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Biomedical subjects

R E Baker

Publications and source records attributed to R E Baker.

At least 91 records · Page 5Linked to original sources
PubMed1981

Peripheral reinnervation patterns and dorsal root ganglion topography in skin-grafted frogs: a behavioral and histological examination.

Cutaneous respective fields for the first ventrolateral (VL1) and dorsomedial nerve trunks were mapped out behaviourally in normal and in skin-grafted Discoglossus pictus frogs. Ventrally directed wiping responses were obtained from stimulation of dorsally located belly skin grafts in all experimental animals. These misdirected responses were abolished completely by cutting either the dorsomedial nerve trunk or both the dorsomedial and the VL1 nerve trunks. The topography of cutaneous neurons of the dorsal root ganglion innervating dorsal skin areas was demonstrated by back-filling the dorsomedial nerve trunk with cobalt. In both normal and skin-grafted frogs, twice as many cobalt-filled neurons were observed in the dorsal half of the ganglion as in the ventral half although the absolute number of filled cells in different regions was the same in both groups. It was concluded that misdirected responses following skin rotation cannot be explained on the basis of a re-establishment of the original peripheral nerve connections.

Animals↗
PubMed1979

Measurement of phenylalanine hydroxylase turnover in cultured hepatoma cells.

A substantially new method has been developed to measure protein turnover. Its basis is the notion that in labeling experiments a secreted protein can be used to determine the specific radioactivity of the intracellular amino acid precursor pool. To measure protein turnover in the Reuber hepatoma H4 cell line, cultures were labeled with [3H]leucine for specified periods after which phenylalanine hydroxylase was isolated and its leucine specific radioactivity determined. Serum albumin secreted by the cultures was also isolated and used to estimate the leucine precursor pool specific radioactivity. The protein half-life of phenylalanine hydroxylase could them be calculated. Experiments performed at long and short labeling times and with high and low concentrations of leucine in the medium yielded equivalent results. Phenylalanine hydroxylase half-life in the H4 cells was investigated under both normal and hydrocortisone-induced growth conditions. Average half-lives of 7.4 and 8.2 h were found for induced and uninduced cultures, respectively. Although these measured enzyme half-lives were not essentially different, the steady state level of phenylalanine hydroxylase was increased 6.2-fold upon hydrocortisone induction, from 0.076 to 0.47 microgram/10(6) cells. The results demonstrated that hydrocortisone induces phenylalanine hydroxylase in the H4 cells by causing an increase in the rate of enzyme synthesis.

Animals↗
PubMed1978

Topography of cutaneous mechanoreceptive neurones in dorsal root ganglia of skin-grafted frogs.

1. Topographical distribution patterns of dorsal root ganglion (d.r.g.) cutaneous neurones providing innervation to various body surfaces were examined in doublypithed Discoglossus pictus frogs.2. Using electrophysiological methods, sensory neurones innervating back skin were observed to predominate on the dorsal ganglionic surfaces, while belly skin neurones were most prevalent in the caudal half of the d.r.g. ventral surfaces. Flank neurones clustered in the medial half of d.r.g. ventral surfaces.3. Cutaneous neuronal distribution patterns within the d.r.g. of 180 degrees skin grafted animals were indistinguishable from those observed in control frogs.4. Sensory neurone distribution patterns were found to be altered in all animals with single skin type grafts. Projection patterns were always heaviest towards the autograft, which was on the opposite body surface (i.e. dorsally located d.r.g. sensory neurones projected to back skin on the frog's ventrum, while ventrally located neurones projected to belly skin on the frog's dorsum).5. The results are discussed in the light of several selective outgrowth mechanisms which have been proposed as a possible underlying basis for the development of misdirected wiping reflex behaviour in skin grafted anurans. The findings indicate that none of the proposed selective growth mechanisms can account adequately for the development of misdirected wiping reflexes, at least in the species studied.6. It is suggested that selective cell replacement, based upon competition among prespecified cutaneous neurones, might best account for the development of normal and misdirected wiping reflexes in frogs.

Action Potentials↗
PubMed1977

Effect of cutaneous stimulation on the development of misdirected wiping reflexes in skin-grafted Discoglossus pictus.

The frog, Discoglossus pictus, has been studied with respect to wiping reflex behavior developing after skin rotations performed at larval stages. Misdirected wiping reflexes were obtained only from belly skin-grafts placed on the animals' back; back skin-grafts on the belly failed to elicit any misdirected limb movements in this species. We found that misdirected reflexes occurred more readily in 3-week and older animals if not subjected to any previous test experience, than in younger naive frogs. Frogs that had been exposed to daily cutaneous stimulation between 2 to 4 weeks after metamorphosis showed a delayed development of misdirected responses.

Age Factors↗
PubMed1976

Gonococcal ribosomes as skin test antigens. I. Preliminary tests of sensitivity and specificity.

Ribosomes isolated from N. gonorrhoeae and N. meningitidis were used as skin test antigens in guinea-pigs which had been previously sensitized with killed Neisseria cells in incomplete Freund adjuvant. Intradermal injection of ribosomes from skin test dose N. gonorrhoeae into the skin of animals sensitized to the homologous organism was characterized by a specificity based upon ribosomal skin test dose 50's (STD50) sensitivity which was at least five-fold greater than that of the animals sensitized to the heterologous organism. The sensitized guinea-pigs had lost their skin-test reactivity within 3 months of the cessation of immunization but regained it immediately on reimmunization. The results of this model system indicate that gonococcal ribosomes may be used as antigens in skin testing or other testing modes in gonorrhoea.

Animals↗
PubMed1974

Delayed hypersensitivity reactions provoked by ribosomes from acid-fast bacilli: physical characteristics and immunological aspects of core ribosomal proteins from Mycobacterium smegmatis.

Ribosomal subunits from Mycobacterium smegmatis were analyzed by using sedimentation velocity, sedimentation equilibrium, and acrylamide gel electrophoresis experiments. These s(20.w) values for the subunits are 48.7S and 28.1S. The molecular weight of the 49S subunit is about 1.65 x 10(6), and that of the 28S subunit is 7.8 x 10(5). Both subunits contain about 37% protein and 63% ribonucleic acid. A protein-deficient particle having an s(20.w) value of 15.7S contains about 11% protein and 89% ribonucleic acid. Skin tests showed all subunits and proteins to be active as agents in provoking delayed hypersensitivity, but the 16S protein-deficient particle, as well as the proteins derived from it, was more specific than the subunits themselves.

Animals↗
PubMed1973

Ribosomes of acid-fast bacilli: immunogenicity, serology, and in vitro correlates of delayed hypersensitivity.

Ribosomal fractions obtained from Mycobacterium bovis (BCG) and M. smegmatis (strain butyricum) were studied to determine their antigenicity, their ability to stimulate the production of soluble mediators of delayed hypersensitivity (in vitro correlates) by sensitized peritoneal exudate cells, and the antigenic relations of ribosomal antigens of BCG to BCG protoplasm and H37Rv culture filtrates. The crude ribosomes and the 50-30S ribosomal subunit pool obtained from each of the organisms induced both delayed and immediate hypersensitivity when injected in incomplete Freund adjuvant into rabbits, and skin reactions could be elicited in sensitized rabbits with those antigens. The crude ribosomes and 50-30S ribosomal subunit pool of M. smegmatis stimulated lymphocytes of guinea pigs sensitized with viable organisms to produce macrophage migration inhibition factor. Comparable ribosomal fractions from BCG bacilli caused lymphocytes of guinea pigs sensitized with viable M. bovis (BCG) to produce skin reactive factor. Immunoelectrophoretic studies showed that H37Rv culture filtrate, protoplasm, crude ribosomes, and 50-30S ribosomal subunits of BCG contain multiple precipitinogens and that many of these were shared between the different antigen systems. Comparative electrophoresis revealed that BCG protoplasm and H37Rv culture filtrate shared a major portion of their components with each other and relatively few with ribosomal systems. The ribosomal systems shared the major portion of their components with each other and relatively few with the other antigen systems.

Animals↗
PubMed1973

Resistance of mice to infection with Friend disease virus after subcutaneous injection of Friend virus and Friend spleen cells.

Swiss mice injected subcutaneously with suspensions of spleen cells or an extract of spleens from mice infected with Friend virus develop resistance to subsequent intravenous inoculation of Friend virus. A single injection of either Friend virus or Friend cells induces resistance. Immunized mice display resistance when challenged 6 months after immunization and survive for at least 20 weeks after infection. Neutralization tests indicate that serum, but not lymphoid cells of resistant animals, can neutralize Friend virus. In vitro neutralization tests indicate that residence of virus within the peritoneal cavity of immune mice for 1 h sharply reduces the infective titer of the virus.

Animals↗
PubMed1972

Delayed hypersensitivity reactions provoked by ribosomes from acid-fast bacilli. I. Ribosomal isolation, characterization, delayed hypersensitivity, and specificity.

Ribosomes and ribosomal subunits of Mycobacterium bovis (strain BCG) and M. smegmatis have been isolated and employed as skin test antigens in guinea pigs sensitized with homologous or heterologous organisms. Ribosomes and ribosomal subunits were found to be potent antigens for skin test purposes, and the 30S subunits were found to be more specific and active than the 50S subunits.

Animals↗
PubMed1972

Herpesvirus hominis type 2 infections in rabbits: effect of prior immunization with attenuated Mycobacterium bovis (BCG) cells.

Angora, New Zealand, and Dutch-belted rabbits were tested for their susceptibility to graded doses of Herpesvirus hominis type 2 administered by vaginal instillation, intracorneal injection, and scarification of the cornea. Central nervous system involvement and death occurred after infection by the various routes employed. Prior immunization of Dutch-belted and New Zealand rabbits with viable Mycobacterium bovis (BCG) cells injected intravenously provided protection against subsequent infections with type 2 virus.

Animals↗