Perisynaptic astroglial processes: dynamic processors of neuronal information

Abstract

Neuroglial interactions are now recognized as essential to brain functions. Extensive research has sought to understand the modalities of such dialog by focusing on astrocytes, the most abundant glial cell type of the central nervous system. Neuron-astrocyte exchanges occur at multiple levels, at different cellular locations. With regard to information processing, regulations occurring around synapses are of particular interest as synaptic networks are thought to underlie higher brain functions. Astrocytes morphology is tremendously complex in that their processes exceedingly branch out to eventually form multitudinous fine leaflets. The latter extremities have been shown to surround many synapses, forming perisynaptic astrocytic processes, which although recognized as essential to synaptic functioning, are poorly defined elements due to their tiny size. The current review sums up the current knowledge on their molecular and structural properties as well as the functional characteristics making them good candidates for information processing units.

Accumulation of Polyribosomes in Dendritic Spine Heads, But Not Bases and Necks, during Memory Consolidation Depends on Cap-Dependent Translation Initiation

“…These spines also accumulated cap-dependent polyribosomes in their heads after training, but when this was blocked, the spines proliferated. This is reminiscent of the shift toward small, immature spines seen in a number of intellectual disabilities, most notably Fragile X syndrome, which may result from dysregulated translation (Irwin et al, 2000;Fiala et al, 2002).…”

Correlative STED and Atomic Force Microscopy on Live Astrocytes Reveals Plasticity of Cytoskeletal Structure and Membrane Physical Properties during Polarized Migration

“…Astrocytes are dynamic and motile signaling elements of the brain (Haber et al, 2006; Bernardinelli et al, 2014; Ghézali et al, 2016). They undergo intense morphological maturation during development, changing from sparsely branched cells to polarized motile and massively ramified cells (Bayraktar et al, 2014; Molofsky and Deneen, 2015).…”

Human astrocytes are distinct contributors to the complexity of synaptic function

“…The close and dynamic interaction of astrocytes with mature synapses is enabled by protrusions of fine, ramified membrane structures termed perisynaptic astrocyte processes (PAPs), so far almost exclusively studied in rodent astrocytes. These protrusions from the periphery of astrocytes have been difficult to investigate due to their small size and lack of abundant protein markers, though recently they have become more recognized as integral components of the neuronal synapse modulatory machinery (Ghezali et al, 2015). The structural plasticity of PAPs, including the amount of synaptic area that is surrounded by these membranes, is partly regulated by the level of excitatory synapse activity and is associated with an increased stability of spines (Bernardinelli et al, 2014).…”

“…Expansion of the size and number of astroglial processes, a phenomenon observed across multiple models of neurodevelopmental syndromes including autism spectrum disorders, has been hypothesized to lead to hyperconnectivity or “mega-domains” that could underlie savant abilities (Mitterauer, 2013b) and increased intuition when combined with a highly developed memory capability (Mitterauer, 2013a). This may not be a farfetched notion considering the fine synaptic tuning possibilities at the dynamic PAPs (Ghezali et al, 2015). We have recently found that human astrocytes secrete multiple components of perineuronal net proteins that are known to enwrap subpopulations of interneurons in the cortex and stabilize synapses (Krencik et al, 2015), and a compelling hypothesis has been proposed that these structures may be another mechanism for very long term memories (Tsien, 2013).…”