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Biomedical subjects

T J O'Brien

Publications and source records attributed to T J O'Brien.

At least 145 records · Page 8Linked to original sources
PubMed1978

Developmental restrictions on hormone modulated gene transcription. II. Hormone induced interactions of RNA polymerase with chromatin.

Chromatin-bound and soluble RNA polymerase subspecies have been isolated and fractionated by isoelectric focusing at various times (0, 6, 12 and 18 h) following auxin treatment of 4 day (responsive) and 8 day (unresponsive) soybean hypocotyls. Young 4 day seedlings displayed two well defined phases of auxin induced gene transcription. Phase I (6 h) evidenced the selective dissociation of many RNA polymerase subspecies from the chromatin complex which was accompanied by the retention of three class II enzymes. Phase II occurred after 12 h of treatment when the dissociated enzymes including some species which were soluble in the 0 h controls became re-associated with chromatin. These induced RNA polymerases may be responsible for the synthesis of auxin induced RNAs. In contrast, the unresponsive 8 day hypocotyl did not display two phases of auxin induction. Phase one, the dissociation of the chromatin bound enzymes, occurred at 12 h (compared to 6 h for the 4 day seedling) and was not followed by the later translocation of any soluble enzymes towards the chromatin complex. The results support earlier findings suggesting that the developmental "phasing out" of RNA polymerase subspecies limits the hormone induced growth response of this tissue and thus is regarded as an off switch for the transcription of such hormone controlled gene sequences.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1978

Solubilization and developmental distribution of embryonic antigen of the chick red blood cell plasma membrane.

An antigen(s) on the surface of embryonic and newly hatched chick red blood cells was studied with antiserum absorbed with adult red blood cells. Because of the reappearance of the antigen or some cross-reactive antigen during myeloblastosis, attempts at solubilization and characterization of the antigen were pursued. Antigen was solubilized from whole red blood cell lysates or from red blood cell ghosts with 0.01 M Tris:0.1% Nonidet P40, pH 8.0. Antigen was assayed with an enhancement of agglutination assay. Enhancement apparently occurs because of available specific receptors for the antigen on newly hatched chick red blood cells. Antigen was also found to be present in plasma, and both the membrane-derived antigen and the plasma antigen were excluded from Sephadex G-100. Isoelectric focusing of the antigen extract indicated the presence of more than one molecular species with antigenic activity.

Age Factors↗
PubMed1978

A preliminary study of the superoxide dismutase content of some human tumors.

The cell cytosol superoxide dismutase (SODase) content of 46 human tumors was investigated. The extraction procedure of McCord and Fridovich was used with the epinephrine assay of Misra and Fridovich (J. Biol. Chem., 247; 3170-3175, 1975). The purpose of the study was to determine whether SODase could be reliably assayed from small, biopsy-sized pieces of tumor (0.5 to 1.0 g). In most cases it was possible to examined larger masses of tumor, which served as a control of the methodology. In this preliminary study SODase values, calculated from a standard curve derived from purified bovine blood SODase with a specific activity of 2584 units/mg, ranged from as little as 0.23 to as much as 160.5 units/g of tumor. These findings suggested that the procedures used might be feasable on a routine basis to determine the SODase content of tumors and its possible relationship to the radiation sensitivity of the tumors.

Breast Neoplasms↗
PubMed1977

Conditioned narcotic withdrawal in humans.

Subjective and physiological manifestations of the narcotic withdrawal syndrome were produced as a conditioned response. Withdrawal reactions precipitated by the narcotic antagonist naloxone in methadone-dependent volunteers were the unconditioned response. These data support clinical anecdotes of withdrawal symptoms occurring in former addicts when they return to their drug-related environment.

Adult↗
PubMed1975

Conditioning of narcotic abstinence symptoms in human subjects.

Clinical evidence suggests the possibility of conditioning of narcotic abstinence symptoms. Addicts report subjective and objective signs of withdrawal/craving when exposed to certain stimuli. This may partially explain the high rate of relapse to drug seeking behavior when treated addicts return to their home environment. Conditioning of narcotic abstinence symptoms was produced experimentally in five of eight volunteer subjects. Brief naloxone precipitated abstinence was the unconditioned response. The conditioned stimulus was a tone and odor. After an average of seven training trials, the tone and odor produced a conditioned abstinence response. The conditioned response consisted of subjective components (feelings of sickness, nausea, cramps, craving) and objective components (yawning, tearing, rhinorrhea, irregular respiration and transiently increased blood pressure). These laboratory findings support the anecdotal evidence regarding the existence of conditioned abstinence phenomena.

Acoustic Stimulation↗
PubMed1975

Tonic immobility in the blue crab (Callinectes sapidus, Rathbun) its relation to threat of predation.

The tonic immobility. response in the blue crab (Callinectes sapidus, Rathbun) was investigated in a series of seven experiments. Although reported to be a powerful variable in other species, preinduction electric shock produced inconsistent increases in the duration of tonic immobility with the blue crab; Manipulations that were more directly relevant to the fear of predation had considerably greater effects than shock. Physical damage to the chelipeds, mirror image stimulation, and immobilization beneath artificial glass eyes all produced significant prolongation of the immobility episode; Crabs immobilized on a bed of sand rather than on a hard surface showed shorter immobility durations, suggesting that opportunity for escape is an important variable affecting the immobility reactionmthe present results support the contention that threat of predation is the organizing principle behind tonic immobility

Animals↗