Rhythmic activity evoked by adequate stimulation in the fish retina

The distribution of evoked rhythmic responses on the surface and in the depths of the retina of the carp (Cyprinus carpio) and tench (Tinca tinca) and the dependence of the amplitude — frequency characteristics of the response on stimulus intensity and duration were investigated by recording the local electroretinogram and unit activity of the ganglion cells. Rhythmic on- and off-responses to light differed in various characteristics, including their distribution between the cellular and synaptic layers of the retina. The frequency, amplitude, and number of waves in the response were found to depend on the parameters of the stimulus. On-, off-, and on — off-ganglion cells were represented in the records. Their spike discharge usually corresponded to a phase angle of the negative half-wave of the rhythmic response of close to /2. The results of experiments in which conduction along the optic nerve was blocked by cold showed that the system of generation of the rhythmic response in the retina is under the tonic influence of the centers.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 61–68, January–February, 1977.     

"Instantaneous" growth rates of fish scales and their use in studies of fish populations

A technique has been devised for measuring the incorporation of ¹⁴C-glycine into fish scales. This provides an indication of the rate of growth of the scale at the time of sampling. The growth of fish scales is classically considered to be related to the growth of the whole fish' hence the method devised has been used to investigate aspects of fish growth in a number of environmental situations.     

Rhythmic mycelial growth in Podospora anserina

Summary Treatment of mycelial fragments with EMS and NMU yielded 15 revertants of the pleiotropic mutant zonata of Podospora anserina. Analysis by biological, biochemical and genetical methods has revealed that the reversions are caused by back mutation within the zonata locus. This leads to the conclusion that a point mutation causes the morphological and biochemical alterations in this mutant.A working hypothesis for the primary action of this gene and its significance for the elucidation of morphogenesis and of pleiotropism are discussed.With support of the Deutsche Forschungsgemeinschaft, Bad Godesberg (Germany).     

Rhythmic autocrine activity in cultured insect epidermal cells

It is now well established that ecdysteroids can be produced in insects in the absence of prothoracic glands. In this respect, it has been shown that cells in culture can produce ecdysteroids. Our aims were: (1) to determine whether ecdysteroid target cells of epidermal origin could also be the source of ecdysteroids; (2) to monitor more accurately the kinetics of ecdysteroid production; and (3) to check for possible relationships between this synthetic activity and dynamics of cell division. An insect cell line (IAL-PID2) established from imaginal discs of the Indian meal moth, Plodia interpunctella, with wild-type sensitivity to ecdysteroids was used in our study. Our results showed that the Plodia cell line exhibited autocrine activity. When division of IAL-PID2 cells was synchronized, a rhythmic production of ecdysteroids was observed. However, further experiments indicated that this rhythmicity could be cell autonomous. This led us to anticipate the existence of two cell subpopulations that would be able to produce ecdysteroids rhythmically, a minor one that would be cell cycle serum-independent population, and a major population that would need serum growth factors to proliferate and produce ecdysteroids. Qualitative study of the ecdysteroid content of the media clearly showed that ecdysone was the major immunoreactive product. Taken together, our findings clearly show that an insect cell line of epidermal origin is capable of rhythmic autocrine production of ecdysteroids. These results support the hypothesis that alternate sites for ecdysteroid production in vivo may exist and could play a role in local regulation of development. We now plan to determine the cellular basis of this rhythmic autocrine activity and to confirm the existence of growth factor-autonomous cells in the culture as well as the potent role played by ecdysteroids in the cross-talk between various cell subpopulations.     

Cytoskeletal organization and collagen orientation in the fish scales

Summary Immunofluorescence and electron microscopy were used to analyze the relationships between the organization of collagen fibrils in elasmoid scales, and the orientation of microtubules and actin microfilaments in the scleroblasts producing this collagenous stroma. Attention was focused on the basal plate of the scales because of the highly ordered three-dimensional arrangement of the collagen fibrils in superimposed plies forming an acellular plywood-like structure. The collagen fibrils are synthesized by the scleroblasts forming a monolayered pseudo-epithelium, the hyposquama, at the lowest surface of the scale. Fully developed scales with a low collagen deposition rate were compared with regenerating scales active in fibrillogenesis. When an ordered array of the collagen fibrils is found, the innermost collagen fibrils are coaligned with microtubules and actin microfilaments. Thus, because of this coalignment, microtubules and actin microfilaments of the hyposquamal scleroblasts are subjected to consecutive alterations during the formation of the plies of the basal plate. The sequence of events when the collagen fibrils change their direction from one ply to the other in the basal plate is deduced from immunofluorescence and phase-contrast-microscopic observations. During the formation of the orthogonal plywood-like structure in the regenerating scales, first microtubules may change their curse with a rotating angle of about 90°; then, actin microfilaments are disorganized and reorganized by interacting mechanically with the microtubules with which they are coaligned. Collagen fibrils are synthesized in a direction that is roughly perpendicular to that of the preceding ply. The unknown signals inducing the change in direction of the cytoskeleton may be transmitted throughout the hyposquama via gap junctions.This work is dedicated to the memory of Jacques Escaig     

Rhythmic metrazol activity and cortical spreading depression

The incidence of segments of rhythmic metrazol activity (RMA) in cortical leads and in the thalamus and hippocampus was studied in acute experiments on nine male albino laboratory rats. First of all we studied activity after administering metrazol in an i.p. dose of 50 mg/kg, without any further treatment, and then, after a control recording, we induced cortical spreading depression and observed its effect on the incidence and synchronization of RMA in the individual leads. We came to the conclusion that the thalamus is incapable of isolated production of RMA. The cortex is able to produce RMA without participation by the studied structures of the specific thalamus and hippocampus; RMA probably originates in the cortex itself. Generalization is impaired, but not eliminated, by a cortical block. The hippocampus independently produces another type of rhythmic activity.     

Long-term demographics of a coral-reef fish: growth,survival and abundance at several spatial scales

Coral Reefs - In marine organisms, pelagic larval dispersal often results in genetic panmixis among widely separated populations; however, local conditions may produce populations of marine...     

Studies on formation and resorption of fish scales

Summary Scale formation in Cyprinodon variegatus was found to be initiated at about 26 to 30 days after hatching. Ultrastructural investigation revealed that within 4 to 6 h in the first-formed scales the marginal cells begin to flatten and differentiate into osteogenic cells, which later change to osteoblasts and fibroblasts. These cells are separated from the surrounding epithelial cells by a basal lamina. The osteoid is formed by the marginal and osteogenic cells; the osseous layer by the osteoblasts; and the fibrillary plate by the fibroblasts.The osteoid is formed within 2 to 3 h after the initiation of the scale, and within 20 to 24 h the osseous layer is formed. Hydroxyapatite crystals are deposited in the matrix of the osseous layer without apparent association with collagen fibers. No matrix vesicles or dense bodies are evident at the sites of calcification. The fibrillary plate arises 18 to 20 h after the initiation of the scale. It is also partially calcified, but not before the third week of scale formation. The crystals develop almost exclusively between the collagen fibers at the extreme edge of the calcifying front, but solid calcification of the fibers results with further growth of the crystals. The fibroblasts appear to participate in calcification of the fibrillary plate.Contribution No. 332, Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, South Carolina, 29208, USA     

A method for assessing factors influencing'false check'formation in fish scales

Scales are widely used to determine both the growth rates and the age of fish. Their use in this method of scale reading is however complicated by the occurrence of false checks. It has been difficult to investigate the particular environmental factors that normally cause these interruptions in growth because it usually takes many weeks before a check can be detected and the growing scale is a complex system. A technique has therefore been devised in which a scale is isolated from the fish and used to measure its metabolism of radioactive glycine. This gives a measure of protein synthesis which correlates well with the normal growth of the scale and of the whole fish. It is, however, a measurement of the'instantaneous growth rate'of the fish instead of one compounded over a long period of time and it thus opens up the possibility of investigating specific environmental factors that might cause changes in growth. The effects of handling, low oxygen levels, starvation, light and temperature changes have been studied by this technique. It has been shown that handling has the most marked effect but that oxygen levels and starvation also have direct effects that could induce false checks.