The coupling between synaptic vesicles and Ca²⁺ channels determines fast neurotransmitter release

SummaryIn order to release neurotransmitter synchronously in response to a presynaptic action potential, synaptic vesicles must be both release competent and located close to presynaptic Ca2+ channels. It has not been shown, however, which of the two is the more decisive factor. We tested this issue at the calyx of Held synapse by combining Ca2+ uncaging and electrophysiological measurements of postsynaptic responses. After depletion of the synaptic vesicles that are responsible for synchronous release during action potentials, uniform elevation of intracellular Ca2+ by Ca2+ uncaging could still elicit rapid release. The Ca2+ sensitivity of remaining vesicles was reduced no more than 2-fold, which is insufficient to explain the slow-down of the kinetics of release (10-fold) observed during a depolarizing pulse. We conclude that recruitment of synaptic vesicles to sites where Ca2+ channels cluster, rather than fusion competence, is a limiting step for rapid neurotransmitter release in response to presynaptic action potentials

Clinical essentialising: a qualitative study of doctors’ medical and moral practice

While certain substantial moral dilemmas in health care have been given much attention, like abortion, euthanasia or gene testing, doctors rarely reflect on the moral implications of their daily clinical work. Yet, with its aim to help patients and relieve suffering, medicine is replete with moral decisions. In this qualitative study we analyse how doctors handle the moral aspects of everyday clinical practice. About one hundred consultations were observed, and interviews conducted with fifteen clinical doctors from different practices. It turned out that the doctors’ approach to clinical cases followed a rather strict pattern across specialities, which implied transforming patients’ diverse concerns into specific medical questions through a process of ‘essentialising’: Doctors broke the patient’s story down, concretised the patient’s complaints and categorised the symptoms into a medical sense. Patients’ existential meanings were removed, and the focus placed on the patients’ functioning. By essentialising, doctors were able to handle a complex and ambiguous reality, and establish a medically relevant problem. However, the process involved a moral as well as a practical simplification. Overlooking existential meanings and focusing on purely functional aspects of patients was an integral part of clinical practice and not an individual flaw. The study thus questions the value of addressing doctors’ conscious moral evaluations. Yet doctors should be aware that their daily clinical work systematically emphasises beneficence at the expense of others—that might be more important to the patient

Ambivalence related to potential lifestyle changes following preventive cardiovascular consultations in general practice: A qualitative study

<p>Abstract</p> <p>Background</p> <p>Motivational interviewing approaches are currently recommended in primary prevention and treatment of cardiovascular disease (CVD) in general practice in Denmark, based on an empirical and multidisciplinary body of scientific knowledge about the importance of motivation for successful lifestyle change among patients at risk of lifestyle related diseases. This study aimed to explore and describe motivational aspects related to potential lifestyle changes among patients at increased risk of CVD following preventive consultations in general practice.</p> <p>Methods</p> <p>Individual interviews with 12 patients at increased risk of CVD within 2 weeks after the consultation. Grounded theory was used in the analysis.</p> <p>Results</p> <p>Ambivalence related to potential lifestyle changes was the core motivational aspect in the interviews, even though the patients rarely verbalised this experience during the consultations. The patients experienced ambivalence in the form of conflicting feelings about lifestyle change. Analysis showed that these feelings interacted with their reflections in a concurrent process. Analysis generated a typology of five different ambivalence sub-types: perception, demand, information, priority and treatment ambivalence.</p> <p>Conclusion</p> <p>Ambivalence was a common experience in relation to motivation among patients at increased risk of CVD. Five different ambivalence sub-types were found, which clinicians may use to explore and resolve ambivalence in trying to aid patients to adopt lifestyle changes. Future research is needed to explore whether motivational interviewing and other cognitive approaches can be enhanced by exploring ambivalence in more depth, to ensure that lifestyle changes are made and sustained. Further studies with a wider range of patient characteristics are required to investigate the generalisability of the results.</p

Cancer patients’ experiences of using an Interactive Health Communication Application (IHCA)

Interactive Health Communication Applications (IHCAs) are increasingly used in health care. Studies document that IHCAs provide patients with knowledge and social support, enhance self- efficacy and can improve behavioural and clinical outcomes. However, research exploring patients’ experiences of using IHCAs has been scarce. The aim of this study was to explore cancer patients’ perspectives and experiences related to the use of an IHCA called WebChoice in their homes. Qualitative interviews were conducted with infrequent, medium and frequent IHCA users—six women and four men with breast and prostate cancer. The interviews were transcribed and analyzed inspired by interactionistic perspectives. We found that some patients’ perceived WebChoice as a “friend,” others as a “stranger.” Access to WebChoice stimulated particularly high frequency users to position themselves as “information seeking agents,” assuming an active patient role. However, to position oneself as an “active patient” was ambiguous and emotional. Feelings of “calmness”, “normalization of symptoms”, feelings of “being part of a community”, feeling “upset” and “vulnerable”, as well as “feeling supported” were identified. Interaction with WebChoice implied for some users an increased focus on illness. Our findings indicate that the interaction between patients and an IHCA such as WebChoice occurs in a variety of ways, some of which are ambivalent or conflicting. Particularly for frequent and medium frequency users, it offers support, but may at the same time reinforce an element of uncertainty in their life. Such insights should be taken into consideration in the future development of IHCAs in healthcare in general and in particular for implementation into patients’ private sphere

Interaction with potential donors' families: The professionals' community of concern—a phenomenological study

The aim of this paper was to explore the health professionals' experiences and gain a deeper understanding of interaction with families of critically ill or traumatized patients with severe brain injuries. The methodological approach was qualitative and phenomenological. Data were collected through participant observation and in-depth interviews with nurses, physicians, and chaplains working in two ICUs in a Norwegian university hospital. A thematic analysis was used for analyzing data. Two main themes emerged from analysis: Patient oriented even when present and Family oriented even when absent. Each main theme is divided into two sub-themes. The themes appeared as phases in an interaction process. In the two first phases the interaction may be characterized as Alternating between being absent and present and Following up and withholding information and in the two last phases as Turning point and changing focus and Partly present when waiting for death. The findings are in the discussion illuminated by the phenomenological concept of concern. Concern is visible as care, and the distinction in care between “leaps in” and “leaps ahead” and “ready-to-hand” and “unready-to-hand” are topics in the discussion. Because of the complexity of caring for both patient and family, the situation demands efforts to relieve nurses in particular, during the most demanding phases of the process

Morphological docking of secretory vesicles

Calcium-dependent secretion of neurotransmitters and hormones is essential for brain function and neuroendocrine-signaling. Prior to exocytosis, neurotransmitter-containing vesicles dock to the target membrane. In electron micrographs of neurons and neuroendocrine cells, like chromaffin cells many synaptic vesicles (SVs) and large dense-core vesicles (LDCVs) are docked. For many years the molecular identity of the morphologically docked state was unknown. Recently, we resolved the minimal docking machinery in adrenal medullary chromaffin cells using embryonic mouse model systems together with electron-microscopic analyses and also found that docking is controlled by the sub-membrane filamentous (F-)actin. Currently it is unclear if the same docking machinery operates in synapses. Here, I will review our docking assay that led to the identification of the LDCV docking machinery in chromaffin cells and also discuss whether identical docking proteins are required for SV docking in synapses

Modelling Vesicular Release at Hippocampal Synapses

We study local calcium dynamics leading to a vesicle fusion in a stochastic, and spatially explicit, biophysical model of the CA3-CA1 presynaptic bouton. The kinetic model for vesicle release has two calcium sensors, a sensor for fast synchronous release that lasts a few tens of milliseconds and a separate sensor for slow asynchronous release that lasts a few hundred milliseconds. A wide range of data can be accounted for consistently only when a refractory period lasting a few milliseconds between releases is included. The inclusion of a second sensor for asynchronous release with a slow unbinding site, and thereby a long memory, affects short-term plasticity by facilitating release. Our simulations also reveal a third time scale of vesicle release that is correlated with the stimulus and is distinct from the fast and the slow releases. In these detailed Monte Carlo simulations all three time scales of vesicle release are insensitive to the spatial details of the synaptic ultrastructure. Furthermore, our simulations allow us to identify features of synaptic transmission that are universal and those that are modulated by structure