Isolation and Characterization of the Olfactory Epithelial Cells of the Catfish

A preparation enriched in olfactory receptor cells has beenobtained from the olfactory mucosa of the catfish (Ictaluruspunctatus). The tissue was treated successively with trypsin,DNase, trypsin inhibitor, EDTA in Ca^{+ +} , Mg^{+ +} free mediumaccording to a method derived from that of Cohen, et al.⁽¹⁾.After mechanical disruption of the isolated olfactory lamellae,the cells were isolated by centrifugation on a Ficoll gradient.Each type of cell was morphologically identified by comparingin situ and in vitro preparations by SEM. Small round cellswere collected on 10% Ficoll. The nature of these cells is notknown but part of them are certainly basal cells which havebeen shown⁽²⁾ to be the precursors of the constantly regeneratingolfactory neurons. Respiratory cells settled mainly on 20% Ficoll.A fraction containing 60% sustentacular cells was collectedon 33% Ficoll. Olfactory cells characterized by an axon, a dendriteand several cilia, were found on 37% Ficoll. This fraction alsocontains up to 40% sustentacular cells. A yield of 20% was measuredfor olfactory cell isolation. Vital staining and ability tosynthesize RNA indicate a viability of the final preparationof 70% to 80%. Further identification of the cells was performedby measuring the binding activity of a series of amino acidsto a preparation enriched in olfactory cells. A good correlationwas determined between the extent of the binding and the reportedelectrophysiological activities of these amino acids recordedin vivo. Although the final olfactory cell suspension is notpure, it constitutes the first step in the study of the olfactoryreceptor sites.     

Relationship of visual and olfactory signal parameters in a food-deceptive flower mimicry system

Pollinators such as bees are attracted to flowers by their visualdisplay and their scent. Although most flowers reinforce visitsby providing pollen and/or nectar, there are species—notablyfrom the orchid family—that do not but do resemble rewardingspecies. These mimicry relationships provide ideal opportunitiesfor investigating the evolution of floral signals and theirimpact on pollinator behavior. Here, we have reanalyzed a caseof specialized food mimicry between the orchid Orchis israeliticaand its model, the lily Bellevalia flexuosa. Based on currentknowledge of insect sensory physiology, we were able to characterizeboth the visual and olfactory signals of model and mimic, aswell as of two phylogenetically related orchids. By using acolor vision model, we mapped each species' visual signals tothe perceptual space of honeybees and found an apparent shiftof the mimic's visual signals towards the model. We confirmthat visual mimicry is present. We analyzed the flower odorsby using gas chromatography/mass spectroscopy. We related thesesignals to the perceptual space of the pollinators by testingthe scent extracts physiologically, using in vivo brain imaging.We found no evidence of olfactory mimicry. The results indicatethat evolutionary pressure acts on the visual, but not olfactory,traits of O. israelitica toward a higher similarity to its model.Apparently, odor mismatch does not prevent a bee from landingon a flower that has the expected visual display. The resultstherefore argue for the dominance of visual stimuli in short-distanceflower choice. The orchid may still depend on long-distanceolfactory attraction originating from neighboring model plants.     

Amitriptyline reduces olfactory neuron adenylyl cyclase activity

Adenylyl cyclase plays an important role in olfactory signaltransduction. Recently, a novel type III adenylyl cyclase hasbeen localized in olfactory neurons (Pfeuffer et al., 1989;Bakalyar and Reed, 1990). Because amitriptyline (AMI), a tricyclicantidepressant, appears to have an inhibitory effect on adenylylcyclase activity in other in other neuronal tissue (Yamaokaet al., 1988; Wong et al., 1991), we measured the effect ofAMI on forskolin-stimulated adenylyl cyclase activity in membranepreparations of olfactory mucosa from adult rats. In the presenceof 5'-guanylyl-imidodiphosphate, AMI (0.5–8.0 µM)inhibited forskolin-stimulated adenylyl cyclase activity ina dose-dependent manner. To determine whether this effect wasspecific for olfactory neurons, as opposed to other cells inthe olfactory epithelium, rats were unilaterally bulbectomizedin order to reduce selectively the number of olfactory neuronson the side ipsilateral to the bulbectomy. In membrane preparationsfrom unilaterally bulbectomized animals we saw significantlylower adenylyl cyclase activity in ipsilateral olfactory mucosa,compared with adenylyl cyclase activity from non-bulbectomizedmucosa. These results indicate that AMI inhibition of adenylylcyclase activity is primariy localized in olfactory neurons.     

Investigations on the Growth and Metabolism of Plant Cells: V. Tumorous Growth in Relation to Growth Factors of the Type found in Coconut

1. It has been shown that aqueous extracts of plant tumours,induced by Agro-bacterium tumefaciens (Smith and Townsend) onBryophyllum and Kalanchoe, will act in place of coconut milkusing the tissue-culture procedures previously described inthis series of papers. 2. In a large number of experiments it has been shown that tumoursof this kind yield extracts which have a growth-promoting effectsimilar to that of coconut milk. This effect may be enhancedby, though it is distinguishable from the effects of, addedcasein- hydrolysate in the basal medium. The activity of thetumour extracts was consistently greater than the activity ofextracts of stems and leaves of the same plants and of normal,non-tumorous plants. 3. Partial fractionation of the tumour extracts has shown thatactivity was concentrated in the alcohol extracts, and to alesser extent in the water extracts. Activity was completelylacking in the ether extracts. 4. The effect of coconut milk, which is replaceable wholly orin part by tumour extracts, is primarily an effect on cell divisionin the carrot tissue. 5. The bearing of these results on tumorization in plants isdiscussed.     

瓢虫和草蛉对小麦挥发物组分的行为及电生理反应

利用触角电位（electroantennogram, EAG）和嗅觉测定技术,比较分析了4种捕食性天敌昆虫七星瓢虫Coccinella septempunctata、龟纹瓢虫Propylaea japonica、中华通草蛉Chrysoperla sinica和大草蛉Chrysopa septempunctata对麦蚜取食诱导小麦挥发物的行为和电生理反应,揭示了瓢虫及草蛉类天敌昆虫的嗅觉反应特点。4种捕食性天敌昆虫对麦蚜取食诱导挥发物都有较高的EAG反应值,七星瓢虫和龟纹瓢虫对6-甲基-5_庚烯-2-酮、6-甲基-5-庚烯-2-醇的反应值较大;中华通草蛉和大草蛉对6-甲基-5-庚烯-2-醇和水杨酸甲酯的反应值较大,七星瓢虫对6-甲基-5-庚烯-2-醇的反应值最大,为0.96±0.18 mV;4种天敌昆虫对苯甲醛的EAG反应值较低,对反-2-己烯醛无反应。“Y”型管嗅觉测定结果表明,4种天敌昆虫对2-莰烯、6-甲基-5-庚烯-2-酮、6-甲基-5-庚烯-2-醇和水杨酸甲酯具有正趋性。说明4种多食性的捕食性天敌昆虫对麦蚜取食诱导挥发物各组分的嗅觉与行为反应各具特点;寄主麦蚜生境中的嗅觉线索在这4种捕食性天敌昆虫的寄主定位和生境选择中起重要作用。     

Olfactory properties of some gases in hyperbaric atmosphere

The first demonstration of olfactory perception, at hyperbaricatmosphere, for gases inodorous at normal atmosphere, was madeby Laffort (1966, 1968). Nevertheless, two difficulties arosewith this earlier experimentation. First, the pressure was limitedto 5 absolute atmospheres (ATA) on account of the safety ofthe subjects. Secondly, the temperature was not maintained constantand it is well known that the olfactory perception depends onthis parameter (Tucker, 1963; Grundvig et al., 1967; Laffort,1969). The present experiment was carried out in a range of2–23 ATA, at a constant temperature, using methane andkrypton. The dose–response curve was obtained as a wholewith methane and partially with krypton. This work shows theexistence of olfactory sensitivity for these seemingly ‘inodorous’gases. Moreover, planning a QSAR study (quantitative structure–activityrelationships), it is possible to know the olfactory thresholdsof small mol. wt compounds (the human olfactory thresholds ofn-paraffin were known in a range of C₂–C₁₀ until now)(Van Gemert and Nettenbreijer, 1977).     

The Olfactory System as a Model for the Analysis of the Contribution of Gene Expression to Programmed Cell Death

The process of programmed cell death is frequently attenuatedby inhibitors of protein and RNA synthesis. This implies thatgene expression is necessary for the active elimination of somecell types. Genes such as bcl-2 and bax have been implicatedin the direct control of cell death, while cellular immediate-earlygenes (clEGs), such as c-fos and c-jun have been repeatedlyassociated with neuronal degeneration. We are using the olfactoryneuroepithelium as a model system to investigate the role thatexpression of such genes might play in cell death. The advantagesof this system is that even in the adult, there is spontaneousdegeneration of olfactory receptor neurons followed by theirreplacement by the division and differentiation of precursors.Futhermore, the receptor neurons can be induced to die synchronouslyby removal of the olfactory bulb or intranasal administrationof toxic agents. We have generated fos-lacZ and jun-lacZ transgenicmice that can be used to assess expression of c-fos and c-junfollowing these various manipulations. In addition, a line oftransgenic mice has been derived that express Bcl-2 under thecontrol of the olfactory receptor protein promoter. These micehave high levels of Bcl-2 selectively in receptor neurons ofthe primary neuro-epithelium and vomeronasal organ. Since insome circumstances, Bcl-2 can protect against programmed celldeath these mice are being assessed for neuronal turnover underbasal conditions and following olfactory bulbectomy.     

Growth Substances in Relation the the Rooting of Salix fragilis Cuttings

An attempt has been made to correlate seasonal variations inthe rooting responses of Salix fragilis cuttings with theircontent of growth-promoting substances. Although they were bothlow in early dormancy and higher in late dormancy and in summerthere was not an exact correlation in all months. It was found that extracts of S. fragilis cuttings taken indormancy strongly inhibited the action of IAA on the growthof Avena coleoptile segments. This inhibitory influence wasless in extracts of cuttings taken at the end of dormancy andin summer. Extracts of cuttings which had been left in waterto root showed a striking decrease in their inhibitory actionon IAA.     

Lotus Lectin Labels Subpopulation of Olfactory Receptor Cells

Experiments were performed to test the hypothesis that subsetsof olfactory receptor cells could be recognized based on theirlectin binding and that mapping of their projections onto theolfactory bulb would reveal details of anatomic organizationof the olfactory nerve projection to the olfactory bulb. Theresults from one lectin, Lotus, were examined in detail. Olfactoryreceptor cells in the lateral part of the main epithelium werelabeled, as well as scattered cells in the remainder of theepithelium. Glomeruli labled by Lotus were concentrated primarilyin the region of the olfactory bulb that receives its inputfrom the lateral epithelium, although scattered glomeruli couldbe identified in other regions. Within the terminal field ofthese axons there was a mosaic pattern, with some glomerulidensely labeled, some lightly labeled and others unlabeled.These findings support the notion that there are biochemicallydistinct populations of olfactory receptor cells having localizeddistributions in the epithelium, with axons that coalesce toterminate in specific glomeruli, rather than diffusely overtheir projection field. Chem. Senses 21: 13–18, 1996     

Catecholaminergic contributions to the neuronal machinery of the olfactory bulb: aftoradiographic, immunohistochemical and evoked feild potential studies

aftographic exeperiments on the localization of radiolabelednoradrenaline, dopamine and dopa, as well as immunohistochemicalstudies on hydroxylase-like activity, are summarized and comparedin both rat and turtle olfactory bulbs. Evoked field potentialstudies on effects of dopamine are also discussed. The histochemicalstudies suggest that dopaminergic periglomerular neurons arethe most significant cellular component of the catecholaminergicsystem in the olfactory bulb of both species. Scattered fluorescentcell group was also present in the internal plexiform layerand superficial granule cell layer of the turtle olfactory bulb.Other fibres, not related to intrinsic bulbar neuronal cellbodies, were also labeled, mostly in the granule cell layerbut also in the external plexiform layer. These might belongto a centrifugal catecholaminergic system from brain stem neurons.In the in vitro turtle olfactory bulb, dopamine and apomorphinedepressed the amplitude of field potentials evoked by a singlevolley in the olfactory nerve or lateral olfactory tract, andreduced the depression and latency of reponses when paired volleywere delivered. It is suggested that catecholaminergic systemsplay a key role in modulating mitral cell activity through actionsin both superficial (glomerular) and deep (granule) layers.This may involve direct actions, or other, non-catecholaminergicinterneurons.     

Comparing peripheral olfactory coding with host preference in the rhagoletis species complex

Recent studies have shown that flies from sympatric populationsof Rhagoletis pomonella infesting hawthorn, apple, and floweringdogwood fruit can distinguish among unique volatile blends identifiedfrom each host. Analysis of peripheral chemoreception in Rhagoletisflies suggests that changes in receptor specificity and/or receptorneuron sensitivity could impact olfactory preference among thehost populations and their hybrids. In an attempt to validatethese claims, we have combined flight tunnel analyses and singlesensillum electrophysiology in F₂ and backcross hybrids displayinga variety of behavioral phenotypes. Results show that differencesin peripheral chemoreception among second-generation adultsdo not provide a direct correlation between peripheral codingand olfactory behavior. We conclude that either the plasticityof the central nervous system in Rhagoletis can compensate forsignificant alterations in peripheral coding or that peripheralchanges present subtle effects on behavior not easily detectablewith current techniques. The results of this study imply thatthe basis for olfactory behavior in Rhagoletis has a complicatedgenetic and neuronal basis, even for populations with a recentdivergence in preference.     

THE OLFACTORY-GUSTATORY BASIS OF FOOD PREFERENCE IN THE HERBIVOROUS PROSOBRANCH, LITTORINA LITTOREA (LINNAEUS)

Studies of food preference often measure the rate of consumptionof prey items by a predator; this confounds the factors determiningattractiveness and edibility, ignoring the fact that preferencesare probably resolved at the pre-ingestive stage of a consumer'sfeeding behaviour. In this paper, a novel technique has beendeveloped to measure the importance of chemical stimuli to feed,perceived by olfactory and gustatory means, as determinantsof the subsequent feeding behaviour of the generalist intertidalherbivore,Littorina littorea (L.). Cell-free extracts of a rangeof algae were presented simultaneously, impregnated in artificialcellulose-based substrates. Subsequent ranking of feeding preferencesreveals hierarchies which correspond with those establishedby other workers, using intact algae to feed L. littorea. Extractsof ephemeral early successional species (e.g. Ulva lactuca,Porphyra umbilicalis) generally provoke a more positive feedingresponse than perennial late successional species (e.g. Fucusvesiculosus, Asco-phyllum nodosum). Animals fed a preferredalga (Ulva lactuca) prior to preference trials displayed a reductionin the strength of preference relative to starved animals. Therewas no evidence of ‘switching’ of preference rankingsdue to satiation, however. These findings confirm the importanceof olfactory-and gustatory-mediated feeding behaviour as theprimary determinant of food preference in L. littorea. Theyare consistent with the hypothesis that the factors which determinethe attractiveness of a food type, such as chemical cues, arethe criteria by which consumers predict the value of that food.     

Odor suppression of voltage-gated currents contributes to the odor-induced response in olfactory neurons

Olfactorychemotransduction involves a signaling cascade. In addition totriggering transduction, odors suppress ion conductances. Bystimulating with brief odorant pulses, we observed a current associatedwith odor-induced suppression of voltage-gated conductances and studiedits time dependence. We characterized this suppression current inisolated Caudiverbera caudiverberaolfactory neurons. All four voltage-gated currents are suppressed byodor pulses in almost every neuron, and suppression is caused by odorsinducing excitation and by those inducing inhibition, indicating anonselective phenomenon, in contrast to transduction. Suppression has a10-fold shorter latency than transduction. Suppression was morepronounced when odors were applied to the soma than to the cilia,opposite to transduction. Suppression was also present in rat olfactory neurons. Furthermore, we could induce it inDrosophila photoreceptor cells,demonstrating its independence from the chemotransduction cascade. Weshow that odor concentrations causing suppression are similar to thosetriggering chemotransduction and that both suppression and transductioncontribute to the odor response in isolated olfactory neurons.Furthermore, suppression affects spiking, implying a possiblephysiological role in olfaction.

     

Changes in Levels of Naturally Occurring Gibberellin-like Substances during Germination of Seed of Lycopersicon esculentum Mill.

Naturally occurring gibberellin-like substances possessing acidic,basic, and neutral properties were detected, by paper partitionchromatography, in ethanolic extracts of tomato seed and ofetiolated seedlings after 72 and 116 hours' growth. Dwarf maizemutants of the d-1 and d-5 types, ‘Meteor’ pea seedlingsand young ‘Potentate’ tomato plants were used asbioassay material. Hydrolysis of seed and seedling proteinsby ficin in phosphate buffer, pH 6.2, after removal of ethanol-solublesubstances, liberated more and different ‘bound’gibberellin-like substances. It is suggested that protein hydrolysisduring germination is an important means of liberating thesesubstances at different stages of seedling development. Acidic substances were present in all the extracts prepared,but in general two with Rfs 0.25 and 0.55 in iso-propanol: ammonia:water : : 10:1:1 v/v were differentiated on d-2 and d-5 maizerespectively. Neutral substances in dry seed extracts chromatographedin the same solvent, had Rfs of 0.05, 0.35, and 0.95 and thesewere found only in the ethanolic (‘free’) extracts.They were active on d-1 and d-2 maize and ‘Meteor’pea. Basic gibberellin-like substances with Rfs of 0.05 and0.35 were found in ‘free’ extracts of both dry seedand etiolated seedlings after 116 hours' growth which were activeon d-2 maize only. Two others with Rfs 0.45 and 0.95 were extractedfrom seedlings after 72 hours' growth and these were activeon young ‘Potentate’ tomato plants. It is suggested that certain gibberellin-like substances, capableof reversing dwarfism in test plants, may be responsible formorphogenetic or other responses not involving stem extensionin the parent species. Changes were found in the levels of gibberellin-likesubstances but there was no evidence of changes in levels ofseed inhibitors relative to seed growth substances.     

The Effects of Pectic Enzymes and Phosphatidases on Potato Tuber Tissue

Extracts from rots of potato tubers caused by Erwinia atrosepticaand Corticium praticola were fractionated by precipitation withammonium sulphate and by gel filtration. For the various fractionsof the E. atroseptica extracts there was a close relation betweenthe activity of pectate franj-eliminase and capacity to increasethe permeability of protoplasts as assessed by loss of electrolytes.There was no such relation with phosphatidase acting on lecithin. For certain fractions of C. praticola extracts there was a similarclose relation between increase in permeability and activityof a polygalacturonase but for other fractions with low polygalacturonaseactivity there was a better relation with phosphatidase thoughall fractions that caused increase in permeability did havesome polygalacturonase activity. Phosphatidases which probablyplay no part in the killing of cells in E. atroseptica rotsmay, therefore, have some role in the killing of cells in C.praticola rots though they are likely to be less important thanpectic enzymes. Extracts from E. atroseptica rots caused marked increases inuptake of oxygen by tuber discs. Dialysis decreased and heatingeliminated this increase and had corresponding effects on permeability.However, after fractionation with ammonium sulphate, fractionswith high trans-eliminase activity had little effect on oxygenuptake whereas fractions with low trans-eliminase had littleeffect on permeability and greatly increased oxygen uptake. Similar results were obtained with C. praticola rot extracts.In contrast, nigericin and Triton X-100 both increased permeabilityand caused large increases in oxygen uptake The significance of these results is discussed especially inrelation to the killing of protoplasts by extracts from bothtypes of rot.     

Xanthoxin: A Growth Inhibitor in Light-grown Sunflower Seedlings, Helianthus annuus L.

Methanol extracts from light- and dark-grown sunflower seedlings,Helianthus annuus L., var. ‘Inra No. 6501’, weresubjected to solvent partition. The neutral diethyl ether fractionfrom the light-grown seedlings contained material(s) which inhibitedcress seed germination. Such inhibition was scarcely detectablein extracts of the etiolated seedlings. Sometimes inhibitionalso occurred in the petroleum spirit fraction. A mixture ofcis, trans- and trans, transxanthoxin showed the same partitioncharacteristics as the inhibiting substance(s); the latter co-chromatographedwith xanthoxin in all paper, thin layer, and high pressure liquidchromatography separation procedures tried. The inhibition wasalso detectable with the Avena colcoptile straight growth bioassay. It is concluded that xanthoxin is formed during illuminationof sunflower seedlings; its role in the phototropic responseof these seedlings is discussed.     

Avian Olfaction

The literature and status of knowledge concerning olfactionin birds is reviewed, and the general anatomical plan of theavian olfactory chamber is discussed. Birds that show olfactoryability through the possession and utilization of well-developedolfactory equipment, or are suspect of olfactory perceptionbecause of behavioral patterns or olfactory equipment are discussed.These are: (1) the kiwi (Apteryx) of New Zealand, (2) procellariiformbirds, such as albatrosses, shearwaters, and petrels, (3) thecathartine vultures, particularly the turkey vulture (Cathartesaura), (4) the oilbird (Steatornis caripensis) of the islandof Trinidad, and northern South America, and (5) the honey guidesof the family Indicatoridae. Some new data suggesting a well-developedsense of smell in the honey guides (Indicatoridae) are alsopresented.     

The Production of Ethylene by Whole Apple Fruits and by Tissue 1

It is shown that the production of ethylene by whole apples,discs of peel prepared from them, and extracts prepared fromthe discs and supplied with linolenic acid, increases simultaneouslyduring the development of the respiration climacteric in apples.As the climacteric peak is reached, the ability of the extractsto produce ethylene declines and this is associated with a rapidloss of ethylene-producing activity on short term (up to 24h) ageing of the peel discs from which the extracts were obtained. It is suggested that the gmn.ll ethylene production by extracts(with linolenic acid) from pre-climacteric fruits, which arenot themselves evolving sufficient ethylene for its detectionin the ambient atmosphere, may be explained on the grounds thateven before the climacterio the fruit is producing small amountsof ethylene within the tissue; the tissue, as the climactericphase is approached, becomes more sensitive to ethylene andautocatalysed production of the gas then stimulates the fruitinto the respiration climacteric.     

Exploitation of floral signals by crab spiders (Thomisus spectabilis, Thomisidae)

Flowers exhibit characteristics through which they exploit thesensory biases of pollinating insects, and both signaler andreceiver benefit from this interaction, either through reproductiveservice or food reward. However, the preferences of pollinatorsfor certain flower traits such as color or odor might be exploitedby predators that target pollinating insects. Crab spiders,Thomisus spectabilis, position themselves on flowers to preyon pollinators such as honeybees, Apis mellifera. We gave bothhoneybees and crab spiders the choice between two randomly chosenwhite Chrysanthemum frutescens, including olfactory signalsin one experiment and excluding odor in a second experiment.When olfactory signals were included, crab spiders and honeybeesclearly preferred the same flower out of a pair. However, agreementlevel was at chance in the absence of olfactory signals. Wealso analyzed the visual flower characteristics that might influencethe decision of the animals. Neither the size of flowers (diameterof flower and diameter of reproductive flower center) nor thereflectance properties (receptor excitation values in ultraviolet,blue, and green; overall brightness) influenced the choicesof crab spiders and honeybees. Therefore, odor seems to be thefloral signal that bees use to identify high-quality flowersand that crab spiders exploit to encounter honeybees.     

Rate and pattern of migration of lineally-related olfactory bulb interneurons generated postnatally in the subventricular zone of the rat

A spatially discrete region of the anterior part of the postnataltelescephalic subventricular zone, referred to as the SVZa generatesvast numbers of lineally-related neurons destined for the olfactorybulb (Luskin, 1993). The cells originating in the SVZa migrateto the olfactory bulb along a highly restricted pathway whichis in a direction orthogonal to the orientation of radial glialfibers. In this study we analysed the number, distribution,orientation and rate of migration of SVZa-derived cells as theyapproach the olfactory bulb. In order to track the SVZa-derivedcells, a retroviral lineage tracer, encoding the reporter geneE.coli ß-galactosidase (lacZ) was injected preciselyinto the rat SVZa at postnatal day 1 (Pl). The lacZ-positivecells were visualized 1, 2 and 3 days later by X-Gal histochemistryin cryostat sections. As the number of SVZa-derived cells inthe pathway increased with survival time, their distributionchanged systematically. The distribution pattern of lacZ-positivecells by 2 and 3 days postinjection suggested that some of theprogeny of infected progenitor cells were undergoing neurogenesisas they proceeded to the olfactory bulb; a large percentageof the lacZ-positive cells were substantially displaced fromthe SVZa injection site. To investigate whether lacZ-positivecells migrate in a directed fashion, their orientation preferencewas scored. For the majority of lacZ-positive cells (>94%),their leading process was directed toward the olfactory bulb,possibly reflecting a response to migratory cues present alongthe pathway. The estimated average rate of cell migration tothe olfactory bulb was 23 µm/h, which is approximatelytwice the speed of radially directed neuronal migration fromthe telencephalic ventricular zone to the cortical plate (O'Rourkeet al, 1992). Collectively, these results suggest that SVZa-derivedintemeurons en route to the olfactory bulb may employ a novelmode of tangential migration.