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Biomedical subjects

K Fraser

Publications and source records attributed to K Fraser.

At least 37 records · Page 2Linked to original sources
PubMed1991

Photoinactivation of the crayfish segmental giant neuron reveals a direct giant-fiber to fast-flexor connection with a chemical component.

The escape tail flip of the crayfish is "commanded" by 2 sets of giant-fiber (GF) interneurons. In each hemisegment, these drive the motor giant (MoG) abdominal flexor motor-neuron through a monosynaptic electrical connection, but the remaining 8 or 9 fast-flexor (FF) motorneurons receive most of their input via a disynaptic electrical pathway through the segmental giant (SG) neuron. We have investigated a monosynaptic GF-FF pathway, which operates in parallel to the disynaptic GF-SG-FF pathway, by using dye-mediated photoinactivation to remove the SGs from the tail-flip circuit. SG photoinactivation involves an initial broadening of the spike, leading to a long-duration, massively depolarized plateau. This is followed by loss of spike capability, a gradual reduction in the resting potential, and eventual total loss of electrical responsiveness. After bilateral photoinactivation of the SGs, a spike in one set of GFs, the medial giants (MGs), produces little if any effect in FFs in any ganglion. A spike in the other set, the lateral giants (LGs), produces an EPSP in FFs with a declining anterior-to-posterior segmental gradient in amplitude. These differences in LG and MG outputs, which are obscured in the intact circuit by the common MG/LG-SG-FF pathway, give clues to a probable early evolutionary form of the circuit. The LG-FF connection in anterior ganglia has a significant electrical component. However, it also has an apparent monosynaptic chemical component, as revealed by the response to saline containing cadmium ions, and to cooling the preparation. This is the first physiological evidence for chemical output from a crayfish GF.

Animals↗
PubMed1987

The structure and cloning of orf virus DNA.

A map of cleavage sites for the restriction endonucleases EcoRI, HindIII, BamHI, HpaI, and KpnI for a New Zealand strain of orf virus (NZ2) DNA has been deduced. Also, the entire genome, apart from approximately 0.1 kbp at each end, has been cloned into various vectors. The genome is 139 kbp in length and, in common with other poxviruses, has inverted terminal repetitions and crosslinked ends.

Cloning, Molecular↗
PubMed1987

Conservation and variation in orf virus genomes.

The genomes of several orf virus strains were analyzed with the restriction endonucleases EcoRI, HindIII, BamHI, and KpnI, and cleavage site maps were deduced. In general, the right half of the genome showed conservation of restriction sites compared with the left half. Variations in size of up to 0.5 kbp were found within an inverted terminal repetition, and a 1-kbp deletion was detected in some strains in a subterminal fragment at the left end. A region of approximately 20 kbp, some 12 kbp in from the left end, showed the greatest cleavage site variability although there was no evidence of large deletions in this region. A 1.55-kbp cloned DNA fragment from the internal variable region of NZ2 failed to hybridize to the DNA from three other strains. A fragment in the variable region of strain NZ7 was cloned and compared by hybridization and restriction endonuclease analysis with cloned NZ2 fragments from the same region. The region of nonhomology extended for at least 2.75 kbp. It is suggested that this internal variable region may provide sites for the insertion of foreign genes.

Animals↗
PubMed1986

The significance of the adrenergic nerves in the etiology of vesicoureteral reflux.

We studied 40 puppies serially from birth to 6 months of age for the presence of vesicoureteral reflux. Of these dogs 36 underwent biopsy of the bladder dome and trigone in search of adrenergic fibers that could be identified by catecholamine fluorescence. The results show that the incidence of vesicoureteral reflux decreased dramatically as adrenergic fibers began to appear. This inverse relationship between reflux and adrenergic bladder fibers seems to suggest a cause-and-effect relationship.

Adrenergic Fibers↗
PubMed1985

Ultrastructure of the segmental giant neuron of crayfish.

The ultrastructure of the crayfish segmental giant (SG) neuron is described, and compared to other identified and unidentified crayfish neurons. The SG was specifically stained by intracellular injection of horseradish peroxidase and is divided into four regions of interest. In the dorsal region, finger-like dendrites of the SG make contact with the through-conducting giant fibres (GF). These contacts are physiologically defined rectifying electrical synapses. They are characterized by the presence of 30-95 nm agranular vesicles in the presynaptic GFs, some postsynaptic density in the SG, and a narrowing of the intermembrane cleft to approximately 5 nm. There is little evidence for connecting cytoplasmic bridges. Unidentified neurons make chemical input with either round or elliptical vesicle types onto SG bottlenecks close to the electrical synapses. Ventral to the GFs, dendritic profiles of the SG make three sorts of contact with unidentified neurons. (a) Regions of close membrane apposition (approximately 5 nm) are presumed to be electrical output synapses, but there are no vesicles such as at the input synapses, and, again, little sign of connecting bridges. (b) Chemical input is received from unidentified presynaptic neurons containing either round or elliptical vesicles. These synapses are characterized by 30-75 nm presynaptic agranular vesicles, widened cleft (approximately 20 nm), granular cleft material and postsynaptic density. There is no sign of any presynaptic density. (c) Very occasional SG profiles containing vesicles and making output synapses to unidentified neurons occur. In the lateral neuropil at the edge of the ganglion the SG gives rise to a small tuft of very fine dendrites. These are nearly all laden with vesicles and ramify in a complex region of neuropil containing many small profiles which are also vesicle-laden. The SG axon diminishes in diameter as it progresses along its peripheral nerve root, and finally terminates at a blind ending near the base of the swimmerets. It is sheathed along its entire length, and there is no sign of vesicles within it. We conclude that the SG axon makes no peripheral output.

Abdomen↗
PubMed1978

A bladder tumor model response to immunotherapy.

The author presented results of BCG and Corynebacterium parvum treatment of the transplantable mouse FANFT bladder tumor carried in the host's leg. A comparison was made of the results of treatment with BCG alone and C. parvum alone or either used in conjunction with Cytoxan upon effectiveness in increasing animal survival and retarding tumor growth.

Animals↗
PubMed1977

Second closed mitral valvotomy for recurrent mitral stenosis.

Sixty-seven patients undergoing a second closed mitral valvotomy between 1957 and 1974 have been reviewed. Since 1951, 510 patients have had a primary closed valvotomy in the same unit. The incidence of restenosis severe enough to warrant further surgery is higher after a finger fracture procedure (40%) than after a Tubbs dilator valvotomy (9.2%). There is an operative mortality of 10.4%, and a further late mortality of 23.8% after a second closed valvotomy. Of the surviving patients, 70.5% have had a good or excellent result. The group with poor results is characterised by the presence of a calcified fixed valve, making valvotomy difficult and incomplete. In the presence of a non-calcified valve, a second valvotomy still has a place when surgery for restenosis is required.

Follow-Up Studies↗
PubMed1976

Closed mitral valvotomy.

The results of closed mitral valvotomy operations in 359 patients operated on from August 1957 to October 1974 were assessed at July 1975. About 60% of the patients were in good health. These results suggest that there is still a place for closed mitral valvotomy in carefully selected cases.

Follow-Up Studies↗