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PubMed1995

Olfactory ensheathing cells: potential for glial cell transplantation into areas of CNS injury.

Ensheathing cells are the glial cells that ensheath olfactory axons within both the PNS and CNS portions of the primary olfactory pathway. These glial cells express a mixture of astrocyte-specific and Schwann cell-specific phenotypic features, support axonal growth by olfactory as well as by non-olfactory neurons, and survive transplantation into injured areas of the CNS. This review article focuses on those phenotypic features that are expressed by ensheathing cells that make them ideal candidates for transplantation into wound cavities in the damaged spinal cord of humans. Although much work remains to be done before such a therapeutic approach can be tried, the likelihood that ensheathing cells could simultaneously perform the roles of both astrocytes and Schwann cells following transplantation is the justification for developing such a therapeutic approach using animal models of spinal cord injury.

Animals↗
PubMed1990

Involvement of specific placental antigen X-P2 in rat olfaction: an immunohistochemical study in the olfactory bulb.

Human placental antigen X-P2 (hPAX-P2), an antigen complex associated with cytochrome P-450 of aromatase within estrogen synthesizing tissues, has been reported to be present in a distinct group of rat primary olfactory receptors involved in suckling behavior. In this study, most of the mitral and tufted cells in the rat olfactory bulb were found to possess hPAX-P2 immunoreactivity. This suggests that the activity of these cells can be hormonally modulated and that hPAX-P2 is involved in rat olfaction not only at the receptor level but also at integrative brain levels via the secondary projecting neurons of the olfactory pathway.

Animals↗
PubMedDate not supplied

Local neurons play key roles in the mammalian olfactory bulb.

Over the past few decades, research exploring how the brain perceives, discriminates, and recognizes odorant molecules has received a growing interest. Today, olfaction is no longer considered a matter of poetry. Chemical senses entered the biological era when an increasing number of scientists started to elucidate the early stages of the olfactory pathway. A combination of genetic, biochemical, cellular, electrophysiological and behavioral methods has provided a picture of how odor information is processed in the olfactory system as it moves from the periphery to higher areas of the brain. Our group is exploring the physiology of the main olfactory bulb, the first processing relay in the mammalian brain. From different electrophysiological approaches, we are attempting to understand the cellular rules that contribute to the synaptic transmission and plasticity at this central relay. How olfactory sensory inputs, originating from the olfactory epithelium located in the nasal cavity, are encoded in the main olfactory bulb remains a crucial question for understanding odor processing. More importantly, the persistence of a high level of neurogenesis continuously supplying the adult olfactory bulb with newborn local neurons provides an attractive model to investigate how basic olfactory functions are maintained when a large proportion of local neurons are continuously renewed. For this purpose, we summarize the current ideas concerning the molecular mechanisms and organizational strategies used by the olfactory system to encode and process information in the main olfactory bulb. We discuss the degree of sensitivity of the bulbar neuronal network activity to the persistence of this high level of neurogenesis that is modulated by sensory experience. Finally, it is worth mentioning that analyzing the molecular mechanisms and organizational strategies used by the olfactory system to transduce, encode, and process odorant information in the olfactory bulb should aid in understanding the general neural mechanisms involved in both sensory perception and memory. Due to space constraints, this review focuses exclusively on the olfactory systems of vertebrates and primarily those of mammals.

Animals↗
PubMed2006

Immunocytochemical localization of the GABAB2 receptor subunit in the glomeruli of the mouse main olfactory bulb.

The olfactory input to the brain is carried out by olfactory nerve axons that terminate in the olfactory bulb glomeruli and make synapses onto dendrites of glutamatergic projection neurons, mitral and tufted cells, and GABAergic interneurons, periglomerular cells. The dendrites are reciprocally connected through asymmetric synapses of mitral/tufted cells with periglomerular cells and symmetric synapses of the opposite direction. Transmission at the first synapse in the olfactory pathway is regulated presynaptically, and this regulation is mediated, in part, by metabotropic GABAB receptors that, when activated, inhibit transmitter release from the olfactory nerve. Functional GABAB receptors are heterodimers composed of the GABAB1 and GABAB2 subunits. Studies using double immunofluorescence have shown colocalization of both subunits in the glomerular neuropil, and ultrastructural studies have localized GABAB1 to extrasynaptic, synaptic, and perisynaptic sites on the plasma membrane of olfactory nerve terminals. We studied the subcellular localization of GABAB2 in the mouse olfactory glomeruli using a subunit-specific antibody and preembedding immunogold labeling. Immunoreactivity for GABAB2 was associated with symmetric dendrodendritic synapses of periglomerular cells with mitral/tufted cells and was localized to the extrasynaptic plasma membrane of presynaptic dendrites, and extrasynaptic, synaptic, and perisynaptic sites on the plasma membrane of postsynaptic dendrites. The results suggest that postsynaptic, and perhaps presynaptic, GABAB receptors may be expressed at GABAergic synapses between dendrites of periglomerular interneurons and projection neurons. Immunolabeling was observed at junctions of the olfactory nerve with mitral/tufted cell dendrites, providing ultrastructural evidence for the expression of the GABAB2 subunit at the primary olfactory synapse.

Animals↗
PubMed2006

Olfactory loss in aging.

Olfactory loss is a common age-related complaint that may be caused by changes in the anatomy of the structures required for olfaction (for example, loss of olfactory receptor cells) or in the environment surrounding the receptor cell (for example, altered nasal mucus composition). However, aging, as well as age-related diseases and medications, may also alter the distribution, density, or function of specific receptor proteins, ion channels, or signaling molecules that affect the ability of neural elements throughout the olfactory pathway to signal and process odorant information. Although a great deal has been learned about the prevalence and nature of age-related olfactory loss, we are just beginning to explore avenues to prevent or alleviate this sensory deficit. Some studies suggest that, rather than being a necessary outcome of aging, age-associated factors such as chronic diseases, medications, and dental and sinus problems are the primary culprits in causing olfactory impairment. This idea suggests optimism in that, as we address these other age-related health issues, the prevalence of olfactory loss will lessen as well.

Aged↗
PubMed1999

Olfactory stimulation enhances light-induced phase shifts in free-running activity rhythms and Fos expression in the suprachiasmatic nucleus.

There is evidence to suggest that the olfactory and circadian systems are linked, functionally, and that olfactory stimuli can modulate circadian rhythms in mammals. Furthermore, olfactory bulb removal can alter free-running rhythms in animals housed in constant darkness and can attenuate the effect of social stimuli on photic entrainment of circadian rhythms. The mechanisms through which olfactory stimuli influence circadian rhythms are not known. One possibility is that olfactory stimuli influence circadian rhythms by modulating the activity of the circadian clock located in the hypothalamic suprachiasmatic nucleus. To study this, we assessed the effect of olfactory stimulation on free-running rhythms and on photic resetting of the circadian clock in rats using phase shifts in wheel-running rhythms and expression of the transcription factor Fos in the suprachiasmatic nucleus. We found that brief exposure to an olfactory stimulus, cedar wood essence, in the subjective day or subjective night had no effect on either free-running rhythms or Fos expression in the suprachiasmatic nucleus, but that when presented in combination with light, the odor dramatically enhanced light-induced phase shifts and Fos expression in the suprachiasmatic nucleus. Olfactory stimulation alone induced Fos expression in several structures that innervate the suprachiasmatic nucleus, pointing to ways by which stimulus information transmitted in the olfactory pathways could gain access to the suprachiasmatic nucleus to modulate photic resetting. These findings, showing that clock resetting by light can be facilitated by olfactory stimulation, point to a mechanism by which olfactory cues can modulate entrainment of circadian rhythms.

Animals↗
PubMed1999

Mapping membrane potential transients in crayfish (Procambarus clarkii) optic lobe neuropils with voltage-sensitive dyes.

Voltage-sensitive dyes NK 2761 and RH 155 were employed (in conjunction with a 12 x 12 photodiode array) to study membrane potential transients in optic lobe neuropils in the eye stalk of the crayfish Procambarus clarkii. By this means we investigated a pathway linking deutocerebral projection neurons, via hemiellipsoid body local interneurons, to an unidentified target (most likely neurons processing visual information) in the medulla terminalis. Rapid (10- to 20-ms duration), transient changes in absorption with the characteristics of action potentials were recorded from the optic nerve and the region occupied by deutocerebral projection neurons after stimulation of the olfactory globular tract in the optic nerve and were blocked by 1 microM tetrodotoxin. Action potentials appeared to propagate to the glomerular layer of the hemiellipsoid body where synaptic responses were recorded from a restricted region of the hemiellipsoid body occupied by dendrites of hemiellipsoid body neurons. Action potentials were also recorded from processes of hemiellipsoid body neurons located in the medulla terminalis. Synaptic responses in the hemiellipsoid body and medulla terminalis were eliminated by addition to the saline of 500 microM Cd2+ or 20 mM Co2+, whereas the action potential attributed to branches of deutocerebral projection neurons in the hemiellipsoid body remained unaffected. Action potentials of hemiellipsoid body neurons in the medulla terminalis evoked postsynaptic potentials (50- to 200-ms duration) with an unidentified target in the medulla terminalis. Transient absorption signals were not detected in either the internal or external medulla nor were they recorded from other parts of the optic lobes in response to electrical stimulation of axons of the deutocerebral projection neurons. Functional maps of optical activity, together with electrophysiological and pharmacological findings, suggest that gamma-aminobutyric acid affects synaptic transmission in glomeruli of the hemiellipsoid body. Synapses of the olfactory pathway located in the medulla terminalis may act as a "filter," modifying visual information processing during olfactory stimulation.

Animals↗
PubMed2003

[Gustatory disorders during multiple sclerosis relapse].

Gustatory dysfunction is a known but uncommon element in the course of multiple sclerosis. Gustatory dysfunction has been described during the chronic progressive phase and during the relapse phase. We report five patients with clinically definite multiple sclerosis who developed transient gustatory disorders during the relapse phase of their disease. Agueusia occurred as one of the first symptoms in three patients, revealing the disease. Symptoms generally improved with remission or corticosteroid administration. These disorders are due to demyelinating lesions of the gustatory pathways in the thalamus or brainstem. MRI studies were not performed during the relapse phase and no clinical neuroimaging correlations could be established. Agueusia may be accompanied by olfactory dysfunction which is due to plaque demyelinization of the olfactory pathways, particularly in the temporal and inferior frontal lobes. Taste anomalies can also be observed in other diseases, including systemic diseases such as sarcoidosis or Sjogrën's syndrome. Drug-induced gustatory disorders are also reported.

Adult↗
PubMed1997

Continuous neurogenesis in the olfactory brain of adult shore crabs, Carcinus maenas.

To scrutinize the common belief that the number of neurons in the CNS of adult decapod crustaceans stays constant, in spite of their dramatic postlarval increase in size, I counted olfactory projection neurons (OPNs) in the brains of differently-sized postlarval shore crabs, Carcinus maenas, and performed in vivo labeling of proliferating cells with 5-bromo-2'-deoxyuridine (BrdU) on brains of adults. The number of OPNs increases continuously throughout the postlarval life of shore crabs and approximately doubles from the very young to the oldest animals. Brain sections from adult crabs labeled with BrdU revealed ongoing proliferation of cells in the lateral soma cluster, which consists of OPN cell bodies, and in the cluster of somata of hemiellipsoid body local interneurons, which are the targets of the OPNs. Post-injection survival times from 5.5 to 120 h revealed a small but relatively constant number of labeled nuclei with neuronal morphology in both soma clusters of all specimens (31.3 +/- 9.5 S.D. nuclei per lateral cluster, n = 29; 20.1 +/- 4.5 S.D. nuclei per hemiellipsoid body cluster, n = 10). The labeled nuclei were located in a distinct proliferative zone in each cluster. There were significantly more labeled nuclei in both soma clusters after a prolonged post-injection survival time of 1 month (71.3 +/- 7.8 S.D. nuclei per lateral cluster, n = 4; 38.2 +/- 7.1 nuclei per hemiellipsoid body cluster, n = 6). In both soma clusters the labeled nuclei formed a compact group that was dislocated from the proliferation zone towards the outer edge of the cluster. In the proliferation zone of the lateral cluster histological stainings revealed cell bodies of typical neuronal shape that are slightly smaller and more intensely stained than the surrounding OPN somata. Some of these cell bodies were captured in various stages of mitosis. Collectively, these data indicate that continuous neurogenesis occurs in the central olfactory pathway of the brain of shore crabs throughout their entire adult life. This unexpected structural plasticity may enable long-lived decapod crustaceans to adapt to ever-changing olfactory environments.

Age Factors↗
PubMed2007

Anatomical organization of antennal lobe projection neurons in the moth Heliothis virescens.

A prerequisite for understanding how odor information is coded in the central nervous system is to know the morphology and spatial relationship of the principal neurons forming the olfactory pathways. The present account provides an anatomical description of the morphology of the neuronal connections between the antennal lobe and the protocerebrum in the moth Heliothis virescens, a species used for studies of olfactory processing and learning. Intracellular labeling and antennal lobe focal injections with dextran fluorescent markers were combined with neuropil immunostaining and three-dimensional reconstructions. The experiments revealed four antennocerebral tracts, the inner, middle, outer, and dorsomedial, and eight morphological types of projection neurons in addition to a neuron with an unpaired median soma in the subesophageal ganglion. Multiglomerular projection neurons, present in all but the dorsomedial antennocerebral tract, project in several olfactory foci of the protocerebral neuropil. With few exceptions, these neurons do not innervate the calyces of the mushroom body. Uniglomerular projection neurons appear most numerous in the inner antennocerebral tract but are also present in the outer and dorsomedial tracts. These neurons always ramify in the calyces of the mushroom body and in the lateral horn. The projection areas of the neurons following different tracts are largely separated in the secondary olfactory centers. This is most evident in the lateral horn, whereas, in the calyces, the axonal ramifications are more intermingled. The mushroom body architecture, revealed by neuropil immunolabeling, showed striking similarities to that of other lepidopteran species as well as insects of other taxa.

Afferent Pathways↗
PubMed1989

Electro-olfactogram (EOG) in olfactometry.

The electro-olfactogram (EOG) is a potential originated in olfactory epithelium evoked by odorous stimulation, which has been demonstrated and termed by Ottoson (1959). In order to ascertain the clinical application of EOG, we attempted to record similar potentials in human subjects. In some preliminary experiments using rabbits, it was quite easy to produce Ottoson's findings. In human subjects, however, there were sometimes great technical difficulties owing to the hidden anatomical position of the olfactory epithelium. Then we utilized Olympus selfoscope endoscopy for placing and retaining the electrode to the olfactory portion precisely and safely, with a tube for sending airborne odor. As results, we succeeded in recording negative spike discharge similar to Ottoson's findings. We examined a total of 27 nasal cavities in 22 patients with peripheral olfactory disorders and 11 nasal cavities in 12 patients with central olfactory disorders. The positive EOG rate in patients with peripheral or central olfactory disorders was 28 and 69%, respectively. Moreover, the positive rate was decreased in proportion to the degree of olfactory disorders in chronic rhinosinusitis. No positive EOG was observed in anosmic nasal cavities, while it was 68% in normal persons and resulted in an equal value to anosmia group caused by the damage of central olfactory pathway. From these results, it is considered that the positive EOG study is the only method which provides objective finding for the differential diagnosis of anosmia caused by disorders of olfactory epithelium or disorders of central olfactory tract.

Chronic Disease↗
PubMed1983

Mode of entry of a neurotropic arbovirus into the central nervous system. Reinvestigation of an old controversy.

The mechanism by which neurotropic arboviruses gain access to the central nervous system remains uncertain, although it is generally assumed that viremic infection results in growth across or passive diffusion through brain capillaries. In contrast to the natural reservoir hosts of these arboviruses, clinical hosts (e.g., horses, humans) have viremias of very brief duration and low magnitude. We investigated the question of neuroinvasion in 5- to 6-week-old Syrian hamsters infected with St. Louis encephalitis virus (strain TBH-28). This model shares with the human disease low or undetectable viremia and many clinical and pathoanatomical features. The mortality rate after intraperitoneal inoculation of a moderate viral dose was 88%. No viremia was detectable by a sensitive assay in 31% of the animals. In the remaining hamsters, the mean peak viremia was 1.0 log10 plaque-forming units/0.05 ml and the mean duration 1 to 2 days. There was no correlation between viremia and outcome of infection, length of incubation period, or brain virus titer. Tissue infectivity studies showed a rise in titer in the olfactory neuroepithelium on day 4 postinoculation, then in the olfactory bulbs (day 5 postinoculation), and finally in the remainder of the brain (day 6 postinoculation). Specific immunofluorescence was demonstrated in the bipolar neurons of the olfactory epithelium, their dendrites, and in axon bundles of the olfactory nerves in the submucosa. By electron microscopy, virus particles and associated tubular structures were demonstrated within dendrites, perikarya, and axons of olfactory neurons, and to a lesser extent in macrophages and Bowman's gland cells in the lamina propria. In cells of Bowman's glands large numbers of virions were sequestered within secretory granules. Virus was recovered from nasal washings on day 4 postinoculation. Similar findings were obtained in weanling mice inoculated intraperitoneally with another (mouse-virulent) St. Louis encephalitis viral strain (77V-12908). These data taken together indicate that the olfactory pathway is the principal route of viral entry into the central nervous system. After peripheral inoculation a low-level viremia results in infection of highly susceptible cells in the olfactory neuroepithelium, allowing centripetal axonal transport of virus to the olfactory bulb, whence spread is unimpeded throughout the neuropil of the central nervous system. Infection of Bowman's gland cells in the olfactory mucosa and shedding of virus in nasal mucus may be an adaptation for nonarthropod-borne transmission, a feature of many flaviviruses.

Animals↗
PubMed2003

Blockade of neurotransmission in Drosophila mushroom bodies impairs odor attraction, but not repulsion.

Olfaction can elicit a rich perceptual experience. It is not known, however, whether olfactory information is decomposed into various components and processed in distinct perceptual centers as in other sensory systems, such as vision, where neural representations of different visual sensations are segregated in different cortical regions, despite the fact that multiple structures of the primary olfactory cortex receive projections from the olfactory bulb. Here, we use Drosophila as a model to investigate whether different olfactory information may be processed in separate brain structures. Organizations of the peripheral olfactory system are remarkably similar from mammals to insects. As in vertebrates, the olfactory pathway in Drosophila follows similar convergence and divergence, and multiple high-order structures in the Drosophila brain, including the mushroom body (MB) and lateral horn (LH) of the protocerebrum, receive olfactory input. We specifically blocked neurotransmission in the MB while leaving the LH unaffected and examined its effect on olfactory avoidance and attraction behaviors. We show that blocking MB activity disrupted responses to attractive, but not repulsive, odors, and this finding suggests that attractive and repulsive olfactory information may be separately processed in higher olfactory centers of the Drosophila brain.

Animals↗
PubMed1990

Immunohistochemical and biochemical evidence for the putative inhibitory neurotransmitters histamine and GABA in lobster olfactory lobes.

As an initial effort to investigate possible inhibitory interactions in the olfactory system of the spiny lobster, studies were conducted to identify and localize the putative inhibitory neurotransmitters histamine and GABA in the olfactory lobe. Biochemical studies demonstrated that olfactory lobe tissue was capable of synthesizing histamine from radioactive histidine and GABA from glutamic acid. Immunohistochemistry was used to localize histamine and GABA in brain sections, by using either avidin-biotin conjugated peroxidase or fluorescein conjugated secondary antibody. Specific histamine-like and GABA-like immunoreactivity was found in soma clusters of olfactory interneurons, adjacent to the olfactory lobe. Small, putative glial cells displaying intense histamine-like immunoreactivity were found interspersed among the glomeruli of the lobe. The accessory lobe exhibited moderate immunostaining for both histamine and GABA. Positive immunostaining for histamine and GABA was also found in the olfactory lobes, with a predominance of staining in the outer caps of the glomeruli, which are thought to be the regions where the primary afferent terminals contact the processes of second-order olfactory neurons. These findings collectively implicate inhibition at the first synaptic level of the olfactory pathway in the spiny lobster.

Animals↗
PubMed1993

Pathways linking the olfactory bulbs with the medial preoptic anterior hypothalamus are important for intermale aggression in mice.

Manipulations affecting olfaction, as well as bilateral lesions of the medial preoptic anterior hypothalamic (MPAH) continuum, decrease intermale aggression in mice. In the present study, unilateral removal of an olfactory bulb was combined with a contralateral lesion of the MPAH. This surgery, like bulbectomy and bilateral lesions of the MPAH, substantially decreased aggressive behavior. This surgery bilaterally destroys the ipsilateral links between the olfactory bulbs and the MPAH, and it is this disruption that presumably causes the decrease in aggression. The effect is not due to removal of an olfactory bulb combined with hypothalamic damage per se, because ipsilaterally lesioned/bulbectomized males continued to fight without decrement after surgery. These results provide compelling evidence that multisynaptic neural pathways linking the chemosensory systems of the olfactory bulbs with the rostral hypothalamus are involved in the regulation of intermale aggression in mice.

Aggression↗
PubMed2001

Functional genomics of odor-guided behavior in Drosophila melanogaster.

The avoidance response to repellent odorants in Drosophila melanogaster, a response essential for survival, provides an advantageous model for studies on the genetic architecture of olfactory behavior. Transposon tagging in a highly inbred strain of flies in combination with a rapid and simple statistical behavioral assay enables the identification of not only large phenotypic effects, but also small aberrations from wild-type avoidance behavior. The recent completion of the sequence of the Drosophila genome facilitates the molecular characterization of transposon-tagged genes and correlation between gene expression and behavior in smell-impaired (smi) mutant lines. Quantitative genetic analyses of a collection of smi lines in a co-isogenic background revealed an extensive network of epistatic interactions among genes that shape the olfactory avoidance response. Candidate genes for several of these transposon-tagged smi loci implicate genes that mediate odorant recognition, including a novel odorant binding protein; signal propagation, including a voltage-gated sodium channel; and a protein containing multiple leucine rich repeats and PDZ domains likely to be involved in postsynaptic organization in the olfactory pathway. Several novel genes of unknown function have also been implicated, including a novel tyrosine-regulated protein kinase. The discovery and characterization of novel gene products that have major, hitherto unappreciated effects on olfactory behavior will provide new insights in the generation and regulation of odor-guided behavior. The identification and functional characterization of proteins encoded by smi genes that form part of the olfactory subgenome and correlation of polymorphisms in these genes with variation in odor-guided behavior in natural populations will advance our understanding of the genetic architecture of chemosensory behavior.

Animals↗
PubMed1994

Central processing of sex pheromone, host odour, and oviposition deterrent information by interneurons in the antennal lobe of female Spodoptera littoralis (Lepidoptera: Noctuidae).

Physiological and anatomical characteristics of antennal lobe interneurons in female Spodoptera littoralis (Boisd.) were investigated using intracellular recording and staining techniques. Responses of local interneurons and projection neurons to female sex pheromone components, host plant odours, and behaviourally active oviposition deterrents were recorded. We found local interneurons and projection neurons that responded specifically to only one or two of the tested odours, but we also found less specific cells, and neurons that responded to most of the tested odourants. These findings show that there are not only specific olfactory pathways in female moths up to the protocerebral level, but also that integration can begin in the antennal lobe. No correlation was found between the degree of specificity of either local interneurons or projection neurons and their respective morphological characteristics. Specialized and unspecialized local interneurons arborized throughout the antennal lobe. Specialized and unspecialized projection neurons had uniglomerular arborizations in the antennal lobe and sent their axons to the calyces of the mushroom body, and to the lateral horn of the protocerebrum. One specific projection neuron had multiglomerular arborizations and projected only to the lateral horn of the protocerebrum. Projection neurons arborizing in the glomeruli closest to the entrance of the antennal nerve always responded to pheromone components. No other correlations were found between the arborization pattern of projection neurons in the antennal lobe or in the protocerebrum and their response characteristics. The sensitivity of local interneurons and projection neurons was in the same range as that of receptor neurons in olfactory sensilla on the antennae, suggesting a much lower convergence in the central nervous system in females than in the pheromone-processing pathway in males.

Animals↗
PubMed1979

Responses of olfactory bulb neurones to the dipeptide carnosine.

Carnosine has been applied by microiontophoresis ot identified neurones in the olfactory bulb of the rat from solutions of different pH. Although mainly without effect when compared with conventional excitatory and inhibitory amino acids, the dipeptide tended to be depressive when ejected as a cation and excitant when ejected as an anion. The results obtained are not in favour of this substance being an excitatory transmitter in the primary olfactory pathway.

Amino Acids↗