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PubMed1990

Changes in electric activity (EEG) of the telencephalon of conscious toads (Bufo paracnemis) caused by cholinergic stimulation of the mesencephalic tegmentum.

Studies were carried out to investigate the effect of microinjection of cholinergic agonist carbamylcholine (carbachol) into the mesencephalic tegmentum of conscious toads (Bufo paracnemis), subjected or not to section of the olfactory nerves, on the electrical activity (EEG) of the telencephalon. The response depended on the type of preexisting EEG activity. Marked desynchronization was observed both in animals with intact nerves and in animals with sectioned nerves, whose previous basal activity was already desynchronized (high frequency and low amplitude). In toads with synchronized basal activity and with intact nerves, an increase, a fall or even abolition of preexisting spindle-like activity occurred, whereas in animals with sectioned nerves the effect was reduction or abolition of spindle-like activity. The data show that stimulation of the mesencephalic tegmentum can alter the electrical activity of the telencephalon and that this effect is not only secondary to a change in nasal air flow alterations since it occurs in toads with sectioned olfactory nerves.

Animals↗

PubMed1991

Immunocytochemical demonstration of salmon GnRH and chicken GnRH-II in the brain of masu salmon, Oncorhynchus masou.

We have recently developed sensitive and specific radioimmunoassays (RIAs) for salmon gonadotropin-releasing hormone (sGnRH) and chicken GnRH-II (cGnRH-II) and have measured the contents of both GnRHs in the rainbow trout brain. Our results showed that contents of the two GnRHs are variable among different brain regions. Therefore, in order to confirm the differential distribution of the two GnRHs by a different technique, we examined the distribution of immunoreactive sGnRH and cGnRH-II in the brain of masu salmon by using immunocytochemical techniques. sGnRH immunoreactive (ir) cell bodies were scattered in the transitional areas between the olfactory nerve and the olfactory bulb, the ventral olfactory bulb, between the olfactory bulb and the telencephalon, the ventral telencephalon, and the preoptic area. These sGnRH-ir cell bodies were dispersed in a strip-like region running rostrocaudally in the most ventral part of the ventral telencephalon. sGnRH-ir fibers were distributed in the various brain regions from the olfactory bulb to the spinal cord. They were especially abundant in the olfactory bulb, ventral telencephalon, preoptic area, hypothalamus, deep layers of the optic tectum, and thalamus. sGnRH-ir fibers also innervated the pituitary directly. cGnRH-II-ir cell bodies were found in the nucleus of the medial longitudinal fasciculus (nMLF). The distribution of cGnRH-II-ir fibers was similar to that of sGnRH-ir fibers, except that cGnRH-II-ir fibers were absent in the pituitary. The number of cGnRH-II-ir fibers was much fewer than that of sGnRH-ir fibers. The results of the present immunocytochemical study are in basic agreement with those of our previous RIA study. Thus, we suggest that in masu salmon, sGnRH not only regulates gonadotropin (GTH) release from the pituitary but also functions as a neuromodulator in the brain, whereas cGnRH-II functions only as a neuromodulator.

Aging↗

PubMed1991

Immunohistological demonstration of spread of Aujeszky's disease virus via the olfactory pathway in HPCD pigs.

The spread of Aujeszky's disease virus (ADV) from nasal mucosa via the olfactory pathway was studied in HPCD pigs. ADV antigen was detected in the epithelial cells, nasal gland cells, olfactory nerve cells and peripheral nerve fibres in the nasal cavity and in neuroglial cells in the olfactory bulb. Results indicate that the olfactory pathway is one of the most important neuronal pathways of ADV infection in pigs.

Animals↗

PubMed1974

Olfactory Basis of Homing Behavior in the Giant Garden Slug, Limax maximus.

Time lapse photography of slugs living in an experimental enclosure shows that these animals can return to a homesite from over 90 cm by a direct route. Slime trail following and vision are not involved in this behavior. In the presence of a low velocity wind, homing occurs upwind. Surgical disconnection of the presumptive olfactory apparatus (digitate ganglion) from the central nervous system eliminates homing. Neurophysiological recordings from the receptor surface associated with the digitate ganglion and the olfactory nerve demonstrate the olfactory function of the digitate ganglion. The olfactory acuity and capacity for directed locomotion via olfactory cues are also relevant to studies of slug feeding behavior, ecology, and learning ability.

Journal Article↗

PubMed1981

Analysis of a long-duration inhibitory potential in mitral cells in the isolated turtle olfactory bulb.

1. An inhibitory potential of long duration has been analysed in intracellular recordings from mitral cells in the isolated turtle olfactory bulb preparation. 2. A single volley in the olfactory nerves or lateral olfactory tract elicited synaptic inhibition in mitral cells, followed by a long-lasting hyperpolarization of the cell. This slow potential has been termed the Is component, to distinguish it from the earlier I1 and I2 components to the inhibitory post-synaptic potentials (i.p.s.p.s). 3. The slow Is component was inhibitory, as shown by the interruption of spontaneous discharges, and the blockage of responses to injected current and incoming volleys. The duration of the hyperpolarization following a single volley usually lasted up to 5 sec, and occasionally longer. 4. The Is response decreased in amplitude with either depolarizing or hyperpolarizing current injection, without showing a reversal potential. This contrasted with the earlier I1 and I2 components, which showed reversal potentials characteristic of i.p.s.p.s. 5. Tests of membrane conductance showed that the conductance, which was increased during the preceding i.p.s.p., decayed to control values during the early part of the Is potential. 6. The Is response shares some characteristics with slow potentials reported in certain other vertebrate neurones. This type of response may be involved in longer-term neuromodulatory control of the excitability of the mitral cell.

Animals↗

PubMed1982

Feline viral rhinotracheitis virus: explant and cocultivation studies on tissues collected from persistently infected cats.

Tissues from 16 feline viral rhinotracheitis (FVR) carrier cats and 15 controls were examined by the techniques of homogenisation, cocultivation and explant cultivation. The tissues examined included trigeminal ganglion and maxillary nerve, olfactory lobe and nerve endings, tonsils, submandibular lymph node, spleen and parotid salivary gland. Most of the cats were shedding FVR virus in the oropharynx at the time the tissues were collected. No evidence of a persistent FVR virus infection was found in any of the tissues. Trigeminal ganglion explant cultures from six FVR virus carrier cats were shown to be latently infected with feline syncytia forming virus by treatment with 5-iododeoxyuridine. Five control cats had trigeminal ganglion explant cultures similarly treated but produced no evidence of infection. The possible significance of this is discussed.

Animals↗

PubMed1993

[The sense of smell: analysis of odors and olfactory memory].

Olfactory transduction is mediated by neuroepithelial cells localized on turbinal crests in naris. Odorant molecules are uptaked by the mucosa which flows on epithelial surface and some of the molecules enter in contact with olfactory cells tentacles. Odorant molecules interact with molecular receptors bound to cell membrane and induced successive reactions leading to ion channels opening and then to receptor potential appearance. The receptor cells degenerate when molecular receptors are saturated and, further regenerate, according a genetic program and olfactory learning action potentials which appear at the basal pole of the receptor cell are propagated along the small olfactory nerves to the olfactory bulb glomerulus. Several hundred axons enter in one glomerulus among others and make synaptic contacts with one dendritic tree of a mitral cell. The selection of the numerous signals which converge in the glomerulus, the codage in intensity, duration and contrast are made at this level. One odorant molecule activates some glomeruli (rarely one); a complex odor activates a great number of glomeruli according a complex spatial distribution. Following odor stimulation, the electrical signals are analysed in the olfactory bulb which delivers to the olfactory cortex various informations about the odor components that are to be selected and compared to anterior olfactory learning. Animal experimentation and clinical data show that memory storage is made using short, medium and long term memorization. This memory is integrated in the limbic system at the interface of neural structures which regulate the main behaviors and physiological functions. This explains the modulatory role of smell in some behaviors but complicate our understanding of access to olfactory memory.

Epithelial Cells↗

PubMed2006

Brain and sensory organ morphology in Antarctic eelpouts (Perciformes: Zoarcidae: Lycodinae).

Eelpouts of the family Zoarcidae comprise a monophyletic group of marine fishes with a worldwide distribution. Centers of high zoarcid diversity occur in the North Atlantic and North Pacific, with important radiations into the Arctic, along southern South America, and into the Southern Ocean around Antarctica. Along with snailfishes (Liparidae), zoarcids form an important component of the non-notothenioid fauna in the subzero shelf waters of Antarctica. We document the anatomy and histology of the brains, cranial nerves, olfactory apparatus, cephalic lateral lines, taste buds, and retinas of three Antarctic zoarcid species, living at depths of 310-939 m, representing three of the nine genera from this region. The primary emphasis is on Ophthalmolycus amberensis, and we provide a detailed drawing of the brain and cranial nerves of this species. Although this brain reflects general perciform neural morphology, it exhibits a reduction of the (optic) tecta and the eminentia granulares and crista cerebellares of the lateral line system. Interspecific differences among the three species are slight. The olfactory rosette consists of three to four lamellae and the nasal sac, contrary to the claim of Fanta et al. ([2001] Antarct Rec, Natl Inst Polar Res, Tokyo 45:27-42), is not in communication with the cephalic lateral line system. Primary olfactory neurons are abundant and converge on branches of the olfactory nerve. Numerous taste buds are located in the lips. All three species lack an ocular choroid rete and have relatively thin retinas with a low cell density and a single bank of rods as the only type of photoreceptor. Neural diversification among Antarctic zoarcids has not involved the evolution of sensory specialists; brain and sensory organ morphologies do not approach the condition seen in primary deep-sea fishes, or even that of some sympatric non-perciform secondary deep-sea fishes, including liparids and muraenolepidids (eel cods). There may be phylogenetic constraints on brain morphology in perciforms such that we do not see extreme specialization in sensory and neural systems for deep habitats. We suggest that the brains and sensory organs of Antarctic zoarcids reflect habitation of 500-2,000-m depths and likely reflect morphologies seen in zoarcids living on continental slopes elsewhere in the world. This balance among the sensory modalities makes zoarcids relatively generalized among secondary deep-sea fishes and may be one of the reasons this opportunistic and adaptable group has been successful in colonizing a variety of emergent and ephemeral habitats.

Animals↗

PubMed2000

Evidence for intrinsic development of olfactory structures in Pax-6 mutant mice.

It has been reported that the arrival of primary olfactory axons is required to induce the development of the olfactory bulb (OB). On the other hand, the Sey(Neu)/Sey(Neu) mutant mouse (Small eye) has been previously described as a model for the absence of olfactory bulbs, owing to the lack of olfactory epithelium (OE). In the present report, we take advantage of this mutant and study a neural structure in the rostral pole of the telencephalon that phenotypically resembles the prospective OB. We named this formation olfactory bulb-like structure (OBLS). We also report the occurrence, in the mutants, of small epithelial vesicles in the malformed craneofacial pits, resembling an atrophic OE, although a mature olfactory nerve was not identified. Axonal tracing, birthdating, immunohistochemistry, and in situ hybridization using antibodies and probes expressed in the olfactory system, indicated that two distinct structures observed in the OBLS correspond to the main and accessory olfactory bulbs of the control mouse. We propose that the OBLS has developed independently of the external influences exerted by the olfactory nerve. The presence of a prospective OB in the mutants, without intervening olfactory fibers, suggests that intrinsic factors could define brain territories even in absence of the proper afferent innervation. The intrinsic mechanisms and environmental cues in the telencephalon could be sufficient to promote axonogenesis in the projection neurons of the OB and guide their axons in a lateral prospective tract, in the absence of olfactory axons.

Animals↗

PubMed1998

Two novel monoclonal antibodies (1.9.E and 4.11.C) against olfactory bulb ensheathing glia.

We produced and characterized two monoclonal antibodies, termed 1.9.E and 4.11.C, that specifically recognize olfactory bulb ensheathing glia. Both antibodies were generated using the olfactory nerve layer (ONL) of newborn rat olfactory bulbs (P0, P1) as immunogens. The specificity of these antibodies was tested by immunofluorescence techniques on tissue sections and cultures of adult and neonatal rat olfactory bulbs, and by Western blot analysis. 1.9.E labeled the ONL and glomerular layer of the olfactory bulb (OB) of adult rats. In newborn rats, 1.9.E immunostained ensheathing cells from the ONL and peripheral olfactory fascicles. Furthermore, 1.9.E reacted with some processes of the radial glia in the periventricular germinal layer of the newborn rat. Although 4.11.C also specifically labeled ensheathing cells in the adult OB, it did not stain any cell type in the ONL of newborn rats. The lack of double labeling with either 1.9.E or 4.11.C and anti-olfactory marker protein (OMP) antibody, a specific marker for olfactory axons, indicated that none of the monoclonals recognized olfactory axons. Double immunostaining of adult OB cultures with 1.9.E or 4.11.C and anti-p75-nerve growth factor receptor revealed that both antibodies specifically recognized ensheathing glia in those cultures. Filaments were strongly labeled throughout the entire cytoplasm of ensheathing cells, suggesting that 1.9.E and 4.11.C immunoreacted with ensheathing glia cytoskeleton. 4.11.C stained a few Schwann cells in adult sciatic nerve sections. Moreover, 4.11.C immunostained cortical astrocyte cultures from newborn rats (P1). In Western blot analysis both antibodies recognized a major component, migrating with an apparent molecular weight of 60 kDa, from olfactory nerve and glomerular layer (ONGL) extracts of adult and neonatal rats. The pattern of immunoreactivity of 1.9.E and 4.11.C antibodies suggest that both antibodies are specific markers for olfactory ensheathing glia in the adult rat central nervous system (CNS).

Animals↗

PubMed1992

Functional consequences of unilateral olfactory deprivation: time-course and age sensitivity.

Unilateral olfactory deprivation in the rat profoundly modifies olfactory bulb anatomy, chemistry and function. The present report examined the time-course of the functional effects of unilateral deprivation on inhibition in the olfactory bulb using paired-pulse stimulation of the lateral olfactory tract and olfactory nerve. In addition, an attempt was made to correlate these physiological measures with olfactory bulb dopamine and norepinephrine levels and tyrosine hydroxylase immunoreactivity. Deprivation from postnatal day 1 to postnatal day 20 or postnatal day 40 significantly enhanced lateral olfactory tract paired-pulse depression, while late onset deprivation (postnatal day 20) had no effect. Olfactory nerve paired-pulse depression was enhanced by 40 days of deprivation regardless of the age at onset. The time-course of these deprivation-induced physiological changes did not correlate well with reductions in dopamine. Dopamine levels were reduced in all deprivation conditions by 70-80% compared with control bulbs. Norepinephrine content was slightly elevated in deprived bulbs. These results suggest that early olfactory deprivation modifies olfactory bulb synaptic activity and further, as with other sensory systems, these effects are age and duration dependent.

Aging↗

PubMed1992

Rapid structural changes in nerve fibers evoked by electric current pulses.

Using the garfish olfactory nerve, the time-courses of lateral expansion (swelling) and birefringence changes in nerve fibers have been examined at the site of application of electric current pulses. The effects of various chemical agents on these non-electrical signs of rapid structural changes in the nerve fibers have been examined. These studies have shown that a pulse of outwardly-directed current through the superficial layer evokes a fast increase, followed by a slow, gradual increase, in the water-content of the nerve fibers. The full significance of these findings in studies of the process of nerve excitation is discussed.

Animals↗

PubMed2004

Magnetoreception and its trigeminal mediation in the homing pigeon.

Two conflicting hypotheses compete to explain how a homing pigeon can return to its loft over great distances. One proposes the use of atmospheric odours and the other the Earth's magnetic field in the 'map' step of the 'map and compass' hypothesis of pigeon homing. Although magnetic effects on pigeon orientation provide indirect evidence for a magnetic 'map', numerous conditioning experiments have failed to demonstrate reproducible responses to magnetic fields by pigeons. This has led to suggestions that homing pigeons and other birds have no useful sensitivity to the Earth's magnetic field. Here we demonstrate that homing pigeons (Columba livia) can discriminate between the presence and absence of a magnetic anomaly in a conditioned choice experiment. This discrimination is impaired by attachment of a magnet to the cere, local anaesthesia of the upper beak area, and bilateral section of the ophthalmic branch of the trigeminal nerve, but not of the olfactory nerve. These results suggest that magnetoreception (probably magnetite-based) occurs in the upper beak area of the pigeon. Traditional methods of rendering pigeons anosmic might therefore cause simultaneous impairment of magnetoreception so that future orientation experiments will require independent evaluation of the pigeon's magnetic and olfactory systems.

Animal Migration↗

PubMedDate not supplied

Ultrastructure of the olfactory epithelium in intact, axotomized, and bulbectomized goldfish, Carassius auratus.

The ultrastructure of the olfactory epithelium in intact, axotomized, and bulbectomized goldfish was studied by scanning and transmission electron microscopy. A total of 58 adult goldfish of various survival times were examined to determine whether the different types of surgery--either olfactory nerve transection or bulbectomy--yielded differences in the extent or time course of cellular degeneration and renewal. Control animals were also examined in detail to elucidate previous controversial findings concerning the types of olfactory receptor neurons present in goldfish. We found that the intact olfactory epithelium of unoperated control goldfish contains the previously observed ciliated and microvillous receptor neurons, and the crypt cell, a cell type not yet seen in the goldfish but recently reported in other species of teleosts. Following either olfactory nerve transection or bulbectomy, the olfactory receptor neurons showed similar signs of degeneration and subsequent cell death, but, surprisingly, the thickness of the olfactory epithelium did not change significantly with either treatment. The time course of receptor cell renewal was different in axotomized and bulbectomized goldfish. In axotomized goldfish, the amount of receptor cells decreased continuously until 8-13 days after surgery, followed by rapid cell renewal. For bulbectomized goldfish, cell replacement began almost immediately after surgery, with degeneration and cell renewal occurring simultaneously. Six weeks after bulbectomy, cell death and cell proliferation reached a "steady state," and the epithelia did not further improve.

Animals↗

PubMed1998

The expression of tenascin-C along the lamprey olfactory pathway during embryonic development and following axotomy-induced replacement of the olfactory receptor neurons.

Extracellular guidance molecules affect the pathway of growing axons by both attractive and repulsive interactions. Tenascin-C, a glycoprotein of the extracellular matrix, is localized along developing axonal pathways where it may function by repulsion, restricting axons within specific boundaries. The lamprey olfactory pathway offers an advantageous model for studying the role of extracellular matrix proteins in axon guidance because the entire pathway is readily seen in horizontal sections and because lesioning the olfactory nerve will induce the system into a new phase of coordinated neurogenesis and axon outgrowth. Although tenascin-C expression was absent during embryonic development, olfactory nerve fascicles contained tenascin-C-immunoreactivity (IR) during the larval stage. During retrograde degeneration, the fascicles lost tenascin-C-IR. Diffuse unfasciculated axonal processes extending from the olfactory epithelium did not express tenascin-C-IR; however, acetylated tubulin and GAP-43-IR was present, indicating axonal outgrowth. When the newly extended axons of olfactory receptor neurons converged to form fascicles, tenascin-C-IR was evident within the fascicular boundaries. The absence of tenascin-C expression when axonal process were short and diffuse, and its return when axons coalesced within fascicles, supports the view that tenascin-C functions as a boundary molecule in the olfactory pathway.

Animals↗

PubMed1982

Mitogenic effect of myelinated vs unmyelinated garfish nerve extracts.

Mitogenic activities in crude extracts of unmyelinated olfactory nerves and myelinated trigeminal nerves of the garfish Lepisosteus osseus were compared. Extracts of each nerve type were added in a range of protein concentrations to serum-starved, subconfluent cultures of BALB/c 3T3 cells. At low protein concentrations (50-250 micrograms/ml) myelinated nerve extracts produced more [3H]thymidine incorporation in the cultured cells than unmyelinated nerve extracts, while at higher concentrations (500-1000 micrograms/ml), the latter caused as much DNA synthesis as the myelinated nerve extracts, surpassing them at the highest concentrations tested. The results suggest that both axonal and myelin components contribute to the growth-promoting activity in nerve tissue.

Animals↗

PubMed1998

Cancer treatment and growth cone-associated protein in human olfactory bulb glomeruli.

BACKGROUND: Growth cone-associated protein (GAP43) is found in growing axons and we hypothesized that systemic treatment with antineoplastic agents should disrupt regeneration of olfactory receptor cells. Disruption of regeneration should be evidenced by decreased presence of growing axons in the olfactory bulb. OBJECTIVE: To evaluate GAP43 in human olfactory bulb in normal controls and in individuals receiving treatment for neoplasms. DESIGN: Immunocytochemical studies were performed on autopsied human olfactory bulbs to identify both GAP43 and olfactory marker protein immunoreactivity. The former recognizes growing axons and the latter is a definitive marker of adult olfactory nerve. SUBJECTS: Twenty-seven subjects were evaluated. Seven had received either antineoplastic agents and/or x-irradiation of the whole head. Four subjects were young, untreated controls, 10 were age matched to the treated group, and 2 had neoplasms but did not receive antineoplastic agents or irradiation of the head. In addition, 3 subjects with end-stage renal disease were immunostained. RESULTS: Subjects treated with antineoplastic agents or x-irradiation of the whole head displayed no statistically significant loss of olfactory bulb glomeruli, but GAP43 immunoreactivity was markedly reduced in all but 1 subject (P<.32). The subjects with end-stage kidney disease showed frank loss of both GAP43 immunoreactivity and olfactory glomeruli. CONCLUSIONS: Treatment with antineoplastic agents apparently does not damage olfactory epithelium directly but inhibits growth of new axons into the olfactory bulb. This observation suggests that the quality of olfactory experience may change during the course of treatment with antineoplastic agents because the olfactory nerve is not replaced.

Adult↗

PubMed1998

Spatiotemporal patterns of expression of extracellular matrix molecules in the developing and adult rat olfactory system.

Using immunocytochemical methods, we have examined extensively the spatial and temporal patterns of expression of three extracellular matrix molecules-laminin, fibronectin, and type IV collagen-in the embryonic, postnatal (days 2 and 11) and adult rat olfactory system. The study started at embryonic day 14 when olfactory fibres and their associated migrating cells course through the nasal mesenchyme. From embryonic day 14 to the adult, a sheet-like pattern of labelling for laminin, fibronectin and type IV collagen was observed along the basal surface of the olfactory epithelium and around the telencephalon. This type of labelling was continuous around the telencephalic vesicle, whereas it appeared disrupted in the basal lamina of the olfactory epithelium to permit exit of the olfactory axons and their associated migrating cells into the mesenchyme. From embryonic day 14 to day 20, punctate labelling for the three molecules studied was observed along the mesenchymal olfactory pathway, the ventral part of the olfactory bulb, the olfactory nerve layer and the presumptive glomerular layer, respectively. By embryonic day 17, the punctate labelling initially detected in the mesenchymal olfactory pathway was replaced by a sheet-like pattern related to the mature basal lamina surrounding the olfactory axon fascicles. Punctate labelling for laminin and type IV collagen persisted in the olfactory nerve layer and around the glomeruli through adult life whereas that of fibronectin declined and disappeared by postnatal day 2. The spatiotemporal distribution of the punctate pattern for laminin, fibronectin and type IV collagen observed in the embryonic olfactory system suggests a role in delineating the pathway for olfactory axon elongation. The continuous expression of laminin and type IV collagen in the adult olfactory bulb may be related to the regenerative activity and high plasticity of the olfactory system.

Animals↗