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PubMed1993

Purification of olfactory nerve ensheathing cells from the olfactory bulb.

Cells of the olfactory nerve layer of the olfactory bulb are labeled with the O4 antibody, which also labels Schwann cells, oligodendrocytes, and many oligodendrocyte-type-2 astrocyte (O-2A) progenitors. Purification of cells which were O4+, but did not express galactocerebroside (GC), from spinal cord, hippocampus, corpus callosum, and cerebellum of perinatal rats always yielded cells with the expected characteristics of O-2A progenitors. In contrast, the great majority of O4+GC- cells isolated from the olfactory bulb expressed an antigenic phenotype and pattern of differentiation in vitro which did not correspond with that of any previously described glial populations. As the localization of O4 staining in the olfactory bulb indicates that these cells are olfactory nerve ensheathing cells (ONECs), our results therefore suggest that ONECs represent a novel glial cell-type which can now be analyzed as a purified population.

Animals↗
PubMed1992

Monoclonal antibody immunohistochemistry of a temporal relationship between axonal elimination of aberrant olfactory nerves and synaptogenesis in the rabbit olfactory bulb during middle embryonic periods.

Immunostaining using olfactory nerve- and synaptic vesicle protein-specific monoclonal antibodies revealed their characteristic appearance in the rabbit olfactory bulb during prenatal development. Prior to formation of glomeruli, olfactory nerve fibers extended beyond their target region deep into the bulb zones. Subsequently the aberrant axons decreased in number, and correspondingly, synaptic vesicle protein occurred in the innermost region of the olfactory nerve layer. It is concluded that the lack of synaptogenesis causes axonal elimination of aberrant olfactory nerves. Present results support the hypothesis that supernumerary axons degenerate unless synaptic contacts are secured; the olfactory nerves must arrive at the appropriate terminal zone in the glomeruli.

Animals↗
PubMed1988

Slow transport in a nerve with embryonic characteristics, the olfactory nerve.

The kinetics for slowly transported polypeptides have been examined in intact garfish olfactory nerves. The shape of the slow peak is essentially determined by alpha-and beta-tubulin which are by far the major polypeptides of the entire wave. The proximal area of the peak is similar to the slow component a (Sca) subcomponent defined in other nerves and contains discretely moving neurofilament proteins. The distal peak area, however, is more reminiscent of Scb. The two subcomponents were found to overlap considerably. Traces of polypeptides comigrating with tubulin and actin move far ahead of the slow wave at rates similar to the rate of slow transport measured in growing fibers and to the maximal velocity of axonal elongation. One of the most striking properties of slow transport in this nerve is the difference in the spreading of the various transported polypeptides along the axon, following their release from the perikarya. Labeled tubulin and actin can cover more than 20 cm of nerve; while neurofilament proteins can be found only on a 6 cm segment. Comparisons between slow transport in garfish olfactory axons and other vertebrate nerves indicate that despite major differences, the basic characteristics of slow transport are conserved. The features specific to the olfactory nerve may reflect its specialized properties. The constant turnover of olfactory neurons implies that these cells have an excellent growth potential but a short life span and, therefore, never reach full maturity. It can, therefore, be expected that their molecular composition is reminiscent of that embryonic neurons with a high level of plasticity but a slow stability.

Animals↗
PubMed2005

[Impact of olfactory nerve transection on the apoptosis of mice olfactory receptor neurons].

OBJECTIVE: To analyze the impact of olfactory nerve transection on the apoptosis of mice olfactory receptor neurons (ORN), and discuss the reliability of this experimental model. METHODS: After olfactory nerve transection of mice, anterograde horseradish peroxidase (HRP) tracing was performed to confirm the completion of nerve transection. On 8 h, 2 d, 3 d and 5 d after surgery, TdT mediated deoxyuridine triphosphate-biotin nick end labelling (TUNEL) was used to observe the apoptosis of ORN, while relative semi-quantitative RT-PCR and immunohistochemistry were used to reflect the expression of olfactory marker protein (OMP, special marker of mature ORN) in olfactory epithelium. RESULTS: No HRP label was observed in olfactory bulb after olfactory nerve transaction. Both TUNEL-positive and OMP-positive cells were ORN. After the surgery, TUNEL-positive cells increased remarkably and peaked on 2 d after the surgery. Meanwhile OMP mRNA in olfactory epithelium began to decrease markedly till 5 d after the surgery, and the olfactory epithelium got thinner accordingly. CONCLUSIONS: This experimental model can be used reliably to sever mice olfactory nerve and manipulate simultaneous apoptosis of mice ORN.

Animals↗
PubMed1994

Evidence for GABAB-mediated inhibition of transmission from the olfactory nerve to mitral cells in the rat olfactory bulb.

The GABAB agonist baclofen blocks transmission from the olfactory nerve to second order neurons in the frog olfactory bulb, and GABAB receptors in the rat olfactory bulb are selectively located in the glomerular layer. A reasonable hypothesis, therefore, is that inhibition in the glomerular layer is mediated, at least in part, by GABAB receptors. Here, we investigated the role of GABAB receptors in regulating the responses of mitral cells to activation of the olfactory nerve in the rat. Topical application of baclofen to the surface of the rat olfactory bulb reduced the amplitude of field potentials evoked by olfactory nerve stimulation (orthodromic response). Baclofen reduced the orthodromic response in a dose-dependent manner but the drug had no effect on the field potential evoked by antidromic activation of mitral cell axons (antidromic response). Baclofen also reduced olfactory nerve-evoked responses of mitral cells in an olfactory bulb slice preparation. The pharmacological specificity of the inhibition was confirmed by showing that the GABAB antagonist, CGP 55845A, blocked the inhibitory action of baclofen. These results suggest that transmission from olfactory nerve terminals to second order neurons is negatively regulated by periglomerular GABAergic interneurons; this inhibition is mediated, at least partially, by GABAB receptors.

Animals↗
PubMed1957

Electron microscopic observations of the olfactory mucosa and olfactory nerve.

The olfactory receptor cell is characterized by a distal process (the dendrite) which terminates in the olfactory passage as the olfactory rod. The olfactory rod is provided with numerous cilia which are similar in structure to those seen in other tissues. The central processes of the bipolar cell constitute the fila olfactoria. The cytoplasmic organelles of the sustentacular cell are concentrated at the apical and basal ends of the cell with a paucity of cytoplasmic elements in the region of the nucleus. The plasma membrane of the supporting cell forms a mesaxon for both the dendrite and axon of the bipolar cell. Terminal bars are present in the epithelial cells. The axons constituting the fila olfactoria form fascicles which are ensheathed by mesaxons of adjacent Schwann cells. Thus the olfactory neurons are ensheathed throughout their course by the membranes of sustentacular and Schwann cells. Observations of the olfactory mucosa with the electron microscope are discussed with respect to recent electrophysiological studies.

Axons↗
PubMed1981

Evoked potential and single unit responses to olfactory nerve volleys in the isolated turtle olfactory bulb.

An in vitro preparation of the whole olfactory bulb of the turtle has been investigated using extracellular evoked potentials and unitary spikes. The compound action potential has a slow conduction velocity (0.15 mm/msec), brief relatively refractory period (10 msec) and prolonged supernormality (several hundred msec). The evoked potentials undergo prolonged periods of partial and complete suppression, as tested by the responses to paired volleys in the olfactory nerves. The suppression has a complex temporal pattern, and lasts more than 4 sec. Similar periods were revealed by the unitary spike responses of presumed mitral cells to olfactory nerve volleys. The results are similar to those reported in in vivo studies of turtle and other species. They suggest that the basic properties of mitral cells and their synaptic interactions with local interneurons are maintained in this isolated olfactory bulb preparation.

Animals↗
PubMed1997

Glutathione and glutathione S-transferase in the rainbow trout olfactory mucosa during retrograde degeneration and regeneration of the olfactory nerve.

In the peripheral olfactory organ, continual olfactory receptor neuron (ORN) turnover exposes neighboring cells to potentially damaging cellular debris such as free radicals. These, in turn, may be inactivated by binding directly onto glutathione (GSH) or by enzymatic conjugation with glutathione S-transferase (GST). In this study, we have investigated GSH and GST during retrograde degeneration and regeneration of the olfactory nerve in rainbow trout. In these fish, prolonged ORN physiological activity and structural integrity following transection of the olfactory nerve may be mediated by GSH and GST. In the olfactory mucosa, early changes following nerve lesion and prior to ORN degeneration included a shift of intense GSH labeling from the dendrites and perikarya of a subpopulation of ORN, and from melanophores, to olfactory nerve fascicles. GSH levels were unchanged, but GST activity decreased by 33% and GST-immunoreactivity (GST-IR) in nerve fascicles diminished slightly. When the process of massive degeneration terminated and ORN were largely absent, GSH levels and GST activity decreased further, GSH labeling was confined to melanophores, and GST-IR was absent. As ORN repopulated the olfactory mucosa, GST-IR was widespread. The combination of increased GST activity (92% of preoperative values) and low GSH levels suggests GSH utilization for GST conjugation reactions. These changes imply that GSH provides protection from cellular debris associated with ORN degeneration. Recovery of GST activity and widespread GST-IR during regeneration indicates modulation of neuroprotective, developmental, and/or physiological processes by GST.

Animals↗
PubMed1997

Chemically defined neuron groups and their subpopulations in the glomerular layer of the rat main olfactory bulb--II. Prominent differences in the intraglomerular dendritic arborization and their relationship to olfactory nerve terminals.

In the glomerular layer of the rat main olfactory bulb, we previously reported three chemically defined interneuron groups: GABA-like immunoreactive, calretinin-immunoreactive and Calbindin-D28k-immunoreactive groups [Kosaka K. et al. (1995) Neurosci. Res. 23, 73-88]. In the present study, we analysed the structural features of these three neuron groups using confocal laser scanning light microscopy, focusing on their dendritic arborization pattern, especially on their close apposition to olfactory receptor terminals labeled by olfactory marker protein. Each glomerulus consisted of two zones, the olfactory nerve zone and the non-olfactory nerve zone. The former was mainly occupied by olfactory nerve preterminals and terminals as well as their targets, postsynaptic fine dendritic portions of intrinsic neurons. The latter non-olfactory nerve zone was occupied mainly by olfactory marker protein-negative profiles. Processes of GABAergic neurons and those of one of their subpopulations, tyrosine hydroxylase-immunoreactive neurons, were numerous both in the olfactory nerve and non-olfactory nerve zones, resulting in their frequent close apposition to olfactory marker protein-immunoreactive elements. Combined confocal laser scanning light microscopic electron microscopic examination revealed synaptic contacts from olfactory nerve terminals on tyrosine hydroxylase-immunoreactive processes at these sites of close apposition. In contrast, calretinin-immunoreactive and Calbindin-D28k-immunoreactive processes, particularly Calbindin-D28k-immunoreactive ones, were distributed almost exclusively in the non-olfactory nerve zone, as if they avoided the olfactory nerve zone, showing a net or honeycomb pattern. Thus, calretinin-immunoreactive and Calbindin-D28k-immunoreactive processes were not or very rarely closely apposed to olfactory nerve terminals. These findings suggested that there might be some differences among chemically defined interneuronal groups in their synaptic contacts from olfactory nerves. Further quantitative image analysis clearly exhibited the prominent differences among these neuron groups in their intraglomerular dendritic arborization in relation with the olfactory nerve zone, i.e. the percentages of the area in the olfactory nerve zone occupied by GABAergic and tyrosine hydroxylase-immunoreactive processes were about 10%, respectively, whereas those of calretinin-immunoreactive and Calbindin-D28k-immunoreactive processes were only about 1% and 0.3%, respectively. These findings suggested that so-called periglomerular cells in glomeruli might be heterogeneous not only in their chemical nature, but also in their dendritic arborization pattern and synaptic contacts from olfactory nerve terminals.

Animals↗
PubMed1985

Changes in the electrical properties of olfactory epithelial cells in the tiger salamander after olfactory nerve transection.

Transection of olfactory nerves causes degeneration of receptor neurons in the olfactory epithelium, followed by generation of new receptor neurons. We have carried out intracellular recordings to document changes in epithelial cell populations during receptor neuron degeneration and regrowth at 1, 2, and 4 weeks following olfactory nerve transection in the salamander. Receptor neurons were greatly reduced in numbers at 1 week, and gradually returned to the normal percentage of intracellular penetrations by 4 weeks. They had a resting membrane potential between -30 and -50 mV and high input resistance, 100 to 600 megohms, characteristically seen in normal epithelium. However, at 1 week, the receptor neurons were able to generate only a single spike in response to injected current, and did not re-acquire their ability to respond repetitively until 4 weeks. Cells with the properties of immature receptor neurons (resting membrane potential between -30 and -50 mV and high input resistance, 100 to 600 megohms, but unable to generate spikes) increased significantly in number in the post-transection period. This correlates with the burst of mitotic activity giving rise to new receptor neurons after nerve transection. Supporting cells changed their properties in the aftermath of transection. One type (A) showed a decrease in resting membrane potential and a small increase in input resistance. A second type (B) showed a very large increase in input resistance. These results imply that the degenerating receptor neurons transmit a signal that leads to changes in the functional properties of the glial-like supporting cells. These may involve changes in the membrane properties or in electrical coupling between cells.

Ambystoma↗
PubMed2002

Administration of transforming growth factor-alpha enhances anatomical and behavioral recovery following olfactory nerve transection.

Although replacement of olfactory receptor neurons (ORNs) and subsequent reinnervation of the olfactory bulb occur following ORN injury, the intrinsic and extrinsic factors that contribute to the regulation of this dynamic process have not yet been fully identified. Recent research indicates that several growth factors have neurogenic effects on ORNs in vitro, and that chronic in vivo administration of either basic fibroblast growth factor, epidermal growth factor, or transforming growth factor-alpha (TGF-alpha) following chemical lesion can enhance the normal rate of ORN reinnervation of the olfactory bulb. The primary goal of the present experiments was to further assess the extent to which growth factor-related enhancements in the rate of anatomical recovery during ORN reconstitution and subsequent reinnervation of olfactory bulb are accompanied by enhancements in the rate of recovery of odor-guided behavior.A series of experiments in rats was conducted to initially characterize the time course of the anatomical and behavioral recovery normally observed following ORN reconstitution as a consequence of olfactory nerve transection, and to subsequently characterize the anatomical and behavioral effects of TGF-alpha administration on this normal rate of recovery. Consistent with a host of prior studies, olfactory nerve transection produced consistent and substantial deafferentation of olfactory bulb followed by a time-dependent anatomical recovery which was significantly enhanced by administration of TGF-alpha. The effect of TGF-alpha on functional recovery following olfactory nerve transection was also assessed using an odor-guided fear conditioning task. ORN lesioned animals receiving injections of TGF-alpha during recovery were found to display enhanced conditioned responding to an olfactory stimulus compared to untreated subjects. Further behavioral analyses suggested that this enhanced functional recovery was likely not due to non-specific effects of TGF-alpha on cognition or motor activity, but rather to enhanced olfactory input to the CNS. Future studies will likely reveal the exact mechanism of action mediating the anatomical and concomitant behavioral effects of this growth factor. Since ORNs are one of only a few populations of neurons capable of regeneration or replacement, the continued study of the cellular and molecular factors that coordinate this regenerative process may ultimately lead to the development of therapeutic strategies to promote an enhanced functional recovery following injury to other neuronal populations.

Animals↗
PubMed1981

Ultrastructural changes in olfactory receptor neurons following olfactory nerve section.

Unilateral olfactory nerve section was performed in the salamander, Ambystoma tigrinum. An ultrastructural study was performed to investigate the changes occurring during degeneration and replacement of the mature olfactory receptor neurons. Experimental and contralateral control tissues were examined following postoperative survival periods ranging from 12 hours to 90 days. Normal bipolar receptor neurons have a fusiform cell body containing a thin rim of cytoplasm and an ovoid nucleus with a characteristic "checkerboard" chromatin pattern. A single apical dendrite projects to the surface of the epithelium, where numerous cilia extend from its apex into the overlying mucus. A single, unmyelinated, unbranching axon originates at the basal pole of the cell. After nerve section, retrograde degeneration of the mature neurons occurs. Early degenerative changes include pronounced condensation of the nuclear chromatin, increased number of nuclear membrane infoldings, and dilation of the space between the membranes of the nuclear envelope. At a later stage, the cytoplasm of the cell increases in volume and its organelle systems break down, resulting in accumulation of various forms of cell inclusions. Subsequently, proliferation of cells in the basal region of the epithelium occurs. Between 3 week and 2 months following nerve section, these cells differentiate into mature neurons. By 3 months, neurons within the epithelium have resumed their normal ultrastructure. Correlation of the time course of the ultrastructural changes with previously reported neurophysiological studies indicates that neuronal activity of the epithelium is dependent upon the presence of fully differentiated olfactory receptor neurons.

Ambystoma↗
PubMed1975

A quantitative analysis of isotope concentration profiles and rapid transport velocities in the C-fibers of the garfish olfactory nerve.

In the olfactory nerve of the long-nosed garfish (Lepisosteus osseus), unusually well-defined isotope concentration distributions can be established with the rapid transport process. Transport velocities of two profile loci can be accurately described and a quantitative profile analysis is possible after profile normalization. Results from such studies indicate that: (1) peak amplitudes decrease exponentially as a function of distance from the olfactory mucosa according to the equation p = 2130 exp (-0.109chi); (2) the wavefront base and the peak apex loci move at rates of 221 +/- 2 and 201 +/- 4 mm/day, respectively (at 23 degrees C), revealing a peak dispersion or broadening during transport; (3) the broadening is asymmetric with material shifting to the rear of the peak; (4) plateau regions are established behind the peak with material deposited by the peak; (5) only 20% of the total radioactivity in a cut nerve reaches the nerve terminals in the rapid transport peak while 80% is deposited along the axon; (6) profile areas from cut nerves decrease and lose 15% of their activity in 20 hr, while intact nerve profiles increase 10% in 16 hr due to continued somal contribution to the profile; (7) the displacement of the wavefront base (WFB) and peak apex (PA) profile loci can be described by the functions s(WFB) = (0.055T - 0.345)t - 1.43 s(PA) = (0.053T - 0.391)t - 2.71 (8) transport velocities are linear functions of temperature between 10 and 25 degrees C and increase 370% in that range. A linear extrapolation of the WFB and PA functions to 37 degrees C yields 410 and 377 mm/day, respectively.

Animals↗
PubMed1976

Techniques to prevent olfactory nerve reconstitution in the pigeon.

Transectioned olfactory nerves in birds can reestablish structural and functional connections with the olfactory bulbs in comparatively short time spans, thereby hampering long-range studies of avian olfaction and behavior. Accordingly, techniques are described that are suitable for impeding the reconstitution of the olfactory nerve after its transection in the pigeon. These involve the use of inexpensive and easily obtainable materials including cotton pellets, glass beads, and polyethylene tubing.

Animals↗
PubMed1993

Transection of the olfactory nerves induces expression of nerve growth factor receptor in mouse olfactory epithelium.

Expression of nerve growth factor receptor (NGFR) was found in the mouse olfactory epithelium after olfactory nerve transection, although no immunoreactivity to NGFR was detectable in the olfactory epithelium in the control animals. After axotomy, however, NGFR-immunoreactive cells transiently appeared in the supporting cells, receptor neurons and basal cells between postoperative day 7 and 35, and thereafter disappeared by postoperative day 49. The results indicate that nerve growth factor may contribute to the regeneration of olfactory receptor neurons after olfactory nerve transection.

Animals↗
PubMed2000

Expression of EphA5 during development of the olfactory nerve pathway in rat.

The olfactory neuroepithelium is a highly plastic region of the nervous system that undergoes continual turnover of primary olfactory neurons throughout life. The mechanisms responsible for persistent growth and guidance of primary olfactory axons along the olfactory nerve are unknown. In the present study, we used antibodies against the Eph-related receptor, EphA5, to localise EphA5, and recombinant EphA5-IgG fusion protein to localise its ligands. We found that although both EphA5 and its ligands were both expressed by primary olfactory neurons within the embryonic olfactory nerve pathway, there was no graded or complementary expression pattern. In contrast, the expression patterns altered postnatally such that primary olfactory neurons expressed the ligands, whereas the second-order olfactory neurons, the mitral cells, expressed EphA5. The role of EphA5 was analysed by blocking EphA5-ligand interactions in explant cultures of olfactory neuroepithelium using anti-EphA5 antibodies and recombinant EphA5. These perturbations reduced neurite outgrowth from explant cultures and suggest that intrafascicular axon repulsion may serve to limit adhesion and optimise conditions for axon growth.

Aging↗