Biomedical subjects

J Baker

Publications and source records attributed to J Baker.

At least 271 records · Page 15Linked to original sources

PubMed1982

Oculomotor reflexes after semicircular canal plugging in cats.

The horizontal ocular reflexes of cats were studied before and after plugging all 6 semicircular canals (2 cats) or the horizontal canals only (2 cats). After plugging, the vestibulo-ocular reflex (VOR) was virtually absent in the cats with all canals plugged; a small phase-advanced VOR was detectable only at high velocities of rotation. There was no VOR recovery over several months. A compensatory cervico-ocular reflex (COR) appeared within a few days of plugging in all cats, and increased in gain slowly over time. The cats with horizontal canals plugged had little VOR during yaw rotation with the head pitched near 30 degrees down from the stereotaxic plane. When the head was pitched nose up from this null plane, a horizontal VOR appeared and increased as the sine of pitch angle, indicating that the cats relied on normal or increased coupling of vertical canals to horizontal eye movers for generation of compensatory eye movements. Periods of compensatory and anticompensatory eye movements were recorded during downward pitched yaw.

Animals↗

PubMed1982

Identification of eleven human hemoglobin variants by high-performance liquid chromatography: additional data on functional properties and clinical expression.

Eleven abnormal hemoglobins were detected in the course of cord blood screening or in the evaluation of evident hematological problems in individual cases. Identification of the variant in each case was done by high-performance liquid chromatography (HPLC); HPLC provides a rapid, sensitive means for the examination of abnormal hemoglobins. Some of the 11 variants that were identified have been described repeatedly and are included to provide information on the HPLC behavior of tryptic peptides. Others are much rarer. Additional information is provided about the hematological and clinical expression as well as ethnic and geographical distribution of the abnormal hemoglobin.

Chromatography, High Pressure Liquid↗

PubMed1982

Non-specific factors can induce s-IgD on the intermediate, "pre-progenitor" B cells that give adoptive primary responses.

The intermediate or "pre-progenitor" B-cell subpopulation giving primary adoptive responses has been found by this laboratory to be s-IgD-, whereas other laboratories have reported the progenitors of primary adoptive responses to be s-IgD+. This difference appears to depend on the recent history of environmental stimuli received by the mice. Deliberate administration of a complex non-specific stimulus, designed to mimic the effects of infection or certain types of experimental manipulation, shifted "pre-progenitor" activity from the s-IgD- compartment to the s-IgD+ compartment within 24 h. Neither horse erythrocytes (HRC) nor lipopolysaccharide (LPS) alone produced a reproducible effect, but the combination of HRC with low doses of LPS produced a marked shift to s-IgD+ activity. Some earlier experiments from this laboratory suggesting a striking effect with HRC alone probably resulted from suspension of HRC in saline contaminated by LPS-like material. Priming with HRC alone, under conditions which did not induce s-IgD, nevertheless stimulated the "pre-progenitors" to enter cell cycle. Three conclusions are drawn: (1) The stimulus for induction of s-IgD is not identical with the non-specific stimulus which selectively induces cell division in this intermediate B-cell subset; (2) the presence of IgD on the surface per se does not prevent the non-specific activation of these cells into division; (3) the absence of s-IgD is only a useful marker of the "pre-progenitor" subset if the mice are maintained under specific pathogen-free conditions and exogenous stimuli are controlled.

Animals↗

PubMed1982

An NK-like cell limits the adoptive response from "pre-progenitor" B cells.

Evidence is presented that a dividing, Thy 1 . 2 positive and NK 1 . 2 positive cell with a suppressive effect on adoptive responses is present in the spleens of normal and athymic mice, and that its function may be enhanced by non-specific antigenic stimulation. NK cells may thus exert a controlling function on the proliferation and differentiation of B cells. The main experimental observation is that under certain assay conditions incubation of spleen cells with 3H-TdR in order to kill dividing, non-specifically activated 'pre-progenitor' B cells may actually give a marked increase rather than a decrease in a subsequent hapten-specific primary adoptive response. An activated 'suppressor' population was proposed as the reason for this effect. This anomalous effect may be avoided and the cycle state of the B cells assessed by prior elimination of cells bearing Thy 1 antigen, together with the use of a more reliable hydroxyurea incubation to kill dividing B cells.

Animals↗

PubMed1981

Structural features associated with movement and 'catch' of sea-urchin spines.

Spine catch ligaments of a sea urchin Arbacia punctulata were extended under constant load. Ligaments from an undisturbed animal may show any extension rate from zero (catch state) to rapid extension to failure. Replacing the preparation bath with CA(2)- and Mg(2+)-free sea water reversibly abolishes the catch state. The fine structure of the outermuscle layer and inner ligament cone associated with the spine base is described. The unstriated paramyosin muscles bear thin flanges and form compact interlocking rows. Subsurface cisternae are associated with the plasma membrane. The muscles are innervated by glia-free axons ending in bulbous terminals containing lucent synaptic vesicles. The ligament comprises cylindrical bundles of collagen fibrils: one or more minute muscle fibers (paramyosin) lie parallel with and closely adjoining each bundle. The mean diameter of these muscles is 0.3 micrometers and they occupy 2-3% of the ligament's cross-sectional area. Axons containing electron-opaque secretory droplets accompany the muscles between the collagen bundles: the cell bodies of these neurones generally lie on the outer surface of the ligament. When an urchin points a spine, the ligament on the side of the contracting spine muscle shortens but does not buckle. A function of the intraligamental muscles is to effect this non-buckled shortening. The catch mechanism (which reside entirely within the ligament) may be due either to the intraligamental muscles and/or to a locked polymer mechanism in which matrix molecules between collagen fibrils are reversibly cross-linked by divalent cations.

Animals↗

PubMed1981