Modulation of Hydra attenuata rhythmic activity: phase response curve.

We investigated the effect of photic stimulation on the frequency of Hydra attenuata column contractions. We used positive or negative abrupt light transitions, single or repetitive light or darkness pulses, and alternation of light and darkness periods. The main results are: (a) The frequency of the contraction pulse trains (CPTs) varies transiently in response to an abrupt variation of the light intensity. (b) CPTs in progress can be inhibited by different types of photic stimuli. (c) The response time to a single photic stimulus varies during the inter-CPT interval and depends also on the polarity of the stimulus. (d) The CPTs are entrainable with repetitive light stimulation of various frequencies. (e) Long-lasting variations of the frequency of CPTs occur after the end of a repetitive light stimulation. We suggest that the mechanism responsible for the rhythym of column contractions is quite similar to that on which other biological rhythmic phenomena are based.     

The morphology, physiology, and neural projections of supernumerary compound eyes in Drosophila melanogaster

Supernumerary compound eyes in Drosophila melanogaster produced by the extra eye (ee) mutation were analyzed with regard to their morphology, physiology, and neural projections. Electron and light microscopy revealed that large extra eyes often possess the normal complement of compound-eye cell types and that these cells usually have standard fine structure. In addition, the array of photoreceptor cell rhabdomeres within individual supernumerary ommatidia is standardly trapezoidal, and ommatidial subpopulations having mirror-image configurations of their rhabdomeric trapezoids are separated by an equator in extra eyes. Light stimulation of supernumerary eyes can elicit photoreceptor depolarization potentials as evidenced by electroretinographic recordings from them. In addition, extra-eye photoreceptor cells have a functional pupillary response to light stimulation. Although the supernumerary eyes can be functionally and anatomically standard, examination of serial, silver-stained sections of extra-eye heads has shown that their photoreceptor axons seldom innervate the brain. This situation obtains even in a case in which the normal, ipsilateral compound eye was removed by the eyeless mutation. In contrast, rare supernumerary antennae occasionally found in ee stocks have receptor cells whose axons innervate ventral brain. In addition to duplications of cuticular epithelia, extra glial cells, muscle fibers, and ocellar interneurons are sometimes found in extra-eye bearing flies. Discussion of these results focuses on a polarity guidance hypothesis which models the growth of adult photoreceptor axons into the brain during normal development.     

Changes in volume of the rhabdom in the compound eye of Aedes aegypti L.

The volume of the rhabdom in compound eyes of mosquitoes decreases upon illumination. This decrease is probably mediated by a bleaching of the visual pigment, since blue light is most effective in producing the change and red light is least effective. The reduction in rhabdom volume appears to be a result of rhabdomal membrane loss to coated vesicles and multivesicular bodies. These organelles were seen most frequently in blue adapted eyes, markedly less frequently in red adapted eyes, and only rarely in dark adapted eyes.     

Reversible ultrastructural changes in the rhabdom of the locust eye are induced by long term light deprivation

Summary Quantitative electron microscopic analysis of the compound eyes of locusts (Schistocerca gregaria) subjected to long term light deprivation showed that disorganization of rhabdomal microvillus structure and disruption of rhabdomere fusion were significantly more prevalent in deprived animals than in controls. These structural changes accompanied a reduction in sensitivity to photic stimulation in the deprived eyes. The disorganization of microvillus structure was reversible after 14 days recovery in light while the disruption of rhabdomere fusion was irreversible. Deprivation also resulted in an irreversible increase in number of ommatidia bearing fewer than normal retinula cells. These results are consistent with disruption by light deprivation of some aspect of normal photoreceptor membrane synthesis or degradation.We thank Ms. Irene Kwan for her excellent technical assistance, Dr. H. Silverman for useful discussions through all stages of this study, and Drs. H. Injeyan and S. Tobe for supplying the hatchling locusts. This work was supported by Ontario Graduate Fellowships to J.W.B. and a National Research Council of Canada operating grant to H.L.A.     

Structure of eyes in trombidioid mites (Acariformes: Trombidioidea)

The eyes or ocelli of trombidioid mite larvae of Euschoengastia rotundata, Hirszutiella zachvatkini and Camerotrombidium pexatum, and larvae and adults of Platytrombidium fasciatum were studied by means of transmission electron microscopy. These species together with larvae of Odontacarus efferus, Ericotrombidium hasgelum, Walchia chinensis and adult E. rotundata and H. zachvatkini were also studied under scanning electron microscope. The eyes of larvae are not inverted and characterized by an epicuticular lamellar lens. The group of phoreceptor cells with rhabdomeres arranged typically of Chelicerata is underlaid by a pigment cup. The eyes of adult mites are inverted, perikarions of photoreceptor cells are situated between the lens and rhabdomeres; tapetum occupies the space between the pigment cup and rhabdomeres. Sensitivity of eyes to light is similar to that of primary eyes of spiders dwelling on soil surface.     

Development of woronin bodies from microbodies inFusarium oxysporum f. sp.lycopersici

Summary Woronin bodies are cytoplasmic organelles which commonly lie near the septa in ascomycetous fungi. Although these organelles were observed nearly 100 years ago, little is known about their origin and development. The present ultrastructural investigation describes the ontogeny of Woronin bodies inFusarium oxysporum f. sp.lycopersici [Sacc.] Snyd. and Hans. In this fungus, Woronin bodies are produced by microbodies. Development of the Woronin body begins with the appearance of electron dense material within the microbody. This material aggregates adjacent to the membrane of the microbody and condenses into a single paracrystalline inclusion. Following its formation, the inclusion is gradually extruded and is eventually separated from the parent organelle by an exocytotic mechanism. After the separation, the paracrystalline inclusion is found at the septal pore. Although many recent electron microscopic studies have used various terms to designate these membrane bound organelles, inFusarium these inclusions are believed to correspond to the Woronin bodies initially described by light microscopists.     

Freeze-fracture study of the Drosophila photoreceptor membrane: mutations affecting membrane particle density

The photoreceptor membrane of Drosophila melanogaster (wild type, vitamin A-deprived wild type, and the mutants ninaAP228, ninaBP315, and oraJK84) was studied by freeze-fracture electron microscopy. The three mutations caused a decrease in the number of particles on the protoplasmic face of the rhabdomeric membrane. The ninaAP228 mutation affected only the peripheral photoreceptors (R1-6), while the ninaBP315 mutation affected both the peripheral (R1-6) and the central photoreceptors (R7). The oraJK84 mutation, which essentially eliminates R1-6 rhabdomeres, was found to drastically deplete the membrane particles in the vestigial R1-6 rhabdomeres but not in the normal rhabdomeres of R7 photoreceptors, suggesting that the failure of the oraJK84 mutant to form normal R1-6 rhabdomeres may be due to a defect in a major R1-6 photoreceptor-specific protein in the mutant. In all cases in which both the rhabdomeric particle density and rhodopsin content were studied, the mutations or vitamin A deprivation was found to reduce both these quantities, supporting the idea that at least the majority of the rhabdomeric membrane particles are closely associated with rhodopsin. Vitamin A deprivation and the mutations also reduced the number of particles in the plasma membrane as in the rhabdomeric membrane, suggesting that both classes of membrane contain rhodopsin.     

Assembly of rhabdomeric membrane from smooth endoplasmic reticulum can be activated by light in chromophore-deprived photoreceptors of Manduca sexta

Summary Deficiency of the photopigment chromophore, resulting from carotenoid/retinoid (vitamin A) deprivation, that severely impairs the visual function of Manduca sexta also leads to the hypertrophy of smooth endoplasmic reticulum in the photoreceptors. The excess endomembrane accumulates in the stacked cisternae of myeloid bodies. Although 11-cis retinal promotes substantial recovery of function in the retinas of deprived moths maintained in darkness, the myeloid bodies remain. When such recovering photoreceptors were exposed to light of moderate intensities, the amount of endomembrane diminished to normal levels over a period of several hours, while rhabdomeres grew larger. Since there was no endocytolysis, the myeloid bodies must have provided the membrane for rhabdomere enlargement. Bright light similarly mobilized the myeloid bodies in deprived receptors. Thus the persistence of myeloid bodies in moderately illuminated chromophoredeficient receptors is a consequence of their insensitivity. However, the initial hypertrophy of endomembrane does not appear to result from the lack of adequate stimulation: normal, chromophore-replete photoreceptors maintained in darkness from before the period of retinal development had large rhabdomeres and no myeloid bodies. The development of myeloid bodies during the differentiation of vitamin A-deprived photoreceptors appears to entail an influence of the chromophore at another level of receptor cell function.     

Calcium-induced fusion of proteoliposomes and protein-free liposomes Effect of their phosphatidylethanolamine content on the structure of fused vesicles

The acidic phospholipid cardiolipin was shown to be very efficient in promoting calcium-induced fusion of proteoliposomes. The degree of fusion was dependent on the phosphatidylethanolamine content of the vesicles. Addition of CaCl₂ to proteoliposomes containing phosphatidylcholine and cardiolipin but without phosphatidylethanolamine did not induce fusion. Fusion of cytochrome oxidase vesicles, containing less than 50 mol% phosphatidylethanolamine resulted in monolamellar vesicles with a diameter of about 200 nm. The vesicles could be induced to fuse further by establishing an osmotic pressure across their membranes. When proteoliposomes containing more than 50 mol% phosphatidylethanolamine were fused, large vesicles with a diameter exceeding 1 μm were formed. They appeared in the electron microscope as a mixture of multilamellar and monolamellar vesicles. Fusion of corresponding liposomes resulted in formation of even larger structures appearing as dense multilamellar bodies and paracrystalline honeycomb-like lattices.     

The transmission of impulses in the ectodermal slow conduction system of the sea anemone Calliactis parasitica (Couch).

1. The SS 1 fatigues in response to repetitive electrical stimulation. This fatigue is manifested by an increased conduction delay and a decreased SS 1 pulse amplitude. 2. Continued repetitive stimulation leads to the failure of the system. Recovery may take many seconds. Narrow strips of column fail more rapidly than wide strips. 3. The increased conduction delay is explained in terms of a decrease in the population of spiking cells. 4. A computer model is described and analysed. It suggests that conduction between electrically coupled ectoderm cells could be the basis for the SS1. The SS 1 may have properties not so far experimentally demonstrated; for example, under certain conditions it could behave as a local system.     

Properties of barnacle photoreceptor cells in culture

1. Properties of median photoreceptor cells in cultured ocelli from the giant barnacle (Balanus nubilus) were compared in isolated ocelli, ocelli maintained with the supraesophageal ganglion, and fresh ocelli. 2. Cultured photoreceptor cells exhibited slight deterioration after 2-4 weeks. Cell bodies maintained their structure but apparently lost some dendrites. Electron micrographs revealed fewer rhabdomeres. Axons did not degenerate. 3. Intracellularly recorded responses to light in both cultured preparations were qualitatively normal with a small decrease in sensitivity and increase in input resistance. The waveforms of the light responses were normal. 4. The characteristic shadow reflex was maintained after 6 weeks.     

ECL cell morphology.

Using immunohistochemistry at the conventional light, confocal and electron microscopic levels, we have demonstrated that rat stomach ECL cells store histamine and pancreastatin in granules and secretory vesicles, while histidine decarboxylase occurs in the cytosol. Furthermore the ECL cells display immunoreactivity for vesicular monoamine transporter type 2 (VMAT-2), synaptophysin, synaptotagmin III, vesicle-associated membrane protein-2, cysteine string protein, synaptosomal-associated protein of 25 kDa, syntaxin and Munc-18. Using electron microscopy in combination with stereological methods, we have evidence to suggest the existence of both an exocytotic and a crinophagic pathway in the ECL cells. The process of exocytosis in the ECL cells seems to involve a class of proteins that promote or participate in the fusion between the granule/vesicle membrane and the plasma membrane. The granules take up histamine by VMAT-2 from the cytosol during transport from the Golgi zone to the more peripheral parts of the cells. As a result, they turn into secretory vesicles. As a consequence of stimulation (e.g., by gastrin), the secretory vesicles fuse with the cell membrane to release their contents by exocytosis. The crinophagic pathway was studied in hypergastrinemic rats. In the ECL cells of such animals, the secretory vesicles were found to fuse not only with the cell membrane but also with each other to form vacuoles. Subsequent lysosomal degradation of the vacuoles and their contents resulted in the development of lipofuscin bodies.     

Studies on the transport of secretory granules in the magnocellular hypothalamic neurons of the rat

Intrathecal administration of 20 mug of vincristine sulphate in the rat induced in vivo the formation of paracrystalline inclusions mainly in axonal processes. This is associated with an impairment in the migration of neurosecretory granules as shown by their accumulation in the perikarya of the magnocellular neurons. The granules are intermixed with numerous dense bodies of various shape, sometimes with a fibrillar content, and probably of lysosomal origin. In addition to the impairment of the flow of neurosecretory granules, there is also a striking accumulation of mitochondria and synaptic vesicles, and an apparent proliferation of the smooth endoplasmic reticulum. In the posterior lobe, the axonal endings contain a large number of neurosecretory granules, intermingled with bodies of varying shapes and electron density. Occasionally, a dense membrane surrounding a group of elementary granules is observed, reacting positively for acid phosphatase. This suggests an attempted crinophagia.     

Role of the Age Factor in Eye Regeneration in the Gastropod Achatina fulica

The dependence of the ability to regenerate the eye on the age of experimental animals was studied in the snail Achatina fulica. The degree of regeneration was estimated by light-microscopic and electrophysiological methods and by analyzing the motor response to visual stimuli. In older age groups, the number of regenerated eye-bearing tentacles decreased, whereas the period of regeneration increased. The regenerated eyes of the snails operated at the age of more than two months remained smaller than normal eyes even after six months. Regeneration of the distal part of the optic nerve was observed, and the regenerated eyes recovered the ability to respond to stimulation by light. In the electroretinogram, the responses of the regenerated eye, compared to the control, were characterized by lower amplitude and longer repolarization and refractory periods. Manifestations of the motor response to visual stimuli in the young snails with regenerating eyes could be regarded as evidence for the recovery of connection between the organ of sight and the central ganglia.     

The fine structure of the visual system of Lycosa (Araneae: Lycosidae)

Summary Wolf spiders have four pairs of eyes distributed in three rows. The first row which lie in the frontal region of the caparace, just above the chelicera, contains four eyes: a medial pair known as the anterior medial eyes (AM eyes or principal eyes) and two smaller eyes known as the anterior lateral eyes (AL eyes). The second row which is located also in the frontal region of the prosoma consists of two big eyes. These are the posterior median eyes (PM eyes). The third row contains the posterior lateral eyes (PL eyes) which lie in the flanks of the prosomal caparace. The AL, PM and PL eyes are the so-called secondary eyes.The electron microscope shows that the AM eye photoreceptor cells have the rhabdomere in their distal segment, just behind the vitreous body. The rhabdomere consists of closely packed microvilli about 0.5 long exhibiting a uniform diameter of 500 Å. Each rhabdom consists of two rhabdomeres. The distal segment of the photoreceptor has a prismatic shape with four or five faces depending of their location within the retina.The distribution of the rhabdoms follows two different patterns or organization. In the peripheral portion of the retina they lie oriented either parallel or perpendicular to the retinal radii. In this zone most cells have four sides while in the central region five sided cells are predominant. These cells bear microvilli in three of their five faces and the rhabdoms show no preferential mode of orientation. Each retina contains approximately 450 photoreceptors. In the secondary eyes the rhabdoms lie far from the vitreous body behind the level of the cell nuclei. A light reflecting layer or tapetum is present in the three pairs of secondary eyes. The microvilli forming the rhabdomeres of the AL eyes are 0.5 long and 500 Å wide, while the microvilli of the rhabdomeres in the PM and PL eyes are longer and thicker (1.5 long and 550–660 Å wide). In these eyes the rhabdomeres are surrounded by abundant extracellular material. Like in the principal eyes each rhabdom consists of two rhabdomeres.In the AL eyes the photoreceptor cells send out collateral branches which end, without any specialization, in contact with other photoreceptors. Clear fibers running parallely to the tapetum have been found in the secondary eyes. These fibers show specialized regions corresponding to the zones of contact with the photoreceptor cells. These areas are characterized by an increased density of the membranes and groups of vesicles (the vesicles lie within the fibers).The optic nerves consist of photoreceptor axons, glial cells and a fibrous perineural sheath. The AM and AL eyes are connected to the CNS by a single compact optic nerve while in the PM and PL eyes the optic nerve consists of several individual bundles. The total number of optic fibers entering into the brain is about 12.000.A layer of glial cytoplasm covers each photoreceptor axon and the mesaxons appear as double lines which bifurcate frequently.Research sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under AFOSR Grant Nr. 618-64.     

Retinal structure in Synbranchus marmoratus with observations on two new cone myoid inclusions.

The retina of a South American swamp eel, Synbranchus marmoratus (Synbranchidae), was studied by Golgi impregnation, light and electron microscopy. Its principal features include (1) the presence of a dense matrix, possibly a new type of tapetum lucidum, in the pigment epithelium, (2) a well developed photoreceptor layer containing large rods, single, double and triple cones, and (3) well developped inner nuclear and plexiform layers, with the exception of horizontal cells which are few and relatively small. These and other observations are discussed in relation to the photic environment and habits of this fish. The presence of microfilament bundles and two unusual features, microtubuleladen dense bodies and paracrystalline inclusions, in cone myoids are discussed in terms of their possible involvement in retinomotor responses.     

Localization of visual pigments within rhabdoms of the compound eye of Spodoptera exempta (Insecta,Noctuidae)

Summary In the noctuid moth Spodoptera exempta, the distribution of visual pigments within the fused rhabdoms of the compound eyes was investigated by electron microscopy. Each ommatidium regularly contains eight receptor cells belonging to three morphological types: one distal, six medial, and one basal cell (Meinecke 1981); four different visual pigments — absorption maxima at approximately 355, 465, 515, and 560 nm — are known to occur within the eye (Langer et al. 1979). The compound eyes were illuminated in situ by use of monochromatic light of different wavelengths. This illumination produced a wide scale of structural changes in the microvilli of the rhabdomeres of individual cells. Preparation of eyes by freeze-substitution revealed the structural changes in the rhabdomeres to be effects of light occurring in vivo.The degree of structural changes may be considerably different in rhabdomeres within the same ommatidium; it was found to depend on the wavelength and the duration of illumination, the intensity received by the ommatidia as well as the spectral sensitivity of the receptor cells. Therefore, it was possible to estimate the spectral sensitivities of the morphological types of receptor cells. Generally, all medial cells are green receptors and all basal cells red receptors; distal cells are blue receptors in about two-thirds of the ommatidia, while in the remaining third of them distal cells are sensitive to ultraviolet light.Supported by Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 114 (Bionach)     

Effect of visual deprivation on evoked potentials in the visual cortex and superior colliculus in rabbits

Evoked potentials arising in the visual cortex and superior colliculus to stimulation of the collateral eye by single, paired, and repetitive flashes were recorded in rabbits reared in darkness or in normal illumination. The absence of significant change in the latent period and amplitudes of the first two components of the collicular responses and of the recovery cycle and response to repetitive stimulation in the light-deprived animals suggest that photic stimulation does not affect the normal functional development of the rabbit retinotectal system. However, functional deafferentation in the early postnatal period gives rise to serious disturbances of visual cortical function, as reflected in a marked decrease in amplitude of the primary response, lengthening of the recovery cycle, and narrowing of the range of rhythm-binding frequencies of flashes. These disturbances were reversible. The period of maximal sensitivity of the rabbit retinocortical system to visual deprivation begins at the end of the first month of postnatal life. The possible mechanisms lying at the basis of these functional disturbances in light-deprived animals are discussed.     

Failure of neuromuscular propagation during human maximal voluntary contraction

The mechanism for fatigue of the adductor pollicis was studied in normal subjects during maximal voluntary contractions (MVC) sustained for 90-100 s, by comparing the force and electrical response of this muscle to voluntary motor drive with that obtainable with artificial stimulation of the ulnar nerve. The adequacy of nerve stimulation was checked by recording simultaneously the electrical response of a nonfatiguing muscle, the abductor of the small finger. The decrease in force and in the natural electrical activity with fatigue was accompanied by a parallel decrease in the amplitude of synchronous muscle action potentials (M waves) evoked by artificial stimulation of the ulnar nerve at different frequencies. The decline in M-wave amplitude in the adductor pollicis was not due to a submaximal nerve stimulation, since the amplitudes recorded simultaneously from the nonfatiguing abductor digiti minimi remained unchanged. The force and the electrical responses from the adductor pollicis recovered in parallel with a half time of approximately 1 min. These results suggest that the loss of force of the adductor pollicis with fatigue and its subsequent recovery are largely determined by the extent of neuromuscular propagation failure. The slow recovery of the M-wave amplitude during repetitive stimulation suggests that it may be related to some aspect of muscle metabolism.