BIG-2 Mediates Olfactory Axon Convergence to Target Glomeruli
ABSTRACT Olfactory sensory neurons expressing a given odorant receptor converge axons onto a few topographically fixed glomeruli in the olfactory bulb, leading to establishment of the odor map. Here, we report that BIG-2/contactin-4, an axonal glycoprotein belonging to the immunoglobulin superfamily, is expressed in a subpopulation of mouse olfactory sensory neurons. A mosaic pattern of glomerular arrangement is observed with strongly BIG-2-positive, weakly positive, and negative axon terminals in the olfactory bulb, which is overlapping but not identical with those of Kirrel2 and ephrin-A5. There is a close correlation between the BIG-2 expression level and the odorant receptor choice in individual sensory neurons. In BIG-2-deficient mice, olfactory sensory neurons expressing a given odorant receptor frequently innervate multiple glomeruli at ectopic locations. These results suggest that BIG-2 is one of the axon guidance molecules crucial for the formation and maintenance of functional odor map in the olfactory bulb.
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ABSTRACT: Rodents depend on the main olfactory and accessory olfactory systems to detect and process chemical-communication signals important for complex reproductive and social behaviors. As the medial amygdala is the first site of convergence of these two pathways in the brain, examining its role in chemosensory processing is of primary importance. Previous experiments have shown that the hamster medial amygdala exhibits a categorical response to different types of chemical signals. The use of immediate early gene (IEG) expression to assess neural activity in different brain regions showed that chemical signals from the same species (conspecific) activated anterior and posterior medial amygdala, while chemical signals from other species (heterospecific) increased activity in only the anterior medial amygdala. The experiments discussed below aim to provide information about how the mouse medial amygdala responds to categories of chemical signals, how important the main and accessory olfactory systems are to the medial amygdala response and whether oxytocin (which has been shown to be important in a variety of social behaviors) is necessary for the medial amygdala categorization of chemical signals. Upon exposure of male mice to chemical-communication signals, I found that conspecific chemosignals (male, female mouse urine) increased immediate early gene-protein (IEG) expression in both anterior and posterior medial amygdala of male mice, whereas most heterospecific chemosignals (e.g.: hamster vaginal fluid, steer urine) increased expression only in anterior medial amygdala. This categorization of responses in medial amygdala conforms to the previously reported findings in male hamsters. The same characteristic pattern of IEG expression appeared in the medial amygdala of each species in response to conspecific stimuli for that species. These results suggested that the amygdala categorizes stimuli according to the biological relevance for the tested species. Thus, a heterospecific predator (cat collar) stimulus, which elicited behavioral avoidance in mice, increased IEG expression in mouse posterior medial amygdala (like conspecific stimuli). Further analysis suggests reproduction related and potentially threatening stimuli produce increased IEG expression in different sub-regions of posterior medial amygdala (dorsal and ventral, respectively). These patterns of IEG expression in medial amygdala may provide glimpses of a higher-level processing of chemosensory signals beyond the primary-level selectivity of chemosensory neurons, the secondary sorting in main and accessory olfactory bulbs and the tertiary sorting by the medial amygdala into “biologically relevant and non-relevant” categories. Both non-volatile and volatile chemical-communication signals may be detected by the vomeronasal organ, which sends projections to the accessory olfactory bulb and on to the medial amygdala. Results of the first experiment (above) argue that the mouse medial amygdala sorts complex chemosensory information categorically, according to its biological relevance (salience). In order to determine the role of AOS in categorization, male mice underwent vomeronasal removal surgery (VNX) or a sham-operation (SHAM) and then were exposed to conspecific (male and female mouse urine) or heterospecific (hamster vaginal fluid and worn cat collar) chemical stimuli. As with the mice in the above experiment, SHAM mice exhibited different IEG expression patterns in the medial amygdala dependent upon the biological relevance of the chemical stimuli. However, regardless of biological relevance, vomeronasal organ removal eliminated the different IEG response patterns in the medial amygdala to any of the chemical stimuli. Interestingly, VNX also disrupted the avoidance of (an unfamiliar) predator odor, worn cat collar. These experiments show that the medial amygdala response to these tested chemical signals is dependent upon an intact vomeronasal organ. Normal function of the neuropeptide oxytocin (OT) in the medial amygdala is necessary for social recognition. In the final set of experiments, male mice having undergone intracerebroventricular cannulation (i.c.v.) were injected with either PBS (control) or oxytocin antagonist (OTA) and exposed to conspecific (female mouse urine) and heterospecific (steer urine and worn cat collar) chemical stimuli. As in the above experiments, PBS-injected mice exhibited different IEG expression patterns in the medial amygdala dependent upon the biological relevance of the chemical stimuli. However, OTA injection eliminated the increase in IEG expression in the medial amygdala to all of the tested conspecific or heterospecific stimuli. Importantly, OTA injection disrupted defensive and non-defensive behaviors after exposure to the unfamiliar predator odor, worn cat collar. The disruption of the social/individual recognition behavior in male mice deficient in OT may be due to the inability of the medial amygdala to process all biologically relevant chemical-communication signals.
Conference Paper: Kouchoul cycle implication in the Tailer engine cycle[Show abstract] [Hide abstract]
ABSTRACT: The authors present here the study of the Tailer heat engine cycle, modified using the concept of load transfer for the Kouchoul cycle. Theoretical equations and numerical simulations of the Tailer engine cycle modification which implicate the Kouchoul cycle are developedEnergy Conversion Engineering Conference, 1996. IECEC 96. Proceedings of the 31st Intersociety; 09/1996
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ABSTRACT: Stereotypical connections between olfactory sensory neuron axons and mitral cell dendrites in the olfactory bulb establish the first synaptic relay for olfactory perception. While mechanisms of olfactory sensory axon targeting are reported, molecular regulation of mitral cell dendritic growth and refinement are unclear. During embryonic development, mitral cell dendritic distribution overlaps with olfactory sensory axon terminals in the olfactory bulb. In this study, we investigate whether olfactory sensory neurons in the olfactory epithelium influence mitral cell dendritic outgrowth in vitro. We report a soluble trophic activity in the olfactory epithelium conditioned medium which promotes mitral/tufted cell neurite outgrowth. While the trophic activity is present in both embryonic and postnatal olfactory epithelia, only embryonic but not postnatal mitral/tufted cells respond to this activity. We show that BMP2, 5 and 7 promote mitral/tufted cells neurite outgrowth. However, the BMP antagonist, Noggin, fails to neutralize the olfactory epithelium derived neurite growth promoting activity. We provide evidence that olfactory epithelium derived activity is a protein factor with molecular weight between 50-100 kD. We also observed that Follistatin can effectively neutralize the olfactory epithelium derived activity, suggesting that TGF-beta family proteins are involved to promote mitral/tufted dendritic elaboration.PLoS ONE 02/2008; 3(11):e3816. DOI:10.1371/journal.pone.0003816 · 3.53 Impact Factor