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Biomedical subjects

R S Wilkinson

Publications and source records attributed to R S Wilkinson.

29 records · Page 2Linked to original sources
PubMed1979

Mixed lymphocyte reactions in serum-free medium.

Tissue culture medium supplemented with bovine serum albumin (BSA), rather than human serum, was found capable of supporting the proliferative response of cryopreserved human lymphocytes to allogeneic cells in a one-way mixed lymphocyte culture. Although total tritiated thymidine uptake was lower in BSA supplemented cultures than in serum supplemented cultures, stimulation indices were equivalent. Using 0.5% (w/v) BSA, peak tritiated thymidine uptake was observed on day 5 using 2 X 10(5) responders and 4X 10(5) stimulators per microtitre well. Calf skin gelatin was also found capable of substituting for serum, but gave lower levels of proliferation. Use of BSA offers distinct advantages for investigating the proliferative responses of human lymphocytes in serum-free media.

B-Lymphocytes↗
PubMed1978

Ionic basis of the receptor potential in primary endings of mammalian muscle spindles.

The effect of changing the ionic composition of bathing fluid on the receptor potential of primary endings has been examined in isolated mammalian spindles whose capsule was removed in the sensory region. After impulse activity is blocked by tetrodotoxin, ramp-and-hold stretch evokes a characteristic pattern of potential change consisting of a greater dynamic depolarization during the ramp phase and a smaller static depolarization during the hold phase. After a high-velocity ramp there is a transient post-dynamic undershoot to below the static level. On release from hold stretch, the potential shows a postrelease undershoot relative to base line. The depolarization produced by stretch is rapidly decreased by the removal of Na+ and Ca2+. Addition of normal Ca2+ partly restores the response. Stretch appears to increase the conductance to Na+ and Ca2+ in the sensory terminals. The postdynamic undershoot is diminished by raising external K+ and blocked by tetraethylammonium (TEA). It apparently results from a voltage-dependent potassium conductance. The postrelease undershoot is decreased by raising external K+, but is not blocked by TEA. It is presumably caused by a relative increase in potassium conductance on release. Substitution of isethionate for Cl- or the addition of ouabain does not alter the postdynamic and postrelease undershoots.

Action Potentials↗
PubMed1977

Responses of isolated Golgi tendon organs of the cat.

1. The responses to stretch have been studied in living, isolated Golgi tendon organs (GTOs) from tail muscles of cat. Experiments were performed in vitro and consisted of subjecting single GTOs to controlled ramp-and-hold stretch while recording the response from their sensory axons raised in oil. 2. The threshold force required for sustained afferent discharge was measured directly, and found to be between 8 and 170 dynes at 24 degrees C for nine GTOs tested. Beyond threshold, the discharge frequency is approximately proportional to applied static tension over a wide range. Sensitivy to tension varies among different GTOs and appears to be inversely correlated with mechanical stiffness. 3. With impulse activity blocked by tetrodotoxin, graded receptor potentials could be recorded whose amplitude varied in proportion to applied static tension. All GTOs examined showed in addition a dynamic response, which became larger with increasing velocity of ramp stretch. This dynamic sensitivity appears in the receptor potential and is then augmentd by an apparent accommodative process at the impulse initiating site. 4. Based on the above findings, possible mechanical models are discussed for the sensory transduction mechanism.

Action Potentials↗
PubMed1967

Public safety.

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Accident Prevention↗
PubMedDate not supplied

Multiple innervation of tonic endplates revealed by activity-dependent uptake of fluorescent probes.

During development of the vertebrate nervous system, there is a widespread reduction in the number of axons innervating target cells. This phenomenon, often called synapse elimination, has been particularly well studied at the neuromuscular junction of developing twitch muscle fibres: following a period of polyneuronal innervation, axonal branches are retracted, usually leaving each twitch fibre endplate innervated by only one axon. Here we describe a new technique for the study of synapse elimination--activity-mediated uptake of fluorescent probes. These probes selectively and supravitally label all the terminals of individual axons. The technique is used here in adult and embryonic snakes to study the innervation pattern of a thin muscle containing two fibre types: twitch fibres, which are fast-contracting and have propagated action potentials, and tonic fibres, which are slow-contracting and lack action potentials. We find that twitch muscle fibres, as expected, eliminate all polyneuronal innervation during development; in contrast, tonic fibre endplates remain polyneuronally innervated into adulthood. The persistence of multiple innervation at tonic endplates may be related to the lack of action potential activity in tonic muscle fibres.

Action Potentials↗