Olfaction

vignette| L'odorat des canidés est réputé être l'un des meilleurs parmi les mammifères. C'est une des raisons qui expliquent qu'ils ont été très utilisés comme chien de chasse, de garde ou de sauveteur. L'olfaction ou l'odorat est le sens qui permet d'analyser les substances chimiques volatiles (odeurs) présentes dans l’air. L'olfaction est un sens vital pour de nombreuses espèces ; il est par exemple utile ou nécessaire pour les activités de recherche alimentaire (chasse, recherche de végétaux appétents), l’évitement des prédateurs, la localisation du lieu de nidification, ponte, reproduction, mise bas, pour la reconnaissance et le marquage du territoire, pour la communication entre individus par messages olfactifs, pour la recherche de partenaires sexuels, et pour la pollinisation des fleurs Ce sens est moins utilisé chez l’être humain que chez de nombreux mammifères pour lesquels il est prépondérant, néanmoins, l'odeur personnelle semble encore jouer un ou plusieurs rôles chez l'

Structure and function of the olfactory bulb microcircuit

Michele Pignatelli

The aim of this study is to contribute to understand the physiology of the Olfactory System through detailed microcircuit investigation, adopting advanced electrophysiological and anatomical techniques. Multiple patch clamp recordings allow understanding the structural foundations supporting the network architecture, the biophysical rules adopted by the microcircuit connectivity and the fine dynamic of the synaptic transmission. The study focuses on the Olfactory Bulb microcircuit as a first neuronal processor of sensory inputs. The excitatory elements of the Olfactory Bulb microcircuit are anatomically defined by affiliation to the same receptive field: the Glomerulus. A correlated subthreshold activity between microcircuit elements defines the physiological signature of the microcircuit. We experimentally addressed three fundamental issues: origin of the correlated subthreshold activity, connectivity rules and dynamic of the synaptic transmission. In the first study we attribute the origin of correlated subthreshold activity to a class of pacemaker cells responsible for the synchronization of the population onset and acting therefore as a timer of the microcircuit response. In the second study we investigated the connectivity rules supporting the interaction between excitatory cells. The tight apposition between gap junctions and chemical synapses on the excitatory cells dendrites allows gap junctions to propagate postsynaptic potentials toward surrounding compartments. The result of the propagation is represented by an enhancement in the amplification of the sensory information and an increase in the speed of the reaction time. In the third study we extensively analyzed the mechanisms of the synaptic transmission and the activity dependent properties of synapses, revealing a potential role for the short-term plasticity in the development of the sensory processing. The results of our investigation are going to constitute the foundation of a database available for high definition multi-compartmental modeling of the Olfactory Bulb network.

EPFL2009

Cellular mechanisms regulating adult neurogenesis and olfactory perception in mice

Thomas Brionne, Maria del Carmen Sandi Perez

In the adult mammalian brain, neural stem cells persist in the subventricular zone and the hippocampus, producing new functional neurons throughout life. Whether and how adult neurogenesis maintains brain function remains highly debated. This question is of primary interest due to the potential therapeutic use of adult neurogenesis in treating neurodegenerative disease. Furthermore, understanding the functional impact of adult neurogenesis on the sense of smell may help deciphering the neural code underlying odor recognition. In this thesis work, we impaired adult neurogenesis using molecular, transgenic and focal irradiation approaches. We assessed olfactory function using in vitro and in vivo electrophysiology, in vivo optical imaging and behavioral psychophysical measurements. We show that reducing the number of newborn interneurons decreases the level of synchronized firing of the projection neurons and leads to impaired olfactory discrimination performance in behaving mice. By isolation of specific olfactory bulb cellular populations, we provide a series of genetic markers differentiating newborn cells from mature neurons that mediate the observed function of olfactory neurogenesis. This thesis work demonstrates that adult neurogenesis represents a new form of plasticity that supports brain function, controlling olfactory information processing already at the first central relay. Finally our data give also insights about the cellular and molecular mechanisms occurring in the olfactory bulb network controlling sensory perception, and help define key genes in the neuronal maturation process.

EPFL2007

Structure and function of the olfactory bulb microcircuit

Michele Pignatelli

EPFL2009

Structure and function of the olfactory bulb microcircuit

Towards a Canonical Microcircuit of the Olfactory Bulb

Cellular mechanisms regulating adult neurogenesis and olfactory perception in mice

Structure and function of the olfactory bulb microcircuit

Cellular mechanisms regulating adult neurogenesis and olfactory perception in mice

Towards a Canonical Microcircuit of the Olfactory Bulb