The Study On In Vivo Bioelectronics Nose For Odor Detection And State-dependent Sensory Gating In Mammalian Olfactory System

The mammalian olfactory system is recognized as one of the most effective chemosensing system due to its extraordinary ability in odor detection.Detection of odors has been applied to many real applications,such as quality control of food products,safety and security,environmental monitoring,medical diagnosis and so on.Based on the research experience in electronic nose and in vitro bioelectronics nose,we recently propose a novel system which we called 'in vivo bioelectronics nose'.In this system,regarding olfactory sensory neurons as primary odor sensors,microelectrode array was chronically implanted in behaving animal's olfactory system,which allows long-term in vivo recording of extracellular action potentials from many neurons.The recorded neurons were considered as chemosensor array.Relevant signal analysis was employed to address the odor representation of neural activities.Here we first investigate its working life,repeatability,reproducibility,specificity and sensitivity,respectively;then,we explore the approach to develop its specificity by recording responses from lateral olfactory tract and specific M72 glomeruli region;further,we investigate its application potential in assessing food freshness and TNT detection.On the other hand,from the aspect of fundamental research,we studied about the state-dependent sensory gating in olfactory system.To address the question why animals can smell the odors in awake state but not in sleep state,we use transgenic mice that express ChR2 in olfactory sensory neurons,and stimulate the neurons by blue laser(473 nm).We find that the light-induced potential and spike firing rate is the same or even larger in sleep state than awake state,which means sensory gating does not rely on response amplitude.However,what we find significantly different is that a large amount of neurons are much more synchronized in awake state,which lead us to conclude that neural synchrony may contribute to olfactory sensory gating.Our main work and innovations are shown as follows:1.Further investigate odor detection and discrimination performance of in vivo bioelectronics nose using monomolecular and natural odorsTo achive the goal of high-sensitive odor detection,we recorded and analyzed the odor-evoked neuronal responses by chronically implanting 16-channel microelectrode into the dorsal aspect of OB.Due to the in vivo condition and intact olfactory system,high-quality neuronal activity could be continuously recorded for at least three weeks,which shows longer working life than in vitro bioelectronics nose.Using PCA to analyze the responses of multiple mitral/tufted cells,we not only effectively classified six monomolecular odors with different function group,but also classified monomolecular odors and natural odors that smell the same.Further,we find food with different storage days could evoke specific spike response pattern.And the detection threshold of carvone was as low as 10-10 mol/L.The results show that the in vivo bioelectronic nose presents a promising platform for specific trace odor detection and determining the degree of food spoilage in real application.2.To explore the approach to develop specificity of in vivo bioelectronic nose by recording lateral olfactory tract responseInstead of recording from olfactory bulb,we extract responses of lateral olfactory tract(LOT)using same method.For LOT is the sole efferent pathway from the OB to the olfactory cortex,the olfactory information is much more integrated in LOT compared with olfactory bulb.The results show that odor-evoked neural activity is much more significant in LOT,which increase the response signal-noise ration and improve the detection sensitivity.In addition,the activities of mitral/tufted cells were modified and integrated by granule cells and other interneurons,which make the response more specific.Thus,by recording from LOT,the specificity of in vivo bioelectronics nose has been improved.3.To investigate sensitivity and specificity of in vivo bioelectronic nose for TNT detection using genetically labeled miceHere,we utilize M72-IRES-tauGFP mouse which expresss green flsorescent protenin in M72 OSNs as sensing components.Using optical imaging method to orient M72 glomeruli,and implant the MEA probe into M72 glomeruli,which make it posssible for recording from the same region in different mice.The results show that M72 glomeruli possesse high sensitivity and specificity for odors which contain benzene ring.Further,we explored its potential in TNT detection.We found its detection threshold below 10-6 M and can discriminate TNT from chemicals with similar structure.The results show that this method not only can be used to detecting odors containing benzene ring,but also can be used to detecting explosives such as TNT.4.State-dependent sensory gating mechanism study in mammalian olfactory systemUsing M72-ChR2-YFP and OMP-ChR2-GFP mice,we can activate the olfactory sensory neurons by blue light instead of odor and then record response from different olfactory regions.By analyzing the stimuli-induced LFP amplitude and spike firing rate,we find the response amplitude is the same or even larger in sleep state than awake state,which indicate that sensory gating does not rely on the neuron firing rate and response amplitude.Further,we find the y oscillation(30-80 Hz)in different olfactory regions will increase after light stimulation in awake state,but not increase during sleep state.Actually,y oscillation or LFP reflect the synchrony degree of local neural population,we thus conclude that neural synchrony may contribute to olfactory sensory gating.