Knowledge about STD/AIDS and sexual behavior among high school students in Rio de Janeiro, Brazil Conhecimento sobre DST/AIDS e comportamento sexual entre estudantes do ensino médio no Rio de Janeiro, Brasil

The incidence of AIDS and other sexually transmitted diseases (STDs) is increasing among adolescents. In order to better understand high-risk sexual behavior among students, a cross-sectional study based on a self-answered anonymous questionnaire was conducted in 10 public and private high schools in Rio de Janeiro, Brazil. Data were obtained on sociodemographics, knowledge of STD/AIDS, and sexual behavior. Among 945 students aged 13-21, 59% were sexually initiated, and the median age at first sexual intercourse was 15 years (range: 7-19). Although 94% reported being aware of the need for condom use for protection, only 34% informed always using condoms during sex. Low family income was associated with unsatisfactory knowledge (OR = 9.40; 95% CI = 6.05-14.60) and inconsistent condom use (OR = 11.60; 95% CI = 5.54-24.30). However, unsatisfactory knowledge was not associated with inconsistent condom use. School-based educational programs should focus on sexual behavior more than on transmission of knowledge, as well as targeting low-income students.<br>A incidência da AIDS e outras doenças sexualmente transmissíveis (DST) vem aumentando entre adolescentes. Com o objetivo de melhor conhecer o comportamento sexual de risco entre estudantes do ensino médio, foi realizado um estudo transversal baseado em um questionário anônimo e auto-aplicado em dez escolas do Rio de Janeiro. Obtivemos dados sócio-demográficos e informações sobre o conhecimento de DST/AIDS e sobre o comportamento sexual. Entre os 945 estudantes de 13 a 21 anos, 59% já haviam iniciado a sua vida sexual. A mediana de idade da primeira relação sexual foi de 15 anos (amplitude 7-19). Embora 94% conhecessem a proteção conferida pelo uso do preservativo, somente 34% declararam usá-lo sempre. Houve associação entre baixa renda familiar e conhecimento insatisfatório (OR = 9,40; IC95% = 6,05-14,60) e do uso inconstante de preservativos (OR = 11,60; IC95% = 5,54-24,30). Não houve entretanto associação entre conhecimento insatisfatório e uso inconstante de preservativo. Programas educacionais devem focalizar o comportamento mais do que a transmissão da informação e priorizar jovens de baixa renda familiar

Chemosensitivity of rat medullary raphe neurones in primary tissue culture

The medullary raphe, within the ventromedial medulla (VMM), contains putative central respiratory chemoreceptors. To study the mechanisms of chemosensitivity in the raphe, rat VMM neurones were maintained in primary dissociated tissue culture, and studied using perforated patch-clamp recordings. Baseline electrophysiological properties were similar to raphe neurones in brain slices and in vivo.Neurones were exposed to changes in CO2 from 5% to 3 or 9% while maintaining a constant [NaHCO3]. Fifty-one per cent of neurones (n = 210) did not change their firing rate by more than 20% in response to hypercapnic acidosis. However, 22% of neurones responded to 9% CO2 with an increase in firing rate (‘stimulated’), and 27% of neurones responded with a decrease in firing rate (‘inhibited’).Chemosensitivity has often been considered an all-or-none property. Instead, a method was developed to quantify the degree of chemosensitivity. Stimulated neurones had a mean increase in firing rate to 298 ± 215% of control when pH decreased from 7.40 to 7.19. Inhibited neurones had a mean increase in firing rate to 232 ± 265% of control when pH increased from 7.38 to 7.57.Neurones were also exposed to isocapnic acidosis. All CO2-stimulated neurones tested (n = 15) were also stimulated by isocapnic acidosis, and all CO2-inhibited neurones tested (n = 19) were inhibited by isocapnic acidosis. Neurones with no response to hypercapnic acidosis also had no response to isocapnic acidosis (n = 12). Thus, the effects of CO2 on these neurones were mediated in part via changes in pH.In stimulated neurones, acidosis induced a small increase in the after-hyperpolarization level of 1.38 ± 1.15 mV per −0.2 pH units, which was dependent on the level of tonic depolarizing current injection. In voltage clamp mode at a holding potential near resting potential, there were small and inconsistent changes in whole-cell conductance and holding current in both stimulated and inhibited neurones. These results suggest that pH modulates a conductance in stimulated neurones that is activated during repetitive firing, with a reversal potential close to resting potential.The two subtypes of chemosensitive VMM neurones could be distinguished by characteristics other than their response to acidosis. Stimulated neurones had a large multipolar soma, whereas inhibited neurones had a small fusiform soma. Stimulated neurones were more likely than inhibited neurones to fire with the highly regular pattern typical of serotonergic raphe neurones in vivo.Within the medullary raphe, chemosensitivity is a specialization of two distinct neuronal phenotypes. The response of these neurones to physiologically relevant changes in pH is of the magnitude that suggests that this chemosensitivity plays a functional role. Elucidating their mechanisms in vitro may help to define the cellular mechanisms of central chemoreception in vivo