into E(2) may play a key limiting role in both the activation of male sexual behavior and the induction of VT synthesis. This dimorphism has an organizational nature: administration of E(2) to quail embryos (a treatment that abolishes male sexual behavior) results in a dramatic decrease of the VT immunoreactivity in sexually dimorphic regions. Conversely, the inhibition of E(2) synthesis during embryonic life (a treatment that stimulates the expression of male copulatory behavior in treated females exposed in adulthood to T) results in a malelike distribution of VT immunoreactivity. The VT parvocellular system of the Japanese quail can therefore be considered an accurate marker of the sexual differentiation of brain circuits mediating copulatory behavior and could be a very sensitive indicator of the activity of estrogenlike substances on neural circuits

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

<p>Abstract</p> <p>Background</p> <p>Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.</p> <p>Results</p> <p>Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.</p> <p>Conclusion</p> <p>These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.</p

A novel chromosome segregation mechanism during female meiosis.

In a wide range of eukaryotes, chromosome segregation occurs through anaphase A, in which chromosomes move toward stationary spindle poles, anaphase B, in which chromosomes move at the same velocity as outwardly moving spindle poles, or both. In contrast, Caenorhabditis elegans female meiotic spindles initially shorten in the pole-to-pole axis such that spindle poles contact the outer kinetochore before the start of anaphase chromosome separation. Once the spindle pole-to-kinetochore contact has been made, the homologues of a 4-μm-long bivalent begin to separate. The spindle shortens an additional 0.5 μm until the chromosomes are embedded in the spindle poles. Chromosomes then separate at the same velocity as the spindle poles in an anaphase B-like movement. We conclude that the majority of meiotic chromosome movement is caused by shortening of the spindle to bring poles in contact with the chromosomes, followed by separation of chromosome-bound poles by outward sliding

What greenium matters in the stock market? The role of greenhouse gas emissions and environmental disclosures

Abstract This study provides evidence on the existence of a negative greenium, i.e. a risk premium related to the greenness of a firm, based on European individual stock returns. We define a priced 'greenness and transparency' factor based on companies' greenhouse gas emissions and the quality of their environmental disclosures, and show that what is priced by the market is the combination of environmental performance and environmental transparency. Based on this factor, we offer a tool to assess the exposure of a portfolio to the risk associated with the low-carbon transition, and hedge against it. We estimate that in a stressed scenario where greener and more transparent firms very much outperform brown stocks, there would be losses at the global level, including for European large banks, should investors fail to price climate-transition risks. These results call for the introduction of climate stress tests for systemically important financial institutions