Olfactory bulb is a critical component in encoding and processing olfactory signals, characterized by its intricate neural projections and networks dedicated to this function. It has been found that descending neural projections from the olfactory cortex and other advanced brain regions can modulate the excitability of olfactory bulb output neurons in the olfactory bulb, either directly or indirectly, which can further influence olfactory discrimination, learning, and other abilities. In recent years, advancements in optogenetic technology have facilitated extensive application of neuron manipulation for studying neural circuits, thereby greatly accelerating research into olfactory mechanisms. This review summarizes the latest research progress on the regulatory effects of neural projections from the olfactory cortex, basal forebrain, raphe nucleus, and locus coeruleus on olfactory bulb function. Furthermore, the important role that photogenetic technology plays in olfactory mechanism research is evaluated. Finally, the existing problems and future development trends in current research are preliminarily proposed and explained. This review aims to provide new insights into the mechanisms underlying olfactory neural regulation as well as applications of optogenetic technology, which are crucial for advancing the research on olfactory mechanism and the application of optogenetic technology.
Olfactory Bulb/physiology* ; Optogenetics/methods* ; Animals ; Humans ; Olfactory Pathways/physiology* ; Olfactory Cortex/physiology* ; Smell/physiology*

External tufted (ET) cells are the major excitatory elements coordinating the activities of glomerulars and mediating the input from the olfactory neurons to mitral cells. The ET cells participate in inter-and intra-glomerular microcircuits in the olfactory bulb, link the isofunctional odor columns within the same olfactory bulb, and play an important role in olfactory information processing. This paper reviews the research progress of the anatomy and physiological properties and electrophysiological modeling of ET cells, elaborate the problems and defects in the field. And then it further gives some proposals for the future research of electrophysiological properties, development of olfactory information coding and performance of modeling of ET cells.
Electrophysiological Phenomena ; physiology ; Humans ; Olfactory Bulb ; cytology ; physiology ; Olfactory Pathways ; physiology ; Olfactory Receptor Neurons ; cytology

BACKGROUNDStroke and traumatic injury to the nerve system may trigger axonal destruction and the formation of scar tissue, cystic cavitations and physical gaps. Olfactory ensheathing cells (OECs) can secrete neurotrophic factors to promote neurite growth and thus act as a prime candidate for autologous transplantation. Biological scaffolds can provide a robust delivery vehicle to injured nerve tissue for neural cell transplantation strategies, owing to the porous three-dimensional structures (3D). So transplantation of the purposeful cells seeded scaffolds may be a promising method for nerve tissue repair. This study aimed to evaluate the compatibility of a novel collagen-heparan sulfate biological scaffold with olfactory ensheathing cells in vitro.

METHODSCollagen-heparan sulfate (CHS) biological scaffolds were made, and then the scaffolds and OECs were co-cultured in vitro. The viability of OECs was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) assay at days 1, 3, 5 and 7. Statistical analysis was evaluated by student's t test. Significance was accepted at P < 0.05. OECs were labeled with carboxyfluorescein diacetate succinimidyl ester (CFSE), and the CFSE-labeled OECs were seeded into CHS scaffolds. The attachment and growth of OECs in CHS scaffolds were observed and traced directly by fluorescent microscopy and environmental scanning electron microscope (ESEM).

RESULTSCHS biological scaffolds had steady porous 3D structures and no cytotoxicity to OECs (F = 0.14, P = 0.9330). CHS biological scaffolds were good bridging materials for OECs attachment and proliferation, and they promoted the axonal growth.

CONCLUSIONThe compatibility of CHS biological scaffolds with OECs is pretty good and CHS biological scaffold is a promising cell carrier for the implantation of OECs in nerve tissue bioengineering.

Animals ; Cell Adhesion ; physiology ; Cells, Cultured ; Collagen ; chemistry ; Flow Cytometry ; Heparitin Sulfate ; chemistry ; Immunohistochemistry ; Microscopy, Electron, Scanning ; Olfactory Pathways ; cytology ; Rats ; Rats, Wistar ; Tissue Engineering ; methods ; Tissue Scaffolds ; adverse effects ; chemistry

OBJECTIVETo explore the feasibility of functional magnetic resonance imaging (fMRI) in analysis of olfaction function with modified OEP-98C olfactometer and event-related design.

METHODSSix young right-handed men underwent olfactory fMRI with event-related design. OEP-98C olfactometer was modified to accommodate MR environment. There were 2 types of tasks in the experiment. In one task, only isoamyl acetate was used as odorant. In the other task, to avoid possible decreased olfactory attention, vanillin was given before each presentation of isoamyl acetate.

RESULTSIn both tasks, uniform activation in piriform cortex and secondary olfactory cortexes was determined. The activation of piriform cortex was not significantly different between the two tasks (P > 0.01).

CONCLUSIONSWith isoamyl acetate as odorant, modified OEP-98C olfactometer, and event-related design, olfaction fMRI can depict cortex activation at primary and secondary olfactory cortex. Applying other odorant with similar quality to avoid olfactory attention decrease can not promote depiction of activation in primary olfactory cortex.

Adult ; Evoked Potentials ; physiology ; Feasibility Studies ; Humans ; Magnetic Resonance Imaging ; methods ; Male ; Olfactory Pathways ; physiology ; Olfactory Perception ; physiology ; Pentanols

Compared with other sensory system, olfactory neural system may be the most unknown one. And it is reported that the research of the complicated olfactory system is beneficial to clarifying the whole mechanism of the sensory system. Focused on spatiotemporal coding and decoding mechanism, the studies on the olfactory neural system recognition models are especially introduced. Finally, this paper presents the research work carried out in our lab, and prospects the development of this field in the future.
Computer Simulation ; Humans ; Models, Neurological ; Neural Networks (Computer) ; Olfactory Pathways ; anatomy & histology ; physiology ; Olfactory Receptor Neurons ; cytology ; metabolism

Olfactory processing involves a large number of central olfactory structures, interconnected with each other in complex fashion, and incorporating both feed forward and feed back interaction. Thus understanding how these structures in odor acquisition, perception, and memory perform functional roles is a central question in olfactory disorders that can only be addressed using a combination of approaches, including neuroimaging, neurophysiology and behavioral analyses. Recent whole-brain imaging studies have shown that multiple diverse neural structures become activated during tasks involving olfactory stimulation. This article reviews the current understanding of anatomy, sensory physiology of central olfactory structures. Especially the sensory physiology of main olfactory bulb, pyriform cortex, and orbitofrontal cortex will be emphasized here.
Memory ; Neuroimaging ; Neurophysiology ; Odors ; Olfactory Bulb ; Olfactory Pathways* ; Physiology ; Smell