Glial Cx43 hemichannels and neuronal Panx1 hemichannels and P2X7 receptors orchestrate presynaptic homeostatic plasticity.

The emerging role of glial cells in modulating neuronal excitability and synaptic strength is a growing field in neuroscience. In recent years, a pivotal role of gliotransmission in homeostatic presynaptic plasticity has been highlighted and glial-derived ATP arises as a key contributor. However, very little is known about the glial non-vesicular ATP-release pathway and how ATP participates in the modulation of synaptic strength.

P2X7 receptors and pannexin1 hemichannels shape presynaptic transmission.

Over the last decades, since the discovery of ATP as a transmitter, accumulating evidence has been reported about the role of this nucleotide and purinergic receptors, in particular P2X7 receptors, in the modulation of synaptic strength and plasticity. Purinergic signaling has emerged as a crucial player in orchestrating the molecular interaction between the components of the tripartite synapse, and much progress has been made in how this neuron-glia interaction impacts neuronal physiology under basal and pathological conditions. On the other hand, pannexin1 hemichannels, which are functionally linked to P2X7 receptors, have appeared more recently as important modulators of excitatory synaptic function and plasticity under diverse contexts.

Gestational and Lactational Iron Deficiency Anemia Impairs Myelination and the Neurovascular Unit in Infant Rats.

Iron deficiency anemia is a prevalent health problem among pregnant women and infants, particularly in the developing countries that causes brain development deficits and poor cognitive outcomes. Since tissue iron depletion may impair myelination and trigger cellular hypoxic signaling affecting blood vessels, we studied myelination and the neurovascular unit (NVU) in infant rats born to mothers fed with an iron deficient (ID) or control diet from embryonic day 5 till weaning. Blood samples and brains of rat pups at postnatal day (PND) 14 and 30 were analyzed.

Pericyte Mapping in Cerebral Slices with the Far-red Fluorophore TO-PRO-3.

This protocol describes a method for high-resolution confocal imaging of pericytes with the far-red fluorophore TO-PRO-3 Iodide 642/661 in cerebral slices of murine. Identification of pericytes with TO-PRO-3 is a short time-consuming, high cost-effective and robust technique to label pericytes with no need for immunostaining or generation of reporter mice. Since the TO-PRO-3 stain resists immunofluorescence, and lacks spectral overlap, the probe is well suited for multiple labelling.

A nuclear fluorescent dye identifies pericytes at the neurovascular unit.

Perivascular pericytes are key regulators of the blood-brain barrier, vascular development, and cerebral blood flow. Deciphering pericyte roles in health and disease requires cellular tracking; yet, pericyte identification remains challenging. A previous study reported that the far-red fluorophore TO-PRO-3 (642/661), usually employed as a nuclear dye in fixed tissue, was selectively captured by live pericytes from the subventricular zone.

Glial ATP and Large Pore Channels Modulate Synaptic Strength in Response to Chronic Inactivity.

A key feature of neurotransmission is its ability to adapt to changes in neuronal environment, which is essential for many brain functions. Homeostatic synaptic plasticity (HSP) emerges as a compensatory mechanism used by neurons to adjust their excitability in response to changes in synaptic activity. Recently, glial cells emerged as modulators for neurotransmission by releasing gliotransmitters into the synaptic cleft through pathways that include P2X receptors (P2XR), connexons, and pannexons.

Glutaric Acid Affects Pericyte Contractility and Migration: Possible Implications for GA-I Pathogenesis.

Glutaric acidemia I (GA-I) is an inherited neurometabolic childhood disease characterized by bilateral striatal neurodegeneration upon brain accumulation of millimolar concentrations of glutaric acid (GA) and related metabolites. Vascular dysfunction, including abnormal cerebral blood flow and blood-brain barrier damage, is an early pathological feature in GA-I, although the affected cellular targets and underlying mechanisms remain unknown. In the present study, we have assessed the effects of GA on capillary pericyte contractility in cerebral cortical slices and pericyte cultures, as well as on the survival, proliferation, and migration of cultured pericytes.

Synaptic Functions of Hemichannels and Pannexons: A Double-Edged Sword.

The classical view of synapses as the functional contact between presynaptic and postsynaptic neurons has been challenged in recent years by the emerging regulatory role of glial cells. Astrocytes, traditionally considered merely supportive elements are now recognized as active modulators of synaptic transmission and plasticity at the now so-called "tripartite synapse." In addition, an increasing body of evidence indicates that beyond immune functions microglia also participate in various processes aimed to shape synaptic plasticity.

Activated microglia impairs neuroglial interaction by opening Cx43 hemichannels in hippocampal astrocytes.

Glia plays an active role in neuronal functions and dysfunctions, some of which depend on the expression of astrocyte connexins, the gap junction channel and hemichannel proteins. Under neuroinflammation triggered by the endotoxin lipopolysacharide (LPS), microglia is primary stimulated and releases proinflammatory agents affecting astrocytes and neurons. Here, we investigate the effects of such microglial activation on astrocyte connexin-based channel functions and their consequences on synaptic activity in an ex vivo model.

The connexin43 mimetic peptide Gap19 inhibits hemichannels without altering gap junctional communication in astrocytes.

In the brain, astrocytes represent the cellular population that expresses the highest amount of connexins (Cxs). This family of membrane proteins is the molecular constituent of gap junction channels and hemichannels that provide pathways for direct cytoplasm-to-cytoplasm and inside-out exchange, respectively. Both types of Cx channels are permeable to ions and small signaling molecules allowing astrocytes to establish dynamic interactions with neurons.

Connexin 30 sets synaptic strength by controlling astroglial synapse invasion.

Astrocytes play active roles in brain physiology by dynamic interactions with neurons. Connexin 30, one of the two main astroglial gap-junction subunits, is thought to be involved in behavioral and basic cognitive processes. However, the underlying cellular and molecular mechanisms are unknown.

Connexin-based channels in astrocytes: how to study their properties.

A typical feature of astrocytes is their high level of connexin expression. These membrane proteins constitute the molecular basis of two types of channels: gap junction channels that allow direct cytoplasm-to-cytoplasm communication and hemichannels that provide a pathway for exchanges between the intra- and extracellular media. An unusual property of these channels is their permeability for ions but also for small signaling molecules.

Endogenous presynaptic nitric oxide supports an anterograde signaling in the central nervous system.

The source size and density determine the extent of nitric oxide (NO) diffusion which critically influences NO signaling. In the brain, NO released from postsynaptic somas following NMDA-mediated activation of neuronal nitric oxide synthase (nNOS) retrogradely affects smaller presynaptic targets. By contrast, in guinea pig trigeminal motor nucleus (TMN), NO is produced presynaptically by tiny and disperse nNOS-containing terminals that innervate large nNOS-negative motoneurons expressing the soluble guanylyl-cyclase (sGC); consequently, it is uncertain whether endogenous NO supports an anterograde signaling between pre-motor terminals and postsynaptic trigeminal motoneurons.

Amyloid β-induced death in neurons involves glial and neuronal hemichannels.

The mechanisms involved in Alzheimer's disease are not completely understood and how glial cells contribute to this neurodegenerative disease remains to be elucidated. Because inflammatory treatments and products released from activated microglia increase glial hemichannel activity, we investigated whether amyloid-β peptide (Aβ) could regulate these channels in glial cells and affect neuronal viability. Microglia, astrocytes, or neuronal cultures as well as acute hippocampal slices made from GFAP-eGFP transgenic mice were treated with the active fragment of Aβ.

FGF-1 induces ATP release from spinal astrocytes in culture and opens pannexin and connexin hemichannels.

Spinal astrocytes are coupled by connexin (Cx) gap junctions and express pannexin 1 (Px1) and purinergic receptors. Fibroblast growth factor 1 (FGF-1), which is released in spinal cord injury, activated spinal astrocytes in culture, induced secretion of ATP, and permeabilized them to relatively large fluorescent tracers [ethidium (Etd) and lucifer yellow (LY)] through "hemichannels" (HCs). HCs can be formed by connexins or pannexins; they can open to extracellular space or can form gap junction (GJ) channels, one HC from each cell.

Astroglial metabolic networks sustain hippocampal synaptic transmission.

Astrocytes provide metabolic substrates to neurons in an activity-dependent manner. However, the molecular mechanisms involved in this function, as well as its role in synaptic transmission, remain unclear. Here, we show that the gap-junction subunit proteins connexin 43 and 30 allow intercellular trafficking of glucose and its metabolites through astroglial networks.

Mechanical sensitivity of carotid body glomus cells.

Cultured glomus cells from rat carotid bodies were prepared for optical studies of intracellular calcium using the Fura-2 dye. The baseline calcium had a mean of about 40 nM showing either a relatively steady level or large calcium spikes. Some cells did not show measurable levels of [Ca(2+)](i).

Behavior of junction channels between rat glomus cells during normoxia and hypoxia.

The activity of gap junction channels between cultured and clustered carotid body glomus cells of the rat was studied with dual voltage clamping during normoxia (PO(2) 300 Torr) and hypoxia induced by sodium dithionite (Na(2)S(2)O(4)) or 100% N(2). Na(2)S(2)O(4) reduced the saline PO(2) to approximately 10 Torr, whereas 100% N(2) reduced ambient O(2) to approximately 60 Torr. The following observations were made.

Nitric oxide as an anterograde neurotransmitter in the trigeminal motor pool.

We demonstrate the presence of nitric oxide synthase containing fibers within the guinea pig trigeminal motor nucleus and describe the effects of nitric oxide (NO) on trigeminal motoneurons. Using immunohistochemical techniques, we observed nitrergic fibers displaying varicosities and giving rise to bouton-like structures in apposition to retrogradely labeled motoneuron processes, most of which were dendrites. NO-donors evoked a membrane depolarization (mean 7.