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PubMed1996

A learned odor decreases the number of Fos-immunopositive granule cells in the olfactory bulb of young rats.

Olfactory stimulation evokes a column of activity within the olfactory bulb extending from the glomerular layer to the granule cell layer that can be visualized with 2-deoxyglucose autoradiography, optical imaging, Fos protein immunohistochemistry and c-fos mRNA in situ hybridization. The Fos response to odors is typified by the activity of relatively few juxtaglomerular cells, which often occur in foci, and a large number of granule cells extending through much of the bulb. In this study, we characterized the granule cell response to an odor for which young rats had acquired a preference. Fos-like immunoreactive granule cells were quantified by image analysis, and densely stained cells were counted in a region previously shown to be responsive to peppermint odor. We found that odor-trained pups have about half the number of Fos-immunopositive superficial granule cells which respond to a learned odor than do control pups. We then determined whether there was a correlation between the juxtaglomerular cell response and the response of the superficial granule cells deep to those glomerular layer cells. We found a positive correlation between the number of juxtaglomerular cells and the number of granule cells demonstrating Fos immunoreactivity in both control and trained pups, a relationship that changed with early olfactory training.

Animals↗
PubMed1992

Postnatal X-ray irradiation effects on glomerular layer of rat olfactory bulb: quantitative and immunocytochemical analysis.

In the rat olfactory bulb, the majority of interneurons in the glomerular layer (GL) are supposed to be generated during first postnatal week. Low and repeated doses of X-rays (200 rad x 4 and 200 rad x 6) were used during this period to impair the development of interneurons. The resulting effects of olfactory bulb neurons were examined stereologically and immunocytochemically in animals of 4 and 12 weeks of age. Quantitative analysis showed that, 1) the volume of the GL decreased to 55% (1200 rad) - 70% (800 rad) of control, 2) numerical cell densities in GL decreased to 40% (1200 rad) - 60% (800 rad) of control, thus resulting in 3) a decrease of the total cell number in GL to 20% (1200 rad) - 40% (800 rad) of control in irradiated olfactory bulbs of animals 4 weeks old. In comparison, mitral cells, which are generated prenatally, were much less affected (total cell number: 70-80% of control), indicating a selective loss of cells generated during the first postnatal week in GL. Effects on somata and processes immunoreactive for GABA, tyrosine hydroxylase (TH), calbindin D-28K and parvalbumin (PV) were examined in irradiated bulbs of both 4 and 12 week-old rats. All of these immunoreactive elements showed a drastic decrease in all layers. Semiquantitative analysis showed that in the GL, calbindin D-28K immunoreactive (calbindin D-28K(+)) neurons decreased more extensively than TH immunoreactive (TH(+)) and GABA-like immunoreactive (GABA(+)) neurons; that is, TH(+) and GABA(+) neurons decreased to 20% (1200 rad) - 40% (800 rad) of control, whereas calbindin D-28K(+) neurons decreased to 10% (1200 rad) - 30% (800 rad) of control in the GL of irradiated bulbs. These findings indicated that larger proportions of calbindin D-28K(+) neurons might be generated during the first postnatal week than those of GABA(+) and TH(+) neurons. Furthermore, in irradiated bulbs the proportion of GABA(-)TH(+) cells in TH(+) cells increased to about twice of control, and the estimated total numbers of GABA(-)TH(+) cells in irradiated rats were 95% (800 rad) and 40% (1200 rad) of control. These observations suggest that the majority of GABA(-)TH(+) neurons were less affected by X-ray irradiation during the first postnatal week and thus that they might be generated in the prenatal period. Since during the first 2 postnatal weeks, neurons showing GABA(-)TH(+) were not seen in GL (Kosaka et al. 1987a), the majority of GABA(-)TH(+) neurons in adult olfactory bulb were assumed to change their phenotype at some postnatal developmental period.

Animals↗
PubMed1980

Analysis and simulation of the bioelectric 55 counts/sec rhythm produced by the olfactory bulb.

To analyse the olfactory bulb 55 counts/sec rhythm a frequency analyser with three narrow band filters was used, distortions introduced into recordings by these filters were corrected, the original 55 counts/sec rhythm was synthesised graphically by means of geometrical addition of the corrected frequency components, an electron device was designed for physical simulation of the above-mentioned rhythm and an example of a program for this rhythm synthesis, using this device, was given. After distortion corrections 'bursts' of 55 counts/sec rhythm frequency components are seen not as 'spindles', but as 'packets' of oscillations with the same amplitude (the oscillation amplitude varies only in different packets). These 'spindles of bursts' for 55 counts/sec rhythm are formed not due to the recruiting and then to the derecruiting of neurons (or of their elements), but to algebraic addition of activities of several neuron pools producing oscillation packets.

Animals↗
PubMed2005

Early development of functional spatial maps in the zebrafish olfactory bulb.

In the adult olfactory bulb (OB), particular chemical classes of odorants preferentially activate glomeruli within loosely defined regions, resulting in a coarse and fractured "chemotopic" map. In zebrafish, amino acids and bile acids predominantly stimulate glomeruli in the lateral and medial OB, respectively. We studied the development of these spatial response maps in zebrafish. At 3 d postfertilization (dpf), the OB contained protoglomerular structures that became refined and more numerous during subsequent days. In a transgenic zebrafish line expressing the Ca2+ indicator protein inverse pericam, mainly in mitral cells, odor responses in the OB were first detected at 2.5-3 dpf. Already at this stage, amino acids and bile acids evoked activity predominantly in the lateral and medial OB, respectively. Two-photon Ca2+ imaging using a synthetic indicator was used to reconstruct activity patterns at higher resolution in three dimensions. Responses to amino acids and bile acids were detected predominantly in the lateral and medial OB, respectively, with little overlap. Between 2.5 and 6 dpf, the number of odor-responsive units increased, but the overall spatial organization of activity persisted. Hence, a coarse spatial organization of functional activity maps is established very early during OB development when glomeruli are not yet differentiated. This spatial organization is maintained during development and growth of neuronal circuits and may have important functions for odor processing in larvae, for the differentiation of glomeruli, and for the refinement of activity maps at later developmental stages.

Animals↗
PubMed1992

Differential localization of G-proteins Gi and Go in the accessory olfactory bulb of the rat.

To clarify the functional differences among G-proteins, we investigated the localization of Gi and Go in the olfactory bulb of rats by both immunohistochemical and immunochemical techniques, using purified antibodies specific to the alpha-subunits of Gi1 (Gi1 alpha), Gi2 (Gi2 alpha), and Go (Go alpha), respectively. We found that Gi2 alpha is localized exclusively in the accessory olfactory bulb, but it is present at only low levels in the main olfactory bulb. The unique pattern of immunoreactivity specific for Gi2 alpha and Go alpha within the glomeruli of the accessory olfactory bulb and the results of immunoassays indicate that the accessory olfactory bulb is divided into two parts: the anterior region is rich in Gi2, while the posterior region is rich in Go. These findings suggest that the accessory olfactory bulb has two different functions. In addition, we found that the concentration of Gi2 alpha in the accessory olfactory bulb increases during puberty and reaches the adult level at 12 weeks after birth, while that in the main olfactory bulb remains constant. By contrast, the concentrations of Go alpha in the accessory olfactory bulb and the main olfactory bulb increase with similar kinetics. These findings suggest that Gi2 is a key protein in signal transduction in the accessory olfactory bulb, and increases in its level seem to be related to sexual maturation.

Animals↗
PubMed1994

Recovery of olfactory behavior. II. Neonatal olfactory bulb transplants enhance the rate of behavioral recovery.

Previous experiments in this laboratory have shown that transplants of a fetal olfactory bulb into a neonatal rat are viable and that they establish connections with the olfactory peduncle and olfactory cortex. The focus of this experiment was to investigate the anatomical correlates of any behavioral recovery seen in rats that had one olfactory bulb removed along with an immediate transplant of a fetal olfactory bulb. Anatomical details, such as transplant organization and olfactory nerve repenetration patterns were analyzed using a variety of histological and immunohistochemical techniques. The rats in this experiment showed behavioral recovery of olfactory ability. The recovery rates observed in these animals were compared to two other groups of rats that this laboratory has shown to be behaviorally competent: normal rats and rats with neonatal ablations of the olfactory bulb but no transplant. Although the animals with transplants did not recover to completely normal levels of olfactory ability, they did start behavioral testing in a more behaviorally competent condition than rats with simple neonatal lesions. Anatomical analysis revealed that the transplanted olfactory bulb was heavily penetrated by incoming olfactory nerve fibers but olfactory nerve penetration was not limited to the transplanted olfactory bulb. The extra-bulbar host regions that were penetrated included the orbital frontal cortex and three olfaction-related areas; olfactory cortex, olfactory peduncle and the subependymal cell layer. The olfactory nerve penetration patterns observed beyond the transplant were essentially the same as those observed in rats with only neonatal lesions of the olfactory bulb. Thus, multiple pathways may have contributed to the recovery observed in the rats with olfactory bulb transplants.

Animals↗
PubMed2004

Electrophysiological demonstration of independent olfactory receptor types and associated neuronal responses in the trout olfactory bulb.

The present study attempts to highlight the principles by which peripheral olfactory information of across- and within-class odorant signals is transformed into bulbar neuron responses. For this purpose, we performed electro-olfactogram cross-adaptation and mixture experiments as well as single unit recording of olfactory bulb neurons using amino acid, bile acid and F-prostaglandin stimulants in brown and rainbow trout. The results show that amino acids, a bile acid and a F-prostaglandin activate independent receptor types. However, within the class of amino acids, different receptor types are only partially independent. Neurons responsive to bile acid and amino acids were segregated to the mid-dorsal and latero-posterior olfactory bulb, respectively. Of the 43 responsive olfactory bulb neurons studied in brown trout, 41 showed specificity for one odorant class. Olfactory bulb neurons gained responsiveness to new amino acids with increasing stimulant concentration. We conclude that different odorant classes activate specific neurons located in different regions of the trout olfactory bulb, and that information distinguishing related amino acids can be represented in a limited number of bulbar neurons with distinct response profiles under the conditions investigated.

Amino Acids↗
PubMed1987

Localized changes in olfactory bulb morphology associated with early olfactory learning.

Young rats exposed to an odor while receiving reinforcing stimulation come to approach that odor upon subsequent presentation. In addition, such pups have increased 14C-2-deoxyglucose (2DG) uptake within focal areas of the glomerular layer in response to that odor, compared to control animals experiencing the odor for the first time. In this study, the morphology of the glomerular areas underlying these 2DG foci was examined to determine whether early olfactory learning imposed local structural changes that could produce the enhanced 2DG uptake. Alternate sections either were processed with a silver and a Nissl stain to label both cell bodies and their processes or were histochemically treated for the mitochondrial enzymes cytochrome oxidase (CO) or succinic dehydrogenase (SDH) to define the glomerular core of the bulb; 2DG autoradiographs were aligned with adjacent stained sections, and regions underlying the high 2DG uptake foci were examined. In odor-familiar animals, large glomerular clusters that protruded into the external plexiform layer or the olfactory nerve layer were associated with the focal areas of increased 2DG uptake. Morphometric analysis of these regions revealed that the glomerular layer underlying the foci of high 2DG uptake was 30% wider in odor-familiar animals than comparable areas in odor-unfamiliar animals; the cross-sectional areas of individual glomeruli were 21% larger in odor-familiar animals. The foci of enhanced 2DG uptake therefore appear to be associated with groups of enlarged glomeruli. These data demonstrate that early olfactory learning influences the morphology of the olfactory bulb.

Animals↗
PubMed2001

New method of purification for establishing primary cultures of ensheathing cells from the adult olfactory bulb.

Ensheathing cells exclusively enfold olfactory axons. The ability of olfactory axons to reinnervate the adult mammalian olfactory bulb throughout the lifetime of an organism is believed to result from the presence of this unique glial cell in the olfactory system. This theory has been substantiated by research demonstrating the ability of transplanted ensheathing cells to promote axonal regrowth in areas of the central nervous system that are normally nonpermissive. A simple method for purifying ensheathing cells resulting in a large yield of cells is therefore invaluable for transplantation studies. We have developed such a method based on the differing rates of attachment of the various harvested cell types. The greatest percentage of cells (70.4%) that attached during the first step of the separation was determined to be fibroblasts. The remainder of the cells were classified as astrocytes (20.8%) and ensheathing cells (6.8%). The percentage of attached astrocytes (67.6%) was greatly increased during the second purification step while the percentage of fibroblasts decreased greatly (27.9%) and the percentage of ensheathing cells (5.3%) slightly decreased. In the final cultures, 93.2 % of the attached cells were ensheathing cells, while astrocytes (5.9%) and fibroblasts (1.4%) were only minor components. This simple, inexpensive method of purifying ensheathing cells will facilitate their use in central nervous system regeneration research.

Age Factors↗
PubMed2006

Effects of nicotine on regional blood flow in the olfactory bulb in rats.

Effects of nicotine on blood flow in the olfactory bulb were examined in anesthetized rats. Nicotine administered intravenously at 100 microg/kg increased regional blood flow in the olfactory bulb, irrespective of changes in systemic arterial pressure. Nicotine administered locally into the internal carotid artery at 10 microg increased blood flow, without changing arterial pressure; this response was abolished by hexamethonium. These results indicate that nicotine produces vasodilatation in the olfactory bulb via activation of nicotinic receptors located close to the olfactory bulb. Nicotine may be of therapeutic value in improving blood flow in the olfactory bulb.

Animals↗
PubMed1985

Pattern of rat olfactory bulb mitral and tufted cell connections to the anterior olfactory nucleus pars externa.

The pattern of output of mitral and tufted cells of the rat olfactory bulb (OB) to layer Ia overlying the pars externa (pE) of the anterior olfactory nucleus (AON) has been studied in the rat by iontophoresis of horseradish peroxidase and Phaseolus vulgaris-leucoagglutinin. These agents labeled mitral and tufted cells and at least the proximal portion of their axons. In most cases we observed small branches from axons of the lateral olfactory tract that appear to terminate in the region of the pE AON, while the main axon could often be traced for considerable distances past these branches. These branches are assumed to terminate in the pE AON because they could not be traced to other terminal regions, because they ramify in layer Ia, and because they usually show small swellings characteristic of axons in terminal regions. Although each ramification could be extensive, we found that the positions of these small branches were related to the positions of the injections within the OB. Dorsal medial injections labeled dorsal branches. Ventral medial injections labeled ventral branches. Injections on the lateral face of the OB labeled intermediate branches. The centers of the regions within which branches were labeled were strongly correlated with the positions of the injection around the circumference. Comparison of the anterior-posterior axis of the OB produced no such strong correlation. Reconstructions of axons showed that terminal branches arise from both mitral and tufted cells, although at least some mitral cells are shown not to have such branches in the pE AON. Studies of the patterns of dendrites and terminals in the pE AON indicate that this region has the same pattern of layer Ia and Ib terminals seen in other olfactory cortical regions. The pE AON cell layer is intercalated just below the boundary between layers Ia and Ib. Since dendrites of the underlying pars lateralis of the AON (pL AON) penetrate into layer Ia over much of the pE AON, it is necessary to remember that at least part of the pL AON may also receive topographically organized inputs.

Animals↗
PubMed1998

Influence of olfactory innervation on neurogenesis in the developing olfactory bulb of the frog, Xenopus laevis.

Previous research on development of the Xenopus olfactory bulb from our laboratory has shown that mitral cells begin to differentiate after olfactory axons make contact with the olfactory bulb, and the number of olfactory axons is correlated with the number of mitral cells throughout development. In embryos, removal of all afferent innervation before the mitral cells begin to differentiate results in a failure of the bulb to form; removal of half the olfactory axons, results in development of half the normal number of mitral cells. At larval stages, transection of the olfactory nerve results in a decrease in the number of neurons in the olfactory bulb. Thus, the olfactory axons play a major role in stimulating or maintaining development of the olfactory bulb neurons. Since we have found that neurogenesis in the bulb continues through metamorphosis, the goal of the current study was to determine whether olfactory axons influence cell genesis and/or neuronal maturation in the larval olfactory bulb. To study cell genesis, we cut the olfactory nerves, and 6 days later, injected the animals with [3H]thymidine. After 6 hr, the animals were killed and the tissue was processed for autoradiography. The number of labeled cells in the ventricular zone of the olfactory bulb was determined in every fifth section through the bulb in control and experimental animals. There was no statistical difference (Mann-Whitney rank sum test) in the number of labeled ventricular cells between controls and experimentals. Thus, olfactory axon innervation does not appear to play a role in precursor cell division during larval development. To study the influence of olfactory axon innervation on the ability of newly generated neurons to mature, we followed the same procedures. However, the animals were killed 21 days after the [3H]thymidine injection. The results from this experiment showed that there are many fewer labeled mitral cells in the experimental animals at 21 days. Together these results suggest that sensory deafferentation influences mitral cell differentiation or survival even during late stages of larval development.

Animals↗
PubMed1990

Transneuronal regulation of neuronal specific gene expression in the mouse olfactory bulb.

Peripheral afferent denervation (deafferentation) of the rodent main olfactory bulb produces a marked decrease in tyrosine hydroxylase (TH) activity and immunoreactivity in a population of juxtaglomerular dopaminergic neurons. Preservation of activity and immunostaining for aromatic L-amino acid decarboxylase implies that these cells do not die, but change phenotype. We now report that the steady-state level of TH mRNA markedly decreases in the adult mouse olfactory bulb in response to deafferentation. This reduction is permanent following intranasal irrigation with 0.17 M zinc sulphate (ZnSO4) but reversible following deafferentation produced by intranasal irrigation with 0.7% Triton X-100. The initial declines in TH activity, protein and mRNA of dopaminergic juxtaglomerular neurons observed after Triton X-100 treatment are all reversible as the steady-state level of TH mRNA gradually returns to control levels. Steady-state levels of mRNA for olfactory marker protein (OMP), a protein found in high concentrations in olfactory receptor neurons and their processes which innervate the olfactory bulb, were also monitored following deafferentation. Following treatment with either ZnSO4 or Triton X-100, the pattern of changes in steady-state levels of OMP mRNA was similar to that observed for TH. The steady-state level of PEP19 mRNA, a peptide previously localized to granule cells in the olfactory bulb, was not altered by deafferentation. These data indicate selective and parallel regulation of TH and OMP message and protein levels following deafferentation.

Afferent Pathways↗
PubMed1986

Effects of the potentiation of the GABAergic neurotransmission in the olfactory bulbs on mouse-killing behavior.

Intra olfactory bulb administration of three classes of GABA-mimetics (GABAa agonists, inhibitors of reuptake, inhibitors of GABA degradation) clearly inhibit mouse-killing behavior, without sedation. A linear correlation is observed between GABA levels increase in the olfactory bulbs and muricidal inhibition following local injection of valproic acid and gamma-vinyl GABA, two GABA-T inhibitors; the differences observed between these two compounds may be due to the differences in their mechanism of action on GABA-T activity and to the different pool of GABA on which they act. No diffusion to extra bulbar sites were observed after local administration of gamma-vinyl GABA. This evidence suggests an inhibitory role of GABA from olfactory bulbs in the modulation of mouse-killing behavior.

Aggression↗
PubMed1984

The olfactory bulbs in Alzheimer's disease.

The olfactory bulbs have been examined in patients with Alzheimer's disease and compared with those in elderly undemented and younger undemented control patients. In Alzheimer's disease neurofibrillary tangles were found in the anterior olfactory nucleus but not elsewhere in the olfactory bulb. Cell loss in the anterior olfactory nucleus was also found in Alzheimer's disease. It is clear that the olfactory sensory pathway is pathologically affected in Alzheimer's disease and would merit further study.

Alzheimer Disease↗
PubMed2006

Functional synapse formation between cultured rat accessory olfactory bulb neurons and vomeronasal pockets.

To investigate the interaction between vomeronasal receptor neurons and accessory olfactory bulb neurons during pheromonal signal processing and specific synapse formation, partially dissociated rat vomeronasal receptor neurons were co-cultured with accessory olfactory bulb neurons. Between 7 and 14 days in co-culture, a few bundles of fibers from a spherical structure, termed the vomeronasal pocket, of cultured vomeronasal receptor neurons extended to the accessory olfactory bulb neurons. An optical recording of the intracellular Ca(2+) concentration was used to monitor the synaptic activation of cultured accessory olfactory bulb neurons. Electrical stimulation of the vomeronasal pocket between 7 and 14 days in co-culture had no effects on most of the cultured neurons tested, although it occasionally evoked weak responses in a small number of neurons. In contrast, vomeronasal pocket stimulation after 21 days in co-culture evoked clear calcium transients in a substantial number of cultured accessory olfactory bulb neurons. These responses of accessory olfactory bulb neurons were reversibly suppressed by the application of 6-cyano-7-nitroquinoxaline-2,3-dione; the calcium transients disappeared in most of the neurons and were diminished in the others. The application of d-2-amino-5-phosphonopentanoic acid partially affected the calcium transients, but blocked spontaneous calcium increases, which were observed repeatedly in accessory olfactory bulb-alone cultures. The application of both 6-cyano-7-nitroquinoxaline-2,3-dione and d-2-amino-5-phosphonopentanoic acid completely blocked the evoked calcium transients. These results suggest that functional glutamatergic synapses between vomeronasal receptor neurons and accessory olfactory bulb neurons were formed at around 21 days in co-culture.

2-Amino-5-phosphonovalerate↗
PubMed1994

Differential distribution of the synapsins in the rat olfactory bulb.

The distribution of the different forms of synapsin in the rat olfactory bulb was investigated by biochemical and immunocytochemical methods. Western blots of tissue derived from microdissection of the surface and core regions of the olfactory bulb were performed using antibodies to synapsin I and synapsin II. The relative levels of the synapsins in the core region of the olfactory bulb were similar to the cerebral cortex. In contrast, the surface region of the olfactory bulb had significantly higher levels of synapsin IIa and significantly lower levels of synapsin I, relative to the cortex. Immunocytochemical localization of synapsin I and synapsin II revealed that synapsin I immunoreactivity was the most dense in the external plexiform layer and in the glomeruli; immunoreactivity was also present in the granule cell layer and the periglomerular regions. Synapsin II immunoreactivity was the most dense in the glomeruli. The external plexiform layer, internal plexiform layer, and granule cell layer exhibited much lower immunoreactivity. To determine the source of synapsin II immunoreactivity in the glomeruli, the olfactory epithelium was damaged to decrease the primary afferent input to the bulb. Three to four days later, olfactory bulb sections were double labeled with anti-olfactory marker protein (OMP) antibodies and anti-synapsin II antibodies. Following denervation, both OMP and synapsin II immunoreactivities were diminished, and continued to colocalize in regions retaining immunoreactivity. Individual puncta were immunoreactive for both OMP and synapsin II. Occasional puncta contained only synapsin II immunoreactivity. These results indicate that the distribution of the synapsins in the olfactory bulb differs from most other brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

The locus and cytoarchitecture of the projection areas of the olfactory bulb in Macaca mulatta.

A study was made of the normal and experimental anatomy of the olfactory system of the young adult male rhesus monkey. The cytoarchitecture of the central olfactory areas was studied with cell and fiber stains, while the extent and pattern of the projections of the olfactory bulb were determined by the Fink-Heimer and autoradiographic methods. The brain of one animal that had sustained damage to the olfactory bulb two days prior to sacrifice, and of one that had a transection of the olfactory tract ten days prior to sacrifice, were processed with the Fink-Heimer technique. The first of these and four others received injections of 3H-proline or 3H-leucine into the olfactory bulb, and following a survival period of 18 hours, or 2, 4, 12, or 20 days, their brains were processed with the autoradiographic technique. The results were the same for both experimental methods and for all survival periods. The projections of the olfactory bulb in this microsmatic animal are entirely ipsilateral. All of the structures that receive direct olfactory afferents have a laminar organization except for the anterior olfactory nucleus, which is laminated only in its anterior, peduncular, portion. While the olfactory bulb projects to the entire extent and depth of the anterior olfactory nucleus, the olfactory afferents of all other structures are confined to layer IA of the plexiform layer. These structures are: all divisions of the olfactory tubercle; the frontal and temporal prepiriform cortices; the oral, medial, and dorsal divisions of the superficial amygdaloid nucleus; and polar and anterior entorhinal cortex. The rhesus monkey does not have a recognizable accessory olfactory bulb, and no projections were seen to one of its targets, the nucleus of the stria terminalis. Also, no projections were seen to the taenia tecta or the ventral division of the superficial amygdaloid nucleus. With these exceptions, the projections of the olfactory bulb in the rhesus monkey are similar to those in macrosmatic species.

Afferent Pathways↗