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Biomedical subjects

A K Johnson

Publications and source records attributed to A K Johnson.

At least 19 recordsLinked to original sources
PubMed2006

Application of broken-line analysis to assess floor space requirements of nursery and grower-finisher pigs expressed on an allometric basis.

Few issues in swine production are as complex as floor space allowances. One method for pork producers to calculate floor space allowance (A) is to convert BW into a 2-dimensional concept yielding an expression of A = k * BW(0.667). Data on ADG, ADFI, and G:F were obtained from published peer-reviewed studies. Five data sets were created: A = grower-finisher pigs, fully slatted floors, and consistent group size; B = grower-finisher pigs and fully slatted floors (group size did not need to be consistent); C = grower-finisher pigs, partially slatted floors, and consistent group size; D = grower-finisher pigs, partially slatted floors (group size did not need to be consistent); and E = nursery pigs, fully slatted or woven wire floors (group size did not need to be consistent). Each data set was analyzed using a broken-line analysis and a linear regression. For the broken-line analyses, the critical k value, below which a decrease in ADG occurred, varied from 0.0317 to 0.0348. In all cases the effect of space allowance on ADG was significant (P < 0.05). Using the linear analyses based on data with k values of < 0.030, the critical k values for the 4 grower-finisher data sets did not differ from those obtained using the broken-line analysis (0.0358 vs. 0.0336, respectively; P > 0.10); however, none of the linear regressions explained a significant proportion of the variation in ADG. The slopes for the nonplateau portion of the broken-line analyses based on percent values varied among data sets. For every 0.001 decrease in k (approximately 3% of the critical k value), ADG decreased by 0.56 to 1.41%, with an average value of 0.98% for the 5%-based analyses. The use of an allometric approach to express space allowance and broken-line analysis to establish space requirements seem to be useful tools for pig production. The critical k value at which crowding becomes detrimental to the growth of the pig is similar in full- and partial-slat systems and in nursery and grower-finisher stages. The critical point for crowding determined in these analyses approximated current recommendations to ensure the welfare of pigs.

Animal Husbandry↗
PubMed2005

A quantitative real-time RT-PCR assay to measure TGF-beta mRNA and its correlation with hematologic, plasma chemistry and organo-somatic indices responses in triamcinolone-treated Atlantic menhaden, Brevoortia tyrannus.

A quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) assay was developed to measure transforming growth factor-beta (TGF-beta) in Atlantic menhaden (Brevoortia tyrannus), an estuarine-dependent species plagued by ulcerative skin lesions in the estuaries along the eastern United States. Atlantic menhaden were acclimated in a closed system for two weeks prior to initiation of the study. The synthetic glucocorticoid, triamcinolone acetonide (10mg/kg body weight) was administered by intracoelomic injection and its effect on the splenic mononuclear cell TGF-beta mRNA transcription, liver-somatic index, spleno-somatic index, hematology, and plasma chemistry were compared to untreated fish at 48 and 96h post-treatment. Triamcinolone-treated Atlantic menhaden showed suppression of TGF-beta mRNA production, neutrophilia, monocytosis, lymphopenia, and an increase in blood glucose concentrations. The health indices used in this study may help us interpret some of the changes observed during the development of ulcerative skin lesions in wild-caught menhaden.

Animals↗
PubMed2005

Environmental prevalence and persistence of Salmonella spp. in outdoor swine wallows.

Swine can harbor Salmonella in their gastrointestinal tracts. It has been estimated that up to 48% of the U.S. swine herd may carry Salmonella. Housing sows in farrowing stalls has become controversial due to animal welfare-based criticisms. An alternative production system is to keep sows outdoors on pasture with access to individual farrowing huts. This study was designed to determine the effects of two production systems on indicator bacteria and Salmonella of sows housed indoors in farrowing stalls (n = 52) compared to sows housed outdoors (n = 52) in English style huts. Each farrowing radial contained one wallow, from which mud (n = 290) and water (n = 290) samples were collected weekly. All samples were analyzed for generic E. coli, coliforms and Salmonella. No differences (p > 0.05) were detected in Salmonella, generic E. coli and coliform populations between indoor farrowing stalls and outdoor farrowing huts. However, all 8 outdoor wallows contained Salmonella spp. at some point during the study (n = 49 Salmonella isolates). Salmonella genotypes persisted within some wallows for >5 months, and genetically indistinguishable Salmonella isolates were found in multiple wallows. Salmonella isolated from outdoor sow feces were genetically indistinguishable by PFGE from Salmonella isolated from wallows (n = 33) throughout the study, indicating that pathogenic bacteria were cycling between swine and their environment. In conclusion, the role of wallows in disseminating Salmonella within an outdoor swine herd appears to be significant.

Animal Husbandry↗
PubMed2005

Effect of water sprinkling on incidence of zoonotic pathogens in feedlot cattle.

Heat stress and dusty conditions are common challenges for cattle during the summer, and a typical method of alleviating these problems involves sprinkling cattle and pens with water. The effect of sprinkling water on the incidence of zoonotic pathogens has not been previously studied. Four pens of heifers (n = 41) were cooled using sprinklers, and four pens (n = 43) served as controls. Heifers were crossbred Charolais, with white and red hair coats. Sprinkling was initiated when cattle were on full concentrate feed (July). Fecal samples, hide swipes, and BW were collected on d 0, 28, 63, 95, and 98. Average daily gain, DMI, and G:F were calculated, and carcass traits were collected 36 h after processing. Performance data were analyzed as a randomized complete block design, and zoonotic pathogen data were analyzed using chi2 analysis. Sprinkling tended (P = 0.054) to increase the incidence of fecal Salmonella spp. populations on d 98, but simultaneously tended to decrease (P = 0.058) the Escherichia coli O157:H7 incidence on hides on d 98. The most prevalent Salmonella serovars in this study were Kentucky, Muenster, Meleagridis, and Cerro. Performance measures and carcass traits did not differ between treatments (P > 0.10). Under our conditions, sprinkling cattle with water did not affect the incidence of zoonotic pathogens in feces or on hides.

Animal Husbandry↗
PubMed2003

Fender design and insulation of farrowing huts: effects on performance of outdoor sows and piglets.

Two studies assessed sow and litter performance when design features of farrowing huts varied. A fender is a structure that extends out the front of the hut to create a veranda that prevents young piglets from leaving. In Exp. 1, 206 lactating sows and their litters were used to assess litter performance and the time required to process litters for two fender designs (short wooden [WS] vs. tall metal with a board front [MT-b]) and insulation status (insulated [IN] vs. uninsulated [UN]) farrowing huts. A significant fender x insulation interaction was observed for total litter weaning weight. Lighter litters weaned (P = 0.013) from WS fenders with UN huts compared with the other treatments. Fender design did not (P > 0.05) influence the time required to process a litter with one stockperson. Less total time (P = 0.001) was required to process a litter when two people were present (10.60 +/- 0.74 min) compared with one stockperson (14.52 +/- 0.74 min). There were no (P > 0.05) differences between IN and UN huts for temperature and relative humidity measurements. In Exp. 2, 331 lactating sows and their litters were used to determine sow and litter performance when using one of two fender front designs (boards [MT-b] vs. roller [MT-r]). The front design of the fender did not influence (P > 0.05) most litter performance measures. We conclude that fender design, fender fronts, and insulation effects did not have large influences on sow and litter performance in a West Texas environment.

Animal Husbandry↗
PubMed2002

Effects of the transportation of beef cattle from the feedyard to the packing plant on prevalence levels of Escherichia coli O157 and Salmonella spp.

Two hundred steers and heifers from a large feedyard (65,000-head capacity) were used to determine the prevalence levels of enterohemorrhagic Escherichia coli O157 (EHEC O157) and Salmonella spp. prior to and after shipping to a commercial packing facility. Two samples, a ventral midline hide swab and a fecal sample, were aseptically collected from each animal 2 weeks prior to the date of transportation and at the packing plant immediately after exsanguination. Samples were collected from all trailers (n = 46) before animals were loaded for transport to the packing facility. The average prevalence levels of EHEC O157 on hides (18%) and in feces (9.5%) at the feedyard decreased (P > 0.05) at the packing plant to 4.5 and 5.5%, respectively. The average prevalence levels of Salmonella spp. on hides (6%) and in feces (18%) at the feedyard increased to 89 and 46%, respectively, upon arrival at the packing plant. Average prevalence levels for EHEC O157 and Salmonella spp. on the trailers were 5.43 and 59%, respectively. The results of this study demonstrate that transportation may be a potential stressor for cattle, as evidenced by the increased shedding of Salmonella spp.

Animals↗
PubMed2001

Effects of chronic lesions of the anteroventral region of the third ventricle on cardiac beta-adrenoceptor function in conscious rats.

This study examined whether cardiac beta-adrenoceptor (beta-AR) function was altered in conscious rats with lesions surrounding the anteroventral third ventricle (AV3V). The findings were: (1) beta(1,2)-AR-mediated tachycardia was similar in sham and AV3V-lesion rats, (2) beta(3)- and/or atypical beta-AR-mediated tachycardia elicited by isoproterenol (10 microg/kg, i.v.; ISO) was diminished in AV3V-lesion rats treated with beta(1,2)-AR antagonists, but was not in similarly-treated sham-lesion rats, and (3) the tachycardia elicited by the membrane permeable cAMP-analogue, 8-(4-chlorophenylthiol)-cAMP (10 micromol/kg, i.v.), was similar in AV3V- and sham-lesion rats. The possibility that increased plasma sodium/osmolality in AV3V-lesion rats down-regulated cardiac beta(3)- and/or atypical beta-ARs, but not beta(1,2)-ARs or intracellular cAMP signaling is discussed.

Adrenergic beta-Agonists↗
PubMed2001

Predisposition to vasovagal syncope in subjects with blood/injury phobia.

BACKGROUND: Most subjects with blood/injury phobia experience syncope or presyncope as part of the phobic response. We tested the hypothesis that these subjects have a constitutional autonomic dysregulation that predisposes them to vasovagal syncope during head-up tilt. METHODS AND RESULTS: We studied 11 subjects (9 females, 2 males) who had a history of syncope or presyncope only in response to a blood or injury stimulus and 11 healthy matched controls (10 females, 1 male) without a history of syncope. Blood pressure (BP) and heart rate (HR) were measured during a 15-minute baseline period with subjects in the supine position and then during 45 minutes of head-up tilt to 70 degrees. Measurements at rest did not differ between the blood phobic and control subjects. During tilt, 9 (82%) of the 11 blood phobic subjects experienced presyncope or syncope, leading to termination of the study after 22+/-17 minutes of tilt. Only 1 (9%) of the 11 control subjects experienced presyncope (chi(2)=11.7, P=0.001). Hemodynamic responses to tilt were consistent with a vasovagal mechanism in the blood phobic subjects, with simultaneous decreases in BP and HR during tilt. During tilt, systolic BP fell by 21+/-15 mm Hg (P=0.001), and HR fell by 22+/-25 bpm (P=0.01). By contrast, BP and HR were very stable in the control group. CONCLUSIONS: Subjects with syncope related to blood/injury phobia have an underlying autonomic dysregulation predisposing them to neurally mediated syncope, even in the absence of any blood or injury stimulus. Fainting related to these stimuli may in large part be due to dysfunction in neural circulatory control, which may secondarily lead to the phobia because of repeated syncopal events.

Adult↗
PubMed2001

Elevated blood pressure in transgenic mice with brain-specific expression of human angiotensinogen driven by the glial fibrillary acidic protein promoter.

In addition to the circulatory renin (REN)-angiotensin system (RAS), a tissue RAS having an important role in cardiovascular function also exists in the central nervous system. In the brain, angiotensinogen (AGT) is expressed in astrocytes and in some neurons important to cardiovascular control, but its functional role remains undefined. We generated a transgenic mouse encoding the human AGT (hAGT) gene under the control of the human glial fibrillary acidic protein (GFAP) promoter to experimentally dissect the role of brain versus systemically derived AGT. This promoter targets expression of transgene products to astrocytes, the most abundant cell type expressing AGT in brain. All transgenic lines exhibited hAGT mRNA expression in brain, with variable expression in other tissues. In one line examined in detail, transgene expression was high in brain and low in tissues outside the central nervous system, and the level of plasma hAGT was not elevated over baseline. In the brain, hAGT protein was mainly localized in astrocytes, but was present in neurons in the subfornical organ. Intracerebroventricular (ICV) injection of human REN (hREN) in conscious unrestrained mice elicited a pressor response, which was abolished by ICV preinjection of losartan. Double-transgenic mice expressing the hREN gene and the GFAP-hAGT transgene exhibited a 15-mm Hg increase in blood pressure and an increased preference for salt. Blood pressure in the hREN/GFAP-hAGT mice was lowered after ICV, but not intravenous losartan. These studies suggest that AGT synthesis in the brain has an important role in the regulation of blood pressure and electrolyte balance.

Angiotensinogen↗
PubMed2001

Intracerebroventricular carbachol induces FOS immunoreactivity in lamina terminalis neurons projecting to the supraoptic nucleus.

Central application of the non-selective cholinergic receptor agonist, carbachol, induces water intake, vasopressin (VP) release and an acute increase in arterial blood pressure. Forebrain sites, particularly those located along the lamina terminalis (LT) (i.e. the subfornical organ (SFO), organum vasculosum (OV) and the median preoptic nucleus (MePO)) and in the hypothalamus, have been proposed as the major targets for producing the effects induced by intracerebroventricular (i.c.v.) carbachol injections. However, the functional and neuroanatomical relationship among carbachol-activated cells along the LT and hypothalamic areas such as the supraoptic nuclei (SON), is unclear. The present study investigated the i.c.v. carbachol-induced activity of the soma of LT projections which descend from the SFO, OV and MePO and terminate in the region of the SON. Cells along the LT were retrogradely labeled from SON-targeted injections of fluoro-gold, and FOS-immunoreactivity (FOS-ir) was used to assess activation. A significant number of cells in the SFO, OV and MePO were double-labeled for both FOS-ir and fluoro-gold. The FOS labeling in the cells of the LT-associated structures was significantly reduced by pretreatment with the i.c.v. muscarinic antagonist, atropine. Taken together, the results indicate that neurons located in structures located along the LT and projecting to the region of the SON are activated by i.c.v. carbachol and that these receptors are likely to be muscarinic.

Animals↗
PubMed2001

Adenovirus-mediated gene delivery to cells of the magnocellular hypothalamo-neurohypophyseal system.

The objective of the present study was to define the optimum conditions for using replication-defective adenovirus (Ad) to transfer the gene for the green fluorescent protein (GFP) to the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei and cells of the neurohypophysis (NH). As indicated by characterizing cell survival over 15 days in culture and in electrophysiological whole cell patch-clamp studies, viral concentrations up to 2 x 10(7) pfu/coverslip did not affect viability of transfected PVN and NH cultured cells from preweanling rats. At 2 x 10(7) pfu, GFP gene expression was higher (40% of GFP-positive cells) and more sustained (up to 15 days). Using a stereotaxic approach in adult rats, we were able to directly transduce the PVN, SON, and NH and visualize gene expression in coronal brain slices and in the pituitary 4 days after injection of Ad. In animals receiving NH injections of Ad, the virus was retrogradely transported to PVN and SON neurons as indicated by the appearance of GFP-positive neurons in cultures of dissociated cells from those brain nuclei and by polymerase chain reaction and Western blot analyses of PVN and SON tissues. Adenoviral concentrations of up to 8 x 10(6) pfu injected into the NH did not affect cell viability and did not cause inflammatory responses. Adenoviral injection into the pituitary enabled the selective delivery of genes to the soma of magnocellular neurons. The experimental approaches described here provide potentially useful strategies for the treatment of disordered expression of the hormones vasopressin or oxytocin.

Adenoviridae↗
PubMed2001

Community values for environmental protection in a cane farming catchment in northern Australia: a choice modelling study.

Choice modelling is an emerging approach to estimating the non-use values of environmental services with multiple attributes. In this paper, results are reported of a choice modelling study conducted in the Herbert River District of North Queensland to estimate the value placed on the protection of natural vegetation in areas suitable for cane production by the local community. Resource use options that vary in the level of environmental protection and the level of agricultural production were presented as a series of choice sets and respondents were asked to choose among a set of three discrete alternatives in a given choice set. The alternatives in each choice set were described by four attributes, pertaining to the area of teatree woodlands, the area of vegetation along rivers and in wetlands, regional income from cane production, and an environmental levy. The responses were analysed together with socio-economic data using a nested-logit discrete-choice model to estimate the community willingness-to-pay for the protection of natural vegetation. The results indicate that the environmental values of wetlands are comparable to returns from commercial production of sugar cane and that the values of teatree woodlands are comparable to returns from extensive grazing. It is argued that land allocation policies should recognise these values in tandem with commercial benefits of production to ensure that resources are used more efficiently.

Adult↗
PubMed2001

Neurohumoral regulation in ischemia-induced heart failure. Role of the forebrain.

Congestive heart failure (CHF) is characterized by neurohumoral excitation. Increased sympathetic drive and activation of the reninangiotensin-aldosterone system (RAAS), with vasoconstriction and volume retention, are hallmarks of the CHF syndrome. Treatment strategies have targeted the peripheral influences of these two systems, but have not addressed the central mechanisms that drive them. We monitored the development of CHF following coronary ligation in adult Sprague-Dawley rats. Left ventricular dysfunction characteristic of CHF was confirmed by echocardiography, and the CHF syndrome was validated by measurements of circulating hormones, sodium appetite, thirst, renal sodium and water retention, and renal sympathetic nerve activity (RSNA). In CHF rats, neuronal activity in the hypothalamic paraventricular nucleus (PVN), which mediates downstream effects of forebrain circumventricular organs, was increased and was inhibited by blocking components of the RAAS at the forebrain level. Forebrain (AV3V) lesions and intracarotid (forebrain directed) injections of agents (captopril, losartan, spironolactone) that block RAAS substantially attenuated the behavioral and physiological manifestations of CHF. Intravenous losartan and captopril, in doses that lower arterial pressure, increased RSNA. These findings demonstrate an important role for RAAS-activated forebrain mechanisms in CHF and suggest that the central neural mechanisms driving sympathetic nerve activity and volume retention may persist and promote the progression of CHF despite treatments directed toward the peripheral influences of RAAS.

Animals↗
PubMed2001

Central mineralocorticoid receptor blockade improves volume regulation and reduces sympathetic drive in heart failure.

The mineralocorticoid (MC) receptor antagonist spironolactone (SL) improves morbidity and mortality in patients with congestive heart failure (CHF). We tested the hypothesis that the central nervous system actions of SL contribute to its beneficial effects. SL (100 ng/h for 28 days) or ethanol vehicle (VEH) was administered intracerebroventricularly or intraperitoneally to rats with CHF induced by coronary artery ligation (CL) and to SHAM-operated controls. The intracerebroventricular SL treatment prevented the increase in sodium appetite and the decreases in sodium and water excretion observed within a week of CL in VEH-treated CHF rats. Intraperitoneal SL also improved volume regulation in the CHF rats, but only after 3 wk of treatment. Four weeks of SL treatment, either intracerebroventricularly or intraperitoneally, ameliorated both the increase in sympathetic drive and the impaired baroreflex function observed in VEH-treated CHF rats. These findings suggest that activation of MC receptors in the central nervous system plays a critical role in the altered volume regulation and augmented sympathetic drive that characterize clinical heart failure.

Animals↗
PubMed2001

Interaction of serotonin and cholecystokinin in the lateral parabrachial nucleus to control sodium intake.

Serotonin [5-hydroxytryptamine (5-HT)] and CCK injected into the lateral parabrachial nucleus (LPBN) inhibit NaCl and water intake. In this study, we investigated interactions between 5-HT and CCK into the LPBN to control water and NaCl intake. Male Holtzman rats with cannulas implanted bilaterally in the LPBN were treated with furosemide + captopril to induce water and NaCl intake. Bilateral LPBN injections of high doses of the 5-HT antagonist methysergide (4 microg) or the CCK antagonist proglumide (50 microg), alone or combined, produced similar increases in water and 1.8% NaCl intake. Low doses of methysergide (0.5 microg) + proglumide (20 microg) produced greater increases in NaCl intake than when they were injected alone. The 5-HT(2a/2c) agonist 2,5-dimetoxy-4-iodoamphetamine hydrobromide (DOI; 5 microg) into the LPBN reduced water and NaCl intake. After proglumide (50 microg) + DOI treatment, the intake was not different from vehicle treatment. CCK-8 (1 microg) alone produced no effect. CCK-8 combined with methysergide (4 microg) reduced the effect of methysergide on NaCl intake. The data suggest that functional interactions between 5-HT and CCK in the LPBN may be important for exerting inhibitory control of NaCl intake.

Amphetamines↗
PubMed2001

Agonist activation of cytosolic Ca2+ in subfornical organ cells projecting to the supraoptic nucleus.

The subfornical organ (SFO) is sensitive to both ANG II and ACh, and local application of these agents produces dipsogenic responses and vasopressin release. The present study examined the effects of cholinergic drugs, ANG II, and increased extracellular osmolarity on dissociated, cultured cells of the SFO that were retrogradely labeled from the supraoptic nucleus. The effects were measured as changes in cytosolic calcium in fura 2-loaded cells by using a calcium imaging system. Both ACh and carbachol increased intracellular ionic calcium concentration ([Ca2+]i). However, in contrast to the effects of muscarinic receptor agonists on SFO neurons, manipulation of the extracellular osmolality produced no effects, and application of ANG II produced only moderate effects on [Ca2+]i in a few retrogradely labeled cells. The cholinergic effects on [Ca2+]i could be blocked with the muscarinic receptor antagonist atropine and with the more selective muscarinic receptor antagonists pirenzepine and 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP). In addition, the calcium in the extracellular fluid was required for the cholinergic-induced increase in [Ca2+]i. These findings indicate that ACh acts to induce a functional cellular response in SFO neurons through action on a muscarinic receptor, probably of the M1 subtype and that the increase of [Ca2+]i, at least initially, requires the entry of extracellular Ca2+. Also, consistent with a functional role of M1 receptors in the SFO are the results of immunohistochemical preparations demonstrating M1 muscarinic receptor-like protein present within this forebrain circumventricular organ.

Acetylcholine↗
PubMed2001

Circulating angiotensin II mediates sodium appetite in adrenalectomized rats.

We investigated the role of circulating ANG II in sodium appetite after adrenalectomy. Adrenalectomized rats deprived of their main access to sodium (0.3 M NaCl) for 9 h drank 14.1 +/- 1.5 ml of the concentrated saline solution in 2 h of access. Intravenous infusion of captopril (2.5 mg/h) during the last 5 h of sodium restriction reduced sodium intake by 77 +/- 12% (n = 5) without affecting the degree of sodium depletion and hypovolemia incurred during deprivation. Functional evidence indicates that this dose of captopril blocked production of ANG II in the peripheral circulation, but not in the brain; that is, injection of ANG I into the lateral brain ventricle stimulated intake of both water and 0.3 M NaCl. Intravenous infusion of ANG II (starting 10-15 min before 0.3 M NaCl became available) in adrenalectomized, captopril-treated rats restored both sodium intake and blood pressure to values seen in rats not treated with captopril. Longer (20 h) infusions of captopril in 22-h sodium-restricted rats also blocked sodium appetite, but reduced or prevented sodium depletion. Intravenous infusion of ANG II after these long captopril infusions stimulated sodium intake, but intake was less than in controls not treated with captopril. These results indicate that most or all of the sodium appetite of adrenalectomized rats is mediated by circulating ANG II.

Adrenalectomy↗