Developing Neurons Form Transient Nanotubes Facilitating Electrical Coupling and Calcium Signaling with Distant Astrocytes

Abstract

Despite the well-documented cooperation between neurons and astrocytes little is known as to how these interactions are initiated. We show here by differential interference contrast microscopy that immature hippocampal neurons generated short protrusions towards astrocytes resulting in tunneling nanotube (TNT) formation with an average lifetime of 15 minutes. Fluorescence microscopy revealed that all TNTs between the two cell types contained microtubules but 35% of them were F-actin negative. Immunolabeling against connexin 43 showed that this gap junction marker localized at the contact site of TNTs with astrocytes. Using optical membrane-potential measurements combined with mechanical stimulation, we observed that ∼35% of immature neurons were electrically coupled with distant astrocytes via TNTs up to 5 hours after co-culture but not after 24 hours. Connexin 43 was expressed by most neurons at 5 hours of co-culture but was not detected in neurons after 24 hours. We show that TNTs mediated the propagation of both depolarization and transient calcium signals from distant astrocytes to neurons. Our findings suggest that within a limited maturation period developing neurons establish electrical coupling and exchange of calcium signals with astrocytes via TNTs, which correlates with a high neuronal expression level of connexin 43. This novel cell-cell communication pathway between cells of the central nervous system provides new concepts in our understanding of neuronal migration and differentiation.

Extracellular-vesicle type of volume transmission and tunnelling-nanotube type of wiring transmission add a new dimension to brain neuro-glial networks

“…A model of calcium diffusion alone through TNTs was therefore not supported. Instead, the findings indicated a local influx of calcium ions into neurons through activated low-voltage calcium channels which open at low depolarization thresholds [111]. It may be that VT via ATP and glutamate released from astrocytes in development is not as effective in producing depolarization and increasing neuronal calcium signalling via purinoceptors and NMDA receptors, respectively.…”

“…Developing hippocampal neurons were demonstrated to form transient nanotubes with distant astrocytes [107,111]. TNTs were found to mediate both transient calcium signals and depolarization from distant astrocytes to neurons within a limited maturation period.…”

Membrane nanotubes: Novel communication between distant cells

“…F-actins but not microtubules are found in all MNTs connecting cells such as PC12 cells or myeloid cells [4]. Although F-actin is considered as the hallmark of MNTs, some reports indicated that not all MNTs between immature hippocampal neurons and astrocytes contain F-actin, and more interestingly, F-actin-lacking MNTs were longer than those containing F-actin [14] .…”

Does electromagnetic therapy meet an equivalent counterpart within the organism?

“…Finally, the most prevailing species of free radicals within a cell are radical oxygen species (ROS and hydroxyl radicals) and radicals formed by nitric oxide (NO) [57]. The lifetime of a free radical is varying dramatically -less than a nanosecond till 3-5 s in NO [57].…”

“…The lifetime of a free radical is varying dramatically -less than a nanosecond till 3-5 s in NO [57]. The radical pair phenomenon (NO, ROS) can thus interfere with endogenous oscillations in cell or metabolic systems.…”