How does the brain control the process of puberty?

Summary Puberty is commonly thought to occur as a consequence of the decrease in sensitivity of certain hypothalamic neurons to the negative feedback effect exerted by gonadal steroid hormones. In view of the well-documented participation of adrenergic neurons in the central control of gonadotrophin secretion, it is proposed that the resetting of the hypothalamic gonadostat is caused by the growth and functional maturation of steroid-sensitive adrenergic systems. The ontogenetic development and certain plastic properties of hypothalamic adrenergic neurons are described. Their participation in the induction of experimental and clinical pubertas praecox and their possible mediation of nutritional effects are discussed.Work carried out in the author's laboratory has been supported by a Group Grant in Developmental Neurobiology from the Canadian Medical Research Council.     

Extracellular Na+ removal attenuates rundown of the epithelial Na+-channel (ENaC) by reducing the rate of channel retrieval

Regulation of the epithelial sodium channel (ENaC) is important for the long-term control of arterial blood pressure as evidenced by gain of function mutations of ENaC causing Liddles syndrome, a rare form of hereditary arterial hypertension. In Xenopus laevis oocytes expressing ENaC a spontaneous decline of ENaC currents over time, so-called rundown, is commonly observed. Mechanisms involved in rundown may be physiologically relevant and may be related to feedback regulation of ENaC by intra- or extracellular Na⁺. We tested the effect of extracellular Na⁺ removal on ENaC rundown. Spontaneous rundown of ENaC was largely prevented by extracellular Na⁺ removal and was partially prevented by primaquine suggesting that it is due to endocytic channel retrieval. Liddles syndrome mutation caused a reduced rate of rundown, and in oocytes expressing the mutated channel extracellular Na⁺ removal not only prevented rundown but even increased the ENaC currents (runup). Acute exposure to high extracellular Na⁺ drastically reduced whole-cell currents and surface expression of wild-type ENaC, while these effects were much smaller in ENaC with Liddles syndrome mutation consistent with a stabilization of the mutated channel in the plasma membrane. Interestingly, the apparent intracellular Na⁺ concentration [Na⁺]_i-app was high (>60 mM) in ENaC-expressing oocytes but rundown was not associated with a further increase in [Na⁺]_i-app. We conclude that the inhibitory effect of extracellular Na⁺ removal on rundown is due to an inhibition of endocytic ENaC retrieval.     

Comparison of performance on memory-guided saccade and delayed spatial match-to-sample tasks in monkeys

To investigate the sources of spatial error in memory-guided saccades (MGS), we have trained monkeys on two different tasks: a MGS task and a delayed spatial match-to-sample (MTS) task. We first tested the effect of introducing a post-saccadic visual feedback on the accuracy of MGS. We found that visual feedback had a pronounced effect on the systematic saccade error, but less of an effect on the variable error. Visual feedback can improve the accuracy of saccadic eye movements over several days, while feedback removal can decrease accuracy in a reversible way. These effects also depend both on target eccentricity and the duration of the memory delay. To test whether saccade error is due to the accuracy of spatial memory storage or arises downstream from that memory, we measured behavioral performance on a spatial MTS task both before and after training with visual feedback. The results showed no significant difference in performance of the MTS task before and after feedback training despite significant changes in MGS accuracy. The results suggest that the accuracy of spatial memory is not the source of the systematic errors that accompany MGS.     

Differential ambiguity reduces grouping of metastable objects

Two coaxial, ambiguously rotating objects tend to be perceived as corotating. Such grouping could be the consequence of bottom-up, cooperative interactions between the stimuli, or the top-down selection of object properties consistent with a model of the objects or scene. However, we find that the coupling between an ambiguous and unambiguous object is sharply reduced, presenting a challenge for both explanations of grouping. We describe experiments that support the idea that top-down feedback is necessary to select and stabilize a perceptual interpretation for ambiguous figures. Reduced coupling between objects of differing ambiguity can be explained if the feedback is global and proportional to ambiguity.     

Rate-independent inhibition by norepinephrine of 5-HT release from the somadendritic region of serotonergic neurons

Endogenous adrenergic drive regulates the firing rate of serotonergic neurons. However, advocates of feedback theory assert that 5-hydroxytryptamine (5-HT) released in the somatodendritic region of raphe neurons regulates both rate and release of 5-HT. Experiments were done to determine if the somatodendritic region might have receptors for norepinephrine that inhibit release of 5-HT independently of rate, as this would allow for discrete effects of norepinephrine on rate and release, even in the presence of functional feedback by 5-HT. The release of 5-HT at fixed frequencies of stimulation was substantially reduced when norepinephrine (1 and 3 x 10(-7) M) was present. Norepinephrine also inhibited the release of 3H-5-HT with delivery of a single stimulation pulse ruling out a remote action of the catecholamine. The alpha(1) antagonist prazosin did not modify the profile of norepinephrine inhibition. Further, the alpha(1) agonist phenylephrine had no effect on 3H-5-HT efflux. The alpha(2) antagonist yohimbine antagonized almost entirely the inhibition by norepinephrine at 1 Hz, and reduced it substantially at 3 Hz. Blockade of 5-HT(1) receptor sites with methiothepin did not reduce the inhibitory effect of norepinephrine on 3H-5-HT efflux. It is proposed that release of endogenous norepinephrine at synapses with 5-HT neurons could activate 5-HT neuron firing rate through alpha(1) receptors located at the soma and simultaneously short-circuit ongoing 5-HT feedback inhibition by inhibiting release through adrenergic alpha two receptors likely located at the dendrites.     

Simulation-based education promoting situation awareness in undergraduate nursing students: A scoping review

AimTo examine simulation-based education (SBE) strategies on situation awareness (SA) in nursing students including the strategies of SBE, the measurement tools of SA during SBE and the effectiveness of SBE on SA.BackgroundSA has been reported as an effective way to identify and manage deteriorating patients. Researchers have suggested that SBE is more effective than other instructional modalities in improving SA. However, SA among nursing students and studies regarding the effectiveness of SBE on SA are limited.DesignThe Arksey and O'Malley scoping review framework was used to guide the review process and the PRISMA-ScR checklist was used to report on this scoping review.MethodsThe databases searched were Medline, CINAHL, EMBASE, EBSCO and Google Scholar from December 2020 to November 2021. Thematic analysis was applied to identify the main findings in the literature.ResultsNine eligible articles were included. Five major themes were identified: SBE situations used to teach SA to nursing students, SBE strategies to improve SA in nursing, effectiveness of SBE on SA in nursing, measurements of SA used during the SBE and experimental studies examining the effectiveness of SBE on SA.ConclusionThis review reveals that SBE may be useful to cultivate SA in nursing students. Future studies that use randomized clinical trials to test the effects of combining different simulation strategies on SA are suggested. Developing more reliable and valid SA global assessment queries and standardizing the query process of SA measurement is also recommended.     

2005年全国碘缺乏病实验室外质控考核结果报告

目的评价全国参加尿碘、盐碘实验室外质控网络实验室的检测能力。方法尿碘采用“Z”比评分的方法、盐碘采用标准参考值±不确定度的方法对检测结果进行评价。结果第1轮尿碘考核中，反馈的26个实验室全部考核合格。第2轮考核中，参加考核31个省级尿碘、盐碘实验室全部反馈了质控结果并全部合格；地市级尿碘实验室反馈率为96．6％，合格率为91．6％；地市级盐碘实验室反馈率为96．4％，合格率为90．9％；县级盐碘实验室反馈率为97．8％，合格率为88．8％。结论通过几年的全国实验室网络的运行和持续的技术培训，各级实验室的检测能力均有了明显的提高。