Xiangping He

Stromal cell derived factor-1 acutely promotes neural progenitor cell proliferation in vitro by a mechanism involving the ERK1/2 and PI-3K signal pathways☆

Stromal cell derived factor‐1 (SDF‐1), a member of the chemotactic cytokine family, has attracted attention in recent years. It participates in diverse processes such as the regulation of neuronal migration and activation of CD4+ T cells; it is also a co‐receptor for human immunodeficiency virus‐1 (HIV‐1). Here, we show that the proliferation of neural progenitor cells dissociated from rat cortex and cultured in vitro with basic fibroblast growth factor (bFGF) is stimulated by SDF‐1. PD98059 and wortmannin, which are, respectively, specific inhibitors of the extracellular regulated kinase1/2 (ERK1/2) and phosphatidylinositol‐3 kinase (PI‐3K) signal pathways, markedly attenuate this stimulation of proliferation. These findings indicate that SDF‐1 acutely promotes the proliferation of NPCs in vitro involving the ERK1/2 and PI‐3 kinase pathways, suggesting that it plays a basic role in the development of neural progenitors.

Effects of insulin-like growth factor 1 on synaptic excitability in cultured rat hippocampal neurons

Insulin-like growth factor 1 (IGF-1) has important functions in the brain, including metabolic, neurotrophic, neuromodulatory and neuroendocrine actions, and it also prevents beta amyloid-induced death of hippocampal neurons. However, its functions in the synaptic excitability remain uncertain. Here we investigated the effects of IGF-1 on synaptic excitability in cultured rat hippocampal neurons using whole-cell patch clamp recordings. Incubation the hippocampal neurons with different concentrations of IGF-1 for 24 h or 30 min significantly increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs), but had no effect on the frequency of miniature EPSCs (mEPSCs) and spontaneous inhibitory postsynaptic currents (sIPSCs). The mean amplitudes, rise, and decay kinetics of sEPSCs, mEPSCs, and sIPSCs were not significantly affected by IGF-1, indicating that IGF-1 increased the probability of neurotransmitter release but did not modulate postsynaptic receptors. The effects of IGF-1 were mediated by mitogen-activated protein kinase (MAPK). IGF-1 activated the ERK1/2 signaling pathway in cultured hippocampal neurons, and the inhibitor PD98059 blocked the enhancement of sEPSCs induced by IGF-1. These results demonstrated the regulatory function of IGF-1 on synaptic excitability in hippocampal neurons and its underlying signaling mechanism.

Calcium near the release site is essential for basal ACh release in Xenopus

Extracellular calcium is essential for neurotransmitter release, but the detailed mechanism by which Ca2+ regulates basal synaptic release has not yet been fully explored. In this study, calcium imaging and the whole‐cell patch‐clamp technique were used to investigate the role of Ca2+ in basal acetylcholine (ACh) release in the Xenopus neuromuscular junction and in isolated myocytes exogenously loaded with ACh. Carried out in normal and Ca2+‐free extracellular solution, the results indicate that Ca2+ near the release site is essential for basal neurotransmitter release.

Astragaloside IV inhibits spontaneous synaptic transmission and synchronized Ca2+ oscillations on hippocampal neurons.

AbstractAim:To investigate the changes in the spontaneous neuronal excitability induced by astragaloside IV (AGS-IV) in the cultured hippocampal network.Methods:Hippocampal neurons in culture for 9-11 d were used for this study. The spontaneous synaptic activities of these hippocampal neurons were examined by Ca2+ imaging and whole-cell patch-clamp techniques. In total, 40 mg/L AGS-IV dissolved in DMSO and 2 mL/L DMSO were applied to the neurons under a microscope while the experiments were taking place.Results:AGS-IV inhibited the frequencies of synchronized spontaneous Ca2+ oscillations to 59.39%±3.25% (mean±SEM), the spontaneous postsynaptic currents to 43.78%±7.72% (mean±SEM), and the spontaneous excitatory postsynaptic currents to 49.25%±7.06% (mean±SEM) of those of the control periods, respectively, at 16 min after the AGS-IV applications. AGS-IV also decreased the peak values of the voltage-gated K+ and Na+ channel currents at that time point.Conclusion:These results indicate that AGS-IV suppresses the spontaneous neuronal excitabilities effectively. Such a modulation of neuronal activity could represent new evidence for AGS-IV as a neuroprotector.

Effects of insulin-like growth factor 1 on voltage-gated ion channels in cultured rat hippocampal neurons

Insulin-like growth factor 1 (IGF-1) has important functions in the brain, including metabolic, neurotrophic, neuromodulatory, and neuroendocrine actions, and it is also prevents amyloid beta-induced death of hippocampal neurons. However, its functions on the voltage-gated ion channels in hippocampus remain uncertain. In the present study, we investigated the effects of IGF-1 on voltage-gated potassium, sodium, and calcium channels in the cultured rat hippocampal neurons using the whole-cell patch clamp recordings. Following incubation with different doses of IGF-1 for 24 h, a block of the peak transient A-type K+ currents amplitude (IC50: 4.425 ng/ml, Hill coefficient: 0.621) was observed. In addition, after the application of IGF-1, the amplitude of high-voltage activated Ca2+ currents significantly increased but activation kinetics did not significantly alter (V1/2: -33.45 +/- 1.32 mV, k = 6.16 +/- 1.05) compared to control conditions (V1/2: -33.19 +/- 2.28 mV, k = 7.26 +/- 1.71). However, the amplitude of Na+, K+, and low-voltage activated Ca2+ currents was not affected by the application of IGF-1. These data suggest that IGF-1 inhibits transient A-type K+ currents and enhances high-voltage-activated Ca2+ currents, but has no effects on Na+ and low-voltage-activated Ca2+ currents.

A role of insulin-like growth factor 1 in β amyloid-induced disinhibition of hippocampal neurons

In the present study we investigated the effects of beta amyloid (Abeta) on inhibitory synaptic transmission in the cultured hippocampal neurons using whole-cell patch-clamp recordings and immunocytochemistry, and examined the role of insulin-like growth factor 1 (IGF-1). Incubation with 4 microM Abeta25-35 for 24 h significantly decreased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs), but had no effect on the mean amplitude. Pretreatment with 10 ng/ml IGF-1 for 24h prior to Abeta25-35 exposure blocked Abeta-induced disinhibition of hippocampal neurons. The frequency and mean amplitude of miniature IPSC (mIPSCs) were not significantly affected by Abeta. The rise and decay kinetics of sIPSCs and mIPSCs were similar for the control and Abeta25-35-treated hippocampal neurons. Immunocytochemistry showed no changes in the ratio of gamma-aminobutyric acid (GABA) positive cells subsequent to treatment with Abeta, or IGF-1. Together these data suggest that Abeta-induced the disinhibition in cultured hippocampal neurons, whereas IGF-1 could block this effect.

Effect of new O-superfamily conotoxin SO3 on sodium and potassium currents of cultured hippocampal neurons

The effects of a new O-superfamily conotoxin SO3 on sodium and potassium currents were examined in cultured rat hippocampal neurons using the whole-cell patch clamp technique. SO3 caused a concentration-dependent, rapidly developing and reversible inhibition of sodium currents (I(Na)). The IC(50) value for the blockage of I(Na) was calculated to be 0.49 and the Hill coefficient was 1.7. Using electrophysiological and pharmacological protocols, transient A-type potassium currents (I(A)) and delayed rectifiers potassium currents (I(K)) were isolated. SO3 caused a concentration-dependent, and reversible inhibition of I(K). The IC(50) value for the blockage of I(K) was calculated to be 1.6 and the Hill coefficient was 0.6, with no significant effect on I(A). These results indicate that SO3 can selectively inhibit neuronal sodium and potassium currents.

Reversine inhibits spontaneous synaptic transmission in cultured rat hippocampal neurons.

The dedifferentiation agent “reversine” [2‐(4‐morpholinoanilino)‐N6‐cyclohexyladenine 2], which can induce myogenic lineage‐committed cells to become multipotent mesenchymal progenitor cells, was discovered by Shuibing Chen et al. in 2003. But its effects on neurons were unknown. Using patch‐clamp technique, we found that reversine inhibits spontaneous synaptic transmission in cultured rat hippocampal neurons without influencing the dynamics function of potassium, sodium and calcium channels. This result suggests that reversine may also act as a dedifferentiation agent in neurons, and inhibiting the synaptic transmission maybe the early step of neuronal dedifferentiation.

Effect of Calcium on Spontaneous Quantal Transmitter Secretion from ACh-Loaded Myocytes *

Abstract Spontaneous secretions occur in both neurons and non-neuronal cells, and calcium is important for these secretion processes. However, the detailed roles of calcium on the secretions have not yet been identified. In the present study, cultured Xenopus myocytes loaded with exogenous acetylcholine (ACh) into the cytoplasm in the absence of extracellular Ca2+ undergo spontaneous quantal ACh secretion as detected by the appearance of pulsatile miniature endplate currents. Analysis of the frequencies, amplitudes, and time courses of these currents suggests that similar cellular mechanisms are involved in the secretions of ACh in normal medium and Ca2+-free solution. Various doses of ryanodine were used to regulate the intracellular Ca2+ to different levels. The spontaneous ACh secretion from myocytes in Ca2+-free medium was decreased by reducing intracellular Ca2+ levels and enhanced by increasing cytosolic Ca2+ levels. These observations demonstrate that the spontaneous secretion from isolated myocytes and the effect of ryanodine on ACh-loaded cells are both independent of extracellular Ca2+ while Ca2+ in the sarcoplasmic reticulum plays a crucial role in the secretions.

Spontaneous Neurotransmitter Release Depends on Intracellular Rather than ER Calcium Stores in Cultured Xenopus NMJ

Abstract Calcium ions are important in many vital neuron processes, including spontaneous neurotransmitter release. Extracellular calcium has long been known to be related to spontaneous neurotransmitter release, but the detailed mechanism for the effect of intracellular Ca2+ on synaptic release has not yet been understood. In this research, 1,2-bis-(o-aminophenoxy)-ethane-N, N, N’, N’-tetraacetic acid tetraacetoxy-methyl ester (BAPTA-AM) was used to combine with cytosolic free Ca2+ in a calcium free medium of cultured Xenopus neuromuscular junctions (NMJ). The spontaneous synaptic current (SSC) frequency was obviously reduced. Then, drugs were applied to interrupt and activate the Ca2+ release channels in the endoplasmic reticulum (ER) membrane, but the SSC frequency was not affected. The results show that spontaneous neurotransmitter release depends on intracellular rather than ER calcium in cultured Xenopus NMJ without extracellular calcium.