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A stochastic afterhyperpolarization model of repetitive activity in vestibular afferents (1986)

Smith, C. E. ; Goldberg, J. M.

Springer

Biological cybernetics 54 (1986), S. 41-51

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ISSN: 1432-0770

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Computer Science , Physics

Notes: Abstract A stochastic version of Kernell's (1968, 1972) model with cumulative afterhyperpolarization (AHP) was simulated. A characteristic of the model is that the AHP is the result of an increased potassium conductance (g K) that is time-dependent but not voltage-dependent. Quantal synaptic inputs are assumed to be the only source of interspike interval variability. The model reproduces many features of the steady-state discharge of peripheral vestibular afferents, provided that firing rates are higher than 40 spikes/s. Among the results accounted for are the interspike interval statistics occurring during natural stimulation, their alteration by externally applied galvanic currents and the increase in the interspike interval following an interposed shock. Empirical studies show that some vestibular afferents have a regular spacing of action potentials, others an irregular spacing (Goldberg and Fernández 1971b; Fernández and Goldberg 1976). Irregularly discharging afferents have a higher sensitivity to externally applied galvanic currents than do regular afferents (Goldberg et al. 1984). To explain the relation between galvanic sensitivity and discharge regularity requires the assumption that neurons differ in both their synaptic noise (σv) and the slopes of their postspike voltage trajectories (dμ v/dt). The more irregular the neuron's discharge at a given firing frequency, the greater is σv and the smaller is dμ v/dt. Of the two factors, dμ v/dt is estimated to be four times more influential in determining discharge regularity across the afferent population. The shortcomings of the model are considered, as are possible remedies. Our conclusions are compared to previous discussions of mechanisms responsible for differences in the discharge regularity of vestibular afferents.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00337114

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Characterization of a host response to the myxosporean parasite, Ceratomyxa shasta (Noble), by histology, scanning electron microscopy and immunological techniques (1989)

BARTHOLOMEW, J. L. ; SMITH, C. E. ; ROHOVEC, J. S. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of fish diseases 12 (1989), S. 0

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ISSN: 1365-2761

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: Abstract. The tissue response of Salmo gairdneri Richardson, against the myxosporean parasite. Ceratomyxa shasta (Noble), was investigated using histological techniques, scanning electron microscopy and immunological methods. The progress of infection in C. shasta-susceptible and resistant steelhead and rainbow trout was examined by standard histological techniques and by indirect fluorescent antibody methods using monoclonal antibodies directed against C. shasta antigens. Trophozoite stages were first observed in the posterior intestine and there was indication that resistance was due to the inability of the parasite to penetrate this tissue rather than to an inflammatory response. Examination of a severely infected intestine by scanning electron microscopy showed extensive destruction of the mucosal folds of the posterior intestine. Western blotting and indirect fluorescent antibody techniques were used to investigate the immunological component of the host response. No antibodies specific for C. shasta were detected by either method.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2761.1989.tb00561.x

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Hepatocellular carcinoma and fatty infiltration in the Atlantic tomcod, Microgadus tomcod (Walbaum) (1989)

CORMIER, S. M. ; RACINE, R. N. ; SMITH, C. E. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of fish diseases 12 (1989), S. 0

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ISSN: 1365-2761

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: Abstract. The livers of Atlantic tomcod, Microgadus tomcod (Walbaum), from the Hudson and Pawcatuck Rivers were evaluated histologically and described using paraffin and plastic sections. Fatty infiltration, basophilic foci, areas of cellular alteration and hepatocellular carcinoma were widespread in Hudson River samples. In fact, no truly normal tissues were found. Pawcatuck samples had variable levels of lipid and a low prevalence of other alterations. Evaluation of the histological evidence suggests that hepatocellular carcinoma in Hudson River tomcod results from multiple DNA lesions and that areas of cellular alteration give rise to the larger, more invasive form of hepatocellular carcinoma. Glutaraldehyde and OsO4 fixed livers were used to determine differences in cell types and lipid levels. Pawcatuck samples possessed hepatocytes and dark cells forming the parenchymal tissue, whereas Hudson samples lacked dark cells. Hepatic lipid levels were significantly higher in Hudson River fish than in Pawcatuck fish, 36·3 and 11·0% respectively. The elevated hepatic lipid levels in Hudson River tomcod may represent a metabolic response to detoxification.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2761.1989.tb00282.x

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Studies on the β-crystalline form of isotactic polypropylene (1986)

Jacoby, P. ; Bersted, B. H. ; Kissel, W. J. ; [et al.]

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 24 (1986), S. 461-491

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ISSN: 0887-6266

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: A study has been made of the mechanical, thermal, and morpholigical characteristics of melt-crystallized isotactic polypropylene containing high levels of the β or pseudohexagonal crystalline form. Different levels of β-form crystallinity were produced in the polymer by blending in low levels of quinacridone dye nucleating agent. Microscopical studies of the crystallization process revealed that both α-form (monoclinic), and β-form spherulites nucleated on the dye particles, with α-spherulite growth commencing at a higher temperature. These observations were able to qualitatively explain the dependence of β-form level on both the nucleant concentration and its state of dispersion in the polymer. Improving the dispersion of the nucleant was found to reduce the level of β-form crystallinity if the nucleant concentration exceeded an optimum level. A new procedure for quantifying the volume fraction of β spherulites in a sample was developed which utilized the technique of selective solvent extraction. From volume-fraction, x-ray, and density data, the pure α and β crystal densities were obtained. Dynamic mechanical measurements-obtained on unoriented specimens containing varying levels of β-form crystallinity showed an increase in the magnitude of the damping in the post-Tg region with increasing β content. High levels of the β form lead to lower values of the modulus and yield stress, and higher values of the elongation at break and impact strength.

Additional Material: 22 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/polb.1986.090240301

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