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Biomedical subjects

S K Johnson

Publications and source records attributed to S K Johnson.

At least 19 recordsLinked to original sources
PubMed1992

The effects of deprenyl on methamphetamine-induced dopamine depletions.

The effects of deprenyl on methamphetamine-induced dopamine depletions were studied in mice. Four SC injections of 12.5 mg/kg of methamphetamine at two-hour intervals caused substantial (72-82%) and long-lasting depletions of striatal dopamine. Pretreatment with either 25 or 40 mg/kg of deprenyl did not significantly alter the magnitude of this depletion. These results indicate that, unlike what is observed following MPTP, there is no protection afforded dopaminergic cells by deprenyl pretreatment in the methamphetamine model of parkinsonism.

Animals↗
PubMed1992

Role of prostaglandin F2 alpha in follicular development and subsequent luteal life span in early postpartum beef cows.

In postpartum cows expected to have corpora lutea (CL) of normal (norgestomet-treated) compared to short (control) life spans, function of the largest follicle increases after an increase in concentrations of prostaglandin F2 alpha (PGF). To determine whether PGF alters follicular growth and subsequent life span of the CL, 43 crossbred beef cows (19 to 22 d postpartum) were assigned to one of four treatments: 1) control (C; n = 10), 2) control+PGF (CPGF; n = 10), 3) norgestomet (N; n = 13), 4) norgestomet+flunixin meglumine (NFM; n = 10). Flunixin meglumine inhibits prostaglandin endoperoxide synthase. On day 0, N and NFM cows received a 6 mg implant of norgestomet. From days 3 through 8, CPGF and NFM cows were injected every 8 hr with 10 mg PGF im or 1 g FM iv, respectively. Implants were removed on day 9. On day 11, each cow received 1000 IU of hCG im to induce formation of CL. Follicular growth was monitored by daily ultrasonography from days 6 through 11. In a majority of the cases (25/32), the largest follicle present on day 6 was still the largest on day 11; frequency of persistence did not differ with treatment. Rate of growth of the largest follicle was greater in CPGF than in N cows (.6 +/- .1 vs .3 +/- .1 mm/d, respectively; P less than .05) but did not differ between C and NFM cows (.4 +/- .1 and .5 +/- .1 mm/d, respectively). Concentrations of estradiol in NFM cows were higher (P less than .05) on day 3 and declined to concentrations similar to those of the other treatments on day 9.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of same-modality interference on immediate serial recall of auditory and visual information.

Two studies investigated the effects of same-modality interference on the immediate serial recall of auditorily and visually presented stimuli. Typically, research in which this task is used has been conducted in quiet rooms, excluding auditory information that is extraneous to the auditorily presented stimuli. However, visual information such as background items clearly within the subject's view have not been excluded during visual presentation. Therefore, in both the present studies, the authors used procedures that eliminated extra-list visual interference and introduced extra-list auditory interference. When same-modality interference was eliminated, weak visual recency effects were found, but they were smaller than those that were generated by auditorily presented items. Further, mid-list and end-of-list recall of visually presented stimuli was unaffected by the amount of interfering visual information. On the other hand, the introduction of auditory interference increased mid-list recall of auditory stimuli. The results of Experiment 2 showed that the mid-list effect occurred with a moderate, but not with a minimal or maximal, level of auditory interference, indicating that moderate amounts of auditory interference had an alerting effect that is not present in typical visual interference.

Acoustic Stimulation↗
PubMed1992

Neurochemical and motor effects of high dose haloperidol treatment: exacerbation by tryptophan supplementation.

The neurochemical and motor effects of a high dose (25 mg/kg) of haloperidol were assessed in male Sprague-Dawley rats. In Experiment 1, this high dose of haloperidol caused dramatic increases in striatal dopaminergic and serotonergic turnover that only returned to control levels 100 hr after injection. In the second experiment, the same dose of haloperidol was administered twice over a 3-week interval in the presence or absence of a dietary tryptophan supplement added to the drinking water. Rats were assessed for disruption of locomotor behavior (using the rotorod) as well as the occurrence of spontaneous (dyskinetic-like) chewing and head twitching. It was observed that haloperidol impaired rotorod performance in a manner that paralleled the time course of the neurochemical changes in Experiment 1. In addition, the tryptophan (consumed at an average of 157 mg/kg/day) exacerbated the deficit in rotorod performance in haloperidol-treated rats after the first, but not after the second, haloperidol injection. Finally, the combination of haloperidol plus tryptophan was found to cause a long-lasting increase in spontaneous chewing movements that lasted 56 days after the first injection. These observations are interpreted in the context of tryptophan supplementation to antipsychotic therapy.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1991

Yeast artificial chromosome-based genome mapping: some lessons from Xq24-q28.

Yeast artificial chromosomes (YACs) have recently provided a potential route to long-range coverage of complex genomes in contiguous cloned DNA. In a pilot project for 50 Mb (1.5% of the human genome), a variety of techniques have been applied to assemble Xq24-q28 YAC contigs up to 8 Mb in length and assess their quality. The results indicate the relative strength of several approaches and support the adequacy of YAC-based methods for mapping the human genome.

Chromosome Mapping↗
PubMed1991

Steroids and cAMP in follicles of postpartum beef cows treated with norgestomet.

To determine time of occurrence of follicular changes that may be associated with the length of the subsequent luteal phase, follicles were collected at different times before ovulation from cows expected to have corpora lutea of short (control) or normal (norgestomet-treated) life span. Beginning on d 20 to 23 postpartum (d 0 of study), 34 crossbred beef cows received either a 6-mg implant of norgestomet for 9 d or served as untreated controls. Ovaries were removed from norgestomet-treated cows on d 6 (N6; n = 9), d 8 (N8; n = 8), or the day after implant removal (N10; n = 8). Control cows were ovariectomized on d 6 (C6; n = 4) or d 10 (C10; n = 5). The largest and second largest follicles greater than 8 mm (F1 and F2, respectively) were dissected from the ovaries. Granulosal and thecal layers and follicular fluid were separated and assayed for estradiol-17 beta, progesterone, androstenedione, and testosterone. Cyclic 3'5'adenosine monophosphate (cAMP) was determined in thecal and granulosal tissue. Diameters of the F1 (14.6 +/- .4 mm) and F2 (10.6 +/- .4 mm) did not differ due to treatment. A greater proportion (P less than .05) of the F1 (20/33) than of the F2 (4/27) had estradiol:progesterone ratios of greater than 1 in follicular fluid. Contents of estradiol, androstenedione, and testosterone in theca and granulosa and follicular fluid, androstenedione in theca, and testosterone in theca and follicular fluid (all P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Androstenedione↗
PubMed1990

Characterization and inhibitor sensitivity of human sperm phospholipase A2: evidence against pivotal involvement of phospholipase A2 in the acrosome reaction.

The kinetic properties and inhibitor sensitivity of human sperm phospholipase A2 (PLA2; EC 3.1.1.4) were studied. Phospholipase activity was isolated from human spermatozoa by acid extraction. Hydrolysis of dipalmitoyl phosphatidylcholine was specific to the sn-2 position. Activity was sensitive to product inhibition (60% inhibition by 0.1 mM lysophosphatidylcholine). The effects of Ca2+ and sodium deoxycholate on enzyme activity were biphasic; maximal activities were observed at 0.5 mM concentration of each agent. PLA2 was stimulated (135%) by 3% dimethylsulfoxide and was inhibited by elevated ionic strength (approximately 70% inhibition with either 0.2 M NaCl or 0.2 M KCl). Two molecular forms of PLA2 were kinetically distinguishable, one with an apparent Michaelis constant and maximal reaction velocity of 3.0 microM and 0.64 mlU/mg protein and the other with respective constants of 630 microM and 32.0 mlU/mg protein. Both forms of the enzyme were Ca2+ dependent and heat stable; however, the low-Km activity was less resistant to 60 degrees C preincubation at pH 7.5 (28% inactivation of low-Km activity after 45 min, as compared to no effect on high-Km activity). Quinacrine was a noncompetitive PLA2 inhibitor with Kis for low- and high-Km activities of 0.42 mM and 0.49 mM, respectively. Trifluoperazine (calmodulin antagonist) inhibited the high-Km activity noncompetitively (Ki = 87 microM) and the low-Km activity by a mechanism consistent with the removal of a nonessential activator. Dissociation and rate constants for inactivation of low- and high-Km activities by p-bromophenacyl bromide were 0.28 mM and 0.032 min-1, and 0.73 mM and 0.066 min-1, respectively. PLA2 was inhibited by p-nitrophenyl-p'-guanidinobenzoate, at higher concentrations (10(-4)-10(-3) M) than required to inhibit trypsinlike proteinases; p-aminobenzamidine, another potent trypsin/acrosin inhibitor, stimulated (approximately 40%) PLA2 at concentrations from 2-5 mM but inhibited PLA2 (40-50%) at a concentration of 10 mM. MnCl2 (5mM) inhibited low- and high-Km PLA2 activities by 77% and 76%, respectively. Quinacrine (0.4 mM), trifluoperazine (20 microM), p-bromophenacyl bromide (20 microM), and MnCl2 (5 mM) were tested as inhibitors of the ionophore A23187-induced human acrosome reaction. Inhibition was noted only with quinacrine (32%) and MnCl2 (93%). The effect of MnCl2 was restricted to an interaction with A23187, rather than with PLA2; p-Bromophenacyl bromide inhibited (P less than 0.05) PLA2 (29%) when added to intact spermatozoa but had no effect on the acrosome reaction. PLA2 inhibition was poorly correlated with the acrosome reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Ventral somatosensory determinants of nursing behavior in Norway rats. I. Effects of variations in the quality and quantity of pup stimuli.

By varying the quality and quantity of tactile input that rat dams, between Days 2 and 14 postpartum, received from their pups, we found the following: a) After a 4-hr separation from their litter, mothers continuously display an array of activities, until the onset of nursing, in response to displaced pups and to pups gathered in the nest. b) While the dam hovers over the gathered pups, engaged in an activity such as pup-licking, the young gain access to the dam's ventrum and root for a nipple. c) Pups capable of effective rooting, nipple attachment, and suckling thereby stimulate the dam's immobility (i.e., inhibition of head and limb movements), assumption of the upright crouching posture, and milk ejections. d) Rat dams do not become immobile or crouch in response to pups that are inactive or that are active but incapable of rooting effectively or suckling. e) The likelihood and speed of assuming the quiescent nursing posture, as well as of having milk ejections subsequently, are directly related to the number of effective pups in the nest. We propose that the initiation, maintenance and termination of nursing behavior are related to the spatial and temporal summation of effective ventral somatosensory afferents.

Animals↗
PubMed1989

Perioral somatosensory determinants of nursing behavior in Norway rats (Rattus norvegicus).

Prior to assuming the upright crouching posture over their pups during nursing bouts, lactating rats typically engage in several oral behaviors, including nuzzling, licking and rearranging pups. By acutely depriving dams of various aspects of perioral stimulation from pups (with anesthesia of the mystacial pads or of the tongue, with mouth suturing, or with muzzling), we found the following: (1) Distal stimulation from pups maintains proximity-seeking behavior, but is insufficient to stimulate nursing behavior. (2) Lack of tongue feedback decreases pup licking and hastens the onset of crouching. (3) Snout, but not tongue, contact with pups is required for hovering over them. (4) The position of the dam while hovering over her litter enables the pups to gain access to her ventrum, thereby provoking her upright, crouching posture. (5) Older pups are capable of bypassing the dam's perioral attentions and stimulating crouching directly by burrowing under the dam's ventrum.

Animals↗
PubMed1988

Radiology work-load measurements reflecting variables specific to hospital, patient, and examination: results of a collaborative study.

The authors coordinated the efforts of 44 hospitals in the United States to develop average times required for technologists to perform each of 19 radiologic examinations. When applicable, the overall average times were compared with extant Canadian work-load statistics. In six of the 14 examinations for which Canadian standards exist, the average times differed by 25% or more. The data were further analyzed to adjust time estimates for the effects of different hospital characteristics (e.g., number of beds, teaching status), patient characteristics (e.g., ambulation, outpatient status), and examination characteristics (e.g., number of views, resident involvement). The key factors and the magnitude of their effects varied from examination to examination, but the effects were generally large enough to have managerial significance. The factors can be evaluated by individual hospitals to produce customized estimates of average examination times. The data presented in this report can be used in management control systems by radiology departments in hospitals of varying sizes and teaching characteristics.

Allied Health Personnel↗
PubMed1988

Relationships of pelvic structure, body measurements, pelvic area and calving difficulty.

Data on 186 Hereford heifers from five South Dakota ranches were collected to evaluate the relationships of pelvic structure and body measurements with calving difficulty (CD) and pelvic area. Body measurements obtained prebreeding and precalving included two internal pelvic and seven external rump measurements, three pelvic angles and two slope of rump measurements. A calving difficulty score (CDS) of 1 (unassisted) to 8 (Caesarean) was assigned at birth, and calf birth weight was recorded. Data were analyzed using both regression and discriminant analyses. Stepwise regression analysis including all 49 variables showed that calf birth weight was the most important variable influencing CDS (R2 = .33), with precalving pelvic area ranking second (cumulative R2 = .45). Prediction equations that included all variables or only prebreeding variables accounted for 63% and 25% of the variation in CDS, respectively. Pelvic angles and slope of rump variables had low correlations with CDS and pelvic area. Ratios of prebreeding and precalving pelvic areas to calf birth weight significantly decreased as CDS increased. A prebreeding ratio of 4.7 cm2/kg may be beneficial in selection of replacement heifers. In discriminant analyses, the most informative variable in differentiating among levels of CD was calf birth weight. All models significantly discriminated between two CD categories (assisted and unassisted). Models using prebreeding variables only performed as well as those based on precalving variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Abnormal vitamin D metabolism in Paget's disease of bone.

We have studied several biochemical indices of bone turnover and vitamin D metabolism in 32 untreated patients with Paget's disease and in 32 age-matched control subjects. patients with Paget's disease, as expected, were characterized by high bone turnover, as judged by alkaline phosphatase and urinary excretion of hydorxyproline. Serum values of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and the ratio of 24,25(OH)2D3 to 25-OHD were significantly lower in patients than in control subjects. Serum concentrations of 1,25(OH)2D3 were normal in Paget's disease. The distribution of values for 24,25(OH)2D3 was log normal. On the basis of the normal range computed from control subjects, patients were divided into those with low or normal values for 24,25(OH)2D3. Disease activity, as judged by biochemical indices was significantly higher in the patients with the lower values of 24,25(OH)2D3. We conclude that Paget's disease is characterized by low circulating concentrations of 24,25(OH)2D3, particularly in patients with more extensive or severe disease.

24,25-Dihydroxyvitamin D 3↗
PubMed1985

Effect of unilateral ovariectomy and injection of bovine follicular fluid on gonadotropin secretion and compensatory ovarian hypertrophy in prepuberal heifers.

A study was conducted to determine whether compensatory ovarian hypertrophy occurred in prepuberal heifers, and if so, could compensatory ovarian hypertrophy be prevented by injecting charcoal-extracted bovine follicular fluid (CFF). An additional objective was to determine the effect of CFF injections on follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations following unilateral ovariectomy (ULO). Thirty-one prepuberal Angus, Hereford, and Angus X Hereford heifers were assigned by weight and breed to the following groups: Control-saline injections (C), unilateral ovariectomy-saline injections (ULO) and unilateral ovariectomy-CFF injections (ULO-CFF). In group C, a sham operation was performed on d 0 and both ovaries were removed on d 7. In groups ULO and ULO-CFF, either the right or left ovary was removed on d 0 and the remaining ovary was removed on d 7. From d 0 to 7, each heifer received an injection (iv, 7 ml/injection) of saline or CFF every 12 h. Jugular blood samples were collected immediately before each saline injection from d 0 to 7 and analyzed for FSH and LH. Unilateral ovariectomy increased ovarian (P less than .08) and follicular fluid (P less than .05) weights compared with groups C and ULO-CFF; however, lyophilized ovarian weight was similar (P greater than .05) for all groups. Injections of CFF blocked the increase in ovarian and follicular fluid weight following ULO. The total number of visible follicles per ovary was similar for all groups; however in the ULO group there was an increase (P less than .01) in those 5 to 6 mm and greater than or equal to 9 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Effects of charcoal-extracted, bovine follicular fluid on gonadotropin concentrations, the onset of estrus and luteal function in heifers.

A study was conducted to determine the effect of charcoal-extracted, bovine follicular fluid (CFF) on plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations, the interval from luteolysis to estrus, and subsequent luteal function in heifers. Fifteen Angus, Simmental and Hereford heifers were allotted by age, weight and breed to a control (C, n = 8) or a CFF (n = 7) group. Heifers received injections of saline or CFF (iv, 8 ml/injection) every 12 h from d 1 (d 0 estrus) through d 5 of the estrous cycle. On d 6, each heifer was injected (im) with 25 mg of prostaglandin F2 alpha (PGF2 alpha). Blood samples were collected every 12 h by venipuncture starting just before the first saline or CFF injection and continuing until estrus. Thereafter, blood samples were collected every other day during the subsequent estrous cycle and assayed for FSH, LH, estradiol-17 beta and progesterone by radioimmunoassay. Injections of CFF had no effect (P greater than .05) on circulating FSH or LH concentrations from d 1 to 5 relative to the C group; however, there was a transient rise (P less than .05) in FSH concentrations 24 h following cessation of CFF injections. This transient rise in FSH was not immediately followed by an increase in plasma estradiol-17 beta concentrations. Although CFF injections did not interfere with PGF2 alpha-induced luteolysis, the interval from PGF2 alpha injection to estrus was delayed (P less than .05) by 5 d in the CFF group compared with the C group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

How do tranquilizing agents selectively inhibit conditioned avoidance responding?

A number of tranquilizing agents have been shown to inhibit conditioned avoidance responses (CAR) at doses that do not interfere with escape responses (ER). To test the hypothesis that this selective action may be due to differential response strengths of the two responses, rats were trained to press retractable levers in an operant chamber either to avoid a 0.5 mA shock during a 5.0-s warning period or to escape from a low-intensity shock within 5.0 s. The intensity of the latter shock was adjusted for each animal so that CAR and ER were comparable in terms of probability of occurrence and latency. While doses of chlorpromazine, clonidine, diazepam, and morphine that reduced CAR by 30%-50% did not significantly affect high-shock ER, i.e., ER on CAR trials where no CAR occurred, they interfered with low-shock ER to the same degree as CAR. These and other results suggest that the selective blockade of the CAR by these drugs in the CAR paradigm is primarily due to differential strengths of the CAR and ER. They also support studies concluding that tranquilizing drugs reduce avoidance because of a deficit in the ability to initiate motor responses, rather than interfering with associative processes or reducing situation-induced emotional reactions. However, the finding of a small differential effect, at least with chlorpromazine, on CAR and low-shock ER across trials within sessions indicated that different mechanisms may be involved in the suppression of these two responses.

Animals↗
PubMed1981

Stimulation of the adenylate cyclase of A B16 melanoma cell line by pro-opiocortin-related peptides--a structure-activity study.

The ability of alpha-melanotrophin (alpha-MSH or ACTH 1-acetyl-13 amide) and other structurally related peptides derived from the common precursor, pro-opiocortin, to stimulate adenylate cyclase activity in a pigmented B16 mouse melanoma was investigated. The peptides ACTH 1-39, ACTH 1-24, alpha-MSH, ACTH 1-13 amide and beta-MSH all stimulated the enzyme to a similar maximal extent and with similar potency (ED50 = 1.3 . 10(-6) M) except that ACTH 1-39 was slightly less potent (ED50 = 5 . 10(-6) M). ACTH 4-10 (ED50 = 4 . 10(-5) M) and gamma-MSH (ED50 = 5 . 10(-6) M) were partial agonists. ACTH 1-10 was no more effective than ACTH 4-10 in stimulating the enzyme whereas ACTH 1-13 amide was a full agonist. The peptides beta-endorphin and its derivatives, Met-enkephalin and melanotrophin potentiating factor (MPF), failed to stimulate the enzyme. We suggest that the B16 melanoma requires not only the sequence ACTH 4-10 but also some part of the sequence ACTH 11-13, or a similar sequence in the terminal portion of beta-MSH, for full activation of the receptor-linked enzyme.

Adenylyl Cyclases↗