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PubMed1992

Anatomy and fine structure of neurons in the deutocerebral projection pathway of the crayfish olfactory system.

Golgi impregnation and neurobiotin injection were used to examine details of the neural pathways in the olfactory system of the freshwater crayfish, Procambarus clarkii. Deutocerebral projection neurons (globuli cells) were directly injected with neurobiotin. These neurons have dendritic arborizations in the ipsilateral olfactory and accessory lobes, and they project axons to the lateral protocerebrum, where they terminate in microglomeruli of the hemi-ellipsoid body. The axons of the deutocerebral projection neurons are readily impregnated by Golgi procedures, and they terminate as an expanded membranous knot about 5 microns in diameter. Electron microscopy on Golgi-stained terminals has revealed that each knot makes several hundred synapses with small spine-like or shaft-like processes of postsynaptic neurons. Injection of neurobiotin into local interneurons of the hemi-ellipsoid body and subsequent examination of stained preparations with the electron microscope reveals that these cells are a major postsynaptic target of the deutocerebral projection neurons. Furthermore, the local interneurons make extensive efferent synaptic connections with unidentified neurons in the terminal medulla.

Animals↗
PubMed2003

Activation of the cyclic AMP response element-binding protein signaling pathway in the olfactory bulb is required for the acquisition of olfactory aversive learning in young rats.

Long-term memory formation requires both gene expression and protein synthesis. Phosphorylation of the transcription factor cyclic AMP response element-binding protein (CREB) is thought to be important in processes underlying long-term memory. To clarify the role of CREB in olfactory aversive learning in young rats, we carried out behavioral pharmacology and Western blot analyses. On postnatal day 11, oligodeoxynucleotides were infused directly into the bilateral olfactory bulbs through cannulae implanted prior to training in a classical conditioning paradigm with citral odor and foot shock. On the following day the odor preference test was performed. After training, saline-infused animals spent significantly shorter time over the citral odor zone. Infusion of CREB antisense oligodeoxynucleotides 6 h before or during training, however, prevented olfactory aversive learning without affecting memory retention 1 h after training. CREB scrambled oligodeoxynucleotides infusions had no effect on olfactory learning. When infused 6 h after training, none of oligodeoxynucleotides had an effect on time spent over the odor zone. Using Western blotting, we analyzed CREB in nuclear extracts obtained from the young rats after training. Marked increases in phosphorylated CREB were sustained from 10 to 360 min after the odor-shock pairing in animals which were subjected to both, in comparison with levels 30 min in animals which were subjected to odor only or no stimulation. Total CREB levels showed no differences among groups. Infusion of CREB antisense oligodeoxynucleotides significantly reduced the expression of phosphorylated and total CREBs in the olfactory bulb. These results show that the synthesis and phosphorylation of CREB are required for the acquisition of olfactory aversive learning in young rats, and that this requirement for the CREB signaling pathway has a critical time window.

Animals↗
PubMed1984

The olfactory nervous system of the old world monkey.

This paper reviews work on olfactory function performed in the author's laboratory over the last 10 years. The following aspects of this work are covered. Neocortical olfactory areas were studied in old world monkeys. Olfactory responses were found in the lateroposterior and centroposterior portions of the orbitofrontal cortex (LPOF and CPOF). The routes of the olfactory nerve pathways to the LPOF and the CPOF were examined. An olfactory pathway to the lateral hypothalamic area (LHA) was also studied. Using unanesthetized monkeys, information processing of odors was studied in the OB, PPF-MA, LPOF, MDmc, CPOF, and LHA. In the LPOF and LHA, half or more of the cells responded differentially to one odor. We have thus been able to clearly demonstrate discrimination of odors at the cell level in these areas.

Anesthesia, General↗
PubMed2002

The nitric oxide/cyclic GMP pathway in the olfactory processing system of the terrestrial slug Limax marginatus.

To examine the distribution of nitric oxide (NO)-generative cells and NO-responsive cells in the tentacles and procerebral lobes (olfactory processing center) of terrestrial slugs, we applied NADPH diaphorase (NADPH-d) histochemistry and NO-induced cyclic GMP (cGMP)-like immunohistochemistry. We found that NADPH-d reactive cells/fibers and cGMP-like immunoreactive cells/fibers were different, but they were localized adjacent to each other, in both the tentacles and the procerebral lobes. Then, we measured the concentration of NO that was generated around the procerebral lobes using an NO sensitive electrode, when the olfactory nerve was electrically stimulated as a replacement for an odorant stimulus. Stimulation of the olfactory nerve evoked an increase in NO concentration at nanomolar levels, suggesting that binding of nanomolar concentrations of NO to the prosthetic heme group activates soluble guanylyl cyclase. Taken together with previously reported physiological data, our results, therefore, showed that the NO/cGMP pathways are involved in slug olfactory processing.

Animals↗
PubMed2004

Delivery of insulin-like growth factor-I to the rat brain and spinal cord along olfactory and trigeminal pathways following intranasal administration.

We investigated the CNS delivery of insulin-like growth factor-I (IGF-I), a 7.65 kDa protein neurotrophic factor, following intranasal administration and the possible pathways and mechanisms underlying transport from the nasal passages to the CNS. Anesthetized adult male Sprague-Dawley rats were given [125I]-IGF-I intranasally or intravenously and then killed by perfusion-fixation within 30 min. Other animals were killed following cisternal puncture and withdrawal of cerebrospinal fluid (CSF) or intranasal administration of unlabeled IGF-I or vehicle. Both gamma counting of microdissected tissue and high resolution phosphor imaging of tissue sections showed that the tissue concentrations and distribution following intranasal administration were consistent with two routes of rapid entry into the CNS: one associated with the peripheral olfactory system connecting the nasal passages with the olfactory bulbs and rostral brain regions (e.g. anterior olfactory nucleus and frontal cortex) and the other associated with the peripheral trigeminal system connecting the nasal passages with brainstem and spinal cord regions. Intranasal administration of [125I]-IGF-I also targeted the deep cervical lymph nodes, consistent with their possible role in lymphatic drainage of both the nasal passages and the CNS. Cisternal CSF did not contain [125I]-IGF-I following intranasal administration. Intravenous [125I]-IGF-I resulted in blood and peripheral tissue exposure similar to that seen following intranasal administration but CNS concentrations were significantly lower. Finally, delivery of IGF-I into the CNS activated IGF-I signaling pathways, confirming some portion of the IGF-I that reached CNS target sites was functionally intact. The results suggest intranasally delivered IGF-I can bypass the blood-brain barrier via olfactory- and trigeminal-associated extracellular pathways to rapidly elicit biological effects at multiple sites within the brain and spinal cord.

Administration, Intranasal↗
PubMed1983

The principal projection pathway between the olfactory bulb and the prepyriform cortex in the cat.

The anatomy and neuroelectric properties of the lateral olfactory tract (LOT) were investigated in the cat. Electron micrographs were obtained from sampled areas across the rostro-caudal projection of the pathway. Fiber diameters were estimated and axon spectra were obtained from three regions corresponding to peduncle, mid-LOT, and caudal-LOT. The mean inside diameter for all measured axons was 1.13 +/- 0.53 microns. The greatest number was found in the peduncle (approximately 600,000 axons). Mid-LOT and caudal-LOT each contained approximately 250,000 axons. Unmyelinated processes were estimated to be more numerous than the myelinated axons. Synaptic structures were also observed in the LOT. Cross-sectional area measurements of the LOT were obtained from tissue prepared for light microscopy. The area decreased from about 0.3 to 0.2 mm2 across the projection from olfactory bulb to cortex. The anatomical data were used to predict the conduction properties of transmission over the LOT. The olfactory bulb mitral cells were stimulated electrically and conduction velocity and temporal dispersion were evaluated in the tract. The strength-duration and stimulus-response curves and the potential profile during stimulation were also obtained. The time constant for LOT axons was 0.3 msec. The stimulus-response curve was sigmoidal in shape for both presynaptic and postsynaptic responses. The relationship between input (the action potentials) and output (cortical postsynaptic potentials) was linear up to 90 times threshold. Action potentials were conducted at 20 m/sec across the pathway over the peduncle and decreased to about 10 m/sec in caudal aspects. The potential profile for action potentials decayed exponentially into the depths of the cortex whereas the synaptic potential was a surface negative dipole field. The axon spectra were convolved with the electrophysiological properties of the LOT to mathematically reconstruct action potentials. The empirically derived mono- and biphasic curves fitted reasonably well with experimentally derived data under various stimulus conditions.

Action Potentials↗
PubMed1998

Topographic bulbar projections and dual neural pathways of the primary olfactory neurons in salmonid fishes.

A growing body of evidence indicates spatial patterning of molecular expression and physiological activities in the olfactory epithelium and primary afferent circuits of the vertebrate olfactory bulb. Because our previous studies indicate that olfactory receptors specific for amino acids and a bile acid, taurocholic acid, project to segregated coding centres in the olfactory bulb, we further examined the afferent projections and pathways of the primary neuronal responses to putative pheromones by recording the electroencephalogram from various regions of the olfactory bulb. First, using the electro-olfactogram, we determined olfactory sensitivities of six salmonid species to these odorants. Prostaglandin F2 alpha and 15-keto-prostaglandin F2 alpha were potent olfactory stimulants for all tested salmonids, except rainbow trout (Oncorhynchus mykiss). None of the salmonids responded to 17 alpha,20 beta-dihydroxy-4-pregnen-3-one. However, they were sensitive to etiocholan-3 alpha-ol-17-one glucuronide. In all salmonids examined, electroencephalograms to amino acids and taurocholic acid, applied singly or in combination, projected to two segregated regions, the lateroposterior and mid-olfactory bulb, respectively. Neither prostaglandin F2 alpha, 15-keto-prostaglandin F2 alpha nor etiocholan-3 alpha-ol-17-one glucuronide elicited electroencephalograms. These data indicate that, in salmonids, olfactory neurons responsive to amino acids and taurocholic acid project to spatially segregated regions, and thereby generated signals are encoded spatially and temporarily. The results also suggest that olfactory signals due to hormonal pheromones are processed in a manner distinct from those for amino acids and bile acids, and may possibly be mediated by extrabulbar primary olfactory fibres bypassing the bulb.

Animals↗
PubMed2006

Odorant deprivation reversibly modulates transsynaptic changes in the NR2B-mediated CREB pathway in mouse piriform cortex.

The olfactory system is an outstanding model for understanding activity-dependent neuronal plasticity in mammals. Olfactory sensory neurons (OSNs) in the periphery project onto mitral/tufted cells in the olfactory bulb (OB) and these mitral/tufted cells in turn project to piriform cortex (PC). Numerous studies have examined changes in OB after a permanent OSN ablation, but little is known about "trans-transsynaptic" changes taking place in the PC. Permanent zinc sulfate lesion of the olfactory epithelium resulted in a selective loss of the NMDA receptor NR2B protein and mRNA expression in pyramidal cells in layer IIb of PC after 2-7 d. Regulatory elements affected by NR2B signaling, namely the phosphorylation of CREB, were also downregulated only in layer IIb neurons. These changes could be caused by OSN axon loss in the zinc sulfate lesion, or to a reduced activity. To test this hypothesis, we performed both permanent and reversible naris occlusion, which blocks odorant access to the nasal cavities and OSN activity. The expression of NR2B and phospho-CREB were downregulated 5 d after occlusion and this reduction was fully restored 10 d after reopening of the naris. Subsequently, we identified the subset of pyramidal cells in layer IIb that are especially sensitive to the loss of odor-evoked activity using double retrograde tracers. In summary, the present study provides an initial characterization of the molecular mechanisms associated with odor stimulation on second order neuronal plasticity and phenotype in the olfactory system.

Animals↗
PubMed2005

Structural activation pathways from dynamic olfactory receptor-odorant interactions.

We have simulated an odor ligand's dynamic behavior in the binding region of an olfactory receptor (OR). Our short timescale computational studies (up to 200 ps) have helped identify unprecedented postdocking ligand behavior of ligands. From in vacuo molecular dynamics simulations of interactions between models of rat OR I7 and 10 aldehyde ligands, we have identified a dissociative pathway along which the ligand exits and enters the OR-binding pocket--a transit event. The ligand's transit through the receptor's binding region may mark the beginning of a signal transduction cascade leading to odor recognition. We have graphically traced the rotameric changes in key OR amino acid side chains during the transit. Our results have helped substantiate or refute previously held notions of amino acid contribution to ligand stability in the binding pocket. Our observations of ligand activity when compared to those of experimental (electroolfactogram response) OR-activation studies provide a view to predicting the stability of ligands in the binding pocket as a precursor to OR activation by the ligand.

Aldehydes↗
PubMed2002

Expression and immunohistochemical localization of heparan sulphate proteoglycan N-syndecan in the migratory pathway from the rat olfactory placode.

N-syndecan, a membrane-bound heparan sulphate proteoglycan, is abundantly present in the developing nervous system and thought to play important roles in the neurite outgrowth. In the present study, we examined the distribution of N-syndecan in the migratory route from the rat olfactory placode using immunohistochemistry and in situ hybridization. At embryonic day 15, both heparan sulphate and N-syndecan immunoreactivities were localized in and around the migrating cell clusters, which contained luteinizing hormone-releasing hormone (LHRH) and calbindin D-28k. Immunoreactivity for other glycosaminoglycan chains, such as chondroitin and keratan sulphate, and core proteins of the chondroitin sulphate proteoglycan, neurocan and phosphacan, were barely detected in the migratory pathway from the olfactory placode. By in situ hybridization histochemistry, N-syndecan mRNA was localized in virtually all of migrating neurons as well as in cells of the olfactory epithelium and the vomeronasal organ. N-syndecan immunoreactivity surrounded cells migrating along the vomeronasal nerves that were immunoreactive for neural cell adhesion molecules, NCAM, L1 and TAG-1. Considering that NCAM is implicated in the migratory process of LHRH neurons and specifically binds to heparan sulphate, it is likely that a heterophilic interaction between NCAM and N-syndecan participates in the neuronal migration from the rat olfactory placode.

Animals↗
PubMed2000

Convergence of segregated pheromonal pathways from the accessory olfactory bulb to the cortex in the mouse.

The accessory olfactory system mediates intraspecies pheromonal communication. Two subsets of spatially segregated vomeronasal sensory neurons, presumably handling functionally and structurally different sets of ligand molecules, can be distinguished. The two subsets of sensory neurons project their axons to segregated zones of the accessory olfactory bulb (AOB) and connect with zonally separated mitral/tufted (M/T) cells, suggesting that the accessory olfactory system is divided into two distinct pathways up to the level of the AOB. To examine whether the segregation is maintained at the accessory olfactory cortical (AOC) regions, we selectively tracer-labelled mitral/tufted cells located in the rostral, caudal or in both zones of the adult mouse AOB. The results demonstrate that the axonal projection patterns of rostral zone and caudal zone M/T cells were indistinguishable in the AOC regions. Mitral/tufted cell axons from either zone of the AOB covered the entire area of all four AOC regions: the bed nucleus of the accessory olfactory tract, the medial amygdaloid nucleus, the posteromedial cortical amygdaloid nucleus and the bed nucleus of the stria terminalis. Therefore, over the entire area of each AOC region, ensembles of cortical neurons receive input from both zonal subsets of M/T cells of the AOB. However, the present results do not rule out the possibility that individual cortical neurons sample information from M/T cells of a single zone. These results are consistent with the idea that the segregation of zonal pathways collapses in the AOC regions. Clusters of cortical neurons in each AOC region may combine information from both families of pheromone receptors and thus handle signals from structurally and functionally different categories of pheromone molecules.

Animals↗
PubMed1975

Olfactory bulb connections with basal rhinencephalon in the ferret: an evoked potential and neuroanatomical study.

The lateral olfactory tract (LOT) of the ferret has been shown to project to most of the pyriform lobe, as in the cat. Only a small medio-posterior region of the pyriform cortex (the angular cortex), which has a distinctly different appearance in Nissl stained sections, proves to be devoid of olfactory connections. Despite the fact that sub-areas can be recognized within olfactory cortex, there is an underlying constancy in design throughout. Latency measurements indicate that fine collateral branches of theLOT reach the posterior olfactory cortex, whereas mainly larger diameter (faster conducting) fibres comprise the contribution to anterior olfactory cortex. Thus in the present context it is sufficient to recognise just an anterior and posterior subdivisionof olfactory cortex, contingent on the above criterion and correlated with cytoarchitectural features, chiefly variations in cortical layers II and III of the regions concerned. Pyriform cortex directly in receipt of LOT fibres, and associated deeper cortical zones, generated potentials in the olfactory bulbs which can only be attributed to centrifugal input, thus further substantiating an olfactory role for this cortex. In addition, non-cortical regions in receipt of LOT fibres, namely the anterior olfactory nucleus, olfactory tubercle, cortical amygdaloid nucleus and nucleus of the lateral olfactory tract, also contribute centrifugal input to the bulbs. All these regions are thereby capable of providing a rather direct feedback on olfactory bulb activity. The exact pathways concerned have yet to be determined.

Animals↗
PubMed2004

Expression and immunohistochemical localization of vesicular glutamate transporter 2 in the migratory pathway from the rat olfactory placode.

The localization of vesicular glutamate transporter 2 (VGLUT2) was examined by immunohistochemistry and in situ hybridization histochemistry in the developing rat olfactory region with special relation to the spatiotemporal location of NCAM, a neural cell adhesion molecule expressed in differentiated neurons, and the calcium-binding protein calbindin D-28k, a marker of neurons migrating from the vomeronasal organ anlage (Y. Toba et al. (2001) J. Neuroendocrinol., 13, 683-694). Both VGLUT2 and NCAM immunoreactivities were first detected at embryonic day 11.5 (E11.5) in the neuronal cell mass beneath the telencephalic vesicle. After E12.5, VGLUT2-immunoreactive cells were detected in the migratory pathways from both medial and lateral olfactory pits, anlagen of the vomeronasal organ and olfactory epithelium. Between E15.5 and E19.5, moderate to intense VGLUT2 immunoreactivity was observed in cell clusters situated along NCAM-bearing vomeronasal nerves, and frequently colocalized with calbindin D-28k immunoreactivity. Using in situ hybridization histochemistry, VGLUT2 mRNA signals were detected in the clustered cells as well as in cells of the vomeronasal and olfactory epithelium. After E20.5, migrating cells gradually decreased in number and VGLUT2 immunoreactivity attenuated in the clustered cells, although calbindin D-28k immunoreactivity in these residual cells was still intense. The presence of intense VGLUT2 immunoreactivity in neurons actively migrating from the olfactory placode suggests that this transporter is involved in the migratory process of these neurons.

Animals↗