ODOR DISCRIMINATION BY FROG OLFACTORY RECEPTORS

Single unit activity of olfactory receptors was recorded inthe frog. Seventy per cent of the receptors displayed a restingfrequency lower than 20 spikes min^–1. A 20 ways olfactometerwas designed to automatically stimulate the olfactory epitheliumwith 20 highly purified, simple odorants belonging to severalchemical series, each at a single supraliminal concentration.Twenty three cells failed to respond to any of the 20 stimuli.Following a total of 1160 stimulations delivered to 58 receptorcells, 241 activating and 59 inhibitory responses were recorded,leading to an overall selectivity of 25.8%. Twelve units wereexcited by only one of the 20 chemicals. The activating and inhibitory responses were submitted to mathematicalprocedures (calculation of the Pearson's ‘r’ correlationcoefficient, Benzecri's analysis of correspondences) in orderto determine similarities or proximities between odorants accordingto the response profiles of the receptors. The odour space builtfrom these data was clearly multidimensional. The five primaryaliphatic alcohols of the sample failed to exhibit any specialinter-relationship, except the propanolbutanol pair. Camphorwas quite unrelated to the other chemicals. Six odorants whichpossess in common the aromatic nucleus were found to be relatedby high correlation coefficients; they grouped themselves ina cluster in factor analysis diagrams. They are: benzene, naphthalene,anisole, acetophenone and the almond pair nitrobenzene-benzaldehyde.     

EFFECT OF ACTINOMYCIN D ON THE DIFFERENTIATION OF HATCHING GLAND CELL AND CILIA CELL IN THE FROG EMBRYO

The forehead epidermis of the stage 18–20 R. japonica embryo includes the hatching gland cell (HGC) which contains cell-specific secretory granules. The cilia cell (CC) and common epidermal cell (CEC) constitute the epidermis of the entire body surface, in addition to the forehead region.
Culture of superficial epidermal explants from various embryonic portions at various developmental stages revealed that HGCs are derived from cells localized on the neural crest in the stage 13a (early neural plate) embryo. When explants from the presumptive HGC area were treated with 1 ug/ml actinomycin D (AMD), the formation of secretory granules in HGCs was inhibited either by continuous treatment from stage 13 or by an 8-hr treatment at stage 13b. Similarly, the ciliogenesis in CCs was inhibited. The differentiation of CECs was entirely unaffected by any of the AMD treatment. After release from AMD, mucous vesicles, characteristic of the CEC, were formed in cells whose differentiation into HGC and CC had been suppressed by the antibiotic. Thread complexes and clumps of coiled strings were found in the nuclei of AMD-affected cells.
It is concluded that the DNA-dependent RNA syntheses which direct secretory granule formation in the HGC and ciliogenesis in the CC occur during a limited period at stage 13b, viz. , 20 hr before their cytodifferentiation becomes appreciable.     

THE REGENERATION OF CILIA IN PARTIALLY DECILIATED TETRAHYMENA

Partial deciliation of Tetrahymena resulted in cells losing 75% of their cilia, with the balance being paralyzed. The paralyzed cilia are resorbed in the first 20 min after partial deciliation, and regeneration of cilia begins before resorption is completed. Inhibition of protein synthesis with cycloheximide does not inhibit ciliary resorption or regeneration, whereas vinblastine sulfate inhibits regeneration but not resorption. Inhibition of regeneration occurs in completely deciliated cells when they are treated with cyclohexmimide or vinblastine sulfate. It is concluded that the resorbing cilia contribute materials which allow regeneration to occur in the absence of protein synthesis. The volume of cilia regenerated in the presence of cycloheximide in partially deciliated cells is greater than the ciliary volume which is resorbed. This suggests the Tetrahymena cells have a pool of ciliary precursors. This pool does not contribute materials for regeneration in completely deciliated cells which are treated with cycloheximide. It is concluded that resorbing cilia in partially deciliated cells contribute materials which potentiate assembly of cilia from the pool of precursors.     

FAST AXONAL TRANSPORT IN VITRO IN THE SCIATIC SYSTEM OF THE FROG

Abstract— An in vitro system from the frog has been used to study fast axonal protein transport. The preparation, which was incubated in a specially made chamber, consisted of the gastrocnemius muscle, the sciatic nerve, the dorsal ganglia and part of the spinal cord. The parts were separated from each other by silicone grease barriers, which made it possible to follow the migration of labelled proteins from the spinal cord and ganglia, along the sciatic nerve, towards the muscle. About 80 per cent of transported proteins in the sciatic nerve originated from the dorsal spinal ganglia and moved antidromically at a rate of 60–90 mm per day at 18°C. The rapidly transported proteins were 90 per cent particulate and mainly associated with structures sedimenting in the microsomal fraction.
The effects of cyclohexirnide showed that the synthesis of rapidly moving proteins and their transport were separate processes. A low concentration of colchicine inhibited the transport when it was present in the medium surrounding the ganglia, but had no effect even at a higher concentration, when it was added to the nerve compartment. The presence of vinblastine at a low concentration in either of the two compartments completely arrested the protein transport. Likewise N-ethylmaleimide or p-chloromercuribenzene sulphonic acid in the nerve medium effectively blocked the fast transport. Results from experiments performed to test the possibility of disto-proximal flow and of transfer of proteins from the muscle to the nerve are discussed.     

CILIA AND VESICULAR PARTICLES IN THE ENDOCRINE PANCREAS OF THE MONGOLIAN GERBIL

Though the general appearance and the cellular composition of the pancreatic islets of the Mongolian gerbil (Meriones unguiculatus) conformed to those of most other rodent species, some peculiar ultrastructural details were found. Thus there were diversiform, mainly vesicular particles with varying electron opacity in these islets. The vesicular particles showed a clear association to cilia which seemed to possess a basic fiber pattern of 9 + 0. The basal bodies were localized in the cytoplasm of the islet parenchymal cells, most often in the β-cells, and the vesicular particles occurred in the portions of cilia that were protruding into intercellular spaces. The cilia were often swollen, and the vesicular particles were mainly found in the space between the ciliary membranes and the longitudinal fibers. A few vesicular particles could be seen inside and sometimes seemingly in contact with these fibers. Occasionally, there were morphologically similar structures in the cytoplasm of adjacent β-cells. The vesicular particles were differentiated from the vesicles occurring in nerve structures by their larger size, as well as by their heterogeneous shape and electron opacity. The nature of the vesicular particles and the significance of their presence in cilia and in the cytoplasm of some of the islet cells remain unknown. Among other possibilities, it is, however, suggested that the vesicular particles may represent secretory material.     

THE STRUCTURE AND FORMATION OF CILIA AND FILAMENTS IN RUMEN PROTOZOA

The large oligotrich rumen protozoa Diplodinium ecaudatum and Ophryoscolex caudatus have been studied by electron microscopy during interphase and division. The structure of mature cilia is contrasted with that seen during their formation particularly in a tuft where development lags and is arrested. Here the shaft is only a few micra long and is composed of filaments that have circular cross-sections not in the typical circular arrangement. In their diameter and appearance the filaments are similar to filaments associated with the nuclei during division. The macronucleus has within it randomly directed filaments, while the micronucleus contains well aligned filaments and other arrangements typical of an intranuclear mitotic process. An extranuclear filament system is also present and is elaborated during division. The infraciliary filament system is particularly elaborate in these organisms. Filaments ranging from 14 to 22 mµ have been observed with some tendency for a bimodal distribution in diameters of 15 and 21 mµ. Formation of such filaments has been observed and consists of an initial orientation of very fine elements followed by filament formation. The observations are discussed in relation to filament involvements in cell movements. The concepts are discussed that filaments are metastable structures and that the transitions from one state to another are functionally significant.     

LOCALIZATION OF PERMEABILITY BARRIERS IN THE FROG SKIN EPITHELIUM

Ruthenium red and colloidal lanthanum were used to determine the site of the structural barriers to diffusion within the intercellular spaces of frog skin epithelium. Electron micrographs show that occluding zonules located at the outer border of the stratum corneum and at the outer layer of the stratum granulosum are true tight junctions since they are impermeable to these tracers. Measurement of ¹⁴⁰La uptake by the living skin shows that lanthanum moves across the external surface of the skin readily, into and out of a compartment that has a limited capacity and is bounded on its internal side by a barrier impermeable to lanthanum. Examination of these skins with the electron microscope suggests that the compartment is localized between the external membrane of the cells at the outer layer of the s. granulosum and at the outermost surface of the skin. These observations and other findings described in the literature indicate that the site of the external high resistance barrier of the frog skin is localized at the outer border of the s. granulosum.