Biomedical subjects

C M Hackney

Publications and source records attributed to C M Hackney.

41 records · Page 3Linked to original sources

PubMed1983

Putative sense organs on the pallial tentacles of the limpet, Patella vulgata (L.).

The structure and ultrastructure of ciliary tufts on the pallial tentacles of the limpet Patella vulgata (L.) are described. The tip of each tentacle is covered by a dense crown of tufts and additional tufts can be seen scattered evenly across the surface of each tentacle. The cilia are nonmotile and nerve fibres run from the base of the ciliated cells suggesting a sensory function. Comparisons are made with ciliary tufts found in a Pacific species of limpet, Acmaea scutum, and other molluscan sensory structures.

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PubMed1982

Cobalt mapping of the nervous system: how to avoid artifacts.

Infusion of cobalt ions into cut axons is an established method for tracing neuron projections in the central nervous system. Artifacts, where unintended neurons are stained, however, have been reported, leading to difficulties in interpretation. Experiments in the locust Schistocerca gregaria Forskål show that such artifacts can be induced through damage to axons caused by cutting peripheral nerves and by using high cobalt chloride concentrations (0.4M and above). Mixtures of cobalt and nickel chlorides and nickel chloride alone were introduced into different branches of the same nerve and developed with rubeanic acid to give precipitates of different colors in the two sets of axons. Preparations were examined with the light microscope, where mixing of ions would appear as intermediate colors, and by x-ray probe microanalysis. No evidence for leakage of metal ions from the filled axons or for ion uptake by other axons could be detected, provided that low concentrations of cobalt and nickel chlorides were used and nerve cutting was reduced to a minimum by making preparations in vivo. If extreme conditions are avoided when making the preparation, the risk of producing artifacts is minimized, thus enabling the cobalt method to be used with greater confidence for describing neuronal projections.

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PubMed1981

Distribution of calcium in the suctorian Discophrya collini: an x-ray microanalytical study.

Discophrya collini is a free-living suctorian with tentacles which can be induced to contract by means of a range of experimental stimuli, including the application of CaCl2 and MgCl2 but not BaCl2. X-ray microanalysis of glutaraldehyde-only fixed cells shows Ca to be present in the cytoplasmic ground substance and elongate dense bodies (EDB). In 10(-1) M CaCl2-treated cells, calcium levels remain unchanged except for a three-fold increase in the EDB. Treatment of cells with 10(-1) M MgCl2 and 10(-1) M BaCl2 does not result in their detection in the cell. It is suggested that EDB may act as reservoirs controlling levels of calcium.

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PubMed1981

Tentacle contraction in glycerinated Discophrya collini and the localization of HMM-binding filaments.

The contractile tentacles of the suctorian Discophrya collini contain a central microtubular axoneme as well as filamentous structures in the cortical epiplasm and in a fibrous collar around the axoneme at the tentacle base. The nature and possible roles of these components has been investigated by the use of reactivatable glycerinated cells. In these a mean tentacle contraction to 70% of the original length could be achieved by a 5-min treatment with a reaction mixture containing ATP, calcium and magnesium ions, the same treatment giving retraction to 30% in living cells. Both the microtubules of the axoneme and the filaments of the fibrous collar and epiplasm were present in the glycerinated cells, suggesting that these components consist of large water-insoluble molecules. The addition of heavy meromyosin to whole glycerinated cells resulted in the appearance of 36-50-nm spaced "tails" or filaments attached to the epiplasmic fibres and the aggregation of 3-6-nm filaments and electron-dense material in the region of the fibrous collar. Neither of these 2 features was apparent after treatment with ATP. It is suggested that actin-like filaments are localized in the region of the fibrous collar and in the epiplasm, and that these are involved in tentacle retraction; whilst the microtubules of the axoneme are concerned with feeding, and play only a cytoskeletal role in the contractile mechanism.

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PubMedDate not supplied

Rotated stereociliary bundles and their relationship with the tectorial membrane in the guinea pig cochlea.

Hair cells with rotated stereociliary bundles have been observed in the cochleae of control and kanamycin-treated guinea pigs. The affected outer hair cell bundles have a variable degree of rotation, with some being completely reversed. The inner hair cells are more rarely affected, and only small areas of an individual inner hair cell bundle are abnormal. In counts from ten cochleae, the number of outer hair cells with rotated bundles was most commonly between 10% and 20%, with almost 27% of all outer hair cells affected in the most extreme case. The rotated outer hair cell bundles often have distorted outlines but in other respects closely resemble normal bundles. In particular, they have the usual gradation in stereociliary height, intracellular cross-links and intercellular links to adjacent normally-orientated bundles. There are also corresponding imprints in the tectorial membrane which match the pattern of the stereocilia. In kanamycin-treated guinea pigs, imprints of both normal and rotated hair bundles are present, even when the corresponding bundle is absent, and there are frequently remnants of stereocilia inserted in the imprints. These observations suggest that, apart from their abnormal orientation, the rotated bundles are similar to normal bundles in both their organization and association with the tectorial membrane. The implications of this with respect to transduction and cochlear mechanics are discussed.

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