The olfactory mucosa of the zebrafish consists of 3 morphological types of olfactory receptor neurons (ORNs): ciliated, microvillous, and crypt cells. Previous studies in the zebrafish have revealed differential projections of ciliated and microvillous ORNs, which project to different glomerular fields. However, the bulbar targets of zebrafish crypt cells were not identified. Here, we analyze the relationship between crypt cells of the olfactory epithelium and dorsal glomerular fields of the zebrafish olfactory bulbs, as wells as the connections between these bulbar regions and forebrain regions. For this purpose, a lipophilic carbocyanine tracer (DiI) was used in fixed tissue. Application of DiI to the dorsomedial glomerular field mainly labeled crypt cells in the zebrafish olfactory epithelium. By contrast, application of DiI to the dorsolateral glomerular fields mainly labeled bipolar ORNs and only occasionally crypt cells. Bulbar efferent cells (mitral cells) contacting these dorsal glomerular fields project to different telencephalic areas, with the posterior zone of the dorsal telencephalic area (Dp) as the common target. However, dorsomedial and dorsolateral glomerular fields projected differentially to the ventral telencephalon, the former projecting to the ventrolateral supracommissural region. Retrograde labeling from the ventrolateral supracommissural region revealed mitral cells associated with 2 large glomeruli in the bulbar dorsomedial region, which putatively receives inputs from the crypt cells, indicating the existence of a crypt cell olfactory subsystem with separate projections, in the zebrafish. The comparative significance of the secondary olfactory pathways of zebrafish that convey information from crypt cells is discussed.
"In this latter species, acute treatment with fluoxetine (10 mg/kg) reverts the locomotoryinhibiting effect of exposure to CAS (Barbosa et al., 2012). In the crucian carp, Schrecksreaktion is in part mediated by structures which receive primary and secondary olfactory projections which are conducted by the medial bundle of the medial olfactory tract (Hamdani et al., 2000; Døving and Lastein, 2009); in zebrafish, these projections integrate into a circuit of amygdala-like structures in the telencephalon, as well as hypothalamic structures (Gayoso et al., 2011, 2012). Serotonergic innervation of such structures has been described in zebrafish (Kaslin and Panula, 2001; Lillesaar et al., 2009), as well as monoamine oxidase activity and immunoreactivity (Anichtchik et al., 2006), the presence of 5-HT 1A -like, 5-HT 1B and 5-HT 2C receptors (Norton et al., 2008; Schneider et al., 2012), and serotonin transporters (Norton et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: Alarm reactions to a substance secreted by the damaged skin of conspecifics and closely-related species are increasingly being recognized as fear-like responses in fish. The neurochemical underpinnings of these effects are so far unknown; however, given the role of the serotonergic system on defensive behavior, it is possible that the alarm reaction is mediated by this monoamine. Exposure to conspecific alarm substance (CAS) increased anxiety-like behavior in the light/dark test in zebrafish and decreased nocifensive behavior. These effects were accompanied by increases in blood glucose, hemoglobin, epinephrine and norepinephrine levels, as well as extracellular levels of serotonin in the brain. Pretreatment with fluoxetine blocked the anxiogenic effects of CAS on the light/dark test as well as all physiological parameters and the increase in extracellular brain 5-HT, but not the reduction in nocifensive behavior. Conversely, pretreatment with the 5-HT1AR antagonist WAY 100635 blocked the effects on nocifensive behavior, but not the effects on anxiety-like behavior nor on physiological parameters. These results point to an important and complex role of the serotonergic system in the mediation of fear-potentiated behavior in the light/dark test and in fear-induced analgesia in zebrafish.
"Crypt neurons have engendered considerable interest as a third type of olfactory receptor neurons with a peculiar morphology combining elements of the other two populations, ciliated and microvilllous receptor neurons3. Several attempts have been made to elucidate their neuronal circuits, beginning with studies that sought to identify their target regions in the olfactory bulb141516171834. A cluster of mediodorsal glomeruli has been suggested as potential targets of crypt neurons, based on absence of fluorescence in some genetically labeled zebrafish lines and differential staining in others16. "
[Show abstract][Hide abstract] ABSTRACT: Crypt neurons are a third type of olfactory receptor neurons with a highly unusual "one cell type - one receptor" mode of expression, the same receptor being expressed by the entire population of crypt neurons. Attempts to identify the target region(s) of crypt neurons have been inconclusive so far. We report that TrkA-like immunoreactivity specifically labeled somata, axons, and terminals of zebrafish crypt neurons and reveal a single glomerulus, mdg2 of the dorsomedial group, as target glomerulus of crypt neurons. Injection of a fluorescent tracing dye into the mdg2 glomerulus retrogradely labeled mostly crypt neurons, as assessed by quantitative morphometry, whereas no crypt neurons were found after injections in neighboring glomeruli. Our data provide strong evidence that crypt neurons converge onto a single glomerulus, and thus form a labeled line consisting of a single sensory cell type, a single olfactory receptor and a single target glomerulus.
"Using a double transgenic zebrafish line labeling ciliated and microvillous cells with different fluorophores, studies have shown that ciliated cells mainly project to the dorsal and medial olfactory bulb, whereas microvillous cells project to the lateral olfactory bulb (Sato et al., 2005, 2007). Retrograde labeling of the olfactory epithelium following lipophilic tracer application to different bulbar domains showed that crypt cells project to the ventral olfactory bulb in carp and to the dorsomedial olfactory bulb in zebrafish (Hamdani el and Doving, 2006; Gayoso et al., 2012). This projection pattern, shown in Figure 1, is well-conserved between the two bulbs of the same zebrafish, as well as among individual zebrafish (Baier and Korsching, 1994; Braubach et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: The fish olfactory system processes odor signals and mediates behaviors that are crucial for survival such as foraging, courtship, and alarm response. Although the upstream olfactory brain areas (olfactory epithelium and olfactory bulb) are well-studied, less is known about their target brain areas and the role they play in generating odor-driven behaviors. Here we review a broad range of literature on the anatomy, physiology, and behavioral output of the olfactory system and its target areas in a wide range of teleost fish. Additionally, we discuss how applying recent technological advancements to the zebrafish (Danio rerio) could help in understanding the function of these target areas. We hope to provide a framework for elucidating the neural circuit computations underlying the odor-driven behaviors in this small, transparent, and genetically amenable vertebrate.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.