Uso de fármacos psicoestimulantes en drogodependencias

El uso de medicamentos estimulantes es una cuestión de plena actualidad en psiquiatría, aunque su utilización y prescripción es controvertida . Fármacos como el metilfenidato, las anfetaminas, o el modafinilo están siendo utilizados y estudiados en distintas enfermedades psiquiátricas como el trastorno por déficit de atención e hiperactividad (TDAH), la dependencia de cocaína, en trastornos del sueño y en la depresión resistente. Todos estos fármacos tienen en común, igual que las drogas de abuso, que son medicamentos que actúan sobre el sistema dopaminérgico, que constituye la base neurobiológica del refuerzo fisiológico. Los estimulantes como el metilfenidato o el modafinilo son fármacos eficaces en el TDAH y han sido estudiados en el tratamiento de la dependencia de cocaína. En niños con TDAH el metilfenidato es un factor protector para el desarrollo de fármaco en la dependencia de cocaína, aunque son estudios preliminares, por lo que no se debe considerar que este totalmente demostrado que los fármacos psicoestimulantes sean eficaces en el tratamiento de esta dependencia. Aunque no son conocidos todos los mecanismos fisiopatológicos, parece crítico que el refuerzo, y por lo tanto el riesgo de dependencia, aparece cuando se producen incrementos rápidos dopaminérgicos y que los efectos terapéuticos aparecen cuando son lentos y mantenidos. Las características de uso a dosis bajas administradas por vía oral disminuyen el riesgo de abuso. Para realizar una adecuada prescripción es necesario aclarar, definitivamente, los mecanismos neuroquímicos en los que intervienen, y sus indicaciones en drogodependenciasStimulant drugs prescription is a controversial and current topic in psychiatry. Drugs such as methylphenidate, amphetamine compounds and modafinil have been trialed and used in attention deficit hyperactivity disorder (ADHD), sleep conditions, cocaine dependence and as an adjunct to antidepressants for depression. All these drugs, like stimulant drugs abuse, increase extracellular dopamine in the brain.This effect is associated with reinforcing as well as therapeutic effects. Methylphenidate and modafinil treatment of ADHD are associated with a reduced risk for later substance abuse among ADHD patients. There is evidence of the beneficial effects of the use of modafinil in cocaine dependence, altough there isn't conclusive evidence for the stimulants' efficacy in treatment of the stimulants' dependence. At this time, the physiopathology of drug abuse and dependence is unknown, but it's known that the very critical point is that the reinforcing effects are associated with rapid changes in dopamine increases, whereas the therapeutic effects are associated with slowly and smoothly rising dopamine levels, such as are achieved with low doses and oral administration. Due to this, it's necessary to study the neurobiological bases on which stimulants drugs are related, and their clinical use in dependence treatment

8-K Filings, Twitter Activities and Stock Market Reactions

Twitter has become one of the major channels for information dissemination and communication, which includes companies’ market relevant information. This study investigates how Twitter activities are related to 8-K filings and the corresponding stock price and trading volume reactions. Using a sample of S&P 1500 companies, all 8-K filings are gathered for the calendar year of 2012 and calculate the following three unique Twitter metrics based on the data provided by Topsy, Inc.: abnormal tweeting activities, abnormal sentiment, and network centrality weighted by the influence level of tweeters. The findings show that on average, there are about 32% more tweeting activities around 8-K dates, compared to the benchmark period. In addition, all three Twitter metrics relate positively to both cumulative abnormal returns and cumulative abnormal trading volume in the 3-day window around 8-K filings. Abnormal sentiment and centrality weighted by the influence level of tweeters moderate positively and moderate negatively the association between abnormal tweeting activities and stock market reactions to 8-Ks. These metrics also moderate the relation between different types of 8-Ks and the corresponding stock market reactions. Based on our findings, we conclude that the level and nature of market attention a corporate announcement receives determines the level of price and volume movements of stocks in the capital markets. The study contributes to the literature by suggesting the important role played by social media, Twitter in particular, in the information dissemination process of Form 8-Ks