Astrocytes and synaptic plasticity

October 13, 2008

By mopping up excess neurotrophic factor from neuronal synapses, astrocytes may finely tune synaptic transmission to affect processes such as learning and memory, say Bergami et al.

The major cellular events of learning and memory are long-term potentiation (LTP) and long-term depression (LTD), both of which affect neurons' ability to communicate with one another. Neurons that have undergone LTP display a stronger electrical response to the same level of a stimulus, whereas neurons that have gone through LTD display a weaker response. These changes are thought to result from modifications of the neuronal synapses, such as alterations in the density of postsynaptic receptors, or downstream signaling events.

Secretion of the neurotrophic factor BDNF (brain-derived neurotrophic factor) has been implicated in long-term synaptic modification, and the function of BDNF on synaptic strength depends on its particular form: in its pro-BDNF form it is believed to promote LTD, and in its mature form it prompts LTP. Neurons were thought to secrete pro-BDNF, which then matured into BDNF in the synaptic space. However, a recent study suggests that only mature BDNF is secreted, pro-BDNF being processed intracellularly.

To get to the bottom of things, Bergami et al. investigated the fate of both forms after LTP induction in brain slices from the rat cortex. By fluorescent immunohistochemistry they showed that that neurons indeed secrete both mature and pro-BDNF, but that a large amount of the pro-BDNF is immediately taken up by astrocytes.

Astrocytes, previously thought to be unimportant in neuronal transmission, have recently been implicated in long-term modulation of neuronal synapses. For example, they release the neurotransmitter glutamate into the synapse prompting LTP. By specifically mopping up pro-BDNF, astrocytes seem to have another means to assist in LTP. However, while it's likely that most pro-BDNF gets degraded inside astrocytes, say the authors, some gets recycled and re-released, suggesting that astrocytes in fact fine-tune synaptic plasticity.

Rockefeller University Press

---

---

	Methods in Neuronal Modeling: From Synapses to Networks by Christof Koch (Author), Idan Segev (Author) Methods in Neuronal Modeling is the first technical handbook on computational neuroscience. Written for researchers and theoreticians alike, it outlines methods and techniques used for simulating on digital computers the functional properties of single neurons from synapses, dendrites, single cells; and small invertebrate networks to large scale neural networks in the mammalian nervous system. The use of new experimental tools such as selective staining methods, membrane patch electrodes, voltage and calcium-dependent dyes, and multielectrode recordings, together with the, advent of universally available powerful computing, makes it possible to construct detailed and realistic models of neuronal systems. Methods in Neuronal Modeling addresses such questions as what can and...
	Beyond the Synapse: Cell-Cell Signaling in Synaptic Plasticity by R. Douglas Fields (Author) Formation of synapses and the changes in their connections during life are the basis for learning and memory and recovery from brain disease or injury. Much interest has been focused on how synapses function at the molecular level, while the cell-cell interactions controlling the formation receive far less attention. This book expands the scope of inquiry beyond the synaptic cleft to provide a comprehensive insight into how intercellular signalling enables neurons to communicate beyond the synapse, and to interact with other cells in the brain to alter synaptic connections appropriately. There are chapters devoted to consideration of glia, brain cells which have thus far been ignored in the majority of studies of learning and memory. Writing for academic researchers and professionals,...
	Strengthening your synapses, keys to learning: nurturing these critical neuronal connections can protect your memory and help you stay mentally alert.: An article from: Mind, Mood & Memory by Gale Reference Team (Author) This digital document is an article from Mind, Mood & Memory, published by Thomson Gale on February 1, 2007. The length of the article is 1333 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: Strengthening your synapses, keys to learning: nurturing these critical neuronal connections can protect your memory and help you stay mentally alert. Author: Gale Reference Team Publication: Mind, Mood & Memory (Magazine/Journal) Date: February 1, 2007 Publisher: Thomson Gale Volume: 3 Issue: 2 Page: 4(2) Distributed by Thomson...
	Inhibitory Regulation of Excitatory Neurotransmission (Results and Problems in Cell Differentiation) by Mark G. Darlison (Editor) Darlison’s excellent work reviews aspects of GABA-A receptor function, as well as the properties of a variety of other important inhibitory proteins, such as GABA-C receptors and G-protein coupled receptors including neuropeptides. Glycine receptors and potassium channels are covered too. The consequences of mutations that disrupt the regulation of excitatory neurotransmission, and efforts to target the GABAergic system for therapeutic benefit, are also discussed.
	The Dynamic Synapse: Molecular Methods in Ionotropic Receptor Biology (Frontiers in Neuroscience) by Josef T. Kittler (Editor), Stephen J. Moss (Editor) Exploring the diverse tools and technologies used to study synaptic processes, The Dynamic Synapse: Molecular Methods in Ionotropic Receptor Biology delineates techniques, methods, and conceptual advances for studying neurotransmitter receptors and other synaptic proteins. It describes a broad range of molecular, biochemical, imaging, and electrophysiological approaches for studying the biology of synapses.  Specific topics include the use of proteomics to study synaptic protein complexes, the development of phosphorylation state specific antibodies, post-genomic tools applied to the study of synapses and RNA interference in neurons. In addition, several chapters focus on methods for gene and protein delivery into neuronal tissue. The use of biochemical, electrophysiological and...
	Imaging the maintenance, depression, and elimination of neuronal synapses in the peripheral nervous system of living mice. by Corey M McCann (Author) Synaptic plasticity is thought to underlie the remarkable behavioral adaptability of the mammalian brain, but the mechanisms that maintain and modify neuronal synapses in living animals remain poorly understood. This lack of knowledge is in part due to the fact that changes in the fine details of synaptic architecture have been difficult to monitor over time in living animais. Therefore, for my thesis, I have developed methods to label and image pre- and postsynaptic structures in the parasympathetic peripheral nervous system of living mice. Using these methods, I have imaged the ways in which synapses between neurons are maintained and modified.
	Analysis of Neuronal Microcircuits and Synaptic Interactions (Handbook of Chemical Neuroanatomy) by F.G. Wouterlood (Editor), A.N. Van den Pol (Editor), T. Hökfelt (Editor), A. Björklund (Editor) This volume of the Handbook of Chemical Neuroanatomy describes the techniques used to study the connectivity of chemically defined neurons at the cellular level. Among areas dealt with are the most recent developments in light microscopy and electron microscopy, and the applications to specific subjects of chosen combinations of techniques to demonstrate how elegantly and powerfully they can be applied. As the fiber connections of the brain become increasingly accurately mapped, the desire to understand the instrinsic circuits of these populations of neurons, including their morphology, neurotransmitters, neuromodulators, receptors and their physiology, will grow. It is this desire for knowledge the authors are attempting to stimulate by presenting a comprehensive technical book...
	Synaptic transmission and neuronal interaction (Society of General Physiologists series, v. 28) by Michael V. L Bennett (Author)
	Synapse: Function, Plasticity, and Neurotrophism by Motoy Kuno (Author) The synapse not only provides a bridge from one nerve cell to the next; its function can be modified by experience, making it important for learning and memory, and it plays an important role in the growth and development of the nervous system. This is a central topic in the study of neuroscience on which molecular biology has had a major impact. Professor Kuno has written the first accessible overview of the synapse in these different contexts. He takes the reader through a series of fundamental questions about neuronal function which facilitate an understanding of the rationale and logic behind current research in the area. To achieve a true synthesis on molecular biology and neurophysiology, the terminology and concepts are described in terms accessible to advanced students and...
	Communication in Plants: Neuronal Aspects of Plant Life by Frantiek Baluka (Editor), Stefano Mancuso (Editor), Dieter Volkmann (Editor) Plant neurobiology is a newly emerging field of plant sciences. It covers signalling and communication at all levels of biological organization – from molecules up to ecological communities. In this book, plants are presented as intelligent and social organisms with complex forms of communication and information processing. Authors from diverse backgrounds such as molecular and cellular biology, electrophysiology, as well as ecology treat the most important aspects of plant communication, including the plant immune system, abilities of plants to recognize self, signal transduction, receptors, plant neurotransmitters and plant neurophysiology. Further, plants are able to recognize the identity of herbivores and organize the defence responses accordingly. The similarities in animal and...