scholarly journals Information encoded in volumes and areas of dendritic spines is nearly maximal across mammalian brains

2021 ◽  
Author(s):  
Jan Karbowski ◽  
Paulina Urban
Keyword(s):  
Dendritic Spines ◽  
Excitatory Synapses ◽  
Information Efficiency ◽  
Spine Length ◽  
Entropy Maximization ◽  
Surface Areas ◽  
Heavy Tailed Distributions ◽  
Mean Size ◽  
Heavy Tailed

Long-term information associated with neuronal memory resides in dendritic spines. However, spines can have a limited size due to metabolic and neuroanatomical constraints, which should effectively limit the amount of encoded information in excitatory synapses. This study investigates how much information can be stored in the sizes of dendritic spines, and whether is it optimal in any sense? It is shown here, using empirical data for several mammalian brains across different regions and physiological conditions, that dendritic spines nearly maximize entropy contained in their volumes and surface areas for a given mean size. This result is essentially independent of the type of a fitting distribution to size data, as both short- and heavy-tailed distributions yield similar nearly 100 % information efficiency in the majority of cases, although heavy-tailed distributions slightly better fit the data. On average, the highest information is contained in spine volume, and the lowest in spine length or spine head diameter. Depending on a species and brain region, a typical spine can encode between 6.1 and 10.8 bits of information in its volume, and 3.1-8.1 bits in its surface area. Our results suggest a universality of entropy maximization in spine volumes and areas, which can be a new principle of memory storing in synapses.

scholarly journals Chemical LTD, but not LTP, induces transient accumulation of gelsolin in dendritic spines

2019 ◽  
Vol 400 (9) ◽  
pp. 1129-1139 ◽  
Author(s):  
Iryna Hlushchenko ◽  
Pirta Hotulainen
Keyword(s):  
Synaptic Plasticity ◽  
Dendritic Spines ◽  
Hippocampal Neurons ◽  
Long Term Potentiation ◽  
Excitatory Synapses ◽  
Signal Molecule ◽  
Brain Functions ◽  
Dendritic Shaft ◽  
Term Potentiation

Abstract Synaptic plasticity underlies central brain functions, such as learning. Ca2+ signaling is involved in both strengthening and weakening of synapses, but it is still unclear how one signal molecule can induce two opposite outcomes. By identifying molecules, which can distinguish between signaling leading to weakening or strengthening, we can improve our understanding of how synaptic plasticity is regulated. Here, we tested gelsolin’s response to the induction of chemical long-term potentiation (cLTP) or long-term depression (cLTD) in cultured rat hippocampal neurons. We show that gelsolin relocates from the dendritic shaft to dendritic spines upon cLTD induction while it did not show any relocalization upon cLTP induction. Dendritic spines are small actin-rich protrusions on dendrites, where LTD/LTP-responsive excitatory synapses are located. We propose that the LTD-induced modest – but relatively long-lasting – elevation of Ca2+ concentration increases the affinity of gelsolin to F-actin. As F-actin is enriched in dendritic spines, it is probable that increased affinity to F-actin induces the relocalization of gelsolin.

scholarly journals Stable but not rigid: Chronic in vivo STED nanoscopy reveals extensive remodeling of spines, indicating multiple drivers of plasticity

2021 ◽  
Vol 7 (24) ◽  
pp. eabf2806
Author(s):  
Heinz Steffens ◽  
Alexander C. Mott ◽  
Siyuan Li ◽  
Waja Wegner ◽  
Pavel Švehla ◽  
...  
Keyword(s):  
Dendritic Spines ◽  
Pyramidal Neurons ◽  
Excitatory Synapses ◽  
Memory Locus ◽  
Length Width ◽  
Highly Correlated ◽  
High Degree ◽  
Distinct Features

Excitatory synapses on dendritic spines of pyramidal neurons are considered a central memory locus. To foster both continuous adaption and the storage of long-term information, spines need to be plastic and stable at the same time. Here, we advanced in vivo STED nanoscopy to superresolve distinct features of spines (head size and neck length/width) in mouse neocortex for up to 1 month. While LTP-dependent changes predict highly correlated modifications of spine geometry, we find both, uncorrelated and correlated dynamics, indicating multiple independent drivers of spine remodeling. The magnitude of this remodeling suggests substantial fluctuations in synaptic strength. Despite this high degree of volatility, all spine features exhibit persistent components that are maintained over long periods of time. Furthermore, chronic nanoscopy uncovers structural alterations in the cortex of a mouse model of neurodegeneration. Thus, at the nanoscale, stable dendritic spines exhibit a delicate balance of stability and volatility.

scholarly journals Stable but not rigid: Long-term in vivo STED nanoscopy uncovers extensive remodeling of stable spines and indicates multiple drivers of structural plasticity

2020 ◽  
Author(s):  
Heinz Steffens ◽  
Alexander C. Mott ◽  
Siyuan Li ◽  
Waja Wegner ◽  
Pavel Švehla ◽  
...  
Keyword(s):  
Dendritic Spines ◽  
Pyramidal Neurons ◽  
Excitatory Synapses ◽  
Neck Length ◽  
Memory Locus ◽  
Highly Correlated ◽  
High Degree ◽  
Distinct Features

ABSTRACTExcitatory synapses on dendritic spines of pyramidal neurons are considered a central memory locus. To foster both continuous adaption as well as the storage of long-term information, spines need to be plastic and stable at the same time. Here we advanced in vivo STED nanoscopy to superresolve distinct features of dendritic spines (head size, neck length and width) in mouse neocortex for up to one month. While LTP-dependent changes predict highly correlated modifications of spine geometry, we find both, uncorrelated dynamics, as well as correlated changes, indicating multiple independent drivers of spine remodeling. The magnitude of this remodeling suggests substantial fluctuations in synaptic strength, and is exaggerated in a mouse model of neurodegeneration. Despite this high degree of volatility, all spine features also exhibit persistent components that are maintained over long periods of time. Thus, at the nanoscale, stable dendritic spines exhibit a delicate balance of stability and volatility.

Synaptic organization of the gustatory NST

1994 ◽  
Vol 52 ◽  
pp. 150-151
Author(s):  
M. C. Whitehead
Keyword(s):  
Central Nervous System ◽  
Dendritic Spines ◽  
Fundamental Problem ◽  
Cell Types ◽  
Brain Regions ◽  
Excitatory Synapses ◽  
Solitary Tract ◽  
Synaptic Organization ◽  
Synaptic Junctions ◽  
Afferent Terminals

A fundamental problem in taste research is to determine how gustatory signals are processed and disseminated in the mammalian central nervous system. An important first step toward understanding information processing is the identification of cell types in the nucleus of the solitary tract (NST) and their synaptic relationships with oral primary afferent terminals. Facial and glossopharyngeal (LIX) terminals in the hamster were labelled with HRP, examined with EM, and characterized as containing moderate concentrations of medium-sized round vesicles, and engaging in asymmetrical synaptic junctions. Ultrastructurally the endings resemble excitatory synapses in other brain regions.Labelled facial afferent endings in the RC subdivision synapse almost exclusively with distal dendrites and dendritic spines of NST cells. Most synaptic relationships between the facial synapses and the dendrites are simple. However, 40% of facial endings engage in complex synaptic relationships within glomeruli containing unlabelled axon endings particularly ones termed "SP" endings. SP endings are densely packed with small, pleomorphic vesicles and synapse with both the facial endings and their postsynaptic dendrites by means of nearly symmetrical junctions.

Three-dimensional structure of dendritic spines, neuronal specializations that impart both stability and flexibility to synaptic function

1993 ◽  
Vol 51 ◽  
pp. 92-93
Author(s):  
Kristen M. Harris
Keyword(s):  
Dendritic Spines ◽  
Three Dimensional ◽  
Synaptic Function ◽  
Dimensional Structure ◽  
Excitatory Synapses ◽  
Concept Of Function ◽  
Section Electron ◽  
High Quality Information ◽  
The Central Nervous System ◽  
Mathematical Analyses

Dendritic spines are the tiny protrusions that stud the surface of many neurons and they are the location of over 90% of all excitatory synapses that occur in the central nervous system. Their small size and variable shapes has in large part made detailed study of their structure refractory to conventional light microscopy and single section electron microscopy (EM). Yet their widespread occurrence and likely involvement in learning and memory has motivated extensive efforts to obtain quantitative descriptions of spines in both steady state and dynamic conditions. Since the seminal mathematical analyses of D’Arcy Thompson, the power of establishing quantitatively key parameters of structure has become recognized as a foundation of successful biological inquiry. For dendritic spines highly precise determinations of structure and its variation are proving themselves as the kingpin for establishing a valid concept of function. The recent conjunction of high quality information about the structure, function, and theoretical implications of dendritic spines has produced a flurry of new considerations of their role in synaptic transmission.

Probability and Random Processes

2018 ◽  
Author(s):  
Stefan Thurner ◽  
Rudolf Hanel ◽  
Peter Klimekl
Keyword(s):  
Random Processes ◽  
Distribution Functions ◽  
Basic Logic ◽  
Heavy Tailed Distributions ◽  
Random Components ◽  
Classical Distribution ◽  
Heavy Tailed ◽  
Basic Facts ◽  
Stochastic Events ◽  
Stochastic Event

Phenomena, systems, and processes are rarely purely deterministic, but contain stochastic,probabilistic, or random components. For that reason, a probabilistic descriptionof most phenomena is necessary. Probability theory provides us with the tools for thistask. Here, we provide a crash course on the most important notions of probabilityand random processes, such as odds, probability, expectation, variance, and so on. Wedescribe the most elementary stochastic event—the trial—and develop the notion of urnmodels. We discuss basic facts about random variables and the elementary operationsthat can be performed on them. We learn how to compose simple stochastic processesfrom elementary stochastic events, and discuss random processes as temporal sequencesof trials, such as Bernoulli and Markov processes. We touch upon the basic logic ofBayesian reasoning. We discuss a number of classical distribution functions, includingpower laws and other fat- or heavy-tailed distributions.

Removal of a compressive mass causes a transient disruption of blood-brain barrier but a long-term recovery of spiny stellate neurons in the rat somatosensory cortex

2021 ◽  
pp. 1-17
Author(s):  
Tzu-Yin Yeh ◽  
Pei-Hsin Liu
Keyword(s):  
Somatosensory Cortex ◽  
Blood Brain Barrier ◽  
Dendritic Spines ◽  
Late Onset ◽  
Brain Barrier ◽  
Blood Brain ◽  
Afferent Fibers ◽  
Prolonged Recovery ◽  
Rat Somatosensory Cortex

Background: In the cranial cavity, a space-occupying mass such as epidural hematoma usually leads to compression of brain. Removal of a large compressive mass under the cranial vault is critical to the patients. Objective: The purpose of this study was to examine whether and to what extent epidural decompression of the rat primary somatosensory cortex affects the underlying microvessels, spiny stellate neurons and their afferent fibers. Methods: Rats received epidural decompression with preceding 1-week compression by implantation of a bead. The thickness of cortex was measured using brain coronal sections. The permeability of blood-brain barrier (BBB) was assessed by Evans Blue and immunoglobulin G extravasation. The dendrites and dendritic spines of the spiny stellate neurons were revealed by Golgi— Cox staining and analyzed. In addition, the thalamocortical afferent (TCA) fibers in the cortex were illustrated using anterograde tracing and examined. Results: The cortex gradually regained its thickness over time and became comparable to the sham group at 3 days after decompression. Although the diameter of cortical microvessels were unaltered, a transient disruption of the BBB was observed at 6 hours and 1 day after decompression. Nevertheless, no brain edema was detected. In contrast, the dendrites and dendritic spines of the spiny stellate neurons and the TCA fibers were markedly restored from 2 weeks to 3 months after decompression. Conclusions: Epidural decompression caused a breakdown of the BBB, which was early-occurring and short-lasting. In contrast, epidural decompression facilitated a late-onset and prolonged recovery of the spiny stellate neurons and their afferent fibers.

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