Abstract: Stimulus-evoked oscillatory synchronization of neural assemblies and temporal patterns of neuronal activity have been observed in many sensory systems, such as the visual and auditory cortices of mammals or the olfactory system of insects. In the locust olfactory system, single odor puffs cause the immediate formation of odor-specific neural assemblies, defined both by their transient synchronized firing and their progressive transformation over the course of a response. The application of an antagonist of ionotropic γ-aminobutyric acid (GABA) receptors to the first olfactory relay neuropil selectively blocked the fast inhibitory synapse between local and projection neurons. This manipulation abolished the synchronization of the odor-coding neural ensembles but did not affect each neuron's temporal response patterns to odors, even when these patterns contained periods of inhibition. Fast GABA-mediated inhibition, therefore, appears to underlie neuronal synchronization but not response tuning in this olfactory system. The selective desynchronization of stimulus-evoked oscillating neural assemblies in vivo is now possible, enabling direct functional tests of their significance for sensation and perception.

Abstract: Uptake of manganese and cadmium from the nasal mucosa into the central nervous system via olfactory pathways in rats

Abstract: Severe, repetitive ("binge") ethanol intoxication in adult rats (intragastric delivery 3 times daily for 4 days in a modification of the Majchrowicz method) precipitates neuronal degeneration in selected cerebral cortical regions involved in memory and olfaction, confirming the results of Switzer and colleagues (Anat. Rec. 202: 186a, 1982). Neuronal damage was visualized with the de Olmos cupric silver technique for degenerating neurons and processes (argyrophilia), and was quantitated by total counts and densities of argyrophilic cells/fields. The specificity of the degeneration provides a neuropathological basis for the olfactory memory deficits in chronic alcoholics. In highly intoxicated rats, argyrophilia was most extensive among hippocampal dentate gyrus granule cells, pyramidal neurons in layer 3 of the entorhinal cortex, and olfactory nerve terminals in the olfactory bulb. Degenerating pyramidal neurons were also consistently seen in the insular cortex and olfactory cortical regions, such as the piriform and perirhinal cortices. There were few argyrophilic neurons in the CA regions of the hippocampus and none in the cerebellum--regions generally shown to have cell loss in long-term ethanol feeding models--but degenerating mossy fibers in the CA2 region were observed. Degeneration was maximal before the peak period of abstinence symptoms in this model, because argyrophilic densities were no greater 36 hr, compared with 8 hr after the last ethanol dose. High blood ethanol levels were required, because argyrophilia, absent from isocaloric controls, also was only evident in ethanol-intoxicated rats with mean blood ethanol levels for days 2 to 4 above 300 mg/dl; however, it increased substantially between 350 and 550 mg/dl. The resemblance of the argyrophilic distribution to the regional neuropathology that occurs in experimental seizures indicates that the ethanol-induced degeneration may have an excitotoxic basis. Progressive reductions in the seizure threshold (e.g., kindling phenomena that have been documented during binge ethanol intoxication) might be associated with excitotoxic hyperactivity during the repetitive nadirs between high blood and brain ethanol peaks. However, direct toxic actions of ethanol or its metabolites could also be involved. Overall, the model should be useful for studying mechanisms of ethanol-induced selective cortical and olfactory brain damage.

Abstract: The King Solomon Lectures that occasioned this paper presented findings from studies in my laboratory on the olfactory neurobiology of mate-seeking behavior of the male sphinx moth Manduca sexta in response to the sex pheromone released by the conspecific female moth. My purpose here, however, is neither to reproduce the lectures nor to review in detail the work on which they were based. Instead, I have chosen to consider this line of research in terms of comparative neurobiology and the utility of such invertebrate \"models\" for advancement of general understanding of olfaction. It is also my goal to focus on the functional significance of the glomeruli that are the hallmarks of primary olfactory neuropil in the brains of invertebrate and vertebrate animals alike. Finally, looking ahead, I sketch some of the main themes for our future research. Detailed comparisons between the primary olfactory centers in the brains of vertebrate and invertebrate animals have revealed striking similarities of functional organization and physiology, suggesting that olfactory

Abstract: The neurotransmitter(s) and receptors mediating excitatory transmission at the mammalian olfactory nerve-mitral cell synapse were investigated using extracellular recordings in rat olfactory bulb slices. Single shocks applied to the olfactory nerve elicited both a short latency and a delayed excitatory response in mitral cells. Both responses were blocked after bath application of kynurenic acid, a broad-spectrum glutamate receptor antagonist, or DNQX, a preferential non-NMDA receptor antagonist. The specific NMDA receptor antagonist AP5 selectively attenuated the delayed, but not the initial excitation. These results suggest that glutamate is the major excitatory transmitter in the mammalian olfactory nerve, and excites mitral cells via NMDA and non-NMDA receptors.

Abstract: Mitral cells are the primary output neurons of the vertebrate olfactory bulb and are major recipients of sensory input from the periphery. The morphogenesis of mitral cell dendrites was followed to elucidate their early spatial and temporal interactions with olfactory receptor neurons and glia during the construction of olfactory glomeruli. Monodelphis domestica, a marsupial born at an extremely immature stage, and rats were examined. Mitral cells were retrogradely labeled by application of the lipophilic dye 1,1′dihexadecyl-3,3,3′3′-tetramethylindocarbocyanine perchlorate (DiI) to the lateral olfactory tract. In double-labeling experiments, olfactory receptor neurons were stained with 3,3′ dihexadecyloxacarbocyanine perchlorate (DiO), or olfactory nerve Schwann cells were visualized using S-100 protein immunohistochemistry. Tissue was examined with a confocal laser scanning microscope. Some preparations were subsequently investigated with an electron microscope. In Monodelphis, differentiation of mitral cells starts with an outgrowth of numerous, uniform, and widespread dendrites. As soon as terminals of olfactory receptor axons coalesce into glomerular knots within the presumptive glomerular layer, dendrites of individual mitral cells innervate several adjacent glomeruli where they receive sensory synaptic input. With maturation, supernumerary mitral cell dendrites retract, leaving one primary dendrite bearing a terminal glomerular tuft. Simultaneously, secondary dendrites begin to arise. The formation of glomeruli begins earlier and progresses faster in the rat compared to Monodelphis. Nevertheless, mitral cell differentiation in both species follows a common sequence: overproduction of dendrites, selection of usually one primary apical dendrite, and elimination of supernumerary processes. Since olfactory receptor neurons form synaptic contacts with the widespread mitral cell dendrites, considerable synaptic rearrangement must occur within the olfactory glomeruli during maturation. © 1996 Wiley-Liss, Inc.

Abstract: Healthy controls were compared to patients with decreased olfactory sensitivity (n = 32) to investigate interactions between the olfactory and trigeminal systems. Amplitudes of chemo-somatosensory event-related potentials in response to suprathreshold trigeminal stimuli (CO 2 ) were found to be smaller in patients (P < 0.05) indicating a decrease of trigeminally mediated sensations.

Abstract: The spatial and temporal expression patterns of several extracellular matrix molecules—laminin and fibronectin and cell surface molecules, neural cell adhesion molecule (NCAM), L1, tenascin, chondroitin sulfate proteoglycan, and peanut agglutinin (PNA) binding sites—were investigated during early olfactory nerve development. NCAM and L1 have similar patterns: They are expressed in the olfactory nerve and on the olfactory receptor neurons (ORNs) commencing with the earliest olfactory axon outgrowth (E12-E15). Their expression patterns suggest that both NCAM and L1 are associated with extension and fasciculation of olfactory axons. A comparison of L1 and olfactory marker protein suggests that L1 is expressed predominantly on immature ORNs. Laminin has an unique punctate staining pattern in the developing olfactory pathway as early as E12. These laminin puncta might play a role in olfactory neurite outgrowth and guidance. At E14, when pioneer olfactory axons enter the brain, the laminin-positive meninges on the surface of the olfactory bulb primordium break down but remain intact in the rest of the telencephalon. This suggests a functional interaction between the olfactory axons and the glial-pial barrier. Fibronectin staining is diffuse throughout the cranial mesenchyme but is absent from the olfactory nerve pathway. No specific patterns of tenascin or chondroitin sulfate, were observed during early olfactory development. PNA binding sites were associated with olfactory axon fasciculation. The expression of several extracellular matrix molecules and cell surface molecules is spatially and temporally regulated in the developing olfactory system. These molecules, thus, may play functional roles in olfactory axon outgrowth, fasciculation, and/or guidance. ©1996 Wiley-Liss, Inc.

Abstract: This report describes neurogenesis in the adult human olfactory epithelium in vitro. Olfactory epithelium was collected at autopsy and by biopsy, and grown in serum-free medium. Basic fibroblast growth factor induced the differentiation of bipolar cells which were immunopositive for several neuronal proteins but not glial proteins. [3H]thymidine autoradiography confirmed that these neurones were born in vitro. The results demonstrate that the adult human olfactory epithelium retains the capacity for neurogenesis and neuronal differentiation, at least until the age of 72 years. It is now possible to examine neurones and neurogenesis in biopsies from patients with disorders that may involve a neurodevelopmental or neurodegenerative aetiology such as schizophrenia, bipolar disorder and Alzheimer's disease.

Abstract: Primary olfactory neurons arise from placodal neuroepithelium that is separate from the neuroepithelial plate that forms the neural tube and crest. The axons of these neurons course along a stereotypical pathway and invade the rostral telencephalic vesicle where they induce the formation of the olfactory bulb. In the present study we examined the expression of several extracellular matrix constituents during formation of the olfactory nerve pathway in order to identify putative developmentally significant molecules. Double-label immunofluorescence was used to simultaneously map the trajectory of growing primary olfactory axons by expression of growth associated protein 43 (GAP-43) and the distribution of either laminin, heparan sulfate proteoglycans (HSPG), or chondroitin sulfate proteoglycans (CSPG). At embryonic day 12.5 (E12.5) primary olfactory axons have exited the olfactory neuroepithelium of the nasal pit and formed a rudimentary olfactory nerve. These axons together with migrating neural cells form a large mass outside the rostral surface of the telencephalon. This nerve pathway is clearly defined by a punctate distribution of laminin and HSPG. CSPG is selectively present in the mesenchyme between the olfactory nerve pathway and the nasal pit and in the marginal zone of the telencephalon. At E14.5 primary olfactory axons pierce the telencephalon through gaps that have emerged in the basement membrane. At this age both laminin and HSPG are colocalized with the primary olfactory axons that have entered the marginal zone of the telencephalon. CSPG expression becomes downregulated in this same region while it remains highly expressed in the marginal zone adjacent to the presumptive olfactory bulb. By E16.5 most of the basement membrane separating the olfactory nerve from the telencephalon has degraded, and there is direct continuity between the olfactory nerve pathway and the central nervous system. This strict spatiotemporal regulation of extracellular matrix constituents in the olfactory nerve pathway supports an important role of these molecules in axon guidance. We propose that laminin and HSPG are expressed by migrating olfactory Schwaun cells in the developing olfactory nerve pathway and that these molecules provide a conducive substrate for axon growth between the olfactory neuroepithelium and the brain. CSPG in the surrounding mesenchyme may act to restrict axon growth to within this pathway. The regional degradation of the basement membrane of the telencephalon and the downregulation of CSPG within the marginal zone probably facilitates the passage of primary olfactory axons into the brain to form the presumptive nerve fiber layer of the olfactory bulb.

Abstract: Neurons in the olfactory deutocerebrum of the spiny lobster, Panulirus argus, were recorded intracellularly and filled with biocytin. Recorded neurons arborized in the olfactory lobe (OL), a glomerular neuropil innervated by olfactory and some presumptive mechanosensory antennular afferents. The neurons responded to chemosensory input from the lateral antennular flagellum bearing the olfactory sensilla but not the medial flagellum bearing many non-olfactory chemosensory sensilla. Many neurons received additional mechanosensory input. Thus the OL integrates specifically olfactory with mechanosensory input. OL neurons had multiglomerular arborizations restricted to one or two of the three horizontal layers of the columnar glomeruli. OL local interneurons comprised “core” neurons with tree-like neurites and terminals in the base of the glomeruli and “rim” neurons with neurites surrounding the OL and terminals in the cap/subcap. The somata of OL local interneurons lay in the medial soma cluster (100000 somata). OL projection neurons arborized in the base of the glomeruli and ascended via the olfactory glomerular tract to the lateral protocerebrum. A parallel projection pathway is constituted by projection neurons of the accessory lobe, a glomerular neuropil without afferent innervation but intimate links to the OL. The projection neuron somata constituted the lateral soma cluster (200000 somata).

Abstract: Neurons containing the decapeptide GnRH originate in the olfactory placodes and migrate into the central nervous system during fetal development. The neurotransmitter gamma-aminobutyric acid (GABA) has been proposed as a trophic factor and may also influence neuronal migration. Immunocytochemical analyses were conducted in fetal rats, mice, and humans to identify potential developmental relationships between cells containing GABA, and GnRH neurons. Cells containing GABA were found along the nasal portion of the GnRH migration pathway in rats, mice, and humans during development. A peak number of cells containing immunoreactive GABA was observed in the nasal compartment of rats at embryonic day 15. At this time (E15), a majority of GnRH neurons were clustered in the region of the cribriform plate. By postnatal day 1, all GnRH neurons had migrated into the CNS and GABA cells were virtually absent from the nasal compartment. Double-label and confocal analyses of GABA and GnRH in mice and rats demonstrated th...

Abstract: During the initial assembly of the olfactory pathway, the behavior of olfactory axons changes as they grow from the olfactory epithelium toward the telencephalic vesicle. The axons exit the epithelium singly or in small fascicles, and their growth cones are simple and bullet-shaped. Outside the epithelium, they make a sharp dorsal turn and fasciculate into a single nerve; the growth cones remain simple. Upon entering the ventromedial telencephalon, the axons defasciculate, branch extensively, and end in complex, lamellate growth cones which extend toward the ventrolateral aspect of the telencephalic vesicle. The distribution of laminin, collagen-IV, and fibronectin varies in register with these changes in olfactory axon and growth cone behavior. Each of these extracellular matrix molecules influences olfactory neurite outgrowth and growth cone morphology in vitro consistent with its distribution in vivo. The distribution of E-cadherin, L1, neural cell adhesion molecule (NCAM) and the polysialated form of NCAM also varies in register with changes in olfactory axon behavior. In vitro, L1 modulates embryonic olfactory neurite outgrowth and growth cone morphology consistent with its distribution in vivo. Thus, olfactory axon trajectory, fasciculation, and growth cone morphology change within distinct adhesive environments in the nascent olfactory pathway, and some of the molecules that characterize these environments have differential effects upon olfactory neurite growth and growth cone morphology. Consequently, the patterned expression and activity of extracellular matrix and cell surface adhesion molecules may contribute to the initial assembly of the olfactory pathway.

Abstract: In most sensory systems, afferent innervation regulates morphological and biochemical characteristics of target cells for a limited time during development. Sensory deprivation experiments in adult rats also have suggested a critical period for afferent influences on olfactory bulb structure and function. Previous odorant deprivation studies that employed unilateral naris closure in neonatal rats demonstrated down-regulation of the catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) in dopamine neurons intrinsic to the olfactory bulb. Accompanying the altered biochemical parameters was a decrease in bulb size. To distinguish between deprivation-induced alterations in TH expression secondary to developmental sequelae and those occurring in mature neurons, the consequences of unilateral naris closure were assessed in young adult rats. In agreement with previous studies significant postnatal increases occurred in TH expression and total protein, an indication of bulb size. At 30 days post-closure, total protein was unaltered in the ipsilateral olfactory bulb but showed a small (12.9%), significant decline at 60 days. In contrast to the limited morphological consequences of odor deprivation, profound reductions occurred in TH expression. TH activity ipsilateral to the closure decreased significantly by 14 days post-closure and remained depressed for up to 6 months. In parallel with enzyme activity, TH immunoreactivity did not decline in the first few days post-closure. In situ hybridization revealed that TH mRNA levels decreased rapidly, i.e., by 2 days post-closure, reached a nadir at 1 month, and remained depressed for at least 6 months. The capacity of odor deprivation in the adult rat olfactory system to down-regulate TH expression suggests that this phenotypic alteration occurs independently of a presumed critical period.

Abstract: Male-male courtship behavior was recently reported to be induced in large populations of Drosophila (e.g., 600-1500 flies) by ectopic expression of the white (w) gene. Little is known about the basis of this behavior; in male-female courtship, sensory cues are believed to play an important role. Previous data are consistent with the possibility that misexpression of w causes abnormal reception or processing of sensory information. We show here that w-induced male-male courtship occurs in isolated pairs of flies. Thus the behavior does not depend on sensory cues found only among large populations of flies, or on cues produced only by a small subset of such populations. This finding enabled quantitative analysis of mechanisms that underlie the behavior. Specifically, male-male courtship does not depend on the reception of olfactory information, nor on the reception or generation of auditory cues, as determined by surgical ablation of antennae, maxillary palps, or wings. Although the rapid onset of the behavior following w induction suggested that its basis could lie in a modulation of sensory physiology, we found visual, olfactory, and gustatory function to be normal in physiological or behavioral tests. The only sensory deprivation to produce an effect on male-male courtship was testing under dim red light; the percentage of flies courting another male was reduced to one-fourth of control values. A striking age dependence of the behavior is also documented: courtship between paired male mini-w+ flies was not observed in tests of very young (1-day-old) flies, but occurs at high levels between the ages of 1 and 4 weeks.