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PubMed1987

Olfactory mucosa/air partitioning of odorants.

The present study evaluates the contribution of the receptor cell compartment to the total mucosal odorant uptake. Using radioactive odorants, partition coefficients for normal bullfrog olfactory mucosa were compared to the partition coefficients from mucosa in which the receptor cells had been removed by cutting one of the olfactory nerves and allowing two weeks for complete degeneration. For the more water-soluble odorants (butanol and isobutyric acid), both sides sorbed the same amount of odorant, suggesting that the mucosal uptake mostly reflects uptake by the water in the mucosa. For the less water soluble odorants (octane and amyl acetate), the uncut side did sorb significantly more odorant than the cut side.

1-Butanol↗
PubMed1986

LHRH and catecholamine neuronal systems in the olfactory bulb of the mouse.

The luteinizing-hormone-releasing hormone (LHRH) components of the mouse olfactory system were studied by using the indirect immunohistofluorescence technique. LHRH-positive cell bodies were found in both the main olfactory bulb (MOB) and the accessory olfactory bulb (AOB); two distinct cell groups were found--one located adjacent to the AOB in the dorsal part of the MOB and a second in the superficial ventromedial aspect of the MOB. LHRH-positive fibers were found predominantly in the posterior half of the main olfactory bulb innervating the olfactory nerve layer, the glomerular layer, the external plexiform layer, and the mitral cell layer, and small numbers innervated the AOB. The greatest density of LHRH-immunoreactive fibers was seen adjacent to the AOB where one group of LHRH-positive cells was noted. Sections adjacent to those stained with LHRH antibody were analysed for tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). The TH staining was intense for both cells and fibers in the glomerular layer of the MOB. In the AOB lower numbers of cell bodies and fibers were seen in the glomerular layer. The internal granular layer and internal plexiform layers were both stained, the internal granular layer showing more intensely fluorescent fibers with a higher density. Since no overlapping DBH-positive fibers were found here, these TH-positive nerve endings may be dopaminergic. DBH staining was confined to sparse networks of weakly fluorescent fibers with the highest numbers in the internal plexiform layer of the AOB and fewer fibers in the external plexiform, rostral, and granular layers of the MOB. Elution-restaining experiments revealed that the LHRH-positive and TH-positive elements represent different cell populations.

Animals↗
PubMed1992

Distribution of immunoreactivity for gamma-aminobutyric acid in the salamander olfactory bulb.

Intrinsic neurons provide inhibitory synaptic input to mitral (and tufted) output cells within several laminae of the olfactory bulb. In rodents, the two main types of intrinsic neurons are granule and periglomerular cells, both of which contain gamma-aminobutyric acid (GABA). In the present study, immunocytochemical techniques were used to determine whether intrinsic neurons in the salamander olfactory bulb might also contain GABA. With the aid of two antisera to different GABA-conjugates, immunoreactivity for GABA was localized within the olfactory bulb laminae. In the glomerular layer, periglomerular cells, which were strongly immunoreactive, were concentrated in clusters along the border with the olfactory nerve layer. Dendrites of the cells encircled nearby glomeruli and were presumably a primary source of intraglomerular processes that were also stained. In the subglomerular region and external plexiform layer, relatively few immunoreactive cells were observed, most of which appeared to be periglomerular and tufted cell types with glomerular dendrites. Throughout the external plexiform and mitral cell layers, however, a dense matrix of spiny processes and puncta was stained, outlining large, unstained dendrites derived from the large, unstained cell bodies of mitral cells. The spiny processes and puncta appeared to be derived from granule cells, which were the most abundant immunoreactive cells in the bulb. Granule cell bodies filled the granule cell layer. In tissue fixed with 0.1-0.2% glutaraldehyde, staining in the olfactory bulb laminae was blocked by preadsorption of the two antisera with glutaraldehyde-conjugated GABA-bovine serum albumin. The staining therefore appeared to be specific for fixed GABA.(ABSTRACT TRUNCATED AT 250 WORDS)

Ambystoma↗
PubMed1999

High glucose-6-phosphate dehydrogenase activity contributes to the structural plasticity of periglomerular cells in the olfactory bulb of adult rats.

Glucose-6-phosphate dehydrogenase (G6PD) activity, assayed spectrophotometrically, was found to be higher in the olfactory bulb (OB) than in other brain areas of adult rats [P. Ninfali, G. Aluigi, W. Balduini, A. Pompella, Glucose-6-phosphate dehydrogenase is higher in the olfactory bulb than into other brain areas, Brain Res. 744 (1997) 138-142]. Histochemical demonstration of G6PD activity in cryostat sections of OB, analyzed with optical microscopy, revealed a marked and well defined line of formazan deposition in the internal part of the glomerular layer (Glm), indicating that G6PD was much higher in cells distributed along the glomeruli. Electron microscope analysis showed that G6PD activity was mainly concentrated in cytoplasm and dendrites of periglomerular cells, the interneurons which span glomeruli and connect olfactory nerves with mitral/tufted cells. Since G6PD regulates the flux through the hexose monophosphate shunt (HMS) pathway, which provides NADPH for reductive biosynthesis and pentose phosphates for nucleic acid formation, it can be concluded that high G6PD activity in periglomerular neurons is functional to their differentiating capability. This result is consistent with the occurrence of structural plasticity events in the OB of adult rats.

Animals↗
PubMed2005

Postnatal developmental expression of calbindin, calretinin and parvalbumin in mouse main olfactory bulb.

The distribution of calbindin, calretinin and parvalbumin during the development of the mouse main olfactory bulb (MOB) was studied using immunohistochemistry techniques. The results are as follows: (1) calbindin-immunoreactive profiles were mainly located in the glomerular layer, and few large calbindin-immunoreactive cells were found in the subependymal layer of postnatal day 10 (P10) to postnatal day 40 (P40) mice; (2) no calbindin was detected in the mitral cell layer at any stage; (3) calretinin-immunoreactive profiles were present in all layers of the main olfactory bulb at all stages, especially in the olfactory nerve layer, glomerular layer and granule cell layer; (4) parvalbumin-immunoreactive profiles were mainly located in the external plexiform layer (except for P10 mice); (5) weakly stained parvalbumin-immunoreactive profiles were present in the glomerular layer at all stages; and (6) no parvalbumin was detected in the mitral cell layer at any stage.

Animals↗
PubMed2005

Organization of the main olfactory bulb of lesser hedgehog tenrecs.

Using a confocal laser scanning microscope (CLSM) and an electron microscope, we investigated the organization of the main olfactory bulb (MOB) of tenrecs, which were previously included into insectivores but now considered to be in a new order "Afrosoricida" in the superclade 'Afrotheria'. We confirmed that the overall structural organization of the tenrec MOB was similar to that of rodents: (1) the compartmental organization of glomeruli and two types of periglomerular cells we proposed as the common organizational principles were present; (2) there were characteristic dendrodendritic and axo-dendritic synapses in the glomerulus and external plexiform layer (EPL) and gap junctions in glomeruli; and (3) no nidi, particular synaptic regions reported only in laboratory musk shrew and mole MOBs, were encountered. However, instead of nidi, we often observed a few tangled olfactory nerves (ONs) with large irregular boutons in the glomerular-external plexiform layer border zone, with which dendrites of various displaced periglomerular cells were usually found to be intermingled. Electron microscopic (EM) examinations confirmed characteristic large mossy terminal-like ON terminals making asymmetrical synapses to presumed mitral/tufted cell and displaced periglomerular cell dendrites. In addition, gap junctions were also encountered between dendritic processes in these tiny particular regions, further showing their resemblance to glomeruli.

Animals↗
PubMed1991

Immunohistochemical localization of components of the immune barrier in the olfactory mucosae of salamanders and rats.

Immunohistochemical techniques were used to investigate the cellular distribution of components of the secretory immune system, including secretory immunoglobulin, secretory piece, and J chain, as well as other immunoglobulins and nonspecific defense factors in the olfactory mucosae of salamanders and rats. In the salamander, secretory immunoglobulin M, and J chain were localized in duct and acinar cells of Bowman's glands, in B lymphocytes, and in sustentacular cells in immature regions of the olfactory mucosa. Lactoferrin and lysozyme were also present in Bowman's glands, in sustentacular cells in immature regions of the olfactory mucosa, and in blood cells in the lamina propria. Olfactory nerve section resulted in the presence of increased numbers of secretory immunoglobulin-immunoreactive B lymphocytes and in an altered distribution of IgM, secretory piece, and lactoferrin. In the rat, secretory immunoglobulin A and J chain were localized in duct and acinar cells of Bowman's glands and in B lymphocytes in the lamina propria. Secretory piece could be demonstrated in Bowman's glands only in rats that had a prior viral infection. Other defense factors, localized in the lamina propria, included IgG in the connective tissue stroma and in B lymphocytes, IgD-immunoreactive B lymphocytes, and IgE-immunoreactive cells that were identified as mucosal mast cells. Lactoferrin and lysozyme were present in serous acinar cells of Bowman's glands and in blood cells. These results demonstrate that the olfactory mucosa is protected from pathogenic invasion by the secretory immune system as well as other immunoglobulins, lactoferrin, and lysozyme.

Ambystoma↗
PubMed1988

Real-time imaging of evoked activity in local circuits of the salamander olfactory bulb.

The encoding of olfactory information in the central nervous system (CNS) depends on spatially distributed patterns of activity generated simultaneously in many neuronal circuits. Optical neurophysiological recording permits analysis of neural activity non-invasively and with high spatial and temporal resolution. Here, a video method for imaging voltage-sensitive dye fluorescence in vivo is used to map neuronal activity in local circuits of the salamander olfactory bulb. The method permits the imaging of simultaneous ensemble transmembrane activity in real time. After electrical stimulation of the olfactory nerve, activity spreads centripetally from the sites of synaptic input to generate nonhomogeneous response patterns that are presumably mediated by local circuits within the bulbar layers. The results also show the overlapping temporal sequences of activation of cell groups in each layer. The method thus provides high resolution, sequential video images of the spatial and temporal progression of transmembrane events in neuronal circuits after afferent stimulation and offers the opportunity for studying ensemble events in other brain regions.

Animals↗
PubMed1998

Increased density of olfactory receptor neurons immunoreactive for apolipoprotein E in patients with Alzheimer's disease.

Immunolocalization of apolipoprotein E (apoE) was investigated in human olfactory mucosa in which olfactory receptor neurons (ORNs) were identified with antiserum to protein gene product (PGP) 9.5. Tissue was obtained at autopsy from 10 nondemented middle-aged or elderly subjects and 9 patients with Alzheimer's disease (AD). Double-labeling immunofluorescence established that apoE immunoreactivity was colocalized in a subpopulation of PGP 9.5-immunoreactive ORNs. The mean number of apoE-immunoreactive ORNs per unit epithelial length in AD patients was about 3.5 times greater than that in nondemented patients, although the mean number of PGP 9.5-immunoreactive ORNs was similar. The apoE-immunopositive Schwann cells in olfactory nerve bundles were the probable source of apoE in the ORNs. The increased numbers of apoE-immunoreactive ORNs in AD patients compared to nondemented subjects demonstrates another manifestation of AD-related neuropathology, in addition to cytoskeletal changes, beta-amyloid deposition, and changes in immunoreactivity for other neuroproteins, that parallels changes in neurons in the AD brain.

Aged↗
PubMed2000

Asymptomatic herpes simplex type 1 virus infection of the mouse brain.

An asymptomatic and transitory brain infection takes place in adult Swiss CD-1 mice after intranasal inoculation of HSV-1 strain SC16. Time course and distribution of the infection in the brain are demonstrated, (i) by titration of the nasal tissue and olfactory bulbs for 16 days post-infection (p.i.), showing a maximum production yield on day 7 p.i. and no replicating virus on day 16 p. i.; (ii) expression in the brain of the lac Z reporter gene of HSV-1 strain SC16-DeltaUS5-lac Z consistent with a central spread of the virus through the central olfactory pathways and the trigeminal system as described in acute HSV-1 encephalitis models; (iii) PCR amplifications of a segment of the thymidine kinase gene (HSV-tk) showing the persistence of viral genome in the nasal tissue and olfactory bulbs after clearance of infectious virus. The asymptomatic character of the infection is demonstrated over 2 months p.i. (i) by normal body weight; (ii) a neurological survey which excludes motor, sensory, balance and postural signs; (iii) two behavioral tests, the open-field test for exploratory activity and the cookie-finding test for olfactory search. On the other hand, intracerebral inocula cause encephalitis and death in a few days (LD50 ca. 14 p.f.u.). Intracranial, surgical transection of one olfactory nerve does not prevent infection of the corresponding bulb nor does it modify virus distribution, suggesting multiple entry routes from the nasal cavity to the brain. In conclusion, HSV-1 strain SC16 reaches the brain of CD-1 mice from the nasal cavity and replicates without neurological or behavioral signs.

Animals↗
PubMed1988

Cholinergic innervation of the main and the accessory olfactory bulbs of the rat as revealed by a monoclonal antibody against choline acetyltransferase.

The main and accessory olfactory bulbs (MOB and AOB) of the rat were immunohistochemically stained with a monoclonal antibody against choline acetyltransferase (ChAT) in order to know the difference in the distribution patterns of cholinergic fibers between these two structures. A few ChAT-immunoreactive cell bodies were found in the superficial and middle parts of the external plexiform layer (EPL) of the MOB, in the granule cell layer (GCL) of the MOB, and in the GCL of the AOB. The frequency in appearance of these cells was 0.9 cells/section in the MOB and 0.3 cells/section in the AOB. While the glomerular layer (GL) and the superficial part of the EPL were most densely innervated in the MOB, the internal plexiform layer received the richest innervation in the AOB. There were no immunoreactive structures in the olfactory nerve layer of the MOB and in the vomeronasal nerve layer and glomerular layer of the AOB. In addition to a relatively homogenous distribution of cholinergic fibers in the MOB and AOB, there were several foci of very dense network of immunoreactive fibers at the posterior level of the OB. These foci formed a part of the modified glomerular complex that was recently identified using 2-deoxyglucose method and was presumed to be related to suckling behaviour in the neonatal rat.

Animals↗
PubMed1999

Regional distribution and cell type-specific expression of the mouse F3 axonal glycoprotein: a developmental study.

The expression of the mouse axonal adhesive glycoprotein F3 and of its mRNA was studied on sections of mouse cerebellar cortex, cerebral cortex, hippocampus, and olfactory bulb from postnatal days 0 (P0) to 30 (P30). In cerebellar cortex, a differential expression of F3 in granule versus Purkinje neurons was observed. F3 was highly expressed during migration of and initial axonal growth from cerebellar granule cells. The molecule was then downregulated on cell bodies and remained expressed, although at low levels, on their axonal extensions. On Purkinje cells, F3 was strongly expressed on cell bodies and processes at the beginning of the second postnatal week; by P16 it was restricted to neurites of Purkinje cells subpopulations. In the cerebral cortex, the molecule was highly expressed on migrating neurons at P0; by P16, it was found essentially within the neuropil with a diffuse pattern. In the hippocampal formation, where F3 was expressed on both pyramidal and granule neurons, a clear shift from the cell bodies to neurite extensions was observed on P3. In the olfactory pathway, F3 was expressed mainly on olfactory nerve fibers, mitral cells, and the synaptic glomeruli from P0 to P3, with a sharp decline from P11 to P16. As a whole, the data show that F3 protein expression is regulated at the regional, cellular, and subcellular levels and suggest that, in different regions, it can be proposed as a reliable neuronal differentiation marker.

Aging↗
PubMed2005

Identification and molecular regulation of neural stem cells in the olfactory epithelium.

The sensory neurons that subserve olfaction, olfactory receptor neurons (ORNs), are regenerated throughout life, making the neuroepithelium in which they reside [the olfactory epithelium (OE)] an excellent model for studying how intrinsic and extrinsic factors regulate stem cell dynamics and neurogenesis during development and regeneration. Numerous studies indicate that transcription factors and signaling molecules together regulate generation of ORNs from stem and progenitor cells during development, and work on regenerative neurogenesis indicates that these same factors may operate at postnatal ages as well. This review describes our current knowledge of the identity of the OE neural stem cell; the different cell types that are thought to be the progeny (directly or indirectly) of this stem cell; and the factors that influence cell differentiation in the OE neuronal lineage. We review data suggesting that (1) the ORN lineage contains three distinct proliferating cell types--a stem cell and two populations of transit amplifying cells; (2) in established OE, these three cell types are present within the basal cell compartment of the epithelium; and (3) the stem cell that gives rise ultimately to ORNs may also generate two glial cell types of the primary olfactory pathway: sustentacular cells (SUS), which lie within OE proper; and olfactory ensheathing cells (OEC), which envelope the olfactory nerve. In addition, we describe factors that are both made by and found within the microenvironment of OE stem and progenitor cells, and which exert crucial growth regulatory effects on these cells. Thus, as with other regenerating tissues, the basis of regeneration in the OE appears be a population of stem cells, which resides within a microenvironment (niche) consisting of factors crucial for maintenance of its capacity for proliferation and differentiation.

Animals↗
PubMed1989

Discrimination among odorants by single neurons of the rat olfactory bulb.

1. Intracellular and extracellular recordings were made from rat olfactory bulb mitral and tufted cells during odor stimulation and during electrical stimulation of the olfactory nerve. Neurons were identified by horseradish peroxidase injections and/or antidromic activation. The presentation of multiple concentrations of at least one odorant in a cyclic artificial sniff paradigm, as reported previously (10), allowed the study of odor responses. This approach was extended to multiple odorants to compare their concentration-response profiles. This procedure avoids the problems of interpretation resulting from nonequivalence of the effective concentrations of different odorants used as stimuli that have characterized previous studies of odor quality effects. Comparisons of intracellular events and responses to electrical stimulation with the odor-induced spike train activity allow us to begin to delineate the local circuitry involved in generating odor-induced responses. 2. The concentration-response profiles of the 72 cells in the present study are comparable to those previously reported for output neurons of the olfactory bulb, showing ordered changes in the temporal patterning of spike activity with step changes in odor concentration. However, eight of the neurons exhibited inhibitory responses to lower concentrations, but excitation, at similar latency, to higher concentrations of the same odorant. These data emphasize that to study pattern changes induced by changing odor quality the influence of stimulus intensity must also be carefully examined. The data also provide evidence that the temporal pattern evoked by an odorant is probably not in itself the code for odor quality recognition. 3. Complete concentration-response profiles, including subthreshold concentrations, to more than one odorant show that, although responses to the different odorant can evolve systematically with concentration, the responses to different odorants can evolve through very different patterns. For example, in some cells, the response patterns to different odors were complementary in form. These results demonstrate that the patterned responses of olfactory bulb neurons can reflect changes in odor quality as well as intensity. 4. Intracellular recording was employed to compare the temporal patterning of spikes during odor stimulation with membrane potential changes. In some cases, the spike pattern was closely correlated with apparent postsynaptic potentials. However, there were several clear exceptions. In five cells, a prominent hyperpolarization, seen in the first sniff of a series of 10 consecutive sniffs, was associated with pauses in spike activity. In the following

Animals↗
PubMed1992

Characterization of phospholipase A2 and acyltransferase activities in squid (Loligo pealei) axoplasm: comparison with enzyme activities in other neural tissues, axolemma and axoplasmic subfractions.

Phospholipase A2 and acyltransferase were assayed and characterized in pure axoplasm and neural tissues of squid. Intracellular phospholipase A2 activity was highest in giant fiber lobe and axoplasm, followed by homogenates from retinal fibers, optic lobe and fin nerve. In most preparations, exogenous calcium (5 mM) caused a slight stimulation of activity. EGTA (2 mM) was somewhat inhibitory, indicating that low levels of endogenous calcium may be required for optimum activity. Phospholipase A2 was inhibited by 0.1 mM p-bromophenacylbromide, and was completely inactivated following heating. The level of acylCoA: lysophosphatidylcholine acyltransferase activity was higher in axoplasm and giant fiber lobe than in other neural tissues of the squid. Km (apparent) and Vmax (apparent) for oleoyl-CoA and lysophosphatidylcholine were quite similar for axoplasm and giant fiber lobe enzyme preparations. Acyltransferase activity was inactivated by heat treatment, and greatly inhibited by 0.2 mM p-chloromercuribenzoate, and to a lesser extent by 20 mM N-ethylmaleimide. Phospholipase A2 activity was present in fractions enriched in axolemmal membranes (separated from squid retinal fibers and garfish olfactory nerve) from both tissues, and it was also highly concentrated in vesicles derived from squid axoplasm. In all three preparations, phospholipase A2 activity was stimulated by Ca++ (5 mM) and inhibited by EGTA (2 mM). In addition, axoplasmic cytosol (114,000 g supernatant) retained a substantial portion of a Ca(++)-independent phospholipase A2, active in the presence of 2 mM EGTA. Acyltransferase activity was present at high content in both axolemma membrane rich fractions, and among subaxoplasmic fractions and axoplasmic vesicles.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1976

Field potentials in the olfactory bulb of the rainbow trout (Salmo gairdneri): evidence for a dendrodendritic inhibitory pathway.

Field potentials have been recorded from the olfactory bulb of the teleost fish, Salmo gairdneri. Stimulation of the olfactory nerve generates a complex wave pattern, which when recorded near the surface in the centre of the bulb consists of one positive and three negative components, P, N1, N2 and N3. The N1 has been attributed to depolarization of mitral cell dendrites, N2 to depolarization of the superficial dendrites of granules cells, and P to subsequent hyperpolarization of mitral cells. Possible origins of the N3 wave are discussed. Spikes from single units recorded in the mitral cell layer usually occur superimposed on the N1 wave, and single units recorded in the region of granule cells are usually found coincident with the trailling edge of the deep positive wave. With the exception of N3 the patterns of activity observed are very similar to previously published results obtained from other vertebrates. It is suggested that the dendrodendritic inhibitory pathway proposed for the mammalian olfactory bulb (Rall et al., 1966; Rall and Shepherd, 1968) is common to all vertebrates.

Animals↗
PubMedDate not supplied

[GABA immunoreactivity in the main olfactory bulb of the frog Rana temporaria].

Immunoreactivity for gamma-aminobutyric acid (GABA) was localized at the light microscopic level in the main olfactory bulb (MOB) of the frog, Rana temporaria. By means of free-floating peroxidase-antiperoxidase immunocytochemical technique, GABA was found in a large number of neurons in the granular cell layer, in a few small somata in the mitral cell layer and in two different types of cell somata in the glomerular layer. Individual GABA-immunopositive cells were found in the olfactory nerve layer. GABA immunostaining was also localized in cell processes and fiber fragments. There were many immunoreactive puncta in all layers of the MOB. GABA-positive punctate structures often outlined immunonegative cells in the mitral cell and glomerular layers. Rounded tightly packed groups of immunoreactive puncta were found only along ventral border of the glomerular layer. The results are discussed in comparison with data obtained on mammalian MOB in terms of MOB functional organization.

Animals↗
PubMed2007

Macrophage depletion in the murine olfactory epithelium leads to increased neuronal death and decreased neurogenesis.

Apoptosis of olfactory sensory neurons (OSNs) induced by olfactory bulbectomy (OBX) leads to the activation of resident macrophages within the olfactory epithelium (OE). These macrophages phagocytose degenerating OSNs and secrete chemokines, which recruit additional macrophages into the OE, and cytokines/growth factors, which regulate basal cell proliferation and differentiation and maturation of OSNs. In this study we apply for the first time the use of liposome-encapsulated clodronate to selectively deplete macrophages during the OSN degeneration/regeneration cycle in order to elucidate the role(s) of macrophages in regulating cellular mechanisms that lead to apoptosis and neurogenesis. Mice were injected intranasally and intravenously with either liposome-encapsulated clodronate or empty liposomes prior to and after OBX or sham OBX. At 48 hours after surgery the numbers of macrophages in the OE of both sham and OBX clodronate-treated mice were significantly reduced compared to liposome-treated controls (38% and 35%, respectively, P < 0.05). The reduction in macrophage numbers was accompanied by significant decreases in OE thickness (22% and 21%, P < 0.05), the number of mOSNs (1.2- and 1.9-fold, P < 0.05), and basal cell proliferation (7.6- and 3.8-fold, P < 0.005) in sham and OBX mice, respectively, compared to liposome-treated controls. In OBX mice there was also increased immunoreactivity for active caspase-3 in the OE and olfactory nerves of clodronate-treated OBX mice compared to liposome-treated controls. These results indicate that macrophages modulate the OSN population in the normal and target-ablated murine OE by influencing neuronal survival and basal cell proliferation, resulting in neurogenesis and replacement of mature OSNs.

Analysis of Variance↗