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PubMed2004

Molecular and cellular basis of human olfaction.

The human olfactory systems recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants begins with the binding of an odorant ligand to a specific receptor protein in the ciliary membrane of olfactory neurons. To address the problem of olfactory perception at a molecular level, we have cloned, functionally expressed, and characterized some of the human olfactory receptors from chromosome 17. Our results show that a receptor protein is capable of recognizing the particular chemical substructure of an odor molecule and, therefore, is able to respond only to odorants that have a defined molecular structure. These findings represent the beginning of the molecular understanding of odorant recognition in humans. In the future, this knowledge could be used for the design of synthetic ideal receptors for specific odors (biosensors), or the perfect odor molecule for a given receptor.

Humans↗
PubMed2002

Hypothalamic inferior lobe and lateral torus connections in a percomorph teleost, the red cichlid (Hemichromis lifalili).

The neuroanatomic connections of the inferior lobe and the lateral torus of the percomorph Hemichromis lifalili were investigated by 1,1', dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (DiI) tracing. The inferior lobe and the lateral torus both receive afferents from the secondary gustatory nucleus. Additional afferents reach the inferior lobe from the nucleus glomerulosus, nucleus suprachiasmaticus, dorsal and central posterior thalamic nucleus, nucleus lateralis valvulae, magnocellular part of the magnocellular nucleus of the preoptic region, caudal nucleus of the preglomerular region, posterior tuberal nucleus, area dorsalis of the telencephalon, and a tegmental nucleus (T2). Efferents from the inferior lobe and the lateral torus terminate in the dorsal hypothalamic neuropil and corpus mamillare. Furthermore, the inferior lobe projects to the medial nucleus of the lateral tuberal hypothalamus and perhaps makes axo-axonal synapses in the tractus tectobulbaris rectus. The inferior lobe and the torus lateralis have reciprocal connections with the preglomerular tertiary gustatory nucleus and posterior thalamic nucleus and are also mutually interconnected. The inferior lobe is also reciprocally connected with the medial nucleus of the preglomerular region, reticular formation and sparsely with the anterior dorsal thalamic and the ventromedial thalamic nuclei. Thus, whereas the lateral torus is exclusively connected with the gustatory system, the inferior lobe is of a multisensory nature. In comparison with the goldfish (Carassius auratus), the connectivity pattern of the inferior lobe of Hemichromis lifalili reflects its specialization with respect to the visual system, as it receives qualitative (i.e., dorsal posterior, anterior, and ventromedial thalamic nuclei) as well as quantitative (i.e., nucleus glomerulosus) additional visual input.

Animals↗
PubMed2003

Olfactory-enriched transcripts are cell-specific markers in the lobster olfactory organ.

Genes expressed specifically in a tissue are often involved in the defining functions of that tissue. We used representational difference analysis of cDNA to amplify 20 cDNA fragments representing transcripts that were more abundant in the lobster olfactory organ than in brain, eye/eyestalk, dactyl, pereiopod, or second antenna. We then independently confirmed that the transcripts represented by these clones were enriched in the olfactory organ. The 20 cDNA fragments represent between 6 and 15 different genes. Six of the cDNAs contained sequences highly similar to known gene families. We performed in situ hybridization with these six and found that all were expressed in subsets of cells associated with the aesthetasc sensilla in the olfactory organ. Clones OET-07, an ionotropic receptor, and OET-10, an alpha tubulin, were specific to the olfactory receptor neurons. OET-02, a monooxygenase, was expressed only in the outer auxiliary cells. OET-03, a serine protease, was specific to the collar cells. OET-11, an alpha(2) macroglobulin, was expressed by the receptor neurons and the collar cells. OET-17, a calcyphosine, was expressed in the receptor neurons, inner auxiliary cells, and collar cells. The identities and expression patterns of these six transcripts predict involvement in both known and novel properties of the lobster olfactory organ.

Amino Acid Sequence↗
PubMed2003

Odor-evoked activity is spatially distributed in piriform cortex.

Much data on the olfactory bulb (OB) indicates that structural characteristics of odorant molecules are encoded as ordered, spatially consolidated sets of active cells. New results with "genetic tracing" (Zou et al. [2001] Nature 414:173-179) suggest that spatial order is also present in projections from the OB to the olfactory cortex. For the piriform cortex (PC), results with this technique indicate that afferents conveying input derived from single olfactory receptors (ORs) are distributed to well-defined patches in the anterior PC (APC) but that these patches are much larger than in the OB. We have used c-fos induction to examine how input patterning for single ORs is translated into patterns of odor-evoked cellular activity in the PC. The laminar distribution of labeled cells and dual-immunostaining for gamma-aminobutyric acid (GABA)ergic markers indicated that activity was detected largely in pyramidal cells. In odor-stimulated rats, labeled cells were present throughout the posterior PC (PPC) but were concentrated in prominent rostrocaudal bands in APC. Analysis of responses to different odorants and concentrations revealed that locations and shapes of bands conveyed no apparent information regarding odor quality, rather, they appeared to correspond to subregions of the APC distinguished by cytoarchitecture and connectivity. Small-scale variations in labeling density were observed within APC bands and throughout the PPC that could reflect the presence of a complex topographical order, but discrete patches at consistent locations as observed by genetic tracing were absent. This finding suggests that as a result of afferent overlap and intracortical processing, odor-quality information is represented by spatially distributed sets of cells. A distributed organization may be optimal for discriminating biologically relevant odorants that activate large numbers of ORs.

Animals↗
PubMed2003

Subzonal organization of olfactory sensory neurons projecting to distinct glomeruli within the mouse olfactory bulb.

Olfactory sensory neurons located in the nasal neuroepithelium send their axons directly into the olfactory bulb, where they contact the dendrites of second-order neurons in specialized spherical structures called glomeruli; each sensory neuron projects to a single glomerulus. All neurons expressing the same odorant receptor gene are confined to distinct zones within the epithelium and converge their axons onto a small number of common glomeruli. In the present study, we analyzed transgenic mouse lines in which the projection of a neuron population expressing a particular receptor gene can be visualized as a result of axonal markers that are coexpressed. The target glomeruli could thus reproducibly be identified and allowed to deposit retrograde tracers precisely. After an appropriate incubation time, olfactory sensory neurons within distinct areas of the olfactory epithelium were labeled. The two subpopulations of neurons retrogradely stained by differently colored fluorescent dyes deposited at the dorsal and the dorsomedial glomerulus, respectively, were found to be segregated within distinct areas of the expression zone, where the cells expressing the same receptor type displayed a stochastic distribution.

Animals↗
PubMed2003

Cell surface carbohydrates and glomerular targeting of olfactory sensory neuron axons in the mouse.

Cell surface carbohydrates have been implicated in axon guidance and targeting throughout the nervous system. We have begun to test the hypothesis that, in the olfactory system, a differential distribution of cell surface carbohydrates may influence olfactory sensory neuron (OSN) axon targeting. Specifically, we have examined the spatial distribution of two different plant lectins, Ulex europaeus agglutinin (UEA) and Dolichos biflorus agglutinin (DBA), to determine whether they exhibit differential and reproducible projections onto the main olfactory bulb. Each lectin exhibited a unique spatial domain of glomerular labeling that was consistent across animals. UEA labeling was strongest in the ventral aspect of the olfactory bulb; DBA labeling was strongest in the dorsal aspect of the olfactory bulb. Some evidence for colocalization was present where these two borders intersected. Large areas of the glomerular layer were not labeled by either lectin. To determine whether patterns of lectin labeling were reproducible at the level of individual glomeruli, UEA labeling was assessed relative to M72-IRES-taulacZ- and P2-IRES-taulacZ-labeled axons. Although glomeruli neighboring these two identified glomeruli were consistently labeled with UEA, none of the lacZ positive axons was lectin labeled. Labeling of vomeronasal sensory neuron axons in the accessory olfactory bulb was more uniform for the two lectins. These data are the first to show a differential distribution of UEA vs. DBA labeling in the main olfactory bulb and are consistent with the hypothesis that a differential distribution of cell surface carbohydrates, a glycocode, may contribute to the targeting of OSN axons.

Animals↗
PubMed2004

Altered epithelial density and expansion of bulbar projections of a discrete HSP70 immunoreactive subpopulation of rat olfactory receptor neurons in reconstituting olfactory epithelium following exposure to methyl bromide.

A previously described subpopulation of rat olfactory receptor neurons, the 2A4(+)ORNs, is 1) distinguished by intense constitutive cytoplasmic immunoreactivity to antibodies to the 70-kD heat shock protein (HSP70); 2) occurs sparsely but consistently through ventral and lateral olfactory epithelium (OE); and 3) projects to just two to three consistently located glomeruli in each olfactory bulb (OB) (Carr et al. [1994] J Comp Neurol 348:150-160). Immunoreactivity appears not to be stress-related. To examine the persistence of these features following destruction and reconstitution of the OE, rats were subjected to methyl bromide-induced OE lesion (Schwob et al. [1995] J Comp Neurol 59:15-37; Schwob et al. [1999] J Comp Neurol 412:439-457] and their OE and OBs examined with antibodies to HSP70 6-10.5 weeks postlesion. Lesioned OE showed significantly increased 2A4(+)ORN densities but no alteration of 2A4(+)ORN zonal distribution. The OBs of lesioned animals showed marked expansions of 2A4(+)ORN bulbar projections, with 2-15-fold increases in numbers of glomeruli showing 2A4(+)axons, and projection expansions were greater in animals maintained on chronic food restriction prior to lesioning. Examination of archival 5-month post-MeBr lesion material indicates that altered projection patterns are maintained.

Animals↗
PubMed2004

Caspase-3 and caspase-9 mediate developmental apoptosis in the mouse olfactory system.

Neuronal apoptosis is a key component in the sculpting of tissues during embryonic and postnatal development and is driven largely by the action of caspases. In the mouse olfactory system, caspase-3 and -9 are expressed in olfactory receptor neurons (ORNs) of adult mice, and their selective retrograde activation drives ORN apoptosis following ablation of their target, the olfactory bulb (OB). Here, we show that both of these caspases are expressed at the earliest stages of ORN embryonic development, and their expression is concentrated in outgrowing ORN axons. The retention, in null mice for both caspases, of a population of ORNs that would normally undergo developmental apoptosis beginning at E13 of development, results in a permanently expanded population of ORNs. In turn, in some caspase-3 null mice, the ORN target organ, the OB, also develops abnormally, resulting in the formation of secondary, apparently functional, extracranial ectopic OBs.

Animals↗
PubMed2004

Quantitative analysis of olfactory receptor neuron projections in the antennal lobe of the malaria mosquito, Anopheles gambiae.

Mosquitoes are highly dependent on the olfactory sense to find their hosts. How olfactory information concerning host odors is represented and processed in the brain to elicit olfactory guided behavior is not known. We present an exploratory analysis of central projections of olfactory receptor neurons originating from antennal and maxillary palp sensilla known to be involved in the detection of host odors in the malaria mosquito, Anopheles gambiae. We developed computational neuroanatomic methods to determine quantitatively the positions of olfactory receptor neuron terminal arborizations and compare them between brains. These quantitative analyses suggested the existence of five nonoverlapping projection zones within the antennal lobe, with one zone receiving exclusive input from maxillary palp sensilla and two zones each receiving exclusive input from trichoid or grooved-peg antennal sensilla. Projection patterns were not found to depend significantly on the odorants used during the staining procedure. The separate zones receiving input from different sensillum types seemed to represent a functional segregation because olfactory receptor neurons present in the different sensilla differed in their response profiles.

Animals↗
PubMed2005

Immunolocalization of Bex protein in the mouse brain and olfactory system.

Bex proteins are expressed from a family of "brain expressed X-linked genes" that are closely linked on the X-chromosome. Bex1 and 2 have been characterized as interacting partners of the olfactory marker protein (OMP). Here we report the distribution of Bex1 and Bex2 mRNAs in several brain regions and the development and characterization of an antibody to mouse Bex1 protein that cross-reacts with Bex2 (but not Bex3), and its use to determine the cellular distribution of Bex proteins in the murine brain. The specificity of the antiserum was characterized by immunoprecipitation and Western blots of tissue and transfected cell extracts and by immunocytochemical analyses of cells transfected with either Bex1 or Bex2. Antibodies preabsorbed with Bex2 still recognize Bex1, while blocking with Bex1 eliminates all immunoreactivity to both Bex1 and Bex2. Bex immunoreactivity (ir) was primarily localized to neuronal cells within several regions of the brain, including the olfactory epithelium, bulb, peri/paraventricular nuclei, suprachiasmatic nucleus, arcuate nucleus, median eminence, lateral hypothalamic area, thalamus, hippocampus, and cerebellum. RT-PCR and in situ hybridization demonstrated the presence of Bex mRNA in several of these regions. Double-label immunocytochemistry indicates that Bex-ir is colocalized with OMP in mature olfactory receptor neurons (ORNs) and in the OMP-positive subpopulation of neurons in hypothalamus. This is the first anatomical mapping of Bex proteins in the mouse brain and their colocalization with OMP in ORNs and hypothalamus.

Age Factors↗
PubMed2005

Olfactory marker protein modulates primary olfactory axon overshooting in the olfactory bulb.

Olfactory marker protein (OMP) is expressed by mature primary olfactory sensory neurons during development and in adult mice. In mice that lack OMP, olfactory sensory neurons have perturbed electrophysiological activity, and the mice exhibit altered responses and behavior to odor stimulation. To date, defects in axon guidance in mice that lack OMP have not been investigated. During development of the olfactory system in mouse, primary olfactory axons often overshoot their target glomerular layer and project into the deeper external plexiform layer. These aberrant axonal projections are normally detected within the external plexiform layer up to postnatal day 12. We have examined the projections of primary olfactory axons in OMP-tau:LacZ mice and OMP-GFP mice, two independent lines in which the OMP coding region has been replaced by reporter molecules. We found that axons overshoot their target layer and grow into the external plexiform layer in these OMP null mice as they do in wild-type animals. However, in the absence of OMP, overshooting axons are more persistent and remain prominent until 5 weeks postnatally, after which their numbers decrease. Overshooting axons are still present in these mice even at 8 months of age. In heterozygous mice, axons also overshoot into the external plexiform layer; however, there are fewer axons, and they project for shorter distances, compared with those in a homozygous environment. Our results suggest that perturbed electrophysiological responses, caused by loss of OMP in primary olfactory neurons, reduce the ability of primary olfactory axons to recognize their glomerular target.

Animals↗
PubMed2006

Multiple olfactory receptor neurons and their axonal projections in the antennal lobe of the honeybee Apis mellifera.

The poreplate sensilla of honeybees are equipped with multiple olfactory receptor neurons (ORNs), which innervate glomeruli of the antennal lobe (AL). We investigated the axonal projection pattern in glomeruli of the AL (glomerular pattern), formed by the multiple ORNs of individual poreplate sensilla. We used the different glomerular patterns to draw conclusions about the equipment of poreplate sensilla with different ORN types. ORNs of single poreplate sensilla were stained and analyzed by laser-scanning confocal microscopy and 3D software (AMIRA). In 13 specimens we found between 7 and 23 ORNs. This is in accordance with data found in the literature (5-35 ORNs) suggesting that all ORNs of the single poreplate sensilla were stained. The ORNs innervate the AL via all four sensory tracts (T1-T4), and glomeruli of the anterior part of the AL are more often innervated. Each ORN innervates a single glomerulus (uniglomerular), and all ORNs of one poreplate sensillum project to different glomeruli. Visual inspection and individual identification of glomeruli, based on the honeybee digital AL atlas, were used to evaluate mapping of glomeruli by a rigid transformation of the experimental ALs onto a reference AL. ORNs belonging to individual poreplate sensilla form variable glomerular patterns, and we did not find a common organization of glomerular patterns. We conclude that poreplate sensilla are equipped with different ORN types but that the same ORN types can be found in different poreplate sensilla. The equipment of poreplate sensilla with ORNs is overlapping. The mapping of glomeruli by rigid transformation is revealed to be a powerful tool for comparative neuroanatomy.

Animals↗
PubMed2006

Time frame of mitral cell development in the mice olfactory bulb.

Along with tufted cells, mitral cells are the principal projection neurons in the olfactory bulb (OB). During the development of the OB, mitral cells migrate from the ventricular zone to the intermediate zone, where they begin to send axons along the lateral olfactory tract (LOT) to the cortical olfactory zones. Subsequently, they lose their tangential orientation, enabling them to make contact with the axons of the olfactory sensory neurons (OSN) that innervate the whole OB. Here, we investigated the distinct morphological features displayed by developing mitral cells and analyzed the relationship between the changes undertaken by these neurons and the arrival of the OSN axons. Immunostaining for specific markers of developing axons and dendrites, coupled with the use of fluorescent tracers, revealed the morphological changes, the continuous reorientation, and the final refinement that these cells undergo. We found that some of these changes are dependent on the arrival of the OSN axons. Indeed, we identified three main chronological events: 1) newly generated neurons become established in the intermediate zone and project to the LOT; 2) the cells reorient and spread their dendrites at the same time as OSN axons penetrate the OB (this is a sensitive period between embryonic day (E)15-16, in which the arrival of afferents establishes a spatial and temporal gradient that facilitates protoglomerulus and glomerulus formation); and 3) final refinement of the radially orientated cells to adopt a mature morphology. These results suggest that both afferent inputs and intrinsic factors participate to produce the well-defined sensory system.

Aging↗
PubMed2006

Chemotopic representations of aromatic odorants in the rat olfactory bulb.

Our laboratory has characterized spatial patterns of evoked neural activity across the entire glomerular layer of the rat olfactory bulb using primarily aliphatic odorants that differ systematically in functional groups and hydrocarbon structures. To represent more fully the true range of odorant chemistry, we investigated aromatic compounds, which have a more rigid molecular structure than most aliphatic compounds and are particularly salient olfactory stimuli for humans. We first investigated glomerular patterns of 2-deoxyglucose uptake in response to aromatic compounds that differ in the nature and position of their functional groups (e.g., xylenes, trimethylbenzenes, tolualdehydes, benzaldehydes, methyl toluates, and anisaldehydes). We also studied the effects of systematic increases in the number and length of alkyl substituents. We found that most aromatic compounds activated glomeruli in the dorsal part of the bulb. Within this general area, aromatic odorants with oxygen-containing substituents favored activation of more rostral regions, and aromatic hydrocarbons activated more posterior regions. The nature of substituents greatly affected the pattern of glomerular activation, whereas isomers differing in substitution position evoked very similar overall patterns. These relationships between the structure of aromatic compounds and their spatial representation in the bulb are contrasted with our previous findings with aliphatic odorants.

Administration, Inhalation↗
PubMed1979

The organization of feline entopenduncular nucleus projections: anatomical studies.

The organization of entopeduncular nucleus (EPN) projections was studied in cats using autoradiographic and horseradish peroxidase (HRP) techniques. In autoradiographic studies, EPN axons were found to terminate in a J-shpaed region in the dorsal and medial part of the ventral anterior nucleus (VA) and the rostral portion of the adjacent ventral lateral nucleus (VL). EPN axons also terminated in the rostral portion of the centrum medianum (CM), the ventrolateral portion of the lateral habenular nucleus (LHB), and the pedunculopontine nucleus (PP). The VA included the largest terminal field although the LHB had the greatest density of terminals. Regardless of the region of EPN into which amino acids were injected, the terminal fields were the same: there was no localization within the EPN of the cells projecting to one region. HRP-containing cells were distributed throughout the EPN following injections into the VA, LHB, or PP, although many more cells were labeled following injections into either VA or LHB than PP. EPN cells containing HRP following injections into either VA or LHB were not morphologically different from those not containing HRP in the same respective animals. Following HRP injections into stria medullaris, only cells in the rostral part of the EPN were labeled, providing evidence that rostrally and caudally located EPN neurons have different paths to LHB. Although there may be a rostrocaudal organization of pathways to LHB, individual regions of the nucleus project to the same areas.

Animals↗
PubMed1982

Connections of the amygdala of the rat. IV: Corticoamygdaloid and intraamygdaloid connections as studied with axonal transport of horseradish peroxidase.

The corticoamygdaloid and intraamygdaloid projections of the rat were studied by the use of retrograde transport of horseradish peroxidase (HRP). Observations based on anterograde transport of the enzyme were exploited to determine the course of the intrinsic connections. The HRP was injected stereotactically by means of iontophoresis. Most of the amygdaloid nuclei were selectively injected, and all but a few were reached by more than one approach. The vast majority of corticoamygdaloid fibers was found to originate in cortical areas defined as allocortical (Stephan, '75). From the medial frontal cortex the central amygdaloid nucleus (AC) receives a hitherto undescribed projection originating in the tenia tecta; and both the AC and the lateral amygdaloid nucleus (AL) receive fibers from the prelimbic and infralimbic areas. The anterior cingulate area entertains a weak connection with the basolateral amygdaloid nucleus (BL). As to the insular cortex, the posterior agranular insular area projects to all amygdaloid subdivisions; the BL, AC, and the anterior cortical nucleus (COa) receive, in addition, fibers from the ventral agranular area. The prepyriform cortex connects with the entire amygdala except the medial nucleus (Am). The amygdala receives afferents from a transitional area between the amygdala and the entorhinal area. The entorhinal area proper is related to the amygdala via projections from the ventral part of the lateral entorhinal area to the AL and from the dorsal part of the lateral entorhinal area to the BL. The former nucleus also receives fibers from the perirhinal region. Additional amygdalopetal connections from the hippocampal region include a previously undescribed projection from the temporal two-thirds of CA1 to the AL and BL and to the posterior cortical nucleus (COp) with the adjacent periamygdaloid cortex (PAC). The subiculum projections to the AL, and more modestly to other amygdaloid nuclei. There is an extensive network of intraamygdaloid connections, the Am and AC being the only nuclei not giving rise to the intrinsic fibers.

Amygdala↗
PubMed2006

Misexpression screen for genes altering the olfactory map in Drosophila.

Despite the identification of a number of guidance molecules, a comprehensive picture has yet to emerge to explain the precise anatomy of the olfactory map. From a misexpression screen of 1,515 P{GS} lines, we identified 23 genes that, when forcibly expressed in the olfactory receptor neurons, disrupted the stereotyped anatomy of the Drosophila antennal lobes. These genes, which have not been shown previously to control olfactory map development, encode novel proteins as well as proteins with known roles in axonal outgrowth and cytoskeletal remodeling. We analyzed Akap200, which encodes a Protein Kinase A-binding protein. Overexpression of Akap200 resulted in fusion of the glomeruli, while its loss resulted in misshapen and ectopic glomeruli. The requirement of Akap200 validates our screen as an effective approach for recovering genes controlling glomerular map patterning. Our finding of diverse classes of genes reveals the complexity of the mechanisms that underlie olfactory map development.

A Kinase Anchor Proteins↗