Do dendritic spines, which comprise the postsynaptic component of most excitatory synapses, exist only for their structural dynamics, receptor trafficking, and chemical and electrical ...compartmentation? The answer is no. Simultaneous investigation of both spine and presynaptic terminals has recently revealed a novel feature of spine synapses. Spine enlargement pushes the presynaptic terminals with muscle-like force and augments the evoked glutamate release for up to 20 min. We now summarize the evidence that such mechanical transmission shares critical features in common with short-term potentiation (STP) and may represent the cellular basis of short-term and working memory. Thus, spine synapses produce the force of learning to leave structural traces for both short and long-term memories.
Display omitted
•Actin polymerization in dendritic spines generates the force for spine enlargement.•Enlarged spines push the presynaptic terminal and facilitate evoked neurotransmitter release (mechanical transmission).•Mechanical transmission may underlie short-term potentiation.•Mechanical transmission is a novel building block of short-term and working memory.
Synaptic transmission involves cell-to-cell communication at the synaptic junction between two neurons, and chemical and electrical forms of this process have been extensively studied. In the brain, ...excitatory glutamatergic synapses are often made on dendritic spines that enlarge during learning
. As dendritic spines and the presynaptic terminals are tightly connected with the synaptic cleft
, the enlargement may have mechanical effects on presynaptic functions
. Here we show that fine and transient pushing of the presynaptic boutons with a glass pipette markedly promotes both the evoked release of glutamate and the assembly of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins
-as measured by Förster resonance transfer (FRET) and fluorescence lifetime imaging-in rat slice culture preparations
. Both of these effects persisted for more than 20 minutes. The increased presynaptic FRET was independent of cytosolic calcium (Ca
), but dependent on the assembly of SNARE proteins and actin polymerization in the boutons. Notably, a low hypertonic solution of sucrose (20 mM) had facilitatory effects on both the FRET and the evoked release without inducing spontaneous release, in striking contrast with a high hypertonic sucrose solution (300 mM), which induced exocytosis by itself
. Finally, spine enlargement induced by two-photon glutamate uncaging enhanced the evoked release and the FRET only when the spines pushed the boutons by their elongation. Thus, we have identified a mechanosensory and transduction mechanism
in the presynaptic boutons, in which the evoked release of glutamate is enhanced for more than 20 min.
Most excitatory synapses in the brain form on dendritic spines. Two-photon uncaging of glutamate is widely utilized to characterize the structural plasticity of dendritic spines in brain slice ...preparations in vitro. In the present study, glutamate uncaging was used to investigate spine plasticity, for the first time, in vivo. A caged glutamate compound was applied to the surface of the mouse visual cortex in vivo, revealing the successful induction of spine enlargement by repetitive two-photon uncaging in a magnesium free solution. Notably, this induction occurred in a smaller fraction of spines in the neocortex in vivo (22%) than in hippocampal slices (95%). Once induced, the time course and mean long-term enlargement amplitudes were similar to those found in hippocampal slices. However, low-frequency (1-2 Hz) glutamate uncaging in the presence of magnesium caused spine shrinkage in a similar fraction (35%) of spines as in hippocampal slices, though spread to neighboring spines occurred less frequently than it did in hippocampal slices. Thus, the structural plasticity may occur similarly in the neocortex in vivo as in hippocampal slices, although it happened less frequently in our experimental conditions.
Dendritic spines are the postsynaptic sites of most excitatory synapses in the brain, and spine enlargement and shrinkage give rise to long-term potentiation and depression of synapses, respectively. ...Because spine structural plasticity is accompanied by remodeling of actin scaffolds, we hypothesized that the filamentous actin regulatory protein cofilin plays a crucial role in this process. Here we investigated the diffusional properties of cofilin, the actin-severing and depolymerizing actions of which are activated by dephosphorylation. Cofilin diffusion was measured using fluorescently labeled cofilin fusion proteins and two-photon imaging. We show that cofilins are highly diffusible along dendrites in the resting state. However, during spine enlargement, wild-type cofilin and a phosphomimetic cofilin mutant remain confined to the stimulated spine, whereas a nonphosphorylatable mutant does not. Moreover, inhibition of cofilin phosphorylation with a competitive peptide disables spine enlargement, suggesting that phosphorylated-cofilin accumulation is a key regulator of enlargement, which is localized to individual spines. Conversely, spine shrinkage spreads to neighboring spines, even though triggered by weaker stimuli than enlargement. Diffusion of exogenous cofilin injected into a pyramidal neuron soma causes spine shrinkage and reduced PSD95 in spines, suggesting that diffusion of dephosphorylated endogenous cofilin underlies the spreading of spine shrinkage and long-term depression.
•Knockout of calcineurin reduced small spines in the prefrontal and visual cortices.•The reduction was moderate, possibly due to the presence of intrinsic spine dynamics.•Calcineurin knockouts and ...patients with schizophrenia have similar spine phenotypes.
Calcineurin is required for long-term depression and activity-dependent spine shrinkage, and calcineurin mutations have been identified in patients with schizophrenia. Moreover, mice with conditional knockout of calcineurin B (CNB-KO) exhibit behavioral abnormalities suggestive of schizophrenia. Changes in the dendritic spines of these mice, however, have not been investigated. We therefore examined the dendritic spines of CNB-KO mice, and observed a significant reduction in small spines and an increase in large spines in the prefrontal and visual cortices. The effect of CNB-KO on the spine sizes was relatively moderate, possibly due to the presence of spontaneous fluctuations (dynamics) in the dendritic spines themselves. Thus, CNB-KO mice showed a spine phenotype similar to those recently reported in patients with schizophrenia.
Gender inequality is a pressing issue on a global scale, yet studies on this important issue have stayed on the margins of open and distance learning (ODL) literature. In this study, we critically ...analyse a batch of ODL literature that is focused on gender inequality in post-secondary and higher education contexts. We use Therborn's social justice framework to inform and guide the study. This is a comprehensive social justice lens that sees inequality as "a life and death issue," approaching empowerment as a central area of concern. Qualitative content analysis of 30 years of peer-reviewed literature reveals patriarchy and androcentrism as significant mechanisms that continue to produce gender inequality, in particular in women's access to educational resources and formal learning opportunities. We highlight three themes that emerged in the content analysis: (1) ODL and equal opportunity; (2) Feminism and gender-sensitive curriculum design; and (3) Culturally relevant curriculum design. We critique views of access to technology-enabled education as an instrument for social justice, and provide a pedagogical model for an ODL curriculum centred on empowerment and agency, two concepts closely linked to existential inequality. We argue that such a curriculum is public service and requires a model of education that is based on participation and co-construction, and lies at the intersection of critical, feminist, and culturally relevant pedagogical practices. Keywords: distance education, gender inequality, gender studies, open and distance learning, social justice, women empowerment
Volition explains the transition from desire, or motivation, to action especially when faced with competing goals. In learning environments, the concept refers to acting with the aim of achieving ...learning objectives. Despite the importance of volition in learning environments, research has rarely addressed the volition construct. Thus, the purpose of this study was to explore and develop a valid and reliable scale to measure the volition construct in online and face to face learning environments. The data for this research were collected from 594 undergraduate online learners who also took some courses face to face at a state university in Turkey. After analyzing the validity and reliability of the scale, a two-factor, 13-item volition for learning scale was developed. The scale was comprised of two factors: action planning and action control. Confirmatory factor analysis results confirm the factor structure of the scale. Results indicated that the volition for learning scale is a valid and reliable instrument that can be utilized to measure learners’ volition in learning environments.
Excitatory synapses are often formed at small protrusions of dendrite, called dendritic spines, in most projection neurons, and the spine-head volumes show strong correlations with synaptic ...connectivity. We examined the dynamics of spine volume in the adult mouse visual cortex using time-lapse
two-photon imaging with a resonant Galvano scanner. Contrary to expectations, we found that the spines in the adult neocortex showed fluctuations to a similar degree as that observed in young hippocampal preparations, but there were systematic differences in how the dynamics were dependent on spine volumes, thus allowing for fewer fluctuations in small spines, which could account for the relatively low turnover rates of neocortical spines
. We found that spine volumes fluctuated to a greater extent in a mouse model (
knockout) of fragile X mental retardation than in wild-type mice, and the spine turnover rates were also higher in
knock-out mice. Such features of spine dynamics in
knock-out mice could be represented by a single slope factor in our model. Our data and model indicate a small but significant change in the average spine volume and more eminent differences in the statistical distribution in
knock-out mice even in adulthood, which reflects the abnormal
dynamics of spine volumes.
This exploratory experimental study investigates the impact of motivational strategies based on the Attention, Relevance, Confidence, Satisfaction, and Volition (ARCS‐V) model on online learners' ...academic performance, motivation, volition, and course interest. The research was conducted over an 11‐week semester with 122 undergraduate online learners within two groups. One group received a traditional e‐course, while the other group was offered the course with extra motivational strategies derived from the ARCS‐V model. The results revealed that the group who used motivational strategies showed significantly higher gains in motivation, academic performance, and course interest scores. However, there were no significant differences between the groups regarding the volition. Furthermore, the motivation and interest variables were measured with Attention, Relevance, Confidence, and Satisfaction subscales of the ARCS‐V model. In terms of interest variable, there was only a statistically significant difference on the Attention subscale. Regarding motivation variable, the results also showed a statistically significant difference on the attention, confidence, and satisfaction subsections of the ARCS‐V model. The findings of the present study offer insights into ARCSV model‐based research by examining the effects of the model as a valid and reliable framework for online learning environments. The implications and directions for future research are then discussed.
Practitioner Notes/Lay Description
What is already known about this topic:
Learning motivation is the most vital factor that influencing effective and efficient learning process.
The attention, relevance, confidence, and satisfactionARCS model of motivational design has been used myriad times to design motivational instructions in a wide range of educational settings (from traditional to computer‐assisted instruction and distance education).
Few studies address the online learners” motivation through the attention, relevance, confidence, satisfaction, and volition (ARCS‐V) ‐based motivational strategies.
What this paper adds to this:
A quasi‐experimental study was conducted in online learning environment to research the effects of the ARCS‐V ‐based motivational strategies.
The impact of the ARCS‐V ‐based motivational strategies on online learners” academic performance, motivation, volition, and course interest was investigated.
The results showed that the ARCS‐V ‐based motivational strategies had positive effects on online learners’ regarding to academic performance, motivation, volition, and course interest.
The implications of study findings for practitioners:
This research provided evidences for effects of the ARCS‐V motivational strategies on online learners.
Online learners who took the ARCS‐V ‐based motivational messages had positive effects regarding to academic performance, motivation, volition, and course interest.
PDF
