Induction of long-term oscillations in the γ frequency band by nAChR activation in rat hippocampal CA3 area.

The hippocampal neuronal network oscillation at γ frequency band (γ oscillation) is generated by the precise interaction between interneurons and principle cells. γ oscillation is associated with attention, learning and memory and is impaired in the diseased conditions such as Alzheimer's disease (AD) and schizophrenia. Nicotinic acetylcholine receptor (nAChR) plays an important role in the regulation of hippocampal neurotransmission and network activity. It is not known whether nicotine modulates plasticity of network activity at γ oscillations in the hippocampus. In this study we investigated the effects of nicotine on the long-term changes of KA-induced γ oscillations. We found that hippocampal γ oscillations can be enhanced by a low concentration of nicotine (1µM), such an enhancement lasts for hours after washing out of nicotine, suggesting a form of synaptic plasticity, named as long-term oscillation at γ frequency band (LTOγ). Nicotine-induced LTOγ was mimicked by the selective α4ß2 but not by α7 nAChR agonist and was involved in N-methyl-d-aspartate (NMDA) receptor activation as well as depended on excitatory and inhibitory neurotransmission. Our results indicate that nAChR activation induced plasticity in γ oscillation, which may be beneficial for the improvement of cognitive deficiency in AD and schizophrenia.

CD34 positive cells seeded on small caliber man-made vascular grafts exhibit increased antithrombogenic property compared with unfractioned mononuclear cells.

AIM: The aim of this study was to compare the therapeutic potential of purified CD34+ cells with that of unfractioned mononuclear cells (MNCs) for the antithrombogenic property after seeding on the small caliber man-made grafts. METHODS: Unfractioned MNCs and CD34+ cells were isolated from canine bone marrow. Differentiation of CD34 cells and unfractioned MNCs into endothelial cells were examined by CD31and vWF immunohistochemistry or immunofluorescence stain, endothelial cell function were evaluated via low-density lipoprotein (ac-LDL) - DiL incorpration and in vitro angiogenesis assay. Platelet adhesion assay was performed to determine antiplatelet adhesion property of the cells in vitro. Equal number of both cells were seeded onto the luminal surface of small caliber man-made grafts and implanted to replace a segment of common carotid artery. At different time points (24 h, 72 h, and 1 week) the grafts were retrieved. HE staining and SEM exam were performed. RESULTS: CD34+ cells acquired significantly more CD31 and VWF expression, increased angiogenic potential and low-density lipoprotein (ac-LDL) incorporation compared to unfractioned MNCs under the induction of VEGF. More platelets were found to adhere to the surface of unfractioned MNCs group than to the CD34+ cell group. In vivo study demonstrated that more platelet adhesion and thrombus formation were observed in the unfractioned MNCs group rather than the CD34+ group. All the grafts in both groups were patent after implantation, except one graft seeded with unfractioned MNCs, occluded at 1 week. Statistically lower ratio of thrombi was found in the CD34+ cell seeding group at 24 h and 1 week after implantation, compared with the unfractioned MNCs one (P<0.05). CONCLUSION: CD34+ cell exerted better antithrombogenic property than unfractioned MNCs after seeding onto the small caliber vessel grafts.

Nicotine induction of theta frequency oscillations in rodent hippocampus in vitro.

The hippocampus is an area important for learning and memory and exhibits prominent and behaviourally relevant theta (4-12 Hz) and gamma (30-100 Hz) frequency oscillations in vivo. Hippocampal slices produce similar types of oscillatory activity in response to bath-application of neurotransmitter receptor agonists. The medial septum diagonal band area (MS/DB) provides both a cholinergic and GABAergic projection to the hippocampus, and although it plays a major role in the generation and maintenance of the hippocampal theta rhythm in vivo, there is evidence for intrinsic theta generation mechanisms in the hippocampus, especially in area CA3. The aim of this study was to examine the role of the nicotinic receptor (nAChR) in the induction of oscillatory field activity in the in vitro preparation of the rat hippocampus. Bath-application of a low concentration of nicotine (1 muM) to transversely-cut hippocampal slices produced persistent theta-frequency oscillations in area CA3 of the hippocampus. These oscillations were reduced by both GABA(A) receptor antagonists and ionotropic glutamate receptor antagonists, indicating the involvement of local GABAergic and glutamatergic neurons in the production of the rhythmic theta activity. The nicotine-induced theta activity was inhibited by non-selective nAChR antagonists and partially by an alpha7* nAChR antagonist. The induction of theta frequency oscillations in CA3 by nicotine was mimicked alpha7* nAChR agonists but not by non-alpha7* nAChR agonists. In conclusion, theta activity in the hippocampus may be promoted by tonic stimulation of alpha7* nAChRs, possibly via selective stimulation of theta-preferring interneurons in the hippocampus that express post-synaptic alpha7* nAChRs.

Numb-mediated neurite outgrowth is isoform-dependent, and requires activation of voltage-dependent calcium channels.

Numb is an evolutionarily conserved protein that controls the differentiation of neuronal progenitor cells by unknown mechanisms. Here we report that the neural cells expressing Numb isoforms with short phosphotyrosine-binding (SPTB) domain undergo extensive neurite outgrowth, an effect that can be blocked by voltage-gated Ca2+ channel (VGCC) inhibitor or by Ca2+ chelator. In contrast, tyrosine kinase inhibitor, genistein, and selective receptor tyrosine kinase (TrkA) inhibitor, K252alpha did not affect SPTB Numb-mediated neurite outgrowth. MAP kinase inhibitor, PD98059 partially reduced SPTB Numb-mediated neurite outgrowth. Cells expressing SPTB Numbs exhibit increased whole-cell Ca2+ current densities (ICa) which can be prevented by preincubation of either nifedipine or PD98095. Cells expressing LPTB Numbs expressed little ICa (density) and were not able to grow neurites. Our results indicate that Ca2+ influx through VGCC may be required for SPTB Numb-mediated neurite outgrowth, suggesting that Numb promotes neuronal differentiation by a mechanism involving PTB domain-specific regulation of Ca2+ influx and MAP kinase activation.