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Biomedical subjects

J B Walker

Publications and source records attributed to J B Walker.

At least 73 records · Page 4Linked to original sources
PubMed1977

Ixodes (Afrixodes) Neitzi, n. sp. (Acarina: Ixodidae) from the mountain reedbuck in South Africa.

Ixodes (Afrixodes) neitzi n. sp. is described from females and males collected from the mountain reedbuck (Redunca fulvorufula) at Loskop Dam Nature Reserve, Transvaal, Republic of South Africa. Information is provided to distinguish this new species from other closely related Ixodes species that occur in the Ethiopian region. Its predilection sites are noted and the area in which it occurs is described briefly.

Animals↗
PubMed1976

Creatine biosynthesis during embryonic development. False feedback suppression of liver amidinotransferase by N-acetimidoylsarcosine and 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine).

The level of arginine:glycine amidinotransferase in liver of the developing chick embryo is partially suppressed following injection of arginine into the yolk, and the level can be completely suppressed following injection of guanidinoacetate or creatine (Walker, J.B. (1963), Proc. Soc. Exp. Biol. Med. 112, 245; Walker, J.B., and Wang, S.-H. (1964), Biochim, Biophys. Acta 81, 435). In this investigation structural requirements for the physiological suppressor were examined by testing certain analogues of creatine and its biosynthetic precursors for their ability to suppress liver amidinotransferase levels in developing chick embryos and growing chicks. The creatine analogues, N-acetimidoylsarcosine and 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine), were found to suppress liver amidinotransferase levels of both developing embryos and growing chicks. Compounds ineffective as suppressors included: the arginine analogue, N5-acetimidoylornithine; the guanidinoacetate analogue, N-acetimidoylglycine; and the creatine analogue, 1-carboxymethyl-2-iminohexahydropyrimidine. Our findings suggest that (i) arginine and guanidinoacetate must be converted to creatine before serving as a suppressor, and (ii) creatine, not phosphocreatine, is most closely related to the physiological suppressor of amidinotransferase.

Amidinotransferases↗
PubMed1976

Accumulation of analgo of phosphocreatine in muscle of chicks fed 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine).

Newly hatched chicks fed a commercial diet containing 1% cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) rapidly accumulate in breast muscle a derivative of cyclocreatine; within a few days concentrations up to 35 mumol of this derivative/g fresh weight of muscle are attained. The following evidence suggests that this derivative is N-phosphorylated cyclocreatine. (a) The derivative is adsorbed by Dowex 1 resin and eluted near phosphocreatine. (b) The derivative present in muscle is converted to free cyclocreatine either by homogenization of muscle in water at room temperature, conditions under which endogenous creatine kinase is active, or by heating a cold acidic muscle extract at 65 degrees for 45 min. (c) The isolated derivative reacts in vitro with the specific reagents crystalline creatine kinase and MgADP to give cyclocreatine. Essentially all of breast muscle cyclocreatine appears to be in the form of P-cyclocreatine, which persists in muscle long after cyclocreatine is removed from the diet. Long term conservation of P-cyclocreatine in muscle is aided by the fact that, unlike P-creatine, P-cyclocreatine is not continuously degraded to an inactive cyclic lactam. It is suggested that the maximal concentrations of P-cyclocreatine2- (and P-creatine2-) attained in sarcoplasm not only affect the phosphorylation potential of muscle cells, but also can account for more than half of the normal inorganic cation concentration of muscle sarcoplasm, and hence play an important role in muscle function. Other chick tissues active in accumulation of cyclocreatine are heart (up to 20 mumol/g fresh weight within 11 days on the diet) and brain (up to 10 mumol/g fresh weight after 30 days on the diet). Addition of 1% creatine to the diet of cyclocreatine-fed chicks does not prevent accumulation of cyclocreatine in muscle. Chicks fed cyclocreatine do not grow as rapidly as those on control diets, but they appear healthy, and mortality is very low when oxytetracycline is added to the drinking water. Cyclocreatine is also taken up by rat muscle, heart, and brain. A sensitive and specific assay for cyclocreatine has been developed. Cyclocreatine reacts with an aged aqueous solution of Na3[Fe(CN)8NH3] under alkaline conditions to give a blue product with a molar absorption coefficient (epsilon) of 4,400 M(-1) cm(¿ at 605 nm. The following compounds give an epsilon605 in this assay of less than 4 M%¿ cm(% N-phosphorylcyclocreatine, creatine, P-creatine, creatinine, 1-carboxymethyl-2-iminohexahydropyrimidine, guanidinoacetate, 3-guanidinopropionate, and arginine. Cyclocreatine does not interfere with the diacetyl-alpha-naphthol assay for creatine.

Animals↗
PubMed1976

Ixodes (Afrixodes) Bakeri Arthur & Clifford, 1961 (Acarina: Ixodidae): description of the male and immature stages from rodents and insectivores and notes on its biology in South Africa.

The male, nymph and larva of Ixodes (A), bakeri are described and illustrated with line drawings and scanning electron microscope photographs. This species was originally described from 1 female from Otomys sp., Nyika Plateau, Malawi. The present material consists of 28 collections from insectivores and 19 collections from rodents, Van Riebeeck Nature Reserve, Transvaal, plus 1 collection from a rodent in the Jonkershoek Valley, Cape Province, Republic of South Africa. Its biology in South Africa is also discussed.

Animals↗
PubMed1975

Self-produced locomotion restores visual capacity after striate lesions.

Rats permitted unrestrained movement in a patterned visual environment during the interval between two-stage vilateral lesions of the visual cortex reacquire a preoperatively learned pattern discrimination. Rats passively transported through the identical visual environment do not. This is the first demonstration that interoperative self-produced locomotion is essential for recovery of function in the visual system.

Animals↗
PubMed1975

Selective changes in the permeability of the blood-brain barrier after pharmacological or surgical deafferentation.

Unilateral eye removal results in an increased delivery of blood-borne glucose, norepinephrine, choline, and tyrosine, but not of proline, to the denervated optic lobes. Administration of reserpine to chicks increases penetrance of norepinephrine into the brain but not of tyrosine, choline, or proline. Selective alterations in the permeability of the blood-brain barrier may represent a mechanism for the modulation of the delivery of critical nutrients to the brain.

Animals↗