The Role of Adult-Born Neurons in the Constantly Changing Olfactory Bulb Network

The adult mammalian brain is remarkably plastic and constantly undergoes structurofunctional modifications in response to environmental stimuli. In many regions plasticity is manifested by modifications in the efficacy of existing synaptic connections or synapse formation and elimination. In a few regions, however, plasticity is brought by the addition of new neurons that integrate into established neuronal networks. This type of neuronal plasticity is particularly prominent in the olfactory bulb (OB) where thousands of neuronal progenitors are produced on a daily basis in the subventricular zone (SVZ) and migrate along the rostral migratory stream (RMS) towards the OB. In the OB, these neuronal precursors differentiate into local interneurons, mature, and functionally integrate into the bulbar network by establishing output synapses with principal neurons. Despite continuous progress, it is still not well understood how normal functioning of the OB is preserved in the constantly remodelling bulbar network and what role adult-born neurons play in odor behaviour. In this review we will discuss different levels of morphofunctional plasticity effected by adult-born neurons and their functional role in the adult OB and also highlight the possibility that different subpopulations of adult-born cells may fulfill distinct functions in the OB neuronal network and odor behaviour

Risk Assessment of Heavy Metals Pollution in Urban Environment

This chapter summarizes the results of heavy metal’s human health and ecological risk assessment of multipurpose ecogeochemical studies performed by the Center for Ecological-Noosphere Studies of the National Academy of Sciences of the Republic of Armenia in the young industrial cities of Yerevan and Gyumri and in an old mining region of the city of Kajaran. According to the results children non-carcinogenic risk values were greater than permissible limit of 1 indicating the possibility of an adverse health effect in the whole area of all studied cities. Among all studied elements, the riskiest were those previously identified as primary pollutants. It has also been shown that in biogeochemical provinces, where mining activities and agricultural land of rural communities are spatially juxtaposed, health risk assessment should include all possible exposure pathways. Otherwise, underestimation of possible health risk will take place. Heavy metals in soils of Yerevan and Gyumri are also an ecological risk factor and the riskiest elements having significant contribution to the overall risk and are those (Hg, Cd, and Pb) with the high level of toxicity

Reactive Glia in the Injured Brain Acquire Stem Cell Properties in Response to Sonic Hedgehog

SummaryAs a result of brain injury, astrocytes become activated and start to proliferate in the vicinity of the injury site. Recently, we had demonstrated that these reactive astrocytes, or glia, can form self-renewing and multipotent neurospheres in vitro. In the present study, we demonstrate that it is only invasive injury, such as stab wounding or cerebral ischemia, and not noninvasive injury conditions, such as chronic amyloidosis or induced neuronal death, that can elicit this increase in plasticity. Furthermore, we find that Sonic hedgehog (SHH) is the signal that acts directly on the astrocytes and is necessary and sufficient to elicit the stem cell response both in vitro and in vivo. These findings provide a molecular basis for how cells with neural stem cell lineage emerge at sites of brain injury and imply that the high levels of SHH known to enter the brain from extraneural sources after invasive injury can trigger this response

Characteristics of DNA polymerase I from an extreme thermophile, Thermus scotoductus strain K1

Several native and engineered heat-stable DNA polymerases from a variety of sources are used as powerful tools in different molecular techniques, including polymerase chain reaction, medical diagnostics, DNA sequencing, biological diversity assessments, and in vitro mutagenesis. The DNA polymerase from the extreme thermophile, Thermus scotoductus strain K1, (TsK1) was expressed in Escherichia coli, purified, and characterized. This enzyme belongs to a distinct phylogenetic clade, different from the commonly used DNA polymerase I enzymes, including those from Thermus aquaticus and Thermus thermophilus. The enzyme demonstrated an optimal temperature and pH value of 72–74°C and 9.0, respectively, and could efficiently amplify 2.5 kb DNA products. TsK1 DNA polymerase did not require additional K+ ions but it did need Mg2+ at 3–5 mM for optimal activity. It was stable for at least 1 h at 80°C, and its half-life at 88 and 95°C was 30 and 15 min, respectively. Analysis of the mutation frequency in the amplified products demonstrated that the base insertion fidelity for this enzyme was significantly better than that of Taq DNA polymerase. These results suggest that TsK1 DNA polymerase could be useful in various molecular applications, including high-temperature DNA polymerization.publishedVersio

Integrating new neurons into the adult olfactory bulb: joining the network, life-death decisions, and the effects of sensory experience.

International audienceIn contrast to the situation in the developing brain, neurons born during adulthood must integrate into established neuronal networks characterized by ongoing activity. For sensory systems, this neuronal activity is driven mainly by external stimuli that can lead to experience-dependent morpho-functional changes in adult circuits. Here, we describe new insights into the mechanisms by which sensory experience might govern the targeting of adult-generated neurons to appropriate regions, their differentiation into distinct neuronal subtypes, and finally their survival in the adult olfactory bulb. We propose not only that neurogenesis depends on the degree of sensory experience, but also that new neurons bring unique features to the operational network, allowing a continuous adjustment of information processing in response to an ever-changing external word

GEOCHEMISTRY OF ATMOSPHERIC DUST ON THE TERRITORY OF THE CITY OF YEREVAN

This research is focused on the level of heavy metal contents in dust of a near-ground layer of atmosphere. The dust load level was evaluated as medial. Indicated was a quality composition of dominating dust pollutants. The level of summary load of metals was low

Inhibitory interneurons in the olfactory bulb: from development to function.

International audienceIdentifying and defining the characteristic features of the inhibitory neurons in the nervous system has become essential for achieving a cellular understanding of complex brain activities. For this, the olfactory bulb is ideally suited because it is readily accessible, it is a laminated structure where local interneurons can be easily distinguished from projecting neurons, and, more important, GABAergic interneurons are continuously replaced. How the newly generated neurons integrate into a preexisting neural network and how basic network functions are maintained when a large percentage of neurons are subjected to continuous renewal are important questions that have recently received new insights. Here, it is seen that the production of bulbar interneurons is specifically adapted to experience-dependent regulation of adult neural networks. In particular, the authors report the degree of sensitivity of the bulbar neurogenesis to the activity level of sensory inputs and, in turn, how the adult neurogenesis adjusts the neural network functioning to optimize information processing. By maintaining a constitutive neurogenesis sensitive to environmental cues, this neuronal recruitment leads to improving sensory abilities. This review brings together recently described properties and emerging principles of interneuron functions that may convey, into bulbar neuronal networks, a degree of circuit adaptation unmatched by synaptic plasticity alone

Live imaging of adult neural stem cells in freely behaving mice using mini-endoscopes

Summary: During adulthood, the activation of adult neural stem cells (NSCs) has been mostly studied ex vivo in post-mortem tissues or in vivo in anesthetized animals. This protocol presents an approach that allows for the long-term and minimally invasive investigation of adult NSC activation and physiology in freely behaving animals. By combining specific NSC labeling and mini-endoscopic microscopy, live imaging of NSC division and Ca2+ activity can be performed continuously for 2–3 days and even up to several months.For complete details on the use and execution of this protocol, please refer to Gengatharan et al. (2021)