Association of immune cells with neuroepithelial bodies in the lungs of neonatal dogs,cats and hamsters

A close topographical association between neuroepithelial bodies and immune cells is occasionally observed in the lungs of various neonatal mammalian species. The immune cells concerned are mast cells and neutrophil or eosinophil granulocytes. In the lungs of newborn puppies having undergone left lung autotransplantation, mast cells are particularly numerous in the airway mucosa of both right and left lungs and their association with neuroepithelial bodies is highly significant. Several of the substances known to be synthesized by the neuroepithelial bodies have a chemoattractive effect on immune cells. Thus, our observations indicate that intrapulmonary neuroepithelial bodies contribute to the local immune response.This investigation was supported by a grant from the Fonds voor Geneeskundig Wetenschappelijk Onderzoek (FGWO-NFWO), Belgium     

The differential cardio-respiratory responses to ambient hypoxia and systemic hypoxaemia in the South American lungfish, Lepidosiren paradoxa

Lungfishes (Dipnoi) occupy an evolutionary transition between water and air breathing and possess well-developed lungs and reduced gills. The South American species, Lepidosiren paradoxa, is an obligate air-breather and has the lowest aquatic respiration of the three extant genera. To study the relative importance, location and modality of reflexogenic sites sensitive to oxygen in the generation of cardio-respiratory responses, we measured ventilatory responses to changes in ambient oxygen and to reductions in blood oxygen content. Animals were exposed to aquatic and aerial hypoxia, both separately and in combination. While aerial hypoxia elicited brisk ventilatory responses, aquatic hypoxia had no effect, indicating a primary role for internal rather than branchial receptors. Reducing haematocrit and blood oxygen content by approximately 50% did not affect ventilation during normoxia, showing that the specific modality of the internal oxygen sensitive chemoreceptors is blood PO(2) per se and not oxygen concentration. In light of previous studies, it appears that the heart rate responses and the changes in pulmonary ventilation during oxygen shortage are similar in lungfish and tetrapods. Furthermore, the modality of the oxygen receptors controlling these responses is similar to tetrapods. Because the cardio-respiratory responses and the modality of the oxygen receptors differ from typical water-breathing teleosts, it appears that many of the changes in the mechanisms exerting reflex control over cardio-respiratory functions occurred at an early stage in vertebrate evolution.     

Comparative study of gill neuroepithelial cells and their innervation in teleosts and Xenopus tadpoles

Peripheral O₂ chemoreceptors initiate adaptive cardiorespiratory responses to hypoxia in vertebrates. Morphological and physiological evidence suggests that, in fish, neuroepithelial cells (NECs) of the gill perform this role. We conducted a comparative examination in three species of teleosts (zebrafish, goldfish and trout) and larvae of the amphibian Xenopus laevis, using whole-mount gill preparations and confocal immunofluorescence, to elucidate the distribution, morphology and innervation of gill NECs. Nerve fibres were immunolabelled with the neuronal marker zn-12 and were associated with serotonin-immunoreactive NECs in the gills of all species tested. With the exception of trout, innervated NECs were present on all gill arches in the filaments and respiratory lamellae in fish and on homologous structures in Xenopus (i.e. gill “tufts”, including respiratory terminal branches). Thus, the distribution and innervation of NECs of the internal gills of amphibians and teleosts are relatively well conserved, suggesting an important role for gill NECs as O₂ chemoreceptors in aquatic vertebrates. Furthermore, the size and density of gill NECs is variable among teleosts and developmental stages of Xenopus larvae and may be dependent on general gill dimensions or environmental conditions. This report constitutes the first comparative study of gill NECs in fish and amphibians and highlights the significance of gill NECs as an evolutionary model for studying O₂ sensing in vertebrates. We acknowledge the Natural Sciences and Engineering Research Council (NSERC) of Canada for funding through an operating grant to C.A.N., and the NSERC and the Ontario Graduate Scholarship (OGS) program for postgraduate scholarships to M.G.J.     

Identification of carbonic anhydrase activity in bullfrog olfactory receptor neurons: histochemical localization and role in CO2 chemoreception

The objectives of this study were to determine: (1) the frequency and distribution of carbonic anhydrase (CA) activity in the bullfrog nasal cavities, and (2)␣whether inhibition of nasal CA affects the olfactory receptor response to CO₂ or other odorants. It was found, using Hansson's staining technique, that some olfactory receptor neurons exhibited CA activity and that these CA-positive receptors were distributed throughout the nasal cavity with peak densities in the dorsal and ventral sensory epithelial regions. To test for the role of CA in olfactory transduction, electro-olfactograms (EOGs) were recorded from the surface of the ventral sensory epithelium in response to 2-s pulses of 5% CO₂ and amyl acetate before and after topical CA inhibition with acetazolamide (10⁻³mol · l⁻¹). In 52 bullfrogs, 1222 sites on the ventral epithelium were tested resulting in 23 locations that exhibited a response to 5% CO₂. Inhibition of CA caused an immediate 65% reduction in the EOG response to CO₂ while the response to amyl acetate was not affected. These results, along with the histochemical localization of CA in some olfactory receptor neurons, indicate that CA plays a role in the detection of CO₂ in frog olfactory neurons and that only a small population of olfactory receptor neurons are CO₂ sensitive. Accepted: 31 July 1997     

Neural structures in the receptive field of pleural ganglion mechanosensory neurons of Aplysia californica

The peripheral processes of the mechanoafferents that, when stimulated, initiate the much-studied tail withdrawal reflex of Aplysia californica have not been characterized. We show that immunofluorescence staining for class III -tubulin highlights neurons and reveals nerve tracts and fine neuronal processes in Aplysia tissue. Coupled with transmission and scanning electron microscopy, class III -tubulin immunofluorescence is consistent with the possibility that mechanoafferents in the receptive field of pleural ganglion mechanosensory neurons penetrate the tail epidermis and terminate as ciliated endings. This view is reinforced by comparisons among neuronal processes in several mechanosensory epidermal regions and in a chemosensory epidermis.     

Vascular corrosion replicas of chemo-baroreceptors in fish: The carotid labyrinth in Ictaluridae and Clariidae

Summary Scanning electron microscopy of vascular corrosion replicas and light microscopy revealed a pair of highly vascularized tissues, the carotid labyrinths, in the dorsal head region of the channel catfish, Ictalurus punctatus, the black bullhead, I. melas, and the walking catfish, Clarias batrachus. The labyrinth consists of a myriad of arterioles that arise from the common carotid artery immediately distal to the origin of the common carotid from the efferent branchial (epibranchial) artery of the first gill arch. The arterioles anastomose with each other to form: (1) the internal carotid artery which supplies the brain, and (2) several anteriolateral arteries that extend into the anterior head. In the ictalurids the common carotid artery emerges from the labyrinth intact and continues anteriorly as the large olfactory artery, whereas in Clarias all postlabyrinthine vessels result from arborization of the common carotid and subsequent anastomosis of the arterioles. Similarities between piscine and amphibian carotid labyrinths and the anatomical proximity of the former with the gills suggest that, in Ictaluridae, the labyrinth has a chemoor baroreceptor function.Supported by NSF Grant No. PCM 79-23073The authors wish to thank K. Drajus, D. Kullman, E. Boland and Dr. J. O'Malley for their most capable help. The authors also express their gratitude to P. Shafland and the Florida Game and Fresh Water Fish Commission for providing Clarias     

Ultrastructure of chemoreceptive tarsal sensilla in an armored harvestman and evidence of olfaction across Laniatores (Arachnida,Opiliones)

Harvestmen (Arachnida, Opiliones) are especially dependent on chemical cues and are often regarded as animals that rely mainly on contact chemoreception. Information on harvestman sensilla is scarce when compared to other arachnid orders, especially concerning internal morphology. Using scanning (SEM) and transmission (TEM) electron microscopy, we investigated tarsal sensilla on the distal tarsomeres (DT) of all leg pairs in Heteromitobates discolor (Laniatores, Gonyleptidae). Furthermore, we explored the typological diversity of sensilla present on the DT I and II in members of the suborder Laniatores, which include two thirds of the formally described opilionid fauna, using species from 17 families representing all main laniatorian lineages. Our data revealed that DT I and II of H. discolor are equipped with wall-pored falciform hairs (two types), wall-pored sensilla chaetica (two types) and tip-pored sensilla chaetica, while DT III and IV are mainly covered with trichomes (non-sensory) and tip-pored sensilla chaetica. The ultrastructural characteristics support an olfactory function for all wall-pored sensilla and a dual gustatory/mechanoreceptive function for tip-pored sensilla chaetica. Based on our comparative SEM survey, we show that wall-pored sensilla occur in all investigated Laniatores, demonstrating their widespread occurrence in the suborder and highlighting the importance of both legs I and II as the sensory appendages of laniatorean harvestmen. Our results provide the first morphological evidence for olfactory receptors in Laniatores and suggest that olfaction is more important for harvestmen than previously thought.     

Ultrastructure of the chemosensitive basiconic single-walled wall-pore sensilla on the antennae in adults and embryonic stages of Locusta migratoria L. (Insecta,Orthoptera)

Summary The structure and embryonic development of the two types (A, B) of basiconic sensilla on the antennae of Locusta migratoria were studied in material that had been cryofixed and freeze-substituted, or chemically fixed and dehydrated. Both types are single-walled wall-pore sensilla. Type-A sensilla comprise 20–30 sensory and 7 enveloping cells. One enveloping cell (thecogen cell secretes the dendrite sheath); four are trichogen cells, projections of which form the trichogen process during the 2nd embryonic molt. The trichogen cells form two concentric pairs proximally. Two tormogen cells secrete the cuticular socket of the sensillum. The dendritic outer segments of the sensory cells are branched. Bifurcate type-A sensilla have also been observed. Type-B sensilla comprise three sensory and four enveloping cells (one thecogen, two trichogen and one tormogen). The trichogen process is formed by the two trichogen cells, each of which gives rise to two projections. The trichogen cells are concentrically arranged. The dendritic outer segments of the sensory cells are unbranched. In the fully developed sensillum, all trichogen and tormogen cells border on the outer receptor lymph cavity. It is suggested that the multicellular organization of the type-A sensilla can be regarded as being advanced rather than primitive.Supported by the Dcutschc Forschungsgemeinschaft (SFB 4/G1)     

Structure,development and death of sensory cells and neurons in the pupal labial palp of the butterflies Pieris rapae L. and Pieris brassicae L. (Insecta,Lepidoptera)

Summary The development of neurons possibly related to the outgrowth of axons from the labial palp-pit organ was studied in Pieris rapae. Serial sections of six successive stages between pupation and emergence of the imago were examined with the electron microscope. At pupation the palp contains an apical scolopidial organ (ASO) and cellular strands connected to it. The ASO consists of three type-1 scolopidia, which are characterized by the presence of a ciliary 9 × 2 + 0 pattern throughout the dendritic outer segment and a ciliary dilation beneath the cap. The scolopidia show two special features: (i) the dendritic outer segments reach beyond the cap, and (ii) an intricate junctional complex develops between the dendritic inner segments and the scolopale cells. The cellular strands comprise two types of cells: (1) bipolar cells regarded as neurons due to their cytological features, and (2) enveloping cells, which are wrapped around the bipolar cells. The strands degenerate about 10 h after pupation. The sensory cells of the ASO degenerate consecutively between 28 h and 130 h after pupation. However, their enveloping cells survive and endure in the imago, which emerges about 160 h after pupation. An ASO similarly lacking sensory cells was observed in imagines of Pieris brassicae. It is hypothesized that the ASO and the bipolar neurons of the strands play a role in pathfinding of the axons of the labial palp-pit organ.Supported by the Deutsche Forschungsgemeinschaft (SFB 4/G1)