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PubMed1988

Neurons in the basal forebrain complex of the rat: a Golgi study.

Several types of neurons are coexistent in the basal forebrain nuclear complex of the rat. In the medial septum and vertical limb of the diagonal band 3 classes of neurons occur which are characterized by varicose dendrites. In the horizontal limb of the diagonal band neurons with smooth dendrites and those with varicose dendrites are intermingled. We found 3 classes of neurons in the nucleus preopticus magnocellularis. A giant type with smooth and varicose dendrites occurs in this nucleus, but also in the substantia innominata. In the substantia innominata-nucleus basalis complex 4 classes of neurons with varicose dendrites and 2 classes with spiny dendrites have been observed. Our findings suggest that the nucleus of the vertical limb of the diagonal band forms a unit with the nucleus septi medialis, but is separated from the nucleus of the horizontal limb of the diagonal band by different neuronal composition. The nucleus preopticus magnocellularis is a separate nuclear structure characterized by a content of neurons different from those in the horizontal limb of the diagonal band and in most components also from the substantia innominata-nucleus basalis complex. There is some evidence that the cholinergic neurons have to be searched among those with varicose dendrites.

Animals↗
PubMed1993

Two neurotropic viruses, herpes simplex virus type 1 and mouse hepatitis virus, spread along different neural pathways from the main olfactory bulb.

Several neurotropic viruses enter the brain after peripheral inoculation and spread transneuronally along pathways known to be connected to the initial site of entry. In this study, the pathways utilized by two such viruses, herpes simplex virus type 1 and mouse hepatitis virus strain JHM, were compared using in situ hybridization following inoculation into either the nasal cavity or the main olfactory bulb of the mouse. The results indicate that both viruses spread to infect a unique and only partially overlapping set of connections of the main olfactory bulb. Both quantitative and qualitative differences were observed in the patterns of infection of known primary and secondary main olfactory bulb connections. Using immunohistochemistry for tyrosine hydroxylase combined with in situ hybridization, it was shown that only herpes simplex virus infected noradrenergic neurons in the locus coeruleus. In contrast, both viruses infected dopaminergic neurons in the ventral tegmental area, although mouse hepatitis virus produced a more widespread infection in the A10 group, as well as infecting A8 and A9. The results suggest that differential virus uptake in specific neurotransmitter systems contributes to the pattern of viral spread, although other factors, such as differences in access to particular synapses on infected cells and differences in the distribution of the cellular receptor for the two viruses, are also likely to be important. The data show that neural tracing with different viruses may define unique neural pathways from a site of inoculation. The data also demonstrate that two viruses can enter the brain via the olfactory system and localize to different structures, suggesting that neurological diseases involving disparate regions of the brain could be caused by different viruses, even if entry occurred at a common site.

Animals↗
PubMed1975

Olfactory bulb projections in the bullfrog Rana catesbeiana.

The projections of the accessory and main olfactory bulbs of the bullfrog are described as part of a long term analysis of the morphological differences in amphibian and reptilian telancephalons. Unilateral aspiration of the accessory olfactory bulb results in an ipsilateral projection to the pars lateralis of the amygdala via the accessory olfactory tract. Degenerating fibers from the accessory olfactory bulb are tracable into the cell-free zone between the dorsal striatum and the lateral pallium, and projections to these neural populations may also exist. Unilateral lesions of the main olfactory bulb reveal two major secondary pathways: an ipsilateral medial olfactory tract that projects to the rostral ventromedial portion of the medial pallium, the postolfactory eminence and the rostal, lateral and medial septal nuclei; and an ipsilateral lateral olfactory tract that projects to the dorsal striatum, the lateral pallium and the ventral half of the dorsal pallium. Two crossed secondary olfactory pathways to the contralateral telencephalon decussate via the habenular commissure after entering the ipsilateral stria medullaris. A crossed lateral pathway terminates in the dorsal striatum, the caudal, lateral pallium and the ventral portion of the dorsal pallium. A crossed medial pathway terminates in the internal granule layer of the main olfactory bulb.

Amygdala↗
PubMed1999

Neural invasion of two virulent suid herpesvirus 1 strains in neonatal pigs with or without maternal immunity.

The neural invasion of two virulent Suid Herpesvirus 1 (SHV1) strains was examined in neonatal pigs with or without maternal immunity. One-week-old pigs with comparable levels of maternal immunity (SN-titer = 12-48) were intranasally inoculated with 10(7.0) TCID50 of either of the Ka or E21 strains. The invasion of the strains was examined in the nasal mucosa and in three neuronal levels of the trigeminal nervous pathway as well as in three levels of the olfactory nervous pathway by virus titration and immunohistochemistry (IHC). In control pigs without specific antibodies, both strains invaded up to the end level of each neural pathway. In pigs with maternal immunity, the Ka strain invaded only up to the 2nd level of each pathway with titers being significantly lower (p<0.05) than in the negative controls. However, the E21 strain invaded up to the end levels in both neural pathways of immune pigs with virus titers being similar to those observed in non-immune pigs (p>0.05). IHC revealed that maternal antibodies can protect against a fibroblast-mediated spread of the Ka strain in the lamina propria of the nasal mucosa, as well as against a local spread of the Ka and E21 strains from neurons to their satellite cells in the trigeminal ganglion. In conclusion, the nature of virus strain determines the invasion of SHV1 within the nervous system of maternally-immune neonatal pigs.

Animals↗
PubMed1984

Anterior thalamic nucleus projections to the dorsal pallium in ranid frogs.

Wheat germ agglutinin-horseradish peroxidase (WGA-HRP) applied in the anterior thalamic nucleus of ranid frogs was anterogradely transported to both the medial pallium and a ventral part of the dorsal pallium. Applications of WGA-HRP in the medial pallium labeled cells in the ipsilateral and contralateral anterior nucleus, including those considered to receive retinal input. An identical pattern of labeled cells was found in the anterior nucleus after WGA-HRP applications in the dorsal pallium. These results, combined with those of others, suggest that (1) the dorsal pallium has at least two subfields, (2) the dorsal pallium may receive a variety of non-olfactory sensory information, and (3) receipt of a disynaptic pathway from the retina may not determine isocortical homology among pallial fields in anurans.

Animals↗
PubMed1999

Controversial issues in vertebrate olfactory transduction.

A number of controversial issues in olfactory transduction are discussed including the matter of multiple transduction pathways, with a new experiment proposed. Evidence is reviewed concerning the fact that cyclic AMP is the only pathway mediating olfactory transduction. Two knockout mice have been produced: a knockout for a cyclic nucleotide-gated channel and a G(olf) knockout. The results obtained with both mice are consistent with cyclic AMP being the only second messenger. The evidence for gaseous second channel messengers is also reviewed. Slow gating kinetics of the cyclic nucleotide-gated channel and the detection of single-odorant molecules are reviewed. A new phenomenon in which odorants can block odorant responses is discussed.

Animals↗
PubMed1984

Functional-anatomical studies on sperm release evoked by electrical stimulation of the olfactory tract in goldfish.

Sperm release was evoked by electrical stimulation of the olfactory tracts in male goldfish. Thresholds as low as 5 microA were obtained using suction electrodes while slightly higher currents were necessary using metal electrodes (lowest thresholds of 15-20 microA). Several control procedures were carried out to insure that current-spread to nearby structures was not responsible for the evoked responses. Testing olfactory tract stimulation following transection of one or more divisions of the olfactory tract revealed that connections to the olfactory bulb and pathways involving the lateral olfactory tract were not necessary for the stimulation effect, whereas the medial olfactory tract appears to be both sufficient and necessary for mediation of evoked sperm release. The results are discussed with respect to possible involvement of each of the 3 known functional components constituting the medial olfactory tract: (1) secondary olfactory afferents; (2) olfactory efferents; and (3) fibers of the terminal nerve. The possibility that female sex pheromones normally influence central sperm release mechanisms via pathways in the medical olfactory tract is also considered.

Animals↗
PubMed2003

Modulation of early olfactory processing by an octopaminergic reinforcement pathway in the honeybee.

Processing of olfactory information in the antennal lobes of insects and olfactory bulbs of vertebrates is modulated by centrifugal inputs that represent reinforcing events. Octopamine release by one such pathway in the honeybee antennal lobe modulates olfactory processing in relation to nectar (sucrose) reinforcement. To test more specifically what role octopamine plays in the antennal lobe, we used two treatments to disrupt an octopamine receptor from Apis mellifera brain (AmOAR) function: (1) an OAR antagonist, mianserin, was used to block receptor function, and (2) AmOAR double-stranded RNA was used to silence receptor expression. Both treatments inhibited olfactory acquisition and recall, but they did not disrupt odor discrimination. These results suggest that octopamine mediates consolidation of a component of olfactory memory at this early processing stage in the antennal lobe. Furthermore, after consolidation, octopamine release becomes essential for recall, which suggests that the modulatory circuits become incorporated as essential components of neural representations that activate odor memory.

Amino Acid Sequence↗
PubMed1999

Errors in lamina growth of primary olfactory axons in the rat and mouse olfactory bulb.

In the adult olfactory nerve pathway of rodents, each primary olfactory axon forms a terminal arbor in a single glomerulus in the olfactory bulb. During development, axons are believed to project directly to and terminate precisely within a glomerulus without any exuberant growth or mistargeting. To gain insight into mechanisms underlying this process, the trajectories of primary olfactory axons during glomerular formation were studied in the neonatal period. Histochemical staining of mouse olfactory bulb sections with the lectin Dolichos biflorus-agglutinin revealed that many olfactory axons overshoot the glomerular layer and course into the deeper laminae of the bulb in the early postnatal period. Single primary olfactory axons were anterogradely labelled either with the lipophilic carbocyanine dye, 1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), or with horse-radish peroxidase (HRP) by localized microinjections into the nerve fiber layer of the rat olfactory bulb. Five distinct trajectories of primary olfactory axons were observed in DiI-labelled preparations at postnatal day 1.5 (P1.5). Axons either coursed directly to and terminated specifically within a glomerulus, branched before terminating in a glomerulus, bypassed glomeruli and entered the underlying external plexiform layer, passed through the glomerular layer with side branches into glomeruli, or branched into more than one glomerulus. HRP-labelled axon arbors from eight postnatal ages were reconstructed by camera lucida and were used to determine arbor length, arbor area, and arbor branch number. Whereas primary olfactory axons display errors in laminar targeting in the mammalian olfactory bulb, axon arbors typically achieve their adult morphology without exuberant growth. Many olfactory axons appear not to recognize appropriate cues to terminate within the glomerular layer during the early postnatal period. However, primary olfactory axons exhibit precise targeting in the glomerular layer after P5.5, indicating temporal differences in either the presence of guidance cues or the ability of axons to respond to these cues.

Aging↗
PubMed1999

Histochemistry of classical neurotransmitters in antennal lobes and mushroom bodies of the honeybee.

This paper summarizes histochemical and immunocytochemical investigations of cholinergic, GABAergic, and glutamatergic pathways in the central brain and suboesophageal ganglion of the honeybee. Acetylcholinesterase histochemistry, immunocytochemical staining for nicotinic acetylcholine receptors, and mapping for alpha-bungarotoxin binding sites indicate cholinergic synaptic interactions in the antennal lobe and a cholinergic pathway via a subset of olfactory projection neurons into the mushroom bodies. Calcium imaging experiments in cell cultures prepared from mushroom bodies demonstrate the expression of nicotinic cholinergic receptors on Kenyon cells. Neurons synthesizing GABA and glutamate are stained with well-defined polyclonal antisera against the amino acids. GABA-immunoreactivity is mainly localized in local interneurons of the antennal lobe and in extrinsic neurons innervating the mushroom bodies. High levels of glutamate-immunoreactivity are found in motoneurons of the suboesophageal ganglion, the dorsal lobe, and also in interneurons. A subgroup of the Kenyon cells shows distinct but weaker levels of glutamate-immunoreactivity. The detailed knowledge about the chemical neuroanatomy of the bee provides a framework for behavioral pharmacological approaches, which implicate the involvement of cholinergic mechanisms in olfactory learning and GABAergic mechanisms in odor discrimination.

Acetylcholine↗
PubMed1991

Signal transduction in olfactory neurons.

Recent efforts in our laboratory have focused on cloning the molecular components involved in the cAMP-mediated pathway of olfactory signal transduction. These efforts have resulted in the isolation of olfactory-specific forms of a G protein, an adenylyl cyclase, and a cyclic nucleotide-gated cation channel. Functional expression of each of these proteins in vitro confirms their ability to carry out the function ascribed to them as part of a second-messenger cascade. Putative odorant-receptor molecules which constitute the first step in odorant signal transduction have now been cloned. We have generated oligonucleotide probes which recognize a population of olfactory receptors apparently more heterogeneous than those previously reported. These probes should enable us to answer questions regarding the number of different receptors expressed per cell as well as the nature of receptor-ligand specificity.

Adenylyl Cyclases↗
PubMed2000

A cGMP-signaling pathway in a subset of olfactory sensory neurons.

It is well established that signal transduction in sensory neurons of the rat olfactory epithelium involves a cAMP-signaling pathway. However, a small number of olfactory neurons specifically express cGMP-signaling components, namely a guanylyl cyclase (GC-D) and a cGMP-stimulated phosphodiesterase (PDE2). Here, we show that this subset of olfactory neurons expressing GC-D and PDE2 does also express the subunit of a cGMP-selective cyclic nucleotide-gated (CNG) channel that has been previously identified in cone photoreceptors. Further, components of the prototypical cAMP-signaling pathway could not be detected in this subpopulation of cells. These results imply that these neurons use an alternative signaling pathway, with cGMP as the intracellular messenger, and that, in these cells, the receptor current is initiated by the opening of cGMP-gated channels.

Amino Acid Sequence↗
PubMed2000

Primary olfactory axons form ectopic glomeruli in mice lacking p75NTR.

The restricted expression of the low affinity nerve growth factor receptor p75NTR by olfactory ensheathing cells suggests that this molecule is involved in the development of the olfactory nerve pathway. To begin to understand the role of p75NTR, we examined the development of the primary olfactory system in p75NTR(-/-) and wild-type mice. Our results demonstrate that, although p75NTR is not essential for the initial assembly of the olfactory nerve, it plays an important role in the postnatal maturation of the olfactory bulb. In the absence of p75NTR, there is exuberant growth of some primary olfactory axons into the olfactory bulb. These axons either aberrantly bypass the glomerular layer and project into deeper lamina or grow into an abnormal bleb of tissue protruding from the medial surface of the dorsocaudal olfactory bulb. These blebs become apparent in neonatal mice and contain axons expressing olfactory marker protein that form ectopic glomerular-like tufts. Histochemical staining with the plant lectin Dolichos biflorus agglutinin revealed that axons sorted out and selectively converged on glomeruli within these blebs. Our results suggest that p75NTR indirectly influences axon growth but not glomerular targeting and plays a role in the postnatal maturation of laminar cytoarchitecture in the olfactory bulb.

Animals↗
PubMed1989

A proposed relationship between increases in the number of olfactory receptor neurons, convergence ratio and sensitivity in the developing rat.

In the rat neonate, as in other altricial young, olfaction, in contrast to vision and hearing, is functional at birth, being critically important in feeding, growth and other aspects of infant-mother interaction. Yet, olfactory sensitivity, i.e., the ability to detect odors at low levels, is poor in the newborn, improving dramatically in the first few postnatal weeks. To find a neural explanation for this phenomenon at the level of peripheral olfactory system, we present quantitative light microscopic data which reveal that during the suckling period of postnatal development the surface area of the olfactory receptor sheet and the total number of olfactory receptor neurons increase by about 8- and 12-fold respectively, being about 15 mm2 and 1.0 million on each nasal half of the newborn. Since the number of mitral cells, the principal relay neurons of the olfactory bulb, is already established at birth, at about 40,000 per olfactory bulb, it may be estimated that the convergence ratio of the olfactory neurons to mitral cells increases by more than 10-fold in the suckling period. We propose that the increased number of primary sensory afferent units and the higher convergence upon the central relay cells enhances the physiological capacities of the olfactory afferent pathway, increasing the opportunity for spatial summation and facilitation. The latter changes may lead to reduced olfactory thresholds and improved sensitivity with development. The relative contribution of these peripheral changes in enhancement of olfactory sensitivity during growth is discussed in the light of our knowledge on the developing olfactory system.

Animals↗
PubMed1984

Anatomical evidence for convergence of olfactory, gustatory, and visceral afferent pathways in mouse cerebral cortex.

Flavor perception requires the neural integration of olfactory, gustatory and, possibly, visceral afferent information. Presently, it is not known where, or how this integration takes place in the brain. Neuroanatomical data presented here suggest that pathways subserving these sensory modalities converge in mouse insular cortex after surprisingly few synaptic relays. Orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to label main olfactory bulb (MOB) efferents. A projection into layer I of insular cortex was present in every case. Bulb transections were made to provoke anterograde degeneration and EM analysis confirmed that the olfactory projection to insular cortex was a terminal pathway. WGA-HRP injections in the MOB-recipient zone of insular cortex resulted in ortho and retrograde labeling of ascending and descending gustatory-visceral afferent pathways. It is concluded that in the mouse, there is a remarkably direct convergence of olfactory and gustatory-visceral sensory pathways in insular cortex. Together with the descending connections from insular cortex to the amygdala and to brainstem autonomic structures, it is possible that the cortical integration of olfactory and gustatory-visceral information could modulate mechanisms involved in food selection and autonomic reactions relating to the chemical senses. Basic mechanisms subserving flavor perception might be usefully modelled in mouse insular cortex.

Afferent Pathways↗
PubMed2005

Axonal transport of rubidium and thallium in the olfactory nerve of mice.

Following intranasal administration of radioactive (86)Rb(+) and (201)Tl(+) in mice, we observed this direct transport via the olfactory nerve pathway. The (86)RbCl and (201)TlCl solutions were administered to two groups of mice, the unilateral intranasal and intravenous administration groups. After sacrifice, their heads were divided into the right and left side, which were then subdivided into seven parts; the nasal mucosa and brain regions were separated. Following the unilateral intranasal administration, uptake after 6 h by the olfactory bulb was significantly higher on the ipsilateral side ((86)Rb, 0.7 %dose; (201)Tl, 0.5 %dose) than on the contralateral side ((86)Rb, 0.08 %dose; (201)Tl, 0.15 %dose). Moreover, the (86)Rb and (201)Tl that accumulated in the olfactory bulb were gradually transported to other brain regions of the olfactory tract, the telencephalon and the diencephalon on the side corresponding to the nostril used for administration. Significant differences were observed between the right and left side of the brain regions 6 and 12 h after administration. Further, (201)Tl autoradiography clearly showed striped patterns of dense accumulation, localized in the region around the glomerular layer and granule cell layer of the olfactory bulb and around the olfactory cortex. These results provide clear evidence of axonal transport via the olfactory nerve pathway, from nasal cavity to the olfactory bulb, as well as to the olfactory cortex through the synaptic junctions. The olfactory transport of the (86)Rb(+) and (201)Tl(+) is thought to represent the behavior of K(+) in the olfactory system.

Animals↗