Glial regulation of critical period plasticity

The impact of exogenous Oxytocin on visual cortex plasticity across different stages of visual development

The plasticity of ocular dominance is most prominent during the critical period of visual development, influenced by the balance of excitatory and inhibitory synaptic transmission in the visual cortex. Astrocytes play a crucial role in regulating synaptic plasticity through phagocytosis of synapses. However, the ability of astrocytes to modulate synaptic plasticity after the critical period remains unclear. Oxytocin (OT), a neuropeptide involved in neural circuit formation, has shown potential in enhancing synaptic plasticity. This study explores the role of OT in restoring visual cortical plasticity during and after the critical period of visual development. We performed monocular deprivation (MD) on mice during the critical period and extended the deprivation until adulthood. Visual cortical plasticity was evaluated using pattern visual evoked potentials (PVEPs), immunofluorescence staining, and western blotting. Excitatory synaptic markers (VGLUT1, PSD- 95) and inhibitory synaptic markers (VGAT, Gephyrin) were analyzed. The effects of OT administration, alone or combined with reverse occlusion (RO), on ocular dominance plasticity and astrocyte activity were assessed. During the critical period, MD induced a significant ocular dominance shift with reduced cortical response from the deprived eye, primarily through decreased excitatory synaptic markers (VGLUT1: P < 0.05; PSD- 95: P < 0.05). OT administration further enhanced this shift by reducing GFAP expression and decreasing astrocytic phagocytosis of excitatory synapses. After the critical period, prolonged MD reduced excitatory synaptic marker expression in the visual cortex (P < 0.05), and RO alone did not restore cortical plasticity. However, the combination of OT and RO increased excitatory synaptic marker expression (VGLUT1: P < 0.05; PSD- 95: P < 0.05 and restored ocular dominance plasticity. Our findings demonstrate that OT can modulate astrocyte activity and enhance excitatory synaptic plasticity, facilitating the recovery of visual cortical plasticity both during and after the critical period. These results highlight the potential of OT as a therapeutic intervention for visual impairments caused by disrupted sensory experiences during development.

Neuron-to-glia and glia-to-glia signaling directs critical period experience-dependent synapse pruning

Experience-dependent glial synapse pruning plays a pivotal role in sculpting brain circuit connectivity during early-life critical periods of development. Recent advances suggest a layered cascade of intercellular communication between neurons and glial phagocytes orchestrates this precise, targeted synapse elimination. We focus here on studies from the powerful Drosophila forward genetic model, with reference to complementary findings from mouse work. We present both neuron-to-glia and glia-to-glia intercellular signaling pathways directing experience-dependent glial synapse pruning. We discuss a putative hierarchy of secreted long-distance cues and cell surface short-distance cues that act to sequentially orchestrate glia activation, infiltration, target recognition, engulfment, and then phagocytosis for synapse pruning. Ligand-receptor partners mediating these stages in different contexts are discussed from recent Drosophila and mouse studies. Signaling cues include phospholipids, small neurotransmitters, insulin-like peptides, and proteins. Conserved receptors for these ligands are discussed, together with mechanisms where the receptor identity remains unknown. Potential mechanisms are proposed for the tight temporal-restriction of heightened experience-dependent glial synapse elimination during early-life critical periods, as well as potential means to re-open such plasticity at maturity.

Astrocyte regulation of critical period plasticity across neural circuits

Critical periods are brief windows of heightened neural circuit plasticity that allow circuits to permanently reset their structure and function to facilitate robust organismal behavior. Understanding the cellular and molecular mechanisms that instruct critical period timing is of broad clinical interest, as altered developmental plasticity is linked to multiple neurodevelopmental disorders. While intrinsic, neuronal mechanisms shape both neural circuit remodeling and critical period timing, recent data indicate that signaling from astrocytes and surrounding glia can both promote and limit critical period plasticity. In this short review, we discuss recent breakthroughs in our understanding of astrocytes in critical period plasticity and highlight pioneering work in Drosophila.

Glia control experience-dependent plasticity in an olfactory critical period

Sensory experience during developmental critical periods has lifelong consequences for circuit function and behavior, but the molecular and cellular mechanisms through which experience causes these changes are not well understood. The Drosophila antennal lobe houses synapses between olfactory sensory neurons (OSNs) and downstream projection neurons (PNs) in stereotyped glomeruli. Many glomeruli exhibit structural plasticity in response to early-life odor exposure, indicating a general sensitivity of the fly olfactory circuitry to early sensory experience. We recently found that glia shape antennal lobe development in young adults, leading us to ask if glia also drive experience-dependent plasticity during this period. Here, we define a critical period for structural and functional plasticity of OSN-PN synapses in the ethyl butyrate (EB)-sensitive glomerulus VM7. EB exposure for the first 2 days post-eclosion drives large-scale reductions in glomerular volume, presynapse number, and post- synaptic activity. Crucially, pruning during the critical period has long-term consequences for circuit function since both OSN-PN synapse number and spontaneous activity of PNs remain persistently decreased following early-life odor exposure. The highly conserved engulfment receptor Draper is required for this critical period plasticity as ensheathing glia upregulate Draper, invade the VM7 glomerulus, and phagocytose OSN presynaptic terminals in response to critical-period EB exposure. Loss of Draper fully suppresses the morphological and physiological consequences of critical period odor exposure, arguing that phagocytic glia engulf intact synaptic terminals. These data demonstrate experience-dependent pruning of synapses and argue that Drosophila olfactory circuitry is a powerful model for defining the function of glia in critical period plasticity.

Neural repair function of osteopontin in stroke and stroke‑related diseases (Review)

Stroke, including hemorrhagic stroke and ischemic stroke, is a common disease of the central nervous system. It is characterized by a high mortality and disability rate and is closely associated with atherosclerosis, hypertension hyperglycemia, atrial fibrillation and unhealthy living habits. The continuous development of surgery and medications has decreased the mortality rate of patients with stroke and has greatly improved the disease prognosis. At present, the direction of clinical treatment and research has gradually shifted to the repair of nerve function after stroke. Osteopontin (OPN) is a widely distributed extracellular matrix protein. Due to its structural characteristics, OPN can be cut and modified into terminal fragments with different functions, which play different roles in various pathophysiological processes, such as formation of tumors, inflammation and autoimmune diseases. It has also become a potential diagnostic and therapeutic marker. In order to comprehensively analyze the specific role of OPN in nerve repair and its relationship with stroke and stroke-related diseases, the following key words were used: 'Osteopontin, stroke, atherosis, neuroplasticity, neural repair'. PubMed, Web of Science and Cochrane articles related to OPN were searched and summarized. The present review describes the OPN structure, isoforms, functions and its neural repair mechanism, and its association with the occurrence and development of stroke and related diseases was explored.

Glia control experience-dependent plasticity in an olfactory critical period

Sensory experience during developmental critical periods has lifelong consequences for circuit function and behavior, but the molecular and cellular mechanisms through which experience causes these changes are not well understood. The Drosophila antennal lobe houses synapses between olfactory sensory neurons (OSNs) and downstream projection neurons (PNs) in stereotyped glomeruli. Many glomeruli exhibit structural plasticity in response to early-life odor exposure, indicating a general sensitivity of the fly olfactory circuitry to early sensory experience. We recently found that glia shape antennal lobe development in young adults, leading us to ask if glia also drive experience-dependent plasticity during this period. Here we define a critical period for structural and functional plasticity of OSN-PN synapses in the ethyl butyrate (EB)-sensitive glomerulus VM7. EB exposure for the first two days post-eclosion drives large-scale reductions in glomerular volume, presynapse number, and post-synaptic activity. Crucially, pruning during the critical period has long-term consequences for circuit function since both OSN-PN synapse number and spontaneous activity of PNs remain persistently decreased following early-life odor exposure. The highly conserved engulfment receptor Draper is required for this critical period plasticity as ensheathing glia upregulate Draper, invade the VM7 glomerulus, and phagocytose OSN presynaptic terminals in response to critical-period EB exposure. Loss of Draper fully suppresses the morphological and physiological consequences of critical period odor exposure, arguing that phagocytic glia engulf intact synaptic terminals. These data demonstrate experience-dependent pruning of synapses and argue that Drosophila olfactory circuitry is a powerful model for defining the function of glia in critical period plasticity.

Glial Control of Cortical Neuronal Circuit Maturation and Plasticity

The brain is a highly adaptable organ that is molded by experience throughout life. Although the field of neuroscience has historically focused on intrinsic neuronal mechanisms of plasticity, there is growing evidence that multiple glial populations regulate the timing and extent of neuronal plasticity, particularly over the course of development. This review highlights recent discoveries on the role of glial cells in the establishment of cortical circuits and the regulation of experience-dependent neuronal plasticity during critical periods of neurodevelopment. These studies provide strong evidence that neuronal circuit maturation and plasticity are non-cell autonomous processes that require both glial-neuronal and glial-glial cross talk to proceed. We conclude by discussing open questions that will continue to guide research in this nascent field.

From Immunity to Neurogenesis: Toll-like Receptors as Versatile Regulators in the Nervous System

Toll-like receptors (TLRs) are among the main components of the innate immune system. They can detect conserved structures in microorganisms and molecules associated with stress and cellular damage. TLRs are expressed in resident immune cells and both neurons and glial cells of the nervous system. Increasing evidence is emerging on the participation of TLRs not only in the immune response but also in processes of the nervous system, such as neurogenesis and cognition. Below, we present a review of the literature that evaluates the expression and role of TLRs in processes such as neurodevelopment, behavior, cognition, infection, neuroinflammation, and neurodegeneration.

The Role of Cerebellar Intrinsic Neuronal Excitability, Synaptic Plasticity, and Perineuronal Nets in Eyeblink Conditioning

Evidence is strong that, in addition to fine motor control, there is an important role for the cerebellum in cognition and emotion. The deep nuclei of the mammalian cerebellum also contain the highest density of perineural nets-mesh-like structures that surround neurons-in the brain, and it appears there may be a connection between these nets and cognitive processes, particularly learning and memory. Here, we review how the cerebellum is involved in eyeblink conditioning-a particularly well-understood form of learning and memory-and focus on the role of perineuronal nets in intrinsic membrane excitability and synaptic plasticity that underlie eyeblink conditioning. We explore the development and role of perineuronal nets and the in vivo and in vitro evidence that manipulations of the perineuronal net in the deep cerebellar nuclei affect eyeblink conditioning. Together, these findings provide evidence of an important role for perineuronal net in learning and memory.

Sleep, Glial Function, and the Endocannabinoid System: Implications for Neuroinflammation and Sleep Disorders

The relationship between sleep, glial cells, and the endocannabinoid system represents a multifaceted regulatory network with profound implications for neuroinflammation and cognitive function. The molecular underpinnings of sleep modulation by the endocannabinoid system and its influence on glial cell activity are discussed, shedding light on the reciprocal relationships that govern these processes. Emphasis is placed on understanding the role of glial cells in mediating neuroinflammatory responses and their modulation by sleep patterns. Additionally, this review examines how the endocannabinoid system interfaces with glia-immune signaling to regulate inflammatory cascades within the central nervous system. Notably, the cognitive consequences of disrupted sleep, neuroinflammation, and glial dysfunction are addressed, encompassing implications for neurodegenerative disorders, mood disturbances, and cognitive decline. Insights into the bidirectional modulation of cognitive function by the endocannabinoid system in the context of sleep and glial activity are explored, providing a comprehensive perspective on the potential mechanisms underlying cognitive impairments associated with sleep disturbances. Furthermore, this review examines potential therapeutic avenues targeting the endocannabinoid system to mitigate neuroinflammation, restore glial homeostasis, and normalize sleep patterns. The identification of novel therapeutic targets within this intricate regulatory network holds promise for addressing conditions characterized by disrupted sleep, neuroinflammation, and cognitive dysfunction. This work aims to examine the complexities of neural regulation and identify potential avenues for therapeutic intervention.