The ultrastructure of the sensory cells in the chemoreceptor of the ommatophore of Helix pomatia L.

Most of the sensory cells found in the chemoreceptor of the ommatophore of Helix pomatia are typical bipolar cells. The chemoreceptor is deveded by a furrow into two parts; within the ventral subdivision the layer of sensory cell bodiesis thicker than in the dorsal part. According to the differentiations of the apical surface of the dendrites, it is possible to distinguish six different classes: a) dendrites with one cilium and 75 nm thick cytofila (sometimes dendrites of identical appearance posses more than one cilium); b)dendrites with several cilial and 150 nm thick cytofila; c) dendrites with several cilia, 50 nm thick cytofila, and long, striated rootlets; d) dendrites with several cilia bur without cytofila; e) dendrites with 130 nm thick cytofila but without cilia; and f) dendrites with 65 nm thick cytofila but without cilia; dendrites of this class are the only ones with a cytoplasm more electron dense than that of the surrounding supporting cells. All these dendrites are connected to the surrounding supporting cells by terminal bars, each consisting of zonula adhaerens, aonula intermedia and zonula septata. The perikarya of the sensory cells measure approximately 15 mum by 8 mum and enclose 10 mum by 6 mum large nuclei. Axons, originating from these perikarya, extend to the branches of the digital ganglion. In the distal part of this gangloin the axons come into synaptic contact with interneurons, but in our electron micrography it was not possible to coordinate processes and synapses with the corresponding neurons.     

Sensilla on the third antennal segment of Drosophila melanogaster meigen (Diptera : Drosophilidae)

The distribution and morphology of the sensilla on the 3rd antennal segment of Drosophila melanogaster Meigen (Diptera : Drosophilidae) were studied with light and electron microscopy. Four types of hairs were identified. Three types of hairs innervated by dendrites are sensilla basiconica, sensilla coeloconica and sensilla trichodea. They occur amongst a large number of the 4th type of uninnervated hairs or spinules.Sensilla basiconica and coeloconica can be easily identified by light microscopy on staining with 0.1016 silver nitrate in 70% ethanol. The tips of sensilla basiconica and coeloconica appear dark brown. Most of the sensilla trichodea and spinules remain unstained.Sensilla basiconica conform to the single-walled, multiporous sensilla, having poretubules and branched dendrites. Sensilla coeloconica are double-walled and have longitudinal channels near the tip. No wall pores are found on sensilla trichodea. Dendrites do not branch in sensilla coelonica and trichodea. A mechanosensory dendrite with characteristic tubular body is absent in these sensilla.Populations of sensilla basiconica and sensilla trichodea occur in diametrically opposite, distinct regions on the 3rd antennal segment-the former in the dorsomedial and the latter in the ventrolateral regions, whereas sensilla coeloconica are distributed on most of the anterior and posterior surfaces, including the cavity walls of the sacculus.The axons are arranged in distinct groups in the antennal nerves at the stalk of the 3rd segment. This grouping becomes more pronounced in the nerve prior to its entry into the brain.     

Cytochrome oxidase staining reveals functionally important activity bands in the olfactory epithelium of newborn rat

We used cytochrome oxidase (CytOx) staining intensity, which is correlated with neuronal functional activity, to evaluate maturity and functionality of newborn rat olfactory epithelium (OE) and olfactory receptor neurons (ORNs). Nasal olfactory tissue of neonatal rats was stained with CytOx and analyzed qualitatively and quantitatively. Results revealed that newborn OE shows six differentially stained horizontal bands. Bands run parallel to the OE surface and were categorized as very light, medium or darkly stained. A narrow and pale Band 1 overlapped with horizontal basal cells. Next, a wide and lightly stained Band 2 was observed that coincides with the globose basal cell layer and immature ORNs, deep in OE. Next apically, a medium-staining Band 3 overlapped with ORN perikarya. Closer to the surface, a medium to light Band 4 was discerned where dendrites of mature ORNs normally occur. This band was interrupted with lighter areas due to the presence of supporting cells nuclei. Next, a superficial but dark Band 5 occurred, populated by the apical portions of ORN dendrites and their ciliated knobs and by supporting cell apices; mitochondria in apices of supporting cells contribute predominantly to dense staining of this Band 5. Apical to Band 5, a thin and fairly light Band 6 was observed which overlaps with the mucus layer that contains part of the ORN knobs, their cilia and supporting cell microvilli. Along the length of ORN dendrites, apical segments just below the ORN knobs, and wide basal segments showed a darker staining than the middle segments implying “microzones” of higher neural activity within the most apical and basal regions of dendrites. Our findings agree with ultrastructural studies showing a presence of mitochondria in knobs, basal portions of ORN dendrites and in OE supporting cell apices, suggesting that apical regions of both olfactory and supporting cells near the surfaces are metabolically most active, in odorant detection, signal processing, and detoxification, the latter for supporting cells.     

Ultrastructure of the sensory epithelia of oral tube,fungiform sensory bodies,and terminal knobs of tentacles of Ovatella myosotis Draparnaud (Archaeopulmonata,Gastropoda)

Sensory epithelia of the oral tube, a fungiform body anterior to the tentacles and of the terminal knob of tentacles, were studied in Ovatella myosotis by electron microscopy. All three epithelia consist of columnar support cells, sensory cells, and, except in the oral tube, numerous goblet cells. The epithelia differ significantly in their apical differentiations. In the oral tube an outer layer is formed by irregularly bent villi of support cells completely embedded in a surface coat. Cilia and cytofila of the dendrites of sensory cells intertwine throughout the entire depth of the villous layer. In the fungiform sensory body some of the villi of support cells are singly branched. Their basal region is free of a surface coat. In this region cytofila and cilia of dendrites form a spongy layer, some cytofila extending into the surface coat. In the tentacular terminal knob the villi of the support cells branch dichotomously once or twice, a single villus thus ending with 2–4 tips. Only these terminal twigs are invested with the surface coat. The cytofila and dendritic cilia are confined to a broad spongy layer underneath. Three types of dendrites are present. They differ in their number of cilia, structure of basal bodies and occurrence in the three epithelia. Dendritic cytofila are most abundant in the tentacular terminal knob and least numerous in the oral tube. The observations are discussed with respect to corresponding epithelia in other pulmonates, the homology of the fungiform body, and possible functional correlates of structural features.     

Surface coats of pore tubules and olfactory sensory dendrites of a silkmoth revealed by cationic markers

Negatively charged surface coats have been demonstrated on the pore tubules and dendritic membranes of olfactory hairs of male Antheraea polyphemus silkmoths by application of the cationic markers lanthanum (La3+), ruthenium red (RR), and cationized ferritin (CF). Lanthanum and RR diffused readily into the apically opened hairs, whereas CF penetrated only for a relatively short distance. Deposits of the markers are distributed as follows: the inner surfaces of the hair walls are stained by RR and to a small degree by CF; the surfaces of the pore tubules and the dendritic membranes are stained by all three markers. The pore tubules have the strongest affinity for CF. The number of pore tubule-membrane contacts seems to be increased by the cationic dyes. The dendrites are often penetrated by RR, which forms deposits on the inner membrane leaflets, the cytoplasmic microtubules, and microfilaments, and by La3+, but never by CF. The observations provide support for the assumption that, first, the pore tubule-membrane contacts are formed via surface coats of both structures, possibly influenced by cations and, second, that the dendrites remain intact after pinching off the hair tips.     

Surface specializations of the olfactory epithelium of rainbow trout, Salmo gairdneri

Receptors for olfactory stimulus molecules appear to be located at the surface of olfactory receptor cells. The ultrastructure of the distal region of rainbow trout (Salmo gairdneri) olfactory epithelium was examined by transmission electron microscopy. On the sensory olfactory epithelium, which occurs in the depressions of secondary folds of the lamellae of the rosettes, five cell types were present. Type I cells have a knob-like apical projection which is unique in this species because it frequently contains cilia axonemes within its cytoplasm in addition to being surrounded by cilia. Type II cells bear many cilia oriented unidirectionally on a wide, flat surface. Type III cells have microvilli on a constricted apical surface and centrioles in the subapical cytoplasm. Type IV cells contain a rod-like apical projection filled with a bundle of filaments, and type V cells are supporting cells. Cilia on the sensory epithelium contain the 9 + 2 microtubule fiber pattern. Dynein arms are clearly present on the outer doublet fibers, which suggests that the cilia in the olfactory region are motile. Their presence in olfactory cilia of vertebrates has been controversial. The cilia membrane in this species is unusual in often showing outfoldings, within which are included small, irregular vesicles or channels. In addition, cilia on type II cells frequently contain dense-staining bodies closely apposed to the membranes, along with a densely stained crown at the cilia tip. Previous biochemical evidence indicates that odorant receptors are associated with the cilia.     

Ultrastructure of the nuchal organ in the interstitial polychaete Stygocapitella subterranea (Parergodrilidae)

The nuchal organs of Stygocapitella subterranea are paired narrow pits. They are lined by unciliated cells at the opening and by ciliated cells at the basal parts. The primary sensory cells (6–8) are arranged in a single patch at the bottom of the nuchal pit. The nuclei of the sensory cells are located in the posterior portion of the brain. Their dendrites form the nuchal nerve which is sheathed by the ciliated cells. Each sensory cell bears up to 4 modified sensory cilia and several microvilli extending into the olfactory chamber. The sensory cilia show various patterns of axonemal organization and have no rootlets. The olfactory chamber is covered by a cuticular matrix. Another primary sensory cell lies at the opening of the nuchal pit. It bears cilia which penetrate the cuticle but are enveloped by the epicuticle. Retractor muscles insert caudally on the organ. The nuchal organ of S. subterranea shows similarities to those of opheliids but exhibits several features not to be found in other nuchal organs.     

The phenomenon of ‘Beading’ in olfactory dendrites of the male silkmoth antheraea pernyi GUÉRin-ménéville (Lepidoptera : Saturniidae)

Along the olfactory dendrites of the silkmoth Antheraea pernyi (Lepidoptera : Saturniidae), dilations called beads are formed in vivo during (a) the aging of the animal and (b) after cutting the dendrites. Beads show 3 different morphologies : (i) splaying of the microtubules within them, (ii) detachment of the membrane from the microtubular bundle without the splaying of microtubules, and (iii) total depolymerization of microtubules. The latter is especially common in the tips of the dendrite after cutting with tweezers. The most likely reason for the formation of these beads is the calcium-induced damage to the microtubular and membrane cytoskeleton as evidenced by acridine orange staining. From the electrophysiological point of view, the beaded dendrites at the cut tips are considered to be functional, because normal responses to pheromones can be recorded directly over cut hairs, and such responses have been found similar to recordings from uncut hairs. How age related beading affects electrophysiological recordings is yet to be determined.     

Zonal organization of the mammalian main and accessory olfactory systems

Zonal organization is one of the characteristic features observed in both main and accessory olfactory systems. In the main olfactory system, most of the odorant receptors are classified into four groups according to their zonal expression patterns in the olfactory epithelium. Each group of odorant receptors is expressed by sensory neurons distributed within one of four circumscribed zones. Olfactory sensory neurons in a given zone of the epithelium project their axons to the glomeruli in a corresponding zone of the main olfactory bulb. Glomeruli in the same zone tend to represent similar odorant receptors having similar tuning specificity to odorants. Vomeronasal receptors (or pheromone receptors) are classified into two groups in the accessory olfactory system. Each group of receptors is expressed by vomeronasal sensory neurons in either the apical or basal zone of the vomeronasal epithelium. Sensory neurons in the apical zone project their axons to the rostral zone of the accessory olfactory bulb and form synaptic connections with mitral tufted cells belonging to the rostral zone. Signals originated from basal zone sensory neurons are sent to mitral tufted cells in the caudal zone of the accessory olfactory bulb. We discuss functional implications of the zonal organization in both main and accessory olfactory systems.     

Differential synthesis of β-tubulin isotypes in gerbil nasal epithelia

Compartmentalization of beta-tubulin isotypes within cells according to function was examined in gerbil olfactory and respiratory epithelia by using specific antibodies to four beta-tubulin isotypes (beta(I), beta(II), beta(III), and beta(IV)). Isotype synthesis was cell-type-specific, but the localization of the isotypes was not compartmentalized. All four isotypes were found in the cilia, dendrites, somata, and axons of olfactory neurons. Only two isotypes (beta(I) and beta(IV)) were present in the cilia of nasal respiratory epithelial cells. The beta(IV) isotype, thought to be an essential component of cilia, was present in olfactory neurons and respiratory epithelial cells, which are ciliated, but was not found in basal cells (the stem cells of olfactory sensory neurons, which have no cilia). Olfactory neurons therefore do not synthesize beta(IV)-tubulin until they mature, when functioning cilia are also elaborated. The failure to observe compartmentalization of beta-tubulin isotypes in olfactory neurons sheds new light on potential functions of the beta-tubulin isotypes.     

Structure de l'organe sensoriel apical de l'antenne chez l'Isopode terrestreMetoponorthus sexfasciatus Budde-Lund (Crustacea,Isopoda)

Résumé L'organe sensoriel apical de l'antenne deMetoponorthus a été étudié en microscopie électronique à balayage et par transmission. Il comporte un corps central à la base duquel sont articulées deux longues soies latérales et qui se termine par une touffe de soies très courtes.Les soies de la touffe terminale sont innervées par 4 à 12 neurones bipolaires. Les dendrites traversent le corps central puis pénètrent dans la lumière des soies sans se ramifier. Ils communiquent avec l'extérieur par un pore terminal assez gros. Parmi les dendrites certains paraissent assurer une fonction mécanoréceptrice. Des structures cuticulaires en forme d'écaille protègent la partie terminale des soies du côté axial. Les deux longues soies latérales sont innervées par 5 neurones bipolaires: 4 dendrites pénètrent dans la lumière de la soie; le 5ème, mécanorécepteur, s'arrête au niveau de l'articulation de la soie sur le corps central.La structure fine de cet organe sensoriel apical correspond à celle des chémo-récepteurs de contact connus chez d'autres Arthropodes. Une comparaîson est faite avec les chémorécepteurs de Crustacés marins et terrestres. Chez les formes terrestres on observe un raccourcissement de la partie libre des soies, ainsi qu'une orientation des pores du côté exposé aux stimuli extérieurs. Chez l'Isopode terrestreMetoponorthus étudié dans ce travail, les très courtes soies terminales dépassent à peine du corps central. Le développement des structures cuticulaires au sommet des soies et la tendance des soies à s'intégrer en un organe unique (corps central de l'organe sensoriel) sont autant de spécialisations pour le renforcement de ces soies et leur protection contre la dessication.

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Structure of the apical sensory organ of the antenna in a terrestrial isopod,Metoponorthus sexfasciatus Budde-lund (Crustacea, Isopoda)

Summary The apical sensory organ on the antenna ofMetoponorthus was studied by scanning and transmission electron microscopy. It consists of a tuft of very short terminal hairs which prolongs a central body and two long lateral hairs which are articulated on the central body of the sensory organ.Hairs from the terminal tuft are innervated by 4 to 12 bipolar neurons. The dendritic cilia proceed through the axial body and then enter the lumen of hairs without branching. Dendrites in each hair communicate with environment through a rather wide terminal opening. It is suggested that some dendrites are mechanoreceptive. Scale-like cuticular structures protect the terminal part of the hairs, on the inner side that is not exposed to outer stimuli.The two long lateral hairs are innervated by 5 bipolar neurons: 4 dendrites enter the hair lumen while one, mechanoreceptive, terminates in the socket membrane.The fine structure of this apical sensory organ corresponds to that of known contact chemoreceptors in other Arthropods. A comparison is made with known chemo-receptors in marine and terrestrial Crustacea. In terrestrial forms it can be observed that the hairs become shorter. On the other hand the hair surfaces which are not exposed to outer stimuli show a thickened cuticule. In the terrestrial IsopodMetoponorthus (studied in the present work) the very short terminal hairs barely project past the central body. The development of the cuticular structures at the tip of the hairs and the tendancy of the hairs to be integrated into a single organ (central body of the sensory organ) represent so many adaptations for protection and reduction of evaporation.

     

Localization of Phosphatase Responsible for Hydrolysis of Inositol 1,4,5-Triphosphate in the Olfactory Lining of True Sturgeons

The paper presents results of a cytochemical study of localization of phosphatase responsible for hydrolysis of inositol 1,4,5-triphosphate (ITP) in the olfactory lining of true sturgeons (the sturgeon, starred sturgeon, and sterlet). Reaction products as a dark discrete granules are localized in the apical parts of epithelium, practically in the same manner in all the species studied. The precipitate is found on the plasma membranes of cilia, microvilli, and clava of the olfactory cells. Occasionally, the precipitate is also found in the cilia, basal bodies, and rootlets of microvillar cells. The ITP-hydrolyzing phosphatase is supposed to restrict development of transduction process by removing excess messengers from the operating system. The data obtained indicate that in the true sturgeons, the phospholipase cascade of olfactory transduction is concentrated predominantly in the cilia and microvilli of olfactory cells.     

Ultrastructure of the peg and hair sensilla on the antenna of larval Aedes aegypti (L.)

The antenna of fourth instar larvae of Aedes aegypti has one peg organ of a basiconic type innervated by four neurons. The dendrites are ensheathed to near their terminations at the peg tip by an electron-dense dendritic sheath and by a cuticular sheath. They have easy communication by diffusion with the external environment only at the tip through a peripheral ensheathing membrane and six slit-channels. One of the dendrites resembles a tubular body proximally and may be mechanoreceptive. The peg generally appears to be a contact chemoreceptor. There are three antennal hairs of a typical sensillum trichodeum type innervated at the base by one neuron each. An intricate terminal mechanism at the insertion of the dendrite in the hair is described. These are believed to be tactile hairs. There are also three antennal hairs each innervated by two neurons. The dendrite from one terminates at the base similar to that of a tactile hair, and is believed to function in a similar mechanoreceptive manner. The dendrite from the second neuron extends naked along the length of the hair lumen. It is believed to be primarily chemoreceptive, in a slow-acting general sensory function. In all the sensilla there appear to be secretions produced in the junction body regions of the dendrites, and there is evidence for accumulation of secretory materials in the dendritic tips in some of the sensilla.     

Organization of actin microfilaments in the apical border of oviduct ciliated cells

Actin microfilaments were localized in quail oviduct ciliated cells using decoration with myosin subfragment S1 and immunogold labeling. These polarized epithelial cells show a well developed cytoskeleton due to the presence of numerous cilia and microvilli at their apical pole. Most S1-decorated microfilaments extend from the microvilli downward towards the upper part of the ciliary striated rootlets with which they are connected. From the microvillous roots, a few microfilaments connect the proximal part of the basal body or the basal foot associated with the basal body. Microfilament polarity is shown by S1 arrowheads pointing away from the microvillous tip to the cell body. Furthermore, short microfilaments are attached to the plasma membrane at the anchoring sites of basal bodies and run along the basal body. The polarity of these short microfilaments is directed from the basal body anchoring fibers downward to the cytoplasm. At the cell periphery, microfilaments from microvillous roots and ciliary apparatus are connected with those of the circumferential actin belt which is associated with the apical zonula adhaerens. Together with the other cytoskeletal elements, the microfilaments increase ciliary anchorage and could be involved in the coordination of ciliary beating. Moreover, microvilli surrounding the cilia probably modify ciliary beating by offering resistance to cilium bending. The presence of microvilli could explain the fact that mainly the upper part of the cilia appanars to be involved in the axonemal bending in metazoan ciliated cells.     

Fine Structure and Function of Pharynx Cilia in Glossobalanus minutus Kowalewsky (Enteropneusta)

Two kinds of cilia have been observed in the pharynx of Glossobalanus minutus Kowalewsky. From the present study, a ciliary specialization can be found in order to move a determinate substance, i.e. mucus or water. Mucus-moving cilia (type I cilia) have a single basal centriole and poorly developed ciliary rootlets. Their tips are rounded, bearing an inner, asymmetrical cap attached to some tubules. Water-moving cilia (type II cilia) are exclusively located at lateral epithelia of branchial bars, giving rise to the water current through the gills. They have two basal centrioles, proximal and distal, and a complex system of ciliary rootlets made up of a principal rootlet, a secondary or accessory rootlet and a 'fan' rootlet. The tips of type II cilia have a long process with some tubules inside. All basal structures are precisely orientated in order to assure a good coordination of ciliary beat. The possible functional significance of ciliary substructure is also discussed. From these observations a model for mucus and water currents through gill slits is postulated.     

Ultrastructural Aspects of Olfactory Signaling

The olfactory area of the nasal cavity is lined with olfactoryreceptor cell cilia that come in contract with incoming odormolecules. Ultrastructural immunocytochemical studies in rodentshave shown that these cilia contain all the proteins necessaryto transduce the odorous message into an electrical signal thatcan be transmitted to the brain. These signaling proteins includeputative odor receptors, GTP binding proteins, type III adenylylcyclase and cyclic nucleotide-gated channels. The rest of thecells, including dendrites and dendritic knobs, showed no discerniblelabeling with antibodies to these signaling proteins. Furthermore,freeze-fracture and freeze-etch studies have shown that themembrane morphology of olfactory cilia differs substantiallyfrom that of non-sensory cilia. Olfactory cilia have many moremembrane particles. Transmembrane signaling proteins, such asodor receptors, adenylyl cyclase and cyclic nucleotide-gatedchannels, conceivably appear as membrane particles. Thus, thelong-standing supposition that olfactory cilia are peculiarlyadapted to deal with the reception and initial transductionof odorous messages has now been verified in terms of both ultrastructuralmorphology and cytochemistry. Emerging studies on vomeronasalreceptor cell microvilli indicate that the same is true forthis organ, even though the actual signaling components differfrom those of the main olfactory system. Chem. Senses 22: 295–311,1997.     

Polarized dendritic transport and the AP-1 mu1 clathrin adaptor UNC-101 localize odorant receptors to olfactory cilia

Odorant receptors and signaling proteins are localized to sensory cilia on olfactory dendrites. Using a GFP-tagged odorant receptor protein, Caenorhabditis elegans ODR-10, we characterized protein sorting and transport in olfactory neurons in vivo. ODR-10 is transported in rapidly moving dendritic vesicles that shuttle between the cell body and the cilia. Anterograde and retrograde vesicles move at different speeds, suggesting that dendrites have polarized transport mechanisms. Residues immediately after the seventh membrane-spanning domain of ODR-10 are required for localization; these residues are conserved in many G protein-coupled receptors. UNC-101 encodes a mu1 subunit of the AP-1 clathrin adaptor complex. In unc-101 mutants, dendritic vesicles are absent, ODR-10 receptor is evenly distributed over the plasma membrane, and other cilia membrane proteins are also mislocalized, implicating AP-1 in protein sorting to olfactory cilia.     

Abscisic Acid stimulates elongation of excised pea root tips

Excised Pisum sativum L. root tips were incubated in a pH 5.2 sucrose medium containing abscisic acid. Elongation growth was inhibited by 100 mum abscisic acid. However, decreasing the abscisic acid concentration caused stimulation of elongation, the maximum response (25% to 30%) occurring at 1 mum abscisic acid. Prior to two hours, stimulation of elongation by 1 mum abscisic acid was not detectable. Increased elongation did not occur in abscisic acid-treated root tips of Lens culinaris L., Phaseolus vulgaris L., or Zea mays L.     

Structure of Aesthetascs in Selected Marine and Terrestrial Decapods: Chemoreceptor Morphology and Environment

We have compared the structure of the aesthetascs—thin-walledchemosensory pegs on the antennules—of Coenobita, a terrestrialhermit crab, and of various marine decapods, including the aquatichermit crab, Pagurus hirsutiusculus. In all cases, the aesthetascsare innervated by the dendrites of many bipolar neurons whosecell bodies are grouped beneath the bases of the hairs. Thedendrites have basal bodies and cilia that divide into slenderbranches, each distinguished by ovoid swellings along its lengthand containing one or more microtubules apparently continuouswith the microtubules of the cilia. The arrangement of the dendrites within the aesthetascs is distinctlydifferent in Coenobita from that in the marine animals, evenin its relative, Pagurus. There are many points of structuralconvergence between the aesthetascs of Coenobita and the thin-walledolfactory pegs of the insect antenna. These modifications mayrepresent adaptations for conservation of water in the terrestrialreceptors.     

In vitro effects of colchicine and nocodazole on ciliogenesis in quail oviduct

Oviduct implants from quails which were primarily stimulated in vivo by estrogen so as to induce ciliogenesis in some epithelial cells were cultured in vitro in the presence or absence of colchicine or nocodazole. After 24 or 48 hr of culture, implants were examined by transmission and scanning electron microscopy to determine drug-induced alterations in ciliogenesis. After 24 hr of 10(-5) M colchicine treatment, the formation of basal bodies was totally inhibited, though the precursor material of generative complexes was unchanged. The inhibitory effect was not reversed when colchicine was removed in a 24 hr recovery culture. Treatment with 10(-6) M nocodazole for 24 hr, partially inhibited the assembly of basal bodies, which exhibited altered morphology. The assembly of basal bodies was restored during the 24 hr recovery period, after removal of nocodazole. Colchicine and nocodazole did not prevent polarized migration towards the apical surface of basal bodies formed prior to drug treatment. They anchored to the plasma membrane, but the formation of cilia was strongly disturbed in the presence of the drug. Numerous cells possessed anchored basal bodies which failed to induce the formation of cilia. The elongation of cilia was inhibited, as seen by their abnormal capping structure. In the enlarged tip, microtubules diverged. In contrast, these very short cilia possessed a mature ciliary necklace which was constructed during drug treatment. Differentiation of this membrane ciliary structure appeared to be unrelated to axoneme growth.