New hippocampal neurons are continuously generated in the adult brain. Here, we demonstrate that lipopolysaccharide-induced inflammation, which gives rise to microglia activation in the area where the new neurons are born, strongly impairs basal hippocampal neurogenesis in rats. The increased neurogenesis triggered by a brain insult is also attenuated if it is associated with microglia activation caused by tissue damage or lipopolysaccharide infusion. The impaired neurogenesis in inflammation is restored by systemic administration of minocycline, which inhibits microglia activation. Our data raise the possibility that suppression of hippocampal neurogenesis by activated microglia contributes to cognitive dysfunction in aging, dementia, epilepsy, and other conditions leading to brain inflammation. In the adult mammalian brain, neural progenitor cells located in the subgranular zone (SGZ) of the dentate gyrus (DG) generate thousands of new neurons each day (1). These neurons develop the morphological and functional properties of dentate granule cells and become integrated into existing neuronal circuitries (2). The role of neurogenesis for hippocampal function is still unclear, but some experimental evidence suggests its involvement in memory formation (3) and mood regulation (4). Impairment of hippocampal neurogenesis may be linked to the cognitive decline in aging, Alzheimer's disease (AD), and major depression (5-7).Brain inflammation probably plays an important role in the pathogenesis of chronic neurodegenerative disorders like AD and ParkinsonЈs disease (8, 9). Neurodegeneration caused by inflammation involves activation of the brain's resident immune cells, the microglia, which produce a large number of proinflammatory factors (10-12). Also, acute brain insults, e.g., stroke and status epilepticus (SE), are linked to inflammation (13,14), which contributes to the propagation of the neuropathological events (9, 15). These insults trigger increased neurogenesis in the SGZ (16)(17)(18)(19). After severe SE, there is an 80% loss of newly formed dentate neurons (20), which raises the possibility that the associated inflammatory response is deleterious for hippocampal neurogenesis.Here, we show that the microglia activation associated with inflammation impairs both basal and insult-induced hippocampal neurogenesis. We find that systemic administration of the tetracycline derivative minocycline, which specifically inhibits microglia activation, is an effective treatment to restore neurogenesis suppressed by inflammation. Materials and MethodsSurgery and Induction of SE. Male Sprague-Dawley rats were implanted with a stimulating͞recording electrode into the right ventral hippocampus [coordinates: 4.8 mm caudal and 5.2 mm lateral to bregma, 6.3 mm ventral to dura, and toothbar at Ϫ3.3 mm (21)] under pentobarbital or halothane anesthesia. In 37 animals, a brain infusion cannula (Alzet, Palo Alto, CA) was also placed intracortically on the right side of the brain (2 mm caudal and 1.2 mm lateral to bregma and 2.6 mm ve...

Tumor necrosis factor-␣ (TNF-␣) is a proinflammatory cytokine, acting through the TNF-R1 and TNF-R2 receptors. The two receptors have been proposed to mediate distinct TNF-␣ effects in the CNS, TNF-R1 contributing to neuronal damage and TNF-R2 being neuroprotective. Whether TNF-␣ and its receptors play any role for neurogenesis in the adult brain is unclear. Here we used mouse models with loss of TNF-R1 and TNF-R2 function to establish whether signaling through these receptors could influence hippocampal neurogenesis in vivo under basal conditions, as well as after status epilepticus (SE), which is associated with inflammation and elevated TNF-␣ levels. Notably, in the intact brain, the number of new, mature hippocampal neurons was elevated in TNF-R1Ϫ/Ϫ and TNF-R1/R2 Ϫ/Ϫ mice, whereas no significant changes were detected in TNF-R2 Ϫ/Ϫ mice. Also after SE, the TNF-R1 Ϫ/Ϫ and TNF-R1/R2 Ϫ/Ϫ mice produced more new neurons. In contrast, the TNF-R2 Ϫ/Ϫ mice showed reduced SE-induced neurogenesis. Cell proliferation in the dentate subgranular zone was elevated in TNF-R1 Ϫ/Ϫ and TNF-R1/R2 Ϫ/Ϫ mice both under basal conditions and after SE. The TNF-R2 Ϫ/Ϫ mice either showed no change or minor decrease of cell proliferation. TNF-R1 and TNF-R2 receptors were expressed by hippocampal progenitors, as assessed with reverse transcription-PCR on sorted or cultured cells and immunocytochemistry on cultures. Our data reveal differential actions of TNF-R1 and TNF-R2 signaling in adult hippocampal neurogenesis and identify for the first time TNF-R1 as a negative regulator of neural progenitor proliferation in both the intact and pathological brain.

Neural progenitors in the adult dentate gyrus continuously produce new functional granule cells. Here we used whole-cell patch-clamp recordings to explore whether a pathological environment influences synaptic properties of new granule cells labeled with a GFP-retroviral vector. Rats were exposed to a physiological stimulus, i.e., running, or a brain insult, i.e., status epilepticus, which gave rise to neuronal death, inflammation, and chronic seizures. Granule cells formed after these stimuli exhibited similar intrinsic membrane properties. However, the new neurons born into the pathological environment differed with respect to synaptic drive and short-term plasticity of both excitatory and inhibitory afferents. The new granule cells formed in the epileptic brain exhibited functional connectivity consistent with reduced excitability. We demonstrate a high degree of plasticity in synaptic inputs to adult-born new neurons, which could act to mitigate pathological brain function.

The perspectives offered by vertical arrays of nanowires for biosensing applications in living cells depend on the access of individual nanowires to the cell interior. Recent results on electrical access and molecular delivery suggest that direct access is not always obtained. Here, we present a generic approach to directly visualize the membrane conformation of living cells interfaced with nanowire arrays, with single nanowire resolution. The method combines confocal z-stack imaging with an optimized cell membrane labelling strategy which was applied to HEK293 cells interfaced with 2-11 μm long and 3-7 μm spaced nanowires with various surface coatings (bare, aminosilane-coated or polyethyleneimine-coated indium arsenide). We demonstrate that, for all commonly used nanowire lengths, spacings and surface coatings, nanowires generally remain enclosed in a membrane compartment, and are thereby not in direct contact with the cell interior.

Arrays of nanowires (NWs) are currently being established as vehicles for molecule delivery and electrical- and fluorescence-based platforms in the development of biosensors. It is conceivable that NW-based biosensors can be optimized through increased understanding of how the nanotopography influences the interfaced biological material. Using state-of-the-art homogenous NW arrays allow for a systematic investigation of how the broad range of NW densities used by the community influences cells. Here it is demonstrated that indium arsenide NW arrays provide a cell-promoting surface, which affects both cell division and focal adhesion up-regulation. Furthermore, a systematic variation in NW spacing affects both the detailed cell morphology and adhesion properties, where the latter can be predicted based on changes in free-energy states using the proposed theoretical model. As the NW density influences cellular parameters, such as cell size and adhesion tightness, it will be important to take NW density into consideration in the continued development of NW-based platforms for cellular applications, such as molecule delivery and electrical measurements.

Inflammation influences several steps of adult neurogenesis, but whether it regulates the functional integration of the new neurons is unknown. Here, we explored, using confocal microscopy and whole-cell patch-clamp recordings, whether a chronic inflammatory environment affects the morphological and electrophysiological properties of new dentate gyrus granule cells, labeled with a retroviral vector encoding green fluorescent protein. Rats were exposed to intrahippocampal injection of lipopolysaccharide, which gave rise to longlasting microglia activation. Inflammation caused no changes in intrinsic membrane properties, location, dendritic arborization, or spine density and morphology of the new cells. Excitatory synaptic drive increased to the same extent in new and mature cells in the inflammatory environment, suggesting increased network activity in hippocampal neural circuitries of lipopolysaccharide-treated animals. In contrast, inhibitory synaptic drive was more enhanced by inflammation in the new cells. Also, larger clusters of the postsynaptic GABA A receptor scaffolding protein gephyrin were found on dendrites of new cells born in the inflammatory environment. We demonstrate for the first time that inflammation influences the functional integration of adult-born hippocampal neurons. Our data indicate a high degree of synaptic plasticity of the new neurons in the inflammatory environment, which enables them to respond to the increase in excitatory input with a compensatory upregulation of activity and efficacy at their afferent inhibitory synapses.

The endeavor of exploiting arrays of vertical one-dimensional (1D) nanostructures (NSs) for cellular applications has recently been experiencing a pronounced surge of activity. The interest is rooted in the intrinsic properties of high-aspect-ratio NSs. With a height comparable to a mammalian cell, and a diameter 100-1000 times smaller, NSs should intuitively reach far into a cell and, due to their small diameter, do so without compromising cell health. Single NSs would thus be expedient for measuring and modifying cell response. Further organization of these structures into arrays can provide up-scaled and detailed spatiotemporal information on cell activity, an achievement that would entail a massive leap forward in disease understanding and drug discovery. Numerous proofs-of-principle published recently have expanded the large toolbox that is currently being established in this rapidly advancing field of research. Encouragingly, despite the diversity of NS platforms and experimental conditions used thus far, general trends and conclusions from combining cells with NSs are beginning to crystallize. This review covers the broad spectrum of NS materials and dimensions used; the observed cellular responses with specific focus on adhesion, morphology, viability, proliferation, and migration; compares the different approaches used in the field to provide NSs with the often crucial cytosolic access; covers the progress toward biological applications; and finally, envisions the future of this technology. By maintaining the impressive rate and quality of recent progress, it is conceivable that the use of vertical 1D NSs may soon be established as a superior choice over other current techniques, with all the further benefits that may entail.

A method to fabricate inexpensive and transparent nanowire impalement devices is invented based on CuO nanowire arrays grown by thermal oxidation. By employing a novel process the nanowires are transferred to a transparent, cell-compatible epoxy membrane. Cargo delivery and detailed cell-nanowire interaction studies are performed, revealing that the cell plasma membrane tightly wraps the nanowires, while cell membrane penetration is not observed. The presented device offers an efficient investigation platform for further optimization, leading towards a simple and versatile impalement delivery system.