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PubMed2006

Optical mapping of spatiotemporal emergence of functional synaptic connections in the embryonic chick olfactory pathway.

In order to understand the functional maturation of the CNS, it is essential to first describe the functional maturation of sensory processing. We have approached this topic by following the ontogenetic patterning of neural circuit formation related to cranial and spinal sensory input using voltage-sensitive dye imaging. In previous studies, we have described the functional maturation of synapses in brainstem/midbrain neural circuits. Here, we elucidate the functional maturation of forebrain circuits by investigating neural networks related to the olfactory nerve (N. I) of chicken embryo. In the isolated N. I-olfactory bulb-forebrain preparation, application of electrical stimulation to N. I elicited excitatory postsynaptic potential (EPSP)-related slow optical signals in the olfactory bulb. The slow signal was mainly mediated by glutamate, and was easily fatigued with repetitive stimuli because of the immaturity of synapses in the embryonic CNS. Ontogenetically, the slow signal was detected from the 6-day embryonic stage, suggesting that functional synaptic connections between N. I and olfactory bulb emerge around this stage. In addition, from the 8-day embryonic stage, another response area was discriminated within the forebrain, which corresponded to the higher-ordered nucleus of the olfactory pathway. In comparison with our previous studies concerning the functional development of other cranial nerve-related sensory nuclei in the embryonic brainstem and midbrain, these results suggest that the olfactory pathway is functionally generated in the early stages of development when neural networks related to other visceral and somatic sensory inputs are also in the process of developing.

Aging↗
PubMed1996

Expression of the surface antigen A2B7 in adult and developing honeybee olfactory pathway.

In order to identify molecules involved in the development of the honeybee olfactory pathway, hybridoma technology has been used. Among different cell lines, A2B7 has been selected. It produces a specific antibody for a surface glycoprotein of 91 kDa. This protein is mainly expressed by both the antennal receptor cells and mushroom body neurons. Based on (i) the spatio-temporal pattern of expression during pupal development; (ii) the cell surface location of the antigen; and (iii) the partial molecular characterization of the antigen, a putative role for this protein in axonal fasciculation and guidance is discussed.

Animals↗
PubMed2003

Uptake of cobalt from the nasal mucosa into the brain via olfactory pathways in rats.

In the olfactory epithelium the primary olfactory neurons are in contact with the environment in the nasal cavity and they are also connected to the olfactory bulbs of the brain. These neurons may therefore provide a pathway by which foreign materials may reach the brain. Inhalation of cobalt-containing dust or fumes occurs in several workplaces, which may result in high exposure of the nasal tissues. In the present study, we used autoradiography and gamma-spectrometry to examine the transport of cobalt in the olfactory system after intranasal administration of 57Co2+ in rats. The results showed an uptake of the metal in the olfactory mucosa and a transport to the olfactory bulbs of the brain. The metal accumulated in the olfactory nerve layer and the terminals of the primary olfactory neurons in the glomerular layer of the bulb. In addition, low levels of cobalt were seen to migrate into the interior of the bulbs and the anterior parts of the olfactory cortex, indicating that the metal is able to leave the terminals of the primary olfactory neurons. Occupational exposure to cobalt, which is a neurotoxic metal, occurs in several workplaces, e.g. the hard metal industry. Memory deficits have been observed among workers exposed to hard metal via inhalation, and it was considered that cobalt may be the neurotoxic component of the hard metal. We propose that inhaled hard metal (as a dust powder or in a mist form) is deposited in the nasal passages and that released cobalt, after uptake into the brain via the olfactory pathway, may cause neurotoxicity. We consider that the olfactory route of entry of cobalt into the brain may be important and should be taken into account when risk assessments are performed concerning occupational inhalation of this metal.

Administration, Intranasal↗
PubMed1987

Anterograde transsynaptic transport of WGA-HRP in rat olfactory pathways.

The transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was studied in rat olfactory pathways. After applications of tracer to the vomeronasal organ, the olfactory epithelium or injections into the olfactory bulb, WGA-HRP reaction product was observed in second-order neuron terminal areas of each pathway, e.g. within posteromedial cortical amygdaloid nucleus, primary olfactory cortex and contralateral primary olfactory cortex, respectively. The results indicate that anterograde transsynaptic transport of WGA-HRP occurs in olfactory pathways, as has been shown in visual, somatosensory and limbic systems, and thus, anterograde transsynaptic transport may be a mechanism for neurons to exchange materials and/or messages.

Animals↗
PubMed2005

Transfer of morphine along the olfactory pathway to the central nervous system after nasal administration to rodents.

The aim of this study was to investigate whether morphine can be transferred along the olfactory pathway to the CNS, thereby circumventing the blood-brain barrier, after nasal administration to rodents. Radiolabelled and unlabelled morphine were administered via the right nostril to mice and rats. Olfactory bulbs, brain tissue and blood samples were collected. Morphine-derived radioactivity was measured using liquid scintillation (LS) and the concentrations of morphine and its metabolite morphine-3-glucuronide (M3G) were also assessed with high-performance liquid chromatography. The location of morphine-derived radioactivity in the rat brain was visualised by autoradiography. Overall, the levels of morphine in the right olfactory bulbs (ROBs) significantly exceeded those in the left olfactory bulbs (LOBs) and brain tissue samples 15, 60 and 240 min after right-sided nasal administration. Fifteen minutes after intravenous administration, there were no significant differences between olfactory bulbs and the other brain areas. Five minutes after nasal administration, autoradiography revealed radioactivity surrounding the ROB and reaching one of the ventricles in the brain. After 60 min, radioactivity had reached the peripheral parts of the ROB. All the techniques used in this study demonstrate that morphine was transferred along the olfactory pathway to the CNS after nasal administration to rodents.

Administration, Intranasal↗
PubMed2001

Olfactory learning induces differential long-lasting changes in rat central olfactory pathways.

In the present work, we investigated lasting changes induced by olfactory learning at different levels of the olfactory pathways. For this, evoked field potentials induced by electrical stimulation of the olfactory bulb were recorded simultaneously in the anterior piriform cortex, the posterior piriform cortex, the lateral entorhinal cortex and the dentate gyrus. The amplitude of the evoked field potential's main component was measured in each site before, immediately after, and 20 days after completion of associative learning. Evoked field potential recordings were carried out under two experimental conditions in the same animals: awake and anesthetized. In the learning task, rats were trained to associate electrical stimulation of one olfactory bulb electrode with the delivery of sucrose (positive reward), and stimulation of a second olfactory bulb electrode with the delivery of quinine (negative reward). In this way, stimulation of the same olfactory bulb electrodes used for inducing field potentials served as a discriminative cue in the learning paradigm. The data showed that positively reinforced learning resulted in a lasting increase in evoked field potential amplitude restricted to posterior piriform cortex and lateral entorhinal cortex. In contrast, negatively reinforced learning was mainly accompanied by a decrease in evoked field potential amplitude in the dentate gyrus. Moreover, the expression of these learning-related changes occurred to be modulated by the animals arousal state. Indeed, the comparison between anesthetized versus awake animals showed that although globally similar, the changes were expressed earlier with respect to learning, under anesthesia than in the awake state. From these data we suggest that associative olfactory learning involves different neural circuits depending on the acquired value of the stimulus. Furthermore, they show the existence of a functional dissociation between anterior and posterior piriform cortex in mnesic processes, and stress the importance of the animal's arousal state on the expression of learning-induced plasticity.

Anesthetics↗
PubMed1991

Delineation of olfactory pathways in the frog nervous system by unique glycoconjugates and N-CAM glycoforms.

The olfactory neuroepithelium, which contains the primary sensory olfactory neurons, continually undergoes neurogenesis and axonal outgrowth throughout life. We describe here several new olfactory system-specific glycoforms of the neural cell adhesion molecule N-CAM in the frog, R. catesbeiana. Using immunochemical methods for in situ localization, we show that the lectin dolichos biflorus agglutinin (DBA) and two monoclonal antibodies, 9OE and 3A6, detect three unique N-CAM forms present on primary sensory olfactory axons. In addition, DBA and monoclonal antibody 9OE recognize glycoconjugates and/or N-CAM glycoforms expressed specifically in discrete central olfactory pathways and regions in frog brain. This is a novel example of unique adhesion molecule forms present in a chain of two neurons within a vertebrate neural pathway. Together these glycoconjugates and N-CAM glycoforms may participate in cellular interactions associated with olfactory system pathway formation and renewal.

Animals↗
PubMed1982

Lesions of the olfactory pathways affecting neophobia and learned aversion differentially.

The contribution of ascending olfactory pathways in neophobia and learned aversion to the same food was investigated in male rats bearing lesions of both olfactory peduncles, or one olfactory peduncle and the opposite lateral olfactory tract or anterior limb of the anterior commissure. The animals were fed on usual stock diet (S) offered as a choice with novel vanilla food (V) on test days: during neophobia (N), then before and after aversive conditioning (Aa, At). Daily food intake was measured, and the preference was expressed as V/(V + S). Experiment 1 included a neophobia test, before aversive conditioning (3 mEq/kg LiCl, i.p.). In Experiment 2, aversion only was studied (0.9 mEq/kg). In the neophobia test, the preference ratio was 7% in unoperated controls, and 43-52% in the 3 lesioned groups. The same controls had preference ratios equal to 64% and 22%, before and after aversive learning. Similar drops were observed for any lesioned group in Expt. 1. The decrease was less obvious, although significant, in rats of Expt. 2 with asymmetric lesions; those with both olfactory peduncles cut through maintained the same preference ratio (48%) before and after LiCl treatment. The data are interpreted assuming that: (1) lateral olfactory tract and anterior commissure both contribute to information processing in neophobia and aversion; (2) olfactory cues subserve neophobia prepotently; and (3) one cannot account for the sensory determinism of neophobia and aversion calling for a single mechanism.

Animals↗
PubMed1974

Carnosine in the primary olfactory pathway.

Carnosine (beta-alanyl-L-histidine) is present in mouse olfactory bulbs and nasal olfactory epithelium at concentrations exceeding that previously reported for any brain region of any species. After peripheral deafferentation, carnosine concentrations in the olfactory bulbs decrease to less than 10 percent that of normal, while other amino compounds are unaffected. Carnosine appears to be highly localized to the primary olfactory pathway.

Amino Acids↗
PubMed1997

Computational parallels between the biological olfactory pathway and its analogue 'the electronic nose': Part I. Biological olfaction.

Over the last fifteen years, we have witnessed a rapid expansion in the development of artificial odour sensing systems, or so called 'electronic nose' systems. Whilst the power of this approach to flavour analysis has undoubtedly been demonstrated by its recent application to various complex odours, it will be argued that the original research programme, aimed at developing a comparative model of the biological olfactory pathway, has degenerated into an attempt to obtain an ad hoc workable system, based around readily available sensor and pattern recognition (PARC) technologies. At the time, the first 'model' nose system reflected the limited understanding of sensory information processing carried out within the biological olfactory pathway. We are now presented with an opportunity to evaluate and re-assess the architecture for an electronic nose, in view of the recent advances in understanding the key processing principals exploited by the olfactory bulb and cortex in the identification and characterisation of molecular stimuli. In Part I of this paper, the rapid developments in the understanding of the information processing performed by the biological olfactory system are critically reviewed, and its relevance to current research in artificial olfaction is considered. Not only have the initial biochemical pathways involved in the transduction of odour stimuli been uncovered, but also computational models of the key synaptic circuits have advanced to the point where network simulations are clearly capable of odour discrimination. The key processing principles exploited in the olfactory pathway for overcoming operating constraints such as sensor drift/degeneration, limited sensitivity, and xenobiotic response are highlighted, so that their integration into the electronic analogue may be explored in Part II.

Computer Simulation↗
PubMed2000

Serotonergic nerve fibers in the primary olfactory pathway of the larval sea lamprey, Petromyzon marinus.

In this study, serotonin (5-hydroxytryptamine; 5HT)-immunoreactive (5HT-IR) neuronal fibers were identified in the primary olfactory pathway of the sea lamprey. These neurons are likely part of a nonolfactory neural system that innervates the olfactory sac. Cell bodies with 5HT immunoreactivity predominated in the lamina propria of the rostral portion of the nasal cavity and were less prevalent adjacent to the olfactory epithelium. The 5HT-IR fibers were parallel to axons of the olfactory receptor neurons in the lamina propria of the olfactory mucosa and in the olfactory nerve. Serotonergic fibers crossed from the olfactory nerve into the olfactory bulb or branched in the caudal portion of the olfactory nerve and terminated at the junction of the olfactory nerve with the olfactory bulb. In the dorsal olfactory bulb, 5HT-IR fibers coursed along the layer of olfactory fibers. Throughout the layer with glomeruli and mitral cells, 5HT-IR fibers were seen along the border of glomerular units. Experimental lesion of the olfactory nerve was used to determine the origin of 5HT-IR fibers rostral to the olfactory bulb. The loss of these fibers and their reappearance during outgrowth of olfactory receptor neurons inferred that they emanate from the cell bodies in the olfactory sac. The results from this study suggest that axons of olfactory receptor neurons in larval lampreys receive modulation by 5HT from these neuronal fibers.

Animals↗
PubMed1978

Denervation of the primary olfactory pathway in mice. V. Long-term effect of intranasal ZnSO4 irrigation on behavior, biochemistry and morphology.

Intranasal irrigation of mice with 0.17 M ZnSO4 solution results in the immediate and total loss of the ability to find a buried food pellet. This anosmia persists for 6 weeks in at least 80% of the treated mice and for 4 months in half of the animals. This marked behavioral effect is matched by a long-term reduction of the levels of carnosine synthesis and transport in the primary olfactory pathway. These biochemical parameters are virtually undetectable at two weeks after treatment and even at one year after treatment do not exceed 5-10% of average control values. Light microscopic observations of tissues of the primary olfactory pathway at various times after treatment are consistent with these observations and indicate a substantial destruction of the olfactory epithelium with subsequent atrophy of the olfactory bulb. At very long intervals after treatment, some receptor regeneration is apparent with accompanying reinnervation of the olfactory bulb. Estimates from microscopy and biochemistry suggest that much less than 10% of the normal complement of functioning receptor cells is adequate to give apparently normal food-finding behavior.

Alanine↗
PubMed1994

Olfactory pathways in three patients with cryptococcal meningitis and acquired immune deficiency syndrome.

The olfactory mucosa, bulbs and tracts were examined for the presence of Cryptococcus neoformans in 3 patients with the acquired immune deficiency syndrome (AIDS) and cryptococcal meningitis. Two of them had antibodies against HIV-1 and one had positive serology for HIV-2. Cryptococci were seen in the subarachnoid space around olfactory tracts and bulbs and in the submucosal olfactory nerve fascicles. In one case, olfactory nerve fascicles from the lamina propria were also affected. Olfactory epithelium and respiratory mucosa were not involved. We suggest that Cryptococcus reached the olfactory nerve fascicles through the olfactory pathways for cerebrospinal fluid drainage which might serve as a source of latent cryptococcal infection.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Oestrogenic influences on the electrical activity of the olfactory pathway.

The influence of the oestrogenic hormones over the spontaneous and induced activity of the olfactory pathway was studied in normal female cats. Electrodes were placed chronically or acutely in the olfactory bulb (OB), olfactory tubercle (OT) and in the prepyriform cortex (PPC). Oestrogenic hormones were applied locally in the posterior hypothalamic region. Recordings were made during the two different phases of the oestral cycle. In addition, another group of castrated animals was studied. The oestral phase was induced in these cats by the subcutaneous administration of 17-beta-oestradiol. Results indicate that the pattern of the electroencephalographic spontaneous activity as well as the response induced by hypothalamic stimulation changed. The number of the bursts for each 10 sec trace was higher in oestrus than in anoestrus for all the structures studied. The duration of each burst also changed, being shorter in oestrus than in anoestrus cats. The threshold for significant bursting in the olfactory structures following hypothalamic stimulation was lower in oestrus than in anoestrus. The evoked potentials recorded in the same three olfactory structures by hypothalamic stimulation exhibited changes in correlation with the hormonal administration. In all the structures studied the amplitude of the different components of the evoked potentials increased immediately after the hormones were administered. However, the most dramatic increase was observed in the olfactory tubercle. In order to further investigate these changes in acute preparations, a study evaluating the excitability changes was conducted. Applied pulse pairs, with different interpulse intervals between 200 to 1000 msec, were delivered in the hypothalamus before and after 200 micrograms of the hormone were administered into the posterior hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Histopathology of the olfactory pathway due to ischemia.

Various agents, such as trauma, viral infections and neoplasms cause olfactory dysfunction. However, little is understood concerning the role of ischemia. An experimental model of brain ischemia was developed in the Mongolian gerbil, and the olfactory pathway was studied. This animal was chosen because of its incomplete circle of Willis, since poor patency of the circle of Willis is not an uncommon finding in the aging human. Ischemia was induced by unilateral ligation of one common carotid artery or temporary occlusion of both common carotid arteries. Under both circumstances, ischemic changes occurred in the lateral olfactory tract, the olfactory ventricle, and the olfactory tubercle. Damage is more severe with bilateral temporary occlusion than unilateral ligation. The olfactory bulbs and neuroepithelium, however, are resistant to ischemia.

Animals↗
PubMed2001

Neurogenesis in the central olfactory pathway of the adult shore crab Carcinus maenas is controlled by sensory afferents.

The number of olfactory projection neurons (OPNs) in the brain of the juvenile and adult shore crab Carcinus maenas continues to increase during the life of the animal. In vivo labeling of adult crabs with the proliferation marker bromodeoxyuridine (BrdU) revealed a group of proliferating neuronal precursor cells in the lateral soma clusters (LCs) and in the soma clusters of the hemiellipsoid bodies (HBCs). The LCs contain the cell bodies of the olfactory projection neurons and the HBCs house the cell bodies to which the OPNs project. The aim of the present study was to examine whether the input from primary olfactory afferents has any influence on the rate of proliferation and survival of the neuronal precursors in the central olfactory pathways of C. maenas. Different sets of experiments involving BrdU injection and its immunocytochemical detection combined with unilateral amputation of the antennule that houses the olfactory organ were carried out. Our results show that the missing olfactory sensory input affects the rate of proliferation and the survival of postmitotic cells in the LC and in the HBC compared with control animals. The effect on the survival of postmitotic cells tested by BrdU injection followed by unilateral ablation is lateralized. Proliferation of neuronal precursor cells tested by the reversed experimental order was drastically impaired bilaterally. We conclude that the olfactory sensory input is necessary for a normal rate of proliferation of neuronal precursors and the survival of their progeny in the LC and in the HBC of C. maenas.

Amputation, Surgical↗
PubMed2002

Cadmium-metallothionein interactions in the olfactory pathways of rats and pikes.

Deposition of cadmium onto the olfactory epithelium results in transport of the metal along the primary olfactory neurons to the olfactory bulbs of the brain. The present investigation was undertaken to determine the intracellular ligand binding of cadmium during this process. (109)Cd(2+) was applied on the olfactory epithelium of rats and pikes, and the subcellular distribution of the metal in the olfactory pathways was then examined. Two groups of rats were used: one pretreated with intranasal instillations of nonlabeled cadmium and the other given physiological saline (controls). Cellular fractionations showed that the (109)Cd(2+) was predominantly present in the cytosol of all samples, both in the rats and the pikes. Gel filtrations of the olfactory epithelium of control rats killed 2 h after the (109)Cd(2+) instillation showed that the metal was recovered in two peaks with elution volumes corresponding to metallothionein (MT) and glutathione (GSH)-the latter peak being the predominant one. However, in the epithelium of the cadmium-pretreated rats killed at 2 h, (109)Cd(2+) was recovered in one peak corresponding to MT. In the olfactory epithelium and bulbs of both groups of rats killed at 48 h, as well as in the olfactory epithelium, nerves, and bulbs of pikes killed at this interval, (109)Cd(2+) was recovered in one peak corresponding to MT. Immunohistochemistry of the olfactory system of rats given cadmium in the right nasal cavity showed induction of MT in the neuronal, sustentacular, and basal cells of the right olfactory epithelium, in the nerve fascicles in the lamina propria of the right olfactory mucosa, and in the olfactory nerve layer of the right olfactory bulb. On the left side, the immunoreactivity was low in these structures. MT immunoreactivity was observed in the glomeruli of both the right and the left olfactory bulbs. However, the staining was homogeneously distributed within the entire glomeruli of the right bulb, whereas it showed a mesh-like pattern corresponding to the localization of astrocytes in the glomeruli of the left bulb. We conclude that exposure of the olfactory epithelium to cadmium results in induction of MT in the primary olfactory neurons and a transport of the metal in these neurons as a cadmium-metallothionein (CdMT) complex. Our results further indicate that GSH is a ligand that can interact with cadmium before the metal binds to MT.

Administration, Intranasal↗