Electrophysiological behavior of neonatal astrocytes in hippocampal stratum radiatum
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Neonatal astrocytes are diverse in origin, and undergo dramatic change in gene expression, morphological differentiation and syncytial networking throughout development. Neonatal astrocytes also play multifaceted roles in neuronal circuitry establishment. However, the extent to which neonatal astrocytes differ from their counterparts in the adult brain remains unknown.
Based on ALDH1L1-eGFP expression or sulforhodamine 101 staining, neonatal astrocytes at postnatal day 1–3 can be reliably identified in hippocampal stratum radiatum. They exhibit a more negative resting membrane potential (V M), −85 mV, than mature astrocytes, −80 mV and a variably rectifying whole-cell current profile due to complex expression of voltage-gated outward transient K+ (IKa), delayed rectifying K+ (IKd) and inward K+ (IKin) conductances. Differing from NG2 glia, depolarization-induced inward Na+ currents (INa) could not be detected in neonatal astrocytes. A quasi-physiological V M of −69 mV was retained when inwardly rectifying Kir4.1 was inhibited by 100 μM Ba2+ in both wild type and TWIK-1/TREK-1 double gene knockout astrocytes, indicating expression of additional leak K+ channels yet unknown. In dual patch recording, electrical coupling was detected in 74 % (14/19 pairs) of neonatal astrocytes with largely variable coupling coefficients. The increasing gap junction coupling progressively masked the rectifying K+ conductances to account for an increasing number of linear voltage-to-current relationship passive astrocytes (PAs). Gap junction inhibition, by 100 μM meclofenamic acid, substantially reduced membrane conductance and converted all the neonatal PAs to variably rectifying astrocytes. The low density expression of leak K+ conductance in neonatal astrocytes corresponded to a ~50 % less K+ uptake capacity compared to adult astrocytes.
Neonatal astrocytes predominantly express a variety of rectifying K+ conductances, form discrete cell-to-cell gap junction coupling and are deficient in K+ homeostatic capacity.
KeywordsAstrocytes Hippocampus K+ conductance K+ homeostasis Gap junctions
intracellular K+ concentration
double gene knockout mouse
voltage-gated outward transient K+ current
voltage-gated outward delayed rectifying K+ current
inward K+ current
voltage-gated inward Na+ current
two-pore domain K+ channel
olfactory ensheathing cells
variably rectifying astrocyte
Neonatal astrocytes have been traditionally viewed as immature astrocytes undergoing extensive changes in cell proliferation, establishment of spatially distinct domains, integration into syncytial network through gap junction coupling, wrapping of blood vessels as part of the blood brain barrier, and varying in gene expression to reach functional maturity [1, 2, 3, 4, 5, 6, 7, 8]. Emerging evidence shows that neonatal astrocytes also play a pivotal role in synaptogenesis and facilitate myelination that is essential for neuronal circuit wiring and brain function [8, 9, 10]. In view of the critical role of neonatal astrocytes in developing brain, it becomes important to know the basic functional properties and how they behave electrophysiologically in their early life.
The first wave of astrogliogenesis peaks around E20-P3 in various regions of the rodent brain, and astrocytes in postnatal days 1–3 should mainly arise from direct transformation of ventricular zone (VZ) radial glia and asymmetric division of glial progenitor cells [11, 12, 13, 14, 15, 16, 17]. In contrast, after a short dormant period , the second wave of astrogliogenesis mainly produces astrocytes through symmetric division of differentiated astrocytes and to a less extent asymmetric division of NG2 glia [5, 18]. However, to what extent the newborn astrocytes from the two distinct phases differ in their electrophysiological properties is poorly defined. In the present study, we focused on neonatal astrocytes in the P1-3 dormant period and asked the following questions. First, whether neonatal astrocytes, deriving from the first wave of astrogliogenesis, in the hippocampus share markers which commonly appear in mature astrocytes, such as GFAP, chemical marker sulforhodamine 101(SR101) and gene marker ALDH1L1 [6, 19, 20], as shown in P2 spinal cord astrocytes [12, 21]. Second, whether the diversity in astrocytic origins corresponds to heterogeneity in electrophysiological properties. Third, whether neonatal astrocytes are electrophysiologically distinct compared to proliferating astrocytes in postnatal brain and mature astrocytes. Fourth, whether neonatal astrocytes are strongly electrically coupled as has been observed in the adult brain. Information from this critical early developmental stage is essential for our further understanding of the role of neonatal astrocytes in the developing brain.
By taking advantage of ALDH1L1-eGFP transgenic mouse and SR101 as live cell markers for identification of newborn astrocytes in P1-3 stratum radiatum, we show that neonatal astrocytes are electrophysiologically characterized by a more negative resting membrane potential and a homogeneous expression of a distinct set of rectifying K+ channels. In contrast with mature astrocytes , neonatal astrocytes form discrete electrical coupling early on in postnatal life. Furthermore, neonatal astrocytes are much less capable of redistributing K+ ions across the membrane. These unique features should have profound implications for the complex roles of neonatal astrocytes in the developing brain.
All the experimental procedures were performed in accordance with a protocol approved by the Animal Care and Use Committees of The Ohio State University. The wild type C57BL/6J and BAC-ALDH1L1-eGFP transgenic mice were used in the present study , as well as TWIK-1/TREK-1 double gene knockout mice . Neonatal hippocampal astrocytes from postnatal day (P) 1–3 mice of both sexes were used.
Preparation of acute hippocampal slices
Hippocampal slices were prepared as described previously. Briefly, brains were rapidly removed from skulls and placed into ice-cold oxygenated (95 % O2/5 % CO2) slice cutting aCSF with reduced Ca2+ and increased Mg2+ (in mM): 125 NaCl, 3.5 KCl, 25 NaHCO3, 1.25 NaH2PO4, 0.1 CaCl2, 3 MgCl2 and 10 Glucose. Coronal hippocampal slices (300 μm) were cut at 4 °C with a Vibratome (Pelco 1500) and transferred to the oxygenated standard aCSF (in mM): 125 NaCl, 25 NaHCO3, 1.25 NaH2PO4, 3.5 KCl, 2 CaCl2, 1 MgCl2 and 10 Glucose, osmolality, 295 ± 5 mOsm; pH 7.3–7.4), recovering at room temperature for at least one h before recording or Sulforhodamine 101 (SR101) incubation (see below).
Fresh dissociation of single hippocampal astrocytes
As we described previously in detail [25, 26], coronal hippocampal slices at 250 μm thickness were sectioned from P21–25 mice and incubated in oxygenated aCSF. One to three slices were transferred from standard aCSF to oxygenated Ca2+-free aCSF at 34 °C supplemented with 0.6 μM astrocytic marker SR-101 for 30 min. After incubation, the CA1 regions were dissected out from slices, cut into small pieces (1 mm2), and transferred into a 1.5 ml Eppendorf tube containing oxygenated aCSF supplemented with 24U/ml papain and 0.8 mg/ml L-cysteine for incubation for 7 min at 25 °C. The loosened tissues after papain digestion were gently triturated 5–7 times into a cell suspension, and transferred into the recording chamber mounted on the microscope. Although the cell suspensions contain multiple tissue blocks, only single dissociated astrocytes were used in this study .
Sulforhodamine 101 staining
For sulforhodamine 101 (SR101) , the slices were transferred to a slice-holding basket containing 0.6 μM SR101 in aCSF at 34 °C for 30 min. Then, the basket was transferred back to normal aCSF at room temperature before the experiment. Some of the slices from BAC-ALDH1L1-eGFP transgenic mice were mounted immediately after SR101 staining to analyze the colocalization of SR101 and ALDH1L1-eGFP in CA1 stratum radiatum region using a confocal microscope (LSM510, Carl Zeiss).
A fluorescent imaging system, Polychrome V system (Till Photonics, Germany), was used for identification of astrocytes from ALDH1L1-eGFP or SR101 staining neonatal astrocytes in slices. This system was also used for high resolution visualization of small glial soma for whole-cell astrocyte recording .
The hippocampal slices were fixed in 4 % paraformaldehyde for 1 h (h) at room temperature. Permeabilization was then followed in 0.2 % Triton X-100 PBS for 1 h. The slices were then incubated with a blocking solution consisting of 5 % normal donkey serum (DNS) and 0.01 % Triton X-100 in PBS for 3 h. The primary anti-GFAP antibody, goat anti-GFAP (1:1000, Abcam, Cambridge, MA), was diluted into a 10 % DNS/0.005 % Triton X-100 solution and applied to slices at 4 °C overnight. Following rise of slices with blocking solution, the secondary antibody, Alex555 donkey anti-goat (1:1000), was applied for 1 h at room temperature. Immunofluorescence images were obtained from a confocal microscope (LSM510, Carl Zeiss). To reliably identify colocalization of GFAP immunostaining signal with eGFP in ALDH1L1-eGFP mice, only the cellular somas showing ALDH1L1-eGFP alone, or together with GFAP staining signal, were selected in this analysis.
For brain slice recording, individual hippocampal slices were transferred to the recording chamber mounted on an Olympus BX51WI microscope, with constant perfusion of oxygenated aCSF (2.0 ml/min). Astrocytes located in the stratum radiatum region were visualized using an infrared differential interference contrast (IR-DIC) video camera. Whole-cell patch clamp recordings were performed using a MultiClamp 700A amplifier and pClamp 9.2 software (Molecular Devices, Sunnyvale, CA). Borosilicate glass pipettes (Warner Instrument, Hamden, CT) were pulled from a Micropipette Puller (Model P-87, Sutter Instrument). The recording electrodes had a resistance of 2–5 MΩ when filled with the electrode solution containing (in mM) 140 KCl, 13.4 NaCl, 0.5 CaCl2, 1.0 MgCl2, 5 EGTA, 10 HEPES, 3 Mg-ATP, and 0.3 Na-GTP (280 ± 5 mOsm, PH 7.25–7.35). To examine K+ uptake capacity, the intracellular K+ was fully substituted with Na+ ions.
The membrane potential (V M) was recorded under current clamp mode in PClamp 9.2 program. The liquid junction potential was compensated prior to forming the cell-attached mode for all recordings. In current clamp recording, the input resistance (R in) was measured by “Resistance test” protocol in PClamp 9.2 software (pulse: 63 pA/600 ms) before and after recording. When Rin varied greater than 10 % during recording, the cells were discarded. In recordings where voltage clamping quality was significantly improved after inhibition of gap junction coupling, the access resistance (R a), membrane resistance (R M) and membrane capacitance (CM) were measured from “Membrane test” protocol available in PClamp 9.2 software. Also, only those recordings which achieved an initial R a less than 15 MΩ and varied less than 10 % were included in data analysis. All the experiments were conducted at room temperature.
SR101 was purchased from Invitrogen (New York, NY). All other chemicals and salts used in intracellular and extracellular solutions were purchased from Sigma-Aldrich. 100 μM BaCl2 and the 100 μM meclofenamic acid (MFA) were dissolved directly in aCSF.
Where the ∆V M in C stim. was calculated from ∆V M = ∆IM×(R t-R a). The ∆IM was measured in the end of each V COM step. R a, access resistance, R t, total resistance.
The patch clamp recording data were analyzed by Clampfit 9.0 (Molecular Devices, Sunnyvale, CA) and Origin 8.0 (OriginLab, Northhampton, MA). Results are given as mean ± SEM. Statistical analysis was performed using one-way ANOVA. Significance level was set at P <0.05.
Identification of neonatal astrocytes in hippocampal stratum radiatum
Lack of astrocytic stage-specific markers remains a challenge for the lineage tracing of astrocytes in embryonic and neonatal stages. ALDH1L1 emerged as a highly expressed protein in astrocytes from gene expression profiling and has also been demonstrated to be an early and reliable gene marker for identification of ALDH1L1-expression cells from embryonic day (E) 9.5 onward [6, 10, 23, 29]. In the present study, BAC-ALDH1L1-eGFP transgenic mice were used to identify neonatal astrocytes in the hippocampal stratum radiatum region. We found that eGFP-expression cells in ALDH1L1-eGFP mice were always morphologically correlated with glial cells characterized by a soma size < 10 μm under the IR-DIC in stratum radiatum [23, 25, 30], and none of the recorded eGFP-expression cells turned out to be excitable neurons in patch clamp recording.
Neonatal astrocytes exhibit two distinct electrophysiological phenotypes
Gap junction coupling masks the activation kinetics of intrinsic rectifying K+ conductances
Consistent with our previous observation that MFA does not affect V M and passive conductance in mature astrocytes [3, 22, 36], the V M in neonatal astrocytes was unchanged between control (−84.70 ± 3.35 mV, n = 57) and MFA (−83.19 ± 6.22 mV, n = 12, P > 0.05, Fig. 3e). To determine how coupling affects the activation of intrinsic ion channels in neonatal astrocytes, the rectification index (RI) was intruduced in analysis . The RI increased by 3- and 6-folds in VRAs (2.02 ± 0.64 in control vs. 6.18 ± 3.21 in MFA, n = 6, P < 0.05) and PAs (0.96 ± 0.02 in control vs. 6.44 ± 1.63 in MFA, n = 3, P < 0.05), respectively (Fig. 3f). After 100 μM MFA treatment, the Rin in neonatal VRA increased from 42.0 ± 41.9 MΩ (n = 57) to 223.7 ± 100.3 MΩ (n = 12) (P < 0.05, Fig. 3g). Under this uncoupled condition, the intrinsic K+ conductances could be accurately quantified. The outward and inward steady-state currents were 33.2 ± 14.1 pA/pF, and 5.5 ± 2.7 pA/pF (n =10), respectively (Fig. 3h).
In summary, neonatal astrocytes predominantly express rectifying K+ conductances and are electrophysiologically homogeneous. Additionally, a developmental increase in gap junction coupling progressively masks the activation of rectifying K+ conductances that underlies the passive behavior of neonatal astrocytes.
Neonatal astrocytes predominantly express rectifying K+ conductances
Previously, depolarization-induced inward Na+(INa), outward transient (IKa) and delayed rectifying (IKd) conductances, and hyperpolarization-induced inward K+(IKin) conductances were described in neonatal astroglia [38, 39]. Now the availability of reliable markers for live astrocyte identification and a better voltage-clamping quality achieved through MFA-induced uncoupling allows examination of rectifying K+ conductances in neonatal astrocytes with high fidelity.
To inactivate outward K+ conductances for selective study of sustained inward K+ conductance (IKin), a 0 mV/500 ms prepulse was delivered prior to test pulses from −180 to 0 mV with 10 mV increments and 50 ms durations . The induced IKin showed a characteristic inward rectification and time dependent inactivation of currents at voltages more negative than −140 mV with a whole-cell V rev of −79.7 ± 0.8 mV (n = 6, Fig. 4g). Addition of 100 μM Ba2+ for 10 min substantially reduced the inward currents (Fig. 4h), and the subtracted Ba2+-sensitive currents fit well with the activation kinetic of Kir4.1 (Fig. 4i) . Interestingly, the remaining Ba2+-insensitive currents exhibited a strong outward rectification and still reversed at a quasi-physiological level of −79.1 ± 1.2 mV (n = 6), suggesting its identity as a leak K+ conductance that follows the GHK constant field rectification (Fig. 4j) .
The identity of Ba2+-insensitive leak conductance in neonatal astrocytes
Neonatal astrocytes form discrete cell-to-cell gap junction coupling
Inhibition of gap junction coupling eliminated the inward conductance more evidently than that of the outward conductance in both VRAs and PAs (Fig. 3a, b). To determine whether a rectifying filter effect is exhibited in gap junction channels to account for this observation, the coupling coefficient (CC) was analyzed over a wide range of voltages from −220 mV to +40 mV (Fig. 6f, Methods in details). The CC values varied only slightly from 22.3 to 25.5 % over the tested voltages (n = 9, P > 0.05, Fig. 6g), indicating a linear gating property of gap junction channels in neonatal astrocytes. This analysis also showed that the CC values varied markedly among recording pairs (n = 13, Fig. 6h), which is independent of the distance between the two patched cells (Fig. 6i).
In view of convergence of neonatal astrocytes from multiple resources, the discrete cell-to-cell coupling in early postnatal life suggests that newly generated astrocytes are uncoupled at birth and the syncytial network should be established progressively in later postnatal development.
Neonatal astrocytes exhibit a poor K+ uptake capacity compared to adult astrocytes
In contrast to mature astrocytes, neonatal astrocytes predominantly express voltage-gated outward K+ conductances, whereas the level of leak K+ conductance is evidently lower as indicated by their significantly higher membrane input resistances (Fig. 2f). This suggests that neonatal astrocytes should be less efficient in redistributing K+ ions across the membrane in the event of change in transmembrane K+ driving force .
Increasing evidence suggests that neonatal astrocytes may comprise a unique stage specific population of astrocytes that are multidimensionally involved in postnatal brain development and function. Meanwhile, neonatal astrocytes are diverse in their origins. However, to what extent neonatal astrocytes differ from functionally mature astrocytes, and how their physiological behavior is related to the neonatal brain development and function are questions largely unknown. We show that, compared to mature astrocytes in the same brain region, nascent astrocytes exhibit salient differences in their ion channel expression, gap junction coupling and the ability in regulating the concentration of extracellular K+.
Identification of neonatal astrocytes
A universal marker for identification of astrocytes in the developing and adult brain is still unavailable . In the present study, neonatal astrocytes were identified based on the expression of eGFP in ALDH1L1-eGAP transgenic mice [21, 23] and positive staining to a commonly used chemical marker SR101 [20, 23]. We show that both markers are co-localized well with morphologically identified astro-shaped glial cells in hippocampal stratum radiatum [2, 32, 46]. The eGFP-expression cells were nicely co-localized with SR101 stained cells (Fig. 1a), and the eGFP (+) cells were also well co-localized with the gold standard astrocytic marker GFAP (Fig. 1b). None of the identified cells, based on these markers, turned out to be excitable neurons. A majority of the identified cells showed electrical coupling (Fig. 6). Based on these characteristics, the eGFP-expression and SR101 stained neonatal cells satisfied the criterion to be considered astrocytes .
It should be noted, however, that the stage-specific and origin-specific markers for differentiating astrocytes with diverse origins, such as radial glia, subventricular zone progenitor cells, NG2 glia and local proliferation remain unavailable . Thus, it is possible that some of the neonatal astrocytes deriving from different sources could potentially be excluded in the present study.
Neonatal astrocytes are electrophysiologically homogeneous
To better characterize the electrophysiological properties of neonatal astrocytes, we purposely narrowed the animal age to the dormant P1-3 period for examining potential diversity in ion channel expression among neonatal astrocytes. Interestingly, two electrophysiological phenotypes could be readily identified during this early postnatal age. The neonatal astrocytes in P1 homogeneously show a variably rectifying whole cell current profile, whereas electrophysiologically passive astrocytes (PAs) first appear in P2, and the percentage of PAs rapidly increased from 6.67 % in P2 to 20.83 % at P3. Interestingly, the appearance of PA in mice is 2 days earlier than rats , which seemingly follows a longer gestation time in rats (22 day) than mice (20 day).
We show that the passive behavior of neonatal astrocytes is solely attributable to gap junction coupling (Fig. 3). This differs fundamentally from the passive behavior of membrane conductance in mature astrocytes that is caused by intrinsic K+ channel expression [3, 25, 49, 50]. In our previous studies, MFA was used to inhibit gap junction coupling of mature hippocampal astrocytes that resulted in a 99.3 % of coupling inhibition without altering the passive behavior of membrane conductance, suggesting that MFA-induced transition of PA to VRA was unlikely caused by MFA effect on membrane conductance in neonatal astrocytes.
Several voltage-gated K+, Na+ and Ca2+ conductances have been previously reported to be associated with astro-shaped glia in the early postnatal hippocampus [2, 32, 51, 52, 53]. Now we show that neonatal astrocytes predominantly express depolarization-induced outward IKa and IKd. Under uncoupled conditions, the current density (pA/pF) of steady-state outward K+ conductance is 6-folds higher than that of the inward (Fig. 3h). This markedly differs from the linear passive conductance in freshly dissociated mature astrocytes . With significantly improved voltage clamp quality in recording, depolarization-induced inward Na+ or Ca2+ currents were not detectable in neonatal astrocytes (Fig. 4e). Meanwhile, voltage-gated INa has been shown as a characteristic feature of NG2 glia in the developing and mature brain [39, 54, 55]. Thus lack of INa appears to be diagnostic for differentiating astrocytes from NG2 glia.
Although the density of inward K+ conductance (IKin) is substantially lower in neonatal astrocytes, they exhibit a significantly more negative membrane potential (V M) than mature astrocytes. Furthermore, in the presence of 100 μM Ba2+, the remaining Ba2+ -insensitive current retained a quasi-physiological V M level. Consistent with our recent reports that TWIK-1 and TREK-1 do not contribute to passive conductance and resting V M, the Ba2+ -insensitive currents in TWIK-1/TREK-1 double gene knockout mice remained unchanged. This suggests the presence of additional leak type K+ channels contributing to the resting V M . A more negative V M suggests a further lower Na+ permeability in neonatal astrocytes, and a plausible explanation would be a relatively low expression of non-selective cation channels, such as ionotropic P2X, unpaired gap junction hemichannels and TRP channels .
In summary, neonatal astrocytes are electrophysiologically homogeneous, characterized by expression of a distinct set of rectifying K+ conductances. This ion channel expression profile differs substantially from the passive conductance observed from proliferating astrocytes in the later postnatal developing brain and from mature astrocytes [2, 5].
Neonatal astrocytes form discrete gap junction coupling
During the postnatal brain development, the number of astrocytes expands 6–8 folds in the postnatal brain . Additionally, in the neonatal brain, astrocytes converge from difference sources [10, 48]. A fundamental question to be answered is whether the nascent astrocytes connect with each other through gap junctions and achieve a syncytial network as mature astrocytes do . To answer this important question, we focused on the newborn astrocytes in stratum radiatum to determine how they establish cell-to-cell coupling in their early life. Because we have previously demonstrated that electrical coupling is more sensitive than the dye coupling method , electrical coupling was used in the present study to detect gap junction coupling.
In contrast to astrocytes in the adult hippocampus, neonatal astrocytes form discrete cell-to-cell coupling; the electrical coupling was detected in only 74 % of the recorded pairs, suggesting newly produced astrocytes are uncoupled in embryonic and early neonatal brain. Further evidence in support of this notion include the following. First, the percentage of neonatal PAs, resulting from increasing gap junction coupling, increases with age and the electrical coupling was detected from nearly all the PAs (92 %) compared to a substantially low percentage of VRAs (60 %) (Fig. 6). Second, whether the newborn astrocytes show electrical coupling does not depend on their pair distances, and coupling can be formed in homotypic or heterotypic electrophysiological phenotypes (Fig. 6). Third, a substantial variation in coupling coefficient exhibited among recording pairs, and this variation does not show any association with pair distances (Fig. 6). Interestingly, in the P6-13 postnatal cortex, locally produced astrocytes are electrically passive, functionally mature and integrated into a network during symmetrical cell division . The differences between this study and ours suggest that neonatal astrocytes differ significantly in their basic electrophysiological properties and the manners in forming cell-to-cell coupling and integration into a syncytial network.
Neonatal astrocytes are deficient in their K+ uptake capacity
In the present study, a substantially low leak K+ conductance was detected from neonatal astrocytes. This was indicated by 1) a 6-fold lower inward K+ current density than that of outward, and 2) a significantly large and variable R in in VRAs (Fig. 3). By altering the K+ driving force, we show that the ability of neonatal astrocytes in accumulating intracellular K+ concentration is ~50 % less than that of mature astrocytes (Fig. 7).
It should be noted that lack of a maturely established syncytium to achieve a “sustained K+ uptake” mode would further undermine the K+ uptake and spatial redistribution in the neonatal brain . How the observed difference in K+ conductance and gap junction coupling would be etiologically relevant to the neurological disorders in the neonatal brain needs to be further explored.
Neonatal astrocytes and reactive astrocytes in neurological disorders
Neonatal astrocytes seemingly resemble the reactive astrocytes induced in various pathological conditions in several aspects. First, similar to proliferating neonatal astrocytes, reactive astrocytes reenter the cell cycle for proliferation . Second, the proliferating reactive astrocytes showed virtually no gap junction coupling in dye coupling analysis . Third, neonatal astrocytes predominantly express voltage-gated ion channels, and similar alternation in K+ conductance expression has been reported in lesion induced reactive astrocytes [58, 59, 60]. In cultured spinal cord astrocytes, K+ channels have been demonstrated to play a role in cell cycle progression . Thus, the characteristics of neonatal astrocytes described in this study should serve as an important foundation for further examination into the extent to which reactive astrocytes recapture the features of neonatal astrocytes and their pathological and therapeutic implications [62, 63].
Neonatal astrocytes homogeneously express a distinct set of rectifying K+ conductances, form discrete cell-to-cell coupling and progressively integrate into a syncytial network with age. The passive behavior in some of the neonatal astrocytes is solely attributable to gap junction coupling. The low density expression of the leak K+ conductance and lack of a structurally mature syncytium result in a deficient K+ homeostasis capacity in neonatal astrocytes. The similarities between neonatal and reactive astrocytes favor a notion that pathological conditions may dedifferentiate mature astrocytes into their neonatal stage in neurological disorders.
This study does not need an approval of an ethical committee or consent for publication.
This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
This work is sponsored by grants from National Institute of Neurological Disorders and Stroke RO1NS062784 (MZ), Natural Science Foundation of China (81371212), and a start-up fund from The Ohio State University College of Medicine (to MZ). Shiying Zhong is a recipient of a scholarship from the Chinese Scholarship Council (21406260143).
- 6.Cahoy JD, Emery B, Kaushal A, Foo LC, Zamanian JL, Christopherson KS, Xing Y, Lubischer JL, Krieg PA, Krupenko SA, et al. A transcriptome database for astrocytes, neurons, and oligodendrocytes: a new resource for understanding brain development and function. J Neurosci. 2008;28:264–78.CrossRefPubMedGoogle Scholar
- 12.Tien AC, Tsai HH, Molofsky AV, McMahon M, Foo LC, Kaul A, Dougherty JD, Heintz N, Gutmann DH, Barres BA, Rowitch DH. Regulated temporal-spatial astrocyte precursor cell proliferation involves BRAF signalling in mammalian spinal cord. Development. 2012;139:2477–87.CrossRefPubMedPubMedCentralGoogle Scholar
- 24.Du Y, Kiyoshi CM, Wang Q, Wang W, Ma B, Alford CC, Zhong S, Wan Q, Chen H, Lloyd EE, Bryan RM. Genetic deletion of TREK-1 or TWIK-1/TREK-1 potassium channels does not alter the basic electrophysiological properties of mature hippocampal astrocytes in situ. Front Cell Neurosci. 2016. doi: 10.3389/fncel.2016.00013.Google Scholar
- 42.Hille B. Ion channels of excitable cells. Sunderland: Sinauer; 2001.Google Scholar
- 44.Wang W, Kiyoshi CM, Du Y, Ma B, Alford CC, Chen H, Zhou M. mGluR3 Activation Recruits Cytoplasmic TWIK-1 Channels to Membrane that Enhances Ammonium Uptake in Hippocampal Astrocytes. Mol Neurobiol. 2015. [Epub ahead of print].Google Scholar
- 48.Ge WP, Jia JM. Local production of astrocytes in the cerebral cortex. Neuroscience. 2015. [Epub ahed of print].Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.